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041561473 | summary | This invention relates to neutron absorbing articles. More particularly, it relates to such articles which comprise neutron absorbing boron carbide particles and diluent particles bound together in a matrix of cured phenolic polymer in a form suitable for absorbing neutrons from nuclear material, such as spent nuclear fuel. It is well known that products of the radioactive decomposition of nuclear materials are harmful to human life and to the environment about such materials. Accordingly, where nuclear materials have been employed shielding has often been utilized so as to lower the level of radioactivity in surrounding areas. Nuclear fuels employed in nuclear reactors to produce electric power diminish in activity to such an extent as they are consumed that periodic replacement is required to maintain reactor operations at specification rates. To increase the capacities of storage pools, such as have been employed in the past for temporary storage of such removed fuel and other nuclear wastes, the spent fuel has been stored in the pools in racks with neutron absorbing material surrounding it. Such racks and the storage of nuclear materials, such as spent fuel from nuclear power plants, in them have been described in U.S. patent application Ser. No. 854,966, filed Nov. 25, 1977, by McMurtry, Naum, Owens and Hortman, the disclosure of which is hereby incorporated by reference. The McMurtry et al. application describes boron carbide-phenolic resin neutron absorbers which are preferably in long thin flat plate form and are of exceptionally high neutron absorbing capabilities because of their high contents of B.sup.10 from the boron carbide particles therein. Although such products have met with acceptance by operators of nuclear power generating installations, in which they have been successfully employed, sometimes the greater neutron absorbing capabilities thereof are not required and on other occasions neutron absorption specifications may be lower than those for the McMurtry et al. neutron absorbers. Because it is the B.sup.10 in the boron carbide particles of the boron carbide-phenolic polymer compositions which is the active neutron absorber the absorption properties of boron carbide particles-phenolic polymer product may be lowered by diminishing the quantity of boron carbide therein and increasing the phenolic polymer content accordingly. Although such method allows the production of neutron absorbers of various activities by variations in the boron carbide:phenolic polymer ratio in the neutron absorbing articles made, the physical properties of the product as well as the neutron absorbing power thereof vary and accordingly, to meet specifications, it may often be necessary to make allowances for such variations in the design of the fuel storage racks or other environments wherein the nuclear material to be shielded is present. Such design variations often are not feasible. Additionally, different processing techniques will often have to be employed when the proportions of boron carbide and phenolic resin, from which the final cured polymer matrix is made, are changed. Thus, at high proportions of phenolic resin in the desired final product it may be necessary to utilize different and more expensive manufacturing techniques because, especially when liquid resin is utilized, the "green" article or plate first made from the boron carbide-phenolic resin mixture may not retain its desired form during the curing process unless it is held under a pressing or compacting pressure, which is not practical for the preferred simple oven cures of such articles. Because of the disadvantages accompanying properties changes due to variations in the ratio of boron carbide particles to phenolic resin in neutron absorbing articles containing such materials along and because of difficulties encountered in processes for the manufacture of such changed articles the present invention is especially advantageous. In accordance with this invention a neutron absorbing article comprises boron carbide particles, diluent particles and a solid, irreversibly cured phenolic polymer cured to a continuous matrix binding the boron carbide particles and the diluent particles. In such products usually the total content of the boron carbide particles and the diluent particles is a major proportion of the article and the content of the cured phenolic polymer is a minor proportion. By means of the present invention neutron absorbing articles or plates can be made, utilizing mixtures of boron carbide particles and diluent particles with phenolic resin, the mixture of which can be pressed to green article form, and which articles can be subsequently cured efficiently and easily in an oven with a plurality of others. Because the diluent particles behave similarly to boron carbide particles, except for their lack of neutron absorbing capability, the manufacturing methods employed need not be changed and products of varying neutron absorbing powers may be manufactured, utilizing the same equipment and processes but changing the mixtures of boron carbide and diluent particles utilized. Also, the products made will have the desired physical and chemical characteristics for successful use as neutron absorbers in storage racks for installation in storage pools for spent nuclear fuel. |
description | This application is a Continuation-In-Part of application Ser. No. 14/808,419, filed Jul. 24, 2015, which claims priority from Korean Patent Application No. 10-2014-0095071, filed on Jul. 25, 2014, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference. Apparatuses and methods consistent with exemplary embodiments relate to an image processing apparatus, an image processing method, an X-ray imaging apparatus, and a control method for processing to improve clarity of a desired area of a medical image. Medical imaging apparatuses for imaging the inside of an object to diagnose the object include, for example, a radiation imaging apparatus to irradiate radiation onto the object and to detect radiation transmitted through the object, a magnetic resonance imaging (MRI) apparatus to apply high-frequency signals to the object located in a magnetic field and to receive MRI signals from the object, and an ultrasonic imaging apparatus to transmit ultrasonic waves to the object and to receive echo signals reflected from the object. Since a medical image acquired by a medical imaging apparatus may include a lesion area or a background area other than an area that is to be diagnosed, shutter processing may be performed to render a user's desired area of the medical image appear clearly and the remaining area appear dark or blurry, to improve user convenience and visibility of images. One or more exemplary embodiments provide an image processing apparatus and an image processing method, which are capable of performing shutter processing with respect to a desired area through a user's intuitive and simple input operation. Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the exemplary embodiments. According to an aspect of an exemplary embodiment, there is provided an image processing apparatus including: a display configured to display a medical image; an input unit configured to receive n (n being an integer equal to or greater than three) number of input points with respect to the displayed medical image; and a controller configured to set a window in the medical image based on an area in a shape of a polygon, the area being defined by the input points, and to perform image processing of reducing at least one of brightness and definition of the medical image in a remaining area except for an area of the window. The controller may be configured to set the window based on the area in the shape of the polygon having vertexes corresponding to the input points. The controller may be configured to determine validity of the input points based on whether the input points define the area in the shape of the polygon. In response to receiving an input point, the controller may be configured to determine validity of the input point, and when the controller determines that the input point is invalid, the controller may be configured to indicate a result of determining that the input point is invalid through the display. When a distance between a first input point and a second input point among the input points is less than a reference distance, the controller may be configured to determine that an input point that is last input among the first input point and the second input point is invalid. When at least three input points among the input points are on a straight line, the controller may be configured to determine that an input point that is last input among the at least three input points is invalid. When n is equal to or greater than four and a figure defined by the input points has a concave shape, the controller may be configured to determine that an input point that is last input among the input points is invalid. The controller may be configured to determine whether the figure defined by the input points has a concave shape based on whether an order in which a lastly input point among the input points is connected with previously input points is in a clockwise order or a counterclockwise order. When the controller determines that the input point is invalid, the input unit may be configured to receive a new input point that replaces the input point that is determined to be invalid. When the controller determines that all of the input points are valid, the controller may be configured to connect the input points to define the area in the shape of the polygon. The controller may be configured to connect the input points such that straight lines connecting at least two input points among the input points do not cross each other. The display may be configured to display the input point that is determined to be invalid to have at least one of a color and a shape that is different from at least one of a color and a shape of an input point that is determined to be valid. The display may be configured to display the window on the medical image. The display may be configured to display the medical image on which the image processing is performed. The image processing apparatus may further include: a communicator configured to transmit the medical image on which the image processing is performed to an outside. According to an aspect of another exemplary embodiment, there is provided an image processing apparatus including: a display configured to display a medical image; an input unit configured to receive n (n being an integer equal to or greater than one) number of input points with respect to the displayed medical image; and a controller configured to set a window in the medical image based on an area in a shape of a circle, the area being defined by the input points, and to perform image processing to reduce at least one of brightness and definition of the medical image in a remaining area except for an area of the window. In response to receiving two input points through the input unit, the controller may be configured to set the window based on the area in the shape of the circle, the circle having a diameter or a radius corresponding to a straight line connecting the two input points. In response to receiving an input point and a straight line starting from the input point through the input unit, the controller may be configured to set the window based on the area in the shape of the circle, the circle having a center point corresponding to the input point and a radius corresponding to the straight line. In response to receiving an input point and a straight line starting from the input point through the input unit, the controller may be configured to set the window based on the area in the shape of the circle, the circle having a diameter corresponding to the straight line. In response to receiving an input point through the input unit, the controller may be configured to set the window based on the area in the shape of the circle, the circle having a center point corresponding to the input point, and a radius of which length is determined in proportion to a time period during which an input of the input point is maintained. The controller may be configured to set the window based on the area in the shape of the circle, the circle having a radius of which length is determined at a time when the input of the input point is stopped. According to an aspect of another exemplary embodiment, there is provided an image processing method including: displaying a medical image on a display; receiving n (n being an integer equal to or greater than three) number of input points with respect to the displayed medical image; setting a window in the medical image based on an area in a shape of a polygon, the area being defined by the input points; and performing image processing to reduce at least one of brightness and definition of the medical image in a remaining area except for an area of the window area. The setting may include setting the window based on the area in the shape of the polygon having vertexes corresponding to the input points. The setting may include determining validity of the input points based on whether the input points define the area in the shape of the polygon. The setting may include: determining, in response to receiving an input point, validity of the input point; and indicating, when it is determined that the input point is invalid, a result of determining that the input point is invalid through the display. The determining may include determining, when a distance between a first input point and a second input point among the input points is less than a reference distance, that an input point that is last input among the first input point and the second input point is invalid. The determining may include determining, when at least three input points among the input points are on a straight line, an input point that is last input among the at least three input points is invalid. The determining may include determining, when a figure defined by the input points has a concave shape, that an input point that is last input among the input points is invalid. The determining may include determining whether the figure defined by the input points has a concave shape based on whether an order in which a lastly input point among the input points is connected with previously input points is in a clockwise order or a counterclockwise order. The image processing method may further include: receiving, in response to determining that the input point is invalid, a new input point that replaces the input point that is determined to be invalid. The setting may include connecting, in response to determining that all of the input points are valid, the input points to define the area in the shape of the polygon. The connecting may include connecting the input points such that straight lines connecting at least two input points among the input points do not cross each other. The indicating may include displaying the input point that is determined to be invalid to have at least one of a color and a shape that is different from at least one of a color and a shape of an input point that is determined to be valid. The image processing method may further include displaying the window on the medical image. The image processing method may further include displaying the medical image on which the image processing is performed. According to an aspect of another exemplary embodiment, there is provided an image processing method including: displaying a medical image on a display; receiving n (n being an integer equal to or greater than one) number of input point with respect to the displayed medical image; setting a window in the medical image based on an area in a shape of a circle, the area being defined based on the input point; and performing image processing to reduce at least one of brightness and definition of the medical image in a remaining area except for an area of the window. The setting may include setting, in response to receiving two input points, the window based on the area in the shape of the circle, the circle having a diameter or a radius corresponding to a straight line connecting the two input points. The setting may include, in response to receiving the input point and a straight line starting from the input point, setting the window based on the area in the shape of the circle, the circle having a center point corresponding to the input point and a radius corresponding to the straight line. The setting may include, in response to receiving the input point and a straight line starting from the input point, setting the window based on the area in the shape of the circle, the circle having a diameter corresponding to the straight line. The setting may include, in response to receiving the input point, setting the window based on the area in the shape of the circle, the circle having a center point corresponding to the input point, and a radius of which length is determined in proportion to a time period during which an input of the input point is maintained. The setting may include, setting the window based on the area in the shape of the circle, the circle having a radius of which length is determined at a time when the input of the input point is stopped. According to an aspect of another exemplary embodiment, there is provided an X-ray imaging apparatus including: a display configured to display an X-ray image; an input unit configured to receive n (n being an integer equal to or greater than three) number of input points with respect to the displayed X-ray image; and a controller configured to set a window in the medical image based on an area in a shape of a polygon, the area being defined by the input points, and to perform image processing to reduce at least one of brightness and definition of the medical image in a remaining area except for an area of the window. The X-ray imaging apparatus may further include: an X-ray source configured to irradiate X-rays; and an X-ray detector configured to detect the X-rays and to acquire the X-ray image. According to an aspect of another exemplary embodiment, there is provided an apparatus for processing a medical image, the apparatus including: a display configured to display a medical image; and a controller configured to: set a window in the medical image in a circular shape in response to a user input for designating a preset number of points or less in the medical image, and set the window in the medical image in a shape of a polygon in response to a user input for designating points greater than the preset number in the medical image, the polygon having vertexes corresponding to the points designated by the user input, wherein the controller is configured to perform image processing on the medical image based on the set window. The controller may be configured to perform the image processing such that at least one of brightness and definition of the medical image is different between an area of the window and a remaining area of the medical image. According to an aspect of an another exemplary embodiment, there is provided an image processing apparatus including: a collimator including a plurality of blades to form a collimation area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction; a display configured to display a guide image; an input device configured to receive n (n being an integer equal to or greater than three) number of input points with respect to the displayed guide image; and a controller configured to set a polygon defined by the input points to a window area, and to control the collimator to form a collimation area corresponding to the window area. The plurality of blades are configured to perform at least one movement of a rotational movement and a linear movement The controller may be configured to determine validity of the input points. In response to receiving an input point, the controller may be configured to determine validity of the input point, and when the controller determines that the input point is invalid, the controller may be configured to display the result of that the input point is invalid through the display. When a distance between a first input point and a second input point among input points is less than a reference value, the controller may be configured to determine that an input point that is last input among the first input point and the second input point is invalid. When at least three input points of the input points are located on a straight line, the controller may be configured to determine that an input point that is last input among the at least three input points is invalid. When a figure defined by the input points has a concave shape, the controller may be configured to determine that an input point that is last input among the input points is invalid. The controller may be configured to determine whether the figure defined by the input points has a concave shape based on whether an order in which a lastly input point among the input points is connected with previously input points is in a clockwise order or a counterclockwise order. When the controller determines that the input point is invalid, the input device may be configured to receive a new input point that replaces the input point that is determined to be invalid. When the controller determines that all of the input points are valid, the controller may be configured to connect the input points to define the area in the shape of the polygon. The guide image includes at least one image among an X-ray image acquired by irradiating a low dose of X-rays on an object before main scanning, a camera image acquired by photographing the object with a camera, and a previously acquired X-ray image of the object. The controller may be configured to determine whether the collimator is able to form a collimation area having a polygon shape defined by the input points. When the controller determines that the collimator is unable to form the collimation area having the polygon shape defined by the input points, the controller may be configured to control the collimator to form a collimation area of a shape most similar to the polygon. When the controller determines that the collimator is unable to form the collimation area having the polygon shape defined by the input points, the controller may be configured to control the collimator to perform image processing on the acquired X-ray image. The controller may be configured to perform the image processing in such a way to reduce brightness or definition of the remaining area except for the window area in the acquired X-ray image or to cut off the remaining area. According to an aspect of an another exemplary embodiment, there is provided an image processing apparatus including: a collimator including a plurality of blades to form a collimation area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction; a display configured to display a guide image; an input device configured to receive n points for the guide image, the n points input by a user, wherein n is an integer that is equal to or greater than 1; and a controller configured to set a circle defined by the input points to a window area, to control the collimator to form a collimation area corresponding to the window area, and to perform image processing on an X-ray image acquired by X-rays passed through the collimation area to acquire an X-ray image corresponding to the window area. When two points are input through the input device, the controller may be configured to set a circle whose diameter or radius is a straight line connecting the two points, to the window area. When a point and a straight line starting from the point are input through the input device, the controller may be configured to set a circle whose center point is the point and whose radius is the straight line, to the window area. When a point and a straight line starting from the point are input through the input device, the controller may be configured to set a circle whose diameter is the straight line, to the window area. When a point is input through the input device, the controller may be configured to create a circle whose center point is the input point, and increase a radius of the circle in proportion to a time period for which the point is input. The controller may be configured to set a circle having a radius acquired at time at which the point is no longer input, to the window area. The plurality of blades may be configured to perform at least one movement of a rotational movement and a linear movement. According to an aspect of another exemplary embodiment, there is provided a method of controlling an X-ray imaging apparatus including: displaying a guide image on a display; receiving n points for the guide image, the n points input by a user, wherein n is an integer that is equal to or greater than 3; and setting a polygon defined by the input points to a window area, and controlling a collimator including a plurality of blades to form a collimation area corresponding to the window area, wherein at least one blade of the plurality of blades is rotatable in a clockwise direction or in a counterclockwise direction. The method of controlling an X-ray imaging apparatus further comprises determining whether the collimator is able to form a collimation area having a polygon shape defined by the input points. The controlling of the collimator comprises: when the collimator is unable to form the collimation area having the polygon shape defined by the input points, controlling the collimator to form a collimation area of a shape most similar to the polygon; and controlling the collimator to perform image processing on an acquired X-ray image. According to an aspect of another exemplary embodiment, there is provided a method of controlling an X-ray imaging apparatus including: displaying a guide image on a display; receiving n points for the guide image, the n points input by a user, wherein n is an integer that is equal to or greater than 1; and setting a circle defined by the input points to a window area; controlling a collimator including a plurality of blades to form a collimation area corresponding to the window area, wherein at least one blade of the plurality of blades is configured to be rotatable in a clockwise direction or in a counterclockwise direction; and performing image processing on an X-ray image acquired by X-rays passed through the collimation area to acquire an X-ray image corresponding to the window area. Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Hereinafter, exemplary embodiments of an image processing apparatus and an image processing method according to an inventive concept will be described in detail. Shutter processing that is performed according to the exemplary embodiments of the image processing apparatus and the image processing method does not mean physically adjusting a range of scanning in acquiring an image, but means enhancing a desired area of an already created image by rendering a remaining area except for the desired area appear dark or blurry. In the following description, the desired area enhanced by the shutter processing will be referred to as a window or a window area. FIG. 1 is a control block diagram of an image processing apparatus according to an exemplary embodiment, and FIG. 2 is a view for describing a process of transmitting medical images. Referring to FIG. 1, an image processing apparatus according to an exemplary embodiment may include an input unit 110 to receive a user's selection for forming a shutter, a display 120 to display medical images, a controller 130 to control overall operations of the image processing apparatus 100, and a storage unit 140 to store medical images subject to shutter processing. If a medical image is displayed on the display 120, a user may select a desired area (for example, an area including lesions or an area to be diagnosed) of the displayed medical image through the input unit 110. At this time, the user may select the desired area, for example but not limited to, using a method of inputting three points or more. A window creator 131 of the controller 130 may determine whether the user's input is valid. Details about operations in which an area is selected by the user and the controller 130 determines validity of the selected area will be described later. If the window creator 131 determines that the user's input is valid, the window creator 131 may set the area selected by the user to a window. Then, an image processor 132 may perform shutter processing on the image displayed on the display 120. That is, the image processor 132 may reduce the brightness or definition of the remaining area except for the area set to the window in the image displayed on the display 120. The shutter-processed image may be stored in the storage unit 150. The medical image that is displayed or processed by the image processor 132 may be a radiation image, a magnetic resonance (MR) image, or an ultrasonic image. The radiation image may include a positron emission tomography (PET) image and an X-ray image acquired by irradiating X-rays onto an object and detecting X-rays transmitted through the object, wherein the X-ray image may include a general X-ray projected image and an X-ray tomography image acquired by imaging a section of an object. The X-ray projected image may be acquired by an imaging apparatus, such as general radiography and mammography, according to the kind of an object. The X-ray tomography image may be acquired by an imaging apparatus, such as computerized tomography (CT) and tomosynthesis. However, the above-mentioned medical images are examples of medical images that can be displayed or processed by the image processing apparatus 100, and the kinds of medical images that can be displayed and processed by the image processing apparatus 100 according to an exemplary embodiment are not limited. Generally, before a patient is scanned to acquire a medical image, the patient may consult with a doctor to explain his or her symptoms or show his or her affected area, and the doctor may decide an area to be scanned according to the patient's state to issue a scanning order. The doctor's scanning order may be transmitted to a central server of a medical institution, and the central server may transmit the doctor's scanning order to a medical imaging apparatus to acquire a medical image according to the scanning order. At this time, scanning the patient to acquire a medial image may be performed by a radiological technologist or a doctor. As shown in FIG. 2, if a medical image is acquired by a medical imaging apparatus 20, the medical image may be transmitted to a central server 10 of a medical institution thought a network. For example, the central server 10 may be a picture archiving communication system (PACS), and the PACS 10 may store and manage the received medical image. A user (for example, a doctor) who wants to check a medical image may use the PACS 10 to search for a desired medical image. The PACS 10 may, in addition to a database to store medical images, include various kinds of processors and a user interface, such as an input unit and a display. Accordingly, the user can search for and check a desired medical image though the user interface, and edit the searched medical image as needed. Medical images stored in the PACS 10 may be searched by using a user control apparatus 30. The user control apparatus 30 may include a personal computer that can be used by a user such as a doctor. Accordingly, the user may use the user control apparatus 30 to search for a desired medical image in medical images stored in the PACS 10, without directly accessing the PACS 10. The user may perform shutter processing on the medical image using any one of the medical imaging apparatus 20, the PACS 10, and the user control apparatus 30. Accordingly, the image processing apparatus 100 may be included in the medical imaging apparatus 20, the PACS 10, or the user control apparatus 30. FIGS. 3 and 4 show external appearances of image processing apparatuses according to exemplary embodiments. For example, if the image processing apparatus 100 is included in the medical imaging apparatus 20, the image processing apparatus 100 may include a workstation shown in FIG. 3. The workstation includes an apparatus that receives a user's commands for controlling the medical imaging apparatus 20 or processes medical image data to create and display visible medical images, independently from a configuration of scanning an object to acquire medical image data. The workstation is also called a host apparatus or a console, and may include any apparatus capable of storing and processing medical image data acquired by the medical image apparatus 20. The display 120 may be a liquid crystal display (LCD), a light emitting diode (LED) display, or an organic light emitting diode (OLED) display. The input unit 110 may include one or more keys or buttons that can be manipulated by applying pressure thereto, a trackball or a mouse that can be manipulated by moving its location, and a touch panel that can be manipulated by a user's touch input. If the input unit 110 includes a touch panel, the input unit 110 may be implemented as a touch screen by mounting a transparent touch panel on a side of the display 120, or may be provided separately from the display 120. Although not shown in FIG. 3, the controller 130 and the storage unit 140 may be installed in a main body 101. The controller 130 may be implemented as a processor or controller, such as a central processor unit (CPU), a micro controller unit (MCU), or a micro processor unit (MPU). The storage unit 140 may include at least one of an integrated circuit (IC) memory (for example, a read only memory (ROM), a random access memory (RAM), or a flash memory), a magnetic memory (for example, a hard disk or a diskette drive), and an optical memory (for example, an optical disk). The window creator 131 and the image processor 132 of the controller 130 may be implemented as physically separated devices, however, a part of functions of the window creator 131 and the image processor 132 may be performed by one device or one chip. Also, the storage unit 140 and the controller 130 may be implemented on one chip. The external appearance of the image processing apparatus 100 in a case where the image processing apparatus 100 is included in a workstation may be different from that of the image processing apparatus 100 of FIG. 3. That is, FIG. 3 shows only an example of the external appearance of the image processing apparatus 100. Also, the image processing apparatus 100 is not required to perform all operations of a general workstation. That is, the image processing apparatus 100 may only need to perform operations of the input unit 110, the display 120, the controller 130, and the storage unit 140 which are described above or will be described later. As another example, if the image processing apparatus 100 is included in the user control apparatus 30, the image processing apparatus 100 may have an external appearance as described in FIG. 4. The display 120 may be a monitor of a personal computer, and the input unit 110 may be a keyboard and/or a mouse. Also, in an alternative example, the input unit 110 may be a touch panel to form a touch screen together with the display 120, as described above. Although not shown in the drawings, the controller 130 and the storage unit 140 may be installed in the main body 101, and repetitive descriptions about the controller 130 and the storage unit 140 will be omitted. Also, in a case where the image processing apparatus 100 is included in the user control apparatus 30, the external appearance of the image processing apparatus 100 may be different from that of the image processing apparatus 100 of FIG. 4. That is, FIG. 4 shows only an example of the external appearance of the image processing apparatus 100. Also, the image processing apparatus 100 is not required to perform all operations of a general workstation. That is, the image processing apparatus 100 may only need to perform operations of the input unit 110, the display 120, the controller 130, and the storage unit 140 which are described above or will be described later. In the above, the basic configuration and external appearance of the image processing apparatus 100 have been described. Hereinafter, a method of performing shutter processing on a medical image according to a user's input will be described in detail. For convenience of description, a medical image which is used in the following embodiments is assumed to be an X-ray image. However, it should be noted that the exemplary embodiments are not limited thereto. For example, the medical image may be a magnetic resonance (MR) image, or an ultrasonic image. FIGS. 5 and 6 are views for describing examples of methods of receiving inputs of desired points when performing shutter processing on a medical image in the image processing apparatus 100 according to exemplary embodiments, and FIG. 7 shows a result of shutter processing performed by the image processing apparatus 100 that receives the user inputs of four points. The image processing apparatus 100 according to an exemplary embodiment may display a medical image on the display 120, and if a user selects a desired area from the displayed medical image, the image processing apparatus 100 may set the selected area to a window area, and then perform shutter processing. At this time, by allowing a user to intuitively select a window area, it is possible to improve user convenience and the accuracy of window area setting. For example, the image processing apparatus 100 may receive all vertexes of a polygon that is to be formed as a window, from a user. That is, the image processing apparatus 100 may allow a user to input n points (wherein n is an integer number greater than or equal to 3) on a medical image displayed on the display 120. In FIGS. 5 and 6, an example in which n is 4 is shown. Herein, the user may be a radiological technologist or a doctor although not limited to them. Referring to FIG. 5, when the input unit 110 is implemented as a transparent touch panel to configure a touch screen together with the display 120, a user may use his or her hand H to touch desired four points 121a, 121b, 121c, and 121d on a medical image displayed on the display 120 to be entered. In this case, the image processing apparatus 100 may display the four points 121a, 121b, 121c, and 121d on the display 120 in order for the user to be able to check the points 121a, 121b, 121c, and 121d selected by the user. Referring to FIG. 6, when the input unit 110 is implemented as a mouse, a pointer 122 moving on the display 120 according to a movement amount and a direction of the input unit 110 may be displayed. A user may manipulate the input unit 110 to locate the pointer 122 at locations corresponding to the four points 121a, 121b, 121c, and 121d on the medical image, and then click the input unit 110, thereby inputting the fourth points 121a, 121b, 121c, and 121d. However, the methods of inputting points as shown in FIGS. 5 and 6 are only examples that can be applied to the image processing apparatus 100. According to another example, a user can input desired points using a trackball or a keyboard. If the four points 121a, 121b, 121c, and 121d are input using any one of the above-described methods, a window 123 having the shape of a quadrangle that is defined by the four points 121a, 121b, 121c, and 121d, that is, a quadrangle whose vertexes are the four points 121a, 121b, 121c, and 121d may be created, and the remaining area except for the window 123 in the medical image displayed on the display 120 may be processed to appear dark or blurry. In this way, shutter processing of highlighting only the area included in the window 123 may be performed. Although FIG. 7 illustrates only an image in the area included in the window 123 is shown on the display, it should be understood that the image outside the window 123 that is processed to appear dark or blurry may be shown. The shutter-processed image may be stored in the storage unit 140, and the original medical image not subject to the shutter processing may also be stored in the storage unit 140. In the examples of FIGS. 5 and 6, since the user inputs all of the four points 121a through 121d defining the window 123, the window 123 having a desired shape may be created. In another example, if two points are input to create a window in a shape of a quadrangle, the two points may be used to define the diagonal vertexes of a rectangle and a rectangular window may be created based on the diagonal vertexes, instead of other quadrangles, such as a trapezoid, a diamond, and a parallelogram. If the user wants to edit the window 123, the user may execute a window editing menu, directly edit the window 123 without executing the window editing menu, or again input n points. First, an example of directly editing the window 123 without executing the window editing menu will be described. FIGS. 8, 9, and 10 are views for describing operation of editing the created window 123 according to exemplary embodiments. After the window 123 is created and displayed on the display 120 as shown in FIG. 7, the user can change the shape or size of the window 123 without executing an editing menu. For example, the user may select and move at least one point 121b among the four points 121a, 121b, 121c, and 121d defining the window 123, as shown in FIG. 8. In FIG. 8, an example in which the point 121b is moved by the movement of the pointer 122 displayed on the display 120 is shown. In this case, the input unit 110 may be a mouse, and the user may manipulate the mouse 110 to move the point 121b to a desired location 121b′. However, this operation is only an example of moving the point 121b, and if the input unit 110 is a touch panel, the user may move the point 121b by a touch operation, e.g., touching and dragging the point 121b. When the point 121b moves to the desired location 121b′ having new coordinates, the resultant four points 121a. 121b′, 121c, and 121d may define a new window 123′ having a shape and a size that are different from those of the previous window 123. As another example, as shown in FIG. 9, a user may move at least one line L3 among lines L1, L2, L3, and L4 connecting the points 121a, 121b, 121c, and 121d to each other, respectively. The user may select the line L3 through the input unit 110 to move the line L3 to a desired location. The selected line L3 moved to the desired location may change to a new line L3′, and due to the movement of the selected line L3, the lines L2 and L4 may change to form new lines L2′ and L4′, respectively. Accordingly, the resultant four lines L1, L2′, L3′, and L4′ may define another window 123′ having a shape and a size that are different from those of the previous window 123. When the window 123 is edited, validity of input may be determined. For example, in the example as shown in FIG. 8, validity of an input of the new point 121b′ to move the point 121b may be determined, and if it is determined that the input of the new point 121b′ is invalid, a new input may be received from the user. After the new window 123′ is created, the image processor 132 may perform shutter processing with respect to the new window 123′. At this time, the image processor 132 may use the original medical image stored in the storage unit 140. The image processor 132 may reduce the brightness or definition of the remaining area except for the new window 123′ in the original medical image. Then, the display 120 may display the resultant image acquired by performing shutter processing with respect to the new window 123′. In an exemplary embodiment, editing of enlarging or reducing the size of a window while maintaining the shape of the window is also possible. As shown in FIG. 10, if a point 121b among points 121a, 121b, 121c, and 121d displayed on the display 120 is selected and moved, an enlargement/reduction magnification of a window may be determined according to a movement amount and a direction of the point 121b, and all or a part of the remaining points 121a, 121c, and 121d may move according to the determined enlargement/reduction magnification so that new points 121a′, 121b′, 121c′ and 121d′ may be generated. In this example, all of the four points 121a, 121b, 121c, and 121d are moved according to the movement of the point 121b, however, the exemplary embodiments are not limited thereto. For example, if enlargement or reduction is performed only in the movement direction of the selected point 121b according to the determined an enlargement/reduction magnification, the point 121d may remain at a fixed position. If the window 123 is enlarged or reduced to the window 123′, the image processor 132 may perform shutter processing with respect to the enlarged or reduced window 123′, and display the result of the shutter processing on the display 120. As described above, a user may select and move a point and/or line of the created window 123 to thereby edit the window 123 without executing an editing menu. When a user selects an area in the window 123, instead of a point or a line of the window 123, the window creator 131 may recognize the selection as an input of a new point. That is, if a user selects an area in the window 123 that does not correspond to a point or a line of the window 123 after the shutter-processed medical image including the window 123 is displayed on the display 120, the window creator 131 may recognize that n points are input to create a new window. FIG. 11 shows an example of a graphic user interface that can be used for window setting according to an exemplary embodiment. If the image processing apparatus 100 executes a shutter function, the display 120 may display a graphic user interface (GUI) 125 as shown in FIG. 11. In the following exemplary embodiments, the GUI 125 that can be used for window setting will be referred to as a window setting menu. Referring to FIG. 11, the window setting menu 125 may include icons 125a to adjust the size of a window to a predetermined size, icons 125b and 125c to manually input the size of a window, and an icon 125d to edit a set window. In the examples of FIGS. 8, 9, and 10, operation of directly editing the window 123 without executing an editing menu has been described, however, the window 123 can be edited by selecting the icon 125d for editing a window to execute an editing menu. Also, the window setting menu 125 may include an icon 125f to set a window in a shape of a quadrangle by inputting four points, and an icon 125e to set a window in a shape of a quadrangle by inputting two points, as needed. If a user uses the input unit 110 to select the icon 125f, the input unit 110 may enter a state (e.g., standby state) to receive an input of four points, and if a point is input through the input unit 110, the controller 130 may determine whether the input point is valid. This operation will be described in detail, below. FIG. 12 shows examples of invalid point inputs, FIG. 13 is a flowchart illustrating a method in which the controller 130 determines validity of input points according to an exemplary embodiment, and FIGS. 14 and 15 are views for describing an example of a method of determining whether a concave polygon is formed by input points according to exemplary embodiments. If a figure defined by four points input to set a window of a quadrangle is not a quadrangle or is a concave quadrangle, it may be determined that the input points are invalid. For example, as shown in FIG. 12A, if at least one of the internal angles of a quadrangle formed by connecting four input points 121a, 121b, 121c, and 121d to each other is 180 degrees or more, the quadrangle may be determined to be a concave quadrangle, and the controller 130 may determine that the input points 121a, 121b, 121c, and 121d are invalid. Also, as shown in FIG. 12B, if a distance between at least two points 121a and 121d among input points 121a, 121b, 121c, and 121d is shorter than a reference distance, the controller 130 may determine that the input points 121a, 121b, 121c, and 121d are invalid. Also, as shown in FIG. 12C, if three points 121a, 121c, and 121d or more of input points 121a, 121b, 121c, and 121d are on a straight line, the controller 130 may determine that the input points 121a, 121b, 121c, and 121d are invalid. Points input by a user may have information of two dimensional (2D) spatial coordinates. Accordingly, when the controller 130 or the image processor 132 determines or processes points in the following exemplary embodiments, the controller 130 or the image processor 132 may use the 2D spatial coordinates of the corresponding points. Hereinafter, a method of determining validity of points will be described in detail with reference to FIG. 13. Referring to FIG. 13, a first point of four points may be received, in operation 310. In the flowchart of FIG. 13, the order of “first”, “second”, “third”, and “fourth” represents the order in which points are input, regardless of the order in which input points are connected to create a figure. Since the validity of input points cannot be determined using only the first point, a second point may be received, in operation 311. After the second point is received, the validity of the input point may be determined, in operation 312. More specifically, it may be determined whether a distance between the first point and the second point is longer than a reference distance. For example, if the reference distance has been set to 5 mm, it may be determined that the second point is valid if the second point is spaced 5 mm or more apart from the first point (“Yes” in operation 312), and otherwise, it may be determined that the second point is invalid (“No” in operation 312). If it is determined that the second point is invalid, a second point may be again received, in operation 311. To again receive the second point, it may be notified to a user that the second point is invalid, in operation 313. To notify the user of the invalidity of the second point, various methods such as, for example, a method of flickering the second point displayed on the display 120 flicker, a method of displaying the second point with a color and/or a shape that is different from that of the first point, a method of displaying a message informing that the second input is invalid, and a method of providing acoustic feedback, e.g., outputting warning sound. Also, a method of providing haptic feedback, e.g., transferring vibration signals to a user through the input unit 110 may be used. If it is determined that the second point is valid (“Yes” in operation 312), a third point may be received, in operation 314. Then, it may be determined whether the third point is valid, in operation 315. More specifically, if the third point is located on a straight line connecting the first point to the second point or on an extension line of the straight line connecting the first point to the second point although the third point is spaced apart from the first and second points by the reference distance or more, no quadrangle can be formed regardless of validity of a fourth point. Accordingly, the controller 130 may determine whether the third point is spaced the reference distance or more apart from both the first and second points, and whether the first point, the second point, and the third point are on a straight line. To determine whether the three points are on a straight line, for example, the controller 130 may use a function of calculating a distance between a straight line formed by two points and the remaining point. If a distance calculated by the function is short than the reference distance, the controller 130 may determine that the three points are on a straight line. If the controller 130 determines that the third point is not spaced the reference distance or more apart from at least one of the first point and the second point, or that the first point, the second point, and the third point are on a straight line, the controller 130 may determine that the third point is invalid (“No” in operation 315). Then, the controller 130 may notify the user that the third point is invalid, in operation 316, and a third point may be again received. When the controller 130 determines that the third point is spaced the reference distance or more apart from both the first point and the second point, and that the first point, the second point, and the third point are not on a straight line, the controller 130 may determine that the third point is valid (“Yes” in operation 315). Then, a fourth point may be received, in operation 317, and the controller 130 may determine whether the fourth point is valid, in operation 318. To determine the validity of the fourth point, the controller 130 may determine whether the fourth point is spaced the reference distance or more apart from at least one of the first, second, and third points, whether the first point, the second point, and the fourth point are on a straight line, whether the first point, the third point, and the fourth point are on a straight line, or whether the second point, the third point, and the fourth point are on a straight line. If at least one of the above-mentioned conditions is satisfied, the controller 130 may determine that the fourth point is invalid. In addition, the controller 130 may determine whether any one of the internal angles of a figure defined by the four points is 180 degrees or more. In this manner, whether a figure defined by the four points is a concave quadrangle is determined. If the controller 130 determines that a figure defined by the four points is a concave quadrangle, the controller 130 may determine that the fourth point is invalid. More specifically, the controller 130 may use a function (for example, an IsCW function) of determining whether an arrangement order of points (i.e., an order in which each point is connected to another point) is a clockwise order or a counterclockwise order to determine whether the fourth point is valid. For example, FIGS. 14A, 14B, 14C, and 14D illustrate a first point 121a, a second point 121b, and a third point 121c, which are arranged is a clockwise order. In this case, as shown in FIG. 14A, if an arrangement order of the first point 121a, the second point 121b, and a fourth point 121d is a clockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a clockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a clockwise order, that is, if the fourth point 121d is located in an R5 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. Also, as shown in FIG. 14B, if an arrangement order of the first point 121a, the second point 121b, and the fourth point 121d is a counterclockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a counterclockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a clockwise order, that is, if the fourth point 121d is located in an R1 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. Also, as shown in FIG. 14C, if an arrangement order of the first point 121a, the second point 121b, and the fourth point 121d is a clockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a counterclockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a counterclockwise order, that is, if the fourth point 121d is located in an R3 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. However, in the remaining cases that do not correspond to FIG. 14A, 14B, or 14C, for example, in a case where it is determined that the fourth point 121d is located in an R2 area, an R4 area, an R6 area, or an R7 area as shown in FIG. 14D, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is a concave quadrangle or does not correspond to any quadrangle. Also, as shown in FIG. 15A, when an arrangement order of the first point 121a, the second point 121b, and the third point 121c is a counterclockwise order, if an arrangement order of the first point 121a, the second point 121b, and the fourth point 121d is a counterclockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a counterclockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a counterclockwise order, that is, if the fourth point 121d is located in an R2 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. Also, as shown in FIG. 15B, if an arrangement order of the first point 121a, the second point 121b, and the fourth point 121d is a counterclockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a clockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a clockwise order, that is, if the fourth point 121d is located in an R4 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. Also, as shown in FIG. 15C, if an arrangement order of the first point 121a, the second point 121b, and the fourth point 121d is a clockwise order, an arrangement order of the first point 121a, the third point 121c, and the fourth point 121d is a counterclockwise order, and an arrangement order of the second point 121b, the third point 121c, and the fourth point 121d is a counterclockwise order, that is, if the fourth point 121d is located in an R6 area, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is not a concave quadrangle. However, in the remaining cases that do not correspond to FIG. 15A, 15B, or 15C, for example, in a case where it is determined that the fourth point 121d is located in an R1 area, an R3 area, an R5 area, or an R7 area as shown in FIG. 15D, the controller 130 may determine that a figure defined by the four points 121a, 121b, 121c, and 121d is a concave quadrangle or does not correspond to any quadrangle. In other words, in the cases of FIGS. 14A, 14B, and 14C and FIGS. 15A, 15B, and 15C, the controller 130 may determine that the first to fourth points 121a, 121b, 121c, and 121d are valid, and create a window defined by the four points 121a, 121b, 121c, and 121d, in operation 320. FIGS. 16A, 16B, 16C, and 16D are views for describing operation of creating a window of a quadrangle using four points according to exemplary embodiments. If four points 121a, 121b, 121c, and 121d input by a user are connected by straight lines in the input order of the points to create a window, the straight lines connecting the points to each other may cross each other to create two polygons or more, as shown in FIGS. 16A and 16B. In an exemplary embodiment, the order in which points are input by a user may not be considered in creating a window. Accordingly, the window creator 131 may connect the four points 121a, 121b, 121c, and 121d to each other regardless of the order in which the points are input by a user such that a quadrangular window can be formed as shown in FIG. 16C. To create a quadrangular window, the window creator 131 may connect each point to other two points by straight lines while the straight lines do not cross each other. Also, the window creator 131 may connect a point to other two points such that the connected four points 121a, 121b, 121c, and 121d are prevented from forming an incomplete figure with an opening, etc., or creating two or more polygons. To prevent an incomplete figure with an opening, etc., or two or more polygons from being created, the window creator 131 may rearrange the order in which the points are connected, according to the arrangement order of the points, in operation of determining the validity of the points. Referring again to FIGS. 14A, 14B, and 14C and FIGS. 15A, 15B, and 15C, if the points 121a, 121b, 121c, and 121d are connected in the order in which the points 121a, 121b, 121c, and 121d have been input although all the four points 121a, 121b, 121c, and 121d are valid, an invalid figure such as two triangles may be created. Accordingly, the window creator 131 may connect the points in the order in which the points are connected to create a normal quadrangle, regardless of the order in which the points have been input. Hereinafter, an example of connecting points in a clockwise order to create a window will be described. In the case of FIG. 14A, the four points 121a, 121b, 121c, and 121d may be connected in the order in which the points 121a, 121b, 121c, and 121d have been input to create a window of a quadrangle. However, in the case of FIG. 14B, if the four points 121a, 121b, 121c, and 121d are connected in the order in which the points 121a, 121b, 121c, and 121d have been input, two triangles may be formed. Accordingly, the first point 121a and the fourth point 121d may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d. That is, the fourth point 121d, the second point 121b, the third point 121c, and the first point 121a may be connected in this order to create a window of a quadrangle. Similarly, in the case of FIG. 14C, if the four points 121a, 121b, 121c, and 121d are connected in the order in which the points 121a, 121b, 121c, and 121d have been input, two triangles may be formed. In this case, the third point 121c and the fourth point 121d may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d to thereby create a window of a quadrangle. In the case of FIG. 15A, the second point 121b and the fourth point 121d may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d, that is, in a clockwise order to thereby create a window of a quadrangle. In the case of FIG. 15B, the second point 121b and the third point 121c may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d, and again the third point 121c and the fourth point 121d may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d to thereby create a window of a quadrangle. In the case of FIG. 15C, the second point 121b and the third point 121c may be in the reverse order when connecting the four points 121a, 121b, 121c, and 121d to thereby create a window of a quadrangle. When the window creator 131 determines the validity of a point and feeds the result of the determination back to a user whenever the point is input, as described above, the user can quickly correct any invalid point, and a time period for which shutter processing is performed can be reduced. After creating the window, the window creator 131 may detect coordinates corresponding to coordinates of the window from the medical image displayed on the display 120, and set an area corresponding to the detected coordinates to a window area. If a domain in which the coordinates of the window are defined is different from a domain that is applied to the medical image, the window creator 131 may perform domain conversion using a correlation between the two domains. Also, the image processor 132 may perform shutter processing to reduce the brightness of the remaining area except for the window area in the medical image displayed on the display 120 to render the remaining area appear dark, or to reduce the definition of the remaining area to render the remaining area appear blurry. Since the remaining area except for the window area is not cut off although the image processor 132 performs shutter processing, image information about the remaining area can be maintained without being deleted. FIG. 17 is a control block diagram of the image processing apparatus 100 further including a communicator, according to an exemplary embodiment. Referring to FIG. 17, the image processing apparatus 100 may further include a communicator 150 to perform wired and/or wireless communication with another apparatus or system. A medical image subject to shutter processing by the image processor 132 may be stored in the storage unit 150, and the medical image stored in the storage unit 150 may be transmitted to another apparatus or system through the communicator 150. For example, if the image processing apparatus 100 is included in the medical imaging apparatus 20, a window area may be selected by a radiological technologist, shutter processing may be performed according to the window area, and then, the resultant medical image may be stored in the storage unit 150. The medical image stored in the storage unit 150 may be transmitted to a central server 10 in a medical institution through the communicator 150. At this time, the original image not subject to shutter processing may also be transmitted to the central server 10, together with the shutter-processed medical image, or only the shutter-processed medical image may be transmitted to the central server 10. The central server 10 may store the received image(s). A doctor may search for the shutter-processed image from among images stored in the central server 10 to receive the searched image through the user control apparatus 30 using the communicator 150. Accordingly, the doctor can accurately recognize an area to be diagnosed, based on the shutter-processed image, and perform more accurate and quicker diagnosis. According to another example, if the image processing apparatus 100 is included in the central server 10, the image processing apparatus 100 may receive a medical image from the medical imaging apparatus 20 through the communicator 150, and store the received medical image in the storage unit 140. Accordingly, a doctor or a radiological technologist can search for a desired medical image in the central server 10, and input a selection for setting a window area to the central server 10. Then, a shutter-processed image may be transmitted to the user control apparatus 30 through the communicator 150. According to still another example, if the image processing apparatus 100 is included in the user control apparatus 30, the image processing apparatus 100 may receive a medical image from the central server 10 or the medical imaging apparatus 20 through the communicator 150, and receive a selection for setting a window area of the received image to perform shutter processing. In the exemplary embodiments described above, a case of creating a window of a quadrangle by receiving four points (n=4) has been described. Hereinafter, another exemplary embodiment of receiving user inputs will be described. FIG. 18 is a view for describing an example of receiving inputs of three points for performing shutter processing on a medical image in the image processing apparatus 100 according to an exemplary embodiment, and FIG. 19 shows the result of shutter processing performed by the image processing apparatus 100 that receives the three points. The image processing apparatus 100 may receive n points (wherein n is an integer greater than or equal to 3) from a user, and set a window in a shape of a polygon whose vertexes are the n points, as described above. Accordingly, if n is 3, the image processing apparatus 100 may set a window in a shape of a triangle. As shown in FIG. 18, a user may input three points 121a, 121b, and 121c on an image displayed on the display 120 through the input unit 110. A method in which a user inputs points has been described above with reference to the case of n being 4. The window creator 131 may determine validity of the three points 121a, 121b, and 121c. This operation may be the same as operation of determining validity of the first to third points, as described above with reference to FIG. 13. If the window creator 131 determines that all of the three points 121a, 121b, and 121c are valid, the controller 130 may set a triangle whose vertexes are the three points 121a, 121b, and 121c, to a window, and the image processor 132 may perform shutter processing on the remaining area except for the window area of the medical image displayed on the display 120 to render the remaining area appear dark or blurry, as shown in FIG. 19. FIG. 20 is a view for describing an example in which the image processing apparatus 100 according to an exemplary embodiment receives a user's inputs of inputting five points when performing shutter processing on a medical image, and FIG. 21 shows the result of shutter processing performed by the image processing apparatus 100 that received the five points. When receiving n points, wherein n is 5, a window in a shape of a pentagon may be set. As shown in FIG. 20, a user may input five points 121a, 121b, 121c, 121d, and 121e on an image displayed on the display 120 through the input unit 110. A method in which a user inputs points has been described above with reference to the case of n being 4. The window creator 131 may determine validity of the five points 121a, 121b, 121c, 121d, and 121e. This operation may be performed by determining validity of the fifth point 121e after operation of determining validity of the first to fourth points 121a, 121b, 121c, and 121d as described above with reference to FIG. 13. If the fifth point 121e is not spaced the reference distance or more apart from at least one of the first point 121a, the second point 121b, the third point 121c, and the fourth point 121d, if the fifth point 121e is on a straight line with at least two of the first point 121a, the second point 121b, the third point 121c, and the fourth point 121d, or if a concave figure is formed by the fifth point 121e, that is, if at least one of the internal angles of a figure defined by connecting the five points 121a, 121b, 121c, 121d, and 121e to each other is 180 degrees or more, the window creator 131 may determine that the fifth point 121e is invalid, and again receive an input from a user. If the window creator 131 determines that all of the five points 121a, 121b, 121c, 121d, and 121e are valid, the window creator 131 may set a pentagon whose vertexes are the five points 121a, 121b, 121c, 121d, and 121e to a window, and the image processor 132 may perform shutter processing on the remaining area except for the window area in the medical image displayed on the display 120 to render the remaining area dark or blurry, as shown in FIG. 21. FIG. 22 shows an example of a graphic user interface that can be used to set a window having a triangle or pentagon shape. The image processing apparatus 100 may set a window of a triangle or a pentagon, as well as a window of a quadrangle. Therefore, the image processing apparatus 100 can receive a user's input of selecting a shape of a window to be set. Referring to FIG. 22, a window setting menu 125 may include an icon 125g to set a window of a triangle by selecting three points, and an icon 125h to set a window of a pentagon by selecting five points. If a user selects the icon 125g, the input unit 110 may enter a standby state to receive three points, and if the user selects the icon 125h, the input unit 110 may enter a standby state to receive five points. If the user selects an icon 125f, the input unit 110 may enter a standby state to receive four points. FIG. 23 shows a set window and an enlarged image according to an exemplary embodiment, and FIG. 24 shows an example of a graphic user interface that can be used to enlarge a window area according to an exemplary embodiment. A window area 123 may be defined by points input by a user, as described above, and the size of the window area 123 may also be defined by the points input by the user. However, when a user wants to view the window area 123 in detail in a medical image 230 displayed on the display 120, the user can enlarge the window area 123, as shown in FIG. 23. Herein, enlarging the window area 123 does not mean enlarging an area of the window area 123 in the medical image 230, but means showing an enlarged view of the window area 123. As shown in FIG. 24, the window setting menu 125 may further include an icon 125i to enlarge a window. Accordingly, a user may select the icon 125i for enlarging a window after a window is set, to view the window area in detail. In the exemplary embodiments of the image processing apparatus 100, as described above, the case of setting a window of a polygon has been described, however, the exemplary embodiments are not limited thereto. For example, the image processing apparatus 100 can set a window of a circle. Hereinafter, an exemplary embodiment of setting a window of a circle will be described in detail. FIGS. 25, 26, 27, and 28 are views for describing an example in which an image processing apparatus according to an exemplary embodiment receives a user's selection of setting a circular window when performing shutter processing on a medical image. For example, referring to FIG. 25, if a user may input two points 121a and 121b on a medical image displayed on the display 120, the controller 130 may set a window in a shape of a circle whose circumference is defined by the two points 121a and 121b, that is, a window in a shape of a circle whose diameter corresponds to a straight line connecting the two points 121a and 121b. In another example, the controller 130 may set a window of a circle whose circumference includes at least one of the two points 121a and 121b, and whose center point is the other one of the two points. That is, the controller 130 may set a window of a circle whose radius corresponds to a straight line connecting the two points. Also, the controller 130 may determine validity of the input points. More specifically, the window creator 131 may determine that the second point is invalid if a distance between the two points is shorter than the reference distance, and again receive another input from a user. According to another example, as shown in FIG. 26, a user may input a point 121a and a straight line L starting from the point 121a on a medical image 230 displayed on the display 120. In this case, the controller 130 may set a window of a circle whose center point is the point 121a and whose radius corresponds to the straight line L. Alternatively, as shown in FIG. 27, the controller 130 may set a window of a circle whose circumference includes the input point 121a, and whose diameter corresponds to the straight line L. Similarly, the controller 130 may determine validity of the input point. More specifically, the window creator 131 may determine that the input point is invalid if a length of the straight line is shorter than a reference length, and again receive another input from the user. According to still another example, as shown in FIG. 28, a user may input a point 121a on a medical image 230 displayed on the display 120. If the input unit 110 is a touch panel, the user may touch the corresponding point with the user's hand H. If the user's touch is input, a circle whose center is the input point 121a may be created, and in response to a time duration of the user's touch, the size of the circle may gradually increase. When the user stops touching the point 121a, that is, when the user takes the user's hand H off the input unit 110, the size of the circle may no longer increase, and a circle having a size at which the size of the circle no longer increase may define the shape of a window. FIG. 29 shows an example of a graphic user interface that can be used to set a circular window. As shown in FIG. 29, a window setting menu 125 may include an icon 125j to set a circular window. If the icon 125j is selected by a user, the input unit 110 may enter a standby state to receive a selection for setting a circular window, and the window creator 131 may determine validity of inputs, independently from the case of setting a window of a polygon as shown in FIGS. 25 and 26. The image processing apparatus 100 can be included in the medical imaging apparatus 20, as described above, and hereinafter, the medical imaging apparatus 20 including the image processing apparatus 100 will be described. FIG. 30 shows an external appearance of an X-ray imaging apparatus that performs radiography, according to an example of the medical imaging apparatus 20, FIG. 31 shows an external appearance of an X-ray imaging apparatus that performs mammography, according to another example of the medical imaging apparatus 20, and FIG. 32 shows an external appearance of a computerized tomography (CT) apparatus according to still another example of the medical imaging apparatus 20. If the medical imaging apparatus 20 is an X-ray imaging apparatus to perform radiography, the X-ray imaging apparatus 20 may include an X-ray source 21 to irradiate X-rays to an object, and an X-ray detector 22 to detect X-rays, as shown in FIG. 30. The X-ray source 21 may be mounted on the ceiling of a room for X-ray scanning. If the X-ray source 21 irradiates X-rays toward a target area of an object 3, the X-ray detector 22 mounted on a stand 20-1 may detect X-rays transmitted through the object 3. Referring to FIG. 31, if the medical imaging apparatus 20 is an X-ray imaging apparatus for mammography, an arm 20b may be connected to a housing 20a, an X-ray source 21 may be installed in the upper part of the arm 20b, and an X-ray detector 22 may be installed in the lower part of the arm 20b. When tomosynthesis is performed, the arm 20b may rotate with respect to a shaft 20b-1. The X-ray source 21 may be disposed to face the X-ray detector 22. By locating a breast of the object 3 between the X-ray source 21 and the X-ray detector 22, and irradiating X-rays to the breast, X-rays transmitted through the breast of the object 3 may be detected. Since breasts are soft tissues, the X-ray imaging apparatus 20 for mammography may further include a pressure paddle 23. The pressure paddle 23 may press the breast to a predetermined thickness during X-ray scanning. If the breast is pressed, the thickness of the breast may be thinned to acquire clearer images while reducing a dose of X-rays. Also, overlapping tissues may be spread so that a viewer can observe the internal structure of the breast in more detail. A CT apparatus, which acquires images by transmitting X-rays to an object, similar to the X-ray imaging apparatus 20 of FIGS. 30 and 31, can irradiate X-rays at various angles toward an object to thereby acquire section images of the object. If the medical imaging apparatus 20 is a CT apparatus, a housing 20a may include a gantry 20a-1, and an X-ray source 21 and an X-ray detector 22 may be disposed to face each other in the inside of the gantry 20a-1, as shown in FIG. 32. If an object 3 is conveyed by a patient table 20c and placed inside a bore 20d that is the center of the gantry 20a-1, the X-ray source 21 and the X-ray detector 22 may rotate 360 degrees with respect to the bore 20d to acquire projected data of the object 3. FIG. 33 shows a configuration of the X-ray source 21 included in the X-ray imaging apparatus 20 according to an exemplary embodiment, and FIG. 34 shows a configuration of the X-ray detector 22 included in the X-ray imaging apparatus 20 according to an exemplary embodiment. The X-ray source 21 is also called an X-ray tube, and may receive a supply voltage from an external power supply (not shown) to generate X-rays. Referring to FIG. 33, the X-ray detector 22 may be embodied as a two-electrode vacuum tube including an anode 21c and a cathode 21e. The cathode 21e may include a filament 21h and a focusing electrode 21g for focusing electrons, and the focusing electrode 21g is also called a focusing cup. The inside of a glass tube 21a may be evacuated to a high vacuum state of about 10 mmHg, and the filament 21h of the cathode 21e may be heated to a high temperature, thereby generating thermoelectrons. The filament 21h may be a tungsten filament, and the filament 21h may be heated by applying current to electrical leads 21f connected to the filament 21h. The anode 21c may include copper, and a target material 21d may be applied on the surface of the anode 21c facing the cathode 21e, wherein the target material 21d may be a high-resistance material, e.g., Cr, Fe, Co, Ni, W, or Mo. The target material 21d may be formed to have a slope inclined at a predetermined angle, and the greater the predetermined angle, the smaller the focal spot size. In addition, the focal spot size may vary according to a tube voltage, tube current, the size of the filament 21h, the size of the focusing electrode 21e, a distance between the anode 21c and the cathode 21e, etc. When a high voltage is applied between the cathode 21e and the anode 21c, thermoelectrons may be accelerated and collide with the target material 21d of the anode 21e, thereby generating X-rays. The X-rays may be irradiated to the outside through a window 21i. The window 21i may be a Beryllium (Be) thin film. Also, a filter (not shown) for filtering a specific energy band of X-rays may be provided on the front or rear side of the window 21i. The target material 21d may be rotated by a rotor 21b. When the target material 21d rotates, the heat accumulation rate may increase ten times per unit region and the focal spot size may be reduced, compared to when the target material 21d is fixed. The voltage that is applied between the cathode 21e and the anode 21c of the X-ray tube 21 is called a tube voltage. The magnitude of a tube voltage may be expressed as a crest value (kVp). When the tube voltage increases, velocity of thermoelectrons increases accordingly. Then, energy (energy of photons) of X-rays that are generated when the thermoelectrons collide with the target material 21d also increases. Current flowing through the X-ray tube 21 is called tube current, and can be expressed as an average value (mA). When tube current increases, the number of thermoelectrons emitted from the filament 21h increases, and as a result, a dose of X-rays (that is, the number of X-ray photons) that are generated when the thermoelectrons collide with the target material 21d increases. In summary, energy of X-rays can be controlled by adjusting a tube voltage. Also, a dose or intensities of X-rays can be controlled by adjusting tube current and an X-ray exposure time. Accordingly, it is possible to control the energy, intensity, or dose of X-rays according to the properties of the object such as the kind or thickness of the object or according to the purposes of diagnosis. The X-ray source 21 may irradiate monochromatic X-rays or polychromatic X-rays. If the X-ray source 21 irradiates polychromatic X-rays having a specific energy band, the energy band of the irradiated X-rays may be defined by upper and lower limits. The upper limit of the energy band, that is, the maximum energy of the irradiated X-rays may be adjusted according to the magnitude of the tube voltage, and the lower limit of the energy band, that is, the minimum energy of the irradiated X-rays may be adjusted by a filter disposed in the irradiation direction of X-rays. The filter functions to pass or filter only a specific energy band of X-rays therethrough. Accordingly, by providing a filter for filtering out a specific wavelength band of X-rays on the front or rear side of the window 21i, it is possible to filter out the specific wavelength band of X-rays. For example, by providing a filter including aluminum or copper to filter out a low energy band of X-rays that deteriorates image quality, it is possible to improve X-ray beam quality, thereby raising the upper limit of the energy band and increasing average energy of X-rays to be irradiated. Also, it is possible to reduce a dose of X-rays that is applied to the object 3. The X-ray detector 22 may convert X-rays transmitted through the object 3 into electrical signals. As methods for converting X-rays into electrical signals, a direct conversion method and an indirect conversion method may be used. In the direct conversion method, if X-rays are incident, electron-hole pairs may be temporarily generated in a light receiving device, electrons may move to the anode 21c and holes may move to the cathode 21e by an electric field applied to both terminals of the light receiving device. The X-ray detector 22 may convert the movements of the electrons and holes into electrical signals. In the direct conversion method, the light receiving device may be a photoconductor including amorphous selenium (a-Se), CdZnTe, HgI2, or PbI2. In the indirect conversion method, a scintillator may be provided between the light receiving device and the X-ray source 21. If X-rays irradiated from the X-ray source 21 react with the scintillator to emit photons having a wavelength of a visible-ray region, the light receiving device may detect the photons, and convert the photons into electrical signals. In the indirect conversion method, the light receiving device may include a-Si, and the scintillator may be a GADOX scintillator of a thin film type, or a CSI (TI) of a micro pillar type or a needle type. The X-ray detector 22 can use any one of the direct conversion method and the indirect conversion method, and in the following exemplary embodiment, for convenience of description, under an assumption that the X-ray detector 22 uses the indirect conversion method to convert X-rays into electrical signals, a configuration of the X-ray detector 22 will be described in detail. Referring to FIG. 34, the X-ray detector 22 may include a scintillator (not shown), a light detecting substrate 22a, a bias driver 22b, a gate driver 22c, and a signal processor 22d. The scintillator may convert X-rays irradiated from the X-ray source 21 into visible rays. The light detecting substrate 22a may receive the visible rays from the scintillator, and convert the received visible rays into a light detected voltage. The light detecting substrate 22a may include a plurality of gate lines GL, a plurality of data lines DL, a plurality of thin-film transistors 22a-1, a plurality of light detecting diodes 22a-2, and a plurality of bias lines BL. The gate lines GL may be arranged in a first direction D1, and the data lines DL may be arranged in a second direction D2 that intersects the first direction D1. The first direction D1 may be at right angles to the second direction D2. In the example of FIG. 34, fourth gate lines GL and four data lines DL are shown. The thin-film transistors 22a-1 may be arranged in the form of a matrix that extends in the first and second directions D1 and D2. Each of the thin-film transistors 22a-1 may be electrically connected to one of the gate lines GL and one of the data lines DL. The gate electrodes of the thin-film transistors 22a-1 may be electrically connected to the gate lines GL, and the source electrodes of the thin-film transistors 22a-1 may be electrically connected to the data lines DL. In the example of FIG. 34, 16 thin-film transistors 22a-1 arranged in four rows and four columns are shown. The light detecting diodes 22a-2 may be arranged in the form of a matrix that extends in the first and second directions D1 and D2 and have a one-to-one correspondence with the thin-film transistors 22a-1. Each of the light detecting diodes 22a-2 may be electrically connected to one of the thin-film transistors 22a-1. The N-type electrodes of the light detecting diodes 22a-2 may be electrically connected to the drain electrodes of the thin-film transistors 22a-1. In the example of FIG. 34, sixteen light detecting diodes 22a-2 arranged in four rows and four columns are shown. Each of the light detecting diodes 22a-2 may receive light from the scintillator, and convert the received light into a light detected voltage. The light detected voltage may be a voltage corresponding to a dose of X-rays. The bias lines BL may be electrically connected to the light detecting diodes 22a-2. Each of the bias lines BL may be electrically connected to the P-type electrodes of the light detecting diodes 22a-2 arranged in a direction. For example, the bias lines 22a-2 may be arranged in substantially parallel to the second direction D2 to be electrically connected to the light detecting diodes 22a-2. Alternatively, the bias lines BL may be arranged in a direction substantially parallel to the first direction D1 to be electrically connected to the light detecting diodes 22a-2. In the example of FIG. 34, four bias lines BL arranged in the second direction D2 are shown. The bias driver 22b may be electrically connected to the bias lines BL to apply a driving voltage to the bias lines BL. The bias driver 22b may apply a reverse bias or a forward bias selectively to the light detecting diodes 22a-2. A reference voltage may be applied to the N-type electrodes of the light detecting diodes 22a-2. The bias driver 22b may apply a voltage that is lower than the reference voltage to the P-type electrodes of the light detecting diodes 22a-2 to apply a reverse bias to the light detecting diodes 22a-2. Also, the bias driver 22b may apply a voltage that is higher than the reference voltage to the P-type electrodes of the light detecting diodes 22a-2 to apply a forward bias to the light detecting diodes 22a-2. The gate driver 22C may be electrically connected to the gate lines GL to apply gate signals to the gate lines GL. The gate driver 22C may apply gate signals sequentially in the second direction D2 to the gate lines GL. For example, if the gate signals are applied to the gate lines GL, the thin-film transistors 22a-1 may be turned on. In contrast, if the gate signals are no longer applied to the gate lines GL, the thin-film transistors 22a-1 may be turned off. The signal processor 22d may be electrically connected to the data lines DL to receive sample input voltages from the data lines DL. The signal processor 22d may output image data to the image processing apparatus 100 based on the sample input voltages. The image data may be an analog/digital signal corresponding to the light detected voltage. The image data output from the X-ray detector 22 may itself configure an X-ray image. However, an image that is displayed on the display 120 by the image processing apparatus 100 may be an image resulting from performing various image processing on an X-ray image output from the X-ray detector 22 to improve the visibility of the X-ray image. The controller 130 of the image processing apparatus 100 may perform such image processing. Although not shown in FIG. 34, if the X-ray detector 22 is embodied as a wireless detector or a portable detector, the X-ray detector 22 may further include a battery unit and a wireless communication interface unit. FIG. 35 shows an external appearance of the medical imaging apparatus 20 according to an exemplary embodiment which is a sealing type X-ray imaging apparatus, and FIG. 36 shows an external appearance of the medical imaging apparatus 20 according to an exemplary embodiment which is a mobile X-ray imaging apparatus. If the X-ray detector 22 is embodied as a wireless detector or a portable detector, the X-ray detector 22 may be used for various kinds of X-ray scanning by moving the X-ray detector 22 as needed. In this case, as shown in FIG. 35, the X-ray imaging apparatus 20 may include a manipulator 25 to provide an interface for manipulating the X-ray imaging apparatus 20, a motor 26 to provide a driving force for moving the X-ray source 21, and a guide rail 27 to move the X-ray source 21 according to the driving force of the motor 26, a movement carriage 28, and a post frame 29. The guide rail 27 may include a first guide rail 27a and a second guide rail 27b disposed at a predetermined angle with respect to the first guide rail 27a. The first guide rail 27a may be orthogonal to the second guide rail 27b. The first guide rail 27a may be installed on the ceiling of an examination room where the X-ray imaging apparatus 20 is placed. The second guide rail 27b may be disposed beneath the first guide rail 27a, and slide with respect to the first guide rail 27a. The first guide rail 27a may include a plurality of rollers (not shown) that are movable along the first guide rail 27a. The second guide rail 27b may connect to the rollers and move along the first guide rail 27a. A direction in which the first guide rail 27a extends may be defined as a first direction D1, and a direction in which the second guide rail 27b extends may be defined as a second direction D2. Accordingly, the first direction D1 may be orthogonal to the second direction D2, and the first and second directions D1 and D2 may be parallel to the ceiling of the examination room. The movement carriage 28 may be disposed beneath the second guide rail 27b, and move along the second guide rail 27b. The movement carriage 28 may include a plurality of rollers (not shown) to move along the second guide rail 27b. Accordingly, the movement carriage 28 may be movable in the first direction D1 together with the second guide rail 27b, and movable in the second direction D2 along the second guide rail 27b. The post frame 29 may be fixed on the movement carriage 28 and disposed below the movement carriage 28. The post frame 29 may include a plurality of posts 29a, 29b, 29c, 29d, and 29e. The posts 29a, 29b, 29c, 29d, and 29e may connect to each other to be folded with each other. The length of the post frame 29 fixed on the movement carriage 28 may increase or decrease in an elevation direction (i.e., Z direction) of the examination room. A direction in which the length of the post frame 29 increases or decreases may be defined as a third direction D3. Accordingly, the third direction D3 may be orthogonal to the first direction D1 and the second direction D2. A revolute joint 29f may be disposed between the X-ray source 21 and the post frame 29. The revolute joint 29f may couple the X-ray source 21 with the post frame 29, and support a load applied to the X-ray source 21. The X-ray source 21 connected to the revolute joint 29f may rotate on a plane that is perpendicular to the third direction D3. The rotation direction of the X-ray source 21 may be defined as a fourth direction D4. Also, the X-ray source 21 may be rotatable on a plane that is perpendicular to the ceiling of the examination room. Accordingly, the X-ray source 21 may rotate in a fifth direction D5 which is a rotation direction of an axis parallel to the first direction D1 and the second direction D2, with reference to the revolute joint 29f. To move the X-ray source 21 in the first direction D1 through the third direction D3, a motor 26 may be provided. The motor 26 may be electrically driven, and may include encoders. The motor 26 may include a first motor 26a, a second motor 26b, and a third motor 26c. The first to third motors 26a to 26c may be arranged at appropriate locations in consideration of convenience of design. For example, the first motor 26a that is used to move the second guide rail 27b in the first direction D1 may be disposed around the first guide rail 27a, the second motor 26b that is used to move the movement carriage 28 in the second direction D2 may be disposed around the second guide rail 27b, and the third motor 26c that is used to increases or decreases the length of the post frame 29 in the third direction D3 may be disposed in the movement carriage 28. As another example, the motor 26 may connect to power transfer device (not shown) to linearly move or rotate the X-ray source 21 in the first to fifth directions D1 to D5. The power transfer device may include a belt and a pulley, a chain and a sprocket, or a shaft. As another example, motors 26a to 26c may be provided between the revolute joint 29f and the post frame 29 and between the revolute joint 29f and the X-ray source 21 to rotate the X-ray source 21 in the fourth and fifth directions D4 and D5. If the X-ray detector 22 is embodied as a wireless detector or a portable detector, the X-ray detector 22 may be attached on the stand 20-1 or the patient table 20c when it is used for X-ray scanning. The X-ray detector 22 may be selected as one having an appropriate specification according to the kind of an object to be scanned or the purpose of diagnosis. When the X-ray detector 22 is not a wireless detector or a portable detector, the X-ray detector 22 may be fixed at the stand 20-1 or the patient table 20c. If the X-ray detector 22 is embodied as a wireless detector or a portable detector, the X-ray detector 22 may be used in a mobile X-ray imaging apparatus 20. Referring to FIG. 36, in the mobile X-ray imaging apparatus 20, both the X-ray source 21 and the X-ray detector 22 may move freely in a three dimensional (3D) space. More specifically, the X-ray source 21 may be attached on a movable main body 20-2 through a support arm 20-3, and the support arm 20-3 can rotate or adjust its angle to move the X-ray source 21. Also, since the X-ray detector 22 is a mobile X-ray detector, the X-ray detector 22 may also be placed at an arbitrary location in the 3D space. The mobile X-ray imaging apparatus 20 can be used usefully to scan patients having difficulties in moving to an examination room or in taking a predetermined posture such as standing or lying. In the above, an X-ray imaging apparatus that images the inside of an object using X-rays has been described as an example of the medical imaging apparatus 20, however, the medical imaging apparatus 20 may be any imaging apparatus using other radiation than X-rays. For example, the medical imaging apparatus 20 may be a positron emission tomography (PET) apparatus using gamma rays. The PET apparatus may inject medicine containing radioisotopes emitting positrons into a human body, and detect gamma rays emitted when positrons emitted from the human body disappear to thereby image the inside of an object. FIG. 37 shows an external appearance of a medical imaging apparatus according to an exemplary embodiment which is an MRI apparatus. If the medical imaging apparatus 20 is an MRI apparatus, a static coil 20a-1 to form a static magnetic field in a bore 20d, a gradient coil 20a-2 to form a gradient magnetic field by making a gradient in the static magnetic field, and an RF coil 20a-3 to apply an RF pulse to an object to excite atomic nuclei and to receive an echo signal from the atomic nuclei may be provided in a housing 20a, as shown in FIG. 37. More specifically, if the patent table 20c is conveyed into the bore 20d in which a static magnetic field is formed by the static coil 20a-1, the gradient coil 20a-2 may apply a gradient magnetic field, and the RF coil 20a-3 may apply an RF pulse to excite atomic nuclei consisting of an object 3 and to receive echo signals from the object, thereby imaging the inside of the object 3. The medical imaging apparatus 20 described above with reference to FIGS. 30 to 37 may include the image processing apparatus 100. In this case, the image processing apparatus 100 may perform functions of a general workstation related to acquisition of medical images. Meanwhile, according to another embodiment of the medical imaging apparatus, a window area selected by a user according to the above-described embodiment may be applied to collimate X-rays to adjust an irradiation area of the X-rays. The medical imaging apparatus according to the current embodiment may be an X-ray imaging apparatus. FIG. 38 is a control block diagram of an X-ray imaging apparatus according to another embodiment of the present disclosure and FIG. 39 is a diagram illustrating a position of a camera disposed in the X-ray imaging apparatus according to the another embodiment. Referring to FIG. 38, an X-ray imaging apparatus 200 according to another embodiment of the present disclosure may include an X-ray source 210 to generate and irradiate X-rays, an input device 221 to receive a setting of a window area, a display 222 to guide an input for a window area and to display an X-ray image, a controller 230 to control operation of the X-ray source 210, a storage device 240 to store an X-ray image, and a communication device 250 to communicate with an external device. According to the embodiment of the X-ray imaging apparatus 200, if the display 222 displays a guide image to guide a user's input, and the user sets a window area on the guide image through the input device 221, the controller 230 may control a collimator 213 (see FIG. 42) to form a collimation area corresponding to the window area. The guide image displayed on the display 222 may be at least one image among an X-ray image acquired by irradiating a low dose of X-rays onto an object before main scanning (main X-ray imaging), a camera image acquired by photographing the object with a camera, and a previously acquired X-ray image of the object. For example, the guide image acquired before main scanning may be a scout image. Also, when an X-ray image of the object is again acquired for follow-up examination, a previously acquired X-ray image for the object may be displayed on the display 222 so that the user can set a window area on the previously acquired X-ray image. Also, in case that the guide image is a camera image, a camera may be installed in the X-ray source 210, an object may be photographed by the camera before X-ray imaging, and camera image of the object may be displayed on the display 222. FIG. 39 shows an X-ray source 210 viewed from the front. Here, a direction toward a front of the X-ray source 210 signifies a direction in which X-rays are radiated. Referring to FIG. 39, the collimator 213 may be disposed in front of the X-ray source 110, and the camera 215 may be embedded in a region adjacent to the collimator 213. While the X-ray source 210 captures an X-ray image of an object, the camera 215 captures a real image of the object, e.g., a target. In an embodiment to be described below, an image captured by the X-ray source 210 will be referred to as an X-ray image, and an image captured by the camera 215 will be referred to as a camera image. The camera 215 may be disposed at a position at which a portion of an object to be imaged by X-rays may be captured. For example, the camera 215 may be mounted on the X-ray source 210 in a direction that is the same as a direction in which X-rays are radiated from the X-ray source 210. When the camera 215 is mounted on the X-ray source 210, the user may more easily set settings related to an X-ray image while looking at a camera image since an offset between a region shown in the X-ray image and a region shown in the camera image is reduced. Since a housing 210a may be formed in front of the collimator 213, the housing 210a may be formed with a material such as a transparent resin or glass to minimize its influence on X-rays radiated from the X-ray tube. The camera 215 may be mounted on an inner portion of the housing 110a as illustrated in FIG. 39. Alternatively, the camera 215 may also be mounted on an outer portion of the housing 110a. Here, the camera 215 may be mounted on a bezel provided at a circumference of the housing 210a. However, since an embodiment of the X-ray imaging apparatus 200 is not limited thereto, the camera 215 may be mounted on any position so long as an image of an object can be captured at the position. In addition, a collimator guideline GL in a cross shape may be formed on the housing 210a formed in front of the collimator 213. When the X-ray irradiation region is irradiated with visible rays by a collimator lamp embedded in the X-ray source 210, the collimator guideline GL may be displayed at the center of the X-ray irradiation region and the user may intuitively recognize a position of the X-ray irradiation region by looking at the collimator guideline GL. Hereinafter, an example of receiving a setting of a window area from a user will be described. For a detailed description, some of the above-described embodiments of the X-ray imaging apparatus 100 will be applied to the X-ray imaging apparatus 200 according to the current embodiment. FIGS. 40 and 41 show an example in which the X-ray imaging apparatus according to the other embodiment of the present disclosure receives four points from a user in order to set a window area, and FIG. 42 shows a result obtained after the X-ray imaging apparatus performs collimation based on the four points. An X-ray image is used as the guide image in this example. The X-ray imaging apparatus 200 may allow a user to input n points (n is an integer that is equal to or greater than 3) on a medial image displayed on the display 222. FIG. 40 to FIG. 42 show a case of n=4. If the input device 221 is implemented as a transparent touch panel to form a touch screen together with the display device 222, the user may touch locations corresponding to desired four points 222a, 222b, 222c, and 222d on an X-ray image displayed on the display 222 with his/her hand H to thereby input the four points 222a, 222b, 222c, and 222d, as shown in FIG. 40. At this time, the input points 222a, 222b, 222c, and 222d may be displayed on the display 222 so that the user can check the selected locations. Alternatively, if the input device 221 is implemented as a mouse, a pointer p moving on the display 222 according to a movement amount and a movement direction of the input device 221 may be displayed on the display 222, as shown in FIG. 41. In this case, the user may use the input device 221 to locate the pointer p at locations corresponding to desired four points 222a, 222b, 222c, and 222d on a medical image, and then click the input device 221 to thereby input the four points 222a, 222b, 222c, and 222d. If the four points 222a, 222b, 222c, and 222d are input on the X-ray image using any one of the above-described methods, a quadrangle defined by the four points 222a, 222b, 222c, and 222d, that is, a window 223 having a quadrangular shape whose vertices are the four points 222a, 222b, 222c, and 222d may be formed, as shown in FIG. 41. That is, the controller 230 may set a quadrangle whose vertices are the four points 222a, 222b, 222c, and 222d, to a window 223, and control a collimation area in order to acquire an X-ray image corresponding to a window area. Herein, the window area may be an area defined by the window 223. Also, the controller 230 may determine validity of a point input by the user. For example, whenever a point is input, the controller 230 may determine validity of the input point. If the controller 230 determines that the input point is invalid, the controller 230 may display the result of the determination through the display 222. If a distance between input points is smaller than a reference value, the controller 230 may determine that a last point is invalid. Also, if at least three points of input points are located on a straight line, the controller 230 may determine that a last point is invalid. Also, if a figure formed by input points has a concave shape, the controller 230 may determine that a last point is invalid. Also, the controller 230 may determine whether a figure formed by input points has a concave shape, depending on whether an arrangement direction of a fourthly input point with respect to at least two of three points previously input is a counterclockwise direction or a clockwise direction. If the controller 230 determines that all of the input points are valid, the controller 230 may connect each point to the other two points with a straight line to form a polygon. If the controller 230 determines that any one of the input points is invalid, the input device 221 may receive a new point to replace the point determined to be invalid. In the above-described example, the window area is a polygon, however, the window area may be set to a circle by receiving one or more points from the user, as described above in the embodiment of the image processing apparatus 100. For example, if two points are input through the input device 221, the controller 230 may set a circle whose diameter or radius is a straight line connecting the two points, to a window area. Also, if a point and a straight line starting from the point are input through the input device 221, the controller 230 may set a circle whose center is the input point and whose radius is the straight line, to a window area. Or, the controller 230 may set a circle whose diameter is the straight line, to a window area. Also, if a point is input through the input device 221, the controller 230 may create a circle whose center is the input point, and increase the radius of the circle in proportion to a time period for which the point is input. The controller 230 may set a circle of a radius acquired at time at which the point is no longer input, to a window area. FIG. 43 shows an example in which the X-ray imaging apparatus according to the other embodiment of the present disclosure uses a camera image as the guide image. Referring to FIG. 43, display 222 may display a camera image IG. The user may set a window area using camera image IG as the guide image. Display 222 may further display a protocol list 225 to receive a selection of the imaging protocol from the user. An X-ray imaging region may change for each imaging protocol, and a suitable X-ray irradiation condition may change for each X-ray imaging region. The imaging protocol may be determined according to an X-ray imaging portion, a posture of an object, and the like. For example, imaging protocols may include whole body anterior-posterior (AP), whole body posterior-anterior (PA), and whole body lateral (LAT), may also include chest AP, chest PA, and chest LAT, and may also include long bone AP, long bone PA and long bone LAT for long bones such as a leg bone. In addition, the imaging protocols may also include abdomen erect. If the user select one among the imaging protocols included in the protocol list 225, display 222 may display a region C corresponding to the selected imaging protocol on the guide image IG. The user may set the window area within the displayed region C. Also, display 222 may display a value of X-ray dose which the object is exposed to when the collimation area is adjusted to match the window area set by the user and a value of X-ray dose which the object is exposed to when the collimation area is adjusted to a region generally set for the selected protocol in an region 224. The user may intuitively recognize a dose reduction effect according to the adjustment of the collimation area by looking at the displayed values. Also, above descriptions related to operation of setting a window area in the embodiment of the image processing apparatus 100 can be applied to the X-ray imaging apparatus 200. In order to avoid redundant descriptions, further descriptions about operation of setting a window area will be omitted. FIG. 44 is a control block diagram of an X-ray source of the X-ray imaging apparatus according to the another embodiment of the present disclosure, FIG. 45 is a top view showing a structure of a collimator used in the X-ray imaging apparatus according to the other embodiment of the present disclosure, and FIG. 46 is a side sectional view of blades of the collimator used in the X-ray imaging apparatus according to the other embodiment of the present disclosure, cut along a line A-A′ shown in FIG. 45. Referring to FIG. 44, the X-ray source 210 may include an X-ray tube 211 to generate X-rays, a collimator 213 to perform collimation on X-rays generated by the X-ray tube 211 and to adjust an irradiation area of the X-rays, and a collimator driver 217 to move the blades constituting the collimator 213. The collimator 213 may include at least one movable blade, and the blade may be formed of a material having a high bandgap to absorb X-rays. The blade may move to adjust an irradiation area of X-rays, that is, a collimation area, and the collimator driver 217 may include a motor for supplying power to each blade, and a driving circuit for driving the motor. The controller 230 may calculate a movement amount of each blade in correspondence to a collimation area, and transmit a control signal for moving the blade by the calculated movement amount to the collimator driver 217. For example, the collimator 213 may include four blades 213a, 213b, 213c, and 213d each formed in the shape of a rectangular flat plate, as shown in FIG. 45. Each of the blades 213a, 213b, 213c, and 213d may move in an X-axis direction or in a Y-axis direction, or may rotate in a clockwise direction or in a counterclockwise direction on any location of the flat plane as an axis of rotation. X-rays may be irradiated through a slot S formed by the plurality of blades 213a, 213b, 213c, and 213d. By passing X-rays through the slot S, collimation may be performed. Accordingly, the slot S formed by the plurality of blades 213a, 213b, 213c, and 213d may be defined as a collimation area. Referring to FIG. 46, the collimator 213 may be disposed in a front direction from the X-ray tube 211. Herein, the front direction from the X-ray tube 211 may be a direction in which X-rays are irradiated. X-rays incident onto the blades 213a, 213b, 213c, and 213d among X-rays irradiated from the X-ray tube 211 may be absorbed in the blades 213a, 213b, 213c, and 213d, and X-rays passed through the collimation area may be incident onto an X-ray detector D. Accordingly, an irradiation area of X-rays irradiated from a focal point 2 of the X-ray tube 211 may be limited by the collimator 213, and scattering of the X-rays may be reduced. By preventing X-rays from being irradiated onto an unnecessary area, it is possible to perform X-ray imaging with a low dose of X-rays. In the example of FIG. 46, the first blade 213a and the third blade 213c may be located on the same plane. However, according to another example, the plurality of blades 213a, 213b, 213c, and 213d may be respectively located on different planes. If the plurality of blades 213a, 213b, 213c, and 213d are respectively located on different planes, the plurality of blades 213a, 213b, 213c, and 213d may move while overlapping with each other so as to form more various shapes of collimation areas. The controller 230 may control the collimator 213 based on a relation between the collimation area and the window area to thereby acquire an X-ray image corresponding to the window area. The X-ray image corresponding to the window area may be an X-ray image having the same or similar size and shape as those of the window area. If an X-ray image to be used as a guide image is acquired, the first blade 213a and the third blade 213c may move in the X-axis direction, and the second blade 213b and the fourth blade 213d may move in the Y-axis direction to form a collimation area in the shape of a rectangle. Like the above-described example, if an input for selecting a collimation area is received from a user, the blades 213a, 213b, 213c, and 213d may again move in order to irradiate X-rays to the selected collimation area. The controller 230 may decide a movement direction and a movement amount of which one(s) of the blades 213a, 213b, 213c, and 213d for forming a collimation area corresponding to the window area, generate a control signal, and transmit the control signal to the collimator driver 217. The collimation area corresponding to the window area may be a collimation area required for creating an X-ray image having the same or similar size and shape as those of the window area. The shape of the collimation area may be the same as or similar to that of the window area, and the size of the collimation area may be proportional to that of the window area. The collimator driver 217 may generate a driving signal according to the received control signal, and transmit the driving signal to the corresponding blade(s). FIGS. 47, 48, and 49 show examples in which a blade of the collimator used in the X-ray imaging apparatus according to the other embodiment of the present disclosure moves. For example, at least one of the plurality of blades 213a, 213b, 213c, and 213d may rotate in the clockwise direction or in the counterclockwise direction on the center as an axis of rotation. Referring to FIG. 47, if the third blade 213c rotates in the clockwise direction on the center as an axis R3 of rotation, a collimation area may be formed in the shape of a trapezoid. Also, the first blade 213a may also be configured to be rotatable in the clockwise direction or in the counterclockwise direction on the center as an axis R1 of rotation, the second blade 213b may also be configured to be rotatable in the clockwise direction or in the counterclockwise direction on the center as an axis R2 of rotation, and the fourth blade 213d may also be configured to be rotatable in the clockwise direction or in the counterclockwise direction on the center as an axis R4 of rotation. If the plurality of blades 213a, 213b, 213c, and 213d are rotatable, a collimation area may be formed in the shape of a triangle by rotating the first blade 213a in the counterclockwise direction and rotating the third blade 213c in the clockwise direction, as shown in FIG. 48. Meanwhile, rotational movements and linear movements of the blades 213a, 213b, 213c, and 213d may be combined. For example, by rotating one of the first blade 213a and the third blade 213c and linearly moving the other one in the X-axis direction to approach the one, a collimation area may be formed in the shape of a triangle, as shown in FIG. 48. Accordingly, only a rotation movement or a combination of a rotation movement and a linear movement may be used according to a desired shape of a triangle. According to another example, at least one of the plurality of blades 213a, 213b, 213c, and 213d may use one of its four vertices as a center of rotation. In this case, by rotating the third blade 213c in the clockwise direction on its one vertex as the axis R3 of rotation, a collimation area may be formed in the shape of a triangle, as shown in FIG. 49. The above-described examples relate to cases of forming a collimation area in the shapes of a trapezoid and a triangle by rotating at least one blade, however, the embodiment of the X-ray imaging apparatus 200 is not limited to these examples. That is, by appropriately combining rotational movements and linear movements of the blades 213a, 213b, 213c, and 213d, a collimation area may be formed in the shape of another polygon not shown in the above-described examples. Meanwhile, the controller 230 may additionally perform image processing on an X-ray image created by X-rays passed through the collimation area. More specifically, if a user sets a polygon shape having four vertices or less, such as a quadrangle or a triangle, to a window area, the controller 230 may control the collimator 213 to form a collimation area of the polygon shape, and additionally perform shutter processing on an X-ray image or cut off an unnecessary part from the X-ray image to thereby acquire an X-ray image more similar to the user's desired shape. At this time, the original X-ray image may be stored in the storage device 240, without being deleted. Meanwhile, if the window area set by the user cannot be formed by the collimator 213, the controller 230 may combine the control of the collimator 213 with image processing to acquire an X-ray image corresponding to the window area set by the user. Herein, the X-ray image corresponding to the window area may be an X-ray image having the shape of the window area, or the remaining area excluding the window area may be an X-ray image having low definition and low brightness. For this, the controller 230 may determine whether the collimator 213 can form a collimation area having a polygon shape defined by points input by a user, before controlling the collimator 213. If the controller 230 determines that the collimator 213 cannot form a collimation area having a polygon shape defined by points input by a user, the controller 230 may control the collimator 213 to form a collimation area of a shape most similar to the corresponding polygon. For example, if the window area set by the user is a pentagon or a circle, the controller 230 may form a collimation area of a quadrangle or a triangle most similar to the window area, and perform shutter processing of reducing brightness or definition of the remaining area except for the window area from an X-ray image corresponding to the collimation area, or perform image processing of cutting off the remaining area. FIG. 50 is a view for describing an example of creating an X-ray image corresponding to a window area by combining the control of the collimator with image processing, in the X-ray imaging apparatus according to the other embodiment of the present disclosure. As shown in FIG. 50, if a window area set by a user is in the shape of a circle having a diameter 2r, the controller 230 may determine that it is impossible to form a collimation area having a the shape of the circle. The display 222 may display a collimation window C representing a collimation area that can be formed by the collimator 213 together with the window 223 set by the user. Also, the display 222 may further display region in which image processing is performed within the collimation window C. Thus, the user may intuitively recognize the region in which the collimation is performed and the region in which the image processing is performed. The controller 230 may control the collimator 213 to acquire an X-ray image in the shape of a square whose one side is equal to the diameter 2r of the circle in length. If the X-ray image is acquired in the shape of the square, the controller 230 may perform shutter processing on the remaining area except for an area occupied by the circle having the diameter 2r to thus create an X-ray image corresponding to the window area set by the user. Details about the shutter processing have been described above in the embodiment of the image processing apparatus 100. Alternatively, the controller 230 may cut off the remaining area as necessary. In this case, the original X-ray image may be stored in the storage device 240. The communication device 250 may transmit the original X-ray image or the image-processed image to a central server that manages medical images, or to the user's personal computer. Hereinafter, an image processing method according to an exemplary embodiment will be described. To perform an image processing method according to an exemplary embodiment, the image processing apparatus 100 according to the exemplary embodiments as described above can be used. Accordingly, the above description related to the image processing apparatus 100 can be applied to the image processing method according to an exemplary embodiment. FIG. 51 is a flowchart illustrating an image processing method according to an exemplary embodiment. Referring to FIG. 51, a medical image may be displayed on the display 120, in operation 321. The medical image may be an image stored in the storage unit 150 or an image received from another external apparatus or system. Then, n points may be received to define a window area, in operation 322. If a window to be set is a polygon whose vertexes are n points, n may be an integer that is greater than or equal to 3, and if a window to be set is a circle, n may be an integer that is greater than or equal to 1. The points may be input through the input unit 110. Since a user can input points while viewing the medical image displayed on the display 120, the user can set his/her desired area to a window area. A method of inputting points has been described above in the above exemplary embodiments, and accordingly, further descriptions thereof will be omitted. Then, validity of the input points may be determined, in operation 323. If two points or more are input, it may be determined whether the input points are spaced a reference distance or more apart from each other, and if three points or more are input to set a window of a polygon, it may be determined whether the three points or more are on a straight line. Also, if four points or more are input to set a window of a polygon, it may be determined whether at least one of the internal angles of a quadrangle formed by connecting the four input points to each other is 180 degrees or more to prevent a window having a concave shape from being set. A method of determining validity of input points has been described above in the exemplary embodiment of the image processing apparatus 100. In the flowchart as shown in FIG. 38, for convenience of description, operation of inputting points and operation of determining validity of points are described as different operations, however, by determining, whenever each of a plurality of points is input, validity of the point to allow a user to immediately correct any wrong point, it is possible to increase the speed of process. If it is determined that any one of the input points is invalid based on the results of the determination on the validity of the points (“No” in operation 324), another point may be received, in operation 326, and if it is determined that all of the input points are valid (“Yes” in operation 324), a window that is defined by the input points may be created, in operation 325. Then, shutter processing may be performed to reduce the brightness of the remaining area except for the window area in the medical image displayed on the display 120 to render the remaining area appear dark, or to reduce the definition of the remaining area to render the remaining area appear blurry, and the shutter-processed image may be displayed on the display 120, in operation 327. Since the remaining area except for the window area is not cut off although shutter processing is performed on the medical image to reduce the brightness or definition of the remaining area, image information about the remaining area is not deleted. Accordingly, the user may acquire information about the remaining area, in addition to information about the window area, from the shutter-processed medical image. The shutter-processed medical image may be temporarily or non-temporarily stored in the storage unit 150, and the original image may also be stored in the storage unit 150 without being deleted. Also, the shutter-processed medical image may be transmitted to another apparatus or system through the communicator 150. According to whether the image processing apparatus 100 performing the image processing method is included in the medical imaging apparatus 20, the central server 10, or the user control apparatus 30, the shutter-processed medical image may be transmitted to another apparatus among the medical imaging apparatus 20, the central server 10, or the user control apparatus 30, through the communicator 150. Hereinafter, an embodiment of a method of controlling an X-ray imaging apparatus will be described. The X-ray imaging apparatus may be the X-ray imaging apparatus 200 described above. Accordingly, above descriptions about the embodiments of the X-ray imaging apparatus 200 will be applied to the method of controlling the X-ray imaging apparatus. FIG. 52 is a flowchart illustrating a method of controlling an X-ray imaging apparatus according to an embodiment of the present disclosure. Referring to FIG. 52, a guide image for guiding a user's input may be displayed, in operation 410. The guide image may be an X-ray image acquired with a low dose of X-rays, a camera image photographed by a camera, or a previously photographed X-ray image of the same object. If a user inputs n points (n is an integer that is greater than or equal to 1) for defining a window area on the guide image displayed on the display 222, the controller 230 may set an area defined by the input points to a window area, in operation 411. Also, the controller 230 may determine validity of the input points, and receive a new input from the user according to the result of the determination on the validity. Details about the operation have already been described in the above embodiment of the image processing method. The controller 230 may control the collimator 213 in order to acquire an X-ray image for the set window area, in operation 412. The controller 230 may adjust the collimator 213 based on a relation between a collimation area and a window area to thereby form a collimation area of a shape and size corresponding to those of the window area. The controller 230 may form a collimation area having a desired shape and size by appropriately combining rotational movements and linear movements of the blades 213a, 213b, 213c, and 213d. For example, the controller 230 may rotate at least one of the plurality of blades 213a, 213b, 213c, and 213d constituting the collimator 213 in the clockwise direction or in the counterclockwise direction to form a collimation area of a polygon, such as a triangle or a quadrangle. Details about the control of the collimator 213 have been described above in the embodiment of the X-ray imaging apparatus 200. If X-rays passed through the collimation area is incident onto the X-ray detector 200, an X-ray image corresponding to the window area may be acquired, in operation 413. Or, image processing may be additionally performed on the X-ray image created by the X-rays passed through the collimation area. More specifically, if the user sets a polygon shape having four vertices or less, such as a quadrangle or a triangle, to a window area, the controller 230 may control the collimator 213 to form a collimation area corresponding to the set shape, and additionally perform shutter processing on an X-ray image, or cut off an unnecessary part from the X-ray image to thereby acquire an X-ray image more similar to the user's desired shape. At this time, the original X-ray image may be stored in the storage device 240, without being deleted. Meanwhile, if the window area set by the user cannot be formed by the collimator 213, the controller 230 may combine the control of the collimator 213 with image processing to acquire an X-ray image corresponding to the window area set by the user. For example, if the window area set by the user is a pentagon or a circle, the controller 230 may form a collimation area of a quadrangle or a triangle most similar to the window area, and perform shutter processing on an X-ray image corresponding to the collimation area. According to the image processing apparatus 100 and the image processing method as described above, since points corresponding to n vertexes of a window of a polygon to be set in a medical image displayed on a display are received from a user, the user may accurately set a window. Also, since only an operation of inputting n points is needed to set a window in a medical image, a complicated workflow of entering an editing mode after a window of a quadrangle is created may be avoided. Also, since the validity of a point is determined whenever the point is input by a user, the user may immediately correct the input point that is determined as invalid, thereby resulting in an increase of processing speed. Also, by controlling the collimator to form a collimation area corresponding to a window area, it is possible to prevent X-rays from being irradiated onto an unnecessary area, thereby implementing X-ray imaging with a low dose of X-rays. According to the image processing apparatus and the image processing method according to the exemplary embodiments, by performing shutter processing with respect to a desired area through a simple operation of a user input, it is possible to reduce a workflow and to improve the accuracy of shutter processing. The image processing methods according to the exemplary embodiments may be recorded as programs that can be executed on a computer and implemented through general-purpose digital computers which can run the programs using a computer-readable recording medium. Data structures described in the above methods can also be recorded on a computer-readable recording medium in various manners. Examples of the computer-readable recording medium include storage media such as magnetic storage media (e.g., read-only memories (ROMs), floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs or DVDs). Furthermore, the computer-readable recording media may include computer storage media and communication media. The computer storage media may include both volatile and nonvolatile and both detachable and non-detachable media implemented by any method or technique for storing information such as computer-readable instructions, data structures, program modules or other data. The communication media may store computer-readable instructions, data structures, program modules, other data of a modulated data signal such as a carrier wave, or other transmission mechanism, and may include any information transmission media. Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents. |
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claims | 1. A system comprising:a reactor housing that is fabricated from a radioactive shielding material and has both an internal volume and a surface that comprises an entry port and an exit port;a chromatographic column that bears at least one radioisotope and is positioned within said internal volume;a filter module that is disposed external to said reactor housing and in fluid communication with said column;an adapter disk disposed on said reactor housing, comprising a ridge of material that extends around said entry port and a ridge of material that extends around said exit port, and,an adapter ridge disposed circumferentially internal to said ridge of material that extends around said entry port. 2. The system of claim 1 wherein said radioactive shielding material is lead, tungsten or depleted uranium. 3. The system of claim 1 wherein said reactor housing is substantially rectilinear. 4. The system of claim 1 wherein said reactor housing is substantially cylindrical. 5. The system of claim 1 wherein said reactor housing includes a first end, a second end, and a wall extending between said first end and said second end. 6. The system of claim 5 wherein said entry port and said exit port are positioned at said first end. 7. The system of claim 6 further comprising a ridge of radioactive shielding material extending around said entry port at said first end. 8. The system of claim 6 further comprising a ridge of radioactive shielding material extending around said exit port at said first end. 9. The system of claim 1 wherein said column comprises aluminum oxide particles from about 50 to about 200 μm in size. 10. The system of claim 1 wherein said column comprises silica gel particles from about 20 to about 100 μm in size. 11. The system of claim 1 wherein said column comprises one or more layers or polypropylene filter membranes, deactivated fused silica wool, one or more glass filter membranes from about 0.2 to about 10 μm in size and/or stainless steel tubing with needle and filter adaptors. 12. The system of claim 11 further comprising funnel drains. 13. The system of claim 1 wherein said filter module comprises a sterile 13 to 25 mm filter membrane from about 0.1 to about 0.22 μm size. 14. The system of claim 1 wherein said filter module is attached to said reactor vessel by a thread type adaptor. 15. The system of claim 14 wherein a needle is attached to said filter module. 16. The system of claim 1 wherein a collection housing is connected to said reactor housing via said filter module. 17. The system of claim 1 wherein said at least one radioisotope is Molybdate Mo-99. 18. The system of claim 1 wherein said at least one radioisotope is Pertechnetate Tc99m. 19. The system of claim 1 further comprising a delivery vessel that is disposed external to said reactor housing and in fluid communication with said column. 20. The system of claim 19 wherein said delivery vessel is contained within a delivery housing that is fabricated from radioactive shielding material. 21. The system of claim 20 wherein said delivery housing has a first end that includes a first coupling, a second end that includes a second coupling, and a wall extending between said first end and said second end. 22. The system of claim 21 wherein said first coupling is threaded. 23. The system of claim 21 further comprising a transfer tool that comprises a pick-up and release rod having a handle at a first end thereof and a coupling at a second end thereof that is compatible with said first coupling. 24. The system of claim 23 wherein said transfer tool is a T-bar handle. 25. The system of claim 19 wherein said delivery vessel comprises a solution of at least one radioisotope. 26. The system of claim 25 wherein said at least one radioisotope is Molybdate Mo-99. 27. The system of claim 25 wherein said solution is Sodium Molybdate Mo-99. 28. The system of claim 25 wherein said delivery vessel comprises about 1 to about 50 Ci. 29. The system of claim 19 wherein said delivery vessel comprises Normal Saline [0.9%] solution. 30. The system of claim 20 wherein said delivery housing abuts a ridge of material that is external to said reactor housing and extends around said entry port. 31. The system of claim 20 wherein said delivery housing is at least partially contained within a ridge of material that is external to said reactor housing and extends around said entry port. 32. The system of claim 19 wherein said delivery vessel is at least partially contained within a ridge of material that is external to said reactor housing and extends around said entry port. 33. The system of claim 1 further comprising a collection vessel that is disposed external to said reactor housing and in fluid communication with said column via said filter module. 34. The system of claim 1 wherein said collection vessel is evacuated. 35. The system of claim 1 wherein said collection vessel comprises a solution of at least one radioisotope. 36. The system of claim 35 wherein said at least one radioisotope is Technetium Tc99m. 37. The system of claim 35 wherein said solution is Sodium Pertechnetate Tc-99m. 38. The system of claim 1 further comprising a saline vessel that is disposed external to said reactor housing and in fluid communication with said column. 39. The system of claim 38 wherein said saline vessel comprises Normal Saline [0.9%] solution. 40. The system of claim 1 wherein said filter module abuts a ridge of radioactive shielding material that is external to said reactor housing and extends around said exit port. 41. The system of claim 1 wherein said filter module is at least partially contained within a ridge of radioactive shielding material that is external to said reactor housing and extends around said exit port. 42. The system of claim 1 wherein said collection vessel is contained within a collection housing that is fabricated from radioactive shielding material. 43. The system of claim 42 wherein said collection housing abuts a ridge of material that is external to said reactor housing and extends around said exit port. 44. The system of claim 42 wherein said collection housing is at least partially contained within a ridge of material that is external to said reactor housing and extends around said exit port. 45. The system of claim 1 further comprising a cart that includes a plurality of delivery vessels that each independently comprises a reactor vessel. 46. The system of claim 1 further comprising a cart that includes a plurality of delivery vessels that each independently comprise a solution of at least one radioisotope and are contained within a delivery housing that is fabricated from radioactive shielding material. 47. The system of claim 46 further comprising a conveyor belt for moving said delivery housing. 48. The system of claim 46 further comprising a transfer tool for moving said delivery housing. 49. The system of claim 46 wherein said at least one radioisotope is Molybdenum-99. 50. The system of claim 46 wherein said solution is Sodium Molybdate Mo 99. 51. The system of claim 46 wherein said delivery vessels each independently comprise about 1 to about 50 Ci. 52. The system of claim 1 further comprising a cart that includes a plurality of evacuated collection vessels. 53. The system of claim 1 further comprising a cart that includes a plurality of saline vessels. 54. The system according to claim 1 wherein said column is configured to be reloaded with radioisotope solution at least once. 55. The system according to claim 54 wherein said column is configured to be reloaded with radioisotope solution at least two times, at least four times, or at least six times. 56. The system according to claim 28 wherein said column is configured to be reloaded with radioisotope solution from a further delivery vessel at least once. 57. The system according to claim 56 wherein said column is configured to be reloaded with radioisotope solution from a further delivery vessel at least two times, at least four times, or at least six times. 58. The system according to claim 1 further comprising a column assembly comprising a further chromatographic column for replacing said chromatographic column after said at least some of said radioisotope has been eluted therefrom. 59. The system according to claim 58 wherein said further chromatographic column is configured to be reloaded with radioisotope solution one to six times. 60. The system according to claim 58 wherein said further chromatographic column is configured to be reloaded with radioisotope solution more than six times. |
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claims | 1. A charged particle beam device for inspecting or structuring a specimen comprising:a charged particle beam source to generate a charged particle beam;a focussing lens to focus the charged particle beam onto the specimen; andan aperture system for defining an aperture for the charged particle beam, the aperture system comprising:a first member to block a first portion of the charged particle beam between the charged particle beam source and the focussing lens;a second member to block a second portion of the charged particle beam between the charged particle beam source and the focussing lens;first means for moving the first member to adjust a size of a blocked first portion of the charged particle beam;second means for moving the second member independently of the first member, wherein the first member and the second member have a respective first edge and a second edge capable of defining a respective first boundary and a second boundary of the aperture, the first edge is a first lateral edge and the second edge is a second lateral edge, and the first means and second means for moving the members are each capable of moving the respective member independently in two orthogonal directions;a third, a fourth, a fifth, a sixth, a seventh or an eighth members to selectively block respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam source and the focussing lens; anda third, a fourth, a fifth, a sixth, a seventh or an eighth means for moving the respective third, fourth, fifth, sixth, seventh or eighth members to adjust sizes of the blocked respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam independently. 2. The charged particle beam device according to claim 1, wherein the first edge or the second edge is shaped to provide a first boundary or a second boundary which extend essentially linearly. 3. The charged particle beam device according to claim 1, wherein the first edge and the second edge are shaped to provide a first boundary and a second boundary which extend essentially in parallel. 4. The charged particle beam device according to claim 1, wherein the first edge or the second edge is shaped to provide an angled or rounded first or second boundary. 5. The charged particle beam device according to claim 1, wherein the first means or the second means for moving the respective first or the second member is capable of moving the respective first edge or second edge without changing the shape of the aperture. 6. The charged particle beam device according to claim 1, wherein the first means or the second means for moving the respective first or second member each include a respective first motor or a second motor. 7. The charged particle beam device according to claim 1, wherein the third, fourth, fifth, sixth, seventh or eighth member have respective third, fourth, fifth, sixth, seventh or eighth edges, which are lateral edges, capable of defining respective third, fourth, fifth, sixth, seventh or eighth boundaries of the aperture. 8. The charged particle beam device according to claim 7, wherein the third, fourth, fifth, sixth, seventh or eighth edge is shaped to provide a respective third, fourth, fifth, sixth, seventh or eighth boundary which extends essentially linearly. 9. The charged particle beam device according to claim 7, wherein a third, a fourth, a fifth, a sixth, a seventh or an eighth means for moving the respective third, fourth, fifth, sixth, seventh or eighth member are each capable of moving the respective third, fourth, fifth, sixth, seventh or eighth edges without changing the shape of the aperture. 10. The charged particle beam device according to claim 7, wherein the third edge and the fourth edge, the fifth edge and the sixth edge or the seventh edge and the eighth edge pair-wise extend essentially in parallel with a tolerance of less than 10 degrees. 11. The charged particle beam device according to claim 1, wherein the first, second, fourth, fifth, sixth, seventh or eighth means for moving the respective first, second, fourth, fifth, sixth, seventh or eighth members are capable of moving the respective member with steps having a step size smaller than 10 μm. 12. The charged particle beam device according to claim 1, wherein the first, second, third, fourth, fifth, sixth, seventh or eighth means for moving the respective first, second, third, fourth, fifth, sixth, seventh or eighth member include a respective first, second, third, fourth, fifth, sixth, seventh or eighth motor. 13. The charged particle beam device according to claim 1, wherein the charged particle beam device includes a scanning unit (17) to scan the charged particle beam across the specimen. 14. The charged particle beam device according to claim 1, wherein the charged particle beam device is an electron beam device or a focussing ion beam device. 15. The charged particle beam device according claim 1, wherein the charged particle beam device further comprising a magnetic octupole component or an electrostatic octupole component. 16. The charged particle beam device according claim 1, wherein the charged particle beam device further comprising a magnetic hexapole component or an electrostatic hexapole component to shape the charged particle beam. 17. The charged particle beam device according claim 1 further having the first, second and third members oriented to define a triangular aperture for the charged particle beam. 18. The charged particle beam device according claim 1, wherein each of the first, second, third, fourth, fifth, sixth, seventh or eighth means for moving the respective first, second, third, fourth, fifth, sixth, seventh or eighth member each include a respective first motor and a second motor for driving the respective members in a first direction and a second direction. 19. The charged particle beam device according claim 1, wherein the first lateral edge and second lateral edge are outer circumferential edges of the aperture. 20. Method for focussing a charged particle beam onto a specimen comprising:providing a charged particle beam device wherein the charged particle beam comprises:a charged particle beam source to generate a charged particle beam;a focussing lens to focus the charged particle beam onto a specimen; andan aperture system for defining an aperture for the charged particle beam;the aperture system comprising:a first member to block a first portion of the charged particle beam between the charged particle beam source and the focussing lens;a second member to block a second portion of the charged particle beam between the charged particle beam source and the focussing lens, wherein the first member and the second member have a respective first edge and a second edge capable of defining a respective first boundary and a second boundary of the aperture, the first edge is a first lateral edge, and the second edge is a second lateral edge;first means for moving the first member to adjust a size of the blocked first portion of the charged particle beam;second means for moving the second member independently of the first member, wherein the first means and second means are each capable of moving the respective member independently in two orthogonal directions;a third, a fourth, a fifth, a sixth, a seventh or an eighth members to selectively block respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam source and the focussing lens; anda third, a fourth, a fifth, a sixth, a seventh or an eighth means for moving the respective third, fourth, fifth, sixth, seventh or eighth members to adjust sizes of the blocked respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam independently;generating the charged particle beam;passing the charged particle beam through a rectangular shaped aperture;passing the charged particle beam through a magnetic or electric octupole field; anddirecting the charged particle beam onto the specimen. 21. Method for focussing a charged particle beam onto a specimen comprising:providing a charged particle beam device, wherein the charged particle beam comprises:a charged particle beam source to generate a charged particle beam;a focussing lens to focus the charged particle beam onto a specimen; andan aperture system for defining an aperture for the charged particle beam;the aperture system comprising:a first member to block a first portion of the charged particle beam between the charged particle beam source and the focussing lens;a second member to block a second portion of the charged particle beam between the charged particle beam source and the focussing lens, wherein the first member and the second member have a respective first edge and a second edge capable of defining a respective first boundary and a second boundary of the aperture, the first edge is a first lateral edge, and the second edge is a second lateral edge;first means for moving the first member to adjust a size of the blocked first portion of the charged particle beam; andsecond means for moving the second member independently of the first member, wherein the first means and second means for moving members are each capable of moving the respective member independently in two orthogonal directions;a third, a fourth, a fifth, a sixth, a seventh or an eighth members to selectively block respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam source and the focussing lens; anda third, a fourth, a fifth, a sixth, a seventh or an eighth means for moving the respective third, fourth, fifth, sixth, seventh or eighth members to adjust sizes of the blocked respective third, fourth, fifth, sixth, seventh or eighth portions of the charged particle beam between the charged particle beam independently;generating the charged particle beam;passing the charged particle beam through a triangular shaped aperture;passing the charged particle beam through a magnetic or electric hexapole field; anddirecting the charged particle beam onto the specimen. |
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claims | 1. A mask layout determination system comprising:a pattern determination unit for allocating light-transmitting regions and light-blocking regions to each of a plurality of mask layouts adapted to performing in-situ synthesis on probes of a microarray;a selection unit for selecting any one of the mask layouts;a comparison unit for comparing a proportion of the light-transmitting regions in a selected mask layout with a minimum light-transmitting proportion; anda pattern change unit for exchanging a light-blocking region of the selected mask layout with a light-transmitting region of an unselected mask layout if the proportion of the light-transmitting regions in the selected mask layout is smaller than the minimum light-transmitting proportion. 2. The system of claim 1, wherein the minimum light-transmitting proportion is equal to or greater than about 5% of a total proportion of the light-transmitting and light-blocking regions. 3. The system of claim 1, wherein the light-transmitting and light-blocking regions respectively correspond to probe cells of the microarray. 4. The system of claim 3, wherein the light-blocking region of the selected mask layout and the light-transmitting region of the unselected mask layout, which are exchanged with each other, correspond to the same probe cell. 5. The system of claim 3, wherein the selected mask layout compared by the comparison unit is a mask layout selected by the selection unit and having at least one of the light-transmitting and light-blocking regions exchanged by the pattern change unit. 6. The system of claim 3, further comprising an examination unit for examining whether a desired target probe is in-situ synthesized using the mask layouts which comprise the mask layout whose light-blocking region is exchanged with the light-transmitting region by the pattern change unit. 7. A mask layout determination method comprising:allocating light-transmitting regions and light-blocking regions to each of a plurality of mask layouts which perform in-situ synthesis on probes of a microarray; andexchanging by a computer a light-blocking region of a mask layout with a light-transmitting region of another mask layout wherein a proportion of the light-transmitting regions in each mask layout is equal to or greater than a minimum light-transmitting proportion. 8. The method of claim 7, wherein the minimum light-transmitting proportion is equal to or greater than about 5% of a total proportion of the light-transmitting and light-blocking regions. 9. The method of claim 7, wherein the light-transmitting and light-blocking regions respectively correspond to probe cells of the microarray. 10. The method of claim 9, wherein the light-blocking region of a mask layout and the light-transmitting region of the another mask layout, which are exchanged with each other, correspond to the same probe cell. 11. The method of claim 10, wherein any one of synthesis target monomers is allocated to each of the mask layouts, and the light-blocking and light-transmitting regions are exchanged with each other between different mask layouts to which the same synthesis target monomer has been allocated, wherein an order of the synthesis target monomers allocated to the light-transmitting regions respectively corresponding to the probe cells remains unchanged before and after the exchange. 12. The method of claim 9, further comprising examining whether a desired target probe is in-situ synthesized using the mask layouts which comprise each mask layout whose light-blocking region is exchanged with a light-transmitting region. 13. A method of fabricating a mask set, the method comprising:allocating light-transmitting regions and light-blocking regions to each of a plurality of mask layouts which perform in-situ synthesis on probes of a microarray;exchanging a light-blocking region of a mask layout with a light-transmitting region of another mask layout wherein a proportion of the light-transmitting regions in each mask layout is equal to or greater than a minimum light-transmitting proportion; andfabricating a plurality of masks using the mask layouts which comprise each mask layout whose light-blocking region is exchanged with a light-transmitting region. 14. The method of claim 13, wherein the minimum light-transmitting proportion is equal to or greater than about 5% of a total proportion of the light-transmitting and light-blocking regions. 15. The method of claim 13, wherein the light-transmitting and light-blocking regions respectively correspond to probe cells of the microarray. 16. The method of claim 15, wherein the light-blocking region of a mask layout and the light-transmitting region of the another mask layout, which are exchanged with each other, correspond to the same probe cell. 17. The method of claim 16, wherein any one of synthesis target monomers is allocated to each of the mask layouts, and the light-blocking and light-transmitting regions are exchanged with each other between different mask layouts to which the same synthesis target monomer has been allocated, wherein an order of the synthesis target monomers allocated to the light-transmitting regions respectively corresponding to the probe cells remains unchanged before and after the exchange. 18. The method of claim 15, further comprising examining whether a desired target probe is in-situ synthesized using the mask layouts which comprise each mask layout whose light-blocking region is exchanged with a light-transmitting region. |
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claims | 1. A neutron beam controlling apparatus comprising a plurality of multilayered plate members, each of the plate members having on its one or both surfaces one or a plurality of minute protruding portions, and each of the protruding portions having an inclined surface which is inclined against the beam axis of neutron beam and serves as an incident plane or an outgoing plane for the neutron beam, wherein each of the minute protruding portions is a long and narrow protrusion extending in an area-wise direction and having both the inclined surface and a surface approximately normal to the plate member. 2. The neutron beam controlling apparatus of claim 1 , wherein each of the plate members comprises at least one element selected from the group consisting of oxygen (O), carbon (C), beryllium (Be), fluorine (F) and deuterium (D 2 ). claim 1 3. The neutron beam controlling apparatus of claim 1 , wherein each of the plate members comprises a material selected from the group consisting of polytetrafluoroethylene, carbon, deuterated polyethylene, heavy water and dry ice. claim 1 4. A neutron beam controlling apparatus comprising a plurality of multilayered plate members, each of the plate members having on its one or both surfaces one or a plurality of minute protruding portions, and each of the protruding portions having an inclined surface which is inclined against the beam axis of neutron beam and serves as an incident plane or an outgoing plane for the neutron beam, wherein each of the minute protruding portions is a long, narrow and linear protrusion having both the inclined surface and a surface approximately normal to the plate member, and all of the inclined surfaces incline toward the same direction. 5. A neutron energy measuring apparatus comprising: means for emitting neutrons therefrom in the form of neutron beam; a neutron beam controlling apparatus according to claim 4 to which the neutron beam is incident; and claim 4 a position-sensitive neutron detector for detecting the neutrons emitted from the neutron beam controlling apparatus. 6. The neutron beam controlling apparatus of claim 4 , wherein each of the plate members comprises a material mainly comprising at least one element selected from the group consisting of oxygen (O), carbon (C), beryllium (Be), fluorine (F) and deuterium (D 2 ). claim 4 7. The neutron beam controlling apparatus of claim 4 , wherein each of the plate members comprises a material selected from the group consisting of polytetrafluoroethylene, carbon, deuterated polyethylene, heavy water and dry ice. claim 4 8. A neutron beam controlling apparatus comprising a plurality of multilayered plate members, each of the plate members having a first and second surface and on at least one of the surfaces one or a plurality of circularly protruding portions arranged so as to form a concentric structure around a central axis of the apparatus, each of the circularly protruding portions having a surface approximately normal to the plate member and a surface inclined toward the center of the concentric structure, wherein when the apparatus is observed in a direction parallel to the central axis, the superposition degree of the circularly protruding portions becomes larger as the distance from the central axis becomes longer. 9. A neutron beam controlling apparatus comprising (i) the neutron beam controlling apparatus according to claim 8 ; and claim 8 (iii) a neutron beam controlling apparatus comprising a plurality of multilayered plate members, each of the plate members having a first and second surface and on at least one of the surfaces one or a plurality of circularly protruding portions arranged so as to form a concentric structure around a central axis of the apparatus, each of the circularly protruding portions having a surface approximately normal to the plate member and a surface inclined outward the concentric structure, wherein when the apparatus is observed in a direction parallel to the central axis, the superposition degree of the circularly protruding portions becomes larger as the distance from the central axis becomes longer. 10. The neutron beam controlling apparatus of claim 8 , wherein each of the plate members comprises a material mainly comprising at least one element selected from the group consisting of oxygen (O), carbon (C), beryllium (Be), fluorine (F) and deuterium (D 2 ). claim 8 11. The neutron beam controlling apparatus of claim 8 , wherein each of the plate members comprises a material selected from the group consisting of polytetrafluoroethylene, carbon, deuterated polyethylene, heavy water and dry ice. claim 8 12. A neutron beam controlling apparatus comprising a plurality of multilayered plate members, each of the plate members having a first and second surface and on at least one of the surfaces one or a plurality of circularly protruding portions arranged so as to form a concentric structure around a central axis of the apparatus, each of the circularly protruding portions having a surface approximately normal to the plate member and a surface inclined outward the concentric structure, wherein when the apparatus is observed in a direction parallel to the central axis, the superposition degree of the circularly protruding portions becomes larger as the distance from the central axis becomes longer. 13. The neutron beam controlling apparatus of claim 12 , wherein each of the plate members comprises a material mainly comprising at least one element selected from the group consisting of oxygen (O), carbon (C), beryllium (Be), fluorine (F) and deuterium (D 2 ). claim 12 14. The neutron beam controlling apparatus of claim 12 , wherein each of the plate members comprises a material selected from the group consisting of polytetrafluoroethylene, carbon, deuterated polyethylene, heavy water and dry ice. claim 12 15. The neutron beam controlling apparatus of claim 8 or 12 , wherein at least one of the plate members has an opening portion at the center. claim 8 12 |
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040640019 | claims | 1. An improved pressurized water reactor system having a water cooled reactor core contained within a reactor vessel, means for delivering the water coolant to the reactor core including a coolant pump and means for removing the water coolant from the reactor core, the improvement comprising: a. differential pressure responsive means external to said reactor vessel including a valve connected between said water coolant delivering means downstream of said coolant pump and said water coolant removing means for relieving excess pressure in said water coolant removing means when the pressure in said water coolant removing means exceeds the pressure downstream of said coolant pump in said water collant delivering means. 2. The improvement as recited in claim 1 wherein said excess pressure relieving means includes a pipe and a valve responsive to the differential pressure between said water coolant removing means and said fluid coolant delivering means. 3. The improvement as recited in claim 2 wherein said valve is a differential pressure actuated check valve. 4. The improvement as recited in claim 2 wherein said nuclear reactor power system includes a steam generator and wherein said water coolant removing means includes a pipe connecting said reactor vessel to the inlet side of the said steam generator and wherein said water coolant delivering means includes a pipe connecting said reactor vessel and the outlet side of said steam generator, said water coolant delivering pipe having a reactor coolant pump intermediate its two ends. |
047298677 | abstract | A spring retainer apparatus includes a pair of assemblies adapted to engage and retain pairs of back-to-back springs of a fuel assembly grid in retracted positions for facilitating the loading of fuel rods into cells of the grid in a scratch-free manner. Each spring retainer assembly has elongated holder bars and a handle bar interconnecting the holder bars together at the same ends thereof so that the holder bars can be concurrently extended along and aligned with the straps of the grid which define the pairs of springs. Also, members are supported by each holder bar which correspond in number to the pairs of springs defined by the straps aligned with the holder bar. Each member has a terminal end configured to engage and retain the springs in their retracted positions when the respective holder bar supporting the member is aligned with and moved toward the springs. The terminal end of each member is bifuracted to define a pocket adapted to receive a pair of springs and retain them in their retracted position and a tapered entrance to the pocket for facilitating insertion of the springs into the pocket. |
description | 1. Field of the Invention The present invention relates to a charged particle beam writing method and a charged particle beam writing apparatus. 2. Background Art Recently, along with the development of higher levels of integration in semiconductor devices, the dimensions of the individual component devices have decreased and so has the width of wires and gates making up these components. Photolithographic techniques which help achieve such miniaturization include the following sequential processes: applying a resist material to the surface of the substrate to be processed to form a resist film; irradiating the substrate with light or an electron beam to expose a predetermined resist pattern to form a latent image; heating the substrate as necessary; developing the pattern to form a micropattern; and etching the substrate using this micropattern as a mask. In photolithography, the minimum width of a wiring pattern, etc. that can be resolved is proportionally dependent on the wavelength of the exposure light. Therefore, as one means of allowing miniaturization of patterns, effort has been made to reduce the wavelength of the exposure light used to form the above resist pattern latent image. Further, the development of electron beam lithography, which serves as a higher resolution exposure technique, has also been in progress. This technique inherently provides a superior resolution, since it uses electron beams, which are charged particle beams. Further, electron beam lithography is also advantageous in that great depth of focus is obtained, which enables dimensional variations to be reduced even when a large step feature is encountered. For this reason, the technique has been applied to the development of state-of-the-art devices typified by DRAM, as well as to the production of some ASICs. Further, electron beam lithography is widely used in the manufacture of masks or reticles used as original artwork for transferring an LSI pattern to the wafer. Japanese Laid-Open Patent Publication No. 9-293670 (1997) discloses a variable shape electron beam writing apparatus used for electron beam photolithography. Such apparatus prepares pattern writing data by using design data (CAD data) of a semiconductor integrated circuit designed by a CAD system and processing it, such as correcting the data and dividing the pattern. For example, the division of the pattern into pattern segments is made on the basis of the maximum shot size, which is defined by the size of the electron beam. After this division of the pattern, the apparatus sets the coordinate positions and size of each shot and the radiation time. Pattern writing data is then produced which is used to shape the shot in accordance with the shape and size of the pattern or pattern segment to be written. The pattern writing data is divided on the basis of strip-shaped frames (or main deflection regions), and each frame is divided into sub-deflection regions. That is, the pattern writing data for the entire chip has a hierarchical data structure in which data of each of a plurality of strip-shaped frames, which correspond to the main deflection regions, is divided into a plurality of pieces of data each representing one of the plurality of sub-deflection regions (smaller in size than the main deflection regions) in the frame. The sub-deflector scans the electron beam over the sub-deflection regions at higher speed than the main deflection regions; the sub-deflection regions are generally the smallest writing fields. When writing on each sub-deflection region, the shaping deflector forms a shot of a size and shape corresponding to the pattern or pattern segment to be written. Specifically, the electron beam emitted from the electron gun is shaped into a rectangular shape by the first aperture and then projected to the second aperture by the shaping deflector, resulting in a change in the shape and size of the beam. The electron beam is then deflected by the sub-deflector and the main deflector and directed onto the mask placed on the stage, as described above. Incidentally, irradiating the mask with the electron beam results in generation of reflection electrons. These generated reflection electrons impinge onto the optical system, detectors, etc. in the electron beam writing apparatus, and as a result, charges are built up, thereby generating a new electric field. This changes the path of the electron beam that has been deflected toward the mask, resulting in displacement of the beam impinging position from the desired target position on the mask, which is referred to as “beam drift.” Although other problems can cause beam drift, in any case it is necessary to make corrections to cause the beam to impinge at the desired location by detecting the reference mark position on the stage in the middle of the writing operation and determining the amount of beam drift. Conventional methods make the above corrections or calibrations at predetermined time intervals. This means that in order to reduce the amount of displacement of the electron beam impinging position due to drift, it is effective to reduce the time intervals at which the drift compensation is made. In this case, however, a reduction in the throughput results. To overcome this problem, the compensation intervals may be shortened at the start and end of the writing operation, at which there is a great change in the amount of drift. However, this means that the traveling speed of the stage is not constant, making it difficult to estimate the time of completion of the writing operation. On the other hand, Japanese Laid-Open Patent Publication No. 9-260247 (1997) discloses a method of drift compensation including: dividing the pattern into a plurality of regions based on the allowable displacement range of the electron beam over these regions; determining the largest rate of change of displacement of the electron beam due to drift over these regions; and determining, based on the above largest rate of change and the above allowable displacement range and for each of the plurality of regions, the time intervals at which to make a drift compensation. The method disclosed in this publication measures the amount of drift in one operation and then estimates the amount of drift and its direction that will occur in the next measurement operation and corrects the electron beam impinging position accordingly. It will be noted that this estimation is easy if the areal density of the pattern to be written is constant, i.e., the area of the portion of the pattern in each individual writing region is equal. However, the estimation is difficult if the areal density of the pattern varies from one writing region to another. However, the estimation is difficult if the areal density of the pattern varies. The above publication only discloses a method of determining the time intervals at which to make a drift compensation for each writing region in the pattern writing field and therefore fails to provide a technique for improving the writing accuracy of the electron beam writing apparatus. The present invention has been made in view of the above problems. It is, therefore, an object of the present invention to provide an electron beam writing method and an electron beam writing apparatus capable of writing with high accuracy by improving the accuracy of the drift compensation while preventing a reduction in the throughput. According to one aspect of the present invention, in a method of writing with a charged particle beam, a predetermined region on which writing is effected by the charged particle beam is divided into smaller regions each consisting of one or the same number of frames, and the areal density of a pattern to be written on each smaller region is determined. The amount of change in pattern areal density between each two adjacent smaller regions is determined, and the smaller regions in the predetermined region are grouped into region groups depending on whether nor not the amount of change is greater than a predetermined value. For each region group, a time profile for compensating for the drift of the charged particle beam is determined. A pattern on the predetermined region is written while compensating for the drift of the charged particle beam for each region group in accordance with the time profile. According to another aspect of the present invention, in a charged particle beam writing apparatus which divides a predetermined region on which writing is effected by a charged particle beam into a plurality of region groups and writes a pattern on the predetermined region while compensating for the drift of the charged particle beam in accordance with a time profile for compensating for the drift of the charged particle beam, the time profile being determined for each region group, the charged particle beam writing apparatus comprises grouping means for dividing the predetermined region into smaller regions each consisting of one or the same number of frames, obtaining data indicative of the areal density of a pattern to be written on each smaller region, determining the amount of change in pattern areal density between each two adjacent smaller regions, and grouping the smaller regions into region groups depending on whether or not the amount of change is greater than a predetermined value. An electron beam writing method of an embodiment of the present invention begins by dividing a predetermined region on which writing is effected by an electron beam into smaller regions each consisting of one or the same number of frames. The method then determines the areal density of a pattern to be written on each smaller region. The next step determines the amount of change in pattern areal density between each two adjacent smaller regions, and groups these smaller regions into region groups depending on whether or not the amount of change in pattern areal density is greater than a predetermined value. The method then determines, for each region group, a time profile for compensating for the drift of the electron beam. It should be noted that in this specification, if the pattern areal density in one region is lower than that in the preceding region, the amount of change in pattern areal density between these regions is defined to be negative. On the other hand, if the pattern areal density in one region is higher than that in the preceding region, then the amount of change in pattern areal density between these regions is defined to be positive. FIG. 1 is a schematic plan view of a mask. Referring to FIG. 1, a first region 200A and a second region 200B on the mask 2 are areas on which writing is effected by an electron beam. The writing operation on the first region 200A precedes that on the second region 200B. The first and second regions 200A and 200B are divided into small regions 201 to 209 and small regions 210 to 215, respectively, defined by broken lines in FIG. 1. It should be noted that although in this example each small region consists of 5 frames, each small region may consist of any positive integer number of frames. According to the present embodiment, the areal density of the pattern to be written is determined on a small region basis. This determination may be made by calculation, i.e., finding the actual areal density value; or alternatively the pattern areal density may be determined visually without resorting to calculation. In the example shown in FIG. 1, small regions 201 to 204 and 207 to 209 have the same pattern areal density, and small regions 205 and 206 also have the same pattern areal density which, however, is different from the pattern areal density of the small regions 201 to 204 and 207 to 209. Likewise, small regions 210, 211, 214, and 215 have the same pattern areal density, and small regions 212 and 213 also have the same pattern areal density which, however, is different from the pattern areal density of the small regions 210, 211, 214, and 215. It will be noted that the pattern to be written is not shown in FIG. 1. Next, a determination is made of the amount of change in pattern areal density between each two adjacent small regions. For example, the amount of change in pattern areal density is zero between the small regions 201 and 202, but not zero between the small regions 204 and 205. In this case, if the pattern areal density of the small region 204 is lower than that of the small region 205, then the amount of change in pattern areal density between these regions is positive. Likewise, the amount of change in pattern areal density between the small regions 206 and 207 is negative. It should be noted that if the small region 209 is the last small region in the first region 200A on which the writing is to be performed and the small region 210 is the first small region in the second region 200B on which the writing is to be performed, then these small regions 209 and 210 are regarded as being adjacent each other. Therefore, the amount of change in pattern areal density between these small regions 209 and 210 is also determined. Next, the small regions in the first and second regions 200A and 200B are grouped into region groups based on the determination of whether or not the amount of change in pattern areal density between each two adjacent small regions is zero. In FIG. 1, the region groups in the first region 200A are denoted by reference numerals 220 to 224, and those in the second region 200B are denoted by 230 to 234. The pattern writing is first performed on a selected small region, and then if the next small region on which the writing is to be subsequently performed has the same pattern areal density as the current small region, then the amount of drift is measured on the current small region, and the target electron beam impinging position for the next small region is corrected based on the estimated amount of drift and its direction on the next small region. If the next small region has a different pattern areal density than the current small region, on the other hand, it is difficult to estimate the amount of drift on the next small region in the manner described above. To overcome this problem, the time intervals at which the drift compensation is performed are made shorter in the latter case than in the former. For example, in the first region 200A, the small regions 201 and 202 have the same pattern areal density. Further, the small regions 202, 203, and 204 also have the same pattern areal density. However, there is a change in pattern areal density between the small region 204 and the small region 205. Further, the small regions 205 and 206 have the same pattern areal density, but there is a change in pattern areal density between the small regions 206 and 207. On the other hand, the small regions 207, 208, and 209 have the same pattern areal density. That is, the region groups on which it is difficult to estimate the amount of drift and its direction are the region groups 221 and 223, since they have a different pattern areal density than their preceding region groups. Further, in the second region 200B, the small regions 210 and 211 have the same pattern areal density, but there is a change in pattern areal density between the small regions 211 and 212. The small regions 212 and 213 have the same pattern areal density, but there is a change in pattern areal density between the small regions 213 and 214. Further, the small regions 214 and 215 have the same pattern areal density. That is, the region groups on which it is difficult to estimate the amount of drift and its direction are the region groups 231 and 233, since they have a different pattern areal density than their preceding region groups. As described above, the drift compensation time profile is determined to be such that each region group having a different pattern areal density than the preceding region group is subjected to drift compensation at shorter intervals than region groups having the same pattern areal density as their preceding region groups. For example, referring to FIG. 1, the drift compensation on the region groups 220, 222, and 224 may be made at 20 min. intervals, and the drift compensation on the groups 221 and 223 may be at 5 min. intervals. Likewise, the drift compensation on the region groups 230, 232, and 234 may be made at 20 min. intervals, and the drift compensation on the region groups 231 and 233 may be at 5 min. intervals. It should be noted that although in this example the small regions 209 and 210 have the same pattern areal density, they may have different pattern areal densities. In the case where there is a change in pattern areal density between the small regions 209 and 210, the drift compensation on the region group 230 is made at shorter intervals than that on the region group 224. Thus, the drift compensation on the region groups 221, 223, 231, and 233 are made at shorter time intervals, since it is difficult to estimate the amount of drift and its direction on these groups. This allows the writing accuracy to be improved, as compared to when the drift compensation is made at longer time intervals. On the other hand, since it is easy to estimate the amount of drift and its direction on the region groups 220, 222, 224, 230, 232, and 234, the drift compensation on these groups is made at longer time intervals, thereby preventing a reduction in the throughput. It should be noted that in the above example, the small regions 201 to 204 have the same pattern areal density and so do the small regions 207 to 209 and so do the small regions 205 and 206. Further, the small regions 210, 211, 214, and 215, and the small regions 202, 203 have the same pattern areal density and so do the small regions 212 and 213. With this arrangement, these small regions are grouped into region groups depending on whether or not the absolute value of the amount of change in pattern areal density between each two adjacent small regions is zero. However, according to the present embodiment, the areal pattern densities of the small regions 201 to 204 (as well as other small regions) may not be the same. In this case, the small regions are grouped into region groups depending on whether or not the amount of change in pattern areal density between each two adjacent small regions is greater than a predetermined value, and drift compensation time intervals are determined for each region group in the manner described above. In practice, the above amount of change in pattern areal density is rarely zero and therefore the grouping may be made using a near-zero value as the above predetermined value. According to the present embodiment, the drift compensation time intervals for each small region in a region group may be set differently. Specifically, in the above example, drift compensation time intervals are set only for each region group, so that the drift compensation time intervals for each small region in the region group are the same. However, according to the present embodiment, each region group may be divided into smaller groups or regions, and the drift compensation time intervals are set for each such smaller group or region. In other words, in this case the drift compensation time intervals for each region group vary with the pattern areal density of each smaller group or region in the region group. The time profile of the present embodiment for drift compensation includes both cases. FIG. 2 is a diagram showing the configuration of an electron beam writing apparatus according to the present embodiment. This electron beam writing apparatus includes a writing unit for writing on a workpiece with an electron beam, and a control unit for controlling the writing operation, as shown in FIG. 2. A writing chamber 1 houses a stage 3 on which a mask 2 (a workpiece) is mounted. The mask 2 is a structure in which a chromium film serving as a light shielding film is formed on a transparent glass substrate of quartz, etc. and a resist film is formed on the chromium film, for example. According to the present embodiment, writing is effected on this resist film by an electron beam. A stage drive circuit 4 causes the stage 3 to move in the X-direction (i.e., the lateral direction as viewed in FIG. 2) and the Y-direction (i.e., the direction perpendicular to the plane of the paper). The position of the stage 3 is measured by a position detecting circuit 5 using a laser-based measuring device, etc. An electron beam optical system 10 is disposed above the writing chamber 1. The electron beam optical system 10 includes an electron gun 6, various lenses 7, 8, 9, 11, and 12, a blanking deflector 13, a shaping deflector 14, a main deflector 15 and a sub-deflector 16 for beam scanning, and two beam shaping apertures 17 and 18, etc. FIG. 3 is a schematic diagram illustrating an electron beam writing method. As shown in this figure, a pattern 51 to be written on the mask 2 is divided into strip-shaped frames 52. The pattern is written on the mask 2 by an electron beam 54 on a frame 52 basis while the stage 3 is continuously moved in one direction (e.g., the X-direction). Each frame 52 is divided into sub-deflection regions 53, and the pattern writing is performed only on a selected portion or portions of the sub-deflection regions 53 by the electron beam 54. It will be noted that the frames 52 are strip-shaped writing fields whose size is determined by the deflection width of the main deflector 15, and the sub-deflection regions 53 are unit writing fields whose size is determined by the deflection width of the sub-deflector 16. The main deflector 15 moves the electron beam to a target sub-deflection region 53, and the sub-deflector 16 scans the electron beam over the sub-deflection region 53 for pattern writing. That is, the electron beam 54 is first moved to a predetermined sub-deflection region 53 by the main deflector 15 and then positioned at a target writing position in the sub-deflection region 53 by the sub-deflector 16. Further, the shape and size of the electron beam 54 are controlled by the shaping deflector 14 and the beam shaping apertures 17 and 18. Writing is then performed on the sub-deflection region 53 while the stage 3 is continuously moved in one direction. Upon completion of the writing on this sub-deflection region 53, the writing on the next sub-deflection region 53 is initiated. Further, upon completion of the writing on all the sub-deflection regions 53 in the current frame 52, the stage 3 is moved one step in a direction perpendicular to the direction of the above continuous movement of the stage 3 (e.g., in the Y-direction) and then the next frame is subjected to a writing operation. This procedure is repeated to write on one frame 52 after another. Referring now to FIG. 2, reference numeral 20 denotes an input unit through which pattern writing data for the mask 2 is input from a magnetic disk (a storage medium) to the electron beam writing apparatus. The pattern writing data read from the input unit 20 is temporarily stored in pattern memory 21 on a frame 52 basis. The pattern data for each frame 52 stored in the pattern memory 21, that is, frame information which includes pattern writing position data, pattern shape data, etc. is corrected by a writing data correcting unit 31 and then sent to a pattern data decoder 22 and a writing data decoder 23 which serve as data analysis units. The writing data correcting unit 31 performs a drift compensation on original design value data. Specifically, as shown in FIG. 4, a compensation value calculating unit 101 calculates a compensation value for drift compensation based on the amount of drift measured by a drift amount measuring unit 102. An adder 103 then adds or combines the design value data and the compensation value data. It should be noted that the drift compensation is made at time intervals specified by a drift compensation time interval determining unit 32. According to the present embodiment, based on the pattern writing data input to the input unit 20, a control computer 19 divides a predetermined region on which writing is effected by the electron beam into smaller regions each consisting of one or the same number of frames. The control computer 19 then determines the areal density of the pattern to be written on each smaller region. Alternatively, this determination may be made externally and the determination results may be input to the input unit 20. Next, the drift compensation time interval determining unit 32 determines the amount of change in pattern areal density between each two adjacent smaller regions, and groups the smaller regions in the predetermined region into region groups depending on whether or not the amount of change in pattern areal density is greater than a predetermined value. A time profile for compensating for the drift of the electron beam is then determined for each region group. The writing data correcting unit 31 modifies the design value data to which drift compensation has been applied so that it reflects the position of the stage 3. More specifically, the position data of the stage 3 obtained by the position detecting circuit 5 is sent to the writing data correcting unit 31 in which, as shown in FIG. 4, the adder 104 adds the position data to the design value data to which the drift compensation has been applied. The combined data is sent to the pattern data decoder 22 and the writing data decoder 23. The information from the pattern data decoder 22 is sent to a blanking circuit 24 and a beam shaper driver 25. Specifically, the pattern data decoder 22 generates blanking data based on the above combined data and sends it to the blanking circuit 24. The pattern data decoder 22 also generates the desired beam size data and sends it to the beam shaper driver 25. The beam shaper driver 25 then applies a predetermined deflection signal to the shaping deflector 14 in the electron beam optical system 10 to adjust the size of the electron beam 54. Referring now to FIG. 2, a deflection control unit 30 is connected to a settling time determining unit 29 which is connected to a sub-deflection region deflection amount calculating unit 28. The sub-deflection region deflection amount calculating unit 28 is also connected to the pattern data decoder 22. Further, the deflection control unit 30 is also connected to the blanking circuit 24, the beam shaper driver 25, a main deflector driver 26, and a sub-deflector driver 27. The output from the writing data decoder 23 is sent to the main deflector driver 26 and the sub-deflector driver 27. The main deflector driver 26 then applies a predetermined deflection signal to the main deflector 15 in the electron beam optical system 10 to deflect the electron beam 54 to a predetermined main deflection position. Further, the sub-deflector driver 27 applies a predetermined sub-deflection signal to the sub-deflector 16 to write on a sub-deflection region 53. A writing method using the electron beam writing apparatus will now be described. First, the mask 2 is placed on the stage 3 in the writing chamber 1. Next, the position detecting circuit 5 detects the position of the stage 3, and in response to a signal from the control computer 19, the stage drive circuit 4 moves the stage 3 to position where writing is possible. The electron gun 6 then emits the electron beam 54. The emitted electron beam 54 is focused by an illumination lens 7. The blanking deflector 13 operates so that the mask 2 is either irradiated with the electron beam 54 or not irradiated with the electron beam 54. The electron beam 54 directed to the first aperture 17 passes through the opening of the first aperture 17 and is deflected by the shaping deflector 14 controlled by the beam shaper driver 25. The electron beam 54 is then passed through the opening of the second aperture 18 so that the beam 54 assumes the desired shape and size. This beam shape corresponds to the smallest writing area on the mask 2 that can be independently irradiated with the electron beam 54. After thus being shaped into the desired beam shape, the electron beam 54 is reduced in size by the reducing lens 11. The impinging position of the electron beam 54 on the mask 2 is adjusted by the main deflector 15 and the sub-deflector 16 controlled by the main deflector driver 26 and the sub-deflector driver 27, respectively. The main deflector 15 moves the electron beam 54 to a sub-deflection region 53 on the mask 2, and the sub-deflector 16 positions the electron beam 54 at a writing position in the sub-deflection region 53. When writing on the mask 2 with the electron beam 54, the beam 54 is caused to scan the mask 2 while the stage 3 is moved in one direction. Specifically, a pattern is written in each sub-deflection region 53 while the stage 3 is moved in one direction. Upon completion of the writing on all the sub-deflection regions 53 in one frame 52, the stage 3 is moved to a new frame 52 and the above procedure is repeated to write on the new frame 52. After the completion of the writing on all frames 52 of the mask 2, the mask is replaced by a new mask and the above writing method is repeated. The writing control by the control computer 19 will now be described. The control computer 19 reads pattern writing data for a mask from a magnetic disk through the input unit 20. The read pattern writing data is temporarily stored in the pattern memory 21 on a frame 52 basis. The pattern writing data for each frame 52 stored in the pattern memory 21, that is, frame information which includes pattern writing position data, pattern shape data, etc., is corrected by the writing data correcting unit 31, as described above, and then sent to the sub-deflection region deflection amount calculating unit 28, the blanking circuit 24, the beam shaper driver 25, the main deflector driver 26, and the sub-deflector driver 27 through the pattern data decoder 22 and the writing data decoder 23 which serve as data analysis units. The pattern data decoder 22 produces blanking data based on the pattern writing data and sends it to the blanking circuit 24. The pattern data decoder 22 also produces the desired beam shape data based on the pattern writing data and sends it to the sub-deflection region deflection amount calculating unit 28 and the beam shaper driver 25. The sub-deflection region deflection amount calculating unit 28 calculates the amount of electron beam deflection (or electron beam travel distance) for each shot in the sub-deflection regions 53 based on the beam shape data produced by the pattern data decoder 22. The resultant information is sent to the settling time determining unit 29, which determines a settling time corresponding to the distance of travel of the electron beam due to the sub-deflection. The settling time determined by the settling time determining unit 29 is sent to the deflection control unit 30, and the deflection control unit 30 sends it to the blanking circuit 24, the beam shaper driver 25, the main deflector driver 26, or the sub-deflector driver 27, depending on the pattern writing timing. The beam shaper driver 25 applies a predetermined deflection signal to the shaping deflector 14 in the electron beam optical system 10 to adjust the shape and size of the electron beam 54. The writing data decoder 23 generates, based on the pattern writing data, data for positioning the electron beam in a sub-deflection region 53, and sends it to the main deflector driver 26. The main deflector driver 26 then applies a predetermined deflection signal to the main deflector 15 to deflect the electron beam 54 to a predetermined position in the sub-deflection region 53. The writing data decoder 23 also generates, based on the pattern writing data, a control signal for the sub-deflector 16 to scan the beam. This control signal is sent to the sub-deflector driver 27 which then applies a predetermined sub-deflection signal to the sub-deflector 16. The sub-deflector 16 scans the radiated electron beam 54 over the sub-deflection region 53 for pattern writing after the set settling time has elapsed. It will be understood that the present invention is not limited to the embodiment described above since various alterations may be made thereto without departing from the spirit and scope of the invention. For example, in the present embodiment, the drift compensation time interval determining unit 32 determines the time profile for compensating for the drift of the electron beam. In other embodiments of the present invention, however, this time profile may be determined outside the electron beam writing apparatus. In this case, information about the determined time profile is input to the input unit 20. The control computer 19 then controls the writing data correcting unit 31 to compensate for the drift in accordance with this time profile. Further, although the present embodiment uses an electron beam, it is to be understood that the present invention is not limited to electron beams, but may be applied to other charged particle beams such as ion beams. The features and advantages of the present invention may be summarized as follows. According to the first aspect of the present invention, a predetermined region on which writing is effected by a charged particle beam is divided into smaller regions each consisting of one or the same number of frames, and the areal density of a pattern to be written on each smaller region is determined. Next, a determination is made of the amount of change in pattern areal density between each two adjacent smaller regions, and these smaller regions in the predetermined region are grouped into region groups depending on whether or not the amount of change in pattern areal density is greater than a predetermined value. A time profile for compensating for the drift of the charged particle beam is then determined for each region group. This improves the accuracy of the drift compensation while preventing a reduction in the throughput, thus providing a charged particle beam writing method capable of writing with high accuracy. According to the second aspect of the present invention, a predetermined region on which writing is effected by a charged particle beam is divided into a plurality of region groups by grouping means, and a time profile for compensating for the drift of the charged particle beam is determined for each region group. A pattern is then written on the predetermined region while compensating for the drift of the charged particle beam in accordance with this time profile. This improves the accuracy of the drift compensation while preventing a reduction in the throughput, making it possible to provide a charged particle beam writing apparatus capable of writing with high accuracy. Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described. The entire disclosure of a Japanese Patent Application No. 2009-035275, filed on Feb. 18, 2009 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety. |
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055235131 | claims | 1. A method of decontaminating the surface of a body carrying radioactive contaminants which comprises treating the surface with a decontaminant comprising a solution of tetrafluoroboric acid HBF.sub.4, treating the resultant liquor comprising decontaminant and dissolved species removed from the body surface with a first chemical agent which on reacting with the dissolved species yields insoluble compounds and regenerated decontaminant solution, and characterised in that the regenerated decontaminant solution is further treated to cause removal of the first chemical agent from the decontaminant solution. 2. A method as in claim 1 and wherein the first chemical agent comprises an acid. 3. A method as in claim 2 and wherein the first chemical agent comprises oxalic acid. 4. A method as in claim 1 and wherein the said further treatment comprises an oxidation treatment. 5. A method as in claim 4 and wherein the oxidation treatment comprises addition of a second chemical agent which is an oxidising agent. 6. A method as in claim 5 and wherein the oxidising agent is selected from potassium permanganate, potassium dichromate, lead (IV) compounds and cerium (IV) compounds. 7. A method as in claim 4 and wherein the oxidation treatment comprises photolytic decomposition. 8. A method as in claim 1 and wherein a third chemical agent is added to the decontaminant liquor to increase the rate of removal of the first chemical agent. 9. A method as in claim 8 and wherein the third chemical agent comprises a peroxide. 10. A method as in claim 1 and which includes the step of further treating the regenerated decontaminant solution by passing that solution through an ion exchange medium. 11. A method as in claim 1 and wherein the regenerated decontaminant solution is obtained in substantially pure form and is re-applied in such form to decontaminate further the surface of the said body. 12. A method as in claim 1 and wherein sold matter contained in the decontaminant liquor is separated from the liquor prior to treatment to add the first chemical agent thereto. 13. A method as in claim 1 and wherein precipitate produced by addition of the first chemical agent is separated from the decontaminant liquor prior to treatment to remove the first chemical agent. 14. A method as in claim 1 and wherein addition of the first chemical agent and the treatment to remove the chemical agent are carried out as successive steps in a common reactor vessel. 15. A method as in claim 14 and wherein different chemical agents are added to the vessel via different inlets. 16. A method as in claim 1 and wherein the regenerated HBF.sub.4 decontaminant solution is treated, at the end of decontamination, with a material to neutralise the acid. 17. A method as in claim 16 and wherein calcium hydroxide is added to the regenerated HBF.sub.4 solution. |
abstract | The invention is principally directed to a reduced order model, XEDOR, facilitating the prediction of and the diagnostics of pellet-clad interaction stress-corrosion-cracking failure of nuclear fuel rods. The invention more particularly relates to assessment of susceptibility to PCI failure for guidance in the design of fuel loading in nuclear reactors. The invention additionally relates to the protection against PCI failure by providing operational information to operators of a nuclear reactor during power maneuvering, including predictive calculations prior to executing power maneuvers. Additionally, the invention relates to the diagnostics of an event suggesting a possible PCI cladding failure. |
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063309181 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, a riser spool 10 for use with the invention is generally comprised of a tubular main line 12 surrounded by smaller, tubular ancillary lines 14. The main line 12 and ancillary lines 14 are encased in buoyant foam 16, which is formed with a substantially smooth, continuous outer surface. At one end, main line 12 has a male end 18. A discus support collar 20 having an alignment notch 28 extends outward from male end 18. At the other end, main line 12 has a female end 22 which can sealingly accept male end 18 of a second riser spool 24. A discus alignment collar 26 having an alignment notch 28 extends outward from female end 22. A plurality of dog locks 30 are equally spaced along the outer diameter of main line 12, beneath alignment collar 26. Ancillary lines 14 similarly have an ancillary male ends 32 and an ancillary female ends 34. Ancillary female end 34 of a first riser spool 10 is adapted to sealingly accept the ancillary male end 32 of a second spool 24 when the main lines 12 of spools 10 and 24 are sealed. FIG. 1 depicts the junction of a first riser spool 10 and a second riser spool 24, wherein the male end 18 and ancillary male end 32 of second riser spool 24 are sealingly accepted into female end 22 and ancillary female end 34 respectively of spool 10. Riser spools 10, 24 can be locked in such a joined configuration with dog locks 30. Each dog lock 30 has an actuating screw 36 which when rotated clockwise forces a dog (not shown) from a position along the inner diameter of main line 12, radially inward. The dogs have a profile adapted to engage a corresponding profile on male end 18 of a second riser spool 24. In the locked position, riser spools 10, 24 resist separation and effectively operate as a single unit with which other spools can be joined. The juncture can be released and the two spools 10, 24 separated by rotating actuating screws 36 counterclockwise until dogs release the corresponding profile on male end 18. The torque required to rotate actuating screws 36 is of whether the dogs are engaged or released in that actuating screws 36 will resist turning clockwise when dogs are engaged with the corresponding profile and resist turning counter clockwise when the dogs are fully retracted. Referring to FIG. 2, an automated riser make-up device constructed in accordance with this invention generally comprises a guide tower 38 joined to and extending up from a spider assembly 40. Spider assembly 40 is generally centered about riser axis A1, having a planar deck 42 extending orthogonally from axis A1 and split in halves, first half 42a and second half 42b. A circular riser portal 44 having a diameter greater than the larger of alignment collar 26 or support collar 20, evenly straddles each deck half 42a, 42b. Deck halves 42a, 42b are slidingly mounted to a deck base 46, and are adapted to slide along slide axis A2 from a closed position, wherein the deck halves 42a, 42b abut one another and riser portal 44 is centered about riser axis A1, to an open position outward from axis A1. Although the diameter of riser portal 44 is large enough to pass a riser spool 10, 24, deck 42 in the open position to allows increased clearance to pass riser spool 10, 24. Deck halves 42a, 42b are opened and closed using a hydraulic or mechanical means known in the art. As shown in FIG. 3, a plurality of spider rams 48 are beneath deck 42 and oriented radially from the circumference of riser portal 44. Each spider ram 48 is a beam which can be hydraulically or mechanically extended from a retracted position to an extended position; the extended position being inward toward axis A1. Spider rams 48 are joined to deck 42 and slide with deck 42 to its open and closed positions. When deck 42 is closed, riser spool can be accepted through riser portal 44 and vertically supported by its support collar 20 on extended spider rams 48. Spider rams 48 can be retracted to allow riser spool 24 to pass freely through riser portal 44. Referring again to FIG. 2, a split rotary table 50 is mounted to deck 42 with a first half 50a rotably secured to first deck half 42a and a second half 50b rotably secured to second deck half 42b. Rotary table 50 is shaped generally in a ring having an inner diameter concentric with, and approximately equal to, the diameter of riser portal 44. When deck 42 is opened, rotary table 50 splits and table half 50a moves with deck half 42a and table half 50b moves with deck half 42b. A plurality of gear teeth 52 are spaced along the outer circumference of rotary table 50. Rotary orientation motor 54 is mounted beneath deck 42 and turns a pinion 56 about an axis parallel to axis A1. Pinion 56 is mounted above deck 42 and engages gear teeth 52. As motor 54 turns pinion 56, pinion 56 engages gear teeth 52 and rotates rotary table 50 about axis A1. Sensors indicate the position of rotary table 50. A plurality of dog actuators 58 are arrayed on rotary table 50 oriented radially from its inner diameter. The number and spacing of dog actuators 58 corresponds to the number and spacing of dog locks 30 on riser spool 10, 24. Each dog actuator 58 is comprised of a rotary drive motor 60 with a torque limiting transducer mounted to a slide base 62. Rotary drive motor 60 is adapted to engage and rotate corresponding actuating screw 36. Slide base 62 can be hydraulically or mechanically actuated to position drive motor 60 inward towards axis A1 to allow drive motor 60 to engage actuating screw 36 and outward to allow passage of riser spool 10, 24 through riser portal 44. Slide base 62 is located by a mechanical or electrical limit switch known in the art configured to stop the movement of slide base 62 at a predetermined point relative to axis A1. A male key 64 resides between a pair of dog actuators 58 on rotary table 50. Male key 64 is formed by a generally rectangular block sized to fit in notch 28, and oriented with its long axis vertically. Key 64 is mounted to a vertical base plate 66 in a manner allowing it to slide freely in a radial plane of axis A1. Base plate 66 is secured to and extends vertically up from rotary table half 50b between a pair of dog actuators 58. Male key 64 is biased radially inward by springs 68 mounted between base plate 66 and male key 64. A pneumatic cylinder 70 is joined to male key 64 and base plate 66 such that when actuated, it overcomes springs 68 and retains male key 64 radially outward. With key 64 in this outward position, female end 22 of riser spool 10 can be lowered proximate to deck 42 and centered about axis A1 without interference from key 64. Pneumatic cylinder 70 can then be released allowing springs 68 to force key 64 inward into contact with the circumferential surface of alignment collar 26. As riser spool 10 is rotated, notch 28 will become aligned with key 64 and springs 68 will force key 64 into notch 28, thus preventing further rotation. Notch 28 is positioned on support collar 20 and alignment collar 26 such that when aligned with key 64, dog locks 30 are aligned with dog actuators 58 and ancillary lines 14 of spool 10 are aligned with ancillary lines 14 of spool 24. A vertical position sensor (not shown) is mounted in male key 64 to sense the vertical position of spool 10. At least one power gooseneck 72 is rotably mounted to deck 42. Gooseneck 72 is a pipe supplying water or other fluid which is adapted to be automatically positioned over riser portal 44 to provide flow at various points in the portal 44, and thus fill ancillary lines 14 of spool 24. Further, gooseneck 72 can be automatically rotated clear of riser portal 44 so as not to interfere with rotary table 50 and allow free passage of riser spool 10, 24 through portal 44. Gooseneck 72 is positioned by hydraulic or mechanical means known in the art. Guide tower 38 is a relatively rigid structure which extends outward and upward from one side of spider assembly 40. It has a hinged torque arm 74 which extends from its upper end outward over riser portal 44. Torque arm 74 is generally comprised of two halves, a first half 76 and a second half 78, hingedly joined to guide tower 38 by an articulated hinge 80. As seen in FIG. 4, articulated hinge 80 is comprised of an intermediate link 82 having one end hingedly joined to guide tower 38 and the other, hingedly joined to a half 76 or 78 of torque arm 74. Articulated hinge 80 allows each half 76, 78 of torque arm 74 to hinge from a closed position, in which the halves 76, 78 generally form a ring concentric about axis A1, to an open position apart from one another and away from axis A1, thus allowing ample room to position riser spool 10 over riser portal 44. Articulated hinge 80 hinges at two points which enables torque arm halves 76, 78 to open wider and provide more room than if singly hinged. The opening and closing of torque arm halves 76, 78 is actuated by hydraulics or electric means known in the art, incorporating position sensors which detect the position of the halves 76, 78. A plurality of horizontal rotating actuators 84 are arrayed equally about each half 76, 78 of torque arm 74. Each horizontal rotating actuator 84 includes a roller motor 86 which rotably drives a horizontal roller 88 about an axis parallel to axis A1. A portion of each horizontal roller 88 extends radially inward from torque arm 74 such that torque arm 74 can be closed around riser spool 10 and rollers 88 frictionally contact buoyant foam 16. A hinged guide arm 90 extends from guide tower 38 beneath torque arm 74. Guide arm 90 generally has two halves, a first half 92 and a second half 94. Each half 92, 94 is joined to guide tower 38 by an articulated hinge 80 similar to the hinge joining torque arm 74 and guide tower 38. As with torque arm 74, articulated hinge 80 allows each guide arm half 92, 94 to hinge from a closed position, in which the halves 92, 94 generally form a ring concentric about axis A1, to an open position apart from one another and away from axis A1, thus allowing ample room to position riser spool 10 over riser portal 44. The opening and closing of guide arm halves 92, 94 is actuated by hydraulics or electric means known in the art, incorporating position sensors which detect the position of the halves 92, 94. A plurality of vertical rollers 96, having an axis of rotation perpendicular to axis A1, are arrayed equally about each half of guide arm 90. Unlike horizontal rollers 88, vertical rollers 96 are not motorized and rotate freely. A portion of each roller 96 extends inward from guide arm 90 such that when guide arm 90 is closed around riser spool 10, rollers 96 frictionally contact buoyant foam 16. Referring to FIG. 3, the invention can be used to make-up two riser spools 10, 24. Each make-up begins with torque arm 74 and guide arm 90 opened and deck 42 closed and centered around axis A1. Male end 18 of spool 24 extends upward through riser portal 44, and support collar 20 of spool 24 rests on extended spider rams 48. Pneumatic cylinder 70 is released and springs 68 bias male key 64 inward towards axis A1 until male key 64 forcibly contacts support collar 20 (FIG. 1). Rotary table 50 is rotated about axis A1 by orientation motor 54 driving pinion 56 until male key 64 falls into notch 28 of support collar 20. Motor 54 is then disabled and pneumatic cylinder 70 is actuated to retract male key 64. Gooseneck 72 (FIG. 2) is automatically rotated to a position allowing it to fill ancillary lines 14 of spool 24. When ancillary lines 14 of spool 24 have been filled, gooseneck 72 is then rotated away from axis Al so as not to interfere with rotary table 50. A handling tool 98 is used to grasp and lower spool 10 over spool 24 such that alignment collar 26 is adjacent to male key 64 and female end 22 of spool 10 is in close proximity to male end of spool 24. Torque arm 74 is then closed around spool 10 and horizontal rollers 88 fictionally contact buoyant foam 16. In some cases spool 10 will not require buoyancy and thus have no buoyant foam 16. If this is the case, a tubular housing (not shown) can be fitted around the ancillary lines 14 to provide rollers 88, 96 a continuous surface to contact. Position sensors ensure that torque arm 74 is completely closed. Pneumatic cylinder 70 is released and springs 68 bias male key 64 inward towards axis A1 until male key 64 forcibly contacts alignment collar 26 (FIG. 1). Horizontal rotation actuators 84 in torque arm 74 are actuated and spool 10 is rotated until notch 28 in alignment collar 26 is aligned with male key 64, thus allowing male key 64 to extend into notch 28 and prevent further rotation. With male key 64 engaged in notch 28 ancillary lines 14 of spool 10 are aligned with ancillary lines 14 of spool 24 and actuating screws 36 of dog locks 30 are aligned with dog actuators 58. Guide arm 90 is then closed around spool 10 and vertical rollers 96 contact buoyant foam 16. Position sensors ensure that guide arm 90 is completely closed, and torque arm 74 is actuated back to its original position away from spool 10. Spool 10 is lowered onto spool 24 and vertical rollers 96 prevent spool 10 from rotating while keeping spool 10 centered over spool 24. Male end 18 and ancillary male end 32 of spool 24 are concentrically accepted into female end 22 and ancillary female end 34 respectively of spool 10. The sensor in male key 64 verifies spool 10 is at the correct elevation. Slide bases 62 are actuated to position dog actuators 58 inward toward axis A1 and engage rotary drive motor 60 of each dog actuator 58 with actuating screws 36 of each dog lock 30. Rotary drive motors 60 are activated to turn actuating screws 36 and engage dog locks 30, thus locking spool 10 to spool 24. Torque transducers in drive motors 60 sense when dog locks 30 are fully engaged and deactivate drive motors 60. Slide bases 62 are actuated to return dog actuators 58 to their original position. Guide arm 90 is opened and retracted to its original position. Deck halves 42a, 42b are opened. Spider rams 48 are retracted away from axis A1 and spool 10 is lowered such that its male end 18 is proximate to deck 42. Pneumatic cylinder 70 is actuated to retract male key 64. Deck halves 42a and 42b are closed and spider rams 48 are extended inwards. Spool 10 is then lowered to allow its support collar 20 to rest on rams 48. Handling tool 98 is released to retrieve the next spool. The invention can be used to break the junction of two riser spools 10, 24. First, handling tool 98 grasps male end 18 of spool 10 and deck halves 42a, 42b are opened. Spool 10 is lifted until alignment collar 26 of spool 10 is in proximity to male key 64. Deck halves 42a, 42b are closed and spider rams 48 are extended. Support collar 20 of spool 24 is then allowed to rest on rams 48. Pneumatic cylinder 70 is released and springs 68 bias male key 64 inward towards axis Al until male key 64 forcibly contacts support collar 20 and alignment collar 26. The sensor in male key 64 verifies spool 10 is at the correct elevation. Rotary table 50 is rotated about axis Al by orientation motor 54 driving pinion 56 until male key 64 falls into notch 28. Motor 54 is then disabled. Slide base 62 of each dog actuator 58 is actuated to move dog actuators 58 inward toward axis A1 until the rotary drive motor 60 of each dog actuator 58 engages corresponding dog actuating screws 36 of each dog lock 30. Rotary drive motors 60 are activated to turn actuating screws 36 and disengage dog locks 30, thus unlocking spool 10 from spool 24. Torque transducers in drive motors 60 sense when dog locks 30 are fully disengaged and deactivates drive motors 60. Slide bases 62 are actuated to move dog actuators 58 outward from axis A1 and to their original position. Pneumatic cylinder 70 is actuated to retract male key 64 out of riser portal 44. Orientation motor 54 is actuated to return rotary table 50 to its original position. Sensors confirm the position of rotary table 50 and disable motor 54. Spool 10 is then lifted from spool 24 and retrieved. The present invention has several significant advantages. The automated riser make up device automates the alignment and connection of riser spools having ancillary lines. The device performs virtually all the tasks required for make up other than lowering the risers together. It aligns the riser spools both radially and angularly while also aligning the connector actuators with the connector. Use of the device reduces the time spent on each connection and requires fewer workers to operate than a manual connection. While the invention is been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. |
063320118 | summary | BACKGROUND OF THE INVENTION This invention relates generally to examination of nuclear reactors, and more particularly, to the examination of a top weld of a core shroud of a boiling water nuclear reactor. A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A top guide, sometimes referred to as a grid is spaced above a core plate within the RPV. A core shroud, or shroud, surrounds the core plate and is supported by a shroud support structure. The core shroud is a reactor coolant flow partition and structural support for the core components. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. A removable shroud head is coupled to a shroud head flange at the top of the shroud. The shroud, due to its large size, is formed by welding a plurality of stainless steel cylindrical sections together. Specifically, respective ends of adjacent shroud sections are joined with a circumferential weld. During operation of the reactor, the circumferential weld joints may experience intergranular stress corrosion cracking (IGSCC) and irradiation-assisted stress corrosion cracking (IASCC) in weld heat affected zones which can diminish the structural integrity of the shroud. In particular, lateral seismic/dynamic loading could cause relative displacements at cracked weld locations, which could produce large core flow leakage and misalignment of the core that could prevent control rod insertion and a safe shutdown. Known methods of inspecting the circumferential shroud welds for IGSCC and IASCC utilize ultrasonic probes positioned on the shroud outer surface at the weld joint. A series of scans are performed while projecting the ultrasonic beam through the weld from the outer side of the shroud to the inner side of the shroud. Some methods position the probe on the inner surface of the shroud and project the ultrasonic beam from the inner surface of the shroud to the outer surface of the shroud. The weld between the shroud head flange and the upper shroud section, sometimes referred to as an H1 weld, is very difficult to access for inspection because of the plurality of shroud head locking lugs located around the outer surface of the shroud head flange which limits access to the weld from the outer surface of the shroud. Typically, less than 80% of the weld area can be examined. Additionally, because the shroud head flange extends radially inward, a probe cannot easily be placed against the weld between the flange and the upper shroud section on the inner surface of the shroud. Placing probes below the weld under the flange ledge and performing scans of the weld and upper heat affected zone by directing the ultasonic sound beam through the weld from the lower side has produced unreliable detection readings. It would be desirable to provide a method of inspecting the H1 weld between the shroud head flange and the upper shroud section that is reliable and that reliably examines greater than 80% of the weld circumference. BRIEF SUMMARY OF THE INVENTION In an exemplary embodiment, a method of inspecting an H1 weld between a shroud head flange and an upper shroud section, and an upper heat affected zone of the H1 weld includes the steps of positioning a phased array ultrasonic probe on a top surface of the shroud head flange, emitting an ultrasonic sound beam from the ultrasonic probe, electronically steering the ultrasonic sound beam to scan the weld joining the shroud head flange and the upper shroud section with the beam moving from an outer surface of the shroud to an inner surface of the shroud, and acquiring scan data over a length of the scan. The ultrasonic probe is then incrementally moved circumferentially along the top surface of the shroud head flange and the weld is again ultrasonically scanned. The ultrasonic probe is continuously moved circumferentially along the top surface of the shroud head flange in increments of between about 0.05 inch to about 1.0 inch with the H1 weld ultrasonically scanned after each incremental move. Initially, the ultrasonic beam is focused so that the focal point of the beam aligns with an upper fusion line of the weld and the outer surface of the shroud head flange. The beam is then repeatedly refocused so that the beam focal point moves along the upper fusion line of the weld from the outer surface of the shroud head flange to the inner surface of the shroud head flange in discrete increments. In one embodiment the beam focal point moves in increments of about 0.01 inch to about 0.5 inch. After the ultrasonic probe has scanned the weld at the initial position on the shroud head flange, the ultrasonic probe is incrementally moved circumferentially along the top surface of the shroud head flange. At each predetermined incremental move of the probe the width of the weld is scanned by focusing the beam and moving the focal point incrementally along the fusion line as described above. Scans are performed at each incremental distance the probe is moved until the probe has traversed the complete circumference of the circumferential weld, or any desired portion of the circumference of the weld. The above described method provides for reliable examination of greater than 80% of the H1 weld circumference because the ultrasonic probe placement and movement are not restricted by the shroud head locking lugs that are located on the outer surface of the shroud head flange. The method provides an examination of the heat affected zone of the weld extending from the upper fusion line of the weld to about 0.5 inch above the upper fusion line. Further, the method provides for detection, length and through-wall sizing of surface-connected planar flaws within the weld metal, heat affected zone, and adjacent base metal material. The planar flaws resulting from IGSCC and IASCC. Also, the above described method can be used for the detection and sizing of cracking associated with attachment welds of the shroud head locking lugs. |
claims | 1. A compact device that generates radiation, comprising:a generator vacuum tube comprising:a source generating charged particles, anda target onto which the charged particles are directed;a high voltage supply comprising a high voltage multiplier ladder located at least partly side-by-side and substantially adjacent to the generator vacuum tube, the high voltage supply being configured to apply a high voltage between the source and the target to accelerate the charged particles to a predetermined energy level; andan electrical coupling between the high voltage supply and the target of the generator vacuum tube, wherein the electrical coupling comprises a high voltage turn-around comprising a split and flip that accommodates an electrical field stress caused by the high voltage multiplier ladder being located side-by-side adjacent to the generator vacuum tube,wherein the split and flip reduces electrical field stress by a split in the high voltage multiplier ladder such that the high voltage multiplier ladder comprises a first portion and a second portion and the first portion of the high voltage multiplier ladder is turned directionally back toward the target. 2. The compact device according to claim 1, the generated radiation comprising neutron radiation. 3. The compact device according to claim 1, the generated radiation comprising x-rays. 4. The compact device according to claim 1, the generated radiation comprising gamma-rays. 5. The compact device according to claim 1, wherein the compact device measures an overall length of less than about twenty (20) inches in length. 6. The compact device according to claim 1, further comprising a corona shield covering the high voltage turn-around to reduce the electrical field stress. 7. The compact device according to claim 1, further comprising a corona shield about the split. 8. The compact device according to claim 1, further comprising an electrically insulating mechanical support that is located proximately to the target and provides mechanical support to an end of the generator vacuum tube, the electrically insulating mechanical support comprising a conductor positioned perpendicular to the axis of the electrically insulating mechanical support. 9. The compact device according to claim 8, further comprising a corona shield that reduces electrical field stress at the high-voltage turn-around. 10. The compact device according to claim 9, wherein the conductor is operatively coupled to the corona shield. 11. The compact device according to claim 8, wherein the electrically insulating mechanical support comprises Aluminum Nitride. 12. The compact device according to claim 1, wherein the generator vacuum tube comprises at least one intermediate electrode located between the source and the target and operatively coupled to an intermediate-voltage point located between multiplier stages at an intermediate potential between an input voltage and an output voltage of the high voltage multiplier ladder. 13. The compact device according to claim 12, further comprising a protective surge resistor coupled between the intermediate electrode and the intermediate-voltage point between the multiplier stages. 14. The compact device according to claim 12, further comprising a diode coupled between the intermediate electrode and the intermediate-voltage point-between the multiplier stages. 15. The compact device according to claim 8, the electrically insulating mechanical support further comprising an internal flow path configured for circulation of an insulating cooling fluid. 16. A radiation logging tool, comprising:a tool housing;a compact generator that produces radiation through a reaction of energetic charged particles accelerated in a DC electrostatic field with a target on which the charged particles impinge;a power supply operatively coupled to the compact generator;control circuitry operatively coupled to the compact generator;wherein the compact generator comprises:a generator vacuum tube comprising:a source generating charged particles, and a target onto which the charged particles are directed; a high voltage supply comprising a high voltage multiplier ladder located at least partly side-by-side and substantially adjacent to the generator vacuum tube, the high voltage supply being configured to apply a high voltage between the source and the target to accelerate the charged particles to a predetermined energy level; andan electrical coupling between the high voltage supply and the target of the generator vacuum tube, wherein the electrical coupling comprises a high voltage turn-around comprising a split and flip that accommodates an electrical field stress caused by the high voltage multiplier ladder being located side-by-side adjacent to the generator vacuum tube by reducing the electrical field stress at the high voltage turn-around,wherein the split and flip and reduces electrical field stress by a split in the high voltage multiplier ladder, wherein the high voltage multiplier ladder comprises a first portion and a second portion and the first portion of the high voltage multiplier ladder is turned directionally back toward the target, wherein the voltage level at an end of the first portion and a beginning of the second portion is lower than an output voltage of the high voltage multiplier ladder. |
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041837843 | summary | BACKGROUND OF THE INVENTION The present invention pertains to a nuclear reactor plant with a prestressed concrete vessel, comprising a high temperature reactor with closed gas coolant circuit for the direct drive of at least one gas turbo apparatus comprising a turbine and a compressor, heat exchangers, and gas lines between the single circuit components. The high temperature reactor is arranged in a cavity, positioned in the center of the prestressed concrete vessel, the heat exchangers and the gas lines are installed in recesses in the wall of the prestressed concrete vessel, and each gas turbo apparatus is arranged in a turbine duct, led horizontally or vertically through the prestressed concrete vessel. Such a plant, in which the nuclear reactor, gas turbo apparatus and the other associated circuit components are arranged in a common pressure vessel (integrated construction), has the advantage that only the mechanical or electrical power produced and the coolant which has not come in contact with the contaminated gas need be led out of the prestressed concrete vessel. Therefore, the space outside the concrete vessel is practically completely protected from contaminated gas and the space inside of the prestressed concrete vessel is optimally used. It can be very conducive to accomplishing the latter goal, if the heated working medium is not led to only one relatively large gas turbo apparatus, as it is provided in most of the nuclear reactors with closed gas coolant circuit, but if several smaller gas turbo units are arranged in the prestressed concrete vessel. These are coupled by the nuclear reactor and form in each case, together with the heat exchangers, an individual circuit for the utilization of heat (loop). Furthermore, special connection elements between the single parts of the plant which carry active gas are avoided by the integrated construction. This works out very favorably in the construction and operation of high temperature reactors. Therefore, the integrated construction is preferred in a great number of special nuclear power plants. German Auslegeschrift No. 1,614,610 is stated as an example of a nuclear power plant having only one circuit for the utilization of heat. The concrete vessel, shown there, has two closed pressurized chambers, one which houses the reactor and the other which serves as a machine chamber. The working medium is led in lines, which penetrate the dividing wall between the both pressurized chambers, from the reactor to the turbine and from the compressor back again in an annular space below the reactor core. It is difficult to realize technically this so-called Igloo-type of construction, and the nuclear power plant does not work very economically, as a result of the arrangement principle. Nuclear power plants of an integrated type of construction with several circuits for the utilization of heat (loops) are described in German Auslegeschriften (DAS) No. 1,764,355, and No. 1,806,471 and Offenlegungsschriften (DOS) No. 1,746,249, and No. 2,062,934. The three last-named patent applications disclose a nuclear power plant in which the turbine aggregates and the heat exchangers are arranged in parallel vertical bores in the pressure vessel wall and in which the single loops form groups symmetrically around the nuclear reactor, which is situated in a central cavity. Both in the wall of the pressure vessel as well as in the spaces between the circuit components, there are provided passages for the coolant. Each loop can be installed with all associated components in one and the same vertical bore (DAS No. 1,806,471) or the heat exchangers, turbines and compressors of each loop are in each case arranged in a separate bore. (DOS No. 1,764,249). The above-mentioned DOS No. 1,764,355 discloses a nuclear power plant in which the circuit components of each loop are connected with each other by tubular channels. On the whole, two loops are provided. All heat exchangers are installed around the nuclear reactor in shaft-like recesses of the vessel wall, while both turbines and the associated compressor are arranged in one cavity below the nuclear reactor, in which there is also situated the gas distributing system for the heat exchangers. The turbines are arranged parallel to each other. As already mentioned, the integrated type of construction does permit a good efficient usage of the prestressed concrete vessel, which moreover can be held relatively small in its measurements by an especially skillful arrangement of the individual circuit components. Thereby, a great role is played by the installation of the gas turbo unit or units if a plant with several loops is involved. As for all other circuit components, the demand is present also for the gas turbo units that they are readily accessible for inspection and maintenance and that they can be removed from the outside, in case of repairs. SUMMARY OF THE INVENTION Therefore, it is an object of the invention to provide an improved nuclear reactor plant of the type described above. It is also an object of the invention to provide such a plant wherein the accessibility and the detachability of the gas turbo units are ensured by the special arrangement and anchoring of each gas turbo unit in its respective turbine duct and by special elements connecting the turbine unit to the coolant circuit. In accomplishing the foregoing objects, there has been provided in accordance with the present invention a nuclear reactor plant, comprising: a prestressed concrete pressure vessel; a high temperature reactor arranged in a first central cavity within the vessel; a closed gas cooling circuit including at least one housed gas turbo unit arranged in a turbine duct in the wall of the vessel, said unit including a turbine and a compressor and having detachable bearings; means for exchanging heat and means for transporting gas in said cooling circuit including hot gas from the reactor to the turbine, said heat exchange means and said gas transport means being arranged in recesses in the wall of the vessel; means for forming a detachable plug-in type connection between the hot gas transport means and each turbo unit; means, positioned at the edge of the turbine duct, for connecting all remaining gas transport means to the turbo unit; means, including peripheral sealing members positioned between the inside wall of the turbine duct and the outer housing of the turbo unit, for separating each of the remaining gas transport means from each other; means for detachably connecting each turbo unit to the inside of its turbine duct; remote control means for detaching these connecting means; means, including at least one lifting device controllable from outside of the vessel through a bore in the wall of the vessel, for dismounting each turbo unit from within its turbine duct; means for detaching from outside of the vessel all connections to each turbo unit which must be removed in order for removal of the turbo unit from its turbine duct; and means, including a duct through the wall of the vessel, for gaining access to each bearing of each turbo unit. In a preferred embodiment, the plug-in type connection means comprises a hot gas conduit having a telescoping portion adjacent the turbine and means for operating the telescoping portion by remote control. Also, the closed gas cooling circuit preferably comprises a plurality of identical loops, each loop comprising a gas turbo unit, heat exchange means and gas transport means, and wherein the turbine ducts for each of these gas turbo units are arranged below the reactor cavity in a horizontal plane and are arranged symetrically, preferably radially to the vertical center axis of the vessel. |
043549993 | summary | Over the past 20 years the scientific community has undertaken one of the most difficult tasks in technology, that of devising a feasible method of, and apparatus for, atomic fusion. Because of the limited supply of fossil fuels (i.e., coal, oil, natural gas), recently much attention has been directed to the problem of developing a nuclear fusion reactor. A device of this type could provide a solution to the world's power supply shortage since one of the basic fuels is deuterium, or heavy hydrogen which is contained in the oceans in nearly inexhaustible amounts. Furthermore, a fusion reactor would be inherently stable and not subject to explosion. Hence, if fusion reactors can be made to yield useful power, it will solve the earth's fuel problem. Of the dozens of proposed nuclear fusion reactors, few seem to show an immediate potential feasibility for producing controlled atomic fusion. The large repellent forces, caused by the positive electronic charges on the nuclei prevent the nuclear collisions that are necessary to produce fusion reactions. Only those reactors with nuclear fusion cross sections larger than a millibar (10.sup.-27 cm.sup.2) or energy below 50 KEV merit consideration. Any system for net power production from nuclear fusion must provide an area where the fuel nucleus undergoes many collisions with other nuclei before leaving the system. Therefore, any fuel entering the system will become randomized and develop a kinetic equilibrium described by a temperature (Maxwellian Distribution) and should be in the form of a hot gas. A great many problems are associated in creating the conditions just described. Two of the most fundamental problems lie in the realm of plasma physics, namely; confinement and heating of plasma. The problem of heating a plasma to the required temperature and confining it for the length of time implied by the Lawson criteria, has occupied the attention of hundreds of scientists and engineers in a dozen countries for about 20 years. Confinement may be accomplished either by a gravitational or electromagnetic field. Failing this only inertially confined system (explosions) can be utilized. All prior magnetic containers for hot plasma devices known to me fall into two general categories: those that are closed and those that are open. Neither of these systems are suitable by themselves for stable confinement. An open system can be made suitable by the addition of conventional "Ioffe bar" named after the Russian Physicist who announced his advancement in 1961. Although the Ioffe bar system creates a stable confinement, those plasma particles with velocities parallel to a field line (i.e., parallel to the longitudinal axis) leave the volume and escapes directly along the line creating large end losses. |
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claims | 1. An X-ray generating apparatus comprising:an X-ray generating tube including:a cathode including an electron emitting source having an electron emitting member,an anode comprising:a target having a target layer receiving an electron beam emitted from the electron emitting source and generating an X-ray, and a support member supporting the target layer and transmitting the X-ray,wherein the electron emitting source and the target layer are disposed to face each other, anda tubular backward shielding member having a connection portion connected to the periphery of the support member and protruded from the connection portion toward the electron emitting source;a collimator having a plurality of movable blades which form an opening for defining an angle for extracting the X-ray at the opposite side of the electron emitting source side of the target; andan adjusting device connected to the plurality of movable blades, and configured to vary an opening diameter of the opening,wherein the target layer is distant from the connection portion via a separate portion so as to reduce an off-focal radiation due to re-entering electrons to the target layer from the tubular backward shielding member or the target layer, andwherein the collimator is configured to be controlled by the adjusting device so as to reduce an off-focal radiation due to the tubular backward shielding member and the separate portion. 2. The X-ray generating apparatus according to claim 1, wherein the separate portion is located annularly around the target layer. 3. The X-ray generating apparatus according to claim 1, wherein the target layer includes at least a target material made of a metal of an atomic number of 42 or greater, andthe backward shielding member includes the target material. 4. The X-ray generating apparatus according to claim 1, wherein, between the periphery of the target layer and the periphery of the support member, the target has a region at which the support member is exposed in the separate portion. 5. The X-ray generating apparatus according to claim 1, wherein the target has an electrode formed to be sequentially arranged within an area from the periphery of the target layer to the periphery of the support member, and the electrode is made of a material having a lower atomic number than the atomic number of the target material. 6. The X-ray generating apparatus according to claim 5, wherein the target is electrically connected to the backward shielding member via the electrode. 7. The X-ray generating apparatus according to claim 1, wherein a diameter of the target layer defined by the periphery of the target layer is larger than an irradiation diameter of the electron beam to be formed on the target layer. 8. The X-ray generating apparatus according to claim 7, wherein the X-ray generating tube includes a forward shielding member which has a tube outgoing opening for allowing a part of the X-ray emitted from the target toward the front of the target to pass through and located between the target and the collimator, and the inner diameter of the tube outgoing opening is larger than the irradiation diameter. 9. The X-ray generating apparatus according to claim 8, wherein a minimum value of an opening diameter of the collimator is at least equal to or less than 2A+2×(B−A)×(C+D)/C, where 2A is a diameter of an electron beam irradiated on the target layer, 2B is a tube outgoing diameter, C is a distance between a virtual plane for defining an inner diameter of the tube outgoing opening and the target layer, and D is a distance between a virtual plane for defining an opening diameter of the collimator, and the virtual plane for defining the inner diameter of the tube outgoing opening. 10. The X-ray generating apparatus according to claim 8, wherein a maximum value of an opening diameter of the collimator is at least equal to or less than −2B+2×(A+B)×(C+D)/C, where 2A is a diameter of an electron beam irradiated on the target layer, 2B is a tube outgoing diameter, C is a distance between a virtual plane for defining an inner diameter of the tube outgoing opening and the target layer, and D is a distance between a virtual plane for defining an opening diameter of the collimator, and the virtual plane for defining the inner diameter of the tube outgoing opening. 11. The X-ray generating apparatus according to claim 9, wherein the opening has a rectangular opening shape having one side of a length P, and the other side of a length Q, a minimum value of the opening diameter to be defined by the mechanism for varying the opening diameter of the opening corresponds to a minimum value of the length of P or Q not longer than the other one. 12. The X-ray generating apparatus according to claim 10, wherein the opening has a rectangular opening shape having one side of a length P, and the other side of a length Q, a maximum value of the opening diameter to be defined by the mechanism for varying the opening diameter of the opening corresponds to a maximum value of the length of P or Q not shorter than the other one. 13. The X-ray generating apparatus according to claim 1, wherein, among the movable blades, a movable blade configured to define a larger opening diameter is to be located at a position closer to the target as compared to movable blades defining a smaller opening diameter. 14. A radiograph system comprising:the X-ray generating apparatus according to claim 1, andan X-ray detector configured to detect an X-ray emitted from the X-ray generating apparatus and transmitted through a subject. 15. The radiography system according to claim 14, further comprising:an opening diameter instruction unit connected to the adjusting device, and configured to instruct an opening diameter determined based on a size of an exposure field to the adjusting device. 16. The radiography system according to claim 15, further comprising:an imaging field acquisition unit having an optical camera configured to define an imaging field toward the X-ray detector, and configured to determine a size of the exposure field based on an image acquired by the optical camera, and send the size of the exposure field to the opening diameter instruction unit. 17. The radiography system according to claim 15, further comprising:a sighting optical system located between a forward shielding member and the collimator, and configured to provide a virtual exposure field to an operator or a subject, and send the size of the exposure field determined based on the virtual exposure field to the opening diameter instruction unit. 18. The radiography system according to claim 17, wherein the sighting optical system includes at least a mirror configured to transmit the X-ray and reflect visible light, and a visible light source configured to emit visible light to the mirror. 19. The X-ray generating apparatus according to claim 1, wherein the tubular backward shielding member is protruded backwardly from the connection portion along a tube axis. |
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047956070 | claims | 1. Gas-cooled high-temperature nuclear reactor having a reactor core comprising a multiplicity of individual particulate fuel elements received in a containment structure, said fuel elements being disposed laterally adjacent and on top of one another, each of said fuel elements being provided with means for forming a barrier against the release of fission products producible therein during reactor operation, said containment structure including a cylindrical barrel formed of an inner graphite layer functioning as a reflector, an outer layer of carbon bricks as insulating material surrounding said inner layer, and a metallic receptacle, said inner and outer layers being formed of respective side, bottom and cover portions, said cover portion being nonmetallic, said containment structure directly supporting said cover portion at the top of the cylindrical barrel exclusively by the side portions thereof, said side and cover portions of said inner layer being formed with first channels into which means for controlling a chain reaction in the reactor are insertible, said means being the sole insertion means for controlling the chain reaction in said reactor, said bottom, side and cover portions of said inner layer being further formed with second channels, means for circulating cooling gas during reactor operation through said second channels under pressure from the bottom to the top of said receptacle, and through the reactor core said bottom portion of said inner layer having first openings for introducing cooling gas into said second channels during reactor operation and second openings for withdrawing during reactor operation cooling gas heated by passage through the reactor core; said inner and outer layers and said metallic receptacle having a heat conductivity and a thermal capacity and the reactor core having such a size, shape, power density and moderation ratio that a first temperature at which said core becomes subcritical for all possible accident conditions is below a second temperature at which said barrier means are destroyed, and, when loss of pressure of said cooling gas down to about 10 bar or less is experienced, after-heat generated in said core is removable solely by heat conduction and radiation through said inner and outer layers and said core barrel to a passive heat removal system located outside said receptacle, so that said fuel elements remain at a temperature below said second temperature, said barrier being effective against the release of fission products up to a second temperature on the order of 1400.degree. C., and said cooling gas being helium, the reactor having a maximum power output of up to substantially 200 MW thermal, an average power density of substantially 3 MW/m.sup.3 of core volume and a maximum local power density of substantially 4 MW/m.sup.2 of core volume, a power production of substantially 20 MW/m of core height, a core diameter of substantially 3 m, and a heat transfer, for fuel elements having attained said second temperature and with said cooling gas at atmospheric pressure, of substantially 3 to 6 KW/m of the outer surface of said receptacle, said graphite reflector and said carbon insulation, respectively, being formed of blocks disposed in the form of concentric rings, and said metallic receptacle comprising a cylindrical steel jacket surrounding said rings of blocks and holding them together, the after-heat from said nuclear core being removable solely through said side portion and said metallic receptable, when the pressure in said cylindrical barrel drops to about 10 bar or less, said passive heat removal system including a multiplicity of U-shaped tubes having coolant therein, said tubes being vertically disposed and uniformly distributed around the circumference of said cylindrical steel jacket, said tubes having a first leg in heat-transferring contact with said steel jacket and a second leg spaced from said steel jacket, a natural circulation of the coolant in said U-shaped tubes being produced due to a temperature difference in said first and said second legs thereof, and means for connecting said tubes with a heat exchanger located outside said metallic receptacle. 2. The reactor according to claim 1, wherein the reactor core has a moderation ratio of substantially 500 to 800. |
description | The present disclosure relates, but is not limited, to systems and methods for inspecting a load with a source of radiation. Inspection systems use inspection radiation through e.g. vehicles for inspecting cargo of the vehicle, for example to detect hidden objects (such as weapons or dangerous material). However objects placed in the line of transmission of opaque materials and/or which appear dark on the view by transmission are difficult to detect on a view by transmission. A user may for example fail to detect some objects in X-ray images, because of their overlaps and/or their location in the line of transmission of low transmission objects. Aspects of the present invention address some of the above issues. Aspects and embodiments of the invention are set out in the appended claims. These and other aspects and embodiments of the invention are also described herein. In the drawings, like elements are referred to by the same numerical references. Overview Embodiments of the present disclosure relate to a system for inspection of a load. The system comprises a plurality of detectors to detect scatter radiation from the load, to allow one or more properties of the load to be determined. The scatter radiation is emitted by a zone of the load in response to the zone being irradiated by radiation transmitted through the zone. The irradiated zone comprises respective portions, each respective portion corresponding for example to a voxel of the zone. The system further comprises a plurality of collimators associated with the plurality of detectors, the plurality of collimators being configured to enable radiation scattered by a respective portion of the load to reach an associated detector in the plurality of detectors. The collimators inhibit any other scatter radiation to reach the associated detector. Each of the detectors of the plurality of detectors is associated with a respective portion of the load. In some examples, the radiation irradiating the zone may be a fan beam irradiating the whole of the zone at the same time. In some examples, the plurality of detectors comprises at least one linear array of detectors. Each of the detectors in the array may correspond for example to a pixel of a 1-dimensional (1D) image of the zone, generated from data associated with the array of detectors. In examples where the load is moved with respect to the detection system in an inspection direction, the system may enable a 2-dimensional (2D) image of the load to be obtained, e.g. by grouping the 1D images of the zone in a direction corresponding to the inspection direction. The 2D image of the load may enable an enhanced detection of hidden objects. In some examples, the plurality of detectors comprises a matrix of detectors, and each of the detectors in the matrix may correspond for example to a pixel of a 2-dimensional (2D) image of the zone, generated from data associated with the matrix of detectors. In some examples, the 2D image of the zone may be referred to as a 2D slice (or cross section) of the load. In examples where the load is moved with respect to the detection system in an inspection direction, the system may enable a 3-dimensional (3D) image of the load to be obtained, e.g. by grouping the 2D images of the zone in a direction corresponding to the inspection direction. The 3D image of the load may enable an enhanced detection of hidden objects. Alternatively or additionally, in some examples, the radiation irradiating the zone may be a pencil beam irradiating a portion of the zone at a time. In such examples, the pencil beam may be travelled on the load to irradiate the zone of the load (sometimes referred to as the pencil beam “parsing” the load). In some examples, the pencil beam is travelled in a direction perpendicular to the direction of the pencil beam. In examples where the plurality of detectors comprises a linear array of detectors and where the pencil beam irradiates the load in a direction parallel to the linear array, each of the detectors in the array may correspond for example to a pixel of a 1-dimensional (1D) image of the zone, generated from data associated with the array of detectors. In examples where the load is moved with respect to the detection system in an inspection direction, the system may enable a 2-dimensional (2D) image of the load to be obtained. In examples where the plurality of detectors comprises a linear array of detectors and where the pencil beam parses the load in a direction perpendicular to the linear array, each of the detectors in the linear array may correspond for example to a pixel of a 2-dimensional (2D) image of the zone (e.g. cross section of the load), generated from data associated with the matrix of detectors. In some examples, the pencil beam may parse the load in a direction perpendicular to the linear array. For example, for a side view beam parsing the load, e.g. from a bottom part of the load to a top part of the load, the linear array may be located above the load, and the linear array may be parallel to the beam direction which is perpendicular to the parsing direction. In examples where the load is moved with respect to the detection system in an inspection direction, the system may enable a 3-dimensional (3D) image of the load to be obtained. Embodiments of the present disclosure relate to a detection system for inspection of a load. The system comprises a matrix of detectors to detect scatter radiation from the load, in order to allow one or more properties of the load to be determined. The scatter radiation is emitted by a zone of the load in response to the zone being irradiated by radiation transmitted through the zone. The irradiated zone comprises respective portions, each respective portion corresponding for example to a voxel of the zone. The system further comprises a selection device configured to enable radiation scattered by a respective portion of the load to reach an associated detector on the matrix. The selection device inhibits any other scatter radiation to reach the associated detector. Each of the detectors of the matrix is associated with a respective portion of the load and may correspond for example to a pixel of a 2-dimensional (2D) image of the zone, generated from data associated with the matrix of detectors. In some examples, the 2D image of the zone may be referred to as a 2D slice (or cross section) of the load. In examples where the load is moved with respect to the detection system in an inspection direction, the system may enable a 3-dimensional (3D) image of the load to be obtained, e.g. by grouping the 2D images of the zone in a direction corresponding to the inspection direction. The 3D image of the load may enable an enhanced detection of hidden objects. In some examples, the selection device may comprise an aperture in a block. As illustrated in the Figures, the system may be described with reference to an orthonormal reference OXYZ, axis (Oz) being the ascending vertical, a plane YOZ being vertical, a plane XOY being horizontal, and a plane XOZ being vertical. In the example of FIG. 1, a detection system 100 comprises a plurality 3 of detectors 4. In some examples, the plurality 3 of detectors 4 comprises at least one linear array of detectors (as illustrated in FIG. 1). Alternatively or additionally, the plurality of detectors comprises a matrix of detectors (as illustrated e.g. in FIG. 6B). Each detector 4 may be configured to detect radiation 23 scattered by an associated respective zone, e.g. the zone 8 in the example of FIG. 1, of a load 10 to inspect. The radiation 23 is scattered in response to the respective zone 8 being irradiated by radiation 22 transmitted through the zone 8. The detection system 100 further comprises a plurality 5 of collimators 6. Each collimator 6 of the plurality 5 may be associated with a detector 4 of the plurality 3 of detectors. The collimators 6 may be located at a proximity of the detectors 4, such as on the detectors 4 and/or between the detectors 4. In the example of FIG. 1, the zone 8 comprises respective portions, e.g. respective portions 18 and 20. In some examples, each detector 4 of the plurality 3 of detectors 4 is configured to detect the radiation 23 scattered by an associated respective portion (e.g. 18 or 20) of the load 10 to inspect. The radiation 23 is scattered in response to the respective portion being irradiated by the radiation 22 transmitted through the portion. As explained in greater detail below, in some examples the radiation 22 may comprise X-ray radiation and the detectors 4 of the plurality 3 may comprise, amongst other conventional electrical elements, X-ray detection detectors. Each of the X-ray detection detectors may be configured to measure an amplitude of a signal in a scintillator. Each ray of the scatter radiation 23 is emitted by the respective portion 18 or 20, respectively, when the radiation 22 irradiates the portion 18 or 20 of the load 10 (for example because of Compton scattering and pair production in examples of X-ray and/or gamma radiation). It should be understood that in some examples (e.g. when the radiation 22 is emitted as a fan beam), both portions 18 and 20 may be irradiated at the same time. The scatter radiation 23 is emitted in all the directions. It should be understood that in a system 100 not comprising the plurality 5 of collimators 6 according to the disclosure, the scatter radiation 23 emitted in all of the directions, by all of the respective portions (e.g. the portions 18 and 20) of the zone 8, would be detected by each one of the detectors 4 of the plurality 3. Imaging of the zone 8 using data collected by the plurality of detectors 4 would not be possible. In the example of FIG. 1, each collimator 6 is configured to, for each detector 4 of the plurality 3, enable radiation 23 scattered by the respective portion (e.g. the portion 18) of the load 10 to reach the associated detector 4 of the plurality 3 of detectors, and inhibit other scattered radiation from reaching the associated detector. FIG. 2A (not to scale) shows an illustration of the system of FIG. 1 showing how the scatter radiation 23 passes through the collimators 6 to be received by the detectors 4. For illustrative purposes the illustration in FIG. 2A shows a selection of rays of the scatter radiation 23 emitted by two respective portions of the zone 8. In the example of FIG. 2A, the scatter radiation 23 from the portion 18 comprises rays in directions 12a-e, and the scatter radiation 23 from the portion 20 comprises rays in directions 14a-e. In the example of FIG. 2A, the detector 4a is configured to detect radiation scattered by the associated respective portion 18 of the load 10 to inspect. In some example, the collimator 6a associated with the detector 4a defines a direction of collimation (O′-O′) (sometimes referred to as a line of sight) which intersects both the detector 4a and the collimator 6a, and the detector 4a and the portion 18 are associated with each other. In some examples, the detector 4a, the collimator 6a and the portion 18 are aligned on the direction of collimation (O′-O′) (or line of sight) defined by the collimator 6a. Similarly, the detector 4b is associated with the portion 20 and is configured to detect radiation scattered by the associated respective portion 20 of the load 10 to inspect. In some examples, the detector 4b, the collimator 6b and the portion 20 are aligned on the direction of collimation (O′-O′) (or line of sight) defined by the collimator 6b. In the example of FIG. 2A, the radiation 23 emitted from the portion 18 in the direction 12c is almost parallel to the direction (O′-O′) and thus passes through the collimator 6a to the detector 4a associated with the portion 18. In the example of FIG. 2A, the scatter radiation 23 emitted by the portion 18 in other directions (e.g. in this illustration radiation 23 emitted in directions 12a, 12b, 12d and 12e) is inhibited from passing to the detector 4a by the collimator 6a. Similarly, the scatter radiation 23 emitted by other portions (e.g. portion 20 as explained below) is also inhibited from passing to the detector 4a by the collimator 6a. Similarly, in this illustration, scatter radiation 23 from the portion 20 emitted in the direction 14c is almost parallel to the direction (O′-O′) and thus passes through the collimator 6b associated with the detector 4b, and reaches the detector 4b of the plurality 3 of detectors. In the example of FIG. 2A, the scatter radiation 23 emitted in directions 14a, 14c and 14d and 14e is inhibited from passing to the detector 4b by the collimator 6b. Similarly, the scatter radiation 23 emitted by other portions (e.g. portion 18 as explained above) is also inhibited from passing to the detector 4b by the collimator 6b. Each of the collimators 6 is thus configured to allow the radiation 23 scattered from a respective portion, and in a certain direction parallel to a collimation direction defined by the collimator, to pass through the collimator 6 to reach the associated detector 4. The radiation scattered 23 by the respective portion in other directions (e.g. not parallel to the collimation direction) and the radiation scattered by other respective portions are prevented from passing through the collimator to the reach the detector associated with the respective portion. In some examples, as illustrated by FIG. 2B (not to scale), each collimator 6 comprises at least two partitions 7 configured to block or at least attenuate scatter radiation (e.g. a partition between the successive detectors, in examples where the plurality of detectors comprises a linear array of detectors). The at least two partitions may define the direction of collimation (O′-O′). In some examples, each collimator 6 may comprise four partitions 7 (e.g. a partition between each of the detectors, in examples where the plurality of detectors comprises a matrix of detectors). The partitions 7 may extend in an extension direction parallel to the direction (O′-O′) of collimation of the collimator 6. Each partition 7 may comprise a sheet of lead or steel, but other configurations and materials are envisaged. As illustrated by FIG. 2B, the collimator 6 may define a ratio r between a dimension Δ of the detector 4 corresponding to a width of the detectors (e.g. in a direction of a desired resolution) and an extension E of the partitions 7 in the extension direction such that: 2 ≤ r = E Δ ≤ 50. It should be understood that a selectivity of the collimator with respect to the scattered radiation which is enabled to reach the associated detector increases as the ratio r increases. With relatively higher values of r, only a small portion of the scattered radiation (e.g. scattered radiation almost parallel to the direction of collimation) may reach the detector (e.g. in applications where the radiation received on the detectors is relatively high (e.g. for relatively high doses), the final image may be relatively not blurred), whereas relatively lower values of r may enable more scatter radiation to reach the detector (e.g. from some non-associated other portions of the load, and the final image may be relatively more blurred, but more radiation is detected by the detector). A compromise between the blurring of the image and the quantity of radiation detected by the detector may be found, for each application of the system. In some examples, each of the collimators 6 is configured such that each respective portion (e.g. the portion 18 or 20, respectively) corresponds to a voxel of the load 10, and/or each respective detector 4 corresponds to a pixel of an image of the load generated using data associated with the plurality 3 of detectors 4. As illustrated in FIG. 1, in examples where the plurality 3 comprises a linear array of detectors 4, the voxel may correspond to a dimension of the load 10 (e.g. 1D voxel, e.g. in a direction of transmission of the radiation 22), depending on the location of the plurality 3 of detectors 4 with respect to the load 10, as explained in greater detail below. As illustrated in FIG. 6B, in examples where the plurality 3 comprises a matrix of detectors 4, the voxel may correspond to a punctual dimension of the load 10. In some examples as illustrated in FIG. 1, dimensions of the collimators 6 (e.g. the dimension E of the partitions 7) may be based on dimensions of the load to inspect; and/or a distance L1 between the load to inspect and a source 1 of radiation; and/or a distance L2 between the load to inspect and the plurality 3 of detectors. Similarly, dimensions of the plurality 3 of detectors 4 may be based on dimensions of the load to inspect; and/or the distance L1 and/or the distance L2. In some examples, dimensions of a detector 4 in the plurality of detectors may be based on a plurality of factors as explained below. A depth p, illustrated on FIG. 2B and sometimes referred to as “thickness”, in a direction parallel to the collimation direction (O′-O′) may be based on an expected energy of the scatter radiation 23. Back scattered radiation (in a direction generally opposite the direction of transmitted radiation as emitted from the source) has less energy than front scattered radiation (in a direction generally in the direction of transmitted radiation as emitted from the source). In some examples, detectors 4 in a plurality 3 of detectors located at the opposite side of the source 1 with respect to the load 10 may be thicker than detectors 4 located on the source 1 side with respect to the load 10 to inspect. The thickness may also depend on the density of the detector material. In some examples, if plastic is used (e.g. because of low cost), then a relatively large thickness may be envisaged (e.g. 5 cm). A width Δ, illustrated e.g. on FIG. 2B, may be based on a desired resolution of the final image. If the load width is 2.5 m, and if a 1 cm resolution is desired, a plurality of detectors may comprise 250 detectors of 1 cm width Δ; if a 5 cm resolution is desired, a plurality of detectors may comprise 50 detectors of 5 cm width Δ. A length L4, illustrated on FIG. 2B, may be a compromise between a cost of the detector and a quantity of radiation detected by the detector. L4 could be as short as 1 cm and as long as 1 m or even more. It should be understood that a quantity of radiation detected by the detector increases with L4, but cost also increases with L4. In the example illustrated by FIG. 2C, p may be equal to 5 cm (50 mm), Δ may be equal to 10 mm (1 cm), L4 may be equal to 500 mm (50 cm) and E may be equal to 500 mm (50 cm). It should be understood that if the thickness of the partitions 7 increases, the partitions 7 may relatively better inhibit scatter radiation from other, non-associated, portions of the load to reach the detectors, but the partitions 7 may also relatively hide more the detector 4 from the associated portion of the load. A compromise may be found for each application. In some examples, each partition 7 may have a thickness of 5 mm. As illustrated in FIG. 6E, in examples where the plurality of detectors comprises at least one linear array of detectors, the linear array may have a length based on (e.g. equal to) a dimension of the load, such as a height L5 (e.g. in a direction parallel to the (Oz) axis) of the load 10 or a width L6 (e.g. in a direction parallel to the (Oy) axis) of the load. In examples where the plurality of detectors comprises a matrix of detectors, the matrix of detectors may have a ratio of dimensions based on a ratio of dimensions of the load. Examples of dimensions below are based on parallel collimation. In some examples, and as illustrated in FIG. 6E, a size (e.g. length) of an array for a side view may be equal to the load height L5, e.g. equal to 5 m. In some examples, a resolution in a direction parallel to the (Oz) may be between 5 mm to 2 cm. The plurality 3 of detectors 4 may comprise, e.g. in a direction parallel to the (Oz) axis, any number of detectors 4, for example from 1000 detectors 4 of 5 mm width to 250 detectors 4 of 2 cm width. In some examples, and as illustrated in FIG. 6E, a size (e.g. length) of an array for a top view may be equal to the load width, e.g. to 2.5 m. In some examples, a resolution (in a direction parallel to the (Oy), as a non-limiting example) may be between 5 mm to 2 cm. The plurality 3 of detectors 4 may comprise (e.g. in a direction parallel to the (Oy) axis) any number of detectors 4, for example from 500 detectors of 5 mm width to 125 detectors 4 of 2 cm width. Similarly, in some examples, and as illustrated in FIG. 6D, a size (e.g. width) of a plurality 3 (such as a matrix, but a linear array is also envisaged) of detectors 4 for a view and/or an angled front view may be equal to the load width L6, e.g. to 2.5 m. In some examples, a resolution in the width of the plurality 3 may be between 5 mm to 2 cm. The plurality 3 of detectors may comprise any number of detectors in that dimension, for example from 500 detectors of 5 mm width to 125 detectors of 2 cm width. Other dimensions and distances are envisaged. In the example of FIG. 1, the radiation 22 is emitted by the source 1. In the example of FIG. 1, the radiation 22 is configured to be transmitted through the load 10. In the example of FIG. 1, the radiation 22 is shown as a collimated almost parallel beam irradiating the load 10 in a direction parallel to the (Oy) axis. However, other forms of beams are envisaged for the radiation 22, and other directions of irradiations are also envisaged. In some examples, the source 1 may be configured to irradiate the load 10 using a fan beam. An example of a fan beam is illustrated in FIG. 5A and has an angular width β such that the load 10 may be irradiated across its width in a direction both parallel to the axis (Oy) and perpendicular to an inspection direction INS, parallel to the axis (Ox). In other examples, the load 10 may be irradiated by other types of beams, such as a pencil beam. In the example of FIG. 5B, the load 10 is irradiated by a fan beam in the (YOZ) plane, in a direction having an angle with respect to the (Oy) axis and the (Oz) axis. In some examples, the source 1 may be configured to emit the radiation 22 for inspection of the load 10 by scatter radiation only. Alternatively or additionally, in some examples, and as illustrated e.g. in FIG. 5B, the source 1 may emit the radiation 22 for inspection of the load 10 by transmission of the radiation 22 through the load 10. In such examples apparatus 1000 comprising the system 100 may further comprise an additional detector 11 to detect the radiation 22 that has been transmitted through the load 10. The additional detector 11 may comprise, amongst other conventional electrical elements, radiation detection lines, such as X-ray detection lines. In the examples described above, the load 10 is irradiated from one direction by a single source 1 of radiation 22. It should be understood that more than one radiation source may also be used, and the apparatus 1000 may thus comprise a plurality of sources 1. For example the load may be irradiated from more than one direction, from more than a source of radiation. Scatter radiation: may have a greater level nearer a source of radiation, because the irradiating radiation has a greater flux; and/or may be more attenuated and/or affected by the load as the irradiating radiation travels in the load away from the source. In some examples, irradiating the load by more than one source may enhance a quality of data corresponding to detected scatter radiation, e.g. detected nearer the respective source. In some examples, the scatter radiation from one or more sources 1 may be detected by a single detection system 100. The system 100 described above may be used in the apparatus 1000 which may also comprise the source 1. In some examples the apparatus may comprise a plurality of systems 100 according to any aspect of the disclosure. In the example of FIG. 5B, shielding 12 is located between the plurality 3 of detectors and the additional detector 11, and is configured to inhibit any radiation scattered from the additional detector 11 to reach the plurality 3 of detectors, and vice versa. The shielding 12 is configured to inhibit (e.g. block or at least attenuate) the radiation scattered by the plurality 3 and/or the additional detector 11. The shielding 12 may comprise lead, but other materials are envisaged. The shielding 12 may form part of the apparatus 1000 external to the system 100, but in some examples the shielding may form part of the system 100. The shielding 12 may also be configured to inhibit the radiation 22 from the source 1 to reach the plurality 3 of detectors. In some examples, the detection system 100 is movable with respect to the load 10. In some examples, the detection system 100 may remain static with respect to the ground and the load 10 is moved with respect to the ground in an inspection direction INS (e.g. parallel to the (Ox) axis on the Figures). The above mode of operation is sometimes referred to as a “pass-through” mode of operation. Examples of pass-through modes of operation include the load being a vehicle such as a truck. In some examples, a driver of the vehicle may drive the truck through the detection system 100, e.g. including a gantry. In some examples (e.g. where the radiation is relatively high), the apparatus 1000 may comprise a conveyor configured to carry the vehicle (such as the truck) through the system 100, e.g. at low speed (e.g. lower than 5 km/h). The above mode of operation is sometimes referred to as a “conveyor” mode of operation. Alternatively or additionally, the load 10 may remain static with respect to the ground and the detection system 100 may be moved with respect to the ground in the inspection direction. This mode of operation is sometimes referred to as a “scan” mode of operation. FIGS. 3 and 4 show that the movement of the load 10 with respect to system 100 allows successive zones, e.g. zones 8 and 13, of the load 10 to be irradiated by the radiation 22 and therefore successively emit the scatter irradiation 23. FIG. 3 and FIG. 4 illustrate an example of the detection system 100 of FIG. 1 in which the load 10 is moved with respect to the detection system 100, e.g. in the inspection direction INS parallel to the axis (Ox). FIG. 3 shows the zone 8 of the load 10 being irradiated by the radiation 22. It should be understood that in some examples several (e.g. all of the) portions of the zone 8 may emit scatter radiation in response to being irradiated. However only the respective portion 18 (also shown in FIG. 1) is represented in FIG. 3, for the sake of clarity. The collimator 6 of the plurality 5 of collimators is configured to enable the radiation 23 scattered by the portion 18 to reach the associated detector 4 in the plurality 3 of detectors. A 1D image of the zone 8 (e.g. in a plane parallel to the (YOZ) plane) may be obtained. In some examples, an analyser 9 may be configured to receive data from the plurality 3 (and/or the additional detector 11 when present) to generate one or more images, such as the 1D image. The analyser 9 conventionally comprises at least a processor and a memory. In some examples, the analyser 9 may form part of the apparatus 1000 external to the system 100 or may form part of the system 100. FIG. 4 shows an example where the load 10 has moved in the inspection direction INS with respect to the detection system 100 and with respect to the position of the load 10 illustrated in FIG. 3. In this example, the load 10 is irradiated by the radiation 22 such that the zone 13 of the load 10 is irradiated and emits scatter radiation. Similarly to what has been described above with reference to the zone 8, a 1D image of the zone 13 in a plane parallel to the (YOZ) plane may be obtained. It should be understood that in examples where the whole of the load is moved along the inspection direction INS and irradiated by the radiation 22, a 2D image of the load may be obtained, e.g. by combining all the obtained 1D images. In some examples, the radiation irradiating the zones (e.g. the zones 8 and 13) may be a fan beam irradiating the whole of the zone at the same time. The 1D image may be obtained at the same time. Alternatively or additionally, in some examples, the radiation 22 irradiating the zone may be a pencil beam irradiating a portion of the zones (e.g. the zones 8 and 13) at a time. In such examples, the pencil beam may be travelled on the load to irradiate the zone of the load, and the 1D image is obtained after all of the portions of the zones have been irradiated. In some examples, the load 10 may be stopped during the travel of beam and/or correction may be applied by the analyser 9 to take into account the movement of the load during the travel of the beam. In some examples, a plurality of views of the load 10 may be obtained using a plurality of systems (and one source or a plurality of sources of radiation). It should be understood that each system 100 may generate a view and hidden objects may be detected using the plurality of views. The one or more systems may be placed at different given positions in the apparatus, depending on the desired views. The one or more sources of radiation may be placed at different given positions in the apparatus, depending on the desired views. As illustrated in FIGS. 6A, 6B, 6C, 6D and 6E, an image of the load corresponding to a location of the plurality of detectors, with respect to the direction of inspection, may be generated. It should be understood that in the present disclosure, “top” and “side” refer to a position of the plurality of detectors with respect to the load and/or with respect to each other. A top view may not be strictly vertical (e.g. not strictly parallel to the (OZ) axis) and may form an angle with respect to the (OZ) axis, and still be referred to as a top view. Similarly, a side view may not be strictly horizontal (e.g. not strictly parallel to the (XOY) plane) and may form an angle with respect to the (OY) and/or (OZ) axes, and still be referred to as a top view. In some examples and as illustrated in FIG. 6A, if the plurality 3 of detectors 4 is located at a location corresponding to a top view (e.g. the plurality of detectors is parallel to the axis (Oy) in a plane parallel to the (YOZ) plane), then a top view of the load 10 may be obtained (e.g. as well as a transmission view in case the additional detector is present). Alternatively or additionally, in some examples and as illustrated in FIG. 6A, if the plurality 3 of detectors 4 is located at a location corresponding to a side view (e.g. the plurality of detectors is parallel to the axis (Oz)), then a side view of the load may be obtained (e.g. as well as a transmission view in case the additional detector is present). It should be understood that a number of scatter views may be obtained simultaneously, depending on the number of systems 100 placed around the load 10. The views of the load which may be obtained with one or more systems as illustrated in FIG. 6A are without any parallax. As illustrated in FIG. 6A, in some examples one of the plurality 3 of detectors may be located at a location corresponding to a side view having an angle α different from 0 with respect to the vertical plane (YOZ), and may provide an enhanced view of hidden objects which may be difficult to detect (e.g. using strictly top (or side) views only), such as objects hidden in doors of a vehicle. In some examples, the direction of collimation (O′-O′) of each collimator of the plurality 5 of collimators may correspond to the angle α. In the example of FIG. 6B, the plurality 3 may comprise a matrix such that the detection system 100 defines a main direction D of detection, the main direction of detection being perpendicular to the main direction INS of inspection of the load 10. In the examples illustrated in FIG. 6B, the system 100 is positioned on the inspection direction INS. The above configuration of the system 100 enables a 2D slice (e.g. a cross section of the load) to be generated in a plane parallel to the plane (YOZ) using data detected by the matrix 3, without any parallax. In other words, the detection system 100 defines a main direction D (shown in FIG. 6B) of detection which is parallel to the inspection direction INS (and e.g. perpendicular to a main plane of irradiation of the load which is parallel to the (YOZ) plane in FIG. 6B). The above configuration of the system 100 may be used, e.g. for relatively small loads. It should be understood that in the above configuration, the system 100 is positioned on the inspection direction INS, and prevents the system 100 from operating in e.g. a full pass-through mode and/or from inspecting relatively large loads, as the system 100 is in the way of the load 10. In examples where the detection system 100 needs to operate in a full pass-through and/or conveyor mode, or where relatively large loads need to be inspected, the system 100 is not located on the inspection direction INS to enable the load 10 to move along the inspection direction INS. In such examples, and as illustrated in FIG. 6C, the system 100 may be positioned at a minimum distance h from the inspection direction INS and enables the load 10 to travel on the inspection direction INS without intersecting the detection system 100. The main direction of detection D of the system 100 may form an angle α with respect to the inspection direction INS. In the example of FIG. 6C, because of the distance h and/or the angle α relative to the inspection direction INS, the final image generated by data obtained by the detection system 100 may be distorted. In some examples, the analyser 9 may be further configured to compensate for the distance which is different for each pair (detector, voxel), based on the values of h and α, as the distance h and the angle α are known for a given detection system 100. In the examples described above, the matrix 3 may be square or rectangular. Alternatively or additionally, in some examples the matrix 3 may have trapezoid shape based the above values of h and α. In some examples, the radiation irradiating the zones (e.g. the zone 8) may be a fan beam irradiating the whole of the zone at the same time. The 2D image may be obtained at the same time. Alternatively or additionally, in some examples, the radiation 22 irradiating the zone may be a pencil beam irradiating a portion of the zones (e.g. the zone 8) at a time. In such examples, the pencil beam may be travelled on the load to irradiate the zone of the load, and the 2D image is obtained after all of the portions of the zones have been irradiated. In some examples, the load 10 may be stopped during the travel of beam and/or correction may be applied by the analyser 9 to take into account the movement of the load during the travel of the beam. The system and apparatus may provide at least one relatively not expensive extra view (such as an extra top view) for an apparatus having a static gantry (e.g. using a pass-through and/or a conveyor mode described in greater detail below) and a single generator, or at least one relatively not expensive extra view (such as an extra side view) for an apparatus having a mobile detection system (e.g. using a scan mode) and a single generator. The system and apparatus may provide at least one relatively not expensive extra view (such as a top and/or side view, for example without parallax) for an apparatus having a single generator. In examples where the plurality of detectors comprises a matrix of detectors, it should be understood that in some examples the cross sections of the load: may overlap each other if the speed of the load is low compared to a frequency of irradiation of the load and/or of detection by the matrix, or may be slightly separated from each other if the speed of the load is higher than a frequency of irradiation of the load and/or of detection by the matrix. In some examples, the analyser 9 may perform, at least partly, the combining of the cross sections to obtain the final 3D image. As explained in greater detail below, the scatter radiation 23 emitted by a respective portion and/or a zone of the load 10 may be attenuated and/or affected by another portion and/or another zone of the load 10. In some examples the attenuation and/or impact of each of the other portions and/or zones of the load on the scatter radiation emitted by a current portion and/or zone may be dependent upon at least one property of other portions and/or zones of the loads, such as a material of the other portions and/or zones and/or an object located in the other portions and/or zones. In some examples, the scatter radiation 23 emitted by a zone (e.g. a current zone) may be attenuated and/or affected by another zone (e.g. a preceding zone) prior to being received by the plurality 3 of detectors. Therefore the magnitude of and/or the data associated with the scatter radiation may not be totally representative of the current zone only. For example, the preceding zone of the load 10 (located between the current portion of the load 10 emitting the scatter radiation 23 and the plurality 3 of detectors) may be highly attenuating and/or may comprise an object which could affect the radiation emitted by the current zone. When the scatter radiation 23 passes towards the plurality 3 of detectors, it passes through the preceding zone of the load 10 and may therefore be attenuated or affected. In some examples, the analyser 9 may be configured to process current data associated with the current zone (e.g. emitting scattered radiation because currently irradiated), to take into account one of the properties of the other zones of the load. In some examples and as explained above, the other zones may be the zones located between the current zone and the detection device 100. In some examples the property of the other zones may be predetermined (e.g. measured by transmission). Alternatively or additionally, the other zones may correspond to zones which have previously emitted scatter radiation because they have been previously irradiated, and the property of the other zones may be have been previously detected using the detection system 100 and/or by another device 100 (for example from another view). In some examples, the processing may take into account the property of the preceding zones by subtracting (e.g. accounting for impact by the preceding zones) and/or adding (e.g. accounting for attenuation by the preceding zones), from and/or to current data associated with the current zone, data corresponding to the preceding zones, in order to correct the current data to obtain more accurate information about the current zone. In the developments above, the radiation scattered from a current zone may be attenuated and/or affected by another zone, i.e. in a direction parallel to the (Ox) axis (e.g. illustrated in FIG. 6B). It should be understood that, similarly, the radiation scattered by a respective portion may be attenuated and/or affected by another respective portion, i.e. in a direction parallel to the (YOZ) plane (e.g. illustrated in FIG. 6B). Current data associated with a respective portion of the load emitting scattered radiation (e.g. portion 20 in FIG. 6B) may be affected by at least one property of another portion located in the plane parallel to the direction of transmission of the radiation 22 (e.g. the portion 18 or the portion 19 in FIG. 6B). Alternatively or additionally the processing performed by the analyser 9 may take into account the property of e.g. the portion 18 and/or 19 to correct the current data from e.g. the portion 20, to obtain more accurate information about the current portion 20. The amount of radiation 23 scattered by a portion of the load decreases as the radiation 22 irradiating the portion is attenuated (e.g. an X-ray flux of the radiation 22 diminishes). In some examples, the X-ray incident flux diminishes with a coefficient in d2, where d is the distance to a focal spot of the source 1. Alternatively or additionally, the analyser 9 is configured to process the current data associated with a current respective portion of the load emitting scattered radiation, to take into account a distance of the portion from the source of radiation, e.g. by applying a correcting coefficient based on the above coefficient in d2. Alternatively or additionally, in some examples, the analyser 9 may be configured to estimate a nature of a material of the load, based on a detection of a level of scattered radiation 23 and/or on a spectrum of energy of the scattered radiation by the plurality of detectors. The level of scattered radiation 23 may be dependent upon the material producing the scatter radiation. Materials having a low Z number (like plastic or water) produce more scatter radiation 23 than materials having a high Z number (like lead or gold). A relatively high level of scattered radiation detected by the plurality of detectors may enable estimation that the irradiated zone comprises an organic material, whereas a relatively low level of scattered radiation detected by the plurality of detectors may enable estimation that the irradiated zone comprises a non-organic material. The system 100 may therefore enable estimation of what type of material is present in the load, based on the detected level of scatter radiation and/or based on a level of scatter photon energy distribution, which may also vary with the material present in the load. In an example, the system 100 may enable enhanced detection of hidden objects and/or certain materials (i.e. explosives) present in the load. In some embodiments and as shown in FIG. 7, a method for inspecting one or more loads comprises: selecting (e.g. collimating), at S2, radiation scattered by each respective portion of a load to inspect, the radiation being scattered in response to the respective portion being irradiated by radiation transmitted through the portion, and. detecting, at S3, on each detector of the matrix, the radiation scattered by the associated respective portion of the load. In some examples, the selecting performed at S2 comprises: enabling the radiation scattered by the respective portion to reach an associated detector of a plurality of detectors, and inhibiting any other scattered radiation from reaching the associated detector. In some embodiments, the selecting performed at S2 may be performed by the plurality 5 of collimators 6 of the system of any one of the aspects of the disclosure. In some embodiments, the detecting performed at S3 may be performed by the plurality 3 of detectors 4 of the system of any one of the aspects of the disclosure. In some examples, the method illustrated in FIG. 7 may optionally comprise, at S1, emitting radiation for irradiation of the loads to inspect. In some embodiments, the emitting performed at S1 may be performed by the source 1 of the apparatus and/or system of any one of the aspects of the disclosure. In some examples, the method illustrated in FIG. 7 may optionally comprise, at S4, detecting radiation after transmission through the load. In some embodiments, the detecting performed at S4 may be performed by the additional detector 11 of the apparatus and/or system of any one of the aspects of the disclosure. In some embodiments, the method of FIG. 7 may further comprise generating, at S5, an image (such as 2D and/or 3D) of the load, e.g. by using data associated with the plurality of detectors and/or the additional detector (when present). In some examples generating the image further comprises processing data associated with the plurality of detectors of the detection system. In some examples, the data comprises current data associated with a current zone of the load emitting scattered radiation, to take into account at least one property of other zones of the load. In some examples, the data comprises current data associated with a current respective portion of the load emitting scattered radiation, to take into account at least one property of other portions in a plane parallel to a direction of transmission of radiation; and/or a distance of the portion from the source of radiation. In some examples, processing the data comprises compensating for a difference in a distance between the detectors of the plurality of detectors to the load caused by the detection system defining a main direction of detection forming an angle with respect to a direction of inspection of the load, and/or the detection system being positioned at a distance from the direction of inspection of the load. In some examples, processing the data further comprises estimating a nature of a material of the load, based on a detection of a level of scattered radiation and/or on a spectrum of energy of the scattered radiation. In some embodiments, the generating performed at S5 may be performed by the analyser 9 of the apparatus and/or system of any one of the aspects of the disclosure. In another aspect of the present disclosure, there is described a computer program product comprising program instructions to program a processor to carry out a method according to any aspect of the disclosure, or to program a processor to provide a system and/or apparatus and/or imager of any aspect of the disclosure. Another example embodiment is disclosed below. Features and properties which are common and/or similar to other embodiments which were already described above are not disclosed in detail below, for the sake of clarity. In the example of FIG. 9, a detection system 100 comprises a matrix 2 of detectors (some detectors are referred to as e.g. detector 14, 15 or 16 in FIG. 9) and a selection device 111 comprising an aperture 112. Each detector 14, 15 or 16 of the matrix 2 of detectors is configured to detect radiation 23 scattered by an associated respective portion (e.g. some portions are referred to as e.g. portion 18, 19 or 20, respectively, in FIG. 9) of a load 10 to inspect. The radiation 23 is scattered in response to the respective portion 18, 19 or 20 being irradiated by radiation 22 transmitted through the portion 18, 19 or 20, respectively. Each ray of the scatter radiation 23 is emitted by the respective portion 18, 19 or 20, respectively, when the radiation 22 irradiates the portion 18, 19 or 20 of the load 10 (for example because of Compton scattering and pair production in the case of X-ray and/or gamma radiation). The scatter radiation 23 is emitted in all the directions. As illustrated in FIG. 9, a zone 8 of the load 10 (the zone 8 comprising the respective portions 18, 19 or 20 in FIG. 9) is irradiated by the radiation 22. The zone 8 of the load 10, upon being irradiated, emits the scatter radiation 23. In the example of FIG. 9, the respective portions 18, 19 and 20 are located in the zone 8, and each respective portion 18, 19 or 20 emits the scatter radiation 23 in a number of example directions. In the example of FIG. 9, the aperture 112 of the selection device 111 is configured to enable radiation 26, 30b and 28b, scattered respectively by the respective portions 18, 19 and 20 of the zone 8 of the load 10, to reach the respective detectors 14, 15 and 16 of the matrix 2 of detectors. In the example of FIG. 9: the portion 18 is associated with the detector 14, because the detector 14 is in the line of sight of the portion 18 through the aperture 112 (i.e. the detector 14, the aperture 112 and the portion 18 are aligned), the portion 19 is associated with the detector 15, because the detector 15 is in the line of sight of the portion 19 through the aperture 112 (i.e. the detector 15, the aperture 112 and the portion 19 are aligned), and the portion 20 is associated with the detector 16, because the detector 16 is in the line of sight of the portion 20 through the aperture 112 (i.e. the detector 16, the aperture 112 and the portion 20 are aligned). In the example of FIG. 9 the scatter radiation 26, 30b or 28b corresponds, respectively, to the line of sight between the respective portion 18, 19 or 20 and the respective detector 14, 15 or 16, and is thus enabled to pass through the selection device 111 via the aperture 112. FIG. 10 (not to scale) provides an illustration of a detail of the detection system 100 of FIG. 9, in which the respective portion 20 of FIG. 9 is emitting the scatter radiation 23 in example directions, such as directions referred to as 28a, 28b, 28c, 28d, 28e and 28f. In the example shown in FIG. 10, the scatter radiation 23 from the respective portion 19 of FIG. 9 is also emitting the scatter radiation 23 in example directions, such as directions referred to as 30a, 30b, 30c, 30d, 30e and 30f. It should be understood that FIG. 10 is a simplified image showing a selection of rays of the scatter radiation 23 emitted by only two respective portions 19 and 20 of the zone 8 of FIG. 9. The number of respective portions and the scatter radiation emitted by each respective portion has been limited for illustrative purposes. In the example of FIG. 10, the radiation emitted from the portion 20 in the direction 28b passes through the aperture 112 to reach the associated detector 16 of the matrix 2 of detectors. Similarly, the scatter radiation from the portion 19 in the direction 30b passes through the aperture 112 to reach the associated detector 15 of the matrix 2 of detectors. The scatter radiation 23 emitted by the portion 19 is prevented from reaching the detector 16, because the portion 19 is not in the line of sight of the detector 16 (the detector 16 is not associated with the portion 19). The scatter radiation 23 emitted by the portion 20 is prevented from reaching the detector 15, because the portion 20 is not in the line of sight of the detector 15 (the detector 15 is not associated with the portion 20). In some examples, the device 111 may comprise a block 114 and the aperture 112 may comprise a hole 17, the hole 17 being located in the block 114. In some examples, the block 114 comprises a material that inhibits the scatter radiation from reaching the matrix 2. For example the block 114 may be made from a material (e.g., lead) that blocks or at least attenuates radiation, and therefore prevents radiation from reaching the matrix 2. In the example described above, the hole 17 may comprise an area without any material, to allow the desired scatter radiation to pass through the aperture 112 to reach the matrix 2. In such an example radiation that is able to pass through the hole 17 is not attenuated when passing through the hole 17. In some examples, the aperture 112 may comprise a filter. In some examples a filter may enable reduction of noise. In the example of FIG. 9, dimensions e and E of the aperture 112 of the device 111 are dependent on a distance L11 between the zone 8 and the device 111, and/or on a distance L21 between the matrix 2 and the device 111, and/or dimensions of the load to inspect. In some examples, the dimensions e and E are predetermined such that: each respective portion (such as the portion 18, 19 or 20) corresponds to a voxel of the zone 8 of the load 10 (e.g. as viewed from the detectors such as the detector 14, 15 or 16), and/or each respective detector (such as the detector 14, 15 or 16) associated with a respective portion detects the radiation scattered from the single voxel formed by the respective portion—each respective detector corresponds to a pixel of the matrix 2 viewed from the respective portion. The selection device 111 enables imaging of the zone 8, using detection of the scatter radiation 23, because each one of the detectors of the matrix 2 is configured to be targeted by a unique voxel of the zone 8 and is configured to correspond to a pixel of a final 2D image of the zone 8. The final 2D image may be generated based on data collected by the detectors of the matrix 2. In some examples, L11 may be greater than 1 m. In such examples, the system 100 may enable reduced noise (and may also avoid intersecting an inspection direction INS as described in greater detail below). In some examples, the matrix 2 may be relatively close to the load 10 and get a relatively large amount of scatter radiation 23. In some examples, L11 and L21 are such that L11+L21<5 m. In some examples, L11 and L21 are such that L21<L11. In such examples, the matrix is smaller than a load slice and is relatively not as expensive as a matrix larger than a slice. In some examples, L11 and L21 are such that: 1 m≤L11≤5 m, typically e.g. 2 m; and 0.3 m≤L21≤5 m, typically e.g. 1 m. In some examples, e is equal to E, but any form ratio can be chosen for the aperture 112, e.g. depending on a form ratio of the load and/or the detectors of the matrix 2. E and e may depend on dimensions of the detectors (e.g. pixel size) of the matrix 2. In examples E and e may have dimensions about half of the size of the detectors of the matrix 2. For example, for a slice of the load 10 having dimensions 5 m×3 m in a plane parallel to the (YOZ) plane (e.g. a cross section of the load), the matrix 2 may comprise 500×300 detectors (corresponding to a 500×300 resolution). In examples where L11=2 m and L21=1 m, the pixel size may be 5 mm×5 mm. In examples E and e may be such that E=2.5 mm and e=2.5 mm. In some examples the device 111 may act as a diaphragm (e.g. a hole collimator). In the examples described above, the aperture 112 has a regular parallelepiped shape. It should be understood that, alternatively or additionally, the aperture 112 may have a truncated pyramid shape, with E and e dimensions being located at the truncated apex. It should also be understood that the above dimensions are example dimensions for loads comprising e.g. vehicles and/or ISO containers. Other dimensions are envisaged, e.g. for applications including inspection of luggage. Dimensions of the matrix 2 of detectors may be selected based on dimensions of the load to inspect. For example, the matrix 2 of detectors may have a ratio of dimensions (such as a height to width ratio) that is based on (e.g. smaller than or equal to) a ratio of dimensions (such as a height to width ratio) of the load. As described in greater detail below, in some examples the load 10 may have a size that corresponds to a standard size, and the matrix 2 of detectors may have a ratio of dimensions corresponding to that standard size (such as an ISO container). Alternatively or additionally, the dimensions of the matrix of detectors may be dependent upon the distances L11 and/or L21. For example, a greater distance L21 between the aperture 112 and the matrix 2 of detectors may lead to a larger projection of the load onto the matrix of detectors (a relatively larger matrix of detectors may be required). Similarly a greater distance L11 between the aperture 112 and the load 10 may lead to a smaller projection of the load 10 onto the matrix 2 of detectors (a relatively smaller matrix of detectors may be required). In some examples, the matrix may have dimensions corresponding to dimensions of a cross section of the load, multiplied by a L21/L11 ratio. In some examples, the matrix may have dimensions such that 2.5 m×1.5 m. In some examples, L21 may be reduced and the matrix may have smaller dimensions and be relatively less expensive. Other dimensions and distances are envisaged. In some examples, a source 1 may be configured to emit the radiation 22 for inspection of the load 10 by scatter radiation only. Alternatively or additionally, in some examples, and as illustrated e.g. in FIG. 9, the source 1 may emit the radiation 22 for inspection of the load 10 by transmission of the radiation 22 through the load 10. In such examples apparatus 1000 comprising the system 100 may further comprise an additional detector 11 to detect the radiation 22 that has been transmitted through the load 10. The additional detector 11 may comprise, amongst other conventional electrical elements, radiation detection lines, such as X-ray detection lines. In the example of FIG. 9, shielding 117 is also located between the additional detector 11 and the matrix 2 of the system 100 and is configured to inhibit radiation scattered by the additional detector 11 from reaching the matrix 2, as in some examples the matrix 2 should detect the scatter radiation 23 only. FIGS. 11 and 12 show that the movement of the load 10 with respect to system 100 allows successive zones, e.g. zones 8 and 13, of the load 10 to be irradiated by the radiation 22 and therefore successively emit the scatter irradiation 23. In the example shown in FIGS. 11 and 12, the load 10 has moved relative to the detection system 100 but the distances between the zone 8 or 13 being irradiated, the aperture 112 and the matrix 2 of detectors are the same both in FIG. 11 and in FIG. 12. An example of a fan beam is illustrated in FIG. 5A and has an angular width R. Using a similar fan beam, the load 10 may be irradiated across its width in a direction both parallel to the axis (Oy) and perpendicular to an inspection direction INS, parallel to the axis (Ox). In other examples, the load 10 may be irradiated by other types of beams, such as a pencil beam. In the example of FIG. 13, the load 10 is irradiated by a fan beam in the YOZ plane, in a direction having an angle with respect to the (Oy) axis and the (Oz) axis. It should be understood that in some examples the 2D slices: may overlap each other if the speed of the load is low compared to a frequency of irradiation of the load and/or of detection by the matrix, or may be slightly separated from each other if the speed of the load is higher than a frequency of irradiation of the load and/or of detection by the matrix. In some examples, an analyser 9 already described in connection with other embodiments may perform, at least partly, the combining of the slices to obtain the final 3D image. As already explained in connection with other embodiments, the scatter radiation 23 emitted by a respective portion and/or a zone of the load 10 may be attenuated and/or affected by another portion and/or another zone of the load 10. In some examples the attenuation and/or impact of each of the other portions and/or zones of the load on the scatter radiation emitted by a current portion and/or zone may be dependent upon at least one property of other portions and/or zones of the loads, such as a material of the other portions and/or zones and/or an object located in the other portions and/or zones. FIG. 14 shows an example in which the load 10 is irradiated in successive zones 34, 36, 38, 40, 42, 44, 46, 48, 50. In the example of FIG. 14, the matrix 2 is located such that the zone 34 is closest to the matrix 2 and the zone 50 is furthest from the matrix 2. Radiation 23 scattered from the load 10 when the zone 34 is irradiated will therefore pass directly to the matrix 2 and will not pass through any other zones of the load 10, whereas radiation 23 scattered by the zone 50 will pass through the zones 34, 36, 38, 40, 42, 44, 46 and 48 before reaching the matrix 2. The scatter radiation emitted by the zone 50 will be attenuated and/or affected by the zones 34, 36, 38, 40, 42, 44, 46 and 48. In some examples, the analyser 9 may be configured to process current data associated with the current zone and/or portion (e.g. emitting scattered radiation because currently irradiated), to take into account one of the properties of the other zones and/or portions of the load. In some examples and as explained above, the other zones may be the zones located between the current zone and the detection device 100. In examples where the detection system 100 needs to operate in a full pass-through and/or conveyor mode, or where relatively large loads need to be inspected, the system 100 is not located on the inspection direction INS to enable the load 10 to move along the inspection direction INS. In such examples, and as illustrated in FIG. 15, the system 100 may be positioned at a minimum distance h from the inspection direction INS and enables the load 10 to travel on the inspection direction INS without intersecting the detection system 100. The main direction of detection D of the system 100 may form an angle α with respect to the inspection direction INS. In the example of FIG. 15, because of the distance h and/or the angle α relative to the inspection direction INS, the final image generated by data obtained by the detection system 100 may be distorted. It can be seen on FIG. 15 that the distortion is created when e.g. the radiation 23 scattered by the portion 18 is received by the matrix 2 at an angle that is different from the angle at which the radiation 23 scattered by the portion 20. The distorted final image of the slices may lead to a distorted image of the load. In some examples, the analyser 9 may be further configured to compensate for the distortion based on the values of h and a, as the distance h and the angle α are known for a given detection system 100. In the examples described above, the matrix may be square or rectangular. Alternatively or additionally, in some examples the matrix 2 may have trapezoid shape based the above values of h and α. In some embodiments and as shown in FIG. 7, a method for inspecting one or more loads 10 comprises: selecting, at S2, radiation scattered by each respective portion of a load to inspect, the radiation being scattered in response to the respective portion being irradiated by radiation transmitted through the portion, and detecting, at S3, on each detector of the matrix, the radiation scattered by the associated respective portion of the load. In some examples, the selecting performed at S2 comprises: enabling the radiation scattered by the respective portion to reach an associated detector of a matrix of detectors, and inhibiting any other scattered radiation from reaching the associated detector. In some embodiments, the selecting performed at S2 may be performed by the selection device 111 of the system of any one of the aspects of the disclosure. In some embodiments, the detecting performed at S3 may be performed by the matrix 2 of the system of any one of the aspects of the disclosure. In some examples, the method illustrated in FIG. 7 may optionally comprise, at S1, emitting radiation for irradiation of the loads to inspect. In some embodiments, the emitting performed at S1 may be performed by the source 1 of the apparatus and/or system of any one of the aspects of the disclosure. In some examples, the method illustrated in FIG. 7 may optionally comprise, at S4, detecting radiation after transmission through the load. In some embodiments, the detecting performed at S4 may be performed by the additional detector 11 of the apparatus and/or system of any one of the aspects of the disclosure. In some embodiments, the method of FIG. 7 may further comprise generating, at S5, an image of the load, e.g. by using data associated with the matrix and/or the additional detector (when present). In some examples, the apparatus may comprise at least a pair of detection systems, each pair comprising a detection system located on either side of an axis (e.g. the axis INS) with respect to the other detection system of the pair, with respect to the axis. The analyser may be configured to determine a position of a scattering object in the load, in a direction (e.g. Oy) perpendicular to the axis, using a ratio and/or a difference of signals associated with each detection system of the pair. As illustrated in FIG. 16, apparatus 1000 may comprise one or more pairs of systems 100, each pair comprising: a system 100 (e.g. 100(a) or 100(c)) located between the source 1 and the line of inspection INS; and a system 100 (e.g. 100(b) or 100(d)) located beyond the line of inspection INS with respect to the source 1, Let s1 be the scattering detection signal associated with the system 100(a); s2 be the scattering detection signal associated with the system 100(b); s3 be the scattering detection signal associated with the system 100(c); and s4 be the scattering detection signal associated with the system 100(d). The ratio R or the difference D, such that: R = ( s 1 ) ( s 2 ) or R = ( s 3 ) ( s 4 ) or D = s 1 - s 2 or D = s 3 - s 4 ,each may give an indication of the position of a scattering object in the load 10, in the (Oy) direction. It should be understood that if the apparatus 1000 comprises a plurality of couples (such as illustrated in FIG. 16), then R or D may be such that: R = ( s 1 + s 3 ) ( s 2 + s 4 ) or D = ( s 1 + s 3 ) - ( s 2 + s 4 ) . Alternatively or additionally, the apparatus may comprise at least one detection system comprising one or more detectors comprising two stacked layers of detection. Each layer of detection may have its own acquisition channel. The analyser may be configured to determine a nature of a scattering object in the load, using a ratio and/or a difference of signals associated with each detection layer. As illustrated in FIG. 16, in some embodiments, one or more of the systems 100 (e.g. the system 100(d) in FIG. 16) may comprise one or more detectors comprising two stacked layers of detection, a first layer 1001 of detection and a second layer 1002 of detection. In some examples, the first layer 1001 may comprise a first scintillator and the second layer 1002 may comprise a second scintillator, each scintillator having its own acquisition channel. Let: s5 be the scattering detection signal associated with the first layer 1001; and s6 be the scattering detection signal associated with the second layer 1002. The ratio R or the difference D, such that: R = ( s 5 ) ( s 6 ) or D = s 5 - s 6 , each may give an indication of the nature of the scattering object, such as radioactive material as a non-limiting example. Alternatively or additionally, the analyser may be configured to detect the presence of radioactive gamma emitting material within the load by using the detection system between the pulses of radiation transmitted through the portion. In some examples, any of the systems 100 illustrated in FIG. 16 may be used to detect the presence of radioactive gamma emitting materials within the load, for example between the pulses of the radiation source. This may be advantageous as the scatter detection systems may be relatively larger than transmission detection systems, and thus relatively more adapted to detect gamma rays. Modifications and Variations The load 10 may be any type of object and/or container, such as a holder, a vessel, or a box, etc. The load 10 may thus be, as non-limiting examples, a trailer and/or a palette (for example a palette of European standard, of US standard or of any other standard) and/or a train wagon and/or a tank and/or a boot of a vehicle such as a truck, a van and/or a car and/or a train, and/or the load 10 may be a “shipping container” (such as a tank or an ISO container or a non-ISO container or a Unit Load Device (ULD) container). It is thus appreciated that the load 10 may be any type of container, and thus may be a suitcase in some examples. In some examples, the apparatus may comprise a filter located between the load and one or more of the systems 100. In some examples a filter may enable reduction of noise. The system is configured to cause inspection of a cargo (not shown in the Figures) of the load through a material (usually steel) of walls of the load 10, e.g. for detection and/or identification of the cargo. The system may be configured to cause inspection of the load, in totality (i.e. the whole load is inspected) or partially (i.e. only a chosen part of the load is inspected, e.g., typically, when inspecting a vehicle, a cabin of the vehicle may not be inspected, whereas a rear part of the vehicle is inspected). The source 1 may comprise an accelerator, i.e. may be configured to produce and accelerate an electron beam on a metal target (such as tungsten and copper), sometimes referred to as a “focal spot”, to generate the photons of the radiation 22 (by the so-called braking radiation effect, also called “Bremsstrahlung”). Alternatively or additionally, the source 1 may be configured to be activated by a power supply, such as a battery of an apparatus comprising a vehicle and/or an external power supply. The radiation 22 may comprise y-ray radiation and/or neutron radiation. Non-limiting examples of irradiation energy from a source may be comprised between 50 keV and 15 MeV, such as 2 MeV to 6 MeV, for example. Other energies are envisaged. In some examples the energy of the X-ray radiation may be comprised between 50 keV and 15 MeV, and the dose may be comprised between 2 mGy/min and 30 Gy/min (Gray). In some examples, the power of the source may be e.g., between 100 keV and 9.0 MeV, typically e.g. 2 MeV, 3.5 MeV, 4 MeV, or 6 MeV, for a steel penetration capacity e.g., between 40 mm to 400 mm, typically e.g., 300 mm (12 in). In some examples, the dose may be e.g., between 20 mGy/min and 120 mGy/min. In some examples, the power of the X-ray source may be e.g., between 4 MeV and 10 MeV, typically e.g., 9 MeV, for a steel penetration capacity e.g., between 300 mm to 450 mm, typically e.g., 410 mm (16.1 in). In some examples, the dose may be 17 Gy/min. In some examples the source 1 may be configured to emit the radiation 22 with successive radiation pulses. In some examples, the source 1 may be configured to emit the radiation as a continuous emission (e.g. the source 1 may comprise an X-ray tube). The system and/or the apparatus may be mobile and may be transported from a location to another location (the system and/or apparatus may comprise an automotive vehicle). Alternatively or additionally, the system and/or the apparatus may be static with respect to the ground and cannot be displaced. It should be understood that the radiation source may comprise sources of other radiation, such as, as non-limiting examples, sources of ionizing radiation, for example gamma rays or neutrons. The radiation source may also comprise sources which are not adapted to be activated by a power supply, such as radioactive sources, such as using Co60 or Cs137. In some examples, the inspection system may comprise other types of detectors, such as optional gamma and/or neutrons detectors, e.g., adapted to detect the presence of radioactive gamma and/or neutrons emitting materials within the load, e.g., simultaneously to the X-ray inspection. In some examples, one or more memory elements (e.g., the memory of the analyser or a memory element of the processor) can store data used for the operations described herein. This includes the memory element being able to store software, logic, code, or processor instructions that are executed to carry out the activities described in the disclosure. A processor can execute any type of instructions associated with the data to achieve the operations detailed herein in the disclosure. In one example, the processor could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., a field programmable gate array (FPGA), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM)), an ASIC that includes digital logic, software, code, electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs, magnetic or optical cards, other types of machine-readable mediums suitable for storing electronic instructions, or any suitable combination thereof. As one possibility, there is provided a computer program, computer program product, or computer readable medium, comprising computer program instructions to cause a programmable computer to carry out any one or more of the methods described herein. In example implementations, at least some portions of the activities related to the analyser and/or the detector may be implemented in software. It is appreciated that software components of the present disclosure may, if desired, be implemented in ROM (read only memory) form. The software components may, generally, be implemented in hardware, if desired, using conventional techniques. Other variations and modifications of the system will be apparent to the skilled in the art in the context of the present disclosure, and various features described above may have advantages with or without other features described above. The above embodiments are to be understood as illustrative examples, and further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims. |
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046510095 | claims | 1. An apparatus wherein a first member bearing a pattern and a second member are placed in close contact facing each other and the second member is exposed to a pattern on the first member with radiation through the first member, said apparatus comprising: means for aligning the first and second members is a predetermined positional relation; means provided to cooperate with a first surface of the first member facing the second member for defining a first substantially gas-tight chamber; means provided to cooperate with a second surface of the first member not facing the second member for defining a second substantially gas-tight chamber which is independent of said first gas-tight chamber; and means for supplying a vacuum to said first and second gas-tight chambers, said vacuum supplying means being operative to maintain said first and second gas-tight chambers substantially at the same vacuum and then operative to reduce the vacuum in said second gas-tight chamber as compared with that in said first gas-tight chamber thereby bringing the first and second members into close contact with each other. aligning the first and second members in a predetermined positional relation; supplying a vacuum to a first substantially gas-tight chamber which includes a surface of the first member facing the second member and to a second substantially gas-tight chamber which is defined independently from said first gas-tight chamber which includes another surface of the first member not facing the second member, so that said first and said second gas-tight chambers are maintained substantially at the same vacuum; and reducing the vacuum in said second gas-tight chamber as compared with that in said first gas-tight chamber to bring the first and second members into close contact with each other. 2. An apparatus according to claim 1, wherein said vacuum supplying means supplies the vacuum to said first and second gas-tight chambers at the same time. 3. An apparatus according to claim 1, wherein said vacuum supplying means is operative to reduce the vacuum in said second chamber to an atmospheric pressure level. 4. An apparatus according to claim 1, wherein said aligning means includes a holder for holding the second member and wherein said apparatus further comprises means provided to cooperate with said holder for defining a third substantially gas-tight chamber which is independent of said first and said second gas-tight chambers. 5. An apparatus according to claim 4, wherein said vacuum supplying means is operative to supply a vacuum to said third gas-tight chamber at the same time as the vacuum supplied to said first and second gas-tight chambers. 6. An apparatus according to claim 1, wherein said first gas-tight chamber defining means has a transmitting portion for allowing passage of the radiation with which the second member is exposed to the pattern of the first member. 7. An apparatus according to claim 6, wherein said aligning means includes a holder for holding the first member and wherein said first gas-tight chamber defining means has an element for elastically forcing the first member to said holder. 8. A method wherein a first member bearing a pattern and a second member are placed in close contact with each other and the second member is exposed to the pattern of the first member with radiation through the first member, said method comprising the steps of: 9. A method according to claim 8, wherein said first and second gas-tight chambers are maintained substantially at the same vacuum while keeping a predetermined gap between the first and second members. 10. A method according to claim 9, wherein the first and second members are brought substantially into contact with each other prior to reducing the vacuum in said second gas-tight chamber. |
claims | 1. A fuel channel assembly (FCA) reactor core, comprising:at least one FCA having a plurality of fuel elements;the at least one FCA comprising:a lower coolant inlet, a lower element plenum, at least one fuel element channel, an upper fuel element plenum, and a defueling chute;a plurality of coolant holes with diameters smaller than the fuel elements, the coolant holes positioned above the upper fuel element plenum to collect outlet flow of salt coolant to an exit plenum;a plurality of flow channels positioned above the fuel element exit plenum to collect outlet flow of salt coolant for transfer to a heat exchanger for removal of decay heat during loss of forced cooling; andone or more shutdown control channels disposed in the reactor core; said control channels being adjacent to and separate from said fuel element channel. 2. A FCA reactor core as recited in claim 1:wherein each fuel element comprises an inert, low-density graphite kernel, an annular fuel layer around the kernel that comprises TRISO particles and graphite binder, and a graphite outer shell around the annular fuel layer; andwherein the low-density graphite kernel is configured such that adjustment of the density of the kernel controls the total buoyancy of the pebble fuel element. 3. A FCA reactor core as recited in claim 1, further comprising at least one neutron absorber element positioned in each shut down control channel. 4. A FCA reactor core as recited in claim 3, wherein the neutron absorber elements comprise a mixture of graphite and a neutron poison. 5. A FCA reactor core as recited in claim 4, wherein the neutron poison comprises boron carbide. 6. A FCA reactor core as recited in claim 3:wherein quantity and density of the neutron absorber elements are selected to provide neutral buoyancy in salt coolant at a temperature between FCA inlet temperature and FCA outlet temperature; andwherein the neutron absorber elements are configured to passively sink into the FCA upon the temperature of the shut down control channel exceeding the neutral buoyancy temperature. 7. A FCA reactor core as recited in claim 3, further comprising:a control rod positioned above the neutron absorber elements;the control rod operable to force insertion of the neutron absorber elements into the FCA. 8. A liquid fluoride salt cooled, high temperature reactor, comprising:a reactor vessel;a reactor core contained in the reactor vessel;the reactor core comprising a plurality of parallel fuel channel assemblies (FCA's), each comprising;a lower coolant inlet, a lower fuel element plenum, a fuel element channel, an upper fuel element plenum, and an upper defueling chute;a plurality of moveable fuel elements;a plurality of coolant holes with diameters smaller than the moveable fuel elements, said coolant holes positioned above the upper fuel element plenum to collect outlet flow of salt coolant to an exit plenum;a plurality of flow channels positioned above the exit plenum to collect outlet flow of salt coolant for transfer to a heat exchanger for removal of decay heat during loss of forced cooling; andone or more shutdown control channels disposed in the reactor core; said one or more control channels being adjacent to and separate from said fuel element channel. 9. A reactor as recited in claim 8:wherein the moveable fuel elements comprise pebble fuel elements;wherein each pebble fuel element comprises an inert, low-density graphite kernel, an annular fuel layer around the kernel comprising TRISO particles and graphite binder, and a graphite outer shell around the annular fuel layer; andwherein the low-density graphite kernel is configured such that adjustment of the density of the kernel controls the buoyancy of the pebble fuel element. 10. A reactor as recited in claim 8, further comprising at least one neutron absorber element positioned in each shut down control channel. 11. A reactor as recited in claim 10, wherein each said neutron absorber element comprises a mixture of graphite and a neutron poison. 12. A reactor as recited in claim 11, wherein the neutron poison comprises boron carbide. 13. A reactor as recited in claim 10:wherein quantity and density of the neutron absorber elements are selected to provide neutral buoyancy in salt coolant at a temperature between FCA inlet temperature and FCA outlet temperature; andwherein the neutron absorber elements are configured to passively sink into the FCA upon the temperature of the shut down control channel exceeding the neutral buoyancy temperature. 14. A reactor as recited in claim 10, wherein salt coolant flows into the shut down control channel from an inlet plenum under forced circulation. 15. A reactor as recited in claim 10, further comprising:a control rod positioned above the at least one neutron absorber element;wherein the control rod is operable to force insertion of the neutron absorber elements into the FCA. 16. A reactor as recited in claim 10, further comprising:a graphite radial reflector connected to the reactor vessel near the top of the vessel;wherein the graphite radial reflector comprises a plurality of reflector blocks configured to float in said coolant; andmetal rods extending from the top of the reactor vessel to a metal reflector support structure below the graphite radial reflector, the metal rods maintaining the reflector blocks in compression during assembly, heating and filling of the reactor vessel. 17. A reactor as recited in claim 8, further comprising:a primary pump to circulate salt coolant through the at least one FCA and through an intermediate heat exchanger;wherein the primary pump is an overhung cantilever type pump;wherein the primary pump includes a suction pipe; andwherein the suction pipe includes an anti-siphon vent line to passively maintain salt coolant inventory. |
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claims | 1. A nuclear power generating facility comprising:a containment building;an elongated reactor vessel housed within the containment building, the reactor vessel having a nuclear core having fissile material in which fission reactions take place and an open end axially spaced from the nuclear core, with the open end sealed by a head at a flange;a spent fuel pool supported outside the containment building at an elevation that extends substantially above the reactor vessel, the spent fuel pool having a pool of coolant in fluid communication with an interior of the reactor vessel through a first valve that is configured to automatically supply coolant from the pool of coolant to the interior of the reactor vessel when the reactor is depressurized and a level of coolant within the reactor vessel is below a given level; andan ultimate heat sink coolant reservoir whose upper coolant level under normal operation of the nuclear power generating facility is supported at an elevation substantially above the spent fuel pool, with a lower portion of the ultimate heat sink coolant reservoir in fluid communication with the spent fuel pool through a second valve whose operation is controlled by a level of coolant in the spent fuel pool to maintain the coolant in the spent fuel pool at approximately a preselected level. 2. The nuclear power generating facility of claim 1 wherein the first valve is either passively operated and/or designed to fail in an open position. 3. The nuclear power generating facility of claim 1 wherein the second. valve is either passively or manually operated. 4. The nuclear power generating facility of claim 3 wherein the second valve is a float valve. 5. The nuclear power generating facility of claim 1 including a passive safety system comprising a coolant reservoir supported within the containment building approximately at or above a first elevation of the reactor vessel flange and structured to maintain the given level of coolant within the reactor vessel for a first selected period of time when the coolant level in the reactor vessel during reactor operation unintentionally drops, the passive safety system being structured to be out of operation during a refueling of the nuclear core. 6. The nuclear power generating facility of claim 1 including:a refueling canal establishing a fluid communication path between an inside of the containment building at an elevation above the reactor vessel flange and the spent fuel pool, through which a fuel assembly can pass; andmeans for closing off the fluid communication path from the inside of the containment building to the refueling canal. 7. The nuclear power generating facility of claim 6 including:a branch coolant line connected to the reactor vessel; anda gauge on the branch coolant line having an output indicative of a coolant level within the reactor vessel, above the core, the gauge having an output that controls the first valve to adjust the coolant level to the given level when the reactor vessel is depressurized. 8. The nuclear power generating facility of Claim l including:a branch coolant line connected to the reactor vessel; anda gauge on the branch coolant line having an output indicative of a coolant level within the reactor vessel, above the nuclear core the gauge having an output which controls the first valve to adjust the coolant level when the reactor vessel is depressurized. 9. The nuclear power generating facility of claim 8 wherein the gauge is a pressure gauge. 10. A nuclear power generating facility comprising:a containment building;an elongated reactor vessel housed within the containment building, the reactor vessel having a nuclear core having fissile material in which fission reactions take place and an open end axially spaced from the nuclear core, with the open end sealed by a head at a flange;a spent fuel pool supported outside the containment building at an elevation that extends substantially above the reactor vessel, the spent fuel pool having a pool of coolant in fluid communication with an interior of the reactor vessel through a first valve that is configured to automatically supply coolant from the pool of coolant to the interior of the reactor vessel when the reactor is depressurized and a level of coolant within the reactor vessel is below a given level;an ultimate heat sink coolant reservoir whose upper coolant level under normal operation of the nuclear power generating facility is supported at an elevation substantially above the spent fuel pool, with a lower portion of the ultimate heat sink coolant reservoir in fluid communication with the spent fuel pool through a second valve whose operation is controlled by a level of coolant in the spent fuel pool to maintain the coolant in the spent fuel pool at approximately a preselected level;a refueling canal establishing a fluid communication path between an inside of the containment building at an elevation above the reactor vessel flange and the spent fuel pool, through which a fuel assembly can pass;means for closing off the fluid communication path from the inside of the containment building to the refueling canal;a branch coolant line connected to the reactor vessel; anda pressure gauge on the branch coolant line having an output indicative of the coolant level within the reactor vessel, the first valve being configured to automatically open responsive to the output of the pressure gauge indicative of the coolant level inside the reactor vessel above the core being below the given level, wherein the first valve opening causes coolant from the spent fuel pool to flow by gravity into the interior of the reactor vessel. |
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abstract | A system and method for assessing failure of fuel rods are disclosed. The method may include monitoring fuel rod operational conditions, comparing the fuel rod parameters to parameters limits, calculating the fuel rod performance parameters to determine the likelihood of failure of individual fuel rods, and updating plant operating parameters based on the calculated fuel rod parameters. The system may input the calculated fuel rod parameters into a fuel failure model to assess the probability of failure, and predict the probability of failure of individual fuel rods based on fuel rod parameters in the fuel failure model. |
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summary | ||
abstract | An apparatus for transmitting or receiving terahertz waves includes an enclosure having a front opening, a rear opening, and an internal passageway therebetween. The enclosure includes an antenna mounting structure and a lens mounting structure. A terahertz photoconductive antenna is mounted within the enclosure against the antenna mounting structure. The terahertz photoconductive antenna has a rear side for being optically energized by an optical beam passing through the rear opening of the enclosure, and a front side for transmitting or receiving the terahertz waves through the front opening. A terahertz lens is mounted within the enclosure against the lens mounting structure. The terahertz lens is positioned between the front opening and the terahertz photoconductive antenna for converging the terahertz waves being transmitted or received. The antenna mounting structure and the lens mounting structure are configured to optically align the terahertz photoconductive antenna and the terahertz lens. |
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052456439 | summary | This invention relates to a fuel bundle for a boiling water nuclear reactor having so-called part length fuel rods. More specifically, a fuel bundle design is disclosed in which part length fuel rods have top filled water regions or containers overlying the end of the part length fuel rods for the improvement of the nuclear performance of the fuel design. BACKGROUND OF THE INVENTION Fuel bundle designs for boiling water nuclear reactors are known. Such fuel designs are fabricated in a standard fashion including a lower tie plate for supporting an upstanding matrix of fuel rods in side-by-side relation and permitting the inflow of water coolant into the fuel bundle. Most of the fuel rods of such a fuel bundle extend from the supporting lower tie plate to an upper tie plate. This upper tie plate serves to maintain the fuel rods in upstanding side-by-side relation and to permit the exit of water and generated steam from the fuel bundle. The fuel bundle is typically surrounded by a fuel bundle channel, which channel surrounds the lower tie plate, extends upwardly around the fuel rod matrix, and surrounds the upper tie plate. This fuel bundle channel isolates the flow path through the fuel bundle so that water and steam generated in the interior of the fuel bundle are separate from the so-called core bypass region surrounding the fuel bundle. This core bypass region contains water moderator and occupies generally cruciform shaped volumes between the fuel rods into which control rods can penetrate for the absorption of thermal neutrons for the control of the nuclear reaction. In operation of the boiling water nuclear reactor fuel bundles, liquid moderator--water--is introduced at the bottom of the fuel bundle through the lower tie plate. The water passes upwardly interior of the fuel bundle and performs two major functions. First, it moderates so-called fast or energetic neutrons produced in the nuclear reaction to slow or thermal neutrons need to continue the nuclear reaction. Secondly, the water moderator generates steam which is utilized for the generation of power. It will be understood that the fuel rods interior of the fuel bundles are long slender sealed tubes containing fissionable material and are flexible. If such fuel rods were to be unrestrained, they would vibrate and even come into abrading contact with one another during the generation of steam. To restrain this tendency as well as maintain the fuel rods in their designed side-by-side spacing for efficient nuclear operation, so-called spacers are utilized. These spacers are placed at selected vertical intervals within the fuel bundle. Usually, seven evenly distributed fuel rod spacers are utilized in a fuel bundle having an overall length in the order of 160 inches. These spacers surround each individual fuel rod maintaining the precise designed spacing of the fuel rods along the entire length of the fuel bundle. It is standard practice to improve the performance of boiling water fuel assemblies by introducing special water regions which distribute controlled amounts of water liquid moderator within the fuel assembly lattice of fuel rods. This is often accomplished by the use of hollow rods ("water rods") or other generally vertically aligned parallel flow conduits, through which substantially single phase water flows. Typically, a small amount of water is bypassed from the lower tie plate region through these water regions--more often referred to as water rods--and finally discharged out the top of the fuel bundle. These controlled water regions are particularly effective in the upper portions of the fuel assembly where neutron moderation is normally reduced by the steam which displaces the liquid water for a large fraction of the coolant flow area. However, since the introduction of such water regions occupies space that would otherwise contain more uranium fuel, the net performance benefits of the water regions are a trade-off between the positive effects of improved neutron moderation and the negative effects of decreased uranium fuel content. As a consequence, careful studies are required to establish optimum shapes and numbers of these water regions in any particular boiling water reactor fuel bundle design. It is further standard practice for these water regions to extend upward from the bottom of the fuel assembly at the lower tie plate. This is done so that flow holes can be allowed for entry of subcooled water to the water regions from the lower tie plate at the bottom of the fuel assembly. This direct entry of subcooled water to the water regions is used in order to avoid the entry of steam into the water regions and to avoid unknown neutron moderation conditions that would result if both water and vapor were present within the water regions. Having a direct flow of subcooled water to the water regions avoids or minimizes subsequent steam formation from neutronic heating at higher elevations in the fuel bundle within the water regions. However, extending a water region from the bottom of a fuel assembly also has a detrimental effect on the fuel assembly performance. The adverse effect results from the removal of uranium fuel in the lower region where the adverse effect resulting from the removal of fuel rods is not compensated by large benefits from increased neutron moderation. Thus, this adverse performance in the lower portion of the fuel assembly limits the overall effectiveness achieved through addition of water regions to the boiling water fuel assemblies. So-called part length rods have been introduced into this standard fuel bundle construction. These part length fuel rods extend from the lower tie plate only partially the distance to the upper tie plate. The fuel rods typically terminate underlying the upper tie plate so as to define an unoccupied vertical interval within the fuel bundle starting at the top of the part length fuel rod and extending to the upper tie plate. These part length fuel rods have many advantages, which advantages are summarized in Dix et al. U.S. patent Ser. No. 07,176,975 entitled TWO-PHASE PRESSURE DROP REDUCTION BWR ASSEMBLY DESIGN now issued as U.S. Pat. No. 5,112,570 on May 12, 1992. SUMMARY OF THE INVENTION Part length water regions are located above part length fuel rods in boiling water nuclear reactor fuel bundles. The part length water regions include discrete containers having water entry ports at the top of the part length water regions for capturing water from the passing liquid-vapor stream, and vent ports for permitting internally generated steam from gamma ray and neutronic heating to escape the water region. The advantages of improved neutron moderation in the upper portion of the fuel assembly are present while the uranium fuel removal requirements from the more reactive lower portion of the fuel bundle are minimized. This design concept allows for greater flexibility in the length, shape, location, and attachment of water regions, since no connection to the region of the lower tie plate is required. In addition, the top filling of the water regions also eliminates the parasitic loss of flow from the active fuel region that occurs with standard bottom entry water region designs. While this design has inherent advantages by eliminating any connection to the fuel assembly inlet, it also has the inherent disadvantage of not providing liquid subcooling to minimize vapor formation within the upper top filled water region. This internal vapor formation reduces the neutron moderation improvement of the water region. Fortunately, the fraction of liquid displaced by vapor formation is small and easily predictable for the low velocity counter-current flow conditions that exist within these water region designs. In the typical design herein set forth, vapor will typically occupy less than 20% of the water region moderator volume. As a consequence, fuel assembly designs using these top filled water regions must balance these additional trade-offs to optimize overall performance. In the disclosed openings within the top filled water regions, accommodation is required to vent vapor produced by nuclear particle heating as well as to enable downward flow into the water regions of replacement liquid. The large density of water relative to the surrounding vapor flow in the upper two phase region of the fuel bundle produces a countercurrent flow condition with downward liquid flow into the water region. However, to assure that sufficient replacement liquid enters the water region, it is advantageous to have devices which deflect liquid into the top openings of the water region. Such devices can act on liquid which flows as a film on the exterior surface of the water region. Flow openings can also be placed adjacent to existing upper tie plate or top fuel rod spacers, and thereby use the normally occurring flow diversions at those locations to deflect liquid into the top of the water regions. |
claims | 1. A method of measuring a relative magnitude of the burnout of a fuel element in a reactor, the method comprising the steps of sequentially:a) transferring a fuel element from the reactor to a measuring position,b) subjecting the transferred fuel element at the position to a neutron flux,c) measuring with a first detector the total γ radiation emitted by the transferred fuel element; andthereafterd) if the radiation measured by the first detector exceeds a predetermined first limit, returning the transferred fuel element back to the reactor ande) if the radiation measured by the first detector does not exceed the first limit, measuring with a second detector a magnitude of high energy γ radiation above 1 MeV emitted by the transferred fuel element; andthereafterf) only if the radiation measured by the second detector exceeds a predetermined second limit, returning the transferred fuel element back to the reactor, the transferred fuel element not being returned to the reactor if the radiation measured by the second detector is below the second limit. 2. The method according to claim 1 wherein the second detector determines a relative magnitude for the high energy γ radiation above 2 MeV emitted by the transferred fuel element. 3. The method according to claim 1 wherein the second detector operates with a count rate of at least 107/s. 4. The method according to claim 1 wherein a scintillation counter is used as the second detector. 5. The method according to claim 1, further comprisinga shield between the measurement position and the second detector. 6. The method according to claim 5 wherein the shield is a lead filter. 7. The method according to claim 1 in which the first detector detects the γ radiation of the fuel element in less than 2 seconds. 8. The method according to claim 1 in which the second detector detects the high energy γ radiation of the fuel element in less than 30 seconds. 9. The method according to claim 1, further comprising the step ofsurrounding the fuel element in the measurement position with water. 10. The method according to claim 1 wherein the first limit is so selected that a proportion of the fuel elements which are required for operating the reactor falls below this first limit. 11. The method according to claim 1 wherein the first limit is so selected that with a 1:10 mode of operating the reactor a maximum of 20% of the fuel elements lies below this first limit. 12. The method according to claim 1 wherein the second limit is so established that a proportion of all fuel elements which are measured but are required for operating the reactor falls below this second limit. 13. The method according to claim 11 in which the second limit is so established that in a 1:10 mode a maximum of 15% of all measured fuel elements lie below this second limiting. 14. A device for measuring a relative magnitude of the burnout of a fuel element in a reactor, the device comprising:means for transferring a fuel element from the reactor to a measuring position,means including a neutron source for subjecting the transferred fuel element to a neutron flux,means including a first detector for measuring the total γ radiation emitted by the transferred fuel element and for comparing the radiation measured by the first detector with a predetermined first limit;means for, if the radiation measured by the first detector exceeds a predetermined first limit, returning the transferred fuel element back to the reactor;means for, if the radiation measured by the first detector does not exceed the first limit, measuring with a second detector a magnitude for high energy γ radiation above 1 MeV emitted by the transferred fuel element and comparing the radiation measured by the second detector with a predetermined second limit; andmeans for, only if the radiation measured by the second detector exceeds the predetermined second limit, returning the transferred fuel element back to the reactor, the transferred fuel element not being returned to the reactor if the radiation measured by the second detector is below the second limit. 15. The device according to claim 14, further comprisinga shield between the measurement position and the second detector. 16. The device according to claim 15 wherein the shield is a lead filter. 17. The device according to claim 14, wherein a scintillation counter is the second detector. 18. The device according to claim 14 wherein the second detector has a counting rate of at least 107/s. 19. The device according to claim 14 wherein the measurement position is at least partly surrounded by water. |
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042784980 | description | Referring now to the drawing and first, particularly, to FIG. 1 thereof, there is shown a reactor pressure vessel identified as a whole by 1 and having a convex cover 2 having a spherical part or cover calotte 2a and a cover flange 2b. Control rod drives identified as a whole by 3 are connected to the vessel cover 2 in the region of the spherical part or cover calotte 2a thereof by means of control rod drive stub tubes, which are not visible in FIG. 1 since they are covered by the support grid that is yet to be described herein and are indicated only by corresponding raster points. The control rod drives 3 can be seen better in FIG. 5, where only two such control rod drives 3 are shown in the interest of greater clarity in the presentation thereof, each thereof being formed of a control rod drive stub tube 3.1 pressure-tightly extending through the cover 2, and a pressure tube 3.2, which is shown in broken lines and is flanged pressure-tightly to the flanges 3.1a of the stub tubes 3.1 in an otherwise non-illustrated manner. In the interior of the pressure tube 3.2, control drive shafts 3.5 diagrammatically indicated in phantom i.e. by respective dot-dash lines, are mounted so as to be axially shiftable and lockable, and are provided with transverse slots and teeth at the outer periphery thereof. Locking and lifting pawls of an electromagnetic ratchet step lifter 3.3 can be brought into engagement with the peripheral teeth of the control drive shafts 3.5, the pawls being controlled by armatures which are movable, axially limited, against stops within the pressure tube, the actuating coils of the armatures, namely, a lifting coil 3.31, a gripper coil 3.32 and a holding coil 3.33 being slid onto the pressure tube 3.2 at the outside thereof and being mounted within a tubular coil housing 3.4 which surrounds the pressure tube 3.2 coaxially. A respective pressure tube 3.2 and a respective stub tube 3.1 form the drive housing for the control rod drive shafts 3.5. The specific construction of the ratchet step lifter is not essential to the invention of the instant application and is moreover well known, for example, from the German Pat. No. 1,439,948. The control drive shafts are connected to the control rods 3.6, likewise shown as dash-dot lines, by couplings which are diagrammatically indicated at 3.7. In addition, the core internals of the pressure vessel 1, and especially the fuel assemblies, which have the absorber channels into which the control rods 3.6 with absorber fingers can be inserted to a greater or lesser extent for the purpose of controlling the reactivity, are not illustrated in the interest of clarity. In FIG. 5, the lower part of the substantially cylindrical hollow pressure vessel 1 is identified as 1.1; also shown is one of the coolant nozzles 1.2 of the vessel that are distributed over the periphery thereof in a plane 1' normal to the axis; additionally shown is one of a number of support lugs 1.3 thereof which are distributed over the periphery of the vessel 1 and by means of which the vessel 1 rests on support brackets 1.6 that are mounted on an annular box girder or beam 1.5 anchored in a concrete structure 1.4 and is secured, as well, against lifting and turning. Also provided is a hollow prestressed-concrete cylinder 1.7 of the biological shield which, with an insulating layer 1.8 fastened to the inner periphery thereof, surrounds the pressure vessel 1 with an annular gap therebetween. Cover studs 1.9 with nuts secure the pressure vessel cover 2a pressure-tightly against the lower vessel part 1.1 and are anchored in the latter. Due to the curvature of the spherical cover 2a, which is outwardly convex in the illustrated embodiments, considered together with the fact that the flanges 3.1a of the stub tubes 3.1 are disposed in a horizontal connecting plane and the pressure tubes 3.2 of all of control rod drives 3 terminate at a level represented by the broken line 4, the control rod drive stub tubes 3.1 are consequently of different lengths i.e. the total length of the control rod drives 3 with stub tubes 3.1 disposed in the outer zones of the spherical cover part or calotte 2a is greater than that of the control rod drives 3 located in the farther inwardly disposed zones, and the latter control rod drives 3 are, in turn, greater in length than the control rod drives 3 with stub tubes 3.1 that are disposed in the central region of the spherical cover part or calotte 2a. The control rod drives 3, therefore, have different resonance frequencies, depending upon the respective length of the control rod stub tubes 3.1 associated therewith. According to FIGS. 1 and 2 and 5, the upper ends 3' of the control rod drives 3 and the pressure tubes 3.2, respectively, are articulatingly connected to each other by grid bars 5 and 6 of a support grid identified as a whole by G. In the illustrated embodiment, the support grid G is formed of two subgrids G5 and G6 (FIG. 2) which are disposed at a spaced distance al from each other and, respectively, in a lower grid plane el and an upper grid plane e2. The upper subgrid G6 of the plane e2 is disposed in the form of a square screen, the grid bars 6 thereof being indicated in FIG. 1 by solid black lines. The other subgrid G5 of the lower grid plane el is formed by diagonally extending rods 5 which are indicated in FIG. 1 by double lines. The grid joints are identified as a whole in FIGS. 1 and 2 by the reference numeral 7. As is apparent, the joints of the grid bars 5 of the lower subgrid G5 lie approximately in the projection of the corners of the upper subgrid G6 onto the lower subgrid G5. Both subgrids G5 and G6 are disposed in respective horizontal planes and are therefore perpendicular to the vertical pressure tubes 3.1 of the control rod drives 3. Due to the square screen or raster construction of the upper subgrid G6, grid bars 6a extend in X-direction and grid bars 6b in Y-direction. The square grid fields or mesh of the upper subgrid G6 are identified by the reference character 6. In FIG. 1, the coordinate cross or intersection of the two principal directions x and y for the subgrid 6G is shown together with the coordinate cross intersection of the likewise mutually perpendicular principal directions n and m of the subgrid G5, the two coordinate crosses or intersections being rotated relative to each other through and angle .alpha.=45.degree.. The grid bars of the subgrid G5 extending in the direction m are identified by the reference character 5a and those extending in the direction n by 5b. It is apparent therefrom that the grid bars of the subgrid G5 are disposed in zig-zag fashion i.e. alternatingly in the principal direction m or in the principal direction n, as viewed in the projection of the raster or screen squares 6' onto the subgrid G5. The grid configuration shown has been found to be particularly advantageous for a control rod field with a square screen or raster. Depending upon the intensity of the earthquake that is anticipated, more than two subgrids disposed on top of each other could also be used. As shown in FIG. 2 in conjunction with FIGS. 3 and 4b, the ends of the grid bars identified as a whole by the reference character g are spherical and, for this purpose, have ball heads 8 (FIG. 3) threadedly secured thereon. The joints 7 constructed as crossheads are fastened to the upper ends 3' of the pressure tubes (see FIG. 2), the grid bars g extending through slots 9 formed in the crosshead plates 10 and being movably supported with the ball heads 8 thereof within cylindrical bores 11 serving as ball joint sockets. FIG. 2 shows that the respective grid joints are formed by two crosshead plates 10, 10 disposed on top of each other and, respectively, provided with ballhead receiving bores 11 and through-slots 9 (FIGS. 4a and 4b) for the grid bars g as well as with a central through-bore 12 for a fastening screw or bolt 13. The bores 11 and 12 and slots 9 formed in the crosshead plates 10, 10 are closed off at the bottom of the joint 7 by a bottom plate 14 and at the top thereof by a cover 15, as viewed in FIG. 2. The pressure tube end 3' is of solid construction and is provided with a central tapped bore 16 for the fastening screw 13 as well as with a flat or planar mounting surface 17. In this manner, a simple and strong means for fastening the grid joint 7 can be attained by providing that the fastening screw 13 disposed in the central bore 12 passes through the crosshead plates 10, 10 together with the bottom plate 14 and the cover 15 and are tightened or clamped against the planar mounting surface 17, a conventional device 18 for preventing unscrewing being advantageously provided at the fastening screw 13, the device 18, in the illustrated embodiment of FIG. 2 being formed of a washer with a bent-up lip engaging one of the lateral flat surfaces of the hexagonal head of the screw 13. In FIG. 3, the grid bars g are shown divided, and the two grid bar halves g' and g" thereof connected together by means of a turnbuckle 19. The latter is formed of a bushing with an internal thread which is brought into threaded engagement with the threaded shank 20 of the one grid bar half g", for example, by means of a right-hand thread 19a and, accordingly, with the threaded shank 20 of the other grid bar half g' by means of a left-hand thread 19b. At the outer periphery of the threaded bushing 19, a region having a polygonal cross section 21, for example, a hexagonal section, is provided for engagement by wrenches. In the embodiment according to FIG. 6, a pressure vessel 1* of a boiling-water nuclear reactor is shown with a spherical bottom part of calotte 1a*, through which control rod drives 3* with respective pressure tubes 3.2* extend in a pressuretight manner and project downwardly and out of the pressure vessel 1* with an axial length 1.sub.a which is substantially the same for all of the control rod drives 3*. Tubular control rod drive shafts 3.5* are supported within the pressure tubes 3.2* so as to be movable lengthwise yet secured against rotation. They can be moved in axial direction, for example, hydraulically or, in combination, electrically and hydraulically by means of drive units 3.3* connected to the pressure tubes 3.2*, absorber rods 3.6* connected to the upper ends thereof being insertable to a lesser or greater extent into intermediate spaces (absorber channels) located between the fuel assemblies 3.0 for thereby controlling the reactivity in the manner explained hereinbefore in connection with the first embodiment of the invention shown in FIG. 5. The pressure tubes 3.2* include the feedthrough stub tubes like those at 3.1 in FIG. 5, but not shown separately in FIG. 6 and, together with the drive units 3.3*, form thimble-like tubular drive housings which are pressure-tight against the outside. Details of the construction of the drive units 3.3* are of no special significance for the invention of the instant application, and can be obtained, for example, from the German Pat. No. 1,169,596. It is important that also in this second embodiment of FIG. 6, earth-quake caused transversal vibrations of the control rod drives 3* having lengths 1.sub.a extending downwardly from the outwardly curving or convex sperical bottom part or calotte 1a* which would basically behave like spring rods clamped at one end thereof, are effectively prevented or reduced to harmless values, by providing that the drive housings be flexibly or articulatingly connected to each other in the vicinity of the lower or free ends thereof by grid bars g* of the support grid G* in such a manner that the free axial lengths 1.sub.a1 * of the drive housings, as measured from the outside of the spherical bottom part of calotte 1a* to the grid joint G6* are different as viewed over the cross section of the support grid G*. For this purpose, an upper subgrid G6* is provided which is disposed in an upper grid plane e2* and may be constructed like the hereinabove-described grid G6 of FIG. 2. The lower subgrid G5, however, is not disposed in a flat plane but in a curved surface e1* which corresponds substantially to the contour of the spherical cover part or calotte 1a*, because all of the drive housings have the same overall length 1.sub.a. Further length sections 1.sub.a2 * of the drive housings are thus provided between the two subgrids G6* and G5*, the respective lengths of which are likewise different as viewed over the cross section of the control rod drive field. Within the length sections 1.sub.a1 * as well as the length sections 1.sub.a2 *, drive housings of different length are coupled flexibly or articulatingly to each other through the subgrids G6* and G5* and also in a vibration-attenuating or vibration-cancelling manner because of the different resonance frequencies of the coupled length sections 1.sub.a1 *, 1.sub.a2 *. The subgrid G5* can be constructed in plan view like the hereinaforedescribed subgrid G5 of FIG. 2; in addition, however, the bars g* of the subgrid G5* extend inclined to the horizontal. For the subgrid G6*, the crossheads, which are not shown in FIG. 6, are hollow-cylindrical, the pressure tubes 3.2* passing through them, the crossheads being fastened at the outer periphery of the pressure tubes 3.2*. On the other hand, the crossheads for the subgrid G5* can, in principle, be constructed as described heretofore in connection with FIG. 2. Internal main reactor coolant pumps 22 are further shown in FIG. 6. The invention of the instant application is also applicable to control rod drives which are disposed in the spherical bottom part of calotte of a pressure vessel but have free ends thereof which extend, in a manner deviating from that of FIG. 6 and in accordance with FIG. 5, up to a common horizontal end plane, so that the lengths 1.sub.a of the drive housings extending out of the pressure vessel are inherently different. In such a case, the support grid construction of the first embodiment of FIG. 5 can again be used, but then, however, at the underside of the pressure vessel rather than at the top thereof. |
abstract | A windshield repair device includes a bridge, an injector attached to the bridge and at least one UV, e.g., light emitting diode (LED), light source attached to the bridge or integrated into bridge or the injector to provide UV light within or around the injector. The UV, e.g., LED, light source can also be attached to an existing windshield repair device having a bridge and an injector attached to the bridge, so as to retrofit an existing windshield repair device to provide UV light within or around the injector. A method for curing resin provided in a crack in a windshield can be carried out by exposing the resin to UV light from at least one UV LED light source. |
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abstract | A work machine is provided. The work machines may include a power module configured to provide power including a battery and an engine and configured to a folding heat exchange device. The work machine may also include a drive module configured with one or more motors and positioned over a track roller frame. The work machine may also include a hydraulic module including one or more devices in a front region and one or more devices in a rear region to cut or rip encountered material |
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abstract | The invention relates to a container for a radioactive source, having reduced radiation leakage from a gap between movable housing components. The container comprises a housing having a bore extending into the housing. A removable cylindrical sleeve having a chamber therein is inserted into the bore. Two co-operating helices are present; the first helix is located on a surface of the housing facing into the bore, and the second helix is located on the sleeve. The co-operating helices block the gap between the housing and the sleeve when the sleeve is inserted into the bore, thereby attenuating the radiation emanating from the gap when a radioactive source is housed within the container. Axial rotation of the sleeve within the bore results in movement of the sleeve between a withdrawn position and an inserted position within the housing. |
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044629559 | summary | FIELD OF THE INVENTION The invention relates to a support device positioned between an element of large mass and a fixed support, enabling the movements and the accelerations of the element with respect to the support to be limited, during movements caused by stresses such as those arising from an earthquake. BACKGROUND OF THE INVENTION In the construction of structures or in the positioning of machines, it is necessary to support structures or equipment of heavy mass on fixed supports such as foundations or support slabs. For example, support devices are known designed to transmit forces between the supported element and the support which are constituted by anchorages or articulations. These devices transmit the forces integrally between the bearing structure and the borne element. This presents drawbacks in particular in the case where large stresses such as those accompanying an earthquake are transmitted to the supported element. In particular, in the case of construction of nuclear reactors, for safety reasons one may be led to avoid the use of such support devices which can place the supported structures or equipment in danger, in the case of a considerable stress coming, for example, from the ground. More elaborate support devices have therefore been conceived which absorb or limit such forces. For example, the use of flat or curved sliding pads or of pads associated with stops or energy absorbers has been proposed. Devices including support parts forming bearing tracks and elements such as balls have also been proposed, assuring in association the support of the structure. Devices have been conceived, for example, associating two disks having concave surfaces with balls arranged between these two concave surfaces and pendular yokes with a spherical journal, for the support of structures or machines in order to reduce the forces transmitted to the borne element from the support. If these devices indeed reduce the forces transmitted, they can only limit the relative movements of the bearer elements and of the borne element by the use of stops or energy absorbers, to avoid too large a deformation of the borne element. On the other hand, systems with balls or with spherical bearings, if they have a good reaction to forces of any direction, are unusable as soon as the borne mass exceeds a certain threshold, i.e., when support by contact on a small surface is not possible. SUMMARY OF THE INVENTION It is an object of the invention, therefore, to provide a support device arranged between an element of large mass and a fixed support, enabling the movements and accelerations of the element with respect to the support to be limited, during movements caused by stresses such as those arising from an earthquake, comprising bearing elements arranged between support parts forming tracks for the bearing elements inclined with respect to the horizontal plane and assuring the transmission of the vertical forces of inertia from the element to the support. The support device must permit reduction of the forces transmitted to the borne element of large mass while avoiding large movements of excessive amplitude, whatever the direction and origin of the forces exerted between the support and the borne element. For this purpose, the support device according to the invention comprises: bearing elements constituted by cylindrical rollers arranged horizontally on superposed sets of at least two rollers, the rollers of one set having their axes perpendicular to the axes of the rollers of the other set, PA0 and a set of three support parts totally independent of one another, comprising a first support part on which the borne element rests directly and supported on the upper set of rollers, a second part on which rests the upper set of rollers and supported on the lower set of rollers, as well as a third support part resting on the fixed support and supporting the lower set of rollers, the first support part having a bearing track on its lower surface, the third part having a bearing track on its upper surface, and the second support part having a track on both its upper surface and its lower surface. In order that the invention may be more clearly understood, there will now be described, with reference to the accompanying drawings, an embodiment of a support device according to the invention applied to the support of racks of fuel elements on the bottom of the storage pool of a pressurized water nuclear reactor. |
claims | 1. A clad metallic nuclear fuel alloy for use in the fast or epithermal neutron spectrum that efficiently fissions or transmutes isotopes present in spent light water reactor fuel, said nuclear fuel alloy comprising:75-95% fertile metallic thorium;5-25% reactor grade fissile plutonium and associated unseparated transuranics; and protium;wherein said metallic nuclear fuel alloy is enclosed in stainless steel cladding and doped with protium such that the ratio of thorium atoms to protium atoms is between approximately 6:1 and 4:1, inclusive, with the exact ratio of fertile to fissile material being a function of reactor power and such that said fuel fissions in the elevated epithermal neutron spectrum or the fast neutron spectrum and consumes and destroys plutonium-239 and other plutonium isotopes in reactor grade fissile plutonium along with the associated unseparated transuranics from spent light water reactor fuel. 2. The metallic nuclear fuel alloy of claim 1, further including deuterium, wherein the ratio of thorium atoms to deuterium atoms and protium atoms is between about 12:1:1 and 8:1:1, inclusive, such that said fuel will consume and destroy plutonium-239 in obsolete weapons grade plutonium fuel. 3. The metallic nuclear fuel alloy of claim 1, wherein the unseparated transuranic portion of the spent light water nuclear fuel includes reactor grade neptunium, plutonium, americium, or curium, either alone or in any combination thereof, wherein said metallic nuclear fuel alloy transmutes and fissions the members of the unseparated transuranic portion as a group without the need to separate the members of the transuranic group from one another before said plutonium is alloyed with said thorium and said protium. |
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043549985 | description | Generally, the present invention is directed to a method and apparatus for removing ions trapped in a thermal barrier formed between a mirror coil and an end plug in a fusion reactor apparatus, such that these trapped ions are caused to drift into a divertor positioned in the path of said ion drift. The ions are caused to diffuse across the magnetic field and drift across said thermal barrier region due to a bend formed along the normal path of the reactor plasma at a point in the area between the end plug and an adjacent mirror corresponding to the thermal barrier region. The bending of the plasma along a curvature of radius R is generated by one or more magnetic turning coils, such that ions trapped in said regions are caused to drift perpendicular to the centrifugal lines of force generated thereby and the direction of the incident magnetic field. Thus, the trapped ions are caused to drift perpendicular to the plane of the bending. The trapped ions continue to be forced away from the plane of plasma bending along a perpendicular path until they come in contact with a divertor, which thereby acts to remove such ions from the plasma chamber. Although removal of all trapped ions constitutes a continuing power loss to the plasma, it is deemed to be, at worst, equivalent to the energy required to operate the magnetic pump required by the prior art to eliminate such trapped ions. For particles in the plasma which are not trapped in the thermal barrier, but continue to be reflected by magnetic mirrors back and forth in the central cell of the fusion reactor apparatus, the plasma column in the thermal barrier regions on each end of the central cell must be bent in opposite directions. This is so that the displacements of orbits due to the curvature drift imparted to ions in each barrier region are cancelled out for such untrapped, i.e., passing, ions. The particular invention may be more clearly understood with reference to the figures, in which FIG. 1 is a top plan view of a fusion reactor apparatus 10 according to the present invention. As seen in FIG. 1, the fusion reactor apparatus 10 includes a central cell or chamber 12 for plasma generation and confinement. A plasma formed in the central cell 12 is maintained therein by means of a plurality of solenoid coils 14 positioned along the length of the central cell 12. As can be seen, the central cell 12 is an elongated chamber preferably in a cylindrical shape. Coils 14 are positioned with respect to chamber 12 by means of supports 15. To impede particles in the plasma from escaping out the open ends 16 and 18 of the central cell 12, mirror means are provided to cause the plasma to be reflected back into the central cell 12. The mirror means at each end includes a respective mirror coil 20, 22 and an adjacent baseball minimum-B magnet 24, 26. The baseball magnets 24, 26 are so called due to their shape, which approximates the shape of the seam on a conventional baseball. Each mirror coil 20, 22 acts to throttle down the flow of plasma from the central cell 12 towards its adjacent baseball magnet. The baseball magnets 24, 26 act as the end plugs for the plasma. In the absence of particle collisions, the plasma density drops as it expands in cross section as it emerges from the high magnetic field at the throat of the mirror coil. The density drop creates a depression .phi..sub.b in the positive potential. As previously described, this creates a potential barrier to the negatively charged electrons, and therefore serves as the electron thermal barrier between each mirror 20, 22 and its respective end plug 24, 26. The area within each reactor chamber 12 in which such thermal barrier regions are created is marked of at 28 and 30. FIG. 2 illustrates axial profiles electrostatic potential and particle density in the thermal barrier and end plug regions at one end of the cell 12. As seen in the electrostatic potential curve, .phi..sub.e is the base potential of the central cell 12 and .phi..sub.c is the increased potential enabled in the end plug due to the existence of the thermal barrier potential, identified as .phi..sub.b. As can be seen, electrons (e.sup.-) tend to fall upward in this curve into the end plug due to their negative charge, while ions tend to fall down into the potential well .phi..sub.b in the thermal barrier due to their positive charge. An exemplary plasma density curve is also shown in FIG. 2, wherein n.sub.c is the central cell plasma density, n.sub.p is the end plug plasma density and n.sub.b is the plasma density in the thermal barrier. Since energetic electrons are trapped in the end plug, n.sub.p .ltorsim.n.sub.c rather than n.sub.p >>n.sub.c. The present invention is directed at keeping n.sub.b at a minimum, to prevent it from equalling or exceeding the density of passing ions. Referring again to FIG. 1, to deposit heating power in the plasma, conventional high energy beams of neutral hydrogen atoms are coupled thereto at points 32 and 34 on respective end plugs 24, 26. These neutral atoms freely enter the plasma magnetic envelope and are then stripped of their electrons by collisions and retained in the plasma as energetic ions. The retained ions heat the plasma as they gradually slow down, transferring energy to the plasma particles. Also included at the end plugs are ducts 36 and 38 for vacuum pumping and microwave heating of the end plug electrons. As previously described, a difficulty with the thermal barrier concept is that collisions of particles passing across the thermal barrier cause some of these particles to lose energy and be trapped in the thermal barrier region. In time, the trapped particle density would grow until the total pressure would equal or exceed the pressure in the central cell 12. The present invention provides a bend in the plasma column at the thermal barrier region to prevent such an increase in trapped particle density. The bend in the plasma is accomplished by means of turning coils, coils 40 and 42 for bending of the plasma in the thermal barrier region 28, and coils 44 and 46 for bending of the plasma in the thermal barrier region 30. This bend in the thermal barrier, having a radius R as seen in FIG. 1, creates a centrifugal force F on the particles, with F being proportional to the inverse of radius R of bending. The effect of this force, in conjunction with the incident magnetic field, is to create a drift velocity in the plasma ions which is perpendicular to the plane of the bending. That is, the direction of the drift velocity V.sub.d is given by the cross product of the centrifugal force F and the magnetic field B, or: EQU V.sub.d .parallel.F.times.B (1) FIG. 3 is a cross-sectional view of the thermal barrier region 30 of FIG. 1. A plasma zone comprising a predominant amount of plasma is also shown in cross section as plasma region 50. The flux lines of the incident magnetic field flow in a direction into the plane of the cross section, as indicated at B. The centrifugal force exerted in plasma region 50 due to the bending of the plasma in this region is shown diagrammatically at F. The direction of ion orbital drift is upward out of the plasma region 50, as shown at a in FIG. 3. FIGS. 1 through 3 also illustrate the position of divertor means, comprising a divertor 52 positioned with respect to thermal barrier region 28 and a divertor 54 positioned with respect to thermal barrier region 30. As seen more clearly in FIG. 3, the divertor 54 is positioned at the top of the thermal barrier region 30 such that it is in the path of ions as they are caused to drift upwards as a result of the bend in the plasma region 50. The divertor 54, as seen in FIG. 3, strips off impurities from the fusion reactor, and is of a conventional design. The divertor includes particle collection vanes 56 and cryopanels 58. The collection vanes 56 are maintained at approximately room temperature, and the cryopanels 58 are kept at a substantially reduced temperature to trap the gas given off by the collection vanes. The reason for this structure is that the particles which hit the divertor 54 are very energetic. Thus, surface heat loading on said vanes 56 is very large. The vanes are kept at room temperature to help prevent overheating of the cryopanels and not desorb trapped gas on cold vanes such that when particles hit vanes, gas desorbs. Therefore, in operation the divertor 54 pumps ions out of the thermal barrier region 30 by neutralizing the ions that hit the divertor. The ions recombine with electrons in the divertor collection vanes 56 forming a neutral gas. To prevent the gas from drifting back into the plasma region 50, it is trapped in the cryopanels 58 by freezing the gas out. Such cryopanels are used since they are the only structure that has the speed needed to effectively take the gas out of the system. The cryopanels are periodically warmed to enable the gas trapped thereon to be pumped off using conventional pump means. An alternative to the divertor means 54 is the use of the gettering material, a metal that has a chemical affinity for the gases that are coming off. Certain metals, e.g., tantalum or titanium, can absorb enormous quantities of foreign gas. The problem with such materials is that they must constantly be replaced or removed and cleaned and then reinserted. Additionally, such materials also tend to inject other impurities into the plasma. FIG. 4 illustrates a perspective view of the thermal barrier region 30, respective turning coils 44 and 46, and the divertor 54 positioned with respect thereto. The fact that ions trapped in a thermal barrier region are eliminated therefrom, i.e., lost to the divertor, in a drift time much less than the filling time of the thermal barrier, is seen from the following equations. Drift velocity V.sub.d is given by: EQU V.sub.d =T.sub.i /ZeBR (2) where Z is the charge number of the trapped ion, R is the radius of curvature of the bend in the plasma in the thermal barrier region, B is the magnetic field strength, and T.sub.i is the ion temperature. Ions are lost from the barrier region in the period .tau..sub.d, the "drift time", given by: EQU .tau..sub.d =ZeBR.alpha./T.sub.i (3) where ".alpha." is the radius of the thermal barrier region, i.e., the distance an ion must travel from the plasma to the divertor. FIG. 3 illustrates this dimension ".alpha." in the exemplary plasma region 50. The filling time of ions into the thermal barrier region, .tau..sub.g, is given roughly by: ##EQU1## where A is the mass number of the ion and .nu..sub.ii is the proton -proton collision frequency. Under typical operating conditions as set forth by Baldwin et al., and at reasonable radii R, these equations show that .tau..sub.d <<.tau..sub.g, so that the thermal barrier regions 28, 30 do not fill up with trapped ions. Further, since .tau..sub.d <<.tau..sub.g, the loss time is determined by .tau..sub.g. Thus, for impurity ions at a high temperature, equation (4) shows that ##EQU2## e.g., for oxygen with Z=8 and A=16, Z.sup.2 /.sqroot.A=16, whereas for hydrogen Z=1 and A=1, so that Z.sup.2 /.sqroot.A=1. As seen from these examples, impurity ions are removed from the thermal barrier region at a much faster rate than hydrogen ions, thereby enhancing the operation of the associated divertor in controlling the level of impurities in the plasma. Divertor functioning is further enhanced for impurity ions, due to the effects of the electrostatic potential on such ions in the thermal barrier region. This electrostatic potential produces an electric field mainly parallel to the magnetic field in the plasma region 50. Since the potential well for ions is proportional to the atomic weight Z of the ion, it is much deeper for the higher atomic weight impurity ions than for hydrogen ions. As a result, the effective mirror ratio for the impurity ions, a measure of the ease with which particles are reflected from a given region, is correspondingly larger. The trapping and subsequent ejection of impurity ions from the plasma are thus further improved. An exemplary trapped ion drift path in the thermal barrier region 30 is illustrated diagrammatically in FIG. 5. The particle path is shown starting at point 1 in the midst of the plasma region 50, and ending at point 11 against a particle collection vane 56 in the divertor 54. Keep in mind that as the trapped ion is reflected back and forth between the mirror 22 and the adjacent end plug 56 while being caused to drift progressively further away from the plasma region 50, it remains stuck in the potential well of the thermal barrier region 30. The orbit of the ion in the well is merely shifted until the particle hits divertor 54, which comprises an obstruction in the well at this outer ion orbit radius. Lastly, as seen in FIG. 1, for the passing plasma ions not trapped in either thermal barrier region 28 or 30, means must be provided so that the drift velocity imparted to the untrapped ions at each end of the plasma cell 12 is prevented from being additive. This means comprises bending of the two ends of cell 12 in opposite directions with respect to one another. Consequently, the displacement of the ion orbits due to the drift velocity imparted to such ions in each thermal barrier region are opposite in direction, thus cancelling each other out. It is to be understood that the foregoing description merely illustrates a preferred embodiment of the present invention, and that various modifications, alternatives and equivalents thereof will become apparent to those skilled in the art. Accordingly, the scope of the present invention should be defined by the appended claims and equivalents thereof . |
050948091 | abstract | The device comprises a threaded rod (11a) capable of being screwed into the threaded bore (10') traversing the core (10) and solid, at one of its ends, with a blocking element (11b) the external diameter of which is greater that the diameter of the rod (11a) and which comes into engagement in that end (7) of the casing (4) of the plug (3) opposite the closure base (5) of the plug when the threaded rod (11a) is screwed into the core (10). The blocking element (11b) cooperates with the end of the casing (4) of the plug to achieve the blocking, against rotation and/or translation, of the obturating device (11). The threaded rod (11a) may comprise a transverse orifice in which a braking part is engaged. |
abstract | The present invention in one of its preferred structural embodiments comprises a plurality of generally rectangular radiation attenuating panels having rollers mounted on the bottom of each panel and rollable in a lower track mounted on a base such as the concrete floor of a building for movement of each panel along the lower track to a designated position to isolate workers in a particular area from a source of harmful radiation, wherein an upper track is mounted on a rigid structure adjacent upper portions of the panels for laterally engaging in a guiding manner upper guide elements on the upper portions wherein the upper track has substantially the same longitudinal configuration (tracking axis) as the lower track. |
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abstract | A system that monitors the health of a computer system is presented. During operation, the system receives a first-difference function for the variance of a time series for a monitored telemetry variable within the computer system. The system then determines whether the first-difference function indicates that the computer system is at the onset of degradation. If so, the system performs a remedial action. |
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description | This invention pertains generally to methods and devices for the insertion and removal of radioactive isotopes into and out of a nuclear core and, more particularly, to the insertion and removal of such isotopes that can be harvested during reactor operation or during a refueling outage. A number of operating reactors employ a moveable in-core detector system such as the one described in U.S. Pat. No. 3,932,211, to periodically measure the axial and radial power distribution within the core. The moveable detector system generally comprises four, five or six detector/drive assemblies, depending upon the size of the plant (two, three or four loops), which are interconnected in such a fashion that they can assess various combinations of in-core flux thimbles. To obtain the thimble interconnection capability, each detector has associated with it a five-path and ten-path rotary mechanical transfer device. A core map is made by selecting, by way of the transfer devices, particular thimbles through which the detectors are driven. To minimize mapping time, each detector is capable of being run at high speed (72 feet per minute) from its withdrawn position to a point just below the core. At this point, the detector speed is reduced to 12 feet per minute and the detector traversed to the top of the core, direction reversed, and the detector traversed to the bottom of the core. The detector speed is then increased to 72 feet per minute and the detector is moved to its withdrawn position. A new flux thimble is selected for mapping by rotating the transfer devices and the above procedure repeated. FIG. 1 shows the basic system for the insertion of the movable miniature detectors. Retractable thimbles 10, into which the miniature detectors 12 are driven, take the routes approximately as shown. The thimbles are inserted into the reactor core 14 through conduits extending from the bottom of the reactor vessel 16 through the concrete shield area 18 and then up to a thimble seal table 20. Since the movable detector thimbles are closed at the leading (reactor) end, they are dry inside. The thimbles, thus, serve as a pressure barrier between the reactor water pressure (2500 psig design) and the atmosphere. Mechanical seals between the retractable thimbles and the conduits are provided at the seal table 20. The conduits 22 are essentially extensions of the reactor vessel 16, with the thimbles allowing the insertion of the in-core instrumentation movable miniature detectors. During operation, the thimbles 10 are stationary and will be retracted only under depressurized conditions during refueling or maintenance operations. Withdrawal of a thimble to the bottom of the reactor vessel is also possible if work is required on the vessel internals. The drive system for insertion of the miniature detectors includes, basically, drive units 24, limit switch assemblies 26, five-path rotary transfer devices 28, 10-path rotary transfer devices 30, and isolation valves 32, as shown. Each drive unit pushes a hollow helical wrap drive cable into the core with a miniature detector attached to the leading end of the cable and a small diameter coaxial cable, which communicates the detector output, threaded through the hollow center back to the trailing end of the drive cable. Each detector has its own drive system. The use of the moveable in-core detector system flux thimbles 10 for the production of irradiation desired neutron activation and transmutation products, such as isotopes used in medical procedures, requires a means to insert and withdraw the material to be irradiated from inside the flux thimbles located in the reactor core 14. Preferably, the means used minimizes the potential for radiation exposure to personnel during the production process and also minimizes the amount of radioactive waste generated during this process. In order to precisely monitor the neutron exposure received by the target material to ensure the amount of activation or transmutation product being produced is adequate, it is necessary for the device to allow an indication of neutron flux in the vicinity of the target material to be continuously measured. Ideally, the means used would be compatible with systems currently used to insert and withdraw sensors within the core of commercial nuclear reactors. Co-pending U.S. patent application Ser. No. 15/210,231, entitled Irradiation Target Handling Device, filed Jul. 14, 2016, describes an Isotope Production Cable Assembly that satisfies all the important considerations described above for the production of medical isotopes that need core exposure for less than a full fuel cycle. There are other commercially valuable radioisotopes that are produced via neutron transmutation that require multiple neuron induced transmutation reactions to occur in order to produce the desired radioisotope product, or are derived from materials having a very low neutron interaction cross section, such as Co-60, W-188, Ni-63, Bi-213 and Ac-225. These isotopes require a core residence time of a fuel cycle or more. Commercial power reactors have an abundance of neutrons that do not significantly contribute to the heat output from the reactor used to generate electrical power. This invention has as an objective and describes a process and associated hardware that may be used to utilize the neutron environment in a commercial nuclear reactor to produce commercially valuable quantities of radioisotopes that require either short term or long-term neutron exposure and either harvesting during reactor operation or during a refueling outage, with minimal impact on reactor operations and operating costs. This invention achieves the foregoing objective by providing a method of irradiating an isotope in a commercial nuclear reactor that has a moveable in-core detector system including detectors that travel in retractable thimbles that extend from a seal table, outside the nuclear reactor, up into a pressure vessel of the nuclear reactor and through instrument thimbles within fuel assemblies supported within a reactor core. The moveable in-core detector system further includes a multi-path selector, positioned on an upstream side of the seal table that selects the retractable thimbles through which the detectors travel. The method comprises the step of providing an elongated, hollow, target specimen cable sized to travel in one of the retractable thimbles with the target specimen cable being sealed at a lead end and having a removable plug that is configured to fit into a trailing end. The target specimen cable has a length sufficient to extend out of the seal table when the target specimen is fully inserted in a preselected, substantially fully extended retractable thimble. The method loads one or more target specimens through the trailing end into a forward location in the hollow of the target specimen cable; closes off the trailing end with the removable plug; and identifies the preselected retractable thimble that extends into the instrument thimble into which the target specimen cable is to be loaded. The method then inserts the lead end of the target specimen cable into the preselected retractable thimble; drives the target specimen cable through the retractable thimble and into the instrument thimble to an elevation that places the target specimen at a predetermined elevation; and irradiates the target specimen at the predetermined elevation for a preselected period of time. After that step the method withdraws the target specimen cable from the instrument thimble after the preselected period of time and out of the preselected retractable thimble to a processing area where it can be loaded into a shielded transportation cask. In one embodiment the driving step or the driving and withdrawing step is performed manually. Preferably, the inserting step is performed downstream of the multi-path selector and upstream of the seal table. In another embodiment, the driving step comprises inserting the target specimen cable through the retractable thimble into the instrument thimble until the lead end of the target specimen cable reaches the sealed end of the retractable thimble causing the inserting step to cease, then withdrawing the target specimen cable to an axial elevation that places the target specimen at the predetermined elevation. Preferably, after the driving step the method includes the step of sealing an outside of the target specimen cable to the seal table with a compression fitting to lock the target specimen cable in place. In the latter case, in one preferred embodiment the method removes any excess material from the target specimen cable that extends approximately more than three inches above the compression fitting. Then the method inserts the removable plug into the trailing end of the target specimen cable. Preferably, the withdrawing step includes the steps of: releasing the compression fitting; attaching temporary tubing to the preselected retractable thimble above the seal table; and extending the temporary tubing to a staging area where the target specimen cable can be offloaded. Preferably, the method also includes the steps of: winding the target specimen cable that is offloaded into a coiled specimen cable, and loading the coiled specimen cable into a transportation cask. Alternately, in the latter case, the step of winding the target specimen cable includes the step of winding the target specimen cable around a spindle and cutting the target specimen cable in segments. In such a case, the separate segments may be wound around different spindles. The method may also include the steps of partitioning the target specimen cable into different axial compartments and loading different target specimens in at least some of the compartments. The invention also contemplates a target specimen cable structured to be inserted into a retractable thimble of a moveable in-core detector system that extends from a seal table up into an instrument thimble of a nuclear fuel assembly within a reactor core. The target specimen cable includes an elongated, hollow tubular member having a sealed closed leading end, the tubular member being flexible enough to negotiate bends in the retractable thimble and strong enough not to collapse on itself as it is pushed through the retractable thimble; and a removable end plug configured to close off a trailing end of the tubular member. In one such embodiment, a forward interior of the tubular member is sectioned off into several axial compartments for housing different specimens at different elevations within the reactor core when the target specimen cable is inserted into the instrument thimble. One preferred embodiment of the radioisotope production apparatus and process of this invention utilizes the retractable flux thimbles, that provide the access conduit for the existing movable in-core detector fission chambers to the instrument thimble in the fuel assembly to periodically measure the reactor power distribution, to insert the target material to be transmuted into a desired radioisotope, into the fuel assembly instrument thimble that is predetermined to be the host location during irradiation. The flux thimble containing the target material, hereafter referred to as the target retractable flux thimble 34, is shown schematically in FIG. 2 and takes the place of the miniature detector 12 shown in FIG. 1 as being inserted into the fuel assembly instrument thimble 60. By “takes the place of the miniature detector” it is meant that while the target specimen occupies the target retractable flux thimble 34, the detector cannot transverse the target retractable flux thimble. The thimbles are designated as retractable because when the reactor is in operation the flux thimbles 34, closed at their lead ends, are fully inserted in the corresponding fuel assembly instrument thimble within the core (as figuratively illustrated by reference character 54 in FIG. 2) and during a refueling outage they are retracted from the instrument thimbles to a level below the core (figuratively illustrated by reference character 58 in FIG. 2). The instrument thimbles are figuratively illustrated by the double lines 60. To deliver the target specimen within the target retractable flux thimble this invention employs an elongated, hollow, tubular member or cable 36, shown in FIG. 3, that is closed at its lead end 38, preferably with a bullet nose to ease its entry into the target retractable flux thimble 34. The trailing end 40 of the cable 36 has a removable seal table, preferably bullet nose plug that is inserted into the trailing end 40 of the cable 36 to seal off the opening in the trailing end of the cable after the target specimen(s) have been loaded. The interior portion of the cable 36 that is to be loaded into the fuel assembly instrument thimble may be partitioned off by spacers 48 to form one or more specimen compartments as identified in FIG. 3 by reference characters 44 and 46 and more fully described in co-pending application Ser. No. 15/341,478 (WEC-FY2016-010), filed Nov. 2, 2016. The cable 36, preferably, has a length that extends from the top of the instrument thimble 60 to slightly above the seal table 20 and is functionally divided into a payload positioning region 50 and payload active fuel region 52. The cable 36, shown in FIG. 3, has a diameter that allows it to be easily inserted into the selected target retractable flux thimble and long enough to ensure that the payload(s) containing the material(s) to be irradiated can be placed at the proper axial position within the corresponding fuel assembly instrument thimble. At any time after the retractable flux thimbles are inserted into their operating positions, the cable 36 containing the target material(s) may be manually inserted into the selected target retractable flux thimble until reaching the end of the thimble causes the insertion to cease. The cable assembly 36 may then be withdrawn as needed to place the axial region of the cable containing the target material(s) in the desired axial position(s) inside the fuel assembly instrument thimble at the selected radial core position. Any excess cable more than approximately three inches above the selected thimble tube compression fitting is removed and the bullet nose removable plug 42 is inserted into the open end of the cable 36. The cable 36 is then locked in place below the moveable in-core detector system 10-path selector 30 using a compression fitting that joins the outer sheath of the cable to the point 62, indicated on FIG. 3, on the cable 36. The compression fitting remains in place until the target specimen reaches the optimum neutron exposure levels. Once the target has obtained the optimum neutron exposure, either during a refueling outage or normal operation, temporary guide tubing 64 is installed over the conduit of the target retractable flux tubing and extended from the selected seal table 20 position to a location 66 of a coiling device 68, like that described in co-pending U.S. patent application, entitled Packaging Device for Radioactive Isotopes Produced in Flexible Elongated Shapes Ser. No. 15/596,002, (WEC-FY2016-013) filed concurrently herewith and shown on FIG. 4, which compacts the cable for shipment to a processing facility. The compression fitting on the target cable is removed and the target cable located above the compression fitting point is inserted through the temporary guide tube 64 from the seal table 20 to the coiling device 68. The cable 36 insertion through the guide tube 64 continues until the cable is inserted through the coiling device input funnel 70, locked in place in the device spindle 72 where indicated on FIG. 4 by reference character 74, and wound onto the target spindle as indicated. The device is operated until there is a known length of between 20 and 25 feet of cable remaining inserted in the target retractable flux thimble tube 34. The cable 36 is then cut at the input funnel 70 of the device. The device is positioned to allow it to be opened to remove the spindle containing the cable collected and the spindle and collected cable are stored. A new target cable spindle 72 is installed and the device is positioned as needed. The end of the inserted portion of the target cable 36 is then inserted into the device input funnel 70 until it is locked into place on the spindle. The device is again operated until the remaining portion of the target cable 36 is wound on the target spindle 72 and both spindles can be lowered into the payload cavity of the transfer cask 76 used to remove the produced radioisotope(s) from containment and transfer it to the processing facility 78. As mentioned above, the target cable 36 may be partitioned into two or more axial regions 44, 46 containing different target materials to allow the simultaneous production of multiple radioisotopes. The ability of the coiling device 68 to enable the device 68 to remotely cut the cable, input and coil the target cable 36 at the coiling device input funnel 70, and deposit the target coils into one or more transfer casks 76 provides the flexibility to satisfy numerous radioisotope production demands to different customers simultaneously. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof. |
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052456412 | summary | CROSS-REFERENCE TO RELATED APPLICATIONS This application is closely related to the disclosure in application Ser. No. 282,991 filed Jul. 14, 1981 now U.S. Pat. No. 4,820,472 granted Apr. 11, 1989, assigned to the assignee by the present invention. BACKGROUND OF THE INVENTION The invention described herein relates to spent fuel storage racks and more particularly to an improved design of racks particularly adapted for storage of fuel assemblies of the type used in boiling water reactors. The delays in undertaking the reprocessing of reactor spent fuel in the United States has required utilities to better utilize the spent fuel storage space at a reactor site in a way to permit the storage of larger quantities of fuel in the same given area. The delays also have provided the economic incentive to increase the storage capacity and thus better control the handling and disposition of spent fuel and costs associated therewith. Initially, plant designers typically included at the reactor site, a spent fuel pool sized to receive a number of spent fuel assemblies less than the total amount expected to be removed from the reactor during its lifetime. The fuel assemblies were located on centers or at a pitch such that the space between assemblies together with the water surrounding each fuel assembly was sufficient to maintain the fuel in a non-critical condition. At this spacing, subcriticality was maintained by utilizing only water as a moderator. As the need for compact storage increased, the first stage of capacity expansion included the use of stainless steel cells for containing each fuel assembly thus permitting reduced spacing between fuel assemblies. This reduction increased the storage capacity by simply changing the design of storage racks without increasing the size of the storage pool. As decisions concerning reprocessing continued to be delayed, greater compaction of fuel assemblies into the allotted pool space was accomplished by applying neutron absorbing materials to the walls of the stainless steel containers or cells which were made to a size to just accept a fuel assembly. This design permitted cells to be spaced on a pitch even less than previous rack designs thus increasing the storage capacity to the extent where the storage pool could accommodate about 10 years of spent fuel. To provide stability and support to prior spent fuel racks, a common arrangement was such that the spent fuel cells were laterally spaced from each other by structural members extending in X and Y directions to thus provide cell support. The egg crate arrangement of cells thus formed allows one fuel assembly to be located in each cell designed to specific tolerances. However, the structural members still utilize space which otherwise could be used more efficiently for fuel assembly storage purposes. Also, fuel racks of the foregoing design contain substantial labor and material content which is reflected in greater manufacturing costs. The parent application provides a spent fuel rack module for overcoming the foregoing disadvantages. This module includes a checkerboard array of cells, each cell sized to accept a fuel assembly. Neutron absorbing material on the walls of each cell serves also to absorb the neutrons from assemblies stored in adjacent cells. The cells of the module are mounted on and secured to a base plate. The underside of the base plate has means at selected positions of the base plate for receiving and locking mechanisms for lifting the module accessible through holes in the base plate. This means includes blocks secured to the underside of the base plates in which the mechanisms are engaged. SUMMARY OF THE INVENTION In accordance with this invention, the means for receiving and locking the mechanism for lifting the module including the blocks is wholly within the periphery of the base plate. The spacing between modules is thus minimized. |
claims | 1. A modular pressurized water reactor having a primary circuit including a reactive core, an upper internals, a steam generator heat exchanger and pressurizer housed within a reactor pressure vessel which is enclosed within a substantially close fitting containment, including a primary coolant hot leg between a coolant flow exit from the core and an upstream side of the steam generator heat exchanger and a coolant cold leg between a downstream side of the steam generator heat exchanger and a coolant flow entrance to the core, the hot leg and cold leg being housed within the reactor pressure vessel, the modular pressurized water reactor further including a combined passive heat removal system and high-head water injection system comprising:a core makeup tank including:a heat exchange assembly supported within the core makeup tank, the heat exchange assembly having a primary side and a secondary side, the primary side having an interior flow path within the heat exchange assembly with a primary side inlet and a primary side outlet, the interior flow path being maintained at a pressure at least equal to a pressure within the reactive core;a primary side inlet plenum that is in fluid communication with the inlet of the interior flow path of the heat exchange assembly and the hot leg exiting the core;a primary side outlet plenum that is in fluid communication with the outlet of the interior flow path of the heat exchange assembly and the cold leg between the downstream side of the steam generator heat exchanger and the coolant flow entrance to the core; anda secondary side plenum within the secondary side of the heat exchange assembly having an inlet end and an outlet end and a secondary side flow path over an exterior of the heat exchange assembly interior flow path, connecting the inlet end to the outlet end of the secondary side plenum;an ultimate heat sink heat exchanger is connected to the core makeup tank between the inlet end and the outlet end of the secondary side plenum, wherein the secondary side plenum and a connection with the ultimate heat sink heat exchanger is pressurized to an extent to prevent boiling under accident conditions; andmeans for isolating the primary side of the heat exchange assembly from the core. 2. The modular reactor of claim 1 wherein the core makeup tank is positioned at an elevation above an elevation of the core. 3. The modular reactor of claim 2 wherein the ultimate heat sink heat exchanger is at an elevation above the elevation of the core makeup tank. 4. The modular reactor of claim 1 wherein the core makeup tank is supported outside of the reactor pressure vessel. 5. The modular reactor of claim 4 wherein the core makeup tank is enclosed within the containment. 6. The modular reactor of claim 5 wherein the ultimate heat sink is positioned outside of the containment. 7. The modular reactor of claim 1 wherein the primary side of the heat exchange assembly is pressurized to at least the same pressure as the core. 8. The modular reactor of claim 7 wherein the primary side of the heat exchange assembly is pressurized to substantially the same pressure as the core. 9. The modular reactor of claim 1 wherein the heat exchange assembly is a tube and shell heat exchanger. 10. The modular reactor of claim 9 wherein the primary side inlet plenum is at a top of the core makeup tank and the primary side outlet plenum is at a bottom of the core makeup tank. 11. The modular reactor of claim 1 wherein the means for isolating the primary side of the heat exchange assembly from the core is a valve in fluid communication with the primary side outlet between the primary side outlet plenum and the cold leg. 12. The modular reactor of claim 1 wherein the ultimate heat sink heat exchanger includes a primary side connected to the secondary side of the core makeup tank heat exchange assembly and a secondary side in heat exchange relationship with a pool of coolant. 13. The modular reactor of claim 1 including a plurality of core makeup tanks. 14. The modular reactor of claim 12 wherein the ultimate heat sink is outside the containment and the pool of coolant is substantially at atmospheric pressure of the surrounding environment. |
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abstract | Various embodiments of a power source and method of forming such power source are disclosed. The power source can include a substrate and a cavity disposed in a first major surface of the substrate. The power source can also include radioactive material disposed within the cavity, where the radioactive material emits radiation particles; and particle converting material disposed within the cavity, where the particle converting material converts one or more radiation particles emitted by the radioactive material into light. The power source further includes a sealing layer disposed such that the particle converting material and the radioactive material are hermetically sealed within the cavity, and a photovoltaic device disposed adjacent the substrate. The photovoltaic device can convert at least a portion of the light emitted by the particle converting material that is incident upon an input surface of the photovoltaic device into electrical energy. |
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description | The present application is continuation of and claims priority of U.S. Ser. No. 10/604,634 filed Aug. 6, 2003, now U.S. Pat. No. 7,031,434 the disclosure of which is incorporated herein by reference. The present invention relates generally to computed tomography (CT) diagnostic imaging systems and, more particularly, to a method of manufacturing a collimator mandrel having variable attenuation characteristics. Typically, in CT imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image. Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction. Pre-patient collimators are commonly used to shape, or otherwise limit the coverage, of an x-ray or radiation beam projected from an x-ray source toward a subject to be scanned. Typically, the CT system will include a pair of collimator mandrels, each of which is mounted on an eccentric drive, such that the collimators may be positioned relative to one another to define a non-attenuated x-ray or radiation path. For example, by increasing the relative distance between the collimators, the width of the x-ray or radiation beam that impinges on the subject increases. In contrast, by moving the collimators closer to one another, the x-ray or radiation beam narrows. The eccentrics are designed to position the collimator mandrels with respect to one another and relative to an x-ray focal point to modulate the width of an x-ray or radiation path that bisects the collimators. Collimators are frequently implemented to provide variable patient long axis (z-axis) coverage when a curvilinear detector assembly is used to detect radiation passing from the x-ray source through and around the subject during data acquisition. Conventional collimator mandrel configurations utilize a solid rod of attenuating material such as tungsten that is machined with a slight increase in diameter in the center of the mandrel relative to its ends. However, as the detector size increases in the z-axis, the constraints on the collimator tighten. Moreover, the collimator must be constructed to accommodate the increase in detector size while limiting x-ray coverage. Increased x-ray coverage increases patient radiation dose and degrades image quality due to the increased scatter in the reconstructed image. Accordingly, the collimator mandrel must be constructed to have a complex shape to accommodate the increase in detector size. One known manufacturing process requires that the solid tungsten rod be machined to provide the complex shape necessary to achieve the desired beam shaping. Tungsten is a rigid material that is highly absorptive of x-rays. As such, tungsten is considered well-suited for collimator assemblies in CT systems. The rigidity of the tungsten, however, makes machining of a solid tungsten rod to have a complex shape difficult and time consuming. Moreover, machining with a precision required for a CT collimator can be difficult thereby compromising system performance. Therefore, it would be desirable to have an accurate and repeatable manufacturing process capable of providing a precise and complex-shaped collimator mandrel for a CT system. The present invention is a directed to a manufacturing process overcoming the aforementioned drawbacks. The present invention provides a repeatable and precise process of constructing a collimator mandrel for a CT system. A rod of rigid material is positioned within a cast. The cast defines a void circumferentially around the rod which serves as a layout or pattern for an attenuating layer of epoxy, resin, or other material. Epoxy or other material is then deposited within the void and is allowed to cure. After curing, the cast is removed, and a complexly shaped collimator mandrel results. Alternatively, a thin layer of variable thickness may be deposited or sputtered directly on the outer surface of the rod to provide the complex shape desired. Therefore, in accordance with one aspect of the present invention, a method of manufacturing a collimator mandrel for a CT imaging system includes the steps of forming a core of base material and applying a tapered layer of attenuating material to the core. In accordance with another aspect of the invention, a CT collimator mandrel comprises a solid cylindrical rod positioned within a layer of attenuating material. The mandrel is formed by shaping a bulk of supporting material into a core and positioning the core in a cast such that a non-uniform void is created between an outer surface of the core and an inner surface of the cast. The mandrel is further formed by injecting attenuating material into the void and removing the cast upon curing of the attenuating material. According to yet another aspect, a process of constructing a mandrel for a CT imaging system is provided and includes the steps of forming a solid cylindrical rod of first material and depositing a layer of second material designed to substantially block x-rays on the cylindrical rod. Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings. The present invention will be described with respect to the blockage, detection, and conversion of x-rays. However, one skilled in the art will appreciate that the present invention is equally applicable for the detection and conversion of other high frequency electromagnetic energy. The present invention will be described with respect to a “third generation” CT scanner, but is equally applicable with other CT systems. Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system 10 is shown as including a gantry 12 representative of a “third generation” CT scanner. Gantry 12 has an x-ray source 14 that projects a beam of x-rays 16 toward a detector array 18 on the opposite side of the gantry 12. Detector array 18 is formed by a plurality of detectors 20 which together sense the projected x-rays that pass through a medical patient 22. Each detector 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuated beam as it passes through the patient 22. During a scan to acquire x-ray projection data, gantry 12 and the components mounted thereon rotate about a center of rotation 24. Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT system 10. Control mechanism 26 includes an x-ray controller 28 that provides power and timing signals to an x-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of gantry 12. A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from detectors 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed reconstruction. The reconstructed image is applied as an input to a computer 36 which stores the image in a mass storage device 38. Computer 36 also receives commands and scanning parameters from an operator via console 40 that has a keyboard. An associated cathode ray tube display 42 allows the operator to observe the reconstructed image and other data from computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray controller 28 and gantry motor controller 30. In addition, computer 36 operates a table motor controller 44 which controls a motorized table 46 to position patient 22 and gantry 12. Particularly, table 46 moves portions of patient 22 through a gantry opening 48. Referring to FIG. 3, a collimator assembly 50 having a pair of collimator mandrels 52 and 54 that are constructed to collimate x-rays projected toward a patient and detector assembly or array. Each collimator mandrel 52, 54 is designed to be rotated along a lengthwise axis by pivot assemblies 56. As will be described in greater detail below, collimator mandrel 52 is rotated clockwise and collimator mandrel 54 is rotated counterclockwise to define the width of the aperture 58 that is formed between the pair of mandrels. However, one skilled in the art would readily recognize that other rotational orientations are possible and contemplated to achieve a desired aperture shape and/or width. X-rays are projected from an x-ray tube toward the collimator assembly 50. The mandrels 52, 54 are positioned relative to one another to define an aperture size tailored to the specific CT study to be carried out. In this regard, each mandrel is designed and constructed of material to block or prevent passage of those x-rays that are not passed through aperture 58. As such, each mandrel 52, 54 has a complexly-shaped outer layer 60, 62 of attenuating material. That is, each outer layer extends circumferentially around a rod 64, 66 of base material and a non-constant diameter. The rods 64, 66 form a solid and rigid base for the layers of attenuating material. Preferably, the rods are constructed of steel, but other materials are possible. The attenuating layers may be fabricated from tungsten or other attenuating epoxy or alloy. As shown, each rod 64, 66 has a circular or constant diameter. In contrast, each mandrel, as a result of the non-circular attenuating layer, has a complex shape. This complexity in shape allows the collimator assembly to provide a more variable aperture size without a change in the collimator assembly itself. Simply, in one preferred embodiment, the mandrels 52 and 54 have oblong or egg-like cross-sectional shapes that extends the entire length of rods 64 and 66, respectively. However, the manufacturing process described herein allows for other mandrel shapes as well as varying attenuating layer thickness along the length of the rods. Referring now to FIG. 4, a side view of the collimator assembly 50 illustrates a first or minimum aperture size that can be achieved by dynamically controlling the rotation of the mandrels 52 and 54. In the relative position illustrated, each mandrel has been rotated to maximize the amount of attenuating material 60, 62 axially positioned between each rod 64, 66. As a result, the size of aperture 58 is affected to control the expanse and coverage of x-ray beams 16 projected toward the patient (not shown) and detector assembly 18. In FIG. 5, the collimator assembly 50 is shown with a maximum aperture size. To achieve a maximum in the size of aperture 58, eccentrics 56 rotate each mandrel 52 and 54 such that the thinnest amount of attenuating material is positioned adjacent the x-ray path through the aperture 58. As a result, more of the x-ray beam is allowed pass through the collimator assembly unaltered by mandrels 52 and 54. Eccentric assemblies 56 may be rotated mechanically by a user or, preferably, by a controller mechanism that is electronically controlled to rotate the mandrels based on a desired aperture size. Further, while FIG. 5 illustrates rotation of both mandrels compared to that shown in FIG. 3, one mandrel may be rotated while the other mandrel remains stationary. Additionally, since each mandrel may be rotated independently by eccentrics 56, one mandrel may be rotated more than the other mandrel. As a result, the number of aperture sizes that is possible is a function of the degree change in attenuating material thickness around each rod. Moreover, one mandrel may have a layer of attenuating material that is dimensionally different from the layer of attenuating material around the other mandrel. In this regard, the number of aperture sizes available is increased. FIG. 6 is a side view similar to that of FIG. 4 but illustrates a second or maximum aperture size that is achieved as a result of the relative rotation of both mandrels 52 and 54. The position of each rod 64 and 66 remains fixed, but each mandrel is caused to rotate along a lengthwise axis through the center of the rod. As a result, the thickness of the attenuating layer placed in the x-ray path is variably controlled to fit the particulars of the CT study. As is shown, aperture 58 has a much larger size in FIG. 6 than in FIG. 4; therefore, the x-ray path therebetween is much larger which allows for greater coverage in the z-direction on detector 18. The collimator mandrel profile illustrated in FIGS. 3-6 represents one embodiment of the shape each collimator mandrel may have. However, as will be described, the manufacturing process disclosed herein is capable of constructing other-shaped mandrels than that illustrated in FIGS. 3-6. For example, the mandrels could be constructed to have lobes or other geometrical shapes to achieve the desired aperture shape. Shown in FIG. 7 is a cross-sectional view illustrating the construction of a collimator mandrel in accordance with the present invention. The construction process begins with the formation of a cylindrically or other shaped rod 68 of base material having a constant cross-section. The rod 68 is constructed to have an eccentric pivot 70 on each end to support rotation of the mandrel once assembled and fit in the CT system. As noted above, the rod is preferably constructed of a solid, rigid material, i.e. steel, that is designed to receive and support a layer of attenuating material, such as tungsten, lead, a high atomic weight alloy, or epoxy laden with high atomic weight material. Rod 68 is placed is a cast 72 that envelops the rod. The cast 72 envelopes the rod such that a void 74 is created circumferentially around the outer surface of the rod 68 between the inner surface of cast. The void defines the dimensions, thickness, and shape of a layer of attenuating material to be deposited or otherwise formed to the outer surface of the rod. In the example illustrated in FIG. 7, a highly attenuative epoxy or resin is deposited in void 74 and is allowed to cure. Once cured, the cast is removed and a tapered layer of attenuating material affixed to the outer surface of the rod results. However, use of a cast and the filling of a void between the cast and rod illustrates only one technique for forming a complexly shaped mandrel. For example, a thin layer of tungsten or other attenuative layer could be vapor or chemically deposited about the rod in a controlled manner such that a non-circular cross-sectioned or other complex shaped mandrel is constructed. In another embodiment, a thin layer of attenuating material could be sealed against the rod or core material using adhesive, glues and other intermediaries. Further, given the cast layer provides the x-ray attenuation, other attenuating materials other than tungsten may be used. As a result, the non-tungsten layer with improved machinability could be sealed against the rod and machined to provide the desired complex shape. Referring now to FIG. 8, package/baggage inspection system 100 includes a rotatable gantry 102 having an opening 104 therein through which packages or pieces of baggage may pass. The rotatable gantry 102 houses a high frequency electromagnetic energy source 106 as well as a detector assembly 108 having scintillator arrays comprised of scintillator cells. A conveyor system 110 is also provided and includes a conveyor belt 112 supported by structure 114 to automatically and continuously pass packages or baggage pieces 116 through opening 104 to be scanned. Objects 116 are fed through opening 104 by conveyor belt 112, imaging data is then acquired, and the conveyor belt 112 removes the packages 116 from opening 104 in a controlled and continuous manner. As a result, postal inspectors, baggage handlers, and other security personnel may non-invasively inspect the contents of packages 116 for explosives, knives, guns, contraband, and the like. Therefore, in accordance with one embodiment of the present invention, a method of manufacturing a collimator mandrel for a CT imaging system includes the steps of forming a core of base material and applying a tapered layer of attenuating material to the core. In accordance with another embodiment of the invention, a CT collimator mandrel comprises a solid core positioned within a layer of attenuating material. The mandrel is formed by shaping a bulk of supporting material into a core and positioning the core in a cast such that a non-uniform void is created between an outer surface of the core and an inner surface of the cast. The mandrel is further formed by injecting attenuating material into the void and removing the cast upon curing of the attenuating material. According to yet another embodiment, a process of constructing a mandrel for a CT imaging system is provided and includes the steps of forming a solid cylindrical rod of first material and depositing a layer of second material designed to substantially block x-rays on the cylindrical rod. The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims. |
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abstract | The fusion-welded nanotube surface signal probe of the present invention is constructed from a nanotube, a holder which holds the nanotube, a fusion-welded part fastening a base end portion of the nanotube to a surface of the holder by fusion-welding, a tip end portion of the nanotube being caused to protrude from the holder; and the tip end portion is used as a probe needle so as to scan surface signals. This fusion-welded nanotube surface signal probe can be used as a probe in AFM (Atomic Force Microscope), STM (Scanning Tunneling Microscope), other SPM (Scanning Probe icroscope) and so on. |
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abstract | A high reliable water injection device is provided that injects water into a reactor containment vessel and can reliably shut off cooling water at normal times and quickly and reliably inject water into the reactor containment vessel without the need for external power, in a case of emergency. The water injection device injects water into a reactor containment vessel includes a flow path through which cooling water is supplied; a disk that closes the flow path; a swing arm that is connected to the disk and performs closing and opening of the flow path by the disk; and a weight that is connected to the swing arm via a swing lever, in which the weight is supported by a support member made of a low melting point alloy. |
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claims | 1. A direct synthesis method, comprising:reacting Na2(WO4)·2H2O with NaF in an inert atmosphere at a reaction temperature of about 950° C. to about 1400° C. 2. A direct synthesis method, comprising:reacting Na2(WO4)·2H2O with NaF and Na2[MO4]·H2O in an inert atmosphere at a reaction temperature of about 950° C. to about 1400° C. according to the reaction:(1−x)Na2[WO4]·2H2O+xNa2[MO4]·H2O+NaF→Na3W1−xMxO4Fwhere0≦x≦0.2; andM is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. 3. The method as in claim 2, wherein x is 0 such that Na3(WO4)F is formed. 4. The method as in claim 3, wherein Na3WO4F is formed into single crystals having an impurity concentration present at a concentration of less than about 500 ppb. 5. The method as in claim 2, wherein 0<x≦0.2. 6. The method as in claim 5, wherein M is Mo such that Na3W1−xMoxO4F is formed. 7. A crystal structure comprising: Na3(WO4)F with impurities present in a concentration of less than about 500 ppb. 8. The crystal structure as in claim 7, wherein impurities are present in concentration of less than about 100 ppb. 9. A scintillator material comprising the crystal structure of claim 7. 10. A phosphor material comprising the crystal structure of claim 7. 11. A composition of matter having the formula:Na+3−a−2b−3cA+aB2+bC3+cW1−xMxO4Fwhere0≦a≦2;A+ is an alkali metal ion;0≦b≦1;B2+ is an alkaline earth metal ion selected from Be2+, Mg2+, Ca2+, Sr2+, and/or Ba2+, a rare earth divalent cation from the atomic numbers 57-71, an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, or any combinations thereof;0≦c≦1;C3+ is a rare earth trivalent cation from the atomic numbers 57-71, an activator trivalent cation of Ac, U, Cr, Mn, As, Sb, Bi, In, Tl, or any combinations thereof;0<x≦0.2; andM is B, Al, Si, P, S, Cr, V, Nb, Ta Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. 12. The composition of matter as in claim 11, where a=b=c=0 such that the composition of matter has the formula:Na3(W1−xMxO4)F,where0<x≦0.2, andM is B, Al, SL P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. 13. The composition of matter as in claim 11, wherein M is Mo. 14. The composition of matter as in claim 11, wherein impurities are present in a concentration of less than 500 ppb. 15. A scintillator material comprising the composition of claim 11. 16. A phosphor material comprising the composition of claim 11. 17. A composition having the formula:Na+3−a−2b−3cA+aB2+bC3+cW1−xMxO4Fwherea is 0;A+ is an alkali metal on;b is 0;B2+ is an alkaline earth metal ion selected from Be2+, Mg2+, Ca2+, Sr2+, and/or Ba2+, a rare earth divalent cation from the atomic numbers 57-71, an activator divalent cation of Cr, Mn, Re, Cu, Ag, Au, Zn, Cd, Hg, Sn, or any combinations thereof;0<c≦0.1;C is Ce, Eu, or a combination thereof;0≦x<0.2; andM is B, Al, Si, P, S, Cr, V, Nb, Ta, Zr, Hf, Sc, Y, La, Ga, Ge, In, Mo, or combinations thereof. 18. A crystal structure comprising: Na3(GeO4)F with impurities present in a concentration of less than about 500 ppb. |
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048878855 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to novel arrangements, including both systems and methods, for generating narrow beams of traveling wave fields in space, and more particularly pertains to several embodiments for integrated radiation cavities (either LASER or MASER cavities) designed to generate in their own medium a Bessel mode diffraction free beam. Much of the disclosure herein is applicable to all types of waves as described by the basic Helmholtz wave equation, including electromagnetic waves such as radio frequency, microwave, infra-red, optical and x-ray waves, relativistic and nonrelativistic quantum waves associated with particle waves, such as electron, neutron, proton, atom and other quantum particle waves, and further including physical elastic waves such as material deformation waves and longitudinal waves including acoustical waves. 2. Discussion of the Prior Art Current state of the art techniques to concentrate a wave or form a parallel beam are generally successful only over a very limited range of beam propagation. This range is conventionally related inversely to the degree of concentration. This inverse relationship arises primarily because all wave fields are subject to diffraction (i.e., beam spreading). The arrangements of the subject invention have several advantages over all prior art techniques currently in use, with a principle advantage thereof being greatly improved resistance to diffraction. Two methods exist in the current state of the art for generating narrow beams, focusing and collimation. Due to the ever present effects of diffraction, a focus is never perfect. Instead, a focus is characterized as a finite region over which a beam has a minimum radius. The distance along the lens axis, on one side or the other of the focus, where the beam exhibits significant convergence is called the depth of field of the focus. The depth of field of a focus is generally limited by the sharpness of the focus. That is, a very small focal spot can be achieved only at the expense of depth of field. All light waves, such as those radiated by the sun, lamps and lasers, can be collimated as well as focused. Collimated (parallel) beams are generally preferred because they have much greater depth of field than focused beams, although they are less bright. Collimation is normally accomplished by a series of aligned apertures, which are basically just holes in opaque screens, which allow the light through along just one direction. A sequence of aligned holes along a collimation axis of a beam provides the normal manner of creating a well-defined parallel or collimated beam. Unfortunately, diffraction affects collimation adversely just as it does focusing. The effects of diffraction on collimation can be described with the explanation that a wave field bends outwardly from the edges of a hole as it proceeds therethrough, and thus the resulting beam is not as well collimated. FIG. 1 illustrates the characteristic behavior of waves traveling through holes. The diffractive bending of water waves that are entering a narrow harbor or passing by a jetty can be shown easily in aerial photographs thereof because of the large scales involved, but the bending of light waves is very difficult to notice under ordinary circumstances because the angle of bending is so small. The bending angle is approximately equal to the ratio of the wavelength of the light to the size of the hole, an angle that is usually less than 10.sup.-3 (one one-thousandth) of a degree. A standard criterion called the "Rayleigh range" identifies the distance over which a collimated beam remains well defined after passing through a hole with a given cross sectional area. The Rayleigh range is the ratio of the area of the hole to the wavelength of the light. The Rayleigh range (here denoted Z) is mathematically characterized by the formula Z=A/.lambda., where A denotes the hole's area and .lambda. denotes the light's wavelength. For visible light .lambda. is very small, in the range 15-30 millionths of an inch. A circular hole with a radius equal to one inch has a Rayleigh range of about Z=2 miles. For this reason the diffraction illustrated in FIG. 1 will ordinarily be simply undetectable. However, if an attempt is made to define the beam extremely well (to be able to illuminate a very small spot quite precisely) then the situation is very different. A spot radius of 50 microns (about two-thousandths of an inch) or smaller is conceivable in applications of modern optical technology. The Rayleigh range for a beam formed by passage through a 50 micron sized hole is only one inch or less. This is much greater than the depth of field of a normal sized lens focal spot, but is still very small on a practical working scale. These estimates indicate that current techniques for creating narrow collimated beams are simply unable to generate beams that have any significant range at all, particularly with respect to commercial operations such as drilling, embossing, scribing, testing, and other manufacturing or laboratory activities that might advantageously use very narrow beams. The present invention appears to have applicability and utilization in the semiconductor industry in areas of high precision instruments for optical surface treatments such as etching and marking operations. In these applications, the ability of ordinary light beams to achieve near-wavelength resolution without concern about depth of field or beam divergence could be applied to high-volume integrated circuit manufacturing operations. Tolerances unknown in wafer processing without electron beam or x-ray techniques could be met with ordinary light, perhaps to great advantage in reducing capital costs, magnetic field sensitivity, and worker protection requirements, while increasing instrument reconfiguration flexibility and reducing deadtime between job-runs. Additionally, in the area of high precision process diagnostics, a major change is evolving in process-flow diagnostic instruments. A new generation of instruments uses laser probes to tag (by excitation of fluorescence, for example) molecules participating in a flowing or mixing process at very precisely located highly sensitive regions of the process. The input probe and the signal received back from the light-sensitized molecule are optical and do not disturb the flow or mix in any way. This is in contrast to all of the previous methods that use mechanical sensors inserted into the process, or macroscopic markers or floats injected to accompany the process. These prior art approaches have the disadvantage that their presence necessarily disturbs the environment being measured. The purpose of localized observations is to provide early warnings of turbulent flow, to monitor the degree of completion of a reaction, etc. The present invention has the advantage of allowing highly precise positioning of its beam center and immunity against beam divergence over relatively great depth of field, compared with all other prior art laser devices. SUMMARY OF THE INVENTION The present invention overcomes the prior art limitations on the range of extremely well defined beams, with the term beam herein being utilized generally to refer to the central bright spot, not the full intensity pattern, and is based on the premise that wave fields are subjects to the laws of diffraction. The subject invention can be explained as an arrangement for causing diffractive influences on a beam to cancel each other, thereby allowing the preparation of narrow beams with extreme range or depth of field. To be specific, reconsider the last example hereinabove of a 50 micron beam. If a diffraction free aperture as described herein, with a radius of one inch, instead of 50 microns, is used to create a 50 micron size beam, the Rayleigh range becomes 500 times greater, about 33 feet. If narrow beams are important for truly distant wave transport, as in reconnaissance and laser range-finding, a somewhat larger diffraction free aperture would suffice. For example, if a diffraction free aperture with a one-foot radius is used to create a one-inch wide beam, the Rayleigh range grows to 30 miles. Accordingly, a principal object of the present invention is to provide an arrangement for transforming travelling wave fields into well-defined beams that are not affected by diffractive spreading. The arrangement depends upon a properly designed aperture, and can be applied to any wave field whose wave amplitude .PSI. satisfied these mathematical relations: EQU .PSI.(x,y,z,t)=.PSI.(x,y,z)e.sup.i.omega.t EQU [.gradient..sup.2 +(.omega./v).sup.2 ] .PSI.(x,y,z,t)=0 The letter v designates the velocity of the wave incident on the transmission plate. It is well known that an extremely wide variety of wave fields satisfy these conditions, including radio, microwave, infra-red, optical, x-ray, and all other electromagnetic waves, many types of sound, water, and elastic waves, and both relativistic and non-relativistic quantum waves associated with electrons, neutrons, protons, atoms and all other quantum particles. Considering, for illustration, only light waves, the beams generated pursuant to the teachings herein can find immediate application to laser printing, laser surgery, high precision instruments for optical treatment of surfaces such as laser etching, laser marking, high precision process diagnostic instruments, and other laser applications where depth of field and control of beam definition are more crucial than the irradiance thereof. Ranging and signalling and targeting with well defined, high power coherent electromagnetic and other waves over long distances may also be possible in nonabsorbing media and atmospheres. Pursuant to the teachings herein, nondiffracting apertures can be constructed by following precise criteria which are based upon mathematical principles of waves. The basic criterion of a nondiffracting aperture is to convert a wavefront of an input plane wave beam, obtained in a standard manner, from a laser beam for example, into a wavefront with a very specific form, so that the height and spacing of the modulations of the output electric field strength of the output beam are related to each other in such a way that the beam travels without any change in the modulations. This means that any very sharp maximum, such as the central beam spot, will maintain its small size and will not spread out. Nondiffracting apertures can be built to satisfy these criteria by using commercially available components such as lenses, screens, wave guides, masks, absorption filters, phase shifters, etc. The term nondiffracting as used herein is meant to apply to a well defined traveling wave beam not subject to beam spreading in the sense that the intensity pattern of the traveling wave beam in a transverse plane is substantially unaltered by propagation over a range which is substantially larger than the Rayleigh range of a Gaussian beam with equal central spot width. Pursuant to the teachings of the present invention, such a wave beam is formed by generating a traveling wave beam the amplitude of which has its transverse dependence substantially identical to J.sub.m (.alpha..rho.), the m.sup.th Bessel function of the first kind, wherein .alpha. is a geometrical constant and .rho. designates the transverse radial coordinate of the wave beam, and further wherein the Bessel function argument is independent of the distance z of propagation, which results in a well defined traveling wave beam not subject to beam spreading. Pursuant to the teachings of the present invention, a well defined traveling wave beam substantially unaffected by diffractive spreading can be generated from a recognition that certain exact, non-singular solutions exist for the free space Helmholtz wave equation which represent a class of fields that are nondiffracting in the sense that the intensity pattern in a transverse plane is substantially unaltered by propagation in free space. More specifically, the present invention recognizes that the only axially symmetric nondiffracting field other than a plane wave is the zero-order Bessel function of the first kind and this beam can have an effective spatial width as small as several wavelengths. In accordance with the teachings herein, the present invention provides arrangements, encompassing both systems and methods, for generating a well defined traveling wave beam substantially unaffected by diffractive spreading, comprising generating a beam having a transverse dependence of a Bessel function, and a longitudinal dependence which is entirely in phaser form, which results in a beam having a substantial depth of field which is substantially unaffected by diffractive spreading. In one disclosed embodiment, the beam is generated by placing a circular annular source of the beam in the focal plane of a focusing means, which results in the generation of a well defined beam thereby because the far field intensity pattern of an object is the Fourier transform thereof, and the two-dimensional Fourier transform of a Bessel function is a circular function. In a second disclosed embodiment, the beam is generated by transmitting a coherent beam sequentially through a phase modulator, having a periodic step function pattern, and a spatial filter, whose transmittance is the modulus of the Bessel function, to generate a beam having a transverse Bessel function profile. In different embodiments, the beam can be an electromagnetic wave, a particle beam, a transverse beam, a longitudinal beam such as an acoustic beam, or any type of beam to which the Helmholtz generalized wave equation is applicable. Moreover, the beam can be generated with a transverse dependence of a zero order Bessel function, or a higher order Bessel function, or any combination of different Bessel functions such as a zero order Bessel function and one or more higher order Bessel functions, as illustrated in FIG. 17. The present invention offers a significant advantage over prior art methods by permitting a bright central core of a beam to remain concentrated and available for use over much greater ranges of propagation than is currently possible with prior art methods of beam formation. The subject invention is generally applicable to processes that are activated by bright spots (of light, for example), but for which the distance at which the activity occurs is not easily controlled extremely well. These processes can vary from normal manufacturing and laboratory processes such as drilling, embossing, scribing, welding or testing, where the distance is in the few-inch range and beam spot sizes may be extremely small (10-100 microns), to open field processes such as ranging and aligning where the distances and beam spot sizes may both be many thousands of times greater, but relative tolerances about the same. Pursuant to the teachings of the present continuation-in-part application, several embodiments are described and disclosed of an integrated radiation cavity, as incorporated in a laser or maser, for increasing the efficiency of production of the radiation beams. More particularly, designs are disclosed for integrated optical or microwave cavities for lasers or masers which will generate directly from their own gain medium a Bessel-mode diffraction-free beam. The different disclosed embodiments for such integrated optical or microwave cavities have several common characteristics: (a) a close relation to a known stable laser or maser cavity design, (b) a large mode volume to permit exploiting the relatively high gain of the laser or maser systems, and (3) little departure in principle from the design that has already led to successful observation of non-diffracting beams. The several disclosed embodiments of FIGS. 12-16 are generally generic to either Light Amplification by Stimulated Emission of Radiation (LASER's) or Microwave Amplification by Stimulated Emission of Radiation (MASER's). Several of these embodiments are diffraction-free mode generators, and have the common characteristic of integrating the radiation source into the diffraction-free mode generator, as opposed to directing an externally generated beam through a diffraction-free aperture. One embodiment is somewhat of a hybrid specy in this regard as a diffraction-free aperture is incorporated into one end of the resonant cavity. All of these embodiments are generally expected to produce much higher output power and increased efficiency of operation. Moreover they can be used to produce intense high beams of very small diameter (60 microns or much smaller) having applications, for example, to precision pointing, micro-welding, and ultra-small scale data deposition and scanning. |
050930702 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In each of the above-described conventional cores, the power distribution in the radial direction of core is kept substantially constant during an operational cycle. The operational cycle is formed by a period from the start-up operation of reactor started after the core has been charged with fuel assemblies to the shutdown of reactor for charging the core with new fuel assemblies. The present inventors investigated the characteristics of the prior art, particularly of U.S. Pat. No. 3,799,839 and of Japanese Patent Laid-Open No. 57-70489. As a result, it was found that the maximum linear heat generation rate which significantly affects the safety margin of fuel is determined by the power distribution in the radial direction of core and by the combination of the power distribution in the axial direction of the core and the local power distribution in fuel assemblies. FIG. 1 shows the power peaking factor during one operation cycle. As shown in FIG. 1, the local power peaking factor in fuel assemblies and the power distribution in the axial direction of the core change in accordance with the passage of time in an operational cycle. Thus, the limiting radial power peaking factor which is necessary to satisfy the limit of maximum linear heat generation rate also changes with the passage of time during an operational cycle, as shown in FIG. 2. Namely, the limit of power peaking in the radial direction of core is low in the beginning of operation cycle and becomes high in the end thereof. In view of these characteristics, the present inventors found a new fact that the value of power peaking in the radial direction of core must be kept small in the beginning of the operation cycle, while a relatively large value of power peaking in the radial direction of the core is permissible in the end of the operation cycle. The present inventors also found a new problem that, since the power peaking in the radial direction of core changes in accordance with the progress of burn-up of fuel, the conventional cores in which it is presumed that the power peaking in the radial direction of core is constant can not attain a preferred efficiency of fuel utilization. In other words, the technical problem of the present invention is an improvement in efficiency of fuel utilization. On the basis of the above investigation that the power peaking in the radial direction of core must be limited to a small value in the beginning of the operation cycle and a relatively large value of power peaking in the radial direction of the core is permissible in the end of the operation cycle, according to the present invention, as shown in FIGS. 3A and 3B, in the beginning of an operation cycle, the power distribution in the radial direction of the core is sufficiently flattened or the power in the central region is lowered and in the end of the operation cycle, the power in the central region having a high level of neutron importance is increased and the power peaking in the radial direction of the core is increased, so that the efficiency of fuel utilization is improved. Such an increase in power peaking in the radial direction of core in the end of the operation cycle causes an increase in reactivity of the core. In order to realize the change from the power distribution in the radial direction of the core of FIG. 3A to that of FIG. 3B in an operation cycle, as shown in FIGS. 4A and 4B, the reactivity of the central region of the core in the beginning of an operation cycle must be made smaller than that of the peripheral region surrounding the central region, and the reactivity of the central region of the core in the end of the operation cycle must be made greater in comparison with the beginning of the operation cycle. The reactivity of the peripheral region of the core in the end of the operation cycle is lower in comparison with the beginning of the operation cycle. In this way, since the distributions of reactivity in the radial direction of the core in the beginning and end of the operational cycle are different from each other, the central region of the core operates to increase the so-called spectral shift effect. In the central region, since the power is low in the beginning of the operation cycle, the margin for maximum permissible linear heat generation rate is increased so that the power generated at the lower portion of central region can be increased. Thus, the start point of coolant-boiling is shifted to the coolant inlet side of fuel assemblies so that a region with a high void fraction is enlarged in the axial direction. That is, the void fraction in the central region can be increased in the beginning of the operation cycle. Contrary, in the end of the operation cycle, the power generated at the lower portion of central region must be decreased because of a high level of power generated in the central region. The boiling start point is therefore shifted upward, and the void fraction in the central region is decreased. The change in void fraction causes a change in neutron spectrum. In the beginning of the operation cycle, the neutron spectrum in the central region is hard, and the amount of plutonium produced by excess neutrons is increased in the central region. In the end of the operation cycle, since the neutron spectrum in the central region becomes soft, the reactivity in the central region becomes high. The change in reactivity distribution in the radial direction of the core enables the above-described spectral shift operation and causes an improvement in efficiency of fuel utilization in the core. It was found that the change in reactivity distribution in the radial direction of the core shown in FIGS. 4A and 4B can be obtained by a change in reactivity of the fuel assemblies which were loaded in the core and subjected to a first operation cycle so that the fuel assembles have the maximum reactivity, and by a change in reactivity of new fuel assemblies containing burnable poison. In particular, it is described below that the infinite multiplication factor of the fuel assemblies containing burnable poison changes in accordance with the progress of burn-up. FIG. 5 shows a relation between the infinite multiplication factor and the exposure of new fuel assemblies containing burnable poison. The relation of FIG. 5 is measured when about 1/3 of the fuel assemblies in the core are replaced by new fuel assemblies containing burnable poison in each operation cycle. The burnable poison is used for keeping a substantially constant degree of excess reactivity. Thus, according to the number of fuel rods containing burnable poison in fuel assemblies and according to the concentration of burnable poison thereof a decrease in reactivity of the fuel assemblies remaining in the core is compensated in and after the second operation cycle by the new fuel assemblies whose reactivity increases in accordance with the passage of time in the operation cycles. In the example shown in FIG. 5, the infinite multiplication factor of new fuel assemblies in the beginning of first operation cycle is smaller than that of the fuel assemblies in the beginning of third operation cycle and the infinite multiplication factor of fuel assemblies becomes maximum at the end of the first operation cycle. On the basis of the results obtained by the above-described consideration, a core structure is improved for achieving spectral shift with a change in reactivity in the radial direction of core. In this core structure, the average infinite multiplication factor in the peripheral region of core is greater than the average infinite multiplication factor in the central region, in the beginning of an operation cycle, and the average infinite multiplication factor in the central region is greater than the average infinite multiplication factor in the peripheral region, in the end of the operation cycle. FIG. 6 shows a preferred embodiment of core structure according to the present invention which is applied to a boiling water type reactor. FIG. 6 shows a cross section of one-quarter part of core 5. In the core 5, 764 fuel assemblies 6 form a lattice, and control rods 7 can be inserted among the fuel assemblies 6. The core 5 has a central region and a peripheral region excepting a region (outermost peripheral region) of fuel assemblies disposed in the outer most periphery. The peripheral region surrounds the central region. The boundaries between the central region and the peripheral region and between the peripheral region and the outermost peripheral region are indicated by broken lines in FIG. 6. In this embodiment, 356 fuel assemblies 6 are mounted in the central region, and 308 assemblies 6 are mounted in the peripheral region. Fuel assemblies 6 include fuel assemblies 1 to 4. The fuel assemblies 1 are loaded in the core 5 as new fuel assemblies before the first operation cycle. The fuel assemblies 2 to 4 are replaced by new ones between the first and second operation cycles, between the second and third operation cycles and between the third and fourth operation cycles, respectively. Each of the fuel assemblies 1 has the cross-sectional form shown in FIG. 7. This cross-sectional form is shown in FIG. 7 of Japanese Patent Laid-Open No. 62-217186. That is, each of the fuel assemblies 1 has 74 fuel rods 8 which form a lattice comprising 9 lines and 9 columns, and two water rods disposed at the central portion. Each of the fuel rods 8 has many fuel pellets therein, and the external diameter of each of the water rods 9 is greater than the pitch between the fuel rods 8. In each of the fuel assemblies 1, the two water rods 9 occupy a region in which 7 fuel rods 8 can be arranged, as shown in the embodiment shown in FIG. 1 of Japanese Patent Laid-Open No. 62-217186 (specifically, refer to 1 to 6 lines of the upper left column on page 3 of Japanese Patent Laid-Open No. 62-217186). Each of the fuel rods 8 has the enrichment distribution in the axial direction, as shown in FIG. 8A. Fuel pellets of natural uranium are arranged in the upper end portion and lower end portion of a fuel effective length portion (the region of each fuel rod 8 charged with fuel pellets). The natural uranium regions occupy 1/24 (or 2/24) of the total axial length of fuel effective length portion. Fuel pellets of enriched uranium fill a part of fuel effective length portion other than the natural uranium region. The enriched uranium region is divided into an upper region and a lower region in the axial direction. The boundary between the upper region and the lower region is at a height of 11/24 of the total axial length of fuel effective length portion from the lower end thereof. Since the enrichment of upper region is higher than that of lower region, the average enrichment of upper region of each fuel assembly 1 is higher than that of the lower region thereof. The average enrichment of each fuel assembly 1 is about 3.85% by weight. The 16 fuel rods 8 included by the 74 fuel rods contain gadolinia serving as burnable poison. FIG. 8B shows the gadolinia distribution in the axial direction of each of the fuel rods 8. Each of two gadolinia-containing fuel rods 8 contains a medium concentration of gadolinia in the upper region having a high enrichment and does not contain gadolinia in the other regions. Each of the remaining 14 gadolinia-containing fuel rods 8 contains gadolinia in the enriched uranium region and does not contain gadolinia in the natural uranium region. Each of these 14 gadolinia-containing fuel rods 8 contains a medium concentration of gadolinia in the upper region in the same way as the two before-mentioned gadolinia-containing fuel rods 8. Each of the 10 gadolinia-containing fuel rods 8 of the 14 gadolinia-containing fuel rods contains a high concentration of gadolinia in the lower portion having a low enrichment. Each of the 4 remaining gadolinia-containing fuel rods 8 of the 14 gadolinia-containing fuel rods contains a low concentration of gadolinia in the lower region. The gadolinia contained in each fuel assembly 1 is completely burnt up in the end thereof. New ones of the fuel assemblies 1 having the above-described arrangement have the exposure of 0 MWd/T. In each of the fuel assemblies 1, the average enrichment of the upper region is higher than that of the lower region, and the amount of gadolinia of the upper region is greater than that of the lower region. The number of the gadolinia-containing fuel rods 8 of the upper region is greater than that of the lower region. In each of the new fuel assemblies 1, the infinite multiplication factor of the upper region is smaller than that of the lower region. To such fuel assemblies 1 is applied the concept of the enrichment distribution and gadolinia distribution which are used in the fuel assembly shown in FIGS. 3A and 3B of U.S. Pat. No. 4,587,090. Each of the fuel assemblies 1 thus has the function of spectral shift shown in line 21 of column 4 to line 17 of column 5 and FIGS. 5, 6, 7, 8 and 9 of U.S. Pat. No. 4,587,090. In each of the fuel assemblies 1, the infinite multiplication factor of the upper region is smaller than that of the lower region in the beginning of the operation cycle, and the infinite multiplication factor of the upper region becomes geater than that of the lower region in the end of the operation cycle. This phenomenon is caused by the possession of the above-described enrichment and gadolinia distributions. Each of the fuel assemblies 2, 3 and 4 which operated in the reactor during at least one operation cycle contains no gadolinia and has the structure shown in FIG. 7. When the fuel assemblies 2, 3 and 4 were new fuel assemblies, each of them also had the same enrichment and gadolinia distributions as those of the fuel assemblies 1. When the control rods 7 are inserted into the core 5, one cell is formed by the four fuel assemblies 6 adjacent to each of the control rods 7. The core 5 comprises a plurality of such cells. One of the cells is a control cell 10. The control cell 10 has four fuel assemblies 3 which have been already burnt up in two operation cycles and which have small infinite multiplication factors. The control rod 7A inserted into the control cell 10 is inserted into the core 5 not only during the shut-down of reactor but also during the operation thereof. The control rod 7A is a control rod for controlling the power distribution during the operation thereof. The 9 control cells 10 are arranged in the central region of the core 5. The control rod 7B inserted into each of the cells other than the control cells 10 is a control rod for shutting down the reactor, which control rod is completely withdrawn from the core 5 during the operation of reactor and is inserted into the core during the shut-down of reactor. Each of cells other than the control cells 10 in the central region of the core 5 contains four fuel assemblies comprising two fuel assemblies 1, one fuel assembly 2 and one fuel assembly 3. The two fuel assemblies 1 are disposed in the diagonal direction of one cell with one control rod 7B arranged therebetween. The fuel assemblies 2 and 3 are disposed in the other diagonal direction with one control rod 7B arranged therebetween. In the peripheral region of the core 5, each of a small number of the cells contains three types of fuel assemblies (the assemblies 1 to 3), as the cells in the central region, and each of most of the cells contains two types of fuel assemblies. That is, each of some cells contains two fuel assemblies 1 and two fuel assemblies 2, and each of the other cells contains two fuel assemblies 2 and two fuel assemblies 3. In each of these cells, the numbers of operation cycles during which the fuel assemblies disposed diagonally have operated are equal to each other. In the peripheral region, each of the cells containing the fuels assemblies 1, 2 and 3 also contains two fuel assemblies 2, and the fuel assemblies 1 are disposed in a part of peripheral region near the central region. Contrary, the fuel assemblies 3 are disposed in a part of peripheral region near the outermost region. In the outermost peripheral region, the fuel assemblies 3 and 4 are disposed. In the core 5 of this embodiment, a distance between the boundary between the central region and peripheral region and the center of the core 5 is about 7/10 of the radius of the core. The central region of the core 5 has 356 fuel assemblies 6 including 160 fuel assemblies 1 which are new fuel and contain gadolinia. The peripheral region of the core 5 has the 308 fuel assemblies 6 including the 68 fuel assemblies 1 described above. The proportion of the fuel assemblies 1 to the fuel assemblies 6 in the central region is greater in comparison with the peripheral region. Namely, in the core 5, a number of the fuel assemblies 1 included by each cell 10B arranged in the peripheral region is smaller than that of the fuel assemblies 1 included by each cell 10A arranged in the central region. Each of the cells arranged in the peripheral region contain at most two fuel assemblies 1. The average number of operation cycles during which the fuel assemblies other than the fuel assemblies 1 operate in the core is 2.50 in the central region and 2.45 in the peripheral region. The central region thus has a greater value. With respect to the fuel assemblies 2 which have the maximum infinite multiplication factor in the beginning of the operation cycle, the proportion of the fuel assemblies 2 to the fuel assemblies 6 in the peripheral region is greater in comparison with the central region. The number of the fuel assemblies 2 included by cells in the peripheral region is greater in comparison with the central region. The characteristics of the core 5 of this embodiment are described below in comparison with the core 11 shown in FIG. 9. In the core 11, the fuel assemblies 1, 2 and 3 which have operated during respective numbers of operation cycles different from each other are substantially uniformly loaded. The characteristics of the core 5 and those of the core 11 which are measured when the core 5 and the core 11 are operated according to the same control rod pattern strategy are compared with each other. FIG. 10A shows the smooth distributions of infinite mulitplication factors of the fuel assemblies 6 in the radial direction of the core in the beginning of the operation cycle. FIG. 10B corresponds to FIG. 10A and shows the state in the end of the operation cycle. Since the core 5 contains burnable poison and a loading fraction of the fuel assemblies 1 having small infinite multiplication factors and loaded in the central region is greater than a loading fraction of fuel assemblies 1 loaded in the peripheral region, the average infinite multiplication factor in the central region is smaller in comparison with the peripheral region in the beginning of the operation cycle. In particular, in this embodiment, since the loading fraction of the fuel assemblies 2 having the maximum infinite multiplication factor in the beginning of the operation cycle is great in the peripheral region, the average infinite multiplication factor in the peripheral region in the beginning of operation cycle is increased more than the average infinite multiplication factor obtained when the loading fraction of the fuel assemblies 1 in the peripheral region is small. That is, an increase in loading fraction of the fuel assemblies 2 in the peripheral region causes an increase in difference between the average infinite multiplication factors in the peripheral region and the average infinite multiplication factors in the central region in the beginning of the operation cycle. In the beginning of the operation cycle, the difference in average infinite multiplication factor between the peripheral region and central region of the core 5 is greater than that of the core 11. In the end of the operation cycle, since the gadolinia contained by the fuel assemblies 1 burns out so that the infinite multiplication factor of the fuel assemblies 1 becomes the maximum, the average infinite multiplication factor of the central region of the core 5 becomes greater than that of the peripheral region. The core of this embodiment, in which the central region has a greater loading fraction of the fuel assemblies 1 which contain burnable poison and which have small infinite multiplication factors in comparison with the peripheral region, and in which the peripheral region has a greater loading fraction of the fuel assemblies 2 in comparison with the central region, is a core in which the average infinite multiplication factor of the peripheral region is greater than that of the central region in the beginning of the operation cycle, and in which the average infinite multiplication factor of the central region is greater than that of the peripheral region in the end of the operation cycle (refer to FIGS. 10A and 10B). In the core 11, the average infinite multiplication factor of the central region is greater than that of the peripheral region in both the beginning and end of the operation cycle. As shown in FIGS. 10A and 10B, since in the distribution of infinite multiplication factors in the radial direction of the core the average infinite multiplication factor of the peripheral region is high in the beginning of the operation cycle, and that of the central region is high in the end of the operation cycle, the spectral shift effect in the central region can be increased, as compared with the effect in U.S. Pat. No. 4,587,090. Thus, the exposure of the core is further increased, thereby further improving the efficiency of fuel utilization. It is a matter of course that the above-described increase in loading fraction of the fuel assemblies 2 in the peripheral region causes a further increase in exposure. The lower the exposure of the fuel assemblies is, the greater the change in reactivity caused by the change in void fraction is. Since the spectral shift is effected mainly in the central region in which a large number of the new fuel assemblies 1 are arranged, therefore, a remarkable improvement of efficiency of fuel utilization is achieved. The power distributions in the radial direction of cores shown in FIG. 11A and 11B correspond to the distributions of infinite multiplication factors in the radial direction shown in FIG. 10A and 10B, respectively. The core 11 has a substantially constant power distribution in the radial direction in both the beginning and end of the operation cycle. In the core 5, during the beginning of the operation cycle, the power of the central region is lower than that of the peripheral region, and during the end of the operation cycle the power of the central region is higher than that of the peripheral region. Therefore, in the beginning of the operation cycle, the neutron leakage amount of the core 5 is greater than that of the core 11 by 0.25% .DELTA.K, and in the end of the operation cycle, the neutron leakage amount of the core 5 is smaller than that of the core 11 by 0.35% .DELTA.K. The neutron leakage amount generated over one operation cycle of the core 5 is smaller than that of the core 11. This improves the utilization factor of neutrons of the core 5, i.e., the efficiency of fuel utilization. In this embodiment, since the loading fraction of the fuel assemblies 1 in the central region is great, and since the average number of the operation cycles during which the fuel assemblies other than the fuel assemblies 1 operate in the central region of the core is greater than the average number of the operation cycles during which the fuel assemblies other than the fuel assemblies 1 operate in the peripheral region of the core as described above, the power distribution in the radial direction of the core becomes substantially flat in the beginning of the operation cycle, as shown in FIG. 11A. The power of the central region can be suppressed by making the above mentioned average number of operation cycles of the central region greater than that of the peripheral region. FIG. 12 shows a relation between the power peaking in the radial direction of cores and the exposure in an operation cycle. The power peaking in the radial direction of the core 5 is smaller than that of the core 11 in the beginning of the operation cycle and the power peaking in the radial direction of the core 5 is greater than that of the core 11 in the end of the operation cycle, since in the beginning of the operation cycle, a loading fraction of the fuel assemblies 1 which contain burnable poison and which have small infinite multiplication factors is large in the central region of the core. The power peaking in the radial direction of core increases simultaneously with the increase maximum linear heat generation rate, in the end of the operation cycle, as shown in FIG. 15 given below. However, the maximum linear heat generation rate obtained is within a permissible range. FIG. 13 shows a change in power peaking in the axial direction of each of the cores 5 and 11 in an operation cycle. In the core 11, the power fraction of the lower portion of core gradually decreases from the early state to the middle state in an operation cycle. But, in the core 5, the power fraction of the lower portion of core is maintained at a high level during the same states. The power fraction of the fuel assemblies 1 having high reactivity in the lower portion becomes higher as gadolinia burns up. In the central region having a high loading fraction of the fuel assemblies 1, therefore, the power peaking in the lower portion of core increases from the beginning of operation cycle to the middle state thereof (exposure, 8 GWd/st). Since this increase in power peaking generated in the central region compensates a monotonous decrease in power peaking of the lower portion of the core in the peripheral region, the power peaking in the lower portion of the core 5 is kept at a high value in the whole of core. On the other hand, the power peaking in the upper portion of the core 5 is greater than that of the core 11 in the end of the operation cycle. That is, since a power generated in the first half of the operation cycle by the upper portion of the core 5 is smaller than that of the core 11 according to the amount of gadolinia of the upper portion of the core which is greater than that of the lower portion thereof, the fissile materials in the upper portion of the core significantly slowly burn, so that in a power distribution a peak is present in the upper portion of the core. In particular, since the peripheral region of the core 5 includes many fuel assemblies 2 and 3 in which gadolinia is burnt out, the core 5 has an axial power distribution on which an extremely large peak is produced in the upper portion of the core. As described above, in the core 5, a change in axial power distribution is increased and an effect of spectral shift is increased as compared with U.S. Pat. No. 4,587,090. In one operation cycle, the part of operation cycle before an exposure of 8 GWd/st is called the first half, and the part after this exposure is called the latter half. In the core 5 the effect of spectral shift is improved by the changes in reactivity distribution in the radial and axial directions. FIGS. 14A and 14B show a state of the spectral shift. FIG. 14A shows the state in the beginning of the operation cycle, and FIG. 14B shows the state in the end of the operation cycle. In both the central and peripheral regions of the core 5, the peak is shifted from the lower portion of core to the upper portion thereof as the operation cycle proceeds from the beginning to the end. The power peak of the central region of the core 5, however, is greater than that of the peripheral region thereof in both the beginning and end of the operation cycle. This phenomenon causes an increase in effect of spectral shift so that the reactivity of the core 5 is greater by about 0.8% .DELTA.k than that of the core 11 at the end of operation cycle. FIG. 15 shows relations between the maximum linear heat generation rates of the cores 5 and 11 and the exposure. Since the core 11 is charged with the fuel assemblies 1, the spectral shift operation shown in U.S. Pat. No. 4,587,090 is possible. The power peak in the lower portion is large because a large amount of gadolinia is contained by the upper portion of each of the fuel assemblies 1. The maximum linear heat generation rate in the core 11 therefore is great in the first half of the operation cycle. The maximum linear heat generation rate in the core 11 of the latter half of the operation cycle is smaller than that of the first half thereof because the gadolinia included by the upper portion of each fuel assembly 1 burns and decreases so that the power peak is shifted to the upper portion of the fuel assemblies 1 containing many voids. In other words, the margin for the limit value of maximum linear heat generation rate of the core 11 is increased in the latter half of the operation cycle. The core 5 of this embodiment employs the margin for the maximum linear heat generation rate of the core 11 increased in the latter half of the operation cycle. This margin is utilized for increasing the power peaking in the radial direction and axial direction of the core, i.e., for increasing the maximum linear heat generation rate of the core 5, in the end of operation cycle so that an increase in reactivity of the core 5 is significantly improved. Although the maximum linear heat generation rate of the core 5 is large in the middle stage of the operation cycle, there is still a margin for the limit value. The maximum linear heat generation rate of the core 5 in the middle stage can be reduced by adjusting the amount of gadolinia contained by the fuel assemblies 1. The above-mentioned characteristics of the core 5 are obtained when the core 5 is operated by the same operation of control rods as the operation of control rods of the core 11. The excess reactivity of the core 5 is smaller in the first half of the operation cycle than that of the core 11. This decrease in excess reactivity enables a reduction in amount of gadolinia or in number of control rods required for controlling the excess reactivity. The reduction in amount of gadolinia causes a prevention of useless absorption of neutrons so that the reactivity is increased. The reduction in number of control rods used for controlling the excess reactivity causes a decrease in number of control rods mounted in the core during the operation of reactor, so that the working life of control rods is increased and the number of burn-out control rods is decreased. The decrease in excess reactivity in the core 5 can be achieved according to two reasons described below. The first reason is that the amount of neutrons leaking from the peripheral region of the core 5 to the outside thereof is large in the beginning of the operation cycle. The second reason is that, in the beginning of the operation cycle, the power peak in the lower portion of the core 5 is high, and the void fraction is also high. The core 5 receives the control cells 10 in the central region. The average infinite multiplication factor of the control cells 10 is smaller than that of the other cells. The control cells 10 thus flatten the radial power distribution of the core 5 over the whole period of operation cycle. In particular, since one of the 9 control cells 10 is disposed at the center of the core and the other control cells form a circular path surrounding the one central control cell, the radial power distribution of the core 5 is constantly flattened. In addition, the amount of gadolinia included by the fuel assemblies 1 can be reduced by disposing the control cells 10 in the central region of the core 5. As a result, the amount of neutrons absorbed by the gadolinia in the central region of the core 5 is reduced, and the amount of neutrons utilized for the production of plutonium is increased, so that the spectral shift effect caused by the change in reactivity in the radial direction of core is increased. After the reactor has been started, the power distribution is controlled by operating the control rods 7A inserted into the control cells 10. At this time, the control rods 7B are withdrawn from the core 5. The control rods 7A also compensate the decrease in reactor power caused by the burn-up of fissile materials. Such operation of control rods enables the simplification of control of the reactor power and facilitates the control from the state shown in FIG. 4A to the state shown in FIG. 4B, i.e., the control for increasing the power peak in the central region in the end of operation cycle. Since the core 5 is charged with the fuel assemblies each having the two large-diameter water rods 9 shown in FIG. 7, the effect disclosed in lines 4 to 14 of the lower right column on page 3 of Japanese Patent Laid-Open No. 62-217186 can be obtained. A work for exchanging the fuel in the core 5 will be described below. When the operation of reactor reaches the end point of one operation cycle, all the control rods 7 are inserted into the core 5 so as to shutdown the reactor. The work for exchanging the fuel is then performed, as described below. The fuel assemblies 4 in the outermost peripheral region, the fuel assemblies 3 in the central region and the fuel assemblies 3 in the peripheral region other than the fuel assemblies 3 mounted in the outermost region are withdrawn as burn-out fuel assemblies from the core 5. In FIG. 6, during the exchange of fuel, the fuel assemblies 2 are moved to the positions of the fuel assemblies 3, and the fuel assemblies 1 are moved to the positions of the fuel assemblies 2. In principle, the fuel assemblies 1 and 2 disposed in the central region are loaded in the peripheral region, and the fuel assemblies 1 and 2 disposed in the peripheral region are loaded in the central region. Part of the fuel assemblies 2 disposed in the peripheral region are loaded in the outermost peripheral region. New fuel assemblies 1 containing gadolinia are loaded at the positions where the fuel assemblies 1 were loaded in the previous operation cycle. The number of the new fuel assemblies 1 loaded in the central region is greater than that of the new fuel assemblies 1 loaded in the peripheral region. Such fuel exchange enables the core 5 shown in FIG. 6 to be formed again before the next operation cycle is started. Thus, the above-described function can also be obtained in the next operation cycle. If most of the cells in the peripheral region of the core 5 are replaced by cells each having one fuel assembly 1, two fuel assemblies 2 and one fuel assembly 3, the effect obtained in the core 5 can be attained. In this core, however, a change in reactivity distribution generated in accordance with the passage of time in one operation cycle is smaller as compared with the change in reactivity distribution generated in the core 5 in which the fuel assemblies 1 are concentrated on the side of peripheral region near the central region, so that the spectral shift effect is decreased slightly. The position of boundary between the central region and the peripheral region will be described below. FIG. 16 shows a relation between an increase in reactivity of core and the position of boundary between the central region and the peripheral region. In FIG. 16, a point A denotes an increase in power peaking in the radial direction and an increase in reactivity of the core obtained when a distance between the boundary and the center of the core is 3/4 of the radius of core. Points B and C denote the characteristics obtained when the distances between the boundary formed between the central and peripheral regions and the center of the core are 1/2 and 1/4 of the radius of the core, respectively. The smaller the central portion is, the smaller the increase in power peaking caused by the increase in reactivity of the core is. If the area of central portion decreases to a certain degree, the reactivity of the core decreases as the power peaking increses. It is therefore preferable that the distance between the boundary formed between the central and peripheral regions and the center of the core is more than 2/5 of the radius of the core. The above-mentioned core 5 is an equilibrium core which have operated during several operation cycles. The concept of the core 5 can be applied to an initial core. All the fuel assemblies mounted in such an initial core are new fuel assemblies. However, fuel assemblies corresponding to the fuel assemblies 1 shown in FIG. 6 contain a highest average enrichment of gadolinia. Fuel assemblies corresponding to the fuel assemblies 2, 3 and 4 shown in FIG. 6 contain no gadolinia and the greater the reference numeral of fuel assemblies is, the smaller the average enrichment is. Such an initial core can attain the same effect as the core 5. FIG. 17 shows another embodiment of a reactor core according to the present invention. The core 15 of this embodiment is divided into three regions con centrically in relation to the center of the core, that is, a first region, a second region and a third region, and a ratio by volume of these regions is 9:14:15. This configuration of the core is characterized in that new fuel assemblies 1 containing gadolinia are loaded in the first region and the second region in a ratio of 2:1. This configuration is further characterized in that the first region is charged with pairs of the new fuel assemblies and fuel assemblies 3, and the second region is charged with pairs of the new fuel assemblies 1 and fuel assemblies 2. With respect to the average number of cycles during which the fuel assemblies operate in each of the regions in the core, the average number of the second region is the smallest, that of the first region is greater than that of second region and that of the third region is greater than that of the first region. In such core 15, in the beginning of the operation cycle, the order of the average infinite multiplication factors of the three regions is k.infin.(first region)<k.infin.(second region)<k.infin.(third region). Thus, the power in the central portion of the core is kept at a lower level so that the excess reactivity in the beginning of the operation cycle can be effectively controlled and the exposure of the new fuel assemblies 1 is decreased. On the other hand, in the end of the operation cycle, since the gadolinia in the new fuel assemblies 1 burns out so that the infinite multiplication factors are increased, the order of the average infinite multiplication factors of the three regions is k.infin.(third region)<k.infin.(first region)<k.infin.(second region). This distribution of infinite multiplication factor effectively keeps the power peaking at a low level in the radial direction of the core and increases the reactivity of the core. The core 15 of this embodiment has a characteristic of that the power peaking in the radial direction of the core 15 is smaller than that of the core 5 by about 5% of that of the core 5. The core 15 attains the same spectral shift effect as the core 5. FIG. 18 shows a core 16 of a boiling water reactor as another embodiment of the present invention. In the core 16 of this embodiment, cells having fuel assemblies 1A, 2 and 3 are disposed in the central region, and cells having fuel assemblies 1B, 2 and 3 are disposed in the peripheral region. The cells in the central region include three types of cells, that is, cells each having two fuel assemblies 1A, cells each having two fuel assemblies 2 and cells each having two fuel assemblies 3. The fuel assemblies 1A and 1B are new assemblies each containing gadolinia and have the structures shown in FIGS. 19 and 20, respectively. Each of the fuel assemblies 1A and 1B has two large diameter water rods 9 at the center thereof and has fuel rods 17 which form a lattice having 9 lines and 9 columns as shown in the fuel assemblies 1. Now fuel rods 17A and 17B included by the fuel rods 17 used in the fuel assemblies 1A contain gadolinia. The gadolinia concentration of each fuel rod 17A is 3.5% by weight, and the gadolinia concentration of each fuel rod 17B is 4.5% by weight. The fuel rods 17 used in fuel assemblies 1B include fuel rods 17A and 17C containing gadolinia. The gadolinia concentration of each fuel rod 17C is 5.0% by weight. Each fuel assembly 1A contains 16 fuel rods containing gadolinia, and each fuel assembly 1B contains 14 fuel rods containing gadolinia. The amount of gadolinia contained by the fuel assemblies 1A is greater than the amount of gadolinia contained by the fuel assemblies 1B. However, the highest gadolinia concentration of the fuel assemblies 1A is smaller than that of the fuel assemblies 1B. The gadolinia concentration of each of the fuel rods 17A, 17B and 17C is constant in the axial direction of the fuel effective length. The enrichment of each of the fuel rods 17A, 17B and 17C is also constant in the axial direction of the fuel effective length. The average enrichment of the fuel assemblies 1A and 1B is about 4.0% by weight. The average gadolinia concentration of the fuel assemblies 1A is 4.0% by weight, the average gadolinia concentration of the fuel assemblies 1B is 4.7% by weight. In the core 16 containing the fuel assemblies 1A and 1B, the average infinite multiplication factor of the peripheral region in greater than that of the central region in the beginning of the operation cycle, and the infinite multiplication factor of the central region is greater than that of the peripheral region in the end of the operation cycle, as in the core 5. FIG. 21 shows a relation between the infinite multiplication factors and the exposure of the fuel assemblies 1A and 1B. The infinite multiplication factor of the fuel assembly 1 is smaller than that of the fuel assembly 1B in the beginning of a first operation cycle. However, the infinite multiplication factor of the fuel assembly 1A is greater than that of the fuel assembly 1B in the end of the first operation cycle at which the gadolinia burns out. The number of fuel rods containing gadolinia of each fuel assembly 1A is greater than that of each fuel assembly 1B. Since the highest gadolinia concentration (4.5% by weight) of the fuel assemblies 1A is smaller than that (5.0% by weight) of the fuel assemblies 1B, the gadolinia of the fuel assemblies 1A burns up earlier than that of the fuel assemblies 1B. In the beginning of the operation cycle, therefore, the infinite multiplication factor of the central region of the core 16 in which the fuel assemblies 1A are loaded is smaller than that of the peripheral region of the core 16. In the end of the operation cycle, contrary, the infinite multiplication factor of the central region of the core 16 is greater than that of the peripheral region of the core 16. The core 16 has the maximum linear heat generation rate within a permissible range and allows the reactivity distribution in the radial direction of core to be changed between the beginning and the end of the operation cycle, as the core 5. In the core 16, therefore, the spectral shift effect can be caused by the change in reactivity distribution in the radial direction of the core, as in the core 5. The core 16 may have the 9 control cells 10 in the central region, as the core 5. This causes the core 16 to obtain the same effect as the effect obtained by the control cells 10 arranged in the core 5. When the concepts of the enrichment distribution and the gadolinia concentration distribution in the axial direction shown in FIGS. 8A and 8B are applied to the fuel assemblies 1A and 1B in the core 16, the spectral shift effect is caused by the change in reactivity distribution in the axial direction as in the core 5. The core 16 can be applied to both an equilibrium core and an initial core. A core of boiling water reator according to the present invention will be described below. The core of this embodiment employs the fuel assembly 18 shown in FIG. 22 in place of the fuel assembly 1 of the core 5 shown in FIG. 5. A gadolinia distribution of the fuel assembly 18 is different from that of the fuel assembly 1 whose gadolinia distribution changes positively the axial power distribution. The fuel assembly 18 has two water rods each having the same outer diameter as each fuel rod 19 in the central region and has the fuel rods 19 form a lattice having 8 lines and 8 columns, as shown in FIG. 22. In each of the fuel rods 19, the upper end and lower end portions of the fuel effective length are charged with natural effective uranium, and the enrichment of the lower enriched uranium region is 3.1% by weight and the enrichment of the upper enriched uranium region is 3.3% by weight, as shown in FIG. 23A. Each of fuel rods 20 containing gadolinia contains 4.0% by weight of gadolinia, as shown in FIG. 23B. The core of this embodiment also allows the reactivity distribution in the radial direction of the to be changed between in the beginning and end of the operation cycle in the same way as the core 5. In other words, the core of this embodiment enables an increase in reactivity in the end of the operation cycle by utilizing the margin for the maximum linear heat generation rate in the end. This embodiment enables the achievement of spectral shift effect by utilizing the change in reactivity distribution in the radial direction of the core. However, in a core the fuel assemblies 2, 3 and 18 of which are uniformly disposed as in the core shown in FIGS. 8A and 8B, the margin for maximum linear heat generation rate of the end of the operation cycle is smaller than that of the beginning of the operation cycle. This tendency is reverse to the tendency of the core 11. Thus, the increase in reactivity in the end of the operation cycle of this embodiment is smaller than that of the core 5. The spectral shift effect of this embodiment is therefore smaller than that of the core 5. In particular, if the power in the upper portion of the core becomes relatively large in the end of the operation cycle, the reactivity can be effectively increased by the structure of the core of this embodiment. Since voids are actively generated in a high power fuel assembly, the reactivity in the upper portion of the core is restrained. If the power in the central region of the core is increased, the axial power distribution in the central region is flattened, so that the power in the central region can be increased without the maximum linear heat generation rate being significantly increased. The present invention can be also applied to pressure water reactors as well as boiling water reactors. |
053032721 | description | PREFERRED EMBODIMENTS OF THE INVENTION The preferred embodiments of the invention will be explained with reference to FIGS. 1 to 5. In the following, the structures which are common to the conventional fuel assembly are given the same designations, and their detailed explanations are omitted. The key manipulator in the embodiment comprises: a plurality of grid supports 20 the number of which is equal to the number of grids 4 (but in FIG. 1 only one unit is shown), and disposed in the direction of the fuel rod 6, wherein each of the grid supports 20 has a tetrahedral framework for supporting the outer surface of grid 4 by contacting with the inner surface thereof; outer spring manipulator 30 fixed on the planes of the grid support 20 facing the outer strap 7a for retracting the outer spring 10a; an inner key manipulator 40 fixed to the grid support 20 for retracting the inner spring 10b formed on the inner strap 7b, by inserting an inner key 12 into the grid 4 and turning the key 12 around the axis thereof. A grid support 20 comprises: a base 21; an L-shaped main support body 22 attached to the upper surface 21a of the base 21 and supports the grid 4 at its inner surface 22a; frames 24-25 which are attached freely rotatably to the ends of the main support body 22 with pins 23; roughly square-rod shaped clamping parts 26-27 disposed on the inner surfaces of the frames 24-25 (opposite surface to the main support body 22), and which is raised or lowered via rod 51 by means of a clamp elevator cylinder 50; a fluid-operated frame locking cylinder 28 (a connecting mechanism) attached to a frame 24 of the frames 24-25, and having a locking rod 28a whose tip is inserted freely removably into the other frame 25. On the exterior surface of the clamping parts 26-27, are disposed guide pins 29 which are freely slidably against the frames 24-25. Two outer spring manipulators 30 are attached to the inner surface of the main support body 22 of the grid support 20, and one each to the inner surfaces of the clamping parts 26-27 so as to face each of the outer strap 7a of the grid 4. All of the four outer spring manipulators 30 have the same construction, and the following explanation is provided only for one which is attached to the main support body 22, and explanations for others are omitted. The outer spring manipulator 30, shown in FIG. 2, comprises: a plurality of pairs of hook stems 31-32, which are inserted into the slit 11, extending from the support body 22 towards the outer strap 7a in such a way to clasp the outer spring 10a therebetween (in FIGS. 2 and 3, only a pair of the hook stems 31-32 is shown); and hook parts 31a-32a which extend from the opposing side surfaces of the hook stems 31-32; and a hook manipulator 60 which, after passing the hook stems 31-32 into the slit 11, squeezes the paired hook stems 31-32 together and engages the hooks 31a-32a to the spring 10a by moving the hook stems 31-32 away from the grid cell 5. In the following, the construction of the hook manipulator 60 will be explained with reference to FIGS. 1 to 4. The hook manipulator 60 comprises: a rectangular-shaped first sliding plate 61 having a plurality of hook stems 31 protruding out at regular intervals toward the interior of the grid 4, and disposed inside a cavity 22b which is formed longitudinally along the support body 22 (refer to FIG. 3); a second sliding plate 62 of the same shape as the first sliding plate 61 having a plurality of hook stems 32 protruding out at regular intervals toward the interior of the grid 4, and disposed inside the cavity 22b along side the sliding plate 61; coil springs 63-64 which force the first and second sliding plates 61-62 towards the interior of the grid 4 through the push pins 63a-64a; two through holes 65a (refer to FIG. 2 which shows only one of such holes) which pass through the two sliding plates 61-62 in the thickness direction, and spaced apart in the length direction of the sliding plates 61-62; home-position cams 65 of a semi-circular cylinder shape each of which is placed inside the two through holes 65a; two through holes 66a (only one shown in FIG. 2) which are formed in about the same way as the two through holes 65a; operational-position cams 66 which are made about the same cross sectional shape as the home-position cams 65, having slightly a smaller diameter, each being housed in the through holes 66a; a valve cam 67 having protrusion portions 67b-67c (refer to FIGS. 4 and 5) formed on the opposite sides of the valve cam 67 so that the protrusion portions are displaced axially, and contained in a through hole 67a which is formed in about the same way as the through hole 65a; driving cylinders 68 for driving the two home-position cams 65 by the rack 68b through pinion 68a (refer to FIG. 1) fixed to each end of the home-position cams 65; driving cylinders 69 which similarly drive the operational-position cams 66 through pinion 69a-rack 69b; and driving cylinders 70 which similarly drive the valve cam 67 through pinion 70a-rack 70b. On the support body 22 and the first sliding plate 61 fitted therein is disposed a through hole 80 (refer to FIG. 3) extending lengthwise, at the position to correspond with the insertion of the key 12, thereby enabling the key 12 to be inserted into the grid 4. Two inner key manipulators 40 are disposed on the outer surface of the support body 22 of the grid support 20, as shown in FIG. 1. The two manipulators 40 are constructed the same way, and therefore, the operation of only one manipulator 40 will be explained, and the explanation for the other unit shown by the dashed line in FIG. 1 on the lower left will be omitted. The inner key manipulator 40 comprises: two slide guide rails 41 extending out of the support body 22; a base plate 42 spanning across the slide guide rails 41 at the tip thereof; key insertion device 43 extending lengthwise and engaged slidingly to the pair of slide guide rails 41; a plurality of pinions 44, disposed along the lengthwise direction in the base of the key insertion device 43, whose axes extend in the direction of the slide guide rails 41, and having one end of the inner key attached thereto; a key rotating cylinder 46 (returning means) for rotating the pinion 44 through the rack 45 disposed on the side of the fuel assembly of the key insertion base 43; a key transfer cylinder 47 (transfer means) which is disposed on the far-side of the fuel assembly of the base plate 42, and moves the insertion base 43, via extension rod 47a, towards and away from the grid 4. Next, the operational process of the manipulator apparatus according to the embodiment will be described. First, by operating the clamp elevator cylinder 50, the clamping parts 26-27 is made to approach the frame 24-25 so as to position the grid 4 within the framework of the support body 22. By means of the clamp elevator cylinder 50, the clamping parts 26-27 are made to clamp the outside surface of the grid 4, thereby fixing the grid to the grid support 20. Next, with the use of the outer spring manipulator 30, the outer spring 10a of the grid 4 is retracted from the grid cell 5. This operation will be explained in detail with reference to FIG. 5. In this figure, to simplify the illustration, at the topmost section of the figure, (a) refers to the home-position cam 65 (hp cam 65); (b) refers to the operational-position cam 66 (op cam 66); and (c) refers to the valve cam 67 (v cam 67). First, in the initial stage (in FIG. 5, the state shown in (I), far left of the figure), the first and the second sliding plates 61-62 are pressed toward the grid 4, by the spring force of the coil springs 63-64, and the arc surface of the hp cam 65 is in contact with the inside surface of the through hole 65a, thereby preventing the movement of the first and the second sliding plates 61-62 toward the grid 4. Next, the op cam 65 is rotated 180 degrees around its axis 01 (in FIG. 5, the state shown in (II)), and the flat surface of the hp cam 65 is made to contact the inside surface of the through hole 65a. Because the distance between the flat surface of the hp cam 65 to its axial center 01 is made to be shorter than the distance between its axial center to the arc surface, the first and the second sliding plates 61-62 can now be moved a distance toward the grid 4, thereby allowing a pair of hook stems 31-32 into the slit 11 formed on the outer strap 7a. Next, the v cam 67 is rotated through 180 degrees around its axis 03 (in FIG. 5, the state shown in (III)). Then positions of the protrusions 67a-67b (refer to FIG. 4) formed on the sides of the v cam 67 are interchanged, thereby the first and the second sliding plates 61-62 are moved relative to each other, thereby squeezing the hook stems 31 and 32, thus engaging the hooks 31a-32a with the outer spring 10a. Next, the op cam 66 is rotated through 180 degrees about its axis 02, and letting the arc surface of the op cam 66 to be in contact with the inside surface of the through hole 66a, and move the first and the second sliding plates 61-62 slightly away from the grid (in FIG. 5, the state shown in (IV)). This allows the outer spring 10a to be retracted from the grid cell 5 by means of hook stems 31-32. In the above step, it is also possible to retract the outer spring 10a by rotating the hp cam 65 to return to the initial position, i.e. rotate the hp cam 65 another 180 degrees. However, in so doing, the amount of movement towards the outside (of the assembly) becomes too large, thereby placing a large strain on the outer spring 10a, causing a plastic deformation and decreasing its holding ability. This is not desirable for these springs. According to the present invention because, the outer spring 10a is retracted with use of the op cam 66, the movement thereof remains within an appropriate amount, thereby assuring the firm holding of the fuel rod 6 by the outer spring 10a. Next, the key transfer cylinder 47 of the inner key manipulator 40 is operated, the key insertion base 43 is moved closer to the grid 4, via extension rod 47a of the cylinder 47, and a plurality of inner keys 12 provide on the base 43 are inserted into the grid 4. Next, the key rotating cylinder 46 is operated, the inner keys are rotated through an appropriate angle (usually 90 degrees) via rack 45 and the pinion 44, thereby retracting the inner spring 10b away from the grid 5. Next, the fuel rods 6 are inserted into the grids by a suitable means to assemble a fuel assembly. At this time, the inner and outer springs 10b-10a are formed on the grid cells 5 are being retracted, therefore, mechanical interference between the fuel rods 6 and the springs is prevented, thereby avoiding the formation of scratches on the surface of the fuel rods 6. Then, the key rotating cylinder 46 is again operated, and the inner keys 12 are rotated, via rack 45 and pinion 44, to return them to the initial position. In this state, the inner springs 10b again protrude out into the grid cell 5, thereby contacting the surface of the fuel rods 6 to provide a firm support thereto. Next, the key transfer cylinder 47 is operated to move the key insertion base 43 away from the grid 4, thereby removing the inner keys 12 from the grid, returning them to the initial position. Next, the op cam 66 of the hook manipulator 60 is rotated through 180 degrees around the axis 02 to return the op cam 66 to the initial position (in FIG. 5, the state shown in (V)). The blocking by the op cam 66 is thus removed; the first and the second sliding plates 61-62 are moved towards the grid 4 by the spring force of the coil springs 63-64; the through hole 65a is made to contact the hp cam 65; thereby permitting the outer spring 10a to protrude into the grid cell 5. In this case, the amount of protrusion is pre-adjusted so that the outer springs 10a would position itself near the surface of the fuel rod 6, therefore, by rotating the op cam 66, the outer springs 10a is automatically positioned near the surface of the fuel rods 6. Next, the v cam 67 is rotated through 180 degrees around the axis 03 to return it to the initial position. By so doing, the positions of the protrusions 67b-67c formed on the side of the v cam 67 are interchanged; the hook stems 31 and 32 are separated; and disengaging the hooks 31a-32a from the outer spring 10a (the state shown in (VI) in FIG. 5). After the above step, the outer spring 10a returns slightly toward the grid side, thus contacting the surface of the fuel rod 6, thereby providing firm holding of the fuel rod 6 in the gird cell 5. Next, the hp cam 65 is rotated through 180 degrees around the axis 01 to return it to the initial position, thus enabling the hook stems 31-32 to be retracted from the slit 11. Next, the clamp elevator cylinder 50 fixed to the frames 24-25 is operated to slightly separate the clamp holding parts 26-27 from the grid 4. Then, the frame locking cylinder 28 is operated to remove the locking rod 28a from the frame 25, thereby disengaging the locking rod 28a from the frame 25. Next, the frames 24-25 are rotated through 90 degrees in the direction around the pin 23 to separate the frames 24-25 so as to clear the top space of the grid 4. The assembled grids 4 with the fuel rods 6 therein can then be suspended and transported to a next processing location. According to the apparatus of the present embodiment, the availability of the outer spring manipulator 30 and the inner spring manipulator 40 provides an advantage that the outer springs 10a and the inner springs 10b formed on the grid 4 can separately and automatically be retracted from the grid cell 5. According to the apparatus of the present embodiment, the inner key manipulator 40 is provided with a known number of inner keys 12 ,and therefore, the inner keys need not be handled manually, thus eliminating the necessity for key quantity management, thereby enabling efficient management of the complex grid assembly operation. The mechanism for rotating the inner keys 12 was constructed of a rack and pinion arrangement in the above embodiment, but it is also permissible to utilize a worm and pinion arrangement. Any arrangement is acceptable so long as it is capable of rotating the inner keys 12 through a specific angle. It is also obvious to replace the rack and pinion arrangement for driving the various cams with a worm and pinion arrangement. Further, the present invention is not limited to the embodiment presented above, and many variations are possible within the scope defined by the claims which follow. |
052232069 | abstract | An improved procedure for producing composite constructed nuclear fuel containers for service in water cooled nuclear fission reactors is disclosed. The improved production procedure maximizes the advantageous characteristics of the respective components of the composite unit. The procedure of the invention comprises heat treating the two components of a tube stock and liner stock separately prior to their assembly. |
description | The present invention relates generally to ion implantation systems, and more specifically to apparatus and methods for improved frequency and phase control and calibration in an ion implantation system utilizing digital frequency and phase synthesis techniques. In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities. High energy (HE) ion implanters are used for deep implants into a substrate in creating, for example, retrograde wells. Implant energies of 1.5 MeV (million electron volts), are typical for such deep implants. Although lower energy may be used, such implanters typically perform implants at energies between at least 300 keV and 700 keV. Some HE ion implanters are capable of providing ion beams at energy levels up to 5 MeV. A LINAC (LINear ACcelerator) is often used to accelerate the ions to achieve these high energy levels required at the wafer. A LINAC is a chain of accelerating assemblies (e.g., stages or slices), applied usually in a straight line. When a beam of ions is accelerated by a LINAC, and applied to a semiconductor substrate to implant the ions into the surface of the semiconductor substrate or wafer, we call the process “ion implantation”. Digital frequency synthesis (DFS) and digital phase synthesis (DPS) are techniques for creating continuous waveforms with high precision and high reproducibility. Their use in communication systems dates from the mid-1970s, and today they are an integral component in nearly every modem at any communication speed. The two methods taken as a whole are frequently called DDS (Direct Digital Synthesis). This powerful method of phase synthesis has also been applied to research type linear accelerators, where it replaced less accurate analog control systems or was incorporated into digital-signal processing (DSP) systems that have accreted significant circuit functionality to simplify and reduce the physical size of the implementation of the LINAC control system. The control of the many electrode phases in a LINAC used as an ion-implantation process tool in a production environment, however, introduces phase-control challenges not common to research accelerators. For example, the specific set of data representing the operating electrode voltage amplitudes and phases for the entire accelerator system (a “dataset”) may need to be reproduced on multiple tools in multiple locations, and the dataset may need to be applied and brought to a fully operational state on the tool quickly. It is particularly important that this dataset be quickly reproduced on a production LINAC when multiple ion implantation processes are applied to the same substrates (e.g., wafers) in what is commonly called a “chained” implant process. In addition, because manual calibration methods are presently used, the ability to transport and implement a dataset among two or more otherwise similar LINAC-based ion-implantation machines is affected by the accuracy with which the non-variant “static” component of the phase errors of the many electrode voltages have been removed from the system during calibration. Such manual phase and amplitude calibrations induce a “human factor” of measurement variations during the calibration process generating machine-specific phase delay errors. Referring to FIG. 1, a typical high energy ion implanter 10 is illustrated, having a terminal 12, a beamline assembly 14, and an end station 16. The terminal 12 includes an ion source 20 powered by a high voltage power supply 22. The ion source 20 produces an ion beam 24 which is provided to the beamline assembly 14. The ion beam 24 is then directed toward a target wafer 30 in the end station 16. The ion beam 24 is conditioned by the beamline assembly 14 which comprises a mass analysis magnet 26 and a radio frequency (RF) LINAC 28. The mass analysis magnet 26 passes only ions of an appropriate charge-to-mass ratio to the LINAC 28. The LINAC 28 includes a series of resonator modules or acceleration stages 28a-28n, each of which further accelerates or decelerates ions from the energy they achieve from prior stages. The accelerator stages are individually energized by a high RF voltage which is typically generated by a resonance method to keep the required average power reasonable. The linear accelerator stages 28a-28n in the high energy ion implanter 10 individually include an RF amplifier, a resonator, and an accelerating electrode. The resonators, for example, operate at a frequency of, for example, 13.56 Mhz, with a voltage of about 0 to 150 kV peak-to-peak, in order to accelerate ions of the beam 24 to energies over one million electron volts per charge state. As the ion beam 24 travels through the various accelerator modules or stages 28, some of the ions therein are properly accelerated, whereas others are not. Inefficiencies in ion transport are increased by the errors produced by inaccuracies in the phase calibrations of the electrodes as well as the phase synchronization between the electrodes. It is necessary to precisely control the frequency and phase of each electrode during implantation of high-energy ions onto a workpiece, such as a semiconductor product. It is important in a production environment, that the dataset representing the electrode voltage amplitudes and phases for an accelerator of an ion implantation system be quickly reproduced and be made fully operational on multiple tools in multiple locations. This is particularly important when the dataset is reproduced on a production LINAC during a “chained” implant process. Accordingly, there is a need in the production environment for an improved HE LINAC-based ion implantation device, utilizing the advantages of direct digital synthesis DDS and a means of automatic phase and amplitude calibrations that avoids the need for error prone manual calibration methods. The present invention is directed to a high-energy linear accelerator based ion implanter that achieves improved frequency and phase control as well as improved efficiency, using direct digital synthesis (DDS). The goals of the present invention are further achieved, in part, by using an automated phase calibration system and method disclosed herein. The DDS control system uses digital frequency synthesis or DFS in the master oscillator, while digital phase synthesis or DPS is used to control and synchronize the voltage phase to each RF electrode of the multi-stage accelerator. The DDS control systems and calibration methods of this technique ensure that the ions are efficiently controlled and accelerated to the target wafer. Preferably, the DFS and DPS controls are centralized utilizing a single integrated circuit (chip) implementation. However, several multi-chip configurations and a few distributed implementations are also illustrated herein, and other such implementations are also anticipated in the context of the present invention. Thus, the invention provides significant advantages over conventional ion implantation device control apparatus and methodologies. As indicated previously, the control of the many electrode phases in a LINAC used as an ion-implantation process tool in a production environment introduces several phase-control challenges not common to research accelerators. For example, the specific set of data representing the operating electrode voltage amplitudes and phases for the entire accelerator system (a “dataset”) may need to be easily reproduced on multiple tools in multiple locations, and the dataset may need to be applied and brought to a fully operational state on these tools quickly. It is particularly important that this dataset be quickly reproduced on a production LINAC when multiple ion implantation processes are applied to the same substrates (e.g., wafers) in what is commonly called a “chained” implant process. DDS is uniquely capable of providing this inter-tool dataset matching together with fast and accurate electrode-phase dataset changes. The advantages of DDS for use in a production ion-implantation process tool can be better assured by incorporating an automated method of electrode voltage phase and amplitude calibration, to eliminate the “human factor” of measurement variations during the calibration process that minimizes machine-specific phase delay errors. In one preferred embodiment of the invention, the variable phase-delay elements of the control system for the LINAC in the ion implantation machine are implemented as a DDS controller coupled to an energy source and adapted to digitally synchronize the frequency and phase of the electric fields of each stage in the linear accelerator. The DDS controller comprises a plurality of DPS circuits individually connected to one of the plurality of RF electrodes and used to modulate the phase of the electric field applied to each RF electrode. The DDS controller further comprises a master oscillator (typically a quartz-crystal oscillator) driving a digital frequency synthesis DFS circuit element which generates a continuous stream of n-bit binary values that represent the phase at each instant in time, of the desired LINAC operating frequency. The DFS circuit element is connected to the plurality of DPS circuits and is adapted to digitally synthesize a master frequency and phase to the DPS circuits. Each DPS circuit controls an RF electrode of a stage of the multi-stage accelerator (LINAC). In another aspect of the invention, the DDS controller further comprises a phase locked loop (PLL) circuit connected between one of the plurality of DPS circuits and a corresponding one of the plurality of RF electrodes. In yet another aspect, the master oscillator comprises a digital accumulator and a look-up table adapted to digitally synthesize a master frequency and phase for each of the DPS circuits, by reconstructing digitally calculated samples derived from the look-up table, by associating the phase of each sample to a corresponding voltage amplitude. The accumulator may comprise a summation circuit and a digital storage register for accumulating sample values. In still another implementation aspect, the DPS phase controls are centrally located within a single chip. In accordance with a further aspect of the invention, the DPS phase control circuits or the output registers of the DPS phase controls are uniformly located at the perimeter of a chip. In another aspect, the output signals of the DPS phase control circuits are uniformly spaced and separated by a common ground or another such supply terminal at the perimeter of the chip. In yet another aspect, the DDS controller is configured such that the output signals of the DPS phase control circuits comprise differential outputs from a chip. In another aspect of the invention, a phase calibration system for an ion implanter comprises a phase detector having an electrode voltage signal input to a first attenuator and a reference phase signal input to a second attenuator. The signals are mixed by a linear phase detector (e.g., implemented as a double balanced mixer (DBM) and terminated into a resistor). The resulting mixed signal is lo-pass filtered to provide a phase error signal representing the phase difference between the electrode voltage signal and the reference signal. The calibration system further comprises a voltage amplitude detector adapted to receive the electrode voltage signal and to provide an electrode voltage amplitude signal used for the voltage calibration of the electrode voltage signal. In yet another aspect, the phase error signal and the electrode voltage signal are connected to a computer measurement and control system adapted to provide phase calibration and amplitude compensation for the electrode voltage signal. The phase calibrations may thus be performed autonomously by the phase calibration system and computer measurement and control system to eliminate the more error prone manual calibrations which were previously done. Thus, a HE ion implantation system is more accurately and efficiently controlled using the DDS techniques and calibration methods. To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout. A DDS controller is provided for digital frequency and phase control of the RF electrodes in a high-energy multi-stage linear accelerator (LINAC) based ion implantation system. The DDS control system may be employed in the accelerating stages of the linear accelerator to provide precise control of the phase of the voltage applied to the individual electrodes, such that the desired implantation energy is achieved with a minimal loss of ions in the linear accelerator. The DDS controller includes digital frequency synthesis (DFS) and digital phase synthesis (DPS), and may be implemented in a single chip configuration to minimize phase delay errors. The DDS controller may also utilize differential outputs to minimize cross-talk and phase deviations that may result therefrom. The invention further includes automated phase calibration apparatus and methods for further improvement of electrode voltage control and for enabling a data set of calibration values which may be used to achieve operation of the implanter at a predetermined calibration point. The present invention will now be described in the context of an ion implanter and in association with the following drawings. Referring now to FIG. 2, an ion implanter 100 is illustrated, having similarities to the conventional implanter of FIG. 1, and as such need not be completely described again for the sake of brevity. Ion implanter 100 comprises an ion source 102, a mass analyzer 104, a linear accelerator 110, and an end station 120. The ion source 102 produces an ion beam 24 which is conditioned for acceptable mass and energy by the mass analysis magnet 26 of the mass analyzer 104. The mass analysis magnet 26 passes only ions of an appropriate charge-to-mass ratio to the LINAC 110. The ion beam 24 is then accelerated to a desired energy state by the radio frequency (RF) linear accelerator LINAC 110. The ion beam 24 is then directed toward a target workpiece or wafer 30 in the end station 120. The LINAC 110 includes a series of acceleration stages 28a-28n, which incrementally accelerate ions of the beam 24 to higher energy levels as the ions traverse the length of the LINAC 110. The accelerator stages 28a-28n are individually energized by a high RF voltage which is typically generated by a resonance method. In accordance with the present invention, a DDS controller 130 controls the stages 28a-28n of the LINAC 110. The DDS controller 130 comprises a master oscillator implemented in a DFS circuit 134 (e.g., a quartz-crystal oscillator) that provides a master frequency signal 136 comprising an N-bit phase word to a plurality of DPS circuits 138 or phase delay elements that individually control the phase of the master frequency signal 136 to an RF electrode within each of the stages 28a-28n. In particular, the variable phase-delay elements 138 of the control system 130 for the LINAC 110 in the ion implantation machine 100 are implemented as a DDS: that is, a master oscillator signal 136 drives a digital frequency synthesis or DFS circuit element 134 which generates a continuous stream of n-bit binary values that represent the phase at each instant in time, of the desired LINAC operating frequency. FIG. 3 illustrates an “N” stage LINAC 300, through which an ion 304 may be accelerated as part of an ion beam 24. LINAC 300 further includes a LINAC control section 301 comprising an ion source 102 and acceleration stages 28a-28n. Each of the acceleration stages 28a-28n contain RF electrodes E1-EN which is individually controlled by variable phase control circuit 310, a gain stage (or amplifier) 320 via a high voltage connection 330 to one of the RF electrodes E1-EN. In the LINAC 300 of FIG. 3, as the ion 304 travels ballistically from left to right, it drifts into the first acceleration gap (G1A), where it is accelerated (or decelerated) by the instantaneous voltage of a high voltage RF (Radio Frequency) electrode E1. The ion 304 drifts through the electrode E1, and enters gap G1B where it is again accelerated or decelerated as a result of the instantaneous voltage present across gap G1B before the ion 304 enters the low-field region of the next inter-cavity drift tube 340. The ion 304 continues to propagate through all N stages 28a-28n of acceleration, ending up with a total energy that may be approximated as the original energy of the ion (E0) plus the sum of the instantaneous voltages at each gap G1A-GNB:EFINAL(N)=E0+(i=0−N)Σ(EGiA−EGiB) a) (Wherein, equation “a” above, indicates a summation of the quantity (EGiA−EGiB) is performed over the range of “i” from 0 to N.) If it is desired to maximize the energy transferred to the ion 304, it is apparent that it is desirable that EGiA and EGiB (the voltages present at electrode Ei), while the ion 304 is being accelerated in the first gap GiA and second gap GiB, should be opposite polarity so that they sum to a greater value. To achieve this, the RF voltage waveform at electrode Ei must be delayed by a time ti that approximates the ballistic transition period of the ion from the center of the previous electrode E(i−1) to electrode Ei. This travel time for the ballistic ion may be re-expressed as a phase delay on electrode Ei relative to electrode E(i−1), where (very approximately):Phase Delay=φdi[degrees]˜360[deg/cycle]·fM[cycles/sec]·t[sec] b) Thus, a set of electrode voltages VN and phase delays φN can be conceived to achieve a specific total final ion energy for a specific initial ion energy, charge, and mass. In practice, many practical real-world influences cause the RF voltage (Vi)'s phase (φi) to be other than predicted, as will be shown in FIG. 4. For example, FIG. 4 illustrates another “N” stage LINAC 400, through which an ion 304 may be accelerated as part of an ion beam 24. LINAC 400 is similar to that of implanter 300 of FIG. 3, and as such need not be completely described again for the sake of brevity. LINAC 400 further includes a control section 401 comprising an amplifier 402 for amplifying the master frequency signal fM 136 to a higher power level master frequency signal fM 404 (e.g., about 25 mW) applied to a power divider 406, for example, a transformer with multiple secondary outputs of 406 extending from stage i−1 to stage i+2 or to stage i=n. In this example, each stage comprises a power divider output cable 408 which feeds a copy of the master frequency signal fM 136 to a phase shifter 410 and a phase lock loop PLL 420 via PLL output cable 424 to gain stage 426 that may comprise an amplifier and a resonator, for example, to drive the RF electrodes E1-En of acceleration stages i−1 to i=n 428 via high voltage HV connection 430. A pick-up electrode 440 receives a sample of the voltage Ei which is returned to PLL 420 via pick-up feedback cable 444 to close the phase control feedback loop. Thus phase shifter 410 provides a phase output signal 414 having the selected phase which is maintained by PLL 420 and the other elements of the feedback circuit. FIG. 4 further illustrates a list of candidate delays between electrodes Ei and E(i+1). Two stages of the overall LINAC 400 are illustrated, although 6-12 stages, for example, may actually be utilized. Operationally, in this embodiment, the RF power amplifiers or “gain” stage 426 is inside a phase locked control loop or PLL 420 so that the variations in phases in the forward path (from the PLL 420, PLL output cable 424, amplifier/gain stage 426, and HV cable 430 to the electrode Ei) are largely eliminated from consideration, leaving the following residual inter-electrode errors: 406a) At the Power divider 406, there are static (fixed) circuit related phase offsets in the power divider circuit 406, or other such methods of reproducing multiple outputs of the master oscillator signal for use by the N stages 428 of the LINAC 400. 406b) At the Power divider 406, there are also drift” terms in these circuits, for example, but not limited to, thermal variations in signal delay, differences in behavior of circuits due to power supply voltage variations causing changes to signal delays. 408) Variation in the length of cable 408 include variations over the range of temperature of the signal phase due to possible impedance mismatching of the cable impedance Z0 to the input impedance ZIN of phase shifter 410. 410) Static and variable phase delays in the phase shifter 410 include non-linearities of phase control wherein the phase shift may have errors from the precise desired value of the phase due to circuit and component variations and inaccuracies in the control signal, for example. 414) As in 408 and 410 above, static and variable phase offsets in the uncompensated forward signal path or the phase output signal cables 414 from the phase shifter 410 output to the PLL 420 input. 420) Variation in the PLL loop behavior of the PLL subsystem 450 manifest themselves as phase offsets (which for modeling purposes are all lumped together herein), including variations in the PLL feedback path 444, and are referred back to the PLL 420 input as lumped static and variable phase offsets. Consider the realities of constructing and wiring the cables within a LINAC ion implanter. There are multiple cables associated with each stage and consider that one model of implanter, for example, the Axcelis GSD/VHE, uses 14 stages. Thus, many delays are associated with cables in this example. In addition, the Axcelis GSD/VHE implanter utilizes a master oscillator with a 13.56 MHz, which is so chosen because this is a frequency reserved by international treaty for industrial use. The delay in a cable is (assuming that the electrical signal in the cable propagates at 66% of the speed of light):1 Degree phase delay=1.6 inches of cable length=0.2 nanoseconds c) Thus, it is easily seen that manufacturing all of the cables associated with the exemplary 14 stages to exacting lengths can be a costly endeavor. Therefore, Axcellis currently employs a different means of controlling the static (non-variant) phase delays by manually calibrating the phase of each electrode. In this manual calibration method, phase offset values are methodically and repeatedly changed, using known test cables and an oscilloscope, until a precise trigger point and an associated phase offset is achieved, wherein each electrode is calibrated to within 1 degree of phase. This phase offset value is communicated to the control electronics associated with each new electrode until the exact same calibration point is achieved, resulting in a table of values of phase offset, having one value for each electrode of the LINAC. Thereafter, control software in the control system of ion implanter uses these calibration phase offsets to adjust the command value of phase at each electrode. This process automatically negates the repetitive static phase shift associated with the multitude of static offsets present within each electrode's control sub-system, as though they were physically manifested as a single lumped value for each electrode. To enable phase control, each electrode generally requires a variable phase element. This element must be capable of setting any arbitrary predetermined phase delay within an initial precision and operational stability suitable for the LINAC's overall operational specifications. For research type accelerators, long term stability and initial repeatability requirements may be very low for several reasons. For example, the uniqueness of a laboratory LINAC may make phase setup tables among similar machines unnecessary. The overall length of time that a LINAC is operated for a single experiment may be small. In addition, the setup time to initially establish operation of a new phase setup table may not be important; the operational scenarios for the LINAC may be limited, requiring little variation in phase setup tables from one experiment to the next. For example, the LINAC used as an injector to a proton storage ring may only be used to accelerate protons (H+) into the ring at a fixed energy (e.g., 103 MeV). Contrast these research LINAC phase stability requirements with those of a LINAC used to accelerate ions in a commercial ion implanter application for implanting dopant species into semiconductor wafers. For example, many production machines must behave similarly and predictably, to allow sharing of phase setup tables, hereinafter “recipes”, among machines in the facility, throughout the company, and among cooperating companies such as partners and foundries. In addition, a single ion implant may require several hours to achieve a particular customer-specified density of implanted ions or “dose”, and the LINAC must be stable to within the customer's energy accuracy requirements. If the final ion energy drifts out of specification undetected, it may impair the functionality of the semiconductor devices being doped. If it is detected during processing, the process may be suspended while the LINAC phase controls are readjusted back into specification. Then, the process may be resumed, resulting in a loss of production time that may require rescheduling other process tasks at considerable expense. Further, each new batch of wafers to be implanted may require a unique recipe, involving variations such as total dose, rate of dose, final ion energy, and ion species (e.g., boron, arsenic, phosphorus). Even within and during processing of a single process, the process may be composed of several sub-processes each with it's own unique recipe. These multiple linked implants are commonly called “chained implants”. As each recipe is loaded and the LINAC is adjusted to achieve the operational specifications called for by the recipe, time delays occur during these many setup events causing loss of availability of the tool and thus lost productivity. Accordingly, the inventor appreciates that the more predictable and repeatable a recipe startup process can be made; the lower will be the operational cost. Thus, it is apparent that fast, efficient, predictable and stable phase control of the LINAC is a critical requirement of a LINAC applied to ion implantation of semiconductors, unique from the usual realm of non-semiconductor environments. Therefore, a discussion of the merits of various phase control methodologies is appropriate in the context of the present invention, to better understand the unique advantages and disadvantages that each method demonstrates. Time Delay Elements One family of circuit topologies for introducing variable phase delay (e.g., 310 of FIG. 3, and 410 of FIG. 4) is known as a variable delay line. This class of methods causes the RF waveform from the master oscillator to be delayed in time, without any inherent knowledge of the phase relationships between the input and output of the time delay device. Recall from our example that at 13.56 MHz, 1° of delay=about 1.6 inches of cable length and about 0.2 nanoseconds of time. Thus, a relay-controlled box of various cable lengths can be constructed to allow a combination of various segments to achieve a desired overall total delay through the assembly. Alternately, an electronic circuit can be devised in an analog continuously variable manner, or as a discrete fixed-step size method to cause the propagation of the master oscillators RF waveform to be delayed by a variable amount. It is critical that this circuit delay be stable and predictable, and yet must achieve a phase delay resolution suitable for the process requirements of a production ion implantation system of about +/−1° resolution minimum. To date, such a time delay circuit has been too expensive, or too variable (e.g., change of delay with temperature) for use in a production ion implantation system. Phase Delay Elements Some electronics circuit phase delay methods are truly phase shifting circuits. Through the interaction of inductances and capacitances with variable attenuating elements, leading and lagging phase signals can be summed to produce a phase delay over the entire 0 to 360° range. FIG. 5 illustrates a quadrature phase modulator 500, which is the most straightforward type of phase shifting circuit, having been used in LINAC control systems for many years. It was such a quadrature phase modulator that was employed in a published paper for control of a research LINAC at about 100 MHz, that was used by Hilton Glavish as a template for the initial prototype control electronics on Eaton's first LINAC beamline, as implemented by Donald Berrian in 1985. Today, a much improved variation of those circuits, which still employ an off-the-shelf commercially available quadrature phase modulator, is utilized to control the phase of the LINAC electrodes in every high-energy ion implantation machine that Axcelis manufactures. Conceptually, and in some instances in actual physical circuit implementations, the master frequency input signal fM 408 from master oscillator 134 is split into 2 paths, through the use of a “hybrid” splitter 510 to produce an unshifted (0°) and a shifted (90°) signal, then each signal is again split into 2 paths through 0° and 180° splitters 515 (equivalent to a linear 1:2 turns ratio transformer with a grounded center tapped secondary), producing a signal stream with ¼ of the input signal, each, at 0°, 180°, 90°, and 270°. These four signals go through independently controllable linear attenuators 520, and the attenuated signals are recombined in power combiner 530 to provide the final phase modulated output 535. For example, if the attenuator 520 in the 0° path is adjusted to provide minimum or no attenuation, and the other attenuators 520 are all adjusted for maximum or complete attenuation, then 0° signal is all that makes it to the output 535. Likewise, each of the other paths can be individually enabled with the other paths disabled, producing solely 90°, 180°, or 270° outputs. Alternately, when the 0° path attenuation is 0.707 (sine of 45°), and the 90° path attenuation is 0.707 (cosine of 45°), with the 180° and 270° paths disabled, these signals will combine to produce an output whose phase is shifted 45 degrees. Likewise, by controlling the several attenuators with signals in a sin(φ) and cos(φ) relationship, any phase shift from 0 to 360° can be produced. However, there are also several error terms that result from this circuit. 1) With only the 0° path enabled, there will be some finite phase shift observed at the output. The baseline or static component of this shift can be eliminated from the forward path phase shift as part of the electrode phase calibration process, that was discussed earlier herein. However, variations with time, temperature, and signal and circuit power supply fluctuations are not eliminated during calibration and will result in phase delay errors when a recipe is initially loaded. 2) The 90° and 180° paths may not be precisely 90° or 180°, due to variations in component values, stray signals coupling between closely spaced components and variation in parasitic stray capacitance and inductance in each circuit path. 3) Variation in performance of each attenuator 520, including the absolute and relative gain, and linearity of the attenuators 520, affect how predictably a particular desired phase angle will be achieved. Using the best available technology today, the phase accuracy is best at the “ordinal points”, (e.g., 0°, 90°, 180°, and 270°) where only a single attenuator dominates the performance. In addition, the error is greatest at the 45° points mid-way between the ordinal points, where two attenuators equally share the signal path. A typical device today achieves a typical overall phase drift for a set point, due to time temperature and power supply variations, of approximately +/−1°, but an initial phase setting error of +/−1.5° (1 sigma/”RMS”, or 1 Std deviation) and +/−4° worst case. However, +/−4° is our established present error threshold level. From the preceding discussion, it may be seen that whenever a recipe is transferred from one LINAC based ion implantation machine to another “identical” machine, then, each electrode phase may have a recipe initialization phase error of about +/−1.73 degrees RMS (=SQRT(2×1.5°)) and +/−8 degrees worst case=(+4°−(−4°)). These initial phase setup inaccuracies are sufficiently large that it may require a specialized “recipe tuning” software method for several minutes to bring the final energy of the ion beam to within the operational parameters required by the recipe for the particular semiconductor doping operation to be performed. Variations of FIG. 5 may be implemented, but such variations achieve the same effect and largely exhibit the same shortcomings and disadvantages. Once a recipe has been re-tuned from one machine to operate acceptably on a second machine, then the revised recipe on the second machine can be stored, and recalled so that the time required to subsequently re-initialize the recipe on the second machine is very quick, because the phase setting errors associated with the quadrature phase modulators are usually very repeatable and reproducible. Digital Frequency Synthesis and Digital Phase Synthesis, or Direct Digital Synthesis (DDS) This frequency and phase control technique has become know as DDS. In DFS (Digital Frequency Synthesis), any repetitive waveform may be “synthesized” by reconstructing it from digitally calculated samples, when those samples are chained together at a sampling rate greater than twice the frequency of the desired output. Then, on average (e.g., after filtering, etc.), the output waveform will be reconstructed. The higher the ratio of waveform sampling rate to the desired output frequency, the more accurate will the reconstructed signal be. Generally, sinusoidal waveforms are of the greatest interest in LINAC devices. For example, FIGS. 6A and 6B illustrate the sampling 600 of a sinusoidal waveform 610 and a DFS circuit 660 for reconstructing the sampled waveform 610. The DFS circuit block 660 comprises a sample source oscillator input 670, a numeric constant (frequency devisor) input 662 to a summation block 664, and a digital storage register 668 that produces a digital phase output word 674. Collectively, the summation block 664, the digital storage register 668, and the feedback path form a digital “accumulator” 672. The DFS circuit 660 also comprises a phase to voltage look-up table 676 and a digital to analog converter (DAC) 678 operable to provide a voltage output 680, which is a digitally sampled representation of the sinusoidal waveform 610. Sinusoidal waveform 610 is sampled at “N” times it's base frequency, which may be shown as:fOUT=fSAMPLES*(1/N) d) The time period between the samples is tsample 602, and the sample value is the instantaneous phase angle 620. Each time a digital storage register 668 is “clocked” by fSAMPLE clock input 670 at rate:fSAMPLE=N(fOUTPUT), e) The register takes on the new sample value I of:Value(i)=Value(i)+(1/N) f) Note: Value is fractional part only [0 . . . <1] carry to 1 or greater is disregarded and the overflow is ignored. This data word “value” is the phase of the output signal waveform, V(t) at time ti. By using a look-up table 676, or another such computational means, the output voltage Vout 680 or V(t=ti) will correspond to the phase data word 674. FIG. 7A further illustrates the instantaneous appearance of the digital output waveform 710 as reconstructed by the DFS circuit 660 of FIG. 6B, which when filtered, and on average resembles the original sinusoidal waveform 610 of FIG. 6A. FIG. 7B illustrates only the most significant bit MSB 760 portion of output 710. It can be observed that the MSB 760 represents those samples 620 which are obtained when the sinusoid 610 goes above zero volts (e.g., +, producing a 1 state output) and when the sinusoid goes below zero volts (e.g., −, producing a 0 state output). Thus, the higher the ratio (N) of sampling rate relative to the output frequency, the greater is the immediate fidelity, or instantaneous accuracy of the reconstruction. A second consideration is the accuracy of the values used in the calculations. Obviously, if the summation, storage register 668 and look-up table 676 are accomplished to an accuracy of about 1 decimal digit (about 3 bits of binary), the samples will be less accurately reconstructed than if the math is done at a higher resolution of about 9 decimal digits (about 30 bits of binary). Therefore, if our goal is to reconstruct a 13.56 MHz frequency from a sampling clock of 231.0 MHz, with an accuracy of better than 0.2 Hz on average, we require:231,000,000 samples/13,560,000 waveform, and 0.2 Hz resolution/13,560,000 output Hz. g) Thus, we need to accomplish our math with an accuracy of:(Word size)=13,560,000/0.2=67,800,000˜67,108,864=2^26=26 bits. h) It is commonplace in digital electronic design to construct circuits using building blocks of 8 bits (or a byte), so a 26 bit circuit would typically be implemented using 4 byte wide circuit elements (32 bits resolution). At 13.56 MHz, this results in a frequency resolution of 0.003 Hz. Digital Phase Synthesis DPS (Digital Phase Synthesis) may build upon our frequency synthesis method above, to add additional phase-shifted outputs. The output 674 of the accumulator 672 of FIG. 6B provides a number equal to the phase output value (0.000-0.999 . . . ) represents the phase angle (0.0-359.99 . . . degrees). Thus, as shown in FIG. 8, a phase control system 800 may be formed, which introduces a phase shifted output 804 by adding an arbitrary phase offset value 802. Phase control system 800 comprises a basic DFS block 660 and a plurality of phase offset registers 810. Each phase offset register 810 comprises a summation element 664 and a phase to voltage look-up table 676, each register 810 operable to receive one of a plurality of phase offset values 802 (offset value 1, 2 . . . N), to provide one of a plurality of phase shifted outputs φREF 680; and φ1, . . . φ2, φN 804. As φREF has no phase shift, it is used as a reference phase signal. FIG. 8 comprises one implementation of a phase control system 800 required for a LINAC. Comparing FIG. 3 to that of FIG. 8 illustrates the following contrast of elements. The LINAC control system 301 of FIG. 3 utilizes a master oscillator, while the phase control system 800 of FIG. 8 utilizes a digital frequency synthesis block DFS 660. In addition, the LINAC control system 301 of FIG. 3 utilizes a variable phase block 310, while the phase control system 800 of FIG. 8 utilizes a phase offset register 810. Although the DFS block 660, as it applies to the master oscillator, is illustrated and described in the context of digital frequency synthesis, it is appreciated that the basic digital frequency synthesis block 660 may be also used with any of the aforementioned methods of phase control for each electrodes phase control. However, it is also possible, in the context of the present invention to utilize digital phase control by partitioning it into either a centralized function together with the DFS, or separately as a stand-alone DDS block (e.g., DFS with DPS). For example, FIG. 9 illustrates a distributed DDS controller 900 comprising a master oscillator or DFS block 134 driving several phase shifters 902, 920, and 940 constructed in different topologies. The first embodiment (type 1) of distributed DFS/DFS includes a variable phase shifter 902 utilizing a DFS block 904 and DPS blocks 906 and 926 to provide the variable phase output 910 to the electrode controls. Phase shifter 902 of FIG. 9 illustrates that it is necessary to incorporate a DFS block in order to develop a digital phase word to which an offset may then be applied. As the master oscillator 134 is the only input, one approach would be to usefSAMPLE=N(fOUTPUT) as the master signal, so that fOUTPUT is locally derived at each point of use (at each phase shifter 902, 920, 940). However, consider a system with many “N” identical blocks of circuit type 1, distributed throughout a LINAC. While each circuit is independently capable of shifting the output to any phase, there is nothing to establish the relative phase output between one distributed type 1 block 902 and the next, as there is no synchronization among the many phase control elements 902. One solution is to perform the phase calibration discussed earlier. However, as soon as power is removed and then restored to any element of the distributed phase control system 900, the calibration of that element is lost and it must be recalibrated, as the digital circuits may not retain any memory of their relationship to the other elements. Another approach is to distribute a second signal along with the master oscillator signal that is used to synchronize the many elements. This signal may even be incorporated into the master oscillator signal as a unique voltage event that would be recognized by the distributed phase shifting elements and utilized to initialize each local element to a “startup phase”. Following the initialization of all phase shifting elements to this “startup phase”, a system phase calibration could be performed. Thereafter, each time it was necessary to resynchronize the many distributed phase shifting elements, the master oscillator would cause the synchronization signal to be sent to all elements, and then a stored copy of the previous phase calibration could be restored to the distributed phase shifting elements to restore all elements to the same synchronous phase output. A second distributed phase shifting implementation is illustrated in FIG. 9 as variable phase shifter type 2, 920. In this second embodiment, a phase locked loop PLL 922 synchronizes the output 930 of the DFS element 904 to the master oscillator signal 136, so that a known fixed and predictable phase relationship is provided between the DFS block 904 output φ, and the master oscillator input 928 to the distributed phase shifting element 920. Then, the phase offset DPS blocks 906 and 926 can create a phase shifted replica of the DFS block 904 output φ. As previously discussed, calibration can be accomplished and restored reliably and repeatably, without the need to distribute any additional synchronization signals. FIG. 10 illustrates an exemplary centralized DPS circuit 1000 for producing multiple phase shifted outputs and the corresponding distributed LINAC electrode control circuits in accordance with the present invention. The centralized DPS circuit 1000 is also useful for identifying sources of phase errors that cannot be eliminated by a single system phase calibration. In the foregoing discussion of digital phase synthesis, it should also be noted, that there are accuracy requirements within the phase offset circuit block. For example, in the LINAC controls, it has been determined that the phase shift needs to be adjustable to a relative resolution of at least three degrees (+/−3°), though better resolution would be beneficial. Changes can be observed in ion beam behavior with relative phase adjustments as small as 1 degree, and so it may be hypothesized that an optimal system would have a control resolution of about ½ degree. This is a resolution of 1:720, and requires ten (10) bits of binary circuitry in the phase offset adder circuit (e.g., 664 of FIG. 10). Again, where digital circuits are commonly specified, utilizing 8-bit byte-wide circuit elements, this would typically be implemented as a 16-bit adder circuit. In addition, the phase look-up table 676 of FIGS. 6B and 8, or its computational equivalent, for example, is not necessary for implementation of phase control of a LINAC. While the summation of the phase offset must be completed to a high accuracy, the most significant bit (MSB) of the summation output may adequately represent the phase of the signal. Recall that the phase control circuit of each distributed electrode phase control element must incorporate a phase locked loop PLL (e.g., 420 of FIG. 4, or 922 of FIG. 10) to eliminate phase error or to reduce the error to below operational requirements. If these distributed PLLs have linear phase detectors that can tolerate fast instantaneous phase errors yet lock to an accurate average phase, and then the fSAMPLED stream of the MSB from the phase offset summation is a viable and adequate signal representing the phase of the desired signal (e.g., sinusoid 610 of FIGS. 6A and 7A). Waveform 710 of FIG. 7A, for example, illustrates the reconstructed waveform of the sinusoid 610, while waveform 760 is a Boolean train of 1's and 0's representing only the MSB of the fOUT calculation. On average, waveform 760 has the desired exact frequency and phase. Provided that the overall system response only responds to the average waveform, then, the MSB is all that is necessary. Advantages and Disadvantages of Various DFS and DPS Embodiments in DDS FIGS. 11, 12, and 13 illustrate several possible system partitioning options for implementing digital phase synthesis in accordance with the present invention. To better understand the problems and issues present in DDS control, the following includes a discussion of some of the sources of phase delay errors and recommendations for preferred embodiments for use of digital phase synthesis in LINAC based ion implantation equipment. The three methods of partitioning and distributing embodied in the LINAC phase delay control circuits of FIGS. 11, 12, and 13, all utilize digital phase synthesis DPS. In addition, all three embodiments have three similar elements; 1) The master oscillator (e.g., 1110, or 134) 2) The variable phase delay DPS (e.g., 926) 3) The electrode PLL (e.g., 1020) FIG. 11, for example, illustrates an exemplary distributed DPS circuit 1100 for producing multiple phase shifted outputs (e.g., VARφ1, VARφ2, . . . VARφN) 1122 and their corresponding distributed LINAC electrode control circuits (e.g., E1, E2, . . . EN) 1020 in accordance with an aspect of the invention. The variable phase shifter circuits (DPS1-DPSN) 1120 are distributed within circuit 1100, and are similar to those of FIG. 9 and as such need not be completely described again. FIG. 12 illustrates an exemplary centralized DFS and DPS circuit 1200 implemented in a multi-chip (e.g., U1, U2 . . . Un) 1204 configuration within a DDS control 1210 in accordance with another aspect of the present invention. Again, the variable phase shifter circuits 1204 function similar to those of FIGS. 9 and 11, except that the PLL and DFS circuits are simplified into a combined PLL & DFS circuit 1212 within each of the multiple chips U1-Un 1204. FIG. 13 illustrates an exemplary DDS controller 1300 implemented in a centralized single-chip DPS circuit (U1)1310 configuration in accordance with still another aspect of the present invention. The phase accuracy of the electrode phase locked loop control 1020 is identical and common to all three embodiments indicated above, and will therefore be ignored in the following discussion. The embodiments of FIGS. 11, 12, and 13 share a similar variation in the phase delay differences between otherwise identical master phase distribution elements (e.g., fOUT1, fOUT2, fOUTN) 1012, or phase shifted outputs (e.g., VARφ1, VARφ2, . . . VARφN) 1122 in the illustrations. In FIG. 11, for example, there is a real phase delay variation between the multiple outputs 1012 of the master oscillator circuit 1110 implementation. In FIG. 12, these delays are transferred to and manifest themselves as variation between the outputs within each functional circuit block (illustrated as though each functional circuit block might be implemented as a single monolithic integrated circuit or chip) (e.g., U1, U2 . . . Un) 1204. Likewise, in the DDS embodiment of FIG. 13, there are still real phase delay variations between the several outputs (e.g., VARφ1, VARφ2, . . . VARφN) 1122 of this single chip embodiment. Note, however, that a third class of phase errors is unique to FIGS. 11 and 12 and not present in FIG. 13. This error is the additional phase error introduced by the additional PLL 922 that is required to resynchronize the DPS circuit block (1120 of FIG. 11, or 1204 of FIG. 12) to the master oscillator (e.g., 1110, or 134), in both the distributed DPS 1100 of FIG. 11 and the multi-chip DPS implementation 1200 of FIG. 12. Another way of understanding this last error source is to consider FIG. 12, modified, wherein the first PLL/DPS block (U1) 1204 would have all “N” outputs (e.g., VARφ1, VARφ2, . . . VARφN) 1122, rather than only three outputs within chip (U1) 1204. Thus, as a single chip solution, the inter-chip delay variation, and this source of phase error may be eliminated, as illustrated in the example of FIG. 13. FIGS. 14A, 14B and 14C illustrate the sources of phase error within a single chip embodiment, for example, chip (U1) 1310 of FIG. 13. In practice, there are multiple circuit or chip implementation characteristics that combine to manifest themselves as phase errors between topological and circuit considerations whose embodiments will controllably affect this total inter-circuit phase error. The first controllable element of inter-circuit phase error is the propagation delay between the output 1122 of each DPS element 926 and the leads 1404 of the device 1410. On the left, this is shown graphically, where DPS1 (926) clearly has a long circuit path compared to that of DPSN 926, which has a very short circuit path. DPS2 and DPS3 have other non-negligible path delays. While, in practice, the “static” or “initial” magnitude of these inter-circuit phase delays can be eliminated during the calibration process discussed earlier, the variation in delay in each path, due to temperature, voltages, or other time-variant processes, will not be eliminated. FIGS. 14B and 14C illustrated circuit implementation solutions which will minimize the variation of the inter-circuit delay error. In both of these examples, the goal is to make the initial physical signal propagation delay between the many DPS blocks and the device leads 1404, identical. When these delays are the same, in a single chip implementation, then the physical mechanisms that cause time-variant delay errors will manifest themselves uniformly among the many circuits. The result is that the variations in delays are very similar and therefore cancel each other out, leaving essentially no net inter-circuit phase delay error. The solution of FIG. 14C accomplishes this minimization of the inter-circuit phase delay errors by co-locating all of the DPS elements 926 uniformly within chip 1430 with respect to the device's output signal leads 1404. However, for a chip implementation with many outputs, this may not be practicable due to physical constraints imposed by the chips internal implementation or configuration. Therefore, another more generalized embodiment is show in FIG. 14B, wherein the individual and many DPS elements 926 may be non-uniformly distributed within the chip 1420, but wherein their signals are each re-clocked through output registers 1425. The output registers 1425 are themselves uniformly distributed with respect to the output leads 1404 of the device 1420. Because the register-to-device lead propagation delays within the chip are uniform and similar, they will eliminate any inter-channel phase delay variations. FIGS. 15A and 15B illustrate another circuit consideration of the single-chip implementation, which is the distribution of chips' ground leads with respect to the output signal leads. In the context of the present discussion, “ground” is used to designate any device lead with a direct power or ground connection between the devices lead and the power and ground circuits of the chip associated with the output signal circuits of the chip. In FIGS. 15A and 15B, chip 1510 and 1520, respectively, comprises signals (e.g., SIG 1, 2, 3, 4) having signal outputs 1512. The current into and out of each output signal device lead must return to or originate from the output circuits power supply or ground device leads labeled (GND). In the example of FIG. 15A, output signals SIG3 and SIG4 have close proximity to the ground pin (GND), while signals SIG1 and SIG2 have a greater distance from the ground pin (GND) and the path 1514 to ground or another such supply voltage 1515. Because any longer paths will have greater inductance between the ground lead and the output lead, there will be differences in any delay among the many non-uniformly implemented device output paths. In FIG. 15B, however, each output signal has a ground pin on both sides of it, resulting in uniform output signal inductance and thus, uniform delays. Finally, a third consideration of chip design to reduce inter-circuit phase error is the circuit configuration of the output driver circuit of the chip. FIG. 16A, for example, illustrates an exemplary single-chip DDS controller configuration 1610, wherein each of the plurality of DPS circuits 926 utilize a “single ended” output driver circuit 1612 configuration. As each output signal 1614 transitions from one logic state to the other and back (e.g., from 1 to 0, then back to 1), current flows into or out of the power and ground device leads 1515 of the device 1610. Because these power and ground pins are shared and common to many or all output circuits on the chip 1610, and all device leads have some inductance, small perturbations will occur in all output signals due to changes on all other output signals. This “crosstalk” can manifest itself as a small phase error on each output that will vary depending on its phase relationship to all the other outputs taken individually and as a whole. FIG. 16B illustrates another exemplary single-chip DDS controller configuration 1620, wherein each of the plurality of DPS circuits 926 utilize a differential output driver circuit configuration 1622, which minimizes cross-talk and phase error issues. In principle, a differential output circuit 1622 provides a pair of differential outputs 1624a and 1624b that are identical in design, wherein one output delivers the logic output without inversion (e.g., 1624a), and the other output inverts the output signal (e.g., 1624b). A true differential output circuit implementation will cause the output signals 1624a/1624b to change nearly simultaneously on both the non-inverting output 1624a and the inverting output 1624b. The result is that the output signal current flow into or out of the non-inverting output 1624a and device lead will be equal and opposite of the current flow out of or into the inverting output device lead. Therefore, the net output current change will be nearly zero, and therefore the “crosstalk” into the other signal outputs on the same chip will be minimized. The differential output configuration 1620 of FIG. 16B further illustrates the use of a transformer 1626 that is used to convert the differential output signals into a new single-ended signal 1628. As this conversion is done outside the chip 1620, it can be implemented in a manner that assures negligible crosstalk with the other output signal circuits 926 and 1622. The most common type of cable utilized to transport the phase control output signal to the many electrode voltage phase control PLLs is “coaxial” cable, which is a single-ended medium that does not accommodate differential signals. Lastly, by utilizing a transformer whose primary is connected solely to the differential output device leads, the currents flowing on the non-inverting and the inverting signal output leads must necessarily be equal and opposite in polarity, assuring that the chip current cancels out in an optimum way. Referring now to FIGS. 17A and 17B, another aspect of the invention provides circuits and an improved method for phase calibration for LINAC systems used in ion implantation equipment. Upon reviewing the inter-electrode phase calibration method discussed previously, the observation method of the phase error during the calibration process is for a human test technician to visually observe the relationship between the reference phase and the electrode voltages phase as a waveform displayed on an oscilloscope. This necessarily introduces a small calibration error, when the technician views and interprets the relationship of each electrodes voltage phase in succession, one after the other. While this variation of signal interpretation may be small, it cannot be eliminated as long as it is a visual interpretation of a manual calibration operation. In accordance with the present invention, an improved circuit embodiment replaces the oscilloscope with an electronic circuit whose output signal is a representation of the phase angle between the reference phase signal and the phase of the electrodes voltage being calibrated. In this exemplary embodiment, the phase detection circuit will have a preferred output signal voltage that represents a preferred input signal phase relationship at which systemic measurement errors (including variations in signal amplitude) are minimized. FIG. 17A, for example, a circuit commonly known as a “double balanced mixer” (DBM) is used as a phase detector 1700. The phase detector 1700 compares the phase difference between an electrode voltage signal 1702 which is to be calibrated and input to attenuator 1706, to a reference phase signal 1704 input to attenuator 1708. When the frequency of both inputs of the RF port “R” and the local oscillator port “L” is identical, and when the signal voltages on the R and L ports are within the recommended signal values specified by the manufacture of the device (e.g., a commercially produced device is a type SRA-1, manufactured by Mini-Circuits, of Brooklyn, N.Y.), then the signal voltage on the intermediate frequency output “I” is:“I” signal voltage˜cosine (phase difference between ports R and L)·(signal amplitude at port R) i) When the phase of the signals on the R and L inputs differs by exactly 90 degrees, then the “I” signal voltage is zero, independent of the signal amplitude at the R input. In the example of FIG. 17A, attenuating circuit elements 1706 and 1708 are located in both the “R” and “I” signal input paths 1702 and 1704, respectively, to assure that appropriate signal voltages are manifested at the “R” and “I” ports of a mixer 1710, and to reduce the amplitude of signal reflections in the “R” and “I” signal paths caused by any impedance mis-match caused by the non-linear behavior of the DBM circuit. The “I” output signal in this embodiment is terminated into a resistor RT 1714, whose value is approximately equal to the characteristic impedance of port “I” signal 1720 path (e.g., typically 50 ohms). The signal 1720 is then filtered by a low-pass filter 1724 to eliminate high frequency components associated with the “R” and “L” input frequency, its harmonics, and the instantaneous variations in phase that may be present in a system whose “L” reference signal (1702) and/or “R” electrode voltage signal (1704) is created by a circuit employing DDS and/or DPS methods. The filtered output signal 1728 is measured by an analog-to-digital converter ADC, whose output signal is a numerical representation of the signal voltage at the output of the filter 1724. A computer based control system (not shown) receives the measured numeric value of the phase, and iteratively sends commands to the variable phase delay circuit element of the electrode control system whose phase is being calculated. By successively measuring the DBMs phase output signal and then adjusting the variable phase delay to the electrode being calibrated, the system can accurately identify the precise variable phase value that precisely results in a zero output signal. The corresponding value of the variable phase element is then stored into memory in the control system as the calibration value. Subsequently, this calibration value is utilized during normal (non-calibration) operation of the LINAC as an offset value to negate the otherwise uncompensated forward path phase delays in the electrodes voltage phase control system. A DBM has an output voltage that is “zero” at both +90° and −90° (ie. 270°) phase angle between the R and L inputs of the mixer 1710. By monitoring the phase angle signal value together with the phase command sent to the variable phase element in the electrode's voltage phase control system, the computer software can be made to identify which polarity of “null” (zero) it is monitoring. In this way, the system may be designed to respond to only one polarity by adjusting the variable phase by 180 degrees, if necessary, to finally achieve a precise null at only one specified phase. FIG. 17B illustrates an exemplary electrode voltage amplitude and phase calibration circuit 1730 similar to the double balanced mixer 1700 of FIG. 17A, which further includes a voltage amplitude detector circuit 1732 used in accordance with the invention. The voltage amplitude detector circuit 1732 is operable to provide an output signal 1734 that is uniformly and accurately related to the magnitude of the electrode voltage signal 1702 which is being calibrated. Alternately, either separately or in combination with the electrode voltage phase signal 1728, the signal output 1734 of the voltage amplitude detector 1732 can be input to a computer measurement system 1740 (not shown), wherein an ADC converts the signal voltage into a numeric value. This numeric representation of the electrode voltage amplitude is utilized by the control system computer together with software instructions, to cause command signals to be sent to the electrode voltage amplitude control circuits. The process is repeated iteratively by successively reading the value of the voltage amplitude signal and then adjusting the value of the command sent to the electrode voltage amplitude control circuit, until a precise predetermined value of the electrode voltage amplitude signal is observed. The values of the predetermined value of the electrode voltage amplitude (or electrode voltage amplitude “calibration point”) and the value of the command that was computed to cause the system to precisely achieve operation at the calibration point are then used to compute one or more calibration values. These calibration values are then stored into the control system memory. During normal operation of the LINAC (non-calibration mode), these calibration values are retrieved by the system control software and used to adjust the commanded electrode voltage amplitude at each electrode to achieve a voltage amplitude whose value is very precisely related to the voltage amplitudes on the other LINAC electrodes. The term “memory” as used herein may include but not be limited to such data storage elements as static or dynamic memory integrated circuits (ICs), disk drives including fixed and removable rotating magnetic or optic storage elements, FLASH memory, magnetic diskettes, tape, or their storage functional equivalent elements. Further, the term “software” includes information stored as firmware in devices such as memory ICs and programmable logic devices such as EPROMs, non-volatile RAM ICs, FLASH memory, diskettes, or EEPROM. In summary: DDS is uniquely capable of providing the inter-tool dataset matching together with fast and accurate electrode-phase dataset changes, particularly during “chained” implant processes. The advantages of DDS for use in a production ion-implantation process tool can be better assured by incorporating an automated method of electrode voltage phase and amplitude calibration, to eliminate the “human factor” of measurement variations during the calibration process that minimizes machine-specific phase delay errors. In one or more embodiments of the present invention (e.g., FIG. 2), the variable phase-delay elements 138 of the control system 130 for the LINAC 110 in the ion implantation machine 100 are implemented as a DDS, wherein a master oscillator signal 136 is derived from a digital frequency synthesis or DFS circuit element 134 which generates a continuous stream of n-bit binary values that represent the phase at each instant in time, of the desired LINAC operating frequency. The frequency synthesis circuit is an accumulator circuit structure, wherein a clock signal (derived from the master oscillator) causes a register to store the current phase value, as n bits of data. This current phase value is summed with a usually fixed value (equal to the ratio of the desired LINAC operating frequency to the clock frequency applied to the register, also n bits in precision) and fed back into the register's input. Upon the next clocking of the register, the register's output signal stores a new value equal to the original phase value plus an additional phase angle equal to the ratio aforementioned, with a binary precision of n bits. As each successive clock signal is applied to the register, the output phase signal advances in phase by this same value. This signal is called the “master digital phase signal”. The value of binary precision, n bits, is chosen to achieve the frequency accuracy required, and in one embodiment, for reasons of common circuit design methods, n is chosen to be 32, being implemented as four sets of 8-bit circuit elements, which exceeds the 26 bits minimum resolution desired for the LINAC in the ion implantation machine. These phase values are applied to the input of several digital phase synthesis circuit elements, one of which is directly associated with the phase-control circuit path of one of the many RF (radio frequency) accelerating electrode voltages in the LINAC. These phase synthesis elements use a binary adder of m-bit precision, to add a phase offset to the master digital phase signal. The value of binary precision, m bits, is chosen to achieve the phase accuracy required for the particular LINAC system, and one embodiment, for reasons of common circuit design methods, m is chosen to be 16, being implemented as two sets of 8-bit circuit elements, which exceeds the 9 bits minimum resolution desired for the LINAC in the ion implantation machine. The output of each digital phase synthesis element (the “electrode phase control” signal) is then applied as the input signal to the phase locked loop (PLL) circuit that causes the phase of the voltage at the LINAC electrode to be precisely controlled to match (or, “lock to”) the value of the electrode phase control signal. In one embodiment, only the MSB (most significant bit) of the digital phase synthesis element is brought out from the circuit for use as the electrode phase control signal. To minimize variations in phase delay between each of the several circuit paths of the digital phase synthesis circuits, due to such factors as variations in propagation delay of the many circuit elements and paths, due to power supply voltage variation, the temperature, and variation of the temperature of and between the many circuit elements, and aging of the many circuit elements, one implementation expresses several methods that may be individually or severally implemented. These implementations achieve reduction of the variations in phase delay, including: causing the several circuits to be implemented into a single integrated circuit to reduce or eliminate the additional phase errors associated with the added PLL circuits required to synchronize a multi-chip implementation; causing the output of each phase-delay generating element within each chip to be so located within the chip so that the signal propagation delays between the internal phase-delay generating element and the device leads of the chip are most nearly equal in value. Another phase delay improvement achieved by the present invention includes causing the many electrode phase control signals to be re-sampled into register circuits so located within the chip so that the signal propagation delays between the re-sampling circuit elements and the device leads of the chip are most nearly equal in value; and assigning the signal output device leads in a symmetrical manner with respect to the physical arrangement of the signal output device leads and the power supply and ground device leads that supply and return the current from each signal output circuit element, so that the mutual coupling of signal currents between the several device output leads is most nearly equal in value, and to cause the resulting phase errors among and between the several output circuit paths to be minimized. Finally, the phase delay improvement achieved by the present invention includes using differential chip output circuit elements as superior to single-ended chip output circuit elements, to minimize phase errors due to cross-talk amongst the several chip output circuits due to the power supply and ground current circuit paths in common among the several outputs, and which common circuit paths have inductance which may increase said phase errors. Even with the previously described circuit embodiments, the ability to transport and implement a dataset among two or more otherwise similar LINAC-based ion-implantation machines is affected by the accuracy with which the non-variant “static” component of the phase-errors of the many electrode voltages have been removed from the system by a calibration method. In another embodiment, the computer and software-based control system of the ion implantation machine are used together with a phase measurement circuit, to automate the calibration of each electrode's voltage phase. This embodiment thus reduces the required skill-set of the person performing the calibration, who would otherwise need to be knowledgeable in the operation of an oscilloscope or other phase-error measurement instrument to observe the phase error, and eliminates the human-factor of measurement error that occurs when the human makes an observation of the phase error and causes it to be entered into and retained by the control system as a calibration coefficient. In another embodiment, the computer and software-based control system of the ion implantation machine are used together with an electrode voltage magnitude measurement circuit, to automate the calibration of each electrode's voltage amplitude. This amplitude measurement, either separately or simultaneously with the calibration of the electrode's voltage phase, again reduces the skills required and minimizes the errors that otherwise might occur due to manual interaction with the control system. Thus, the invention provides significant improvement over conventional apparatus and methodologies for accelerating ions in an ion implantation system. Although the invention has been shown and described with respect to a certain aspects and implementations, it will be appreciated that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure, which performs the function in the herein illustrated exemplary implementations of the invention. In this regard, it will also be recognized that the invention includes a computer-readable medium having computer-executable instructions for performing the steps of the various methods of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “includes”, “including”, “has”, “having”, and variants thereof are used in either the detailed description or the claims, these terms are intended to be inclusive in a manner similar to the term “comprising”. |
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claims | 1. A neutron capture therapy system, comprising:an accelerator configured to generate a charged particle beam;a neutron generator configured to generate a neutron beam having neutrons after an irradiation by the charged particle beam; anda beam shaping assembly configured to shape the neutron beam, wherein the beam shaping assembly comprises a moderator configured to moderate the neutron beam generated by the neutron generator to a preset energy spectrum and a reflecting assembly surrounding the moderator;wherein the reflecting assembly comprises a plurality of reflectors configured to guide deflected neutrons back to the neutron beam to increase an intensity of the neutron beam in the preset energy spectrum and a supporting member configured to hold the plurality of reflectors. 2. The neutron capture therapy system according to claim 1, wherein the reflecting assembly further comprises a plurality of cells correspondingly forming a plurality of cores, each of the plurality of cells forms one of the plurality of cores, the plurality of cores have a plurality of accommodating spaces, each of the plurality of cores has a corresponding accommodating space of the plurality of accommodating spaces, the plurality of reflectors are correspondingly disposed in the plurality of accommodating spaces of the plurality of cores, and the plurality of cores are connected to form the supporting member. 3. The neutron capture therapy system according to claim 2, wherein the supporting member is integrally formed, and the plurality of reflectors comprise a material disposed in the plurality of accommodating spaces of the plurality of cores. 4. The neutron capture therapy system according to claim 2, wherein the reflecting assembly further includes a top plate, a bottom plate disposed opposite to the top plate, and side plates connecting to the top plate and the bottom plate and surrounding the plurality of cores, wherein the plurality of cores, the plurality of reflectors disposed in the plurality of accommodating spaces of the plurality of cores, the top plate, the bottom plate, and the side plates correspondingly form a reflecting module. 5. The neutron capture therapy system according to claim 4, wherein the plurality of cores, the top plate, the bottom plate, and the side plates comprise a material with a low neutron absorption cross section and a low activity with neutrons, and a proportion of a total volume of the plurality of cores, the top plate, the bottom plate, and the side plates in a volume of the plurality of reflectors is less than 10%. 6. The neutron capture therapy system according to claim 5, wherein the plurality of reflectors comprise lead, and the plurality of cores, the top plate, the bottom plate, and the side plates comprise lead-antimony alloy. 7. The neutron capture therapy system according to claim 6, wherein an equivalent total antimony content in the lead-antimony alloy is less than 1%. 8. A neutron capture therapy system, comprising:a beam shaping assembly configured to shape a neutron beam having neutrons, wherein the beam shaping assembly comprises a moderator configured to moderate the neutron beam to a preset energy spectrum, a reflecting assembly surrounding the moderator, and a shielding assembly surrounding the reflecting assembly;wherein the shielding assembly comprises a supporting member configured to hold the reflecting assembly and a plurality of shieldings arranged in the supporting member. 9. The neutron capture therapy system according to claim 8, wherein the shielding assembly further comprises a plurality of cells correspondingly forming a plurality of cores, each of the plurality of cells forms one of the plurality of cores, the plurality of cores have a plurality of accommodating spaces, each of the plurality of cores has a corresponding accommodating space of the plurality of accommodating spaces, the plurality of shieldings are correspondingly disposed in the plurality of accommodating spaces of the plurality of cores, and the plurality of cores are connected to form the supporting member. 10. The neutron capture therapy system according to claim 9, wherein a cross section of each of the plurality of cores is a hexagon. 11. The neutron capture therapy system according to claim 9, wherein the supporting member is integrally formed, and the plurality of shieldings comprise a material disposed in the plurality of accommodating spaces of the plurality of cores. 12. The neutron capture therapy system according to claim 9, wherein the reflecting assembly further includes a top plate, a bottom plate disposed opposite to the top plate, and side plates connecting to the top plate and the bottom plate and surrounding the plurality of cores provided outside the supporting member, wherein the plurality of cores, the plurality of shieldings disposed in the plurality of cores, the top plate, the bottom plate, and the side plates correspondingly form a shielding module. 13. The neutron capture therapy system according to claim 9, wherein the plurality of shieldings comprise lead, and wherein the plurality of cores, the top plate, the bottom plate, and the side plates comprise a material with a low neutron absorption cross section and a low activity with neutrons. 14. The neutron capture therapy system according to claim 13, wherein a proportion of a total volume of the plurality of cores, the top plate, the bottom plate, and the side plates in a volume of the plurality of shieldings is less than 10%. 15. The neutron capture therapy system according to claim 8, wherein the reflecting assembly comprises a plurality of reflectors configured to guide deflected neutrons back to the neutron beam to increase an intensity of the neutron beam in the preset energy spectrum, and the supporting member configured to support the plurality of reflectors, the plurality of reflectors comprise lead, and the supporting member comprises aluminum alloy or lead-antimony alloy. 16. A neutron capture therapy system, comprising:a beam shaping assembly configured to shape a neutron beam having neutrons, wherein the beam shaping assembly comprises a moderator configured to moderate the neutron beam to a preset energy spectrum and a reflecting assembly surrounding the moderator;wherein the reflecting assembly comprises a plurality of reflectors configured to guide deflected neutrons back to the neutron beam to increase an intensity of the neutron beam in the preset energy spectrum and a plurality of cells configured to support the plurality of reflectors, the plurality of cells correspondingly form a plurality of cores, each of the plurality of cells forms one of the plurality of cores, each of the plurality of cores has an accommodating space, the accommodating space is configured to receive one of the plurality of reflectors or to receive a material configured to form a shielding, and the shielding is configured to shield the neutrons. 17. The neutron capture therapy system according to claim 16, wherein the plurality of cores are connected to form a supporting member, the reflecting assembly further includes a top plate, a bottom plate disposed opposite to the top plate, and side plates connecting to the top plate and the bottom plate and surrounding the plurality of cores provided outside the supporting member. 18. The neutron capture therapy system according to claim 17, wherein the plurality of cores, the top plate, the bottom plate, and the side plates comprises a material with a low neutron absorption cross section and a low activity with neutrons, and a proportion of a total volume of the plurality of cores, the top plate, the bottom plate, and the side plates in a volume of the plurality of reflectors is less than 10%. 19. The neutron capture therapy system according to claim 16, wherein the plurality of cores are connected to form a supporting member, the supporting member is integrally formed, and the shielding comprises the material deposited in the accommodating space. 20. The neutron capture therapy system according to claim 16, wherein the plurality of cores are connected to form a supporting member, the material in the accommodating space comprises lead, and the supporting member comprises aluminum alloy or lead-antimony alloy. |
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abstract | Corner of each square pipe is molded into a terrace shape having steps. When a basket is constructed by these square pipes, steps of adjoining square pipes are assembled together face to face. Fuel rod aggregates are housed inside the square pipes and in a cells formed between the square pipes. Since the adjoining square pipes are assembled in a staggered arrangement, boundaries of the cells are defined by the walls of the square pipes itself. |
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abstract | A system for radioisotope production uses fast-neutron-caused fission of depleted or naturally occurring uranium targets in an irradiation chamber. Fast fission can be enhanced by having neutrons encountering the target undergo scattering or reflection to increase each neutron's probability of causing fission (n, f) reactions in U-238. The U-238 can be deployed as one or more layers sandwiched between layers of neutron-reflecting material, or as rods surrounded by neutron-reflecting material. The gaseous fission products can be withdrawn from the irradiation chamber on a continuous basis, and the radioactive iodine isotopes (including I-131) extracted. |
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041893476 | claims | 1. In a reactor vessel for pebble beds at high and varying temperatures having a side wall and a base formed of a multiplicity of stacked blocks of heat-resistant material and held together by an outer cylindrical or polygonal ring and supported on a foundation, the base and the side wall, respectively, being formed of a plurality of sectors having substantially vertical, radial parting lines therebetween, said sectors being supported with slight friction on the foundation and being braced against the outer ring, said sectors having boundary surfaces with a pebble bed, support surfaces on the foundation and abutment surfaces against the outer ring, the respective surfaces of said boundary surfaces, said support surfaces and said abutment surfaces having a convex mutual inclination whereby each of said sectors is held together in itself by external forces and is forced by its own weight and the weight of the pebble bed into a definite position. 2. Reactor vessel according to claim 1 including a first group of roller bodies disposed on the foundation and supporting said sectors, and a second group of roller bodies engaging said outer ring and bracing said sectors thereagainst, said rollers being mounted as said first and second groups thereof in respective planes, and being disposed in each sector in, respectively, two planes inclined convexly to one another so as to form two substantially convex surfaces, said two substantially convex surfaces being inclined at the same angle to a vertical symmetry plane of said sector. 3. Reactor vessel according to claim 2 wherein the base is formed with a funnel-shaped opening for discharging fuel pebbles from the pebble bed, and the inclination of the roller-body planes between the base and the foundation is opposite to the inclination of the funnel member which is disposed vertically thereabove. 4. Reactor vessel according to claim 2 including a plurality of discharge outlets for fuel pebbles of the pebble bed formed in the base, a parting line extending radially outwardly from each of said discharge outlets, and an annular parting line extending through the middle of all of said discharge outlets. 5. Reactor vessel according to claim 4 wherein said annular parting line is substantially circular. 6. Reactor vessel according to claim 4 wherein said annular parting line is polygonal. 7. Reactor vessel according to claim 1 wherein the boundary surfaces of at least one of said sectors between the pebble bed and the base are formed of two surfaces of equal size inclined substantially convexly to one another, and the boundary surfaces of at least one of said sectors between the side wall and the pebble bed are formed of two surfaces of equal size inclined substantially convexly to one another, said two substantially convex surfaces being inclined at the same angle to a vertical symmetry plane of the respective sector. 8. Reactor vessel according to claim 1 wherein said sectors of the side wall have a pentagonal cross section, respectively, and one of said boundary surface with the pebble bed and said abutment surface against the outer ring is planar. |
claims | 1. A device for measuring radiation comprising:a radiation detector which generates an analog signal containing pulse components corresponding to a dosage of an inputted radiation;an A/D converter which converts the analog signal into sampled data;a band pass filter which limits the sampled data outputted from the A/D converter within a predetermined frequency band to generate restricted sampled data;an n-th power calculation unit which calculates the n-th power values of the restricted sampled data outputted from the band pass filter, where n is an integer of not less than two;a first smoothing unit which equalizes the n-th power values of the limited sampled data outputted from the n-th power calculation unit within a first time width to generate a first smoothed n-th power value;a data removal equalization unit which evaluates sizes of the first smoothed n-th power values outputted from the first smoothing unit within a second time width, removes a predetermined data removal number of the first smoothed n-th power values based on the evaluation result, and equalizes the first smoothed n-th power values after the removing within the second time width to generate a second smoothed n-th power value;a second smoothing unit which equalizes the equalized n-th power values outputted from the data removal equalization unit to generate a third smoothed n-th power value; anda converter which converts the third smoothed n-th power value outputted from the second smoothing unit into a radiation intensity of the inputted radiation. 2. The device as recited in claim 1, further comprising:a noise characteristics evaluation unit which sends a signal to at least one of the first smoothing unit and the data removal equalization unit to adjust the first time width of the first smoothing unit to be not less than pulse width of a foreign noise, and to adjust the second time width of the data removal equalization unit to be not less than an interval in which the foreign noise is present. 3. The device as recited in claim 2, wherein:the noise characteristics evaluation unit arranges the data removal number of the data removal equalization unit based on a waveform of the foreign noise so that a removal number of the maximum of all the first smoothed n-th power values is equal to a removal number of the minimum of all the first smoothed n-th power values. 4. The device as recited in claim 1, wherein:the data removal equalization unit replaces at least one of the first smoothed values outputted from the first smoothing unit with a values within a predetermined threshold range when the first smoothed value outputted from the first smoothing unit exceeds the threshold range. 5. The device as recited in claim 1, wherein:the data removal equalization unit deletes at least one of the first smoothed values outputted from the first smoothing unit when the first smoothed value outputted from the first smoothing unit exceeds a predetermined threshold range. 6. The device as recited in claim 1, wherein:n is an odd number integer of not less than three. |
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abstract | The present invention provides a reticle 100 for use in a lithographic process. The reticle, in one embodiment, includes a patterned layer 110 located over a reticle substrate. The reticle 100 may further include a test pattern 130 located over the reticle substrate, wherein a portion of the test pattern 130 is within a step-distance of a portion of the patterned layer. In this embodiment, a variance in the test pattern is indicative of a variance in the patterned layer. |
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053655567 | claims | 1. A storage cell for storing elongated objects, comprising: a straight storage channel having a substantially U-shaped cross section and having first and second side walls separated by an opening running otherwise along said channel, said opening having a width sufficient to allow passage of an elongated object therethrough; means for supporting said storage channel in an inclined position relative to a vertical plane; means for supporting said elongated object in said storage channel, said means being arranged at a bottom end of said storage channel; and means for blocking passage of said stored elongated object through said open front of said storage channel, said blocking means being movable from a non-blocking position to a blocking position in response to displacement of said elongated object from a first object position whereat said object supporting means does not support said object to a second object position whereat said object supporting means supports said object, said blocking means being mounted on said storage channel and comprising a rotatable latch which rotates between a first latch position whereat said latch blocks passage of said elongated object through said open side of said storage channel and a second latch position whereat said latch does not block passage of said elongated object through said open side of said storage channel, a rotatable lever which rotates in response to displacement of said elongated object from said first object position to said second object position, and a rigid actuation rod pivotably coupled to said lever and to said latch for causing rotation of said latch in response to rotation of said lever. first and second rows of storage cells, each of said storage cells comprising a storage channel having an open side of width sufficient to allow passage of a elongated object therethrough, means for supporting said elongated object in said storage channel, and means for blocking passage of said stored elongated object through said open side of said storage channel in response to displacement of said elongated object from a first object position whereat said object supporting means does not support said object to a second object position whereat said object supporting means supports said object, said blocking means being mounted on said storage channel; and means for supporting said first row of storage cells in a first inclined position and said second row of storage cells in a second inclined position, said first and second inclined positions forming an A-shaped configuration. 2. The storage cell as defined in claim 1, wherein said blocking means further comprises a contact plate with a concavity for receiving an end of said elongated object when said object is in said second object position, said contact plate being pivotably coupled to said lever. 3. The storage cell as defined in claim 1, wherein the weight distribution of said blocking means is such that said latch is rotated from said first latch position to said second latch position under the force of gravity alone in response to displacement of said elongated object from said second object position to said first object position. 4. The storage cell as defined in claim 3, wherein said actuation rod is made of stainless steel, and said storage channel, said latch and said lever are made of aluminum. 5. The storage cell as defined in claim 3, wherein said object supporting means comprises a support plate welded inside said storage channel, said support plate having a chamfered aperture for seating a seated portion of said elongated object, said aperture having a size which enables a lowermost portion of said elongated object to extend through said aperture when said seated portion of said object is seated thereon. 6. The storage cell as defined in claim 3, wherein said blocking means further comprises a slotted lock block welded to said storage channel, said lock block being positioned to receive said latch in said slot when said latch is in said first latch position. 7. A storage rack for storing elongated objects, comprising: 8. The storage rack as defined in claim 7, wherein said blocking means comprises a rotatable latch which rotates between a first latch position whereat said latch blocks passage of said elongated object through said open side of said storage channel and a second latch position whereat said latch does not block passage of said elongated object through said open side of said storage channel. 9. The storage rack as defined in claim 8, wherein said blocking means further comprises a rotatable lever which rotates in response to displacement of said elongated object from said first object position to said second object position, and a rigid actuation rod pivotably coupled to said lever and to said latch for causing rotation of said latch in response to rotation of said lever. 10. The storage rack as defined in claim 9, wherein said blocking means further comprises a contact plate with a concavity for receiving an end of said elongated object when said object is in said second object position, said contact plate being pivotably coupled to said lever. 11. The storage rack as defined in claim 9, wherein the weight distribution of said blocking means is such that said latch is rotated from said first latch position to said second latch position under the force of gravity alone in response to displacement of said elongated object from said second object position to said first object position. 12. The storage rack as defined in claim 11, wherein said actuation rod is made of stainless steel, and said storage channel, said latch and said lever are made of aluminum. 13. The storage rack as defined in claim 7, wherein said object supporting means comprises a support plate welded inside said storage channel, said support plate having a chamfered aperture for seating a seated portion of said elongated object, said aperture having a size which enables a lowermost portion of said elongated object to extend through said aperture when said seated portion of said object is seated thereon. 14. The storage rack as defined in claim 8, wherein said blocking means further comprises a slotted lock block welded to said channel, said lock block being positioned to receive said latch in said slot when said latch is in said first latch position. 15. A fuel storage pool for storing fuel bundle assemblies underwater, comprising a plurality of fuel storage racks separated by aisles, each of said racks having first and second rows of storage cells and means for supporting said first row of storage cells in a first inclined position and said second row of storage cells in a second inclined position, said first and second inclined positions forming an A-shaped configuration, wherein each of said storage cells comprises a storage channel having an open side of width sufficient to allow passage of a fuel bundle assembly therethrough, means for supporting said fuel bundle assembly in said storage channel, and means for blocking passage of said stored fuel bundle assembly through said open side of said storage channel in response to displacement of said fuel bundle assembly from a first position whereat said fuel bundle assembly supporting means does not support said fuel bundle assembly to a second position whereat said fuel bundle assembly supporting means supports said fuel bundle assembly, said blocking means being mounted on said storage channel and said open side of said storage channel facing one of said aisles. 16. The fuel storage pool as defined in claim 15 wherein said blocking means comprises a rotatable latch which rotates between a first latch position whereat said latch blocks passage of said fuel bundle assembly through said open side of said storage channel and a second latch position whereat said latch does not block passage of said fuel bundle assembly through said open side of said storage channel. 17. The fuel storage pool as defined in claim 16, wherein said blocking means further comprises a rotatable lever which rotates in response to displacement of said fuel bundle assembly from said first position to said second position, and a rigid actuation rod pivotably coupled to said lever and to said latch for causing rotation of said latch in response to rotation of said lever. 18. The fuel storage pool as defined in claim 16, wherein the weight distribution of said blocking means is such that said latch is rotated from said first latch position to said second latch position under the force of gravity alone in response to displacement of said fuel bundle assembly from said second position to said first position. |
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abstract | A high resolution x-ray microscope with a high flux x-ray source that allows high speed metrology or inspection of objects such as integrated circuits (ICs), printed circuit boards (PCBs), and other IC packaging technologies. The object to be investigated is illuminated by collimated, high-flux x-rays from an extended source having a designated x-ray spectrum. The system also comprises a stage to control the position and orientation of the object; a scintillator that absorbs x-rays and emits visible photons positioned in very close proximity to (or in contact with) the object; an optical imaging system that forms a highly magnified, high-resolution image of the photons emitted by the scintillator; and a detector such as a CCD array to convert the image to electronic signals. |
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description | 1. Field of the Invention The present invention relates to a drawing apparatus, and a method of manufacturing an article. 2. Description of the Related Art Along with the higher integration and miniaturization of semiconductor devices, a drawing apparatus using a charged particle beam (electron beam) and an EUV exposure apparatus using EUV (extreme ultraviolet) rays have been developed as a lithography apparatus of the next generation, which forms (transfers) a pattern on a substrate. For example, in the EUV exposure apparatus, a technique of removing contaminations such as carbon films deposited on a mirror (reflective optical member) has been proposed by Japanese Patent Laid-Open Nos. 2011-86885 and 2011-86886. With the technique of Japanese Patent Laid-Open Nos. 2011-86885 and 2011-86886, active species (ozonide) are generated by mixing unsaturated hydrocarbon and ozone, and contaminations are removed by such active species. In the drawing apparatus as well, contaminations are deposited on a member having an aperture through which charged particle beam passes (for example, an electrostatic lens or aperture) due to outgases emitted from a substrate and a resist applied on the substrate, and secondary electrons generated when a charged particle beam strikes the substrate. Especially, the contamination deposited in the vicinity of the aperture of such member influences an orbit of the charged particle beam which passes through the aperture when it is charged (that is, the charged particle beam is deviated from a target orbit). Since the contamination is deposited, the aperture size of the electrostatic lens or aperture is reduced, and an intensity (current) of the charged particle beam which passes through the aperture is decreased, resulting in a throughput drop. Alternatively, since the contamination is deposited, the roundness of the aperture of the electrostatic lens is changed, thus generating aberrations. Hence, the technique of Japanese Patent Laid-Open Nos. 2011-86885 and 2011-86886 may be applied to a drawing apparatus. However, when active species are separated away from positions where they are generated by reaction between unsaturated hydrocarbon and ozone, they are abruptly deactivated (contamination removing efficiency lowers). Therefore, contaminations deposited in the vicinity of the aperture of the electrostatic lens or aperture cannot be sufficiently removed. The present invention provides, for example, a drawing apparatus advantageous to removal of contamination on a member on which a charged particle impinges. According to one aspect of the present invention, there is provided a drawing apparatus for performing drawing on a substrate with a charged particle beam, the apparatus including a first member in which an aperture, through which the charged particle beam passes, is formed, a chamber including a first space and a second space which are partitioned by the first member, and a removing device including a first supply device configured to supply a first gas containing unsaturated hydrocarbon to the first space and a second supply device configured to supply a second gas containing ozone to the second space, and configured to remove contamination on the first member by active species generated by reaction of the first gas with the second gas. Further aspects of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals denote the same members throughout the drawings, and a repetitive description thereof will not be given. FIG. 1 is a schematic view showing the arrangement of a drawing apparatus 100A according to the first embodiment of the present invention. A drawing apparatus 100A is a lithography apparatus which performs drawing on a substrate using a charged particle beam (electron beam), that is, which draws a pattern on a substrate using a charged particle beam. The drawing apparatus 100A includes a charged particle source 101, collimator lens 102, aperture array 103, electrostatic lens array 104, stopping aperture array 105, blanker array 106, and electrostatic lens array 107. Also, the drawing apparatus 100A includes a deflector 108, stage (movable object) 109, chamber 110, removing mechanism 130, first adjustment unit (regulator) 140A, second adjustment unit (regulator) 140B, and control unit (controller) 160. The control unit 160 includes, for example, a CPU, memory, and the like, and controls the respective units (operations) of the drawing apparatus 100A. The charged particle source 101, collimator lens 102, aperture array 103, electrostatic lens array 104, stopping aperture array 105, blanker array 106, electrostatic lens array 107, and deflector 108 configure a charged particle optical system. The charged particle optical system guides a charged particle beam to a substrate SB. The charged particle source 101 has a function of generating a charged particle beam, and forms a crossover image CI. A charged particle beam diffused from the crossover image CI is nearly collimated by the collimator lens 102, and enters the aperture array 103. On the aperture array (aperture array member) 103, a plurality of apertures (for example, circular apertures) 103a through which the charged particle beam passes are formed in a matrix. The charged particle beam which enters the aperture array 103 is divided into a plurality of charged particle beams by the plurality of apertures 103a of the aperture array 103. The charged particle beams which have passed through the aperture array 103 enter the electrostatic lens array 104 having circular apertures 104a through which the charged particle beams pass. The electrostatic lens array 104 is generally configured by three electrode plates (electrode members), and FIG. 1 integrally illustrates the three electrode plates. At positions where the charged particle beams, which have passed through the electrostatic lens array 104, form crossover images first, the stopping aperture array 105 having small apertures 105a, which are arranged in a matrix, is disposed. A blanking operation for shielding the charged particle beams (those which travel toward the substrate SB) in the stopping aperture array 105 is performed by the blanker array (aperture member) 106. The charged particle beams which have passed through the stopping aperture array 105 are imaged by the electrostatic lens array 107, and form crossover images on the substrate SB such as a wafer or mask. The electrostatic lens array 107 has circular apertures 107a through which the charged particle beams pass, and is configured by three electrode plates (electrode members) in the same manner as the electrostatic lens array 104. Upon drawing a pattern, the crossover images on the substrate SB are deflected in a Y-axis direction by the deflector 108, and the blanking operation is performed by the blanker array 106 while continuously moving the stage 109, which holds the substrate SB, in an X-axis direction. In this case, the crossover images are deflected (scanned) by the deflector 108 with reference to a length measurement result of the stage 109 in real time by a laser length measuring device. Since the charged particle beams are abruptly attenuated in an atmospheric environment, the drawing apparatus 100A, that is, the charged particle source 101 to the stage 109 are housed in the chamber 110, so as to prevent discharging caused by a high voltage. The interior of the chamber 110 is maintained in a vacuum atmosphere, for example, a pressure of 10−5 Pa or less. Since a space where the charged particle optical system is disposed is required to have a high degree of vacuum, it may have an exhaust system independently of a space where the stage 109 from which many gases are generated. In this embodiment, the charged particle source 101 to the deflector 108, which configure the charged particle optical system, are housed in an optical system chamber 111 having an exhaust pipe 141B, and the stage 109 is housed in a stage chamber 113 having an exhaust pipe 141A. The electrostatic lens array 107 includes charged particle lenses disposed on the side closest to the substrate in the charged particle optical system, and faces the substrate SB as a drawing target. The electrostatic lens array 107 is a member (first member) which partitions the interior of the chamber 110 into a first space SP1 and second space SP2. On the electrostatic lens array 107, especially, on an electrode plate on the side closest to the substrate of the three electrode plates which configure the electrostatic lens array 107, contaminations CC such as carbon films (contamination films) are deposited as the drawing is repeated. The reason why contaminations CC are deposited on the electrostatic lens array 107 will be described below. When the substrate SB is irradiated with the charged particle beams, secondary electrons are generated from the substrate SB, and an organic gas containing carbon is generated from a resist applied on the substrate SB. When the electrostatic lens array 107 is irradiated with the secondary electrons generated by the substrate SB while the organic gas exists in the vicinity of the electrostatic lens array 107, the organic gas is decomposed, thus depositing contaminations CC containing carbon as a principal component on the electrostatic lens array 107. When contaminations CC deposited on the electrostatic lens array 107 increase, since they clog the apertures 107a of the electrostatic lens array 107 to influence orbits of the charged particle beams which pass through the apertures 107a, the charged particle beams which pass through the apertures 107a are deviated from the target orbits. When contaminations CC are deposited, the aperture size of the electrostatic lens array 107 is reduced, and the intensities (currents) of the charged particle beams which pass through the apertures 107a are decreased, resulting in a throughput drop. Furthermore, due to deposition of contaminations CC, the roundness of each aperture 107a of the electrostatic lens array 107 is changed, thus generating aberrations. In this manner, when contaminations CC are deposited on the electrostatic lens array 107, they disturb normal drawing processing. Hence, the drawing apparatus 100A includes the removing mechanism 130, which removes contaminations CC deposited on a region including the apertures 107a of the electrostatic lens array 107 by active species (ozonide) generated by reaction between a gas (first gas) containing unsaturated hydrocarbon and a gas (second gas) containing ozone. In this embodiment, the removing mechanism 130 includes a first supply unit 130A which supplies an ethylene gas (gas containing unsaturated hydrocarbon) to the first space SP1, and a second supply unit 130B which supplies an ozone gas (gas containing ozone) to the second space SP2. The first supply unit 130A includes, as a mechanism required to supply the ethylene gas to the first space SP1, a pipe 131A connected to an ethylene generator and the stage chamber 113, and a stop valve 132A and flow rate controller 133A, which are connected to the pipe 131A. The second supply unit 130B includes, as a mechanism required to supply the ozone gas to the second space SP2, a pipe 131B connected to an ozone generator and the optical system chamber 111, and a stop valve 132B and flow rate controller 133B, which are connected to the pipe 131B. The exhaust pipe 141A of the stage chamber 113 is connected to an exhaust pump (not shown) via a stop valve 142A and variable conductance valve 143A. The exhaust pipe 141A, stop valve 142A, variable conductance valve 143A, and exhaust pump configure the first adjustment unit 140A, which adjusts (regulates) the pressure of the first space SP1 by evacuating the first space SP1, under the control of the control unit 160. Likewise, the exhaust pipe 141B of the optical system chamber 111 is connected to an exhaust pump (not shown) via a stop valve 142B and variable conductance valve 143B. The exhaust pipe 141B, stop valve 142B, variable conductance valve 143B, and exhaust pump configure the second adjustment unit 140B, which adjusts (regulates) the pressure of the second space SP2 by evacuating the second space SP2, under the control of the control unit 160. The first and second adjustment units 140A and 140B configure an adjustment unit which adjusts a pressure of at least one of the first or second spaces SP1 and SP2. Removing processing for removing contaminations CC deposited on the electrostatic lens array 107 in the drawing apparatus 100A will be described below. This removing processing is implemented when the control unit 160 systematically controls the respective units of the drawing apparatus 100A. Initially, the control unit 160 stops generation of a charged particle beam in the charged particle source 101. Normally, upon drawing a pattern on the substrate SB, since the stop valves 142A and 142B are in an open state, the control unit 160 maintains that state. Next, the control unit 160 supplies the ethylene gas to the first space SP1 and the ozone gas to the second space SP2 while setting the stop valves 132A and 132B in an open state. In this case, the control unit 160 controls the flow rates of the ethylene gas and ozone gas to, for example, 100 sccm respectively via the flow rate controllers 133A and 133B. Also, the control unit 160 controls (adjusts) the variable conductance valves 143A and 143B (first and second adjustment units 140A and 140B), so that a pressure P1 in the first space SP1 and a pressure P2 in the second space SP2 become, for example, 100 Pa. Thus, the ethylene gas supplied to the first space SP1 and the ozone gas supplied to the second space SP2 react each other in the vicinity of the apertures 107a of the electrostatic lens array 107, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. The active species generated in the vicinity of the apertures 107a of the electrostatic lens array 107 remove contaminations CC by acting on contaminations CC deposited on the electrostatic lens array 107. Most of active species are deactivated while they are diffused over a distance of several cm from their generated (reacting) locations due to their unstable state, and are transformed into a substance in a stable state. In this embodiment, since the active species are generated in the vicinity of the apertures 107a of the electrostatic lens array 107, the concentration of the active species at the locations where contaminations CC are deposited is highest, thus efficiently removing contaminations CC. More specifically, in this embodiment, contaminations CC deposited on the electrostatic lens array 107 can be removed at a removing rate of 100 nm/min. Since the concentration of the active species immediately lowers at positions separated away from the vicinities of the apertures 107a of the electrostatic lens array 107, deteriorations (damages) on other members by the active species can be minimized. As described above, according to the drawing apparatus 100A of this embodiment, active species can be generated in the vicinity of the apertures 107a of the electrostatic lens array 107 where contaminations CC are deposited. Therefore, the drawing apparatus 100A can quickly remove contaminations CC deposited on the electrostatic lens array 107, and can execute normal drawing processing while suppressing throughput and performance drops. This embodiment has exemplified the electrostatic lens array 107 as a member which includes apertures through which charged particle beams pass and on which contaminations CC are deposited. However, the present invention is not limited to this. For example, contaminations CC are deposited on the aperture array 103, electrostatic lens array 104, stopping aperture array 105, and the like. For each of such members, a gas containing unsaturated hydrocarbon and that containing ozone are respectively supplied to spaces which sandwich the apertures, thereby generating the active species in the vicinity of the apertures, and removing contaminations CC. In this embodiment, the pressure P1 of the first space SP1 and the pressure P2 of the second space SP2 are set at 100 Pa. Alternatively, the first and second adjustment units 140A and 140B may be controlled to form a pressure difference between the first and second spaces SP1 and SP2. For example, the first and second adjustment units 140A and 140B are controlled so that the pressure (one pressure) P2 of the second space SP2 is higher than the pressure (the other pressure) P1 of the first space SP1. More specifically, the first and second adjustment units 140A and 140B are controlled, so that the pressure P1 of the first space SP1 is 100 Pa, and the pressure P2 of the second space SP2 is 110 Pa. Then, reaction locations (that is, locations where active species are generated) of the ethylene gas and ozone gas are shifted to the first space side, thereby further efficiently removing contaminations CC mainly deposited on the first space side of the electrostatic lens array 107. It is also effective to control the pressure difference between the first and second spaces SP1 and SP2, so that locations where the active species are generated are changed along with an elapse of time. For example, while the pressure P1 of the first space SP1 is maintained at 100 Pa, operations for maintaining the pressure P2 at 110 Pa for 3 min, and then maintaining the pressure P2 at 95 Pa for 0.5 min are repeated. In other words, the first and second adjustment units 140A and 140B are controlled so that the magnitude relation between the pressure P1 of the first space SP1 and the pressure P2 of the second space SP2 is inverted along with an elapse of time. In this manner, contaminations CC deposited on the apertures 107a of the electrostatic lens array 107 can be efficiently removed while removing contaminations CC deposited on the first space side of the electrostatic lens array 107 at a high removing rate. In this case, only the pressure P2 of the second space SP2 is changed. Alternatively, both the pressures P1 and P2, or only the pressure P1 may be changed as long the relative magnitude relation between the pressure P1 of the first space SP1 and the pressure P2 of the second space SP2 remains the same. FIG. 2 is a schematic view showing the arrangement of a drawing apparatus 100B according to the second embodiment of the present invention. A drawing apparatus 100B has the same arrangement as the drawing apparatus 100A. In this embodiment, a deflector 108 functions as a member for partitioning the interior of a chamber 110 into second and third spaces SP2 and SP3. A stopping aperture array 105 functions as a member for partitioning the interior of the chamber 110 into the third space SP3 and a fourth space SP4. A blanker array 106 functions as a member for partitioning the interior of the chamber 110 into the fourth space SP4 and a fifth space SP5. An electrostatic lens array 104 functions as a member (second member) for partitioning the interior of the chamber 110 into the fifth space SP5 and a sixth space SP6. An aperture array 103 functions as a member (third member) for partitioning the interior of the chamber 110 into the sixth space SP6 and a seventh space SP7. The drawing apparatus 100B further includes a third supply unit 130C required to supply an ethylene gas to the fourth space SP4, a fourth supply unit 130D required to supply an ethylene gas to the sixth space SP6, and a fifth supply unit 130E required to supply an ozone gas to the seventh space SP7. The third supply unit 130C includes, as a mechanism required to supply an ethylene gas to the fourth space SP4, a pipe 131C connected to an ethylene generator and the optical system chamber 111, and a stop valve 132C and flow rate controller 133C connected to the pipe 131C. The fourth supply unit 130D includes, as a mechanism required to supply an ethylene gas to the sixth space SP6, a pipe 131D connected to the ethylene generator and optical system chamber 111, and a stop valve 132D and flow rate controller 133D connected to the pipe 131D. The fifth supply unit 130E includes, as a mechanism required to supply an ozone gas to the seventh space SP7, a pipe 131E connected to an ozone generator and the optical system chamber 111, and a stop valve 132E and flow rate controller 133E connected to the pipe 131E. Also, the drawing apparatus 100B further includes a third adjustment unit 140C, fourth adjustment unit 140D, and fifth adjustment unit 140E. The third adjustment unit 140C includes an exhaust pipe 141C, stop valve 142C, variable conductance valve 143C, and exhaust pump (not shown), and adjusts a pressure P4 of the fourth space SP4 by evacuating the fourth space SP4 under the control of a control unit 160. The fourth adjustment unit 140D includes an exhaust pipe 141D, stop valve 142D, variable conductance valve 143D, and exhaust pump (not shown), and adjusts a pressure P6 of the sixth space SP6 by evacuating the sixth space SP6 under the control of the control unit 160. The fifth adjustment unit 140E includes an exhaust pipe 141E, stop valve 142E, variable conductance valve 143E, and exhaust pump (not shown), and adjusts a pressure P7 of the seventh space SP7 by evacuating the seventh space SP7 under the control of the control unit 160. As described also in the first embodiment, contaminations CC are deposited not only on an electrostatic lens array 107 but also on the aperture array 103 and stopping aperture array 105. This is because the aperture array 103 and stopping aperture array 105 are irradiated with a charged particle beam from a charged particle source 101. Therefore, contaminations CC are readily deposited on a region (especially, on the charged particle source side) including apertures 103a of the aperture array 103 and that (especially, on the charged particle source side) including apertures 105a of the stopping aperture array 105. Hence, in this embodiment, a removing mechanism 130 supplies an ethylene gas (gas containing unsaturated hydrocarbon) to the first, fourth, and sixth spaces SP1, SP4, and SP6, and an ozone gas (gas containing ozone) to the second and seventh spaces SP2 and SP7. Then, the ethylene gas and ozone gas react each other to generate active species (ozonide), thus removing contaminations CC deposited on the aperture array 103, stopping aperture array 105, and electrostatic lens array 107. Removing processing for removing contaminations CC deposited on the aperture array 103, stopping aperture array 105, and electrostatic lens array 107 in the drawing apparatus 100B will be described below. This removing processing can be implemented when the control unit 160 systematically controls the respective units of the drawing apparatus 100B. Initially, the control unit 160 stops generation of a charged particle beam by the charged particle source 101. Normally, upon drawing a pattern on a substrate SB, since the stop valves 142A to 142E are in an open state, the control unit 160 maintains that state. Next, the control unit 160 sets the stop valves 132A to 132E in an open state to supply an ethylene gas to the first, fourth, and sixth spaces SP1, SP4, and SP6, and to supply an ozone gas to the second and seventh spaces SP2 and SP7. In this case, the control unit 160 controls the flow rates of the ethylene gas and ozone gas to, for example, 100 sccm via the flow rate controllers 133A to 133E. Also, the control unit 160 controls (adjusts) the variable conductance valves 143A to 143E (first to fifth adjustment units 140A to 140E), so that the pressures P1, P2, P3, P4, P6, and P7 become, for example, 100 Pa. Thus, the ethylene gas supplied to the first space SP1 and the ozone gas supplied to the second space SP2 react each other in the vicinity of the apertures 107a of the electrostatic lens array 107, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. The active species generated in the vicinity of the apertures 107a of the electrostatic lens array 107 remove contaminations CC by acting on contaminations CC deposited on the electrostatic lens array 107. Also, the ethylene gas supplied to the fourth space SP4 and the ozone gas supplied to the second space SP2 react each other in the vicinity of the apertures 105a of the stopping aperture array 105, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. The active species generated in the vicinity of the apertures 105a of the stopping aperture array 105 remove contaminations CC by acting on contaminations CC deposited on the stopping aperture array 105. Likewise, the ethylene gas supplied to the sixth space SP6 and the ozone gas supplied to the seventh space SP7 react each other in the vicinity of the apertures 103a of the aperture array 103, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. The active species generated in the vicinity of the apertures 103a of the aperture array 103 remove contaminations CC by acting on contaminations CC deposited on the aperture array 103. As described above, according to the drawing apparatus 100B of this embodiment, active species can be generated in the vicinity of the apertures 103a of the aperture array 103, the apertures 105a of the stopping aperture array 105, and the apertures 107a of the electrostatic lens array 107 where contaminations CC are deposited. Therefore, the drawing apparatus 100B can quickly remove contaminations CC deposited on the aperture array 103, stopping aperture array 105, and electrostatic lens array 107, and can execute normal drawing processing while suppressing throughput and performance drops. In this embodiment, the pressures P1, P2, P3, P4, P6, and P7 are set at 100 Pa. Alternatively, the first to fifth adjustment units 140A to 140E may be controlled to form a pressure difference between the respective spaces. For example, the first to fifth adjustment units 140A to 140E are controlled so that the pressures P1 and P4 are 100 Pa, and the pressures P2 and P3 are 110 Pa, the pressure P6 is 100 Pa, and the pressure P7 is 90 Pa. Then, in the vicinity of the apertures 103a of the aperture array 103 and the apertures 105a of the stopping aperture array 105, reaction locations (that is, locations where active species are generated) of the ethylene gas and ozone gas are shifted to the charged particle source side. Therefore, contaminations CC mainly deposited on the charged particle source side of the aperture array 103 and stopping aperture array 105 can be further efficiently removed. Also, in the vicinity of the apertures 107a of the electrostatic lens array 107, reaction locations (that is, locations where active species are generated) of the ethylene gas and ozone gas are shifted to the first space side, thereby further efficiently removing contaminations CC mainly deposited on the first space side of the electrostatic lens array 107. FIG. 3 is a schematic view showing the arrangement of a drawing apparatus 100C according to the third embodiment of the present invention. A drawing apparatus 100C has the same arrangement as the drawing apparatus 100A. In this embodiment, a deflector 108 functions as a member for partitioning the interior of a chamber 110 into second and third spaces SP2 and SP3. A stopping aperture array 105 functions as a member for partitioning the interior of the chamber 110 into the third space SP3 and a fourth space SP4. A blanker array 106 functions as a member for partitioning the interior of the chamber 110 into the fourth space SP4 and a fifth space SP5. The drawing apparatus 100C further includes a sixth supply unit 130F required to supply an ozone gas to the third space SP3, a third supply unit 130C required to supply an ethylene gas to the fourth space SP4, and a seventh supply unit 130G required to supply an ethylene gas to the fifth space SP5. The sixth supply unit 130F includes, as a mechanism required to supply an ozone gas to the third space SP3, a pipe 131F connected to an ozone generator and optical system chamber 111, and a stop valve 132F and flow rate controller 133F connected to the pipe 131F. The third supply unit 130C includes, as a mechanism required to supply an ethylene gas to the fourth space SP4, a pipe 131C connected to an ethylene generator and the optical system chamber 111, and a stop valve 132C and flow rate controller 133C connected to the pipe 131C. The seventh supply unit 130G includes, as a mechanism required to supply an ethylene gas to the fifth space SP5, a pipe 131G connected to the ethylene generator and optical system chamber 111, and a stop valve 132G and flow rate controller 133G connected to the pipe 131G. Also, the drawing apparatus 100C further includes a third adjustment unit 140C and sixth adjustment unit 140F. The third adjustment unit 140C includes an exhaust pipe 141C, stop valve 142C, variable conductance valve 143C, and exhaust pump (not shown), and adjusts a pressure P4 of the fourth space SP4 by evacuating the fourth space SP4 under the control of a control unit 160. The sixth adjustment unit 140F includes an exhaust pipe 141F, stop valve 142F, variable conductance valve 143F, and exhaust pump (not shown), and adjusts a pressure P3 of the third space SP3 by evacuating the third space SP3 under the control of the control unit 160. As described also in the second embodiment, contaminations CC are deposited on an electrostatic lens array 107, an aperture array 103, and the stopping aperture array 105. Although depending on design of a charged particle optical system, especially when contaminations CC are deposited on the stopping aperture array 105, the performance of the drawing apparatus is often impaired. Therefore, the drawing apparatus is required to efficiently remove contaminations CC deposited on the stopping aperture array 105. Hence, in this embodiment, a removing mechanism 130 supplies an ethylene gas (gas containing unsaturated hydrocarbon) to the fourth and fifth spaces SP4 and SP5, and an ozone gas (gas containing ozone) to the third space SP3. Then, the ethylene gas and ozone gas react each other to generate active species (ozonide), thus removing contaminations CC deposited on the stopping aperture array 105. Also, the removing mechanism 130 supplies an ethylene gas to the first space SP1, and an ozone gas to the second space SP2, thus removing contaminations CC deposited on the electrostatic lens array 107 as in the first embodiment. Removing processing for removing contaminations CC deposited on the stopping aperture array 105 in the drawing apparatus 100C will be described below. This removing processing can be implemented when the control unit 160 systematically controls the respective units of the drawing apparatus 100C. Initially, the control unit 160 stops generation of a charged particle beam by the charged particle source 101. Normally, upon drawing a pattern on a substrate SB, since the stop valves 142A, 142B, 142C, and 142F are in an open state, the control unit 160 maintains that state. Next, the control unit 160 sets the stop valves 132A to 132C, 132F, and 132G in an open state to supply an ethylene gas to the first, fourth, and fifth spaces SP1, SP4, and SP5, and to supply an ozone gas to the second and third spaces SP2 and SP3. In this case, the control unit 160 controls the flow rates of the ethylene gas and ozone gas to, for example, 100 sccm via the flow rate controllers 133A to 133C, 133F, and 133G. Also, the control unit 160 controls (adjusts) the variable conductance valves 143A to 143C and 143F, so that the pressures P1, P2, P3, P4, and P5 become, for example, 100 Pa. After the flow rates of the ethylene gas and ozone gas and the pressures P1 to P5 of the respective spaces reach an equilibrium state, the control unit 160 controls (adjusts) the variable conductance valves 143A to 143C and 143F, so that the pressures P1 to P5 of the respective spaces assume the following values. For example, the control unit 160 controls the variable conductance valves, so that the pressure P1 is 90 Pa, the pressure P2 is 100 Pa, the pressure P3 is 100 Pa, the pressure P4 is 90 Pa, and the pressure P5 is 110 Pa. Thus, the ethylene gas supplied to the first space SP1 and the ozone gas supplied to the second space SP2 react each other in the vicinity of apertures 107a of the electrostatic lens array 107, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. In this case, since the pressure P2 of the second space SP2 is higher than the pressure P1 of the first space SP1, reaction locations (that is, locations where active species are generated) of the ethylene gas and ozone gas are shifted to the first space side. Therefore, contaminations CC mainly deposited on the first space side of the electrostatic lens array 107 can be efficiently removed. Also, the ethylene gas supplied to the fourth space SP4 and the ozone gas supplied to the third space SP3 react each other in the vicinity of the apertures 105a of the stopping aperture array 105, that is, in the vicinity of locations where contaminations CC are deposited, thus generating active species. In this case, since the pressure P3 of the third space SP3 is higher than the pressure P4 of the fourth space SP4, reaction locations (that is, locations where active species are generated) of the ethylene gas and ozone gas are shifted to the fourth space side. Therefore, contaminations CC mainly deposited on the fourth space side of the stopping aperture array 105 can be efficiently removed. On the other hand, since active species are deactivated as positions are separated farther away from the reaction locations of the ethylene gas and ozone gas, the concentration of the active species lowers, and a removing rate of contaminations CC often becomes low. In this case, since a time required to remove contaminations CC has to be determined in correspondence with locations where the removing rate is lowest, it is consequently prolonged. In such case, an air current of the reaction locations of the ethylene gas and ozone gas can be disturbed. In this embodiment, since the pressure P4 of the fourth space SP4 is higher than the pressure P5 of the fifth space SP5, an air current in the vicinity of the reaction locations of the ethylene gas and ozone gas (in the vicinity of apertures 105a of the stopping aperture array 105) is disturbed. More specifically, a flow of the ethylene gas which flows from the fifth space SP5 toward the fourth space SP4 via apertures 160a of the blanker array 106 is generated. As a result, an air current in the vicinity of the apertures 105a of the stopping aperture array 105, that is, in the vicinity of the reaction locations of the ethylene gas and ozone gas is disturbed, thus increasing a removing rate of locations where the removing rate of contaminations CC is lowest. Therefore, the time required to remove contaminations CC can be shortened. In this embodiment, the ethylene gas is supplied to the fifth space SP5. However, in place of the ethylene gas, an inert gas, for example, a rare gas of argon, helium, neon, or the like, a nitrogen gas, or a gas mixture of them may be supplied. When an inert gas is supplied to the fifth space SP5, the removing rate of contaminations CC can be similarly uniformed. Also, the ozone gas and ethylene gas may be supplied while being interchanged. More specifically, the ozone gas (gas containing ozone) is supplied to the first space SP1, fourth space SP4, and fifth space SP5, and the ethylene gas (gas containing unsaturated hydrocarbon) is supplied to the second space SP2 and third space SP3, thus obtaining the same effects. FIG. 4 is a schematic view showing the arrangement of a drawing apparatus 100D according to the fourth embodiment of the present invention. A drawing apparatus 100D has the same arrangement as the drawing apparatus 100C. In this embodiment, the drawing apparatus 100D further includes a gas supply chamber 200 which can be disposed in the first space SP1. The gas supply chamber 200 includes a retracting mechanism (not shown). When a pattern is drawn on a substrate SB, the gas supply chamber 200 is retracted from a position below an electrostatic lens array 107. When contaminations CC are removed, the gas supply chamber 200 is disposed below the electrostatic lens array 107. A stage 109 which holds the substrate SB is disposed under the electrostatic lens array 107 (on an orbit of a charged particle beam) when a pattern is drawn on the substrate SB, and is retracted from a position below the electrostatic lens array 107 when contaminations CC are removed. These operations are controlled by a control unit 160. On the upper surface of the gas supply chamber 200, a gas ejection plate 210 having gas ejection holes 210a is disposed. The gas ejection holes 210a may be formed in the gas ejection plate 210 according to an orbit axis 220 of a charged particle beam. In this case, since a gas can be ejected toward locations where an ozone gas is ejected, that is, toward apertures 107a of the electrostatic lens array 107, an air current in the vicinity of the apertures 107a can be disturbed more efficiently. However, even when the gas ejection holes 210a are not formed according to the orbit axis 220 of a charged particle beam, the effect of disturbing an air current in the vicinity of the apertures 107a can be provided. To the gas supply chamber 200, an eighth supply unit 130H, which supplies an ethylene gas to (the interior of) the gas supply chamber 200 is connected. The eighth supply unit 130H includes, as a mechanism required to supply an ethylene gas to the gas supply chamber 200, a pipe 131H connected to an ethylene generator and the stage chamber 113, and a stop valve 132H and flow rate controller 133H connected to the pipe 131H. Removing processing for removing contaminations CC in the drawing apparatus 100D is the same as that described in the third embodiment. The third embodiment has explained that contaminations CC deposited on the stopping aperture array 105 can be removed more efficiently. In this embodiment, contaminations CC deposited on the electrostatic lens array 107 can be further removed more efficiently by the gas supply chamber 200 and eighth supply unit 130H. More specifically, the control unit 160 controls (adjust) the variable conductance valves 143A to 143C and 143F so that the pressures P1 to P5 of the respective spaces assume the following values. For example, the control unit 160 controls the variable conductance valves so that the pressure P1 is 90 Pa, the pressure P2 is 100 Pa, the pressure P3 is 100 Pa, the pressure P4 is 90 Pa, and the pressure P5 is 110 Pa. Furthermore, the control unit 160 controls the eighth supply unit 130H to supply an ethylene gas to the gas supply chamber 200 to maintain the internal pressure of the gas supply chamber 200 to, for example, 110 Pa. In this manner, by setting the pressure of the gas supply chamber 200 to be higher than the pressure P1 of the first space SP1, an air current of the ethylene gas which flow from the gas supply chamber 200 toward the first space SP1 is generated via the gas ejection holes 210a. Thus, an air current in the vicinity of the apertures 107a of the electrostatic lens array 107, that is, in the vicinity of reaction locations of the ethylene gas and ozone gas is disturbed, thus increasing a removing rate of locations where the removing rate of contaminations CC is lowest. Therefore, the time required to remove contaminations CC can be shortened. In this embodiment, the ethylene gas is supplied to the gas supply chamber 200. However, in place of the ethylene gas, an inert gas, for example, a rare gas of argon, helium, neon, or the like, a nitrogen gas, or a gas mixture of them may be supplied. When an inert gas is supplied to the gas supply chamber 200, the removing rate of contaminations CC can be similarly uniformed. Also, the ozone gas and ethylene gas may be supplied while being interchanged. More specifically, the ozone gas is supplied to the first space SP1, fourth space SP4, fifth space SP5, and gas supply chamber 200, and the ethylene gas is supplied to the second space SP2 and third space SP3, thus obtaining the same effects. In place of supplying the ozone gas to the fifth space SP5, an inert gas, for example, a rare gas of argon, helium, neon, or the like, a nitrogen gas, or a gas mixture of them may be supplied. In this case as well, an effect of uniforming a removing rate of contaminations CC deposited on the stopping aperture array 105 can be provided. Even when the fifth space SP5 includes members such as a resin and adhesive, which are readily deteriorated by ozone, deterioration of these members can be prevented. Therefore, the drawing apparatus 100D can be used for a long term. FIG. 5 is a schematic view showing the arrangement of a drawing apparatus 100E according to the fifth embodiment of the present invention. A drawing apparatus 100E basically has the same arrangement as the drawing apparatus 100A. An optical system chamber 111 houses the same (members which configure) charged particle optical system as in the first embodiment although not shown. In the drawing apparatus 100E, a charged particle beam from the optical system chamber 111 (charged particle optical system) passes through an aperture AP, and strikes a substrate held by a stage 109. The aperture AP may be apertures 107a of an electrostatic lens array 107 as in the first embodiment, or may be a hole formed in a plate. As described in the first embodiment, contaminations CC are deposited on the aperture AP. The stage 109 is housed in a stage chamber 113, and is configured to be movable inside the stage chamber 113 so as to allow drawing on a substrate and exchange of a substrate. The aperture AP is a member which partitions the interior of the chamber 110 into first and second spaces SP1 and SP2. The aperture AP has, for example, a diameter ranging from 1 mm to 2 mm. Also, a distance between the stage 109 and aperture AP is, for example, 0.1 mm to 2 mm. However, the size of the aperture AP and the distance between the stage 109 and aperture AP are not limited to them, and the number of apertures AP is not limited to one. In this embodiment, an eighth space SP8 is defined between the (upper surface of the) stage 109 and the (lower surface of the) stage chamber 113 as a narrow gap space which neighbors the aperture AP. Also, a space of the first space SP1 except for the eighth space SP8 is defined as a ninth space SP9. In other words, the first space SP1 is divided into the eighth and ninth spaces SP8 and SP9, and the eighth space SP8 neighbors the second space SP2 via the aperture AP. Also, the drawing apparatus 100E further includes a second supply unit 130J required to supply an ethylene gas to the second space SP2, and an eighth supply unit 130H required to supply an ozone gas to the eighth space SP8. The second supply unit 130J includes, as a mechanism required to supply an ethylene gas to the second space SP2, a pipe 131J connected to an ethylene generator and the optical system chamber 111, and a stop valve 132J and flow rate controller 133J, which are connected to the pipe 131J. The eighth supply unit 130H includes, as a mechanism required to supply an ozone gas to the eighth space SP8, a pipe 131H connected to an ozone generator and the eighth space SP8, and a stop valve 132H and flow rate controller 133H, which are connected to the pipe 131H. Furthermore, the drawing apparatus 100E further includes a first adjustment unit 140A and second adjustment unit 140G. The first adjustment unit 140A includes an exhaust pipe 141A, stop valve 142A, variable conductance valve 143A, and exhaust pump (not shown), and adjusts a pressure P1 of the first space SP1 by evacuating the first space SP1 under the control of a control unit 160. The second adjustment unit 140G includes an exhaust pipe 141G, stop valve 142G, variable conductance valve 143G, and exhaust pump (not shown), and adjusts a pressure P2 of the second space SP2 by evacuating the second space SP2 under the control of the control unit 160. Removing processing for removing contaminations CC deposited in the vicinity of the aperture AP in the drawing apparatus 100E will be described below. This removing processing is implemented when the control unit 160 systematically controls the respective units of the drawing apparatus 100E. Initially, the control unit 160 stops generation of a charged particle beam by a charged particle source. Normally, upon drawing a pattern on a substrate SB, since the stop valves 142A and 142G are in an open state, the control unit 160 maintains that state. Also, the control unit 160 moves the stage 109 to a substrate exchange position to pass the substrate, and then moves the stage 109 to a position below the aperture AP. Next, the control unit 160 sets the stop valves 132H and 132J in an open state to supply an ozone gas to the first space SP1 (eighth space SP8), and to supply an ethylene gas to the second space SP2. In this case, the control unit 160 controls the flow rates of the ozone gas and ethylene gas to, for example, 100 sccm via the flow rate controllers 133H and 133J. Also, the control unit 160 controls (adjusts) the variable conductance valves 143A and 143G, so that the pressure P8 of the eighth space SP8 becomes, for example, 950 Pa, and the pressure P2 of the second space SP2 becomes, for example, 1050 Pa. Thus, the ethylene gas supplied to the second space SP2 and the ozone gas supplied to the eighth space SP8 react each other in the vicinity of the aperture AP and on the eighth space side, that is, in the vicinity of a location where contaminations CC are deposited, thus generating active species. The active species generated in the vicinity of the aperture AP remove contaminations CC by acting on contaminations CC deposited on the aperture AP. Most of active species are deactivated while they are diffused over a distance of several cm from their generated (reacting) location due to their unstable state, and are transformed into a substance in a stable state. In this embodiment, since the active species are generated in the vicinity of the aperture AP, the concentration of the active species at the location where contaminations CC are deposited is highest, thus efficiently removing contaminations CC. The drawing apparatus 100E can also remove contaminations deposited on a sensor 501 used to measure a charged particle beam which strikes the substrate. The sensor 501 measures a focus and shape of a charged particle beam before drawing on the substrate. The sensor 501 is disposed on, for example, the stage 109, and has a structure using a knife edge or fluorescent member. Upon measuring the focus and shape of a charged particle beam, since the sensor 501 is irradiated with the charged particle beam, contaminations are deposited on the sensor 501 as measurements are repeated. When contaminations are deposited on the sensor 501, since the measurement precision of the focus and shape of a charged particle beam lowers, the focus and shape of a charged particle beam cannot be appropriately adjusted, thus disturbing precise drawing. Therefore, in order to maintain the apparatus performance of the drawing apparatus 100E (that is, to execute precise drawing), contaminations deposited on the sensor 501 are required to be removed. As described above, when contaminations CC deposited on the aperture AP are to be removed, the stage 109 is moved to the position below the aperture AP. In this case, the stage 109 is moved so that the sensor 501 is located immediately below the aperture AP (that is, at a measurement position upon measuring the focus and shape of a charged particle beam). In such state, by applying the removing processing for removing contaminations CC deposited on the aperture AP, contaminations deposited on the sensor 501 can be removed. In this embodiment, effects to be described below can be obtained irrespective of whether or not the sensor 501 is located immediately below the aperture AP. For example, when the stage 109 is not located below the aperture AP, since the (volume of the) first space SP1 is large, some active species generated upon reaction of the ethylene gas and ozone gas are diffused in the first space SP1. Therefore, a removing rate of contaminations unwantedly lowers. On the other hand, when the stage 109 is located below the aperture AP, diffusion of active species is suppressed by the stage 109, thus increasing a removing rate of contaminations. In this manner, in this embodiment, the removing rate of contaminations can be increased, a time required to remove contaminations can be shortened, thus improving the throughput of the drawing apparatus 100E. Also, in this embodiment, the ethylene gas is supplied to the second space SP2, and the ozone gas is supplied to the eighth space SP8. Alternatively, the ozone gas may be supplied to the second space SP2, and the ethylene gas may be supplied to the eighth space SP8. FIG. 6 is a schematic view showing the arrangement of a drawing apparatus 100F according to the sixth embodiment of the present invention. A drawing apparatus 100F has the same arrangement as the drawing apparatus 100E. In the drawing apparatus 100F, an ozone supply location by an eighth supply unit 130H is different from the drawing apparatus 100E. A pipe 131H is connected to a stage 109 via a flexible pipe portion 601. The pipe 131H runs inside the stage 109, and is connected to a gas ejection hole 602 formed in the upper surface of the stage 109. Upon removing contaminations CC deposited on an aperture AP, the stage 109 is moved so that the gas ejection hole 602 is located immediately below the aperture AP. In this state, by applying removing processing described in the fifth embodiment, contaminations CC deposited on the aperture AP can be removed. In this embodiment, since the gas ejection hole 602 can be moved to the position immediately below the aperture AP, active species can be generated by reacting an ethylene gas and ozone gas in the vicinity of contaminations CC deposited on the aperture AP. Therefore, contaminations CC deposited on the aperture AP can be removed more efficiently. FIG. 7 is a schematic view showing the arrangement of a drawing apparatus 100G according to the seventh embodiment of the present invention. A drawing apparatus 100G has the same arrangement as the drawing apparatus 100F. In this embodiment, the drawing apparatus 100G includes a movable member 703 as a movable object in addition to a stage 109. The movable member 703 includes a support portion 701 and cup portion 702, and is housed in a stage chamber 113. A pipe 131H extends through the support portion 701 and cup portion 702, and is connected to a gas ejection hole 704 formed in the cup portion 702. When contaminations CC deposited on an aperture AP are to be removed, the stage 109 is retraced from a position below the aperture AP, and the movable member 703 is located below the aperture AP. In this case, an eighth space SP8 is defined between the cup portion 702 and the (upper surface of the) stage chamber 113. In this state, by applying removing processing described in the fifth embodiment, contaminations CC deposited on the aperture AP can be removed. Also, a sensor 501 may be disposed on the movable member 703. By disposing the sensor 501 in the vicinity of the gas ejection hole 704 formed in the cup portion 702, contaminations deposited on the sensor 501 can also be removed in addition to contaminations CC deposited on the aperture AP. In this embodiment, as described in the fifth embodiment, the movable member 703 can suppress diffusion of active species generated upon reaction of an ethylene gas and ozone gas. Also, since the cup portion 702 of the movable member 703 has a concave shape, diffusion of active species can be further suppressed. In the drawing apparatus 100G, the pipe 131H is connected to the movable member 703 in place of connecting the pipe 131H to the stage 109 which moves at high speed unlike in the drawing apparatus 100F. Since the movable member 703 need only be moved when contaminations are to be removed and when the sensor 501 is used (to measure a focus and shape of a charged particle beam), the durability of the pipe 131H need not be considered, thus reducing cost. Also, since the frequency of pulling and moving the pipe 131H can be reduced, a trouble of the pipe 131H occurs at a lower possibility. Note that in the first to seventh embodiments, the ozone generator preferably generates ozone at a concentration of 95% or more. However, even when the ozone generator can only generate ozone of several %, the removing effect of contaminations CC can be obtained. An excessive ethylene gas and ozone gas supplied to the respective spaces, and ketone, aldehyde, alcohol, and the like generated upon reaction of the ethylene gas and ozone gas are burnt (scrubbed) by a scrubber (not shown) and are exhausted as a carbon gas, water, and the like. The gas containing unsaturated hydrocarbon is not limited to the ethylene gas, but it can be a gas containing double or triple bonds of carbon atoms. The ozone gas acts on such double or triple bonds of carbon atoms to open and decompose the double or triple bonds, thus generating active species. More specifically, the gas containing unsaturated hydrocarbon may be an acetylene gas, propene gas, or butene gas. As described above, the drawings apparatuses 100A to 100G are suitable for manufacture of an article such as a micro device (for example, a semiconductor device) or an element having a microstructure since they can execute normal drawing processing while suppressing throughput and performance drops. A method of manufacturing an article includes a step of forming a latent image pattern on a photosensitive agent applied to a substrate using the drawing apparatuses 100A to 100G (a step of performing drawing on a substrate), and a step of developing the substrate on which the latent image pattern is formed in the above step (a step of developing the substrate on which the drawing has been performed). Furthermore, this manufacturing method can include other known steps (oxidation, film formation, vapor deposition, doping, planarization, etching, resist removal, dicing, bonding, packaging, etc.) The manufacturing method of an article of this embodiment is advantageous in at least one of performance, quality, productivity, and manufacturing cost of an article compared to a conventional method. For example, the detailed arrangement of the charged particle optical system is not limited to that described in the first embodiment as long as the arrangement can draw a pattern on a substrate. Also, the ethylene generator can be an ethylene supply source such as an ethylene gas cylinder. While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application Nos. 2012-277440 filed on Dec. 19, 2012, and 2013-197508 filed on Sep. 24, 2013, which are hereby incorporated by reference herein in their entirety. |
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description | This application is a National Stage application of International Application No. PCT/EP2006/008693, filed Sep. 6, 2006, which designates the United States and was published in English as WO 2007/028595 A2, and which claims the benefit of U.S. Provisional Application No. 60/714,556, filed Sep. 6, 2005. These applications, in their entirety, are incorporated herein by reference. U.S. Non-Provisional application Ser. No. 11/991,547, published as US 2009/0256075 A1 on Oct. 15, 2009 is a National Stage application of International Application No. PCT/EP2006/008694, published as WO 2007/028596 A1, which claims the benefit of U.S. Provisional Application No. 60/714,556, filed Sep. 6, 2005. 1. Field of the Invention The invention relates to particle-optical components for manipulating a plurality of beamlets and particle-optical arrangements and electron-beam inspection systems comprising such particle-optical components. Further, the invention relates to a method of manipulating charged particle beamlets, a method of focusing a plurality of charged particle beamlets and methods for manufacturing multi-aperture plates suitable for use in the particle-optical components. In addition, the invention pertains to a charged-particle multi-beamlet lithography system and a method of writing a pattern on a substrate. The invention may be applied to charged particles of any type, such as electrons, positrons, muons, ions (charged atoms or molecules) and others. 2. Brief Description of Related Art The increasing demand for ever smaller and more complex microstructured devices and the continuing demand for an increase of a throughput in the manufacturing and inspection processes thereof have been an incentive for the development of electron microscopy systems that use a plurality of primary electron beamlets in place of a single electron beam, thus significantly improving the throughput of such systems. However, the use of multiple beamlets brings about a whole range of new challenges to the design of electron-optical components, arrangements and inspection and processing systems such as microscopes and lithography systems. A particle-optical arrangement for forming a plurality of charged-particle beamlets wherein the beamlets are arranged in an array pattern is described in WO 2005/024881 A2 (U.S. provisional application Ser. No. 60/500,256) to the same Assignee. In general, such particle-optical arrangements and inspection and lithography systems comprising same use a plurality of charged particle beamlets focused on a specimen to be inspected. In case of an embodiment of an inspection system using electrons as charged particles, for example, an electron source provides a single beam of primary electrons (or, alternatively, multiple beamlets from an array of particle sources), which is incident on a multi-aperture plate having a plurality of apertures formed therein for generating a plurality of beamlets from those electrons of the single beam of electrons that pass through the apertures of the multi-aperture plate. The plurality of electron beamlets is focused on the substrate generally by means of a focussing particle-optical lens downstream of the multi-aperture plate. An array of primary electron spots is thus formed on the substrate. Secondary electrons emitted as a result of impinging primary electrons follow a secondary electron beam path to a respective one of a plurality of detector pixels of a CCD electron detector, with a beam path of beamlets of the primary electrons and the beam path of the beamlets of secondary electrons being separated by means of beam separator, such as a Wien-type filter. This arrangement allows to use a single electron-optical column. Such a system is described in detail in WO 2005/024881 A2 to the same Assignee, as mentioned before. Using such an array or pattern of beamlets of primary electrons requires the electron optical system to provide those beamlets in a reliable and accurate manner such that the beamlets show little, if any, variation in intensity, deviation from a predetermined position within the array, variation in optical properties, such as aberrations and the like. The quality of the array of beamlets and, correspondingly, the quality of the array of primary electron spots generated in an image plane will be dependent on both the properties of the multi-aperture plate used and the characteristics of other components or elements in the electron-optical arrangement. Components upstream of the multi-aperture plates will influence, amongst others, a quality of the single electron beam which will also have an impact on the beamlets generated therefrom. Components downstream of the multi-aperture plate will, amongst others, influence on how well the array of beamlets may be transferred onto the specimen to form primary electron spots. What has been described above for systems using electrons as charged particles is equally applicable to other kinds of charged particles. Given the requirement to provide a precisely defined array of beamlets of charged particles in order to achieve a satisfactory performance of the entire system, there is a constant need to improve on a performance of such a particle-optical system. In U.S. provisional application US 60/500,256 to the same Assignee as cited above, multi-aperture plates of different configurations are disclosed. In one aspect, multi-aperture plates having apertures that vary in size or shape depending on their position on the plate or having the apertures displaced from a respective position in a strictly regular pattern are disclosed. Those changes to aperture size/shape and position allow to correct imaging errors such as a distortion. In addition, a multi-aperture plate having a resistor-network disposed thereon is described, the resistor network being configured such that a voltage applied to the multi-aperture plate results in groups of apertures having a different potential. Since the potential applied to an aperture is related to a focusing effect provided by said aperture, the apertures can be configured to have different focussing effects such that a field curvature of the particle-optical system can be corrected. Although good results can be achieved with the above-described multi-aperture plates, the above described approaches to correct imaging errors of the particle-optical system require multi-aperture plates having apertures that vary in at least one of shape and size and pattern, or having a resistor network, which is often associated with an increase of a complexity of the manufacturing process. In addition, the capacity for correction of imaging errors can typically not be dynamically adjusted in any suitable manner when an imaging error of a particle-optical system changes or the component would need transferring to a different system having different properties. For example, a field curvature introduced by the imaging optics may dynamically change with a change of a total beam current transmitted by the optical system due to space charge effects. It is therefore an object of the present invention to provide particle-optical components and arrangements for manipulating beams and beamlets of charged particles that enhance an overall performance of a particle-optical system comprising said particle-optical component/arrangement. It is a further object of the present invention to provide particle-optical components and arrangements for manipulating beams or beamlets that are configured to correct at least one imaging error of a system comprising said particle-optical component/arrangement. Preferably, the one or more imaging errors comprise in particular one or more aberrations, that are field-dependent, i.e. dependent on a position within a respective field. Examples of imaging errors are a field curvature and any other geometrical aberration, such as coma. It is another object of the present invention to provide a particle-optical component and arrangement that is configured to correct an imaging error of the particle-optical system it is comprised in with a higher degree of flexibility. It is also an object of the present invention to provide a particle-optical component and arrangement configured to correct an imaging error of the particle-optical system it is comprised in, wherein the extent of the correction provided may be adjusted. It is an additional object of the present invention to provide charged particle inspection and lithography systems comprising particle-optical components and arrangements that meet any of the above objects. It is also an object to provide an improved method of writing a pattern on a substrate. It is a further object of the present invention to provide a particle-optical component capable of providing a correction for a particle-optical aberration that is suitable for use in both electrostatic and magnetic environments. It is a further object of the present invention to provide a method of manipulating charged particle beamlets and a method of focussing charged particle beamlets which are suited to provide particle-optical aberration correction. Furthermore, it is an object of the present invention to provide an improved method of operating a particle-optical system and a method of manufacturing a multi-aperture plate suitable for use in the particle-optical component according to the present invention. It is a still further object of the present invention to provide particle-optical components that allow adjusting a numerical aperture of charged particle beamlets. It is another object of the present invention to provide a particle-optical component that enables testing of a position or other properties of a multi aperture plate and/or optical properties of other optical components of a particle-optical system. As will be described in more detail in the following, particle-optical components, particle-optical arrangements and particle optical systems are provided that are configured to provide a better quality array of beamlets of charged particles, such as primary electrons, to a specimen to be exposed/inspected. Additionally, a method for manipulating a plurality of beamlets, a method of operating a particle-optical system and a method of focussing charged particle beamlets as well as methods of manufacturing a component that is used as part of the particle-optical component according to the present invention and a method of writing a pattern on a substrate are provided by the present invention. In addition, the particle-optical component of the present invention provides a device that allows to create and manipulate a desired geometry of an electrical or magnetic field within and/or at least in the vicinity of the device, in particular an electrical or magnetic field that is configured such as to correct for one or more imaging errors, such as aberrations. In a first aspect, the present invention provides a particle-optical component for manipulating a plurality of beamlets of charged particles, comprising: a first multi-aperture plate having a plurality of apertures and a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween; wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; wherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5% greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate. In exemplary embodiments, the first width may be at least 10% greater, or may be at least 20% greater than the second width. In further exemplary embodiments, the first width may be by at least 50%, or 100%, or 200%, or 300% or several 100% greater than the second width. The plurality of apertures typically forms a pattern of apertures, which aperture pattern may be regular or irregular. Generally, regular aperture patterns, such as symmetric patterns are preferred. The pattern may be, for instance, a highly regular rectangular grid of apertures with a number of apertures disposed in rows and columns wherein apertures disposed adjacent to one another in a row or column are generally spaced the same distance apart, and wherein the apertures generally have the same diameter. Various examples of other suitable patterns are disclosed in WO 2005/024881 (PCT/US2004/029079) to the same Assignee. An aperture pattern generally has a center associated therewith, which may serve as a reference point for describing properties of the pattern. Apertures, as used herein, are perforations or through holes, i.e. they extend through the entire thickness of the plate (at the location of the aperture) and thus have openings on both a front side and a back side of the plate they are comprised in. Plate, as used herein, shall also encompass a thin foil or a plate having one or more sections that form a thin foil. The first and second multi-aperture plates have respective pluralities of apertures formed therein having respective sizes, shapes and positions that are configured such that they can be suitably aligned or placed in registry with one another when the first and second multi-aperture plates are positioned adjacent to one another to form the gap between them. Each aperture of the plurality of apertures in the first multi-aperture plate has an aperture of the second multi-aperture plate associated therewith that it is aligned with to form a pair of associated, aligned apertures. In preferred embodiments, the apertures are aligned such that an axis extending through a centre of an aperture cross-section in the first multi-aperture plate coincides with an axis extending through a center of a cross-section of a corresponding, aligned aperture in the second multi-aperture plate, at least within a predetermined alignment precision, which may be in a range of 0.05 times a diameter of the aperture of the first multi aperture plate, for instance. In other exemplary embodiments, alignment may comprise an arrangement of the aligned apertures with respect to each other such that a charged particle beamlet passing through an aperture in the first multi aperture plate may pass through the aligned aperture in the second multi aperture plate without impinging on the second multi aperture plate. The same is valid for alignment of apertures in any further aperture plates. In other embodiments, the apertures may be aligned such that their respective centres are slightly offset from one another. This embodiment is particularly useful for correction of a tilt of the direction of impinging beamlets/the charged particle source or the like, for instance. In addition to providing the apertures with beam-manipulating properties, shapes of the beam-manipulating apertures may be designed such as to compensate for deviations of an electrical field generated by the multi-aperture plate from a desired electrical field. In particular, shapes of the beam-manipulating apertures may be designed such that additional shape features are added to basic shapes of the field manipulating apertures. The basic shapes are designed according to particle-optical design rules in view of providing a desired beam-manipulating effect on the beamlet passing through the aperture. For instance, the basic shape may be a circular shape for providing an effect of a round lens, or the basic shape may be an elliptical shape for providing an effect of an astigmatic lens. The first and second widths of the gap are determined at two different locations of two different apertures in the first multi-aperture plate. Of course, the respective widths would be the same if measured at corresponding locations of the second multi-aperture plates. The width of the gap is determined at a location of an aperture, most suitably an edge of an aperture, such as a point on a periphery of a cross-section of the opening of a circular aperture on the first surface of the first multi-aperture plate. However, it is also conceivable to use a different reference point. A surface of an opening of an aperture in a plane of the first surface of the first multi-aperture plate generally will have a geometric center, which may also be used as a reference point. In an exemplary embodiment of the present invention, the first multi-aperture plate has a plurality of apertures formed therein that are substantially identical in shape, size and relative position to respective apertures of the plurality of apertures in the second multi-aperture plate aligned therewith. In other exemplary embodiments, apertures of the first and second multi-aperture plates that are aligned with one another may have different shape and/or size and/or be arranged so as to be disposed slightly offset from one another. However, these differences should be chosen such that changes of imaging properties remain within a predetermined limit, i.e. effects on an imaging performance introduced by such an asymmetry should be kept to a minimum. The first or the second multi-aperture plates or both may comprise apertures in addition to the plurality of apertures, which have no counterpart, i.e. associated apertures in the respective other multi-aperture plate. Those additional apertures would accordingly generally be used for a purpose other than having charged particles pass through them. They may be provided to correct for so-called edge effects or the like, as described in WO 2005/024881 A2 to the same Assignee. It has been found that a particle-optical component according to the first aspect of the present invention is particularly advantageous in correcting one or more imaging errors, such as particle-optical aberrations. Imaging errors that the particle-optical component of the present invention is particularly suited to correct for are, for instance, a field curvature or other geometrical aberration. A variety of other imaging errors may be corrected for using the particle-optical component of the present invention, such as astigmatism, distortion and others. The inventors of the present invention have found that use of two multi-aperture plates with a particular shape and/or orientation towards one another and having aligned apertures allows to generate an electrical or magnetic field of a particular shape in the gap between the multi-aperture plates upon application of a suitable potential to the multi-aperture plates or induction of a suitable magnetic flux in the multi-aperture plates, which electrical or magnetic field can be suitably configured to compensate for at least one imaging error. The correcting or compensating properties of the electrical or magnetic field in the gap can be controlled, for instance, by the layout of the multi-aperture plates, in particular their shapes and symmetry, their arrangement relative to one another, the resulting width of the gap at different locations, the magnetic flux induced therein and the potential applied as well as a position of the particle-optical component within a particle-optical system. It is to be noted that the particle-optical component of the present invention may be used as a correction device alone, or in combination with its beamlet generating and/or focussing property, depending on its position in an overall system, and the presence and form of electrical or magnetic fields upstream and downstream therefrom, etc. It is to be noted that when no potential difference is created between the first and second multi-aperture plates or no magnetic flux induced therein, a compensating or correcting effect provided by the electrical or magnetic field, respectively, in the gap is practically switched off and the first and second multi-aperture plates may be used as a single multi-aperture plate instead, should no correction, even temporarily, be necessary. Further more, it is possible to use one or more particle-optical components according to the present invention in a particle-optical system. If a plurality of particle-optical components is used, each particle-optical component may be configured individually so as to correct a predetermined type of imaging error, such as a predetermined type of aberration. Each particle-optical component could then be used to correct for one specific imaging error. The individual correcting effects provided by these particle-optical components would then add up and provide a total correcting effect. In a simple exemplary embodiment, the particle-optical component may comprise two plane-parallel multi-aperture plates wherein one multi-aperture plates is tilted with respect to the other. An electrical or magnetic flux density in the gap of such an arrangement would increase steadily with decreasing width of the gap. With the first and second multi-aperture plate being arranged to form a gap between them, the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate. The first surfaces of the first and second multi-aperture plates each have an area that comprises plural apertures of the respective plurality of apertures, and generally includes the first and second location (of apertures). The area may, for instance, include several, the majority or all apertures of the respective plurality of apertures. In exemplary embodiments of the present invention, each first surface has an area comprising plural apertures of the respective plurality of apertures, wherein at least one of the first surfaces is a planar surface within the area. Preferably, the areas of the first surfaces of the first and second multi-aperture plates correspond to each other, i.e. have corresponding, preferably the same, shape and size and encompass the same aligned apertures. In alternative exemplary embodiments, the area of the first surface of the first multi-aperture plate may have an at least partially different size and/or shape and/or position than the area of the first surface of the second multi-aperture plate. A planar surface, as used herein, is one where slopes of tangents applied through any two neighbouring points show only gradual changes, if any, rather than large, sudden changes. For instance, the first surfaces of the first and second multi-aperture plates may be free from trenches, steps, recessions or the like. The characteristic planar refers to a scale, as seen in the direction parallel to the surface, that is in the order of more than one nanometer rather than referring to a scale which would be indicative of a level of surface smoothness, and applies to both flat and curved surfaces. A planar surface allows for good control of the electrical field generated in the gap upon application of a potential to the first and second multi-aperture plates. The same consideration applies in an analogous manner to magnetic applications. In this exemplary embodiment, the surface of the first surfaces may be planar only within the area that includes at least the locations of the apertures where the first and second width are determined, or may be planar across a larger region. In further exemplary embodiments, the at least one first surface is a curved surface within the area. For instance, the area may comprise all apertures of the respective plurality of apertures such that all apertures are located on the curved surface. In other exemplary embodiments, the area may comprise only a portion of the plurality of apertures such that said portion of apertures is disposed on the curved surface. For instance, the at least one first surface may be a convex surface within the area. In alternative exemplary embodiments, the at least one first surface is a concave surface within the area. For instance, the convex or concave shapes may be spherical or aspherical. Aspherical, as used herein, indicates any possible deviation from a spherical shape. In an exemplary embodiment, the particle-optical component may comprise two plano-convex multi-aperture plates. For example, the first surface of the first multi-aperture plate may be convex in the area whereas the first surface of the second multi-aperture plate may be concave, flat or randomly curved, resulting in an asymmetric overall arrangement of the two multi-aperture plates. In exemplary embodiments, shapes of the first surfaces of the first and second multi-aperture plates are symmetric with respect to each other, in particular relative to a plane extending between the first and second multi-aperture plates, i.e. a plane of symmetry, at least within the area. In particular, a shape of the area of the first surface of the first multi-aperture plate may preferably be mirror-inverted with respect to the shape of the corresponding area of the first surface of the second multi-aperture plate. In those embodiments that have an optical axis, the plane of symmetry would preferably be disposed orthogonally with respect to the optical axis. In further exemplary embodiments, a shape of at least one of the first surfaces is symmetric relative to an axis extending transversely to the first and second multi-apertures plates, for instance an optical axis. In those embodiments, the surfaces would therefore be rotationally symmetric. Symmetric exemplary embodiments as lined out above are particularly advantageous since imaging errors that are field-dependent generally show a radial dependency, i.e. their extent depends on a distance from a centre of a radius, with a centre of symmetry typically coinciding with an optical axis of the particle-optical component. In preferred embodiments, both first surfaces are convex surfaces and are mirror-inverted with respect to each other. Thus, a gap is formed that has a smallest width at an apex of the convex surfaces, the width of the gap increasing with increasing distance from the apex. Most preferably, this embodiment is used in connection with an aperture pattern on both the first and second multi-aperture plates that has a center that coincides with a respective apex, and preferably also has a rotational symmetry around the center of the pattern. Preferably also, the apex and center of symmetry coincides with an optical axis. This embodiment has proven to be very advantageous for correction of a field curvature, for example. It has been demonstrated that, from a practical point of view, use of identical first and second multi-apertures plates has substantial advantages. If a mask used in a photolithographic process for production of the multi-aperture plates, for instance, has a fault, the fault can be well compensated for if the individual multi-aperture plates resulting from the manufacturing process with the same mask being used are arranged such that a resulting fault in the first multi-aperture plate is confronted, that is aligned, with the same fault in the second multi-aperture plate, which results in substantially evening out the fault. In exemplary embodiments of the present invention, the second width is in a range of from 100% to 1000% of a diameter of the second aperture of the plurality of apertures of the first multi-aperture plate, for instance between about 150% to about 800% or between about 200% to about 750%. In those embodiments where the second aperture does not have a circular shape, but for instance an elliptical shape or an irregular shape, an area of the aperture in a plane of the first surface is determined and a diameter is calculated therefrom by treating the area as if it was circular, for purposes of determining the width of the gap. Preferably, the second width is measured and the second aperture is located in a centre f the plurality of apertures. Preferably also, the first width is measured and the first aperture located at a periphery, preferably at a furthest distance, compared to distances of the other apertures of the plurality of apertures, from the centre of the plurality of apertures. In further exemplary embodiments, the first width is in a range of from about 150% to about 1500% of a diameter of the first aperture, for instance between about 250% to about 1300% or between about 400% to about 1000%. If the first aperture is not circular, the method mentioned above in connection with the first aperture for deriving a diameter applies. In further exemplary embodiments of the particle-optical component, a width w of the gap between the first and second multi-aperture plates at a location of an Nth aperture from a centre of a pattern of apertures, wherein centres of the apertures are spaced a Pitch P apart, may be described by the following relationship:w=0.08 mm+0.0055×1/mm2×(P×|N|)3 wherein P denotes a pitch of the first multi-aperture plate in mm, i.e. a distance between centres of adjacent apertures; N denotes a number of an aperture, with the numbering starting in the centre of the pattern of apertures and the absolute value of the numbers increasing with increasing distance from the centre,such that (P×|N|) indicates a distance of an aperture N from the centre of the pattern of apertures in mm. In other embodiments, the constant c=0.08 mm as well as constant k=0.055 1/mm2 may have smaller or larger values. In preferred embodiments, a diameter of an aperture of the first multi-aperture plate is substantially equal to a diameter of a corresponding aperture of the second multi-aperture plate aligned with the aperture of the first multi-aperture plate. In further exemplary embodiments, the first multi-aperture plate has apertures formed therein that are substantially identical in at least one of shape, size and relative position to respective apertures in the second multi-aperture plate aligned therewith. These embodiments have the advantage that a beamlet exiting the apertures of the first multi-aperture plate can enter into the corresponding apertures of the second multi-aperture plate without substantial loss of charged particle intensity. Furthermore, the more symmetric the apertures of and the shapes on the first surfaces are, the easier it is to avoid any occurrence of imaging errors that my be introduced by the sequence of two aligned apertures. For instance, in a mirror-inverted symmetry of the first surfaces, a beamlet having passed through an aperture in the first multi-aperture plate is confronted with a mirror-inverted surrounding in the corresponding aperture in the second multi-aperture plate such that any influence exerted onto the beamlet by the first multi-aperture plates is practically reversed and thus nullified by the second multi-aperture plate. In other exemplary embodiments, apertures of the first and second multi-aperture plates that are aligned with one another may have different shape or size or be disposed so as to be slightly offset from one another. However, the difference or offset should be chosen such that no inacceptably adverse effects are introduced by such an asymmetry. The apertures of the respective plurality of apertures may all have the same diameter, or different diameters. Examples of multi-aperture plate wherein a diameter of the apertures varies across the multi-aperture plate are described in the above cited WO publication to the same Assignee. For instance, when the apertures are arranged in a pattern having a center, a diameter of the apertures formed in the multi-aperture plate may change with an increasing distance from the center of the aperture pattern. A diameter may increase or decrease with increasing distance from a center of the aperture pattern, wherein the increase or decrease may be gradual or in the form of steps or any other suitable form. The diameter of the apertures may also change from one side of the aperture plate to the other, for instance increase and then decrease, or vice versa. The diameter of the apertures may be used as a tool to compensate for imaging errors or, in addition or alternatively, to account for variations in an electron density in the charge particle beam or beamlets incident on the multi-aperture plate(s). The apertures may also have elliptical shapes. In those embodiments, a pitch of the apertures may vary, for instance with increasing distance from a center of the aperture pattern, and/or an elliptical shape may vary with respect to a direction of at least one of the axes of the corresponding ellipse. In exemplary embodiments of the particle-optical component of the present invention, a distance between adjacent apertures of the plurality of apertures of the first multi-aperture plate, or pitch P, may be in a range of from about 5 μm to about 200 μm. Pitch refers to a distance between adjacent apertures as measured from a center of one aperture to a center of the adjacent aperture. A distance between apertures adjacent to each other in the first direction of the multi-aperture plate may be the same distance for each pair of adjacent apertures, or may be different. For instance, a distance between adjacent apertures may continuously decreases with increasing or decreasing distance from the center of the pattern of apertures. Diameters D of apertures may be in a range of from 0.1×P to 0.5×P, a range of from 0.3×P to 0.6×P, a range of from 0.4×P to 0.7×P, a range of from 0.5×P to 0.7×P, a range of from 0.5×P to 0.6×P, a range of from 0.6×P to 0.7×P, a range of from 0.7×P to 0.8×P, and/or from 0.8×P to 0.9×P. The apertures of the plurality of apertures may have the same shape or different shapes. A shape may be circular, for instance, or elliptical, or any other suitable shape. At least one of the first and second multi-aperture plates may be made from silicon, for instance. Silicon offers a range of advantages in that, for instance, methods of precise processing of silicon are well established and reliable. In addition, silicon's semiconductor properties are well suited for the component of the present invention since they allow a potential suitable for the purposes of the application of the present invention to be applied. The first or second multi-aperture plate or both may be provided with a thin film, such as a thin film of titanium, gold, platinum, or any other precious metal, preferably on a second side thereof, i.e. a side facing away from the respective other multi-aperture plate. In alternative embodiments, a homogeneous thin film of carbon may also be used on the second side of the first and/or second multi-aperture plate. In addition to the thin film, a bonding agent may be used to enhance adhesion of the thin film to the surface of the multi-aperture plate, for example a thin film of bonding agent may be used in between the plate surface and the thin metal film. As an example, Cr, W or Pt, or any suitable combination thereof, may be used as a bonding agent. These exemplary embodiments are advantageous for protecting the respective multi-aperture plate from contaminations, in particular when a potential is applied to the multi-aperture plate, and may assist in decreasing heat and/or charge accumulating on a respective surface or avoiding oxidation thereof. The particle-optical component further comprises, in exemplary embodiments, a mounting structure for mounting the first multi-aperture plate relative to the second multi-aperture plate. In an exemplary embodiment, the mounting structure comprises a spacer arrangement that comprises one or more spacer elements that are disposed at respective edges of the multi-aperture plates. The spacer elements has dimensions suitable to fix the first and second multi-aperture plates in position whilst forming a gap of a predetermined width between them. In addition, or alternatively, the mounting structure may comprises a frame having fixing elements, with a respective fixing element holding one of the multi-aperture plates at a predetermined distance from the other multi-aperture plate held by another fixing element. It is most preferred that the first and second multi-aperture plates are mounted such that they are electrically insulated from another. In other embodiments, the multi-aperture plates may be suitably bonded together at respective peripheries thereof. The mounting structure may, for instance, comprise at least one actuator for adjusting a position of the first multi-aperture plate relative to the second multi-aperture plate (and thus, automatically, vice versa). The position may be a horizontal or a vertical position or a rotational position, wherein an adjustment of the vertical position allows to adjust a width of the gap formed between the multi-aperture plates whereas the adjustment of the horizontal position or rotational position allows to align apertures of the first multi-aperture plate with corresponding apertures of the second multi-aperture plates. Preferably, the alignment of the apertures of one multi-aperture plate with the corresponding apertures of the other multi-aperture plate is provided with a precision of alignment of better than about 100 nm. For instance, the precision of alignment may be in a range of from about 1000 nm to about 2 μm. It will be apparent to the person skilled in the art, that a necessary precision of alignment will strongly depend on the individual particle-optical system and particle-optical component. Likewise, it is preferred that a width of the gap between the first and second multi-aperture plates can be set at a predetermined value with a precision of about 0.5 μm, or 1 μm, for instance. In those exemplary embodiments wherein the mounting structure provides an actuator, in particular for vertical adjustment of the multi-aperture plate(s), the actuator may be configured such that it readily allows adjustment when the operating parameters or properties of the charged optical beams or beamlets change to allow for a dynamic response to varying operating conditions or a change in environment or the like. For example, the alignment of the multi-aperture plates relative to each other may be optically controlled by generating a Moire pattern or an interferogram from light reflected from or transmitted by components associated with the multi-aperture plates. Background information and examples of high-precision alignment are given in the articles “Self-Aligned Assembly of Microlens Arrays with Micromirrors” by A. Tuantranont et al., Part of the SPIE Conference on Miniaturized Systems with Micro-Optics and MEMS, Santa Clara, September 1999, SPIE Vol. 3878, pages 90 to 100 and “Microassembly Technologies for MEMS” by M. B. Cohn et al., Part of the SPIE Conference on Micromachining and Microfabrication Process Technology IV, Santa Clara, Calif., September 1998, SPIE Vol. 3511, pages 2 to 16, which are incorporated herein by reference. The particle-optical component may, in exemplary embodiments, further comprise a third multi-aperture plate having a plurality of apertures formed therein and being arranged such that the first multi-aperture plate is disposed between the third multi-aperture plate and the second multi-aperture plate, and wherein the plurality of apertures of the third multi-aperture plate is arranged such that each aperture of the plurality of apertures of the third multi-aperture plate is substantially registered or aligned, respectively, with a corresponding aperture of the plurality of apertures of the first multi-aperture plate. In other exemplary embodiments, a third multi-aperture plate may be used so that the second multi-aperture plate is disposed between the first and third multi-aperture plates. The third multi-aperture plate may advantageously be used to generate a plurality of charged particle beamlets from one or more charged particle beams incident thereon. Preferably, the plurality of apertures of the third multi-aperture plate is arranged in a pattern that corresponds at least partially to an aperture pattern of at least one of the first and second multi-aperture plates. Preferably, the first, second and third multi-aperture plates have a pattern (or subpattern) of apertures in common, i.e. the plurality of apertures is arranged in a certain aperture pattern, the apertures of which are brought in alignment with one another. Provision of a third multi-aperture plate has the advantage that a number of charged particle beamlets may be provided such that the number of charged particles incident on the first multi-aperture plate, and in particular a second surface thereof, is decreased (as compared to a single beam of charged particles impinging upon the first multi-aperture plate) and thus heating and charging effects and damage caused by contaminations and the like minimized. In the exemplary embodiments of the particle-optical component comprising the third multi-aperture plate, a diameter of an aperture of the third multi-aperture plate may be smaller than a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. This may be the case for one or more, preferably for all of the plurality of apertures of the third and first multi-aperture plates that are aligned with one another. In this embodiment of the present invention, beamlets can be generated by the third multi-aperture plate that have a diameter that is smaller than a diameter/diameters of corresponding, aligned apertures in the first multi-aperture plate, preferably also than a diameter/diameters of corresponding aligned apertures of the second multi-aperture plate such that losses due to electrons impinging onto a surface adjacent to an aperture in the first and/or second multi-aperture plates and resulting heating effects, contaminations etc. can be substantially avoided or at least minimized. This embodiment of the present invention also allows changing a numerical aperture of the charged particle beamlets. For instance, a third multi aperture plate having apertures with diameters of a first size generates charged particle beamlets having a first numerical aperture and a third multi aperture plate having apertures with a second size which is smaller than the first size generates charged particle beamlets with second numerical apertures which are smaller than the first numerical apertures. In the above described exemplary embodiments, a diameter of an aperture of the third multi-aperture plate is preferably less than from about 100% to about 50%, for instance from about 99% to about 50%, or from about 99% to about 75% of a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. If apertures of the plurality of apertures in the first (and/or second) multi-aperture plates vary in size, corresponding aligned apertures in the third multi-aperture plate may, for instance, have a size that is smaller by a predetermined percentage of the individual aperture or by a constant amount for all apertures (relative to the size of the aligned aperture in the first multi-aperture plate). Above described embodiments of the first and second multi-aperture plates with respect to size, shape, arrangement and variations in connection with the apertures and arrays thereof equally apply to the third multi-aperture plate. In exemplary embodiments, the third multi-aperture plate is disposed at a distance in a range of from about 0 to about a few millimeters from the second surface of the first multi-aperture plate. The third multi-aperture plate may be spaced further apart from the first multi-aperture plate than the second multi-aperture plate, for instance a distance between the first multi-aperture plate and the third multi-aperture plate may be at least twice the first width, or three to five times the first width in the embodiments where the first multi-aperture plate is disposed between the third and second multi-aperture plate. In those embodiments where the second multi-aperture plate is disposed between the first and the third multi-aperture plate, the above considerations apply with the second multi-aperture plate taking the place of the first multi-aperture plate and vice versa. Those exemplary embodiments that comprise the third multi-aperture plate preferably further comprise a mounting structure for mounting the third multi-aperture plate relative to the first multi-aperture plate, wherein the mounting structure preferably comprises at least one actuator for adjusting a position of the third multi-aperture plate relative to the first multi-aperture plate. In exemplary embodiments, the third multi-aperture plate may comprise a number of different aperture arrays, which may comprise a plurality of apertures each. For instance, the third multi-aperture plate may have two arrays of apertures wherein the apertures of one array have smaller diameters than corresponding apertures of the other array. A range of aperture arrays having different properties in terms of aperture size, shape, arrangement (e.g. pitch, position), number and the like and, accordingly, different particle-optical properties, such as transmission properties, may be incorporated into one multi-aperture plate. Using a suitable mounting device, the third multi-aperture plate may then be moved such that, in accordance with specific requirements or a change of particle-optical parameters in the particle-optical system, a different aperture array may be used for a particular application, i.e. is disposed in the path of the one or more beams of charged particles which are subsequently directed onto the first and second multi-aperture plates. This allows, for instance, to change a transmission of the third multi-aperture plate which may be used advantageously with respect to an occurring Coulomb effect. In addition, in order to compensate for a distortion effect, the third multi-aperture plate may be shifted so that the respective plurality of apertures thereof are disposed to be slightly offset with respect to corresponding apertures in the first and second multi-aperture plates. In exemplary embodiments, the third multi-aperture plate is connected to a temperature controlling device for maintaining the third multi-aperture plate at a desired temperature, for instance a heating device for heating the third multi-aperture plate to a desired temperature. Controlling the temperature of the multi-aperture plates to a certain precision, such as 1° C., is helpful in maintaining the accurate alignment of the multi-aperture plates relative to each other. Further, heating of the multi-aperture plates may help to reduce contamination thereof. In addition or alternatively to the above described embodiments, exemplary embodiments of the particle-optical component may further comprise a fourth aperture plate having at least one aperture, the first multi-aperture plate being disposed between the fourth aperture plate and the second multi-aperture plate, and may further comprise a mounting structure comprising at least one actuator for displacing the fourth aperture plate relative to the first multi-aperture plate such that in a first position, one aperture of the at least one aperture of the fourth aperture plate is in alignment with a first aperture of the first multi-aperture plate, and in a second position, which second position is different from the first position, the one aperture is in alignment with a second aperture of the first multi-aperture plate, which second aperture is different from the first aperture. In exemplary embodiments, the mounting structure of the fourth aperture plate is configured such that the fourth aperture plate may be displaced in a horizontal direction or may be rotated about an axis so as to bring the at least one aperture of the fourth aperture plate in alignment with different apertures of the first multi-aperture plate. The fourth aperture plate may also be displaceable in a vertical direction or be tiltable or the like. The fourth aperture plate has at least one aperture, and may have, for instance, two or more apertures. In exemplary embodiments, the fourth aperture plate may have a pattern of apertures which pattern may correspond to at least a portion of a pattern of the plurality of apertures of at least the first multi-aperture plate. For instance, the fourth aperture plate may have a pattern of three apertures which corresponds to a portion of a pattern of apertures in the first multi-aperture plate, i.e. is a sub-pattern of the pattern of the apertures of the first multi-aperture plate, such that apertures of the sub-pattern of the fourth aperture plate and the corresponding apertures of the pattern in the first multi-aperture plate can be brought in alignment with one another in a direction of a path of the one or more beams of particles. The at least one aperture may have a diameter which is smaller than a diameter of an aperture, such as the first aperture, of the plurality of apertures of at least one of the first and second, and, if provided, third multi-aperture plates. For instance, a diameter of at least one of the at least one aperture of the fourth aperture plate has a smaller diameter than an average diameter of apertures of the plurality of apertures, or than a smallest diameter of apertures of the plurality of apertures. The fourth aperture plate may also comprise at least one of apertures of different diameters and different patterns or sub-patterns of apertures having the same or different apertures within a (sub-)pattern. If both a third multi-aperture plate and a fourth aperture plate are provided, the fourth aperture plate may, for instance, be disposed such that the third multi-aperture plate is disposed between the fourth aperture plate and the first and second multi-aperture. In other exemplary embodiments, the third aperture plate and the fourth aperture plate may be disposed on one plate or combined to form only one plate having the characteristics of both the third and fourth aperture plate, wherein in this embodiment, preferably a mounting structure including at least one actuator is provided for positioning either the section of the one plate that holds the third or the section that holds the fourth aperture plate into the beam path of the one or more beams of charged particles. Embodiments of the present invention comprising the fourth multi-aperture plate may be used advantageously for testing an alignment of the first and second multi-aperture plates or for testing properties of individual apertures of the first or second multi-aperture plate, for example, i.e. the fourth aperture plate may be used as a testing aperture plate. In addition, the fourth aperture plate may be used for testing optical properties of other components of a particle-optical system. Accordingly, in a second aspect, the present invention provides a method of operating a particle-optical system, comprising: positioning a testing aperture plate having at least one aperture in a first position relative to a multi-aperture component comprising a plurality of apertures such that in the first position, a first set of apertures of the testing aperture plate is in alignment with a first set of apertures of the multi-aperture,with the respective sets of apertures comprising at least one aperture each,transmitting a set of beamlets of charged particles through the first set of apertures of the testing aperture plate and the first set of apertures of the multi-aperture component aligned therewith,determining at least one of positions, shapes and dimensions of the transmitted beamlets in a predetermined plane and a total intensity or individual intensities of the transmitted beamlets,positioning the testing aperture plate in a second position relative to the multi-aperture component such that the first set of apertures of the testing aperture plate is in alignment with a second set of apertures of the multi-aperture component,transmitting a set of beamlets of charged particles through the first set of apertures of the testing aperture plate and the second set of apertures of the multi-aperture component aligned therewith,determining at least one of positions, shapes and dimensions of the transmitted beamlets in the predetermined plane and a total intensity or individual intensities of the transmitted beamlets. The respective sets of apertures comprise at least one aperture each. Likewise, a set of beamlets comprises at least one beamlet. In preferred embodiments, the number of beamlets in the set of beamlets corresponds to the number of apertures in the respective set of apertures, i.e. only one beamlet is transmitted through one aperture at a time. In other embodiments, it is also conceivable that more than one beamlet may be transmitted through an aperture. In exemplary embodiments, the testing aperture plate may be the fourth aperture plate as described above, for instance also in combination with the third multi-aperture plate, as lined out above. Embodiments described in connection with the first, second, third and fourth multi-aperture plates, for instance with regard to pattern, shape and dimension of apertures are generally also applicable to the testing aperture plate. Determination of position, shape, dimension and intensity of one or more transmitted beamlets may be carried out by conventional methods, such as by placing a suitable detector in the predetermined plane. The predetermined plane may be, for instance, a plane vertical to an optical axis of the particle-optical system. The multi-aperture component may be a single multi-aperture plate, a plurality of multi-aperture plates aligned with one another or, most preferably, a particle-optical component according to the present invention. Transmitting a set of beamlets of charged particles through the first set of apertures of the testing aperture plate may comprise directing one or more beams or a set of beamlets of charged particles onto the first set of apertures of the testing aperture plate such that a set of beamlets of charged particles is formed by the set of apertures and transmitted therethrough. In further exemplary embodiments, the method further comprises adjusting at least one of an optical property and a position of the multi-aperture component based on the at least one of positions, shapes and dimensions of the transmitted beamlets in the predetermined plane and the total intensity of individual intensities of the transmitted beamlets. For instance, adjusting at least one optical property or position of the multi-aperture component may comprise changing a position of the multi-aperture plate in a particle-optical system, changing characteristics of one or more apertures of the multi-aperture component, adjusting a position of a first relative to a second multi-aperture plate in the particle-optical component according to the present invention, such as by rotating, tilting or shifting one multi-aperture plate relative to the other, and the like. Furthermore, in other exemplary embodiments, the method comprises adjusting at last one optical property of the particle-optical system based on the at least one of positions, shapes and dimensions of the transmitted beamlets in the predetermined plane and the total intensity of individual intensities of the transmitted beamlets, for instance by adjusting at least one of a parameter and a position and thus optical properties of other particle-optical components of the particle-optical system, such as an excitation of a deflector of the particle-optical system, by adjusting an excitation of a stigmator comprised in such a system, or by adjusting one or more other optical properties of one or more other components of the charged particle optical system, as will be apparent to those skilled in the art. In those embodiments where the multi-aperture component comprises a multi-aperture plate wherein each of a plurality of apertures has a deflecting arrangement connected thereto, deflecting arrangement for deflecting transmitted beamlets of charged particles. Deflecting arrangements, which are generally also referred to as blanking arrays are described, for instance, in U.S. Pat. No. 5,369,282 and U.S. Pat. No. 5,399,872, the entire contents of which are incorporated by reference herein. The testing may be achieved, for instance, by bringing the same aperture of the testing aperture plate sequentially in alignment with different individual apertures and associated deflecting arrangements to be tested, and transmitting particles there through and detecting at least one of an intensity and position of the transmitted beamlet of charged particles. A deviation of detected position or detected intensity or both from a predetermined position or intensity may give an indication of an error or misalignment or the like of the tested aperture/deflecting arrangement, as will be readily apparent to the person skilled in the art. In other exemplary embodiments, the particle-optical component may comprise a fifth aperture plate having a single aperture of a diameter configured such that only a predetermined number of apertures of the plurality of apertures of the first and/or third multi-aperture plate is irradiated with charged particles of a charged particle beam or charged particle beamlets passing through the fifth aperture plate, for instance the number may comprise half of the apertures of the plurality of apertures or any other fraction thereof. By a suitable choice of the diameter of the single aperture, a transmission of charged particle and a charged particle intensity impinging onto the first multi-aperture plate can be suitably controlled. In a third aspect, the present invention provides a particle-optical arrangement, comprising a charged particle source for generating at least one beam of charged particles; and at least one particle-optical component as described above and arranged such that the second multi-aperture plate is disposed in a beam path of the charged particles downstream of the first multi-aperture plate. Unless otherwise indicated, in the embodiments described herein, the second multi-aperture plate is disposed downstream of the first multi-aperture plate for ease of reference. The charged particle source may be any conventional particle source suitable for use in the present invention. In those embodiments where the charged particles are electrons, the charged particle source would be a an electron source, such as an electron source of a thermal field emission (TFE) type. In those embodiments where ions are used as charged particles, an ion gun would be a suitable charged particle source, for instance. Charged particle sources suitable for use in the present invention are well known in the art and include sources employing a tungsten (W) filament, LaB6 sources and various others. It is to be noted further that the charged particle source may be a source of a single beam of charged particles, may be an array of sources of a single charged particle beam each, or a multi-beam source. Exemplary embodiments of the particle-optical arrangement according to the present invention further comprise a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates. The voltage supply may be any suitable voltage supply known in the art. The voltage supply may be configured to supply voltages in the range of 0 to several 100 kV. Preferably, the voltage supply is an adjustable voltage supply. Adjustment of the potential applied to the multi-aperture plates, in particular the potential difference between the potential applied of the first multi-aperture plate and the potential applied to the second multi-aperture plate, allows to adjust a focussing and/or correcting effect of the particle-optical component of the present invention. Exemplary embodiments of the particle-optical arrangement according to the invention further comprise a controller having a first control portion configured to control the voltage supply system based upon a total beam current of a plurality of charged particle beamlets downstream of the particle-optical component. The charged particles may be primary charged particles, i.e. charged particles as generated by the charged particle source, or in embodiments where the particle-optical arrangement is part of an inspection system wherein primary particles are directed onto a specimen for inspection thereof, a current of secondary particles being emitted from the specimen being inspected may be used as a measure for the total beam current. In view of the transmission characteristics of particle-optical components in a system generally being known, an output signal of a charged particle source may also be used as a measure for the total beam current of the plurality of charged particle beamlets. Other methods of determining a total beam current directly or indirectly, such as measuring a charge building up on an particle-optical component in a system or the like, are also conceivable. In further exemplary embodiments, the particle-optical arrangement additionally comprises a current detector for detecting the total beam current of the plurality of charged particle beamlets. The controller may also have a second control portion for adjusting beam currents of the plurality of charged particle beamlets, wherein the first control portion is responsive to a setting of the second control portion. This embodiment is particularly useful in those embodiments where at least one aperture of the first or second multi-aperture plates comprises a deflection arrangement for deflecting a charged particle beamlet being transmitted through the respective aperture. In those embodiments, the second control portion may control the deflecting arrangement, in particular a deflecting/non-deflecting position associated with the at least one respective aperture such that beam currents of beamlets passing therethrough may be controlled, and transmit a signal indicating the setting of the second control portion to the first control portion which adjusts the voltage supply in response thereto. This allows to adjust a correcting/compensating property of the particle-optical component to be adjusted to a beam current which takes into account an influence of a density of charged particles and resulting charge repulsion on those particle-optical aberrations to be compensated by the particle-optical component. The particle-optical arrangement of the present invention may further, in addition or alternatively to the exemplary embodiments described above, comprise in another exemplary embodiment a first electrode disposed in the beam path of the charged particles upstream of the first multi-aperture plate, a second electrode disposed in the beam path of the charged particles downstream of the second multi-aperture plate, and a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates and the first and second electrodes. The arrangement of electrodes with respect to multi-aperture plates as outlined above and as further described below refers to embodiments of the present invention where the first multi-aperture plate is disposed upstream of the second multi-aperture plate, in the embodiments of the present invention where the arrangement of the multi-aperture plates is the other way round, analogous considerations apply. In those exemplary embodiments of the particle-optical arrangement of the present invention comprising the first and second electrodes, the voltage supply system may be configured to apply voltages to the first electrode and the first multi-aperture plate such that an electrical field generated upstream of the first multi-aperture plate in a vicinity thereof is a decelerating field for the charged particles of the beam of charged particles. Alternatively, the voltage supply system may be configured to apply voltages to the first electrode and the first multi-aperture plate such that an electrical field generated upstream of the first multi-aperture plate in a vicinity thereof is an accelerating field for the charged particles of the beam of charged particles. Alternatively or in addition thereto, in exemplary embodiments of the particle-optical arrangement according to the present invention, the voltage supply system is configured to apply voltages to the second electrode and the second multi-aperture plate such that an electrical field generated downstream of the second multi-aperture plate in a vicinity thereof is an accelerating field for the charged particles of the beam of charged particles. Alternatively, the voltage supply system may be configured to apply voltages to the second electrode and the second multi-aperture plate such that an electrical field generated downstream of the second multi-aperture plate in a vicinity thereof is a decelerating field for the charged particles of the beam of charged particles. Potentials can be applied to at least one of the first multi-aperture plate, the second multi-aperture plate, the first, second and third electrode in various different manners. Suitable choice of applied potentials and thus electrical fields upstream and downstream and within the particle-optical component of the present invention allows, for instance, a variety of different modes of providing, for instance, a focussing effect and/or a correcting effect for the beamlets that are to be incident on the substrate. In one exemplary embodiment, for instance, the potentials may be chosen such that an electrical field providing a major part of a focussing effect is located upstream of the component of the present invention and an electrical field providing a major part of a correcting effect situated downstream of the component, or vice versa. The potentials may also be suitably chosen such that a region upstream or downstream in the vicinity of the component is substantially devoid of any electrical field, for instance. Exemplary embodiments of a variety of such modes will be described in more detail with reference to the drawings. In further exemplary embodiments, the particle-optical further comprises, in addition to the first and second electrode, a third electrode disposed in the beam path of the charged particles between the first electrode and the first multi-aperture plate, wherein the voltage supply system is further configured to apply an electric potential to the third electrode. In further exemplary embodiments, the particle-optical further comprises, in addition to the first and second electrodes, a fourth electrode disposed in the beam path of the charged particles between the second multi-aperture plate and the second electrode, wherein the voltage supply system is further configured to apply an electric potential to the fourth electrode. The first to fourth electrodes may be single-aperture electrodes, for instance. In further exemplary embodiments, the voltage supply may be configured to apply voltages to one or more of the first, second, third and fourth electrodes such that an electrical field upstream of the particle-optical component is a substantially homogeneous electrical field in the vicinity thereof and that an electrical field downstream of the particle-optical component is a substantially homogeneous electrical field in the vicinity thereof and has a field strength different from a field strength of the electrical field upstream of the particle-optical component. The arrangement of the present invention may, for instance, further comprise at least one focussing particle-optical lens disposed in the beam path of the charged particle beam. In this embodiments of the present invention, the arrangement preferably further comprises a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates, for compensating at least one of a field curvature and a spherical aberration of the at least one focussing particle-optical lens. The at least one focussing particle-optical lens may be disposed upstream or downstream of the component of the present invention. In those embodiments of the present invention comprising at least one focussing particle-optical lens, the voltage supply system is preferably configured to apply electric potentials to the first and second electrodes such that beamlets traversing the first and second multi-aperture plates each form a focus in a focusing region downstream of the second multi-aperture plate; further comprising at least one focussing particle-optical lens disposed downstream of the second multi-aperture plate in the beam path of the charged particles; wherein the voltage supply system is further configured to apply different electric potentials to the first and second multi-aperture plates, for compensating at least one particle-optical aberration of the at least one focussing particle-optical lens. Compensating the at least one particle-optical aberration may comprise compensating at least one of a field curvature or a spherical aberration of the at least one focussing particle-optical lens. In a fourth aspect, the present invention provides a multi-beam electron inspection system comprising the particle optical component according to the present invention. In exemplary embodiments of the multi-beam electron inspection system, the particle-optical component is disposed in a primary electron beam path of the system. In a fifth aspect, a multi-beam electron inspection system is provided by the present invention, which multi-beam electron inspection system comprises: an electron source for generating at least one beam of primary electrons; a stage for a specimen to be inspected; a particle-optical component according to the present invention disposed in a beam path of the at least one beam of electrons downstream of the electron source; a voltage supply system for applying electric potentials to the first and second multi-aperture plates of the particle-optical component; at least one focussing particle-optical lens disposed in the beam path of the at least one electron beam downstream of the particle-optical arrangement; and a detector arrangement for detecting at least one of secondary particles and radiation emitted by the specimen as a result of being exposed to the electrons. The exemplary embodiments, considerations and features described in connection with the individual particle-optical component and arrangements according to the present invention are, of course, equally applicable to the component or arrangement when used in a system or a method as described herein. In a sixth aspect, the present invention provides a method of manipulating charged particle beamlets, comprising generating at least one of a charged-particle beam and a plurality of charged-particle beamlets; transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through a particle-optical component according to the present invention, applying a predetermined electric potential to the first and second multi-aperture plates each; and transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through the at least one focussing particle-optical lens. Applying a predetermined electrical potentials to the first and second multi-aperture plates preferably involves applying a first electrical potential to the first multi-aperture plate and a second electrical potential to the second multi-aperture plate, with the first and second potentials being different. Applying an electrical potential, as used herein, is also meant to encompass those embodiments where the respective multi-aperture plate or electrode is grounded. The at least one focussing particle-optical lens may be disposed upstream or downstream of the component according to the present invention, hence the charged particles, such as electrons, may pass through the lens before passing through the component of the present invention, or vice versa. Typically, however, the at least one lens will be disposed downstream of the component of the present invention. In exemplary embodiments of the present invention, the component of the present invention may be used to provide both a correcting and a focussing effect or a correcting effect alone with only a very small focussing effect. In those embodiments of the present invention wherein an additional first or second or third electrode or a third multi-aperture plate or any combination thereof are provided, the method further comprises applying a suitable potential to the respective one or ones of those electrodes and multi-aperture plates. The choice where electrodes are disposed and the choice of applied potentials allows various variants and combinations of focussing, defocusing or no electrical fields upstream and downstream of the component of the present invention such that a main focussing effect may be provided by an electrical field upstream or downstream of the component of the present invention or a combination thereof. In the above method, the predetermined voltage or potential applied to at least one of the first and second multi-aperture plate may be, for instance, in a range of from 0 to 5000 V. In further exemplary embodiments of the method of the present invention, the applied predetermined voltage is chosen such that at least one particle-optical aberration is compensated for, for instance a field curvature or a spherical aberration of the at least one focussing particle-optical lens may be compensated for. In practice, the at least one focusing lens, alone or in combination with other components of a particle-optical system, generally contributes to a field curvature of the particle-optical system such that foci of beamlets, which foci are located in a flat plane of foci, are imaged into a curved plane close to a specimen surface. Therefore, the resulting curved image plane fails to coincide with the flat surface of the specimen, and the foci of the beamlets cannot be perfectly imaged onto the surface of the specimen. The component of the present invention may be advantageously used to correct such a field curvature. In those embodiments where the at least one focusing lens is disposed downstream of the component of the present invention, the component can be suitably configured in terms of its design (shape of the first surfaces, width of the gap etc.) and a potential difference applied thereto, that the plane or region where the foci of the charged particle beamlets are generated (focus plane or region) is a curved focus region. The curvature of this curved focus region can be adjusted such that the at least one focusing particle-optical lens images the curved plane into a flat image plane such that it is possible to position a planar surface of the specimen to coincide with the flat image plane. In electrostatic applications, in general, a focusing effect, more precisely a focal length f provided by each aperture of a single multi-aperture plate may be estimated according to the formula f = 4 q E kin Δ E ,wherein Ekin is a kinetic energy of charged particles at the multi-aperture plate; q is the charge of the charged particle and ΔE represents a difference in electric field strengths (E2-E1) of electrical fields provided upstream and downstream of the multi-aperture plate. In a particle-optical component according to the present invention, the first or second multi-aperture plate, respectively, may be regarded as a multi-aperture arrangement (MAA) which may provide the main focus whereas the combination of the first and second multi-aperture plate, and, in particular, the electrical field generated in the gap between them may be regarded as an immersion MLA (multi-lens arrangement) having a weak focusing effect. Taking the above into account, a combined focusing power would comprise a term 1 f MAA = q · Δ E 4 E kin for the focusing power of the MAA (multi-aperture array)-equivalent of the particle-optical component, and a term 1 f MLA = 3 · q 2 16 w ( Δ U E kin ) 2 for the focusing power of the MLA-equivalent, wherein ΔU is the difference of the potential applied to the first multi-aperture plate (U1) and electrical potential applied to the second multi-aperture plate (U2); and w is a width of the gap between locations at respective apertures in the first and the second multi-aperture plates. In combination, the terms would add to 1 f ∑ = 1 f MAA + 1 f MLA ≈ q · Δ E 4 E kin + 3 · q 2 16 w ( Δ U E kin ) 2 which provides an estimate of the combined focus effect. Given that the width w varies across the gap in between the first and second multi-aperture plates in the particle-optical component of the present invention, it becomes clear that the relatively small focusing effect provided by the electrical field in the gap between the first and second multi-aperture plates varies in dependence of the width and is therefore different for apertures at locations of different gap widths, thus allowing to shape a focus region of the beamlets such that a particle-optical aberration can be compensated for. In a seventh aspect, the present invention provides a method of focusing a plurality of charged particle beamlets, the method comprising: transmitting at least one of a charged particle beam and a plurality of charged-particle beamlets through a first multi-aperture plate and a second multi-aperture plate, each having a plurality of apertures, with centres of the first and second multi-aperture plates being spaced a distance w0 apart,applying a first electric potential U1 to the first multi-aperture plate,applying a second electric potential U2 to the second multi-aperture plate, the second electric potential being different from the first electric potential;at least one of generating an electrical field traversed by the beam path upstream of the first multi-aperture plate and an electrical field traversed by the beam path downstream of the second multi-aperture plate, such that a first field strength E1 of an electrical field upstream and in the vicinity of the first multi-aperture plate differs from a second field strength E2 of an electrical field downstream and in the vicinity of the second multi-aperture plate by at least about 200 V/mm, for instance at least about 500 V/mm, in other embodiments at least 750 V/mm and in further exemplary embodiments at least 1000 V/mm, wherein for charged particles having a charge q and having a kinetic energy Ekin upon traversing the first multi-aperture plate, the following relationship is fulfilled: 0.0001 ≤ 3 4 · q w 0 · E kin ( U 1 - U 2 ) 2 E 1 - E 2 ≤ 0.2 . In other words: electrical field strengths E1 and E2, potentials U1 and U2, a distance w (w0, respectively) between the first and second multi-aperture plates and kinetic energy of the charged particles are chosen such that a multi-aperture array (MAA) as provided by the second multi-aperture plate provides a main focus in a charged-particle system whereas an immersion multi lens array as provided by the combination of the first and second multi-aperture plates only provides a relatively weak focussing effect which is superimposed onto the main focussing effect of the MAA. In those preferred embodiments of the present invention where a width of the gap between the first multi-aperture plate and the second multi-aperture plate varies, a point of focus of beamlets exiting from the second multi-aperture plate varies with a width w of the gap in a location of the aligned apertures where the respective beamlet is exiting from. In exemplary embodiments, the focal length of the main focussing of the MLA may be shortened by about 5%, or 10% or 20% by the focussing effect as provided by the MAA. Preferably, a focal length of the MLA is greater than 2 m. In particular through the choice and adjustment of electrical potentials applied to the first and second multi-aperture plates, a level of the compensating effect provided by the component can be readily adjusted such that the component is suitable for a wide range of operating conditions and system layouts. In the method according to this aspect, the particle-optical component of the present invention may advantageously be used, and preferably a width between the first and second multi-aperture plates increases with increasing distance from the centres thereof such that a field strength of an electrical field generated by applying the first and second electrical potentials U1 and U2 in between the first and second multi-aperture plates decreases with increasing distance from the centre. For instance, in those embodiments, the width w0 may be the first width as referred to above. In exemplary embodiments, a suitable lower limit in the above equation may also be 0.05 or 0.08, and an upper limit may be 0.18 or 0.15, for instance. In an eighth aspect, the present invention a particle-optical arrangement, comprising: a charged particle source for generating at least one beam of charged particles; at least one magnetic lens configured to generate a first magnetic field in a path of the at least one beam; at least a first multi-aperture plate having a plurality of apertures, wherein the at least first multi-aperture plate is disposed to be traversed by a beam path of the at least one beam of charged particles; at least one coil arrangement configured to generate a second magnetic field such that a magnetic flux density at the at least first multi-aperture plate is substantially zero. As will be readily apparent to the person skilled in the art, substantially zero is also meant to encompass those embodiments where there is a negligibly small magnetic field present in the vicinity of the at least first multi-aperture plate as long as this magnetic field does not adversely affect imaging properties of the system, such as lead to a decrease in transmission. In exemplary embodiments, the particle-optical arrangement further comprises a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed there between; wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of the apertures of the second multi-aperture plate; wherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5% greater, for instance at least 10% or 20% greater, and in further exemplary embodiments by at least 50%, 100%, 200%, 500%, or 700% (several 100%) greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate. In addition, in those embodiments, the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate, wherein each first surface has an area comprising plural apertures of the respective plurality of apertures, and wherein at least one of the first surfaces is planar curved surface within the area. Preferably, the first multi-aperture plate in the arrangement according to the eight aspect of the present invention is part of the charged particle-optical component of the present invention as described before or may comprise one or more features of embodiments of the charged-particle components and arrangements of the present invention. The present invention also provides, in a ninth aspect, a method of manipulating charged particle beamlets, the method comprising: generating at least one of a charged-particle beam and a plurality of charged-particle beamlets; transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through at least one magnetic lens generating a first magnetic field; transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through at least one multi-aperture plate having a plurality of apertures; and generating a second magnetic field by applying a predetermined electric current to a coil arrangement traversed by the plurality of charged particle beamlets such that the second magnetic field at least partially compensates the first magnetic field and a magnetic flux density at the at least one multi-aperture plate is substantially zero. Substantially eliminating a magnetic field at a location of the at least one multi-aperture plate or particle-optical component of the present invention is beneficial in that the charged particles are then not exposed to a rotational force exerted by the magnetic field and do not change their paths. Exposure to such a rotational force could, for instance, result in individual charged particles being no longer transmitted through apertures in the second multi-aperture plate. Instead, they would impinge upon spaces in between the apertures, resulting in a loss of transmission. In a tenth aspect of the present invention, a further particle-optical arrangement is provided which comprises: a particle-optical component according to the present invention, with embodiments thereof as described herein, a magnetic lens arrangement comprising a first pole piece and a second pole piece and a coil for inducing magnetic flow in the first and second pole pieces, wherein the first multi-aperture plate is magnetically coupled to or integrally formed with the first pole piece of the magnetic lens arrangement and the second multi-aperture plate is magnetically coupled to or integrally formed with the second pole piece of the magnetic lens arrangement. A varying width of the gap formed in between the first and second multi-aperture plates results in a magnetic field of varying field strength across the length of the gap. For different pairs of aligned apertures of the first and second multi-aperture plates, which multi-aperture plates act as different poles of the magnetic lens, magnetic fields are different from each other such that beamlets passing though one pair of associated apertures may be subject to a stronger or weaker magnetic field than beamlets passing through a different pair of associated apertures. In those embodiments where a width of the gap increases with increasing distance from a centre, i.e. radially outwards, a magnetic flux density of magnetic fields formed in the gap decreases as the width of the gap increases. In principle, analogous considerations as for electrostatic fields also apply here. In an eleventh aspect, the present invention also provides a charged-particle multi-beamlet lithography system for writing a pattern on a substrate, the system comprising: a stage for mounting the substrate, a charged-particle source for generating at least one beam of charged particles, a particle-optical component according to the present invention, and an objective lens for focussing the charged particle beamlets on the substrate. In a twelfth aspect of the present invention, a method of writing a pattern on a substrate is provided, the method comprising: generating at least one beam of charged particles; transmitting the at least one charged-particle beam through a particle-optical component according to the present invention, applying a predetermined first electric potential to the first multi-aperture plate and a predetermined second electric potential different from the predetermined first potential to second multi-aperture plate;and focussing charged-particle beamlets exiting from the particle-optical component onto the substrate. In a thirteenth aspect, the present invention relates to a method of manufacturing a multi-aperture plate having a curved surface, comprising: etching a pattern of holes into a substrate from a front surface of the substrate such that a depth of a hole is smaller than a thickness of the substrate, processing a back surface of the substrate such that at least a portion of the back side of the substrate has a curved shape, and etching the back surface of the substrate to such an extent that at least a portion of the holes etched into the substrate from the front surface thereof extend through the entire thickness of the substrate to form apertures through the substrate. As the thickness of the substrate may vary, etching the holes through the entire thickness of the substrate refers to the thickness of the substrate at a location of the holes to be etched through to form apertures. The term hole, as used herein, implies that the hole is open to only one side, i.e. has only one opening, the opposite side of the opening being closed. In an exemplary embodiment, the steps of etching holes from the front side of the substrate into the substrate and the step of processing the back side of the substrate to form a curved surface may be carried out in the reverse order to the one given above such that the processing of the back surface of the substrate is carried out before the etching of the pattern of holes into the substrate from the front surface of the substrate. In a fourteenth aspect of the present invention, a further method of manufacturing a multi-aperture plate having at least an area having a curved surface is provided, the method comprising: etching a pattern of holes into a substrate from a front surface of the substrate, processing the front surface of the substrate such that at least a portion of the front surface of the substrate has a curved shape, and at least one of processing and etching the back surface of the substrate to such an extent that at least a portion of the holes etched into the substrate extend through the entire substrate to form apertures. The methods according to the thirteenth and fourteenth aspect preferably further comprise filling the holes at least partially with a filler before the processing of the respective surface to form a curved surface. In a fifteenth aspect, the present invention provides a method of manufacturing a multi-aperture plate having at least an area having a curved surface, the method comprising: etching a pattern of apertures into a substrate, and processing one surface of the substrate such that the surface has a curved surface or at least an area having a curved surface, respectively. The method according to the fifteenth aspect preferably further comprises filling the apertures of the etched pattern of apertures at least partially with a filler before the processing of the one surface of the substrate. Preferably, the substrate is a silicon wafer. In exemplary embodiments of the methods for manufacturing a multi-aperture plate according to the present invention, the processing step comprises removing material from the surface of the substrate by mechanical abrasion. Suitable abrasive agents are well known in the art. Depending on the amount of material to be removed and a tolerable coarseness of the process, different abrasive or polishing materials may be used, such as mixtures of glycerine and aluminium oxide particles or silicon carbide particles, or silicon oxide particles or diamond particles in suitable solutions, in the case of silicon, for instance. Preferably, the etching step for etching the holes or apertures into the substrate comprises dry etching, preferably reactive ion etching and most preferably deep reactive ion etching. Generally, etching holes or apertures into a substrate involves a photolithographic technique, wherein a substrate is coated with a photoresist, the coated substrate irradiated through a mask that holds a pattern to be imprinted on the photoresist, in this case the pattern of holes/apertures, and the exposed substrate developed by contacting the exposed substrate with a developing solution. In case of a positive resist, the developer solution removes exposed material, in case of a negative resist, the developer solution removes unexposed material. In certain photolithographic procedures, the holes/apertures may be etched into the thus prepared substrate, in other procedures, the substrate is coated with a layer of material that is subsequently etched to form a mask for the subsequent etching of the actual substrate. In an exemplary photolithographic procedure for silicon substrates, the silicon wafer is cleaned, then oxidized to form a thin film of SiO2 thereon, then coated with photoresist, the photoresist exposed and then developed to uncover the SiO2-layer (in a given pattern), the SiO2-layer etched, for instance by reactive ion etching, so as to produce a mask for the silicon etch, remaining photoresist removed and subsequently the silicon substrate etched, for instance by deep reactive ion etching (DRIE). Generally, in dry etching procedures a gas is excited by a high-frequency field at a low pressure. In case of an inert gas, the gas ions generated by the field are accelerated towards the substrate and remove material by way of physical interaction. In case of a reactive gas, removal of material from the substrate is based on chemical interaction, and may additionally involve physical phenomena. Dry etching techniques generally comprise plasma etching, reactive ion etching and ion beam etching. Reactive ion etching procedures generally make use of radio frequency radiation to ionise a gas that dissociates into a reactive species, with the substrate to be etched being biased to induce ion bombardment. Suitable gases for the reactive ion etch process include compounds containing carbon (C) and halogens such as fluorine (F), chlorine (Cl) or bromine (Br). Control of process parameters such as pressure, high frequency output, gas flow, electrode and substrate temperature as well as the choice of the particular gas used allows to control a shape of a resulting etch profile. Anisotropy/isotropy of the etch process is generally controlled by the extent to which physical and chemical processes dominate. Deep reactive ion etching allows manufacturing of apertures or holes having a high aspect ratio, i.e. a high ratio of depth relative to width. DRIE is often also referred to as “Bosch-process” (as Bosch held the first patent for this kind of process) and involves a plasma etch process with frequent switching between polymerising and etching chemistries. Steps of coating substrate surfaces (passivation) with polymers are alternated with isotropic etch steps, wherein polymer is removed from a bottom of an etched structure. In addition to the Bosch-process, a so-called “Cryo”-process may be used wherein (DRI)etching is carried out as a single-step process at cryogenic temperatures below −100° C. Apart from high aspect ratios, DRIE allows to etch deep structures into a substrate and also allows fast etching due to a high etch rate. In practice, it has proven to be advantageous to use multi-aperture plates that are manufactured using the same mask and that have therefore a substantially identical aperture array. This embodiment is particularly useful if small faults are present in the mask that are transferred to aperture arrays manufactured using the respective mask. In such a case, apertures that were manufactured using the same mask position can be advantageously superimposed thus eliminating any detrimental effect of the faults in the aperture array. Furthermore, practical experience has shown that it is beneficial for the apertures to have smooth edges at least on a surface that charged particles would impinge upon, and a smooth surface at least within a first third of an aperture volume that the particles pass first when passing the respective aperture. Smooth aperture edges and smooth inner surfaces in at least a portion of the aperture volume may be achieved by suitable selection of etching parameters during the etch step. In particular, a slower etch rate is preferred for achieving a smooth surface. In preferred embodiments of the methods for manufacturing as described above, etching the respective side of the substrate having the curved shape (generally referred to as the backside in the methods of the present invention) comprises etching of the substrate such that an equal amount of material is removed from any location on the respective side so as to substantially maintain a shape of the respective surface provided by the processing step. Thus, the curvature of the respective surface is essentially maintained. This may be achieved by wet etching or plasma etching processes, for instance, as known in the art. In other embodiments, processing the respective surface having the curved shape may be carried out such that the respective surface has a first curvature, and subsequently the same respective surface is etched such that it has a second curvature, which is a desired final curvature. In those embodiments, the etching need not occur at the same rate over the entire surface. In preferred embodiments, the methods further comprise at least partially filling the holes or apertures with one or more filling materials, most suitably before the respective surface is further etched or processed. Accordingly, those embodiments preferably also comprise removing the one or more filling materials from the apertures, i.e. after the etching of the respective surface. Filling materials or fillers that may be used in the above manufacturing methods include suitable polymers, adhesives and resins, for instance, such as silicon nitride. In a sixteenth aspect, the present invention provides a method of focusing a plurality of charged particle beamlets, the method comprising: generating an electrical field of at most 5000 V/mm between a first multi-aperture plate having a plurality of apertures and a first electrode such that the first multi-aperture plate has a first focussing power F1, wherein the first electrode is spaced a distance of at least 1 mm apart from the first multi-aperture plate; transmitting at least one of a charged particle beam and a plurality of charged-particle beamlets through the electrical field, the plurality of apertures of the first multi-aperture plate and the first electrode; transmitting the at least one of the charged particle beam and the plurality of charged-particle beamlets through apertures of a particle-optical component comprising at least a second multi-aperture plate having a plurality of apertures, the particle-optical component being configured and operated so as to provide a second focussing power F2, wherein the second focussing power F2 of the particle-optical component is at least five times smaller than the first focussing power F1. In other exemplary embodiments, the electrical field generated between the first multi-aperture plate and the first electrode may have a field strength of at most 2500 V/mm, or at most 1000 V/mm, or at most 500 V/mm. In further exemplary embodiments, the distance between the first electrode and the first multi-aperture plate is at least 5 mm, or may be at least 10 mm, or may be at least 20 mm. The focussing power, as used herein, refers to the inverse of the focal length: F=1/f. Exemplary equations giving the focussing powers of multi-aperture and multi-lens arrays have been given herein before. Preferably, the multi-aperture component in the method according to the 16th aspect is the multi-aperture component according to the present invention, with features and embodiments thereof as described above. The first electrode may be a single-aperture plate, for instance. The first electrode may be disposed between the first multi-aperture plate and the second multi-aperture plate, for example. In other embodiments, the first electrode may be disposed on a side of the first multi-aperture plate that faces away from the second multi-aperture plate. In a seventeenth aspect, the present invention provides a particle-optical component, which comprises a first multi-aperture plate having a plurality of apertures, a fourth aperture plate having at least one aperture, and a mounting structure comprising at least one actuator for displacing the fourth aperture plate relative to the first multi-aperture plate to a first position and to a second position different from the first position. In exemplary embodiments, in the first position, one aperture of the at least one aperture of the fourth aperture plate is in alignment with a first aperture of the first multi-aperture plate, and in the second position, the one aperture is in alignment with a second aperture of the first multi-aperture plate, with the first and second apertures being different. In an exemplary embodiment, the particle-optical component further comprises a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed between them, wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate, and wherein the first multi-aperture plate is disposed between the fourth aperture plate and the second multi-aperture plate. Exemplary embodiments, advantages and features of the particle-optical component have been described above in particular in connection with the first aspect of the present invention. The fourth aperture plate may be advantageously used as a testing aperture plate for testing a position of the first aperture plate and/or optical properties of other components of a particle-optical system. In an eighteenth aspect, the present invention provides a particle-optical component comprising a first multi-aperture plate having a plurality of apertures, and a third multi-aperture plate having a plurality of apertures, wherein the plurality of apertures of the third multi-aperture plate is arranged such that each aperture of the plurality of apertures of the third multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the first multi-aperture plate, and wherein a diameter of an aperture of the third multi-aperture plate is smaller than a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. In an exemplary embodiment, the particle-optical component further comprises a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed between them; wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate, and wherein the first multi-aperture plate is disposed between the third aperture plate and the second multi-aperture plate. In exemplary embodiments, the diameter of the aperture of the third multi-aperture plate is 99% or less, for instance 95% or less, of the diameter of the corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. Further exemplary embodiments, features and advantages have been described above in particular in connection with the particle-optical component according to the first aspect of the invention. Alignment, as mentioned before, may comprise an arrangement of the aligned apertures with respect to each other such that a charged particle beamlet passing through an aperture in the upstream aperture plate may pass through the aligned aperture in the downstream multi aperture plate without impinging on or touching the downstream multi aperture plate. FIG. 1 is a schematic diagram symbolically illustrating basic functions and features of an electron microscopy system 1 as an embodiment of a particle-optical arrangement, a particle-optical system and an electron multi-beam inspection system as well as a method of manipulating charged particle beamlets according to the present invention. The electron microscopy system 1 is of a scanning electron microscope type (SEM) using a plurality of primary electron beamlets 3 for generating primary electron beam spots 5 on a surface of a specimen 7 to be inspected which surface is arranged in an image plane 101 of an objective lens 102 of an objective arrangement 100. Primary electron beamlets 3 are generated by a beamlet generating arrangement 300 comprising an electron source arrangement 301, a collimating lens 303, a particle-optical component 305, illustrated in a simplified form with only one of the two multi-apertures depicted, and a field lens 307. The electron source arrangement 301 generates a diverging electron beam 309 which is collimated by collimating lens 303 to form a beam 311 for illuminating particle-optical component 305. Insert I3 of FIG. 1 shows an elevational view of the first multi-aperture plate 313 forming part of particle-optical component 305. The first multi-aperture plate 313 (and equally the second multi-aperture plate, not shown) has a plurality of apertures 315 formed therein. Centers 317 of apertures 315 are arranged in a pattern or array 319 which electron-optically corresponds to a pattern 103 of primary electron beam spots 5 formed in image plane 101. A pitch P3 of array 319 may be in a range of from about 5 μm to about 200 μm, for instance. Diameters D of apertures 315 may be in a range of from 0.1×P3 to 0.5×P3, a range of from 0.3×P3 to 0.6×P3, a range of from 0.4×P3 to 0.7×P3, a range of from 0.5×P3 to 0.7×P3, a range of from 0.5×P3 to 0.6×P3, a range of from 0.6×P3 to 0.7×P3, a range of from 0.7×P3 to 0.8×P3, and/or from 0.8×P3 to 0.9×P3, for instance. Electrons of illuminating beam 311 pass through apertures 315 (and the corresponding aligned apertures of the second multi-aperture plate, not shown) to form primary electron beamlets 3. Electrons of illuminating beam 311 impinging on plate 313 are intercepted from a primary electron beam path 13 and do not contribute to the formation of the primary electron beamlets 3. In the embodiment depicted in FIG. 1, it is one function of the particle-optical component 305 to form the plurality of primary electron beamlets 3 from the illuminating beam 311. An additional function of the depicted particle-optical component 305 of this embodiment is to focus each primary electron beamlet 3 such that foci 323 are generated in a focus region or focus plane 325. The focus region 325 in FIG. 1 is shown as a planar surface for ease of illustration. In those embodiments of the present invention where a particle-optical aberration to be compensated for or corrected by the particle-optical component 305 is a field curvature, the focus region 325 would generally have a curved shape, as illustrated in FIG. 3. A voltage supply 330 for supplying an electrical potential to at least one of the first and second multi-aperture plates is also shown schematically in FIG. 1. In other embodiments of the present invention, a third multi-aperture plate may be disposed upstream of the first and second multi-aperture plates in the beam path of the illuminating beam 311. In those embodiments, the third multi-aperture plate would have the function of forming the plurality of primary electron beamlets. Provided the third multi-aperture plate is suitably aligned with the first multi-aperture plate, primary electron beamlets 3 would then pass through the apertures of the first and second multi-aperture plates, which has the advantage that the first surface of the first multi-aperture plate, in particular, would not be subject to damage caused by impinging primary electrons. For instance, heating and charging effects as well as contaminations of the first multi-aperture plate, in particular, may be avoided or substantially reduced. Insert I4 of FIG. 1 shows an elevational view of focus plane 325 with foci 323 arranged in a pattern 327. A pitch P4 of this pattern may be the same as or different from pitch P3 of pattern 319 of the first multi-aperture plate 313 (and the second multi-aperture plate, not shown) as will be understood from the following description. A diameter of foci 323 may be in a range of from about 1 nm to about 1 μm, for instance. Field lens 307 and objective lens 102 together perform a function of imaging focus plane or region 325 onto image plane 101 to form the array 103 of primary electron beam spots 5 having a small diameter on the specimen 7 for achieving a high resolution of secondary electron images generated by detecting intensities of secondary electron beamlets 9 by detector arrangement 209. A beam splitter/combiner arrangement 400 is provided in the primary electron beam path 313 in between the beamlet generating arrangement 300 and objective arrangement 100 and in a secondary electron beam path 11 in between the objective arrangement 100 and the detecting arrangement 200. Insert I1 of FIG. 1 shows an elevational view on image plane 101 with a regular rectangular array 103 of primary electron beam spots 5 formed thereon. In FIG. 1, twenty-five primary electron beam spots 5 arranged in a 5×5-array 103 are shown. This relatively low number of primary electron beam spots is depicted for ease of illustration of the principles of the electron microscopy system 1. In practice, the number of primary electron beam spots may be chosen to be substantially higher, such as 30×30, 100×100 or any other number. In the illustrated embodiment, the array 103 of primary electron beam spots 5 is a substantially regular rectangular array with a substantially constant pitch P1 in a range of from about 1 μm to about 10 μm, for instance. It is, however, also possible that the array 103 may be a distorted regular array or an irregular array or an array of some other symmetry, such as a hexagonal array. A diameter of the primary electron beam spots formed in the image plane 101 may be in a range of from about 5 nm to about 200 nm, for instance. The objective arrangement 100 focuses the primary electron beamlets 3 to form the primary electron beam spots 5. The primary electrons incident on the specimen 7 at beam spots 5 generate secondary electrons that emanate from the surface of specimen 7. The secondary electrons form secondary electron beamlets 9 entering the objective lens 102. The electron microscopy system 1 provides a secondary electron beam path 11 for supplying the plurality of secondary electron beamlets 9 to a detecting arrangement 200. Detecting arrangement 200 comprises a projecting lens arrangement 205 for projecting the secondary electron beamlets 9 onto a surface plane 211 of an electron sensitive detector 207 of a detector arrangement 209. The detector 207 can be one or more selected from a solid state CCD or CMOS, a scintillator arrangement, a micro channel plate, an array of PIN diodes and others. Insert I2 of FIG. 1 shows an elevational view on image plane 211 and the surface of detector 207 where secondary electron beam spots 213 are formed as an array 217. A pitch P2 of array 217 may be in a range of from about 10 μm to about 200 μm, for instance. The detector 207 is a position sensitive detector having a plurality of detecting pixels 215. The pixels 215 are arranged in an array matching array 217 of the secondary electron beam spots 213 such that each pixel 215 can detect an intensity of the secondary electron beamlet 9 incident thereon. All numerical values given for physical characteristics such as dimensions, voltages or the like in connection with the described embodiments of the present invention are for illustrative purposes only and not meant to be limiting the scope of the present invention in any way. Electron source arrangement 301 and particle-optical component 305 together form an embodiment of a particle-optical arrangement according to the present invention. As illustrated in FIG. 1, it is one feature of the electron microscopy system 1 that focus region 325 where foci 323 of the primary electron beamlets are generated by the particle-optical component 305 is imaged into an image plane 101 in which the surface of the specimen 7 to be inspected is positioned. Since particle-optical component 305 is capable of compensating particle-optical aberrations such as a field curvature, ideally, image plane 101 and the surface of the specimen 7 coincide. In practice, it has been found that electron-optical elements symbolically illustrated as M in FIG. 2, typically contribute to a field curvature of an electron-optical system. This would lead to flat focus plane 325 being imaged into a curved plane 101 close to the specimen surface 7, as shown in FIG. 2. It is then not possible for the curved image plane 101 to coincide with the flat surface of specimen 7, and, consequently, the foci 323 are not perfectly imaged onto the surface of specimen 7. FIG. 3 shows an embodiment of a particle-optical component according to the present invention, which is configured such as to provide a solution to the problem of field curvature caused by the optical elements M involved in imaging the focus region 325 onto specimen surface 7. The particle-optical component of this embodiment is designed such that the focus region 325 where the foci 323 of the primary electron beamlets 3 are generated is a curved region or plane. The curvature of the focus region is laid out such that the optical elements M image focus region 325 into a flat image plane 101. It is then possible to position the specimen's planar surface 7 so as to coincide with flat image plane 101. In order to give an impression of an order of dimensions of such effects, as an example, a focus 323a of a primary beamlet 3 generated at a periphery of an aperture pattern formed by the plurality of apertures is imaged into a curved plane 101 close to the specimen surface such that image point 101a corresponding to focus point 323a is spaced a distance of about 12 μm from a surface of the specimen 7. The particle-optical component 305 can then be configured such that a focus region 325 is a curved focus region such that focus point 323a′ of peripheral primary beamlet 3 is disposed a distance of about 5.3 mm from a flat focus plane 323 of a multi-aperture plate without field curvature correction, as depicted in FIG. 2, or, worded differently, a distance of 5.3 mm further downstream as compared to a focus 323 of a central primary electron beamlet 3. Thus, due to a predetermined demagnification in the imaging process of the focus region onto the specimen, the resulting image plane 101 will be a flat image plane 101 with primary electron beam spots or image points 101a coinciding with the specimen surface. In FIG. 4, one possibility of arranging the first multi-aperture plate 413 with respect to the second multi-aperture plate 414 is illustrated as a first embodiment 405 of a particle-optical component according to the present invention. Both the first and second multi-aperture plates 413, 414 are substantially plane-parallel plates having an aperture pattern formed therein by the respective pluralities of apertures. The second multi-aperture plate 414 is tilted with respect to the first multi-aperture plate 413, i.e. disposed at an angle γ with respect to the first multi-aperture plate 413, such that a gap is formed between them. The gap has a first width w1 at a location of a first aperture 415 and a second width w2 at a location of a second aperture 415′, with w1>w2. Each aperture of the first multi-aperture plate is aligned with a corresponding aperture of the second multi-aperture plate 414 such that pairs of associated apertures 415 & 415a and 415′ & 415′ a are formed. The arrows in FIG. 4 indicate a direction of the charged particle beam. The first multi-aperture plate 413 is arranged at a right angle with respect to a beam path of the charged particle beam. The arrangement of the first and second multi-aperture plates 413, 414 is symmetric with respect to one another. In FIG. 5, a further possibility of arranging the first multi-aperture plate 513 with respect to the second multi-aperture plate 514 and of a possible design of the first multi-aperture plate 513 is illustrated as a second embodiment 505 of a particle-optical component according to the present invention. The first multi-aperture plate 513 has a varying thickness with the second surface 513a of the first multi-aperture plate being disposed at an angle α with respect to the first surface 513b thereof such that the thickness of the first multi-aperture plate 513 increases from right to left, as shown in FIG. 5. The second surface 513b of the first multi-aperture plate 513 is arranged at a right angle with respect to a beam path of an impinging charged particle beam indicated by the arrows in FIG. 5. The second multi-aperture plate 514 is a plane parallel plate with the first and second surfaces thereof being arranged in parallel to the second surface 513b of the first multi-aperture plate 513 and, accordingly, at an angle α with respect to the first surface 513a thereof. Thus, the gap formed between the first and second multi-aperture plates 513, 514 has a first width w1 at a location of a first aperture 515 and a width w2 at a location of a second aperture 515′, with w1>w2. In FIG. 6, a third, preferred embodiment 605 of the particle-optical component of the present invention is depicted. The first multi-aperture plate 613 has a first surface 613a having a convex, aspherical shape and a second surface 613b having a plane (flat) shape. The second multi-aperture plate 614 is substantially identical to the second multi-aperture plate 613. The first and second multi-aperture plates 613, 614 are arranged such as to be mirror-inverted with respect to one another, with a plane of symmetry MIP extending through the gap formed between the first and second multi-aperture plates 613, 614. The first surfaces 613a, 614a of the first and second multi-aperture plates 613, 614 are arranged so that they face each other. The first and second multi-aperture plates 613, 614 have identical aperture patterns comprising respective pluralities of apertures, with each aperture of the first multi-aperture plate 613 being aligned with a corresponding aperture of the second multi-aperture plate 614. Again, the gap formed between the first and second multi-aperture plates 613, 614 has a first width w1 at a location of a first aperture 615, which is located at a periphery of the aperture pattern, and a width w2 at a location of a second aperture 615′, which is located in the center of the aperture pattern, with w1>w2. A second width may be, in a preferred embodiment about 80 μm, for instance, whereas a first width at an edge of the aperture pattern (which, for ease of illustration, only encompasses 9 apertures in FIG. 6, whereas it would generally comprise a larger number of apertures) may be, for instance, about 290 μm. If the pattern of apertures of the first and second multi-aperture plates 613, 614 have the same and constant pitch P6, the width of the gap at a location of an N-th aperture could be described for instance by wN=0.08 mm+0.0055×1/mm2×(P6×|N|)3. If the aperture in the centre which would be attributed N=0 has a width w2 of 80 μm, as already mentioned above, the width of the gap at an outermost aperture with N=±70 would be about 290 μm if P6 was 48 μm. The first width w1 at aperture N=−4 as indicated in FIG. 6 would for that pitch P6 still be less than about 81 μm if calculated according to the above formula. In FIG. 7, a field curvature correcting or compensating effect of the embodiment of a particle-optical component 605 depicted in FIG. 6 is schematically illustrated. A beam of primary electrons 311 impinges on a second surface 613b of the first multi-aperture plate 613. Those electrons that pass through the apertures 615 formed in the first and second multi-aperture plates 613, 614 form primary electron beamlets 3. Potentials U1, U2 are applied to the first and second multi-aperture plates 613, 614 such that a first electrical field E1 upstream of and in the vicinity of the first multi-aperture plate 613 is substantially zero. The potentials U1, U2 are further chosen such that an electrical field E2 is generated in the gap in between the first and second multi-aperture plates 613, 614. This can, in the depicted embodiment, for instance, be achieved by applying about 500 V (U1) to the first multi-aperture plate 613 and grounding (U2) the second multi-aperture plate 614. Thus, a so-called immersion-type lens is formed between the first and second multi-aperture plates 613, 614. The voltage supply configured to supply suitable potentials is denoted “630” in FIG. 7. In the embodiment depicted in FIG. 7, a third electrical field E3 is provided downstream of the second multi-aperture plate 614 and is configured such that the particle-optical component has a focusing effect on the electrons (charged particles) passing through the apertures of the first and second multi-aperture plates 613, 614 such that the primary electron beamlets are focused in focus region 325. This may be readily achieved by providing a focusing electrical field E3 by means of an electrode in the form of a single aperture plate (not shown) being supplied with a suitable voltage, such as from 20 to 30 kV (relative to the grounded second multi-aperture plate 614), for instance. In this embodiment, the main focusing is achieved by the second multi-aperture plate 614, with the second multi-aperture plate being disposed at an edge of two electrical fields E1 and E3 of different field strengths, whereas a field curvature correcting effect, which is a comparatively small focus influencing effect, is provided by the electrical field E2 generated in the gap between the first and the second multi-aperture plates 613, 614. Thus, a focus region 623 is a curved focus region, with a focal length of a primary electron beamlet 3 passing through the particle-optical component at the center of the aperture pattern being by about 5% shorter as compared to a focal length of a primary electron beamlet 3 passing through an aperture located at a periphery of the aperture pattern. This provides a correction for a field curvature introduced, for instance, by particle-optical elements M downstream of the particle-optical component, as discussed before. In addition, other imaging errors, such as astigmatism or distortion may be corrected by the depicted component. An imaging error correcting or compensating effect of the particle-optical component of the present invention may be varied by adjusting a width w of the gap or adjusting a potential difference ΔU between the first and second multi-aperture plates which makes an adjustment possible without the necessity to exchange the particle-optical component for another one. In addition, the particular design of the multi-aperture plates, in particular the shapes of the first surfaces and other factors can be tailor-made for a particular design of particle-optical system. The shape of one or both of the first surfaces will be influenced by a chosen gap width or range of gap widths, respectively, and a compensating effect to be achieved. In the embodiment depicted in FIGS. 6 and 7, the potential difference ΔU applied between the first and second multi-aperture plates 613, 614 may be in a range of from 0 to 800 V, for instance, which corresponds to electrical field strengths of less than 10,000 V/mm, which is sufficiently low in a vacuum environment to avoid electrical breakthrough. If a potential difference of zero is applied, there would be no field curvature compensating effect so that embodiments with ΔU>0 are preferred. In FIGS. 8a through 8d, a number of configurations of electrical fields in and around an embodiment 605 of the particle-optical component of the present invention are schematically illustrated. Assuming that a kinetic energy of the charged particles is substantially constant over the cross section of illuminating beam 311 impinging on the second surface 613b of the first multi-aperture plate 613 of the particle-optical component, an electrical field E2, and optionally electrical fields E1 and E3 adjacent to the particle-optical component may be shaped such that the focal length f provided by a respective aperture depends on a position of the aperture across the illuminating beam 311. The shaping of electrical field E2 is achieved by the design of the multi-aperture plates 613, 614, for instance a curvature of opposing surfaces and/or their arrangement to one another and resulting shape and dimension of the gap formed between them, as well as potentials applied to the first and second multi-aperture plates 613, 614. Shaping of the electrical fields E1 and E3 to provide an optional, added particle-optical aberration correcting effect may be achieved by one or plural electrodes, which may preferably take the form of single-aperture plates, positioned at a distance upstream or downstream of the particle-optical component. In the configuration depicted in FIG. 8a, a first electrode 665 in the shape of a single aperture electrode having an aperture 611 is provided at a distance upstream of the first multi-aperture plate 613 and a second electrode 670, which is also a single aperture plate with an aperture 661 which is substantially identical to that of the first electrode 665 is provided at a distance downstream of the second multi-aperture plate 614. In the depicted configuration, a potential of 500V is applied to the second multi-aperture plate 614 whereas the first multi-aperture plate 613 is grounded, resulting in a potential difference ΔU of 0.5 kV between the first and second multi-aperture plates 613, 614. A voltage supply configured to supply these potentials is not shown in FIG. 8 for ease of illustration. This embodiment of the particle-optical component 605 is substantially the same as illustrated in FIGS. 6 and 7, i.e. the first and second multi-aperture plates 613, 614 have convex first surfaces opposing each other such that a width of the gap formed there between is smallest in a center of the multi-aperture plates and increases radially outwards. Accordingly, the resulting electrical field E2 within the gap has a highest field strength in the centre which also decreases radially outwards, given that an electrical field strength is given by a ratio of a difference in potentials applied to the respective field-generating electrodes to a distance of the field-generating, electrodes from one another, or the first and second multi-aperture plates, in this case. In the embodiment shown in FIG. 8a, the first electrode 665 is grounded whereas the second electrode has the same potential of 500 V applied to as the second multi-aperture plate 614 such that electrical fields E1 and E3 upstream and downstream of the particle-optical component 605 are zero. Therefore, the particle-optical component 605 provides only a very weak focusing effect which varies radially around the centre of the apertures for providing a field curvature compensating effect as compared to a case where a strong overall focusing effect is provided by a sufficient difference or gradient, respectively, of electrical fields upstream and/or downstream of the particle-optical component. The weak focusing effect provided by the component therefore may be superimposed onto a main focusing effect provided by a non-illustrated focusing arrangement. Charged particles being directed onto the particle-optical component 605 in the form of a charged particle beam 311 are transmitted through apertures 615 of the first and second multi-aperture plates 613, 614 and form beamlets 3 of charged particles, the number of formed beamlets 3 corresponding to the number of apertures 615 in the first and second multi-aperture plates 613, 614. The beamlets are assumed to be mainly focused by a non-depicted focusing element (providing a comparatively large main focusing effect) and form foci 623 in a focus region 625, the focus region 625 having a curved shape due to beamlets transmitted in a central region of the particle-optical component 605 having been subject to a stronger electrical field E2 than beamlets having been transmitted though a peripheral region of the particle-optical component 605 and having been exposed to a comparatively weaker electrical field E2, such that they are exposed to differing total focussing effects resulting in differing focal lengths and a corresponding curvature of the focus region 625. This curved focus region 625 allows to compensate for a field curvature induced by a particle-optical element further downstream of the particle-optical component 605. Apertures 611 and 661 of the first and second electrodes 665, 670 are dimensioned, such that the beam 311 or beamlets 3, generated by the particle-optical component, respectively, may pass. In a different configuration, electrical fields E1 and E3 may be chosen to be different from zero. In those cases, if electrical fields E1 and E3 are the same, there will be no main, strong focussing but just the weak focusing effect provided by the electrical field E2 within the particle-optical component to provide the correcting effect of the particle-optical component, if E1 and E3 are different and/or inhomogeneous, an additional focusing effect may thus be provided. It is to be noted that the position of the focus region 325 as depicted in FIG. 8a, or in any of the other Figures, is just for illustrative purposes. The focus region may be at any other position in the system, for instance further downstream, depending on the kind, position and extent of focusing method used. A configuration of electrical fields which provides an added main focusing effect is depicted in the embodiment of FIG. 8b. The arrangement of the particle-optical component and the first and second electrodes 665 and 670 corresponds substantially to that depicted in FIG. 8a with a third electrode, 680, also in the form of a single aperture plate, being positioned at a distance downstream of the second electrode 680. An aperture 661 of the third electrode 680 is, in this embodiment, substantially the same as apertures 611, 661 of the first and second electrodes 665, 670. An electrical field E1 is generated between the first electrode 665 and the particle-optical component 605 by applying a potential of 30 kV to the first electrode and a potential of 9 kV to the first multi-aperture plate 613 of the particle-optical component 605 such that a homogenous electrical field E1 is present in the vicinity and upstream of the first multi-aperture plate 613, as indicated by equipotential lines. Electrical field E2 within the gap between the first and second multi-aperture plates 613, 614 is generated in a similar manner to the embodiment shown in FIG. 8a, with the exception that the potential difference ΔU of 0.5 kV is applied by applying a potential of 9.5 kV to the second multi-aperture plate 614. The same potential of 9.5 kV is applied to the second electrode 670 downstream of the second multi-aperture plate 614 such that the electrical field E3 there between is zero. Thus, the electrical fields E1 and E3 upstream and downstream of the particle-optical component 605 differ, resulting in a main focusing effect such that charged particles of charged particle beam 311 are focused into focus region 625, which is, in comparison to the embodiment of FIG. 8a, therefore positioned closer to the particle-optical component 605 and, in this embodiment, located in a substantially homogeneous electrical field E4, which is generated by application of a potential of 19.5 kV to the third electrode 680, as indicated by depicted equipotential lines. This embodiment is also exemplary of the method of focusing a plurality of charged particle beamlets according to the seventh aspect of the present invention. In a further embodiment depicted in FIG. 8c, in addition to a main focusing effect as a result of differing electrical fields E1, E3 upstream and downstream of the particle-optical component 605 and a compensating effect provided by the particle-optical component 605, an additional particle-optical aberration correcting effect may be achieved by shaping an electrical field, in the embodiment of FIG. 8c electrical field E4, such that its field strength varies in a given area, in a plane orthogonal to an optical axis, the field strength may, for instance, show a radial dependence. E1 is substantially constant across the cross-section of illuminating beam 311 at positions close to the first multi-aperture plate 613. An imhomogeneous electrical field E3 results from electrical field E4 penetrating from aperture 661 of the second electrode 670, as indicated by curved equipotential lines penetrating from a space between single-aperture plates 670, 680, into a space between the second multi-aperture plate 614 and single-aperture plate 670. An aperture positioned at a center of the aperture pattern will therefore provide a shorter focal length f than an aperture positioned at a periphery of the aperture pattern, resulting in foci 623 of the beamlets 3 being located on a curved focus region 625, as indicated by the broken line in FIG. 8c. Thus, in addition to the field curvature correcting effect or geometrical aberration compensating effect of the particle-optical component according to the present invention, an arrangement of electrodes downstream of the component and suitable application of potentials thereto contributes to a compensation of field curvature. In alternative embodiments, a homogeneous electrical field, for instance E4, may be generated by a suitable choice of suitable diameters of apertures in the electrodes, in the case of E4 for example apertures 661. For instance, a diameter of aperture 661 of electrode 680 may be different from a diameter of aperture 661 of electrode 670. In further embodiments, a thickness of electrodes 670 and 680 may be suitably chosen such that a homogenous electrical field E4 may be achieved. One or more of the parameters diameter of an aperture of electrode 670 or 680 and ratios of aperture diameters of the electrodes 670, 680, thicknesses of electrodes 670 and voltages applied to electrode 670 may be suitably adjusted to enable formation of a substantially homogeneous electrical field between them. Similar consideration apply to other pairs of electrodes and electrical fields formed between them, as will be readily apparent to the person skilled in the art. FIG. 8d shows a configuration which is practically the reverse of the one depicted in FIG. 8c. In FIG. 8d, an inhomogeneous electrical field E2 upstream of the first multi-aperture plate 613 is generated by an electrical field E1 between a single aperture plate 660 disposed at a distance upstream of the first electrode 665 and the first electrode 665 and bowing out into a space between the first electrode 665 and the first multi-aperture plate 613. Generation of electrical field E3 within the particle-optical component 605 and configuration of particle-optical component 605 are substantially the same as in the embodiments described in connection with FIGS. 8a to 8c. Downstream of the second multi-aperture plate 614, an electrical field E4 is generated by applying a potential of 30 kV to single-aperture plate 670 relative to a potential of 9.5 kV being applied to the second multi-aperture plate 614. Thus, electrical fields E2 and E4 upstream and downstream of the particle-optical component 605 differ, resulting in a main focusing effect being provided by particle-optical component 605, or a single multi-aperture plate thereof, respectively. In addition, particle-optical component 605 provides a correcting effect by providing a dependency of a focal length on a position of a respective aperture with respect to a centre or central aperture of the multi-aperture plates 613, 614. Furthermore, an additional field curvature correcting effect is provided by having an inhomogeneous electrical field E2 upstream of the particle-optical component 605. The additional focusing effect due to having an electrical field of a particular shape upstream or downstream, also in connection with virtual foci, of a multi-aperture plate is described in detail in WO 205024881 to the same Assignee, as mentioned before. The embodiment depicted in FIG. 8e is practically identical to the one depicted in FIG. 8d, except that an additional multi-aperture plate 618 is provided downstream of the second multi-aperture plate 614, which comprises a pattern of apertures being arranged in the same manner as that of the first and second multi-aperture plates 613, 614. The same electrical potential of 9.5 kV is applied to the additional multi-aperture plate 618, such that there is no electrical field between the second and the additional multi-aperture plates 613, 618. In alternative embodiments, a potential different from that applied to the second multi-aperture plate 614 may be applied to the additional multi-aperture plate 618 and an electrical field E4 generated there between. Preferably, E4 should not be of the same magnitude and opposite orientation (accelerating/decelerating) as compared to E3. The embodiment shown in FIG. 8e is advantageous in particular for practical reasons as experience with current multi-aperture plate manufacturing methods has shown that often, only one surface of a multi-aperture plate is smooth whereas the opposite one has a certain surface roughness. In the embodiment of FIG. 8e, the multi-apertures plates 613, 614 and 618 are advantageously arranged such that their respective smooth surface faces a region where an electrical field is present, E3 and E5 in the illustrated case, which has proven beneficial for the electrical fields and particle-optical properties of the entire system. In FIG. 9, an embodiment of the present invention is shown wherein a third multi-aperture plate 619 is disposed upstream of the first multi-aperture plate 613, i.e. such that the first multi-aperture plate 613 is disposed between the third multi-aperture plate 619 and the second multi-aperture plate 614. In the depicted embodiment, the third multi-aperture plate 619 has the same number and pattern of apertures 615c as the first and second multi-aperture plates (with apertures 615, 615a, respectively). Apertures 615c are aligned with corresponding apertures 615 of the first multi-aperture plate 613 and apertures 615a of the second multi-aperture plate 614. As shown in FIG. 9, the apertures 615c of the third multi-aperture plate 619 have a smaller diameter than the corresponding apertures of the first and second multi-aperture plates. This embodiment is advantageous in that the third multi-aperture plate 619, rather than the first multi-aperture plate 613, heats up and collects electrical charge as well as contaminations, i.e. is subject to deterioration, as a result of charged particles of charged particle beam 311 being incident onto a surface of the third multi-aperture plate 619 in between apertures 615c. The third multi-aperture 619 forms beamlets 3 which are substantially completely transmitted through apertures 615, 615a of the first and second multi-aperture plates 613, 614, i.e. there is substantially no loss of charged particles due to charged particles being incident and scattered on a surface. In FIG. 9, a mounting structure 690 for displacing the second multi-aperture plate 614 relative to the first multi-aperture plate 613 is also shown schematically. In FIGS. 10a and 10b, a further embodiment of the present invention is shown having a fourth aperture plate 620 disposed upstream of the first multi-aperture plate 613. Fourth aperture plate 620 has a single aperture 615d whose diameter corresponds to a diameter of apertures 615, 615a of the first and second multi-aperture plates in this embodiment. Fourth aperture plate 620 is held by a mounting structure 691 which comprises an actuator (not shown) for displacing the fourth aperture plate 620 relative to the first and second multi-aperture plates 613, 614, in particular in parallel thereto. Such a fourth aperture plate 620 is, for instance, suitable for testing a multi-aperture component. A multi-aperture component may be a single multi-aperture plate, a set of two multi-aperture plates or a particle-optical component according to the present invention, for instance. In this embodiment, the method of operating a multi-aperture component involves testing an alignment of the first and second multi-aperture plates 613, 614 of a particle-optical component according to the present invention. In a first step S1, depicted in FIG. 10a, the fourth aperture plate 620 as a testing aperture plate is positioned in a first position relative to the first and second multi-aperture plates 613 such that the aperture 615d of the testing aperture plate 620 is in alignment, in a direction of a charged particle beam to be transmitted, or in a direction of an optical axis in a charged particle optical system, with a first aperture 615P1 of the first multi-aperture plate 613 and a corresponding aperture 615aP1 of the second multi-aperture plate 614. A beamlet 3 of charged particles is transmitted through the apertures 615d as well as 615P1 and 615aP1, and detected by a detector arrangement D at position DP1 on the detector surface, for instance an intensity of the beamlet 3 may be detected, or its shape or position or all of the same. In a second step S2, the fourth or testing aperture plate 620 is displaced parallel to the first multi-aperture plate 613 and thus positioned in a second position relative thereto such that the aperture 515d of the testing aperture plate 620 is in alignment with a different aperture 615P2 of the first multi-aperture plate 613 as well an aperture 615aP2 of the second multi-aperture plate 614 aligned therewith. Beamlet 3 is then transmitted through apertures 615d, 615P2 and 615aP2 and detected in a second position DP2 of detector D2, in terms of position, shape or intensity, preferably the same parameter or set of parameters as in the first step S1. If an intensity of the beamlet 3 was different for the first and the second position whereas the sizes of apertures the beamlet 3 was transmitted through were the same for both positions, this difference in intensities could indicate a misalignment of the first and second multi-aperture plates, in which case the method could further comprise adjusting a position of the first multi-aperture plate 613 relative to the second multi-aperture plate 614. In FIG. 11, an embodiment of a charged-particle component according to the present invention is shown in use in a magnetic lens 700. The magnetic lens comprises four magnetic poles 701-704, wherein two pairs of adjacent magnetic poles 701 & 702, 703 & 704 form respective gaps 705, 706 between them such that magnetic fields penetrating into a space between the pole pairs or gaps 705, 706, respectively, are formed. In the embodiment depicted in FIG. 11, the particle-optical component comprises a first multi-aperture plate 613 having a plurality of apertures 615, a second multi-aperture plate 614 having a plurality of apertures 615 and a third multi-aperture plate 619 disposed upstream of the first multi-aperture plate 613 and having a plurality of apertures 615 formed therein. The three multi-aperture plates 613, 614, 619 are mounted using a number of spacers SP disposed between them and around peripheral ring portions of the respective multi-aperture plates such that the multi-aperture plates are aligned and fixed at a predetermined distance from each other. The spacers SP are made of an insulating material. In addition, an electrode tube 710 is provided upstream of the third multi-aperture plate 619 and a second electrode tube 711 disposed downstream of the second multi-aperture plate 614. The depicted embodiment may be advantageously used to correct for aspherical aberrations, or any other aberrations showing a dependency on a distance from a center of the magnetic lens. In particular, aberrations exhibiting a radial dependency may be advantageously corrected. In order to provide a compensating effect, in one embodiment, 0 kV are applied to electrode tube 710, and 0 kV are equally applied to the third and first multi-aperture plates 613, 619, whereas a small voltage of 0.5 kV is applied to the second multi-aperture plate to create a small focus correcting field between the first and second multi-aperture plates 613, 614. An upper rim of electrode tube 711 is conveniently supplied with 0.5 kV whereas further downstream (not shown, but indicated by an arrow), a potential of 10 kV may be suitably provided. Although the particle-optical component is shown as being disposed in a region of the gaps 705, 706 in FIG. 10, and therefore in a region of magnetic field, in other embodiments, it may be even more advantageously arranged within the magnetic lens 700 such that it is disposed in a region of zero or only small magnetic flux density. An embodiment of a particle-optical arrangement and system according to the present invention where a magnetic field in the vicinity of the particle-optical component according to the present invention is substantially nullified is illustrated in FIG. 12a, as well as an embodiment of a method of manipulating charged particle beamlets according to a further aspect of the present invention. The particle-optical system of this embodiment comprises charged particle source arrangement 801, a collimating lens 803, a particle-optical component 805 according to the present invention, a field lens 807 and an objective lens 1102 as well as a specimen mount 1007. The functions of these components correspond generally to the ones described in previous embodiments, in particular with reference to FIGS. 1 and 7. At least one of lenses 803, 807 and 1102 in this embodiment is a magnetic lens, for instance collimating lens 803. The particle-optical arrangement in this embodiment further comprises a coil arrangement 880 comprising a coil for generating a magnetic field in a region of the particle-optical component 805 such that a magnetic field generated by one or more of lenses 803, 807 and 1102 is substantially nullified in a vicinity of the particle-optical component 805, in particular in the gap between the first and second multi-aperture plates of the particle-optical component 805. In the embodiment depicted in FIG. 12a, lens 803 is a magnetic lens generating a magnetic field of a given magnetic flux density and orientation. A magnetic flux density on axis z of the embodiment of particle-optical arrangement of FIG. 12a is indicated in FIG. 12b. A magnetic field having a positive magnetic flux density generated by lens 803 is decreased by a second magnetic field generated at least in a region of the particle-optical component 805, a gap between the multi-aperture plates being positioned close to position z1 on axis z as indicated in FIG. 12b. The second magnetic field has an orientation and flux density configured to substantially nullify a magnetic field Bz in position z1. While a magnetic field may not be nullified in a region comprising the entire particle-optical component, it is preferably substantially nullified at a location within the particle-optical component. The flux density and position of the second magnetic field can be determined by a layout and/or position of the coil arrangement 880, a current flowing through the coil thereof and other suitable parameters, as will be readily apparent to the person skilled in the art. In the corresponding embodiment of the method of manipulating charged particle beamlets, a charged particle beam 311 is generated by particle source arrangement 801, collimated by magnetic collimating lens 803, which generates a first magnetic field in a beam path of the charged particle beam 311, and directed onto particle-optical component 805. Charged particles of charged particle beam 311 are transmitted through apertures of the particle-optical component 805 and thus form beamlets 3, which are illustrated as just one beam in FIG. 12a for ease of illustration. A second magnetic field is then generated by coil arrangement 880 which effectively nullifies the first magnetic field generated by collimating lens 803 in a region of the particle-optical component 805. In FIG. 13a, an embodiment of a particle-optical arrangement according to the tenth aspect of the present invention is illustrated wherein a first multi-aperture plate 613 is integrally formed with a first pole piece 753 of a magnetic lens arrangement and a second multi-aperture plate 614 is formed integrally with a second pole piece 754 of the magnetic lens arrangement. As shown in FIG. 13a, the first and second pole pieces 753, 754 are arranged symmetrically about a beam path of charged particles, a direction of which is indicated by axis z. While an inside of the magnetic lens arrangement is shown to take the form of a toroid, other structures of the pole pieces 753, 754, are also conceivable. The first and second multi-aperture plates 613, 614 are disposed to be traversed by the beam path. Upon magnetic flux in the pole pieces 753, 753, generally induced by current flow in coil 751 disposed inside the pole piece arrangement 750 of first and second pole pieces 753, 754, a magnetic field is generated in the gap between the first and second pole pieces 753, 754 on a side facing axis z as well as in the gap between the first and second multi-aperture plates 613, 614. Given the varying width of the gap, a magnetic flux density inside the gap will vary accordingly. Therefore, charged particles traversing an aperture 615a′ in a centre of the multi-aperture plates 613, 614 will travel through a stronger magnetic field than particles traversing an aperture located towards a periphery of the multi-aperture plates. Magnetic flux densities Bz in the direction of axis z inside the gap between different pairs of associated aligned apertures 615a′ (B′), 615a″ (B″), 615a′″ (B″′) are schematically depicted in the graph shown in FIG. 13b. As can be seen from the graph, a maximum flux density Bz decreases with increasing distance from the axis as the gap width between the first and second multi-aperture plates 613, 614 increases. This radial dependence of the magnetic flux density and the influence of the radially decreasing magnetic flux density on charged particles is used advantageously to correct or compensate for particle-optical aberrations in a system comprising such an arrangement. A further embodiment of a particle-optical arrangement or particle-optical system according to the present invention is depicted in FIG. 14. This embodiment comprises, in analogy to the embodiment illustrated in FIG. 12a, charged particle source arrangement 801′, a particle-optical component 805′ according to the present invention with a voltage supply system 830 which is configured to apply different potentials to the first and second multi-aperture plates of particle-optical component 805′. The particle-optical arrangement in this embodiment further comprises a controller 840 having a first control portion 841 configured to control the voltage supply system 830 based upon a total beam current of a plurality of charged particle beamlets downstream of the particle-optical component 805′. This allows for an adjustment of a correcting effect provided by the particle-optical component in dependence of a total current of charged particles in the system, as an extent of particle-optical aberrations tend to be influenced by Coulomb interactions between the charged particles. Thus, if the charged particle source arrangement 801′ is set to emit a higher current of charged particles or multi-aperture plates having a higher number of apertures are used or specimens inspected which produce a higher amount of secondary particles such as electrons, a density of charged particles in the particle beamlets downstream of the particle-optical component 805′ is increased and an adjustment to the compensating effect provided by said component desirable. In the embodiment depicted in FIG. 14, the particle-optical arrangement further comprises a current detector 848 for detecting the total beam current of the plurality of charged particles. In the embodiment shown in FIG. 14, the total beam current is determined by measuring a potential difference between the particle source arrangement 801′ and the specimen mount 1007′ which collects charge in dependence of a total beam current of charged particle beamlets. Particularly in those instances where the second multi-aperture plate comprises deflecting arrangements for effectively opening or closing individual apertures of the multi-aperture plate and thus controlling a total current of the beamlets of charged particles directed onto a specimen mounted onto specimen stage 1007′, the controller may also comprise a second control portion 842 for controlling beam currents of the charged particle beamlets. This may be achieved by having the second control portion send a signal to a control unit 849 of deflecting arrangements disposed on the second multi-aperture plate of charged particle component 805′. It is also advantageous if the first control portion 841 is responsive to the setting of the second control portion 842, i.e. if the second control portion 842 is set to increase or decrease currents of charged particle beamlets, the first control portion 841 may respond to a signal by the second control portion 842 indicating the increase or decrease by adjusting the voltage supply system 830 accordingly to account for the change in beam currents. The first and second control portions 841, 842 may also be responsive to other signal inputs from other sources, such as from signal input 845 which may, for instance be connected to charged particle source arrangement 801 for indicating a change in a generated beam current or, in another example, to a secondary electron detector. The system of the embodiment of FIG. 14 further comprises a collimating lens 803′, a field lens 807′ and an objective lens 1102′ as well as a specimen mount 1007′. The functions of these components correspond generally to the ones described in previous embodiments, in particular with reference to FIGS. 1 and 7. The particle-optical system as shown in FIG. 14, for instance, may be used and configured as a lithography system for writing a pattern on a substrate. It is generally desirable that the first and second multi-aperture plates are aligned as precisely as possible relative to one another in the particle-optical component according to the present invention. Desirably, an alignment of the two multi-aperture plates, or associated apertures thereof, will be better than 100 nm. A slight misalignment leads to distortion of the resulting spot array of primary electron beams in an image plane. Such a distortion effect is illustrated in FIG. 15a, which shows a shift of the spots 623 of primary electron beams 3 in an focus plane 625 as resulting from the misalignment between the first and second multi-aperture plates 613, 614, which will be translated into a corresponding distortion in an image plane. In particular, a distance between adjacent foci 623 decreases from right to left in FIG. 15a. FIG. 16 shows an elevational view of a spot array pattern of primary electron beam spots in an image plane resulting therefrom. However, if a slight misalignment of the multi-aperture plates has to be tolerated, it has been found that an error resulting there from, in particular a distortion, may be readily compensated for by use of a tilted illumination mode. FIG. 15b illustrates how a charged particle beam 311 impinging on the first multi-aperture plate 613 at an angle deviating slightly from a right angle (typically in a range of a few mrad), may be used to compensate for a distortion introduced by the misalignment. This effect may be attributed to a deflection of charged particle beams or beamlets, respectively, in dependence of a local strength of the respective electrical field. A stronger electrical field is generated in a center of the depicted multi-aperture plates 613, 614. Accordingly, a deflection is higher in the center than towards a periphery of the multi-aperture plates 613, 614, thus providing a correcting effect compensating for the distortion. Using a tilted illumination mode, as shown in FIG. 15b therefore results in foci of primary electron beamlets 3 being equidistant in a focus plane 625. Alternatively, for instance in embodiments wherein an additional multi-aperture plate upstream of the first and second multi-aperture plate is used, the additional multi-aperture plate may be positioned with respect to the first and second multi-aperture plates such that centers of the apertures in the additional multi-aperture plate are shifted with respect the centers of the corresponding apertures of the first and second multi-aperture plates in order to achieve a compensation for the misalignment as described above. In FIG. 17, an embodiment of the method of manufacturing a shaped multi-aperture arrangement according to the 15th aspect of the present invention is illustrated. In a first step S1, apertures 905 are etched into a silicon wafer 900 having a wafer thickness WT. Etching of apertures into silicon wafers is well known in the art of silicon technology. The formation of the apertures 905 may be, for instance, carried out by providing a single crystal silicon wafer 900 having a thin film of silicon oxide formed on top of a silicon surface, a thin metal layer on a silicon oxide surface and a thin layer of photoresist on a metal layer surface disposed on at least one side of the silicon wafer. A desired pattern is generated in the photoresist in a suitable manner by exposure to radiation such that a pattern of exposed photoresist portions is formed. The exposed photoresist portions are removed (or, alternatively, the unexposed part of the photoresist removed would form a negative pattern), and subsequently the underlying, exposed metal layer removed by a suitable etching process. The pattern formed in the photoresist is thus replicated in the metal layer. Apertures 905 are then etched into the silicon wafer 900 by a suitable etching process, such as etching of the silicon oxide and the silicon by deep reactive ion etching, which method is advantageous in that it is suited to achieve high aspect ratio apertures through the entire thickness WT of the wafer. Once the apertures 905 extend through the entire thickness of the wafer WT and are accessible from both sides 901, 902 of the wafer, the apertures are filled with a suitable filler in a second step S2 of the embodiment of the method, such as a suitable glue or resin. In a third step S3, a side (or surface) 902 of the wafer 900 is turned on a lathe and polished using a suitable polishing agent or abrasive, respectively, such as diamond, until a curved surface shape results in a region 910, which region 910 comprises all of the apertures 905. Such turning and polishing is well known from the manufacture of conventional optical lens elements made from glass, fused silica, calcium fluoride or the like. A region 920 adjacent to the shaped surface region 910, which in the case of a center-symmetrical pattern would form a frame around the shaped surface region 910, is processed such that it is substantially flat. A rim 930 on the silicon wafer is left out from the turning and polishing step S3 and thus has substantially the original wafer thickness WT. This rim 930 can be advantageously used to provide bonding surfaces for the purpose of bonding two multi-aperture plates together, for instance by application of a suitable insulating material and subsequent bonding. In the embodiment of the method of manufacturing a multi-aperture plate having a shaped surface according to the 13th aspect of the present invention, in a first step S1, a pattern of holes 904 is etched into a silicon wafer 900 from a front side 901 thereof, as illustrated in FIG. 18. In contrast to the embodiment shown in FIG. 17, the holes 904 do not extend through the entire wafer thickness WT, but only reach to a depth corresponding to about half the wafer thickness WT, in this particular embodiment. In other embodiments, the holes may extend to a different depth, as long as the holes do not extend through the entire wafer thickness WT. The etching of the holes 904 can be effected by the same methods as the etching of the apertures 905 in the above described embodiment of FIG. 17. In a second step S2, the wafer is processed on its other side 902, i.e. a back side 902 of the silicon wafer 900 opposite the front side 901. In analogy to the method described above, the silicon wafer is diamond-turned, i.e. turned using diamond material as an abrasive, and polished until enough material is removed from the backside 902 of the silicon wafer 900 to give the back side a curved shape. The turning and polishing is carried out such that a surface of the back side 902 of the silicon wafer 900 has a curved area 910 around a center of the aperture pattern. Finally, the back side 902 is etched in a third step S3 in order to open up the holes 904 from the back side 902 and thus form apertures 905 that extend through the entire thickness of the wafer 900. Isotropic etching substantially removes the same amount of material from any location on the backside of the wafer and thus substantially maintains a shape provided by the turning and polishing step. This etching can be achieved by a physical etching method, such as plasma etching. Thus, a multi-aperture plate is formed. The shape of the curved surface can be readily chosen within a fairly wide range by an appropriate setting of the utilized turning and polishing tools and choice of etchant or etching method. In a different embodiment, an etching step could be adjusted to alter the shape given by the turning and polishing step in a desired manner, using a suitable etchant. In FIG. 19, a further embodiment of the method of manufacturing a multi-aperture plate according to the 13th aspect of the present invention is illustrated, with the steps of producing a curved surface on one side and etching holes into the other side being reversed as compared to the embodiment shown in FIG. 18. Thus, in a first step, a back surface of the silicon, wafer 900 is turned on a lathe using diamond material for polishing and removing material such that the back surface 902 of the silicon wafer 900 has a curved surface CS at least in a predetermined area. In a second step S2, a number of holes 904 is etched into the other side, i.e. the front surface 901 of the silicon wafer 900. In a third step, holes 904, which do not extend through the entire thickness of the wafer and therefore are only open to the front surface 901, are filled with a suitable filling material f. In a fourth step S4, the back side 902 including the curved surface CS is etched by plasma etching such that enough material is removed therefrom to expose the holes 904 and form apertures 905 which are open to both the front and the back surfaces 901, 902, whilst the curvature of the curved shape CS of the back surface 902 is maintained, in the same or similar manner described in connection with FIG. 18. In a fifth step S5, the filler material F is removed from the apertures 905. In an embodiment of the method of manufacturing a multi-aperture plate according to the 14th aspect of the present invention, a silicon wafer 900 having a front surface 901 and a back surface 902 is provided in a first step S1. In a second step S2, holes 904 are etched into the front surface 801 of the silicon wafer 900. In a subsequent third step S3, the front surface 901 is processed such that a curved surface CS, which is at least partially positioned in an area where holes 904 are located, is generated. In a fourth step S4, the back surface 902 of the silicon wafer 900 is processed by polishing or turning or etching such that holes 904 are opened up on the back surface 902 to form apertures 905. In a final sixth step S6, the filler material F is removed from the apertures 905. Etching and processing steps and filler material are as described above in the other embodiments. While the invention has been described also with respect to certain specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention set forth herein are intended to be illustrative and not limiting in any way. Various changes may be made without departing from the spirit and scope of the present invention as defined in the following claims. |
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058964304 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows part of a nuclear power plant comprising a reactor vessel 1 with a removed reactor vessel cover, not shown in the figure, arranged in a water-filled reactor pool 2. Further, a so-called fuel pool 3 is shown arranged adjacent to the reactor pool 2. The fuel pool 3 is substantially designed for temporary storage of new and completely or partially burnt-up fuel assemblies 4, respectively. The reactor vessel 1 comprises a core 5 with a plurality of fuel assemblies 4 and control rods 11 and a core grid 6 arranged above the core 5. The reactor pool 2 is connected to the fuel pool 3 via a closable opening 7. The other internal parts 8 of the reactor can be temporarily arranged in the reactor pool 2. During shutdown of the nuclear reactor, the reactor vessel 1 is filled with water and the reactor vessel cover removed. Then, the reactor pool 2 above the reactor vessel 1 is filled with water, and the port 7 between the reactor pool 2 and the fuel pool 3 is opened. Internal reactor parts 8 arranged above the core 5 are lifted out and arranged in the reactor pool 2. The core grid 6 and the fuel assemblies 4 arranged below the grid are now available for a gripper 9 arranged in the reactor hall. A fuel cassette 12 is arranged in the reactor vessel 1 above the core grid 6. The gripper comprises, for example, a telescopic arm 10 for lowering into the reactor vessel 1 and raising one or more fuel assemblies 4 therefrom and loading these in the fuel cassette 12. When the fuel cassette 12 is filled with the desired number of fuel assemblies 4, it is transported to the fuel pool 3 by the gripper 9. FIG. 1 shows the gripper 9 in dashed lines during transportation of a fuel cassette 12 comprising a group 4a of fuel assemblies 4 and possibly control rods 11. The fuel assemblies 4 are lifted out through the openings in the core grid 6. Also FIG. 2 shows, in principle, the appearance of the core grid 6. The core grid 6 comprises a grid having an opening in the grid which corresponds to the size of a core module, i.e., four adjacently located fuel assemblies 4 and one cruciform control rod 11 arranged therebetween. The control rods 11 may either be lifted out together with the fuel assemblies 4, or be left in the reactor core 5. The removed control rods are placed temporarily in the fuel pool 3 together with the fuel assemblies 4. FIG. 3 shows a two-row fuel cassette 12 intended for eight fuel assemblies 4 or 8 core modules and loading via an opening 13 open at the top. Fuel cassette 12 comprises eight substantially vertically arranged sleeve-formed spaces having a substantially square cross section. Each sleeve-formed space is limited by walls 12a made of a neutron-absorbing material and a bottom part 12b. The sleeve-formed spaces are joined to each other form one unit for transport and storage of fuel assemblies 4 and possibly control rods 11. When a fuel assembly 4 or a group of fuel assemblies 4, which is not a core module, is lifted out of the reactor core 5, these are each arranged in a sleeve-formed space in the cassette 12. Then, an additional fuel assembly 4 or another group 4a is lifted out of the reactor core 5 and is arranged in the fuel cassette 12. When lifting of a core module is made, this is preferably arranged in a sleeve-formed space surrounding the whole core module. The lifting operation continues until the fuel cassette 12 is filled with the desired number of fuel assemblies 4 or core modules, whereupon the fuel cassette 12 is transported to the fuel pool 3 for temporary storage therein. Possibly, one or more of the fuel assemblies 4 are replaced in the fuel cassette 12 while this is stored in the fuel pool 3. Fuel assemblies 4 may also be transferred in or between the fuel cassettes 12 when these are placed in the fuel pool 3. When it is time again for inserting the fuel assemblies 4 into the reactor core 5, the fuel cassettes 12 are transported from the fuel pool 3 to a location in the reactor vessel 1 above the core 5. Thereafter, the fuel assemblies 4 are lifted one by one, by groups, or by core modules out of the fuel cassette 12 and are arranged in the reactor core 5. FIG. 4 shows a single-row fuel cassette 12 intended for eight fuel assemblies 4 or for eight core modules and loading via a vertical opening 14, each arranged in the wall of a sleeve-formed space. Each vertical opening 14 is provided with a stop means 15 for fixing the fuel assemblies 4 in the fuel cassette. FIG. 5 shows a two-row fuel cassette 12 with twelve sleeve-formed spaces intended for twelve fuel assemblies 4. Each sleeve-formed space is provided with a vertical opening 16 extending along the substantial length of the sleeve-formed space. The opening 16 is provided with a port 17 intended for sealing the sleeve-formed space during transport and storage of the fuel assembly 4 arranged therein. During a shutdown of the reactor, the fuel assemblies 4 are normally lifted out whereas the control rods 11 are left in the reactor vessel 1. If it is desired also to lift out the control rods 11, this can be done either by lifting them out together with the core modules as mentioned above, or in a work operation separate from the lifting of the fuel assemblies 4. According to one aspect of the invention, the control rods 11 are arranged in control rod cassettes 18 in a way corresponding to the arrangement of the fuel assemblies 4 in fuel cassettes 12. FIG. 6 shows an embodiment of a control rod cassette 18. The control rod cassette 18 comprises a frame structure 18 formed with eight control rod positions 19. Alternatively, the control rod cassette 18 may be designed so that the control rods 11 can be arranged with their control rod blades lib overlapping each other. The control rod cassette 18 is preferably designed so that it can be loaded laterally, that is, with a vertical opening corresponding to the openings 14, 16 in the fuel cassette 12 in FIGS. 4 and 5, respectively. Preferably, the same gripper 9 is used for lifting the control rods 11 as for lifting the fuel assemblies 4. By arranging a plurality of control rods 11 in one control rod cassette, the emptying of the reactor vessel 1 is further accelerated. The control rod cassette 18 is arranged in the fuel pool for temporary storage in the same way as the fuel assembly cassettes 12. FIG. 7 shows how the fuel pool 3 is divided into a number of positions. Each of these positions consists of a square in the grid shown. When a fuel cassette 12 is arranged in the fuel pool 3, this can be arranged at an arbitrary location therein; for example, in the dashed position relating to a two-row fuel cassette with eight fuel assemblies 4 according to FIG. 3. In one embodiment of the invention, the fuel cassettes 4 are filled and arranged in the fuel pool 3 in such a way that each fuel assembly 4, removed from the reactor core 5, in the fuel pool 3 is given a position which, in relation to the other removed fuel assemblies 4, is the same as in the reactor core 5. In this way, the same geometry is obtained in the fuel pool 3 as in the fuel core 5. In those cases where refuelling or fuel transfer is to take place, this is suitably performed while the fuel cassettes 12 are placed in the fuel pool 3. At the same time as the refuelling and/or the fuel transfer takes place in the fuel pool, the reactor vessel 1, or parts connected thereto, is/are freely available for servicing. When the servicing is completed and the fuel assemblies 4 are possibly replaced or transferred, the fuel assemblies 4 are transferred in their respective fuel cassettes 12 again to a location in the reactor vessel 1 whereupon the fuel assemblies 4 are moved from the fuel cassette 12 and filed down onto their position in the reactor core 5. It is self-evident that the different types of fuel cassettes 12 and control rod cassettes 18 may be arbitrarily provided with any of the openings 12, 14, 16 which are shown and be provided in a suitable way with ports 17 or stop means 15. |
050808583 | summary | The present invention relates to a fuel assembly for a boiling reactor. The fuel assembly comprises a bundle of elongated fuel rods retained by a number of so-called spacers placed with a certain distance between each other along the bundle. A coolant, for example water, is adapted to flow from below and upwards through the fuel assembly which normally is arranged vertically and, upon a nuclear reaction, to cool the fuel rods arranged in the fuel assembly. The object of the invention is to increase the efficiency of this cooling of the fuel rods. In a boiling type nuclear reactor the steam formation in the fuel assembly increases more and more towards the upper part of the assembly, as is clear from FIG. 1 which shows, in rough outline, a cross section of part of a fuel assembly. In FIG. 1, 1 designates a fuel rod and 2 spaces between the rods. This space 2 is in the lower part of the fuel assembly (corresponding to the lower part of the core of the reactor), filled with coolant, in this case water. Further up in the fuel assembly, steam bubbles 3 are formed in the water which, still further up, is transformed into water steam in the region 4. As long as so-called dry out does not take place, however, there is always a film 5 of the cooling water on the fuel rods. It is important that this film 5 is maintained at all points of the rods 1. If at some point it disappears by dry out, serious damage at this point of the fuel rod 1 will rapidly arise. In FIG. 1, 6 designates the wall of the fuel assembly. Also this is normally coated with a water film 5. However, this film 5 is not entirely necessary since the wall 6 of the assembly is considerably more insensitive to superheating compared with the fuel rods. This fact has been observed and attempts have been made to make use of it in some known designs, as, for example, in U.S. Pat. No. 4,749,543, column 8 and FIG. 9. In these designs, the cooling water flowing along the wall 6 of the fuel assembly is diverted towards the centre of the bundle by means of elevations on the wall 6 or recesses in the same. Also fins on the downstream side of the spacers are used to achieve a diversion or deflection of the cooling water. All these embodiments have certain drawbacks. Thus, for example, the elevations may increase the pressure drop in the cooling water and thus reduce the cooling effect whereas recesses in the wall entail certain difficulties from the point of view of manufacturing technique. Further, a deflection of the cooling water flowing along the assembly wall 6 should take place as early as possible in relation to each separate spacer and, in any case, preferably not immediately after the same viewed in the direction of flow. This is due to the fact that dry outs normally occur immediately upstream of a spacer or possibly in the same. The present invention relates to a device for achieving, in a known spacer, the desired deflection of the coolant in a simple manner. The spacer, which in this case consists of a number of cells surrounded by an outer frame formed from a metal band placed on edge, is provided according to the invention with a skirt. This skirt extends the mentioned band in the upstream direction of the flowing coolant. Openings have been arranged in the skirt and in some these openings deflection fins have been inserted in order to deflect the coolant, flowing along the assembly wall, in a direction towards the centre of each respective spacer. By the present device improved cooling is obtained immediately below the respective spacer where dry out normally occurs. The extension or skirt may be made as part of the ordinary spacer frame or as a separate part 7 connected thereto. In the latter case the skirt may be made of Zircaloy for achieving reduced neutron absorption. |
048636738 | abstract | In a hydraulic system of a control rod drive for insertion of control rods, a test apparatus and test process is disclosed for determining the integrity of the hydraulic system check valve for preventing inadvertent control rod ejection responsive to the reactor pressure. The check valve is located between a hydraulic valve for causing rod insertion and the hydraulic cylinder. In this interval downstream of the check valve, alteration is made to the hydraulic path by the installation of a conduit with a quick disconnect connected through an isolation valve. Test apparatus for temporary connection at the disconnect is disclosed consisting of a small positive displacement piston and cylinder. The small positive displacement piston and cylinder connects to the quick disconnect through a complementary quick disconnect fitting and a rapidly opening toggle valve. Provision is made for timing the excursion of piston in the piston and cylinder preferably by end of stroke microswitches. A process for the testing of the integrity of the check valve is disclosed in which quick opening valve is opened with resultant backflow from the hydraulic system through the check valve into the volume defined by the small displacement. Presuming proper check valve operation and closure, the time of excursion of the piston between the two microswitches is long, indicating that the check valve seats and remains sealed to prevent control rod ejection. Alternately, if the time of excursion of the piston between the two microswitches is short, there is an indication that the check valve has not properly seated and that control rod ejection is possible. It is important to note that control rod ejection is not permitted due to the small volume of the interrogating piston and cylinder. Provision is made for the discharging of the contents of the piston back to the hydraulic circuit before removal of the test apparatus for sequential tests at adjacent control rod drives. |
048083704 | abstract | A gas-cooled, high-temperature nuclear reactor includes a metallic core barrel, a graphite or carbon block lining disposed in the core barrel, a hot gas line including an outer pressure-confining metallic pipe and a ceramic flow guidance pipe, insulation separating the metallic pipe from the ceramic pipe, a stub concentric with the hot gas line, a device for detachably connecting the stub to the core barrel, the metallic pipe being tightly disposed in the stub, a device for detachably fastening the metallic pipe to the stub, a sleeve, a device for detachably fastening the sleeve to the lining, a bellows compensator being disposed in the stub and having one end tightly fastened to the stub and another end, and a device for connecting the other end to the sleeve. |
048448400 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of hazardous waste containment and disposal. In particular, the invention relates to a method and structure suitable for both short and long term storage and permanent disposal of hazardous wastes, particularly nuclear wastes, where the containment structure resists failure from earth movement and allows rapid location and isolation of any leaks which should occur. Hazardous wastes include a variety of toxic and radioactive substances which would cause harm if released directly into the environment. The various types of hazardous wastes are generally defined by the United States Environmental Protection Agency (EPA) and the Nuclear Regulatory Commission (NRC). With respect to hazardous wastes of a radioactive nature, the NRC presently identifies the following classes of low level wastes with respect to containment and disposal. Class A: Wastes for which there are no stability requirements but which must be disposed of in a segregated manner from other wastes. These wastes, termed class "A", or "segregated wastes, are defined in terms of maximum allowable concentrations of certain isotopes and certain minimum requirements on waste form and packaging that are necessary for safe handling. Class B: Wastes which need to be placed in a stable form and disposed of in a segregated manner from unstable waste forms. These wastes, termed class "B", or "stable" wastes, are also defined in terms of allowable concentrations of isotopes and requirements for a stable waste form as well as minimum handling requirements. Class C: Wastes which need to be placed in a stable form, disposed of in a segregated manner from nonstable waste forms, and disposed of in such a manner that a barrier is provided against potential inadvertent intrusion after institutional controls have lapsed. These wastes are termed class "C", or "intruder protected" wastes, and are also defined in terms of allowable concentrations of isotopes and requirements for disposal by deeper burial or some other barrier. A fourth class of wastes (mixed wastes) which is not included in the NRC's current listing comprises radioactive wastes contaminated by chemical components classified as hazardous wastes by the EPA. In general, hazardous wastes cannot be completely eliminated, but rather must be contained in a manner which prevents their release into the environment for very long periods of time, which in practical terms would be considered permanent. A variety of approaches have been proposed for such long term containment, including burial of primary containers holding the waste, disposal of such containers at sea, incorporation of the waste and/or containers of the waste in a solid matrix, such as cement, and the like. In general, most of the proposed approaches suffer from certain drawbacks. The disposal of wastes in primary containers, such as barrels or drums, either by burial or at sea, depends on the integrity of the container. Encapsulation of the containers in concrete, in contrast, would appear to provide long term stability and containment, but in fact can be subject to failure from a variety of causes, particularly earth movement resulting from earthquakes, earth subsidence and the like. Such earth movements frequently can fracture even the most solid containment matrixes over a long period of time. An additional problem relates to the detection of leaks in a long term containmnent facility. Although a number of leak detection systems have been proposed, generally they do not allow for precise location of the leak. As many of these containment facilities are quite large, knowledge that a leak has occurred without knowing the precise origin of the leak can be problematic. Moreover, even after the leaks are detected, most storage facilities do not provide for any convenient manner for the leak to be cleaned and facility restored. For the above reasons, it would be desirable to provide a method and structure for the secure containment of radioactive and other hazardous wastes for very long time periods. In addition, it would be desirable to provide methods and systems for leak detection in such containment structures which would allow the immediate location and isolation of leaks which might occur in the structure, and further allow for correction of the leak and restoration of the structure. 2. Description of the Background Art The use of nested containers for the storage of nuclear and hazardous wastes has been proposed. See, e.g., U.S. Pat. No. 4,229,316 which describes the use of an inner metal container for storing liquid wastes, where the container is housed in an outer concrete receptacle, and excess space within the receptacle is filled with a radiation-absorptive substance; U.S. Pat. No. 4,588,088 which describes an inner container, typically a metal drum, housed within an exterior container 20, where the interstitial space between the two containers is filled with a sealant material; U.S. Pat. No. 4,453,857, which discloses the sealing of a plurality of containers, typically steel drums, in a solid concrete block; and U.S. Pat. No. 4,513,205, which discloses the use of nested concrete vaults to hold a plurality of inner containers, typically metal barrels. Monitoring of possible leakage of nuclear and hazardous wastes from underground storage systems is known. See, e.g., U.S. Pat. No. 4,513,205, where an inner vault is placed within an observation vault to allow for monitoring of leakage; U.S. Pat. No. 4,464,081, where an underlying pipe and manifold system is placed beneath an underground storage facility to collect seepage and monitor for hazardous wastes; and U.S. Pat. Nos. 4,624,604 and 4,543,031, both of which disclose a leakage detection system located beneath a landfill site. U.S. Pat. No. 4,362,434 discloses a lined basin for the collection of hazardous wastes in bulk. Monitoring of leakage can be done through a sump system. U.S. Pat. No. 4,375,930 also discloses a hazardous waste site having a sump which allows observation of leakage and leachate. U.S. Pat. No. 4,428,700, describes a particular filler which can be used for sealing hazardous waste, either in containers or otherwise, in underground storage locations. SUMMARY OF THE INVENTION The present invention provides a method and structure for the permanent or temporary containment of hazardous and toxic wastes, particularly nuclear wastes. The method allows for the collection of such wastes over an extended period of time, typically years, in conventional containers, such as metal drums, liners and dry active waste boxes. The containers are collected and sealed within larger canisters, typically concrete boxes. The remaining interstitial space within the canisters will typically be sealed with a curable fluid sealant, such as grout, to provide both mechanical stability and radiation shielding. The individual canisters are shaped in a particular geometry which allows them to be stacked in an interlocking manner to form an integrated monolithic structure in which canisters are held firmly in place by gravity, but are able to shift relative to one another in response to earth movements, such as earthquakes, ground shifting, settling, sliding, and the like. The use of such interlocking canisters which are held in place by gravity has particular advantages. First, the relative shifting of canisters will not generally result in fracturing or other damage to the individual canisters. Thus, the integrity of the canister seal is maintained even when the disposal site is subject to earthquakes, subsidence, and other earth movement. Equally important, should a leak occur in one of the canisters, the integrated structure may be disassembled to allow for removal and repair of the defective canister without disturbing the seal of the other canisters. Finally, the assembly of the integrated structure is greatly simplified as there is no need to tie or otherwise connect the individual canisters together. The integrated disposal structure of the present invention is suitable for above ground, partially buried, and underground disposal sites. In all cases, a barrier layer will be prepared over the site to seal the ground surface to inhibit penetration of water which passes through the structure (to prevent ground water contamination should a leak occur in one of the canisters). Usually, a system will be provided for collecting the water which has passed through the structure, which system may be adapted to monitoring for the presence of hazardous wastes in the water from the structure. In the preferred embodiment, the collection system is zoned to provide for segregated collection of water from a plurality of sections beneath the integrated structure. In this way, the area where a leaking canister is located and from which the hazardous waste is originating may be quickly identified. The integrated structure can then be disassembled in the area of the leak, leaving the remainder of the structure intact. After removal of the defective canister, the integrated structure can then be restored. In the case of particularly hazardous wastes, e.g., the Class C wastes and mixed wastes defined above, the present invention allows for verification of the integrity of the integrated structure prior to and after the final closure of the structure with a permanent earthen cover. Prior to the final closure, the structure may be allowed to remain without the earthen cover for a certain period of time so that the leak tightness of the structure is verified. Before the final earthen cover is placed, it is desirable to expose the structure for an interim period to conditions that are the same or more severe than the conditions the structure will be exposed to while buried under the earthen cover during the long-term isolation period. In this interim period, the structure will be exposed to rainwater, snow, freeze and thaw cycles, and other harsh environmental conditions which will verify the performance expected from the structure. These conditions will test the integrity, leak tightness, stability, strength and other related properties. During this interim period, the existence of a failure in the integrity of the structure, which usually means the existence of a faulty canister, can be easily detected by periodically collecting water from the integrated structure and sampling for contamination. In the event that the existence of a failed canister is indicated by these sampling operations, such canister can be easily remedied by removal from the structure followed by repair and replacement in its original position in the integrated structure. If no failure in the integrity of the structure is detected after a predetermined number of years, the integrated structure can be closed in a permanent manner, typically by placement of an earthen cover over the integrated structure. The present invention is also capable of monitoring the integrity of the structure for a number of years after the final closure with the earthen cover. The method and structure of the present invention has a number of additional advantages. A wide variety of waste streams may be accepted for short-term, long-term or permanent isolation in surface, partially buried, and underground storage. The structure may be adapted to a wide variety of natural features at the disposal site, and employs common construction materials, such as reinforced concrete, which are readily available and known for their long-term reliability and performance. The initial placement of waste containers into the protective canisters is usually handled remotely in an enclosed area for the protection of the workers. All remaining operations, however, can be handled by workers without additional protection as the canisters provide sufficient shielding for worker safety. The monitoring and recoverability of the individual canisters may be performed over extended periods, exceeding one hundred years, and a substantially permanent sealing minimizes contact between the waste and water at all times. |
claims | 1. An auxiliary wedge positioning apparatus for use in a nuclear reactor having at least one jet pump assembly, the wedge positioning apparatus consisting essentially of:(a) a restraint bracket body having a top end flat portion having one hole therethrough and a transverse rail with two bottom integral hooked protrusions each exactly opposite to each other and attached to the transverse rail, said protrusions having an angled gull wing shape with an upward member section and a downward member section;(b) a single triangular slide wedge having a flat side attached to the transverse rail of the restraint bracket body, with an end flat portion and an angled side facing outward;(c) a single slide rod passing through the top flat portion hole to contact the end flat portion of the triangular slide wedge; and(d) a single spring disposed around the slide rod, the spring contacting both the top end flat portion and exerting pressure against the end flat portion of the triangular slide wedge to exert pressure against adjacent bodies in the nuclear reactor; wherein the hooked protrusions contain a parallel member section, a middle upward member section and an end downward member section next to the transverse rail, providing an angled gull wing shape, where the parallel member section is outward at a 90° angle from the restraint bracket body, the middle upward member section is at a 20° to 60° angle to the restraint bracket body and the downward member section is at an angle of 70° to 110° from the upward member section and wherein the parallel member section has an attached upward member section ending and a downward member section; wherein the wedge positioning apparatus utilizes a combination of spring force and gravity to continuously tighten over time. 2. The wedge positioning apparatus of claim 1, wherein the hooked protrusions contain a wing angle stabilizing attachment connected to the upward member section and downward member section, where the wing stabilizing attachment is parallel to the upward member section and the downward member section. 3. The wedge positioning apparatus of claim 2, wherein the parallel member section is outward from and attached to the transverse rail, the downward member section is attached to the upward member section which upward section is in turn attached to the parallel member section. 4. The wedge positioning apparatus of claim 1 used for positioning in close contact with a circular jet pump assembly where the gull wing design conforms to the jet pump assembly using a three-line contact to maintain stability between all of the parts, where the hooked protrusions aid in installation of the apparatus while the jet pump assembly is in place and provide stability under vibration conditions, wherein the at least one gull wing is positioned partially around and in contact with the jet pump assembly. 5. In a nuclear reactor, at least two separate auxiliary wedge positioning apparatus, where the nuclear reactor, contains riser piping that can feed pumped cooled water to at least one jet pump assembly having a circumferential restrainer bracket, which restrainer bracket has at least two vibration damping adjustment set screws, each set in a set screw block contacting the jet pump assembly, the bracket positioned around the jet pump assembly which bracket also contacts the riser piping, such assembly and riser piping subject to vibration during reactor operation, wherein a main wedge is utilized away from the set screws, while the at least two separate auxiliary wedge positioning apparatus being positioned adjacent the set screws; wherein the at least two separate auxiliary wedge positioning apparatus consists essentially of:(a) a restraint bracket body having a top end flat portion having one hole therethrough and a transverse rail with two bottom integral hooked protrusions each exactly opposite to each other and attached to the transverse rail, said protrusions having an angled gull wing shape with an upward member section and a downward member section, structured to contact the at least one set screw block;(b) a single triangular slide wedge having a flat side attached to the top rail of the restraint bracket body, with an end flat portion and an angled side facing outward;(c) a single slide rod passing through the top flat portion hole to contact the end flat portion of the triangular slide wedge; and(d) a single spring disposed around the slide rod, the spring contacting the top end flat portion and exerting pressure against the end flat portion of the triangular slide wedge this pressure on the slide wedge forcing it against the jet pump assembly; wherein the hooked protrusions contain a parallel member section, a middle upward member section and an end downward member section next to the transverse rail, providing an angled gull wing shape, where the parallel member section is outward at a 90° angle from the restraint bracket body, the middle upward member section is at a 20° to 60° angle to the restraint bracket body and the downward member section is at an angle of 70° to 110° from the upward member section. 6. The wedge positioning apparatus of claim 5 in use in a nuclear reactor of claim 5, wherein both adjustment set screw blocks contact the hooked protrusion to stabilize it. 7. The wedge positioning apparatus of claim 5 in use in a nuclear reactor of claim 5, wherein the wedge positioning apparatus utilizes a combination of spring force and gravity to continually tighten over time the wedge disposed next to the at least one jet pump assembly. 8. The wedge positioning apparatus of claim 5, wherein the hooked protrusions contain a parallel member section, an upward member section and an end downward member section next to the transverse rail and a wing stabilizing attachment connected to upward member section and downward member section, where the wing stabilizing attachment is parallel to the upward member section and the downward member section and is adjacent to the at least one set screw block, and assists in preventing excessive circumferential movement of the auxiliary wedge positioning apparatus. 9. The wedge positioning apparatus of claim 8, wherein the parallel member section is outward from and attached to the transverse rail, an end downward member section is attached to a middle upward member section which upward section is in turn attached to the parallel member section next to the transverse rail. 10. The wedge pump positioning apparatus of claim 5 used for positioning in close contact with a circular jet pump assembly where the gull wing design conforms to the jet pump assembly using a three-line contact to maintain stability between all of the parts, where the hooked protrusions aid in installation of the apparatus while the jet pump assembly is in place and provide stability under vibration conditions, wherein the at least one gull wing is positioned partially around and in contact with the jet pump assembly and wherein parallel member section a has an attached upward member section ending and a downward member section; wherein the wedge positioning apparatus utilizes a combination of spring force and gravity to continuously tighten over time. |
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054066018 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is generally related to the transport and storage of radioactive material and particularly to a cask that can be used for transporting or storing spent nuclear fuel. 2. General Background Nuclear reactors require periodic replacement of the nuclear fuel. Fuel removed from reactors in naval vessels and some land based commercial reactors must be transported to a storage site. In some instances, there may be storage room at the site of the land based reactor. The United States Nuclear Regulatory Commission sets standards that must be met for casks that are used to transport or store spent nuclear fuel. Due to the different conditions that may be encountered during transport and static storage, separate standards are set for transport casks and for storage casks. These standards are respectively set forth in 10 CFR 71 and 10 CFR 72. Shipping casks must be able to withstand shock loads during transport while storage casks must be able to withstand temperature transients such as a fire external to the cask without transmitting additional heat to the inside of the cask. As a result, it is common to have separate casks for transport and storage. This presents the need for additional work in the form of transferring the fuel from one cask to another once the shipment has arrived at the storage site. If there is not an immediate need for reuse of the transport cask, then the transport cask which has a radioactive interior after use must also be stored until it is needed again. SUMMARY OF THE INVENTION The present invention addresses the above problem in a straightforward manner. What is provided is a cask that can be used for both transport and storage of spent nuclear fuel. The cask body and basket are designed such that there is a gap between the cask body and basket. The basket is formed from multiple layers of rowed plates that cooperate with the cask body to provide the required radiation shielding, thermal, and structural requirements of 10 CFR 71 and 10 CFR 72. The plates have complementary shapes and partial hex grooves machined therein such that complete channels for the fuel cells are formed when the plates are mated for insertion into the cask body. The plates have narrowed diameter sections and are held together by bands around the circumference of the plates at these sections. Locating keys received in grooves between the plates extend the entire axial length of the basket to hold the plates in alignment during assembly and to block radiation leakage across the vertical gaps between the plates. Centering keys are provided at the upper and lower ends of the basket and cask body to provide a consistent gap between the basket and cask body. The gap expands during a fire due to thermal expansion of the cask body prior to thermal expansion of the basket and thus does not allow conduction of the external heat into the basket and fuel during an external transient temperature rise. |
claims | 1. A system for storing radioactive material, said system comprising:a storage pool for storing a plurality of radioactive objects submersed in a radiation shielding and cooling liquid;an assembly building located above the storage pool for constructing one or more radioactive articles using the radioactive objects transferred from the storage pool, the assembly building including an assembly chamber including a plurality of interior cells and a plurality of radioactive shielding partitions such that each of the plurality of radioactive shielding partitions is between adjacent cells, the cells including a docking cell having a disposition end of each transfer shaft connected thereto, and at least one assembly cell for constructing the one or more radioactive article therein; andat least one transfer shaft connecting the storage pool and the assembly building for transferring the radioactive objects from within the storage pool to an interior of the assembly building and from the interior of the assembly building into the storage pool, the at least one transfer shaft connected to a floor of the assembly building. 2. The system of claim 1, wherein each transfer shaft comprises an elevator system operable to convey the radioactive objects from within the storage pool to an interior of the assembly building and from the interior of the assembly building into the storage pool. 3. The system of claim 1, wherein the shielding partitions are movable within the assembly building. 4. The system of claim 1, wherein the assembly building comprises at least one of a first interlock connected to a first end of the assembly chamber and a second interlock connected to an opposing second end of the assembly chamber. 5. The system of claim 4, wherein the assembly building further comprises a crane device within the interior of the assembly chamber operable to move the radioactive objects over the shielding partitions between the plurality of cells, and between the plurality of cells and the at least one interlock. 6. The system of claim 4, wherein the assembly building further comprises a conveyor system within or beneath a floor of the assembly chamber operable to move the radioactive objects beneath the shielding partitions between the plurality of cells and between the plurality of cells and the at least one interlock. 7. The system of claim 1, wherein at least one cell of the plurality of interior cells has opposing exterior walls, each of the opposing exterior walls of the at least one cell comprise at least one object manipulator opening that extends through the respective exterior wall, each object manipulator opening structured to allow access of a respective object manipulator to an interior of the cell, each object manipulator controllable from outside of the assembly chamber and operable to manipulate the radioactive objects within each of the cells to assemble the one or more radioactive articles. 8. The system of claim 1, further comprising a second assembly building located above the storage pool and connected with the storage pool via at least one second transfer shaft for constructing one or more radioactive article using the radioactive objects transferred from the storage pool via the at least one second transfer shaft. 9. A system for storing radioactive material, said system comprising:a storage pool disposed within and beneath a floor of the system, the storage pool for storing a plurality of radioisotopes submersed in a radiation shielding and cooling liquid;a capsule assembly building disposed on the system floor above the storage pool, the capsule assembly building comprising an assembly chamber including a plurality of interior cells for constructing one or more radioactive capsules using radioisotopes transferred from the storage pool to the capsule assembly building, the assembly chamber further including a plurality of radioactive shielding partitions such that each of the plurality of radioactive shielding partitions is between adjacent cells and the cells comprise a docking cell having a disposition end of each transfer shaft connected thereto, and at least one assembly cell for constructing the one or more radioactive capsule therein; andat least one transfer shaft connecting the storage pool and the capsule assembly building to provide direct access to the storage pool from an interior of the capsule assembly building for transferring the radioisotopes from within the storage pool to the interior of the capsule assembly building and from the interior of the capsule assembly building into the storage pool, the at least one transfer shaft connected to a floor of the capsule assembly building. 10. The system of claim 9, wherein each transfer shaft comprises an elevator system operable to convey the radioisotopes from within the storage pool directly to an interior of the assembly chamber and from the interior of the assembly chamber into the storage pool. 11. The system of claim 9, wherein the shielding partitions are movable within the assembly chamber. 12. The system of claim 9, wherein the capsule assembly building further comprises a pair of opposing interlocks connected to opposing ends of the assembly chamber. 13. The system of claim 12, wherein the assembly building further comprises a crane device within the interior of the assembly chamber operable to move the radioisotopes over the shielding partitions between the plurality of cells and between the plurality of cells and the interlocks. 14. The system of claim 12, wherein the assembly building further comprises a conveyor system within or beneath a floor of the assembly chamber operable to move the radioisotopes beneath the shielding partitions between the plurality of cells and between the plurality of cells and the interlocks. 15. The system of claim 9, wherein at least one cell of the plurality of interior cells has opposing exterior walls, each of the opposing exterior walls of the at least one cell comprise at least one object manipulator opening that extends through the respective exterior wall, each object manipulator opening structured to allow access of a respective object manipulator to an interior of the cell, each object manipulator controllable from outside of the assembly chamber and operable to manipulate the radioactive objects within each of the cells to assemble the one or more radioactive articles. 16. The system of claim 9, further comprising a second capsule assembly building located above the storage pool and connected with the storage pool via at least one second transfer shaft for constructing one or more radioactive capsules using the radioisotopes transferred from the storage pool via the at least one second transfer shaft. 17. The system of claim 1, wherein the at least one transfer shaft is connected to a sidewall of the storage pool. 18. The system of claim 1, wherein a first aperture is provided in a sidewall of the storage pool, a second aperture is provided in the floor of the assembly building, and the at least one transfer shaft extends from the first aperture to the second aperture. 19. The system of claim 18, wherein the first aperture is lower than the second aperture. 20. The system of claim 1, wherein the at least one transfer shaft is directly connected to the floor of the assembly building via an aperture in the floor of the assembly building. |
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052788750 | claims | 1. A process for the synthesis of .sup.11 C-labeled methyl iodide which comprises a .sup.11 CO.sub.2 -producing process of producing carbon dioxide gas labeled with .sup.11 C, supplying .sup.11 CO.sub.2 gas to a reaction vessel and bubbling the .sup.11 CO.sub.2 gas into a reducing agent solution in the reaction vessel to reduce the .sup.11 CO.sub.2 gas to yield an intermediate, a reducing agent solution-removing process of evaporating the reducing agent solution after the termination of the bubbling, and a .sup.11 CH.sub.3 I synthesis process of synthesizing .sup.11 CH.sub.3 I from the intermediate produced by the reduction in the bubbling process and terminating the evaporation in the reducing agent solution-removing process based on a variation of the temperature in an exhaust tube for discharging the vapor of the reducing agent solution connected with the reaction vessel. 2. The process of claim 1, wherein said bubbling process of bubbling the .sup.11 CO.sub.2 gas into the reducing agent solution in the reaction vessel is terminated by terminating the supply of the .sup.11 CO.sub.2 gas based on a variation in radiation produced upon supplying the .sup.11 CO.sub.2 gas into the reaction vessel. 3. An apparatus for the synthesis of .sup.11 C-labeled methyl iodide which comprises a target box in which .sup.11 CO.sub.2 gas is produced, a reaction vessel in which .sup.11 CH.sub.3 I is synthesized from said .sup.11 CO.sub.2 gas and a temperature sensor for detecting the temperature of an exhaust tube and deciding a termination point for discharging the vapor of a reducing agent solution which has reduced .sup.11 CO.sub.2 gas. 4. The apparatus of claim 3, which further comprises a transfer tube connecting said target box and said reaction vessel with radiation detecting means for deciding a termination point for bubbling of .sup.11 CO.sub.2 gas provided adjacent the transfer tube. |
063320118 | description | DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a sectional view, with parts cut away, of a boiling water nuclear reactor pressure vessel (RPV) 10. RPV 10 has a generally cylindrical shape and is closed at one end by a bottom head 12 and at its other end by a removable top head 14. A side wall 16 extends from bottom head 12 to top head 14. A cylindrically shaped core shroud 20 surrounds a reactor core 22. Shroud 20 is supported at one end by a shroud support 24 and includes a removable shroud head 26 at the other end. An annulus 28 is formed between shroud 20 and side wall 16. A pump deck 30, which has a ring shape, extends between shroud support 24 and RPV side wall 16. Pump deck 30 includes a plurality of circular openings 32, with each opening housing a jet pump assembly 34. Jet pump assemblies 34 are circumferentially distributed around core shroud 20. Heat is generated within core 22, which includes fuel bundles 36 of fissionable material. Water circulated up through core 22 is at least partially converted to steam. Steam separators 38 separate steam from water, which is recirculated. Residual water is removed from the steam by steam dryers 40. The steam exits RPV 10 through a steam outlet 42 near vessel top head 14. The amount of heat generated in core 22 is regulated by inserting and withdrawing control rods 44 of neutron absorbing material, such as for example, hafnium. To the extent that control rod 44 is inserted into fuel bundle 36, it absorbs neutrons that would otherwise be available to promote the chain reaction which generates heat in core 22. Control rod guide tubes 46 maintain the vertical motion of control rods 44 during insertion and withdrawal. Control rod drives 48 effect the insertion and withdrawal of control rods 44. Control rod drives 48 extend through bottom head 12. Fuel bundles 36 are aligned by a core plate 50 located at the base of core 22. A top guide 52 aligns fuel bundles 36 as they are lowered into core 22. Core plate 50 and top guide 52 are supported by core shroud 20. FIG. 2 is an enlarged sectional view of shroud 20. Shroud 20 includes a shroud head flange 54, an upper shroud section 56, a top guide support 58, mid shroud sections 60, 62, and 64, a core plate support 66, and a lower shroud section 68. Circumferential welds 70, 72, 74, 76, 78, 80, and 82 couple the shroud elements together. A circumferential weld 84 attaches lower shroud section 68 to shroud support 24. Welds 70, 72, 74, 76, 78, 80, 82, and 84 are sometimes referred to as welds H1, H2, H3, H4, H5, H6A, H6B, and H7 respectively. A steam dam 86 is attached to inner surface 88 of shroud head flange 54. A plurality of shroud head lugs 90 are attached to an outer surface 92 of shroud head flange 54. Shroud head lugs 90 are spaced around the circumference of shroud head flange 54. Companion shroud head lugs 94 are attached to shroud head 26. Shroud head lugs 94 are located on shroud head 26 to be alignable with shroud head lugs 90 located on shroud head flange 54. Shroud head bolts (not shown) engage aligned shroud head lugs 90 and 94 to couple shroud head 26 to shroud 20. FIG. 3 is a side view of a phased array probe 96 positioned on top of shroud head flange 54 in accordance with an exemplary embodiment of the present invention. FIG. 4 is a schematic top view of probe 96. Referring to FIGS. 3 and 4, phased array probe 96 contains one linear array transducer having a plurality of elements 98 which emits an ultrasonic sound beam 100. The basic parameters of phased array probe 96 are defined as frequency, aperture A, element size X, element width Y, pitch or element spacing P, and number of elements 98. A suitable transducer frequency is 2 MHz for the material type and thickness of shroud 20. However, other transducer frequencies can be used for shrouds manufactured from other material types. Additionally, testing has shown that a transducer frequency of 2 MHz is useful for detection and sizing of Intergranular Stress Corrosion Cracking (ISCC). In this exemplary embodiment, shroud 20 is formed from stainless steel. However, other useful materials such as, for example, Ni--Cr--Fe alloy X-750 steel, may be used. The element pitch is determined by calculating the acoustic aperture A needed to focus beam 100 at the required sound path and dividing this value by the total number of elements. The size X of elements 98 is set as the maximum possible per the pitch. The width Y of elements 98 is determined by calculating the effective diameter for a near field of 6 inches to give the smallest beam profile in the y-plane. The physical restrictions of the scanning surface must also be considered in determining the basic parameter values of probe 96. To examine the heat affected zone (HAZ) of H1 weld 70, phased array ultrasonic probe 96 is positioned on an upper surface 102 of shroud head flange 54. Probe 96 is triggered to emit an ultrasonic sound beam 100 which is focused at a point on a line which coincides with the upper fusion line 104 of weld 70 and a lower surface 106 of shroud head flange 54. Focussing beam 100 on upper fusion line 104 permits inspection of the HAZ from upper fusion line 104 extending at least one half inch toward upper surface 102 of shroud head flange 54. Probe 96 can electronically steer ultrasonic sound beam 100 to scan HI weld 70 with the beam moving from shroud head flange outer surface 92 to shroud head flange inner surface 88, and acquiring scan data over a length of the scan. Ultrasonic probe 96 is then incrementally moved circumferentially along upper surface 102 of shroud head flange 54 and weld 70 is again ultrasonically scanned. Ultrasonic probe 96 is continuously moved circumferentially along upper surface 102 of shroud head flange 54 in increments of between about 0.05 inch to about 1.0 inch with the H1 weld ultrasonically scanned after each incremental move. In another embodiment, ultrasonic probe 96 is continuously moved circumferentially along upper surface 102 of shroud head flange 54 in increments of between about 0.05 inch to about 0.5 inch with the H1 weld ultrasonically scanned after each incremental move. In still another embodiment, ultrasonic probe 96 is continuously moved circumferentially along upper surface 102 of shroud head flange 54 in increments of between about 0.05 inch to about 0.1 inch with the H1 weld ultrasonically scanned after each incremental move. Initially, ultrasonic beam 100 is focused so that a focal point 108 of beam 100 aligns with upper fusion line 104 of weld 70 and outer surface 92 of shroud head flange 54. Beam 100 is then repeatedly refocused so that beam focal point 108 moves along upper fusion line 104 and lower surface 106 of shroud head flange 54 from outer surface 92 of shroud head flange 54 toward inner surface 88 of shroud head flange 54 in discrete increments. This electronic refocusing of beam 100 is achieved by programming the individual elements 98 to pulse at preset times in relation to the other elements 98. The programming or pulse sequence is known as a focal law. A set of focal laws is used to electronically repeatedly refocus, or electronically steer, ultrasonic beam 100 along upper fusion line 104 and lower surface 106 of shroud head flange 54. Beam focal point 108 moves from outer surface 92 to at least 0.5 inch past a weld fillet 110 located at the interface of an inner surface 112 of upper shroud section 56 and lower surface 106 of shroud head flange 56. In one embodiment, beam focal point 108 moves in increments of about 0.01 inch to about 0.5 inch. In another embodiment, beam focal point 108 moves in increments of about 0.02 inch to about 0.2 inch. In still another embodiment, beam focal point 108 moves in increments of about 0.05 inch to about 0.1 inch. After ultrasonic probe 96 has scanned weld 70 at the initial position on shroud head flange 54, ultrasonic probe 96 is incrementally moved circumferentially along upper surface 102 of shroud head flange 54. At each predetermined incremental move of probe 96 the width of weld 70 is scanned by focusing beam 100 and moving focal point 108 incrementally along fusion line 104 as described above. Scans are performed at each incremental distance that probe 96 is moved until probe 96 has traversed the complete circumference of circumferential weld 70, or any desired portion of the circumference of weld 70. The above described method provides for reliable examination of greater than 80% of the circumference of H1 weld 70 because ultrasonic probe 96 placement and movement are not restricted by shroud head locking lugs 90 that are located on outer surface 92 of shroud head flange 54. The method provides an examination of the heat affected zone of weld 70 extending from upper fusion line 104 of weld 70 to about 0.5 inch above upper fusion line 104. Further, the method provides for detection, length and through-wall sizing of surface-connected planar flaws within the weld metal, heat affected zone, and adjacent base metal material. In addition, because ultrasonic beam 100 is electronically steered along the scan path, mechanical manipulation of probe 96 occurs in a single axis, which simplifies probe manipulator design and construction. While the invention has been described and illustrated in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. |
description | Referring now to FIG. 1, an electronic enclosure assembly 20 of a cellular phone is a typical clamshell enclosure design and is shown in the assembled configuration, as it would be used. FIG. 2 shows an exploded view of electronic enclosure assembly 20 including a bottom enclosure housing 10 and a top enclosure housing 12. Bottom enclosure housing 10 contains a network of ribs 11, and a plurality of screw bosses 14. Electronic enclosure assembly 20 is fastened together with a plurality of screws 18, and a plurality of screw bosses 14. This fastening method is well known in the art of electronic enclosure design and the details have been omitted so that the focus may be on the present invention. Electronic enclosure assembly 20 also includes an EMI/RFI containment form assembly 24, comprising an EMI/RFI containment form 21 coated with a conductive coating 22, preferably aluminum applied by vacuum metallization techniques, a printed circuit board 32, a plurality of electronic components 36, and a liquid crystal display 44. As shown in FIGS. 2 and 3, printed circuit board 32 is populated by a plurality of electronic components 36 electrically connected to it, and also has an internal ground plane 50 and an EMI/RFI ground trace 46 that is plated and exposed, on its surface facing the form 21. The shape of EMI/RFI ground trace 46 corresponds exactly to the shape of the top surface of EMI/RFI containment form 21, the shape of which in turn corresponds exactly to the shape of ribs 11. Other details of the design such as other active and passive circuit components, speakers, buttons, switches, antennae, wires, batteries, and corresponding holes and features in both bottom enclosure housing 10 and top enclosure housing 12, would be included in a functional design but have been omitted so as not to obscure the present invention. Referring now to FIGS. 2 and 3, EMI/RFI containment form assembly 24 comprises an EMI/RFI containment form 21, a conductive coating 22 on EM/RFI containment form 21, and a gap-filling gasket 25. EMI/RFI containment form 21 is constructed out of either polyester or impact modified syndiocratic polystyrene thin film sheet, with a thickness of 0.003 inches to 0.020 inches depending on application requirements. An example of such a material is VALOX(trademark), manufactured by General Electric Plastics of Pittsfield, Mass., or QUESTRA(trademark), manufactured by Dow Corporation of Midland, Mich. This sheet material is formed into the shape of EMI/RFI containment form 21 by a variety of forming processes that are well known in the industry, such as vacuum forming, pressure forming, vacuum pressure forming, embossing, and injection molding among others. The shape of the compartments 23 in EMI/RFI containment form 21 are dictated by the shape of the cavities 13 in bottom enclosure housing 10, that is, EMI/RFI containment form 21 closely fits into the cavities created by ribs 11 in bottom enclosure housing 10. Containment form 21 includes a peripheral lip 27 which surrounds compartment 23 and extends laterally from outer sidewalls 29 of containment form 21. Compartments 23 are separated by narrow hollow walls 31 which receive ribs 11 of lower housing 10. Ribs 11 and outer wall 33 of lower housing 10 define cavities 13. Lip 27 of containment form 21 overlies ribs 11 or outer wall 33 of lower housing when containment assembly 24 is assembled. Gasket 25 is interposed between ribs 11 and hollow walls 31 and between lip 27 and ribs 11 on outer sidewall 33. Conductive coating 22 is applied to EMI/RFI containment form 21 by either a vacuum deposition or conductive painting process that is well known in the art. Conductive coating is preferably applied to the containment form 21 by the vacuum metalization techniques described in U.S. Pat. No. 5,811,050 to Gabower. Referring now to FIGS. 5 and 6, gap-filling gasket 25 consists of NUVA SIL(trademark), a liquid elastomer material product manufactured by Loctite Corporation. Gap-filling gasket 25 material is applied as a liquid within the recesses of hollow walls 31 of EMI/RFI containment form 21, and cures to an elastomeric state. Referring now to FIGS. 2 and 4, when electronic enclosure assembly 20 is fastened together for use, EMI/RFI containment form assembly 24 is constrained by bottom enclosure housing 10 and top enclosure housing 12. EMI/RFI containment form 21 is compressed between printed circuit board and ribs 11. In an unassembled state, gap-filling gasket 25 is of a thickness that is larger than the actual distance between the top of ribs 11 and the corresponding bottom area of EMI/RFI containment form 21. Because gap-filling gasket 25 is a compliant elastomer, ribs 11 compresses gap-filling gasket 25 which in turn forces EMI/RFI containment form 21 firmly against EMI/RFI ground trace 46 on printed circuit board 32. This firm, conductive connection between EMI/RFI containment form 21 and EMI/RFI ground trace 46 on the printed circuit board 32 creates the necessary contact resistance for an effective EMI/RFI shielding seam within the given areas to be shielded in the electronic enclosure 20. The compliance of gap-filling gasket 25 also acts to fill tolerance gaps or slight misalignments between printed-circuit board 32 and EMI/RFI containment form 21. When electronic enclosure assembly 20 is powered and being used, the flow of electricity through the electronic circuit created by printed-circuit board 32 and electronic components 36 causes EMI or RFI to propagate away from the device. The electromagnetic energy is contained and prevented from propagating outside of electronic enclosure assembly 20 by the continuous conductive enclosure created by the combination of ground plane 50, EMI/RFI ground trace 46, and EMI/RFI containment form assembly 24, which effectively constitutes a sealed Faraday cage. The Faraday cage is a well-known concept in the field of electromagnetics. Referring now to FIG. 7, an alternative embodiment shows that a plurality of gap-filling punctures 28 may be used in place of gap-filling gasket 25. Gap-filling punctures 28 are created by a die-cutting process whereby a die with a plurality of discrete blades punctures through the top surface of lip 27 and hollow walls 31 of EMI/RFI containment form 21. The die is in the exact shape of the top-most surface of EMI/RFI containment form 21. When the blades puncture the polyester material, they deform the material around the puncture slightly up and away from the top surface. Gap-filling punctures 28 are formed into EMI/RFI containment form 21 before conductive coating 22 is applied. When assembled as described above, gap-filling punctures are forced compliantly against EMI/RFI ground trace 46 by ribs 11 and outer wall 33. Since gap-filling punctures 28 are covered with conductive coating 22, a continuous, conductive shield is maintained that prohibits the EMI/RFI that is radiated by electronic components 36 from propagating outside of electronic enclosure assembly 24. The spacing between punctures 28 is chosen to be less than one-half wavelength of the EMI radiation anticipated in order to prevent leaking of EMI. FIG. 8 discloses a close up view of a portion of lip 27 which has been modified with gap-filling bent tabs 52 creating upstanding flaps closely and evenly spaced apart on lip 27 with the spaces between neighboring gap-filling bent tabs 52 being less than one-half wavelength of the frequency to be contained. Such gap-filling bent tabs 52 may also be formed in hollow walls 31 of form 21. The gap-filling bent tabs 52 are forced against ground trace 46 by ribs 11 and outer wall 33 of housing 10 when form 21 and circuit board 32 are mounted in housing 10. Referring now to FIG. 9, another alternative embodiment shows that a plurality of gap-filling dimples 60 may be used in place of gap-filling gasket 25. Gap-filling dimples 60 are created by a forming process whereby small semi-circles are formed along the top surface of EMI/RFI containment form 21. Gap-filling dimples 60 protrude in the direction of printed circuit board 32. Gap-filling dimples 60 are formed into EMI/RFI containment form 21 before conductive coating 22 is applied. When assembled as described above, gap-filling dimples 60 are forced compliantly against EMI/RFI ground trace 46 by ribs 11. Since gap-filling dimples are covered with conductive coating 22, a continuous, conductive shield is maintained that prohibits the EMI/RFI that is radiated by electronic components 36 from propagating outside of electronic enclosure assembly 24. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention, but merely providing illustration of some of the presently preferred embodiments of this invention. EMI/RFI containment form 21 could be manufactured out of a variety of different plastics. Gap-filling gasket 25 could be constructed out of a variety of different compliant materials. For example, gap-filling gasket 25 could be die-cut out of elastomeric sheet material. Other molded-in gap-filling features could be included other than gap-filling dimples 60. For example, gap-filling bent tabs 52 could be molded and die-cut into EMI/RFI containment form 21, as shown in FIG. 8. Although the description of this invention shows a cellular phone, this invention could also be used for RFI shielding such as may be required in radios, portable computers, PDAs (Personal Digital Assistants), or other devices that must be prevented from emitting EMI. |
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053393392 | abstract | Process for carrying out an inspection or monitoring round of a nuclear site (5) consisting of recording in a central computer (22) connected to a radiofrequency transmitter/receiver or transceiver (24) a combination or sequence of different collection or reading points (12) grouping sensors (10) constituting the round to be performed. This sequence is copied again into a memory of a portable microcomputer (26) carried by the watchman during the round and connected to a radiofrequency transceiver (28). Each connection point (12) is validated and this validation is transmitted to the central computer (22). The sensors are checked and any abnormal condition is indicated to the central computer (22). All the checks carried out are recorded in the portable microcomputer (26) and copied again at the end of the round into a central computer (22) in such a way that they can be processed. |
description | The present invention relates to a water lubricated composite thrust bearing, and more particularly to a water lubricated composite thrust bearing of a nuclear main pump. This product is mainly applicable to a bearing of a nuclear island primary loop system of a nuclear power plant for a circulating pump (a nuclear main pump) for driving a coolant in a nuclear radiation condition environment, may also be used in a variety of fields of rotary mechanical support parts bearing a thrust, such as hydropower unit, water pump and deceleration machine, etc., and is also applicable to oil lubrication, especially to high temperature and high speed using conditions. At present, a nuclear island primary loop coolant circulating pump (nuclear main pump for short) is the key equipment of the nuclear power plant. The nuclear main pump plays a vital role on the operation and safety of the entire nuclear power plant, while a bearing of the nuclear main pump is a key component to ensure that the circulating pump operates safely and reliably. Bearings of nuclear main pumps configured for small-capacity generator units of nuclear power plants at home and abroad are water lubricated thrust bearings made of graphite materials. The structure of the water lubricated thrust bearing is that a graphite plate is placed in a clamping groove of a sector-shaped steel tile base and two sides of the graphite plate are fixed with baffle plates. As the graphite is a kind of brittle material which has poorer impact resistance, in the larger impact load and alternating load conditions, the tile is easy to break, poor in safety and reliability and not suitable for long-term safe operation of high-power nuclear main pumps. In addition, due to brittleness and poor adaptability, the graphite bearing material cannot adjust the uneven stress condition on the whole set of bearing and the single tile surface by itself and is prone to causing an unbalanced loading condition. Secondly, the water lubricated thrust bearing is made of a metal plate and an engineering plastic plate using a mechanical combination structure. This structure is mounted and located by a clamping groove on the plane of the steel tile and fastened with bolts. Because this structure is mounted by splicing multiple layers of structures, the fastening screws and the bearing in the long-time running process have defects of loosening, falling and connection instability to increase accident points, thereby bringing potential safety hazards for the running of the nuclear main pump. Nowadays, nuclear power gradually shifts to the development of large-capacity generator units. The prior art has not adapted to the use requirements of high-power nuclear main pumps, and nuclear main pump bearings have become the bottleneck in the development of large-capacity nuclear power equipment. Therefore, it is urgent to provide a thrust bearing for a high-power nuclear main pump, which is resistant to nuclear radiation and adapted to water lubrication, safe and reliable. With respect to the technical problems that graphite plate in the prior art proposed above has poor impact resistance and is not adapted to using requirements of high-power nuclear main pump, and the fastening screws required for splicing a metal plate and an engineering plastic plate are easy to falling off, there is provided a novel thrust bearing pad which engineering plastic with favorable toughness and a stainless steel base are completely formed into an integrated structure, and a water lubricated composite thrust bearing of a nuclear main pump is formed by a circular ring consisting of a plurality of sector-shaped or circular pads. The technical means of the present invention is as follows: A water lubricated composite thrust bearing of a nuclear main pump comprises a stainless steel base and an engineering plastic layer, wherein the stainless steel base is provided with concave-convex surfaces connected to the engineering plastic layer; the concave-convex surfaces and the engineering plastic layer are compositely formed by means of thermoplastic compound molding; a ratio of the area of the concave-convex surface to the area of an orthographic projection of the concave-convex surface on the stainless steel base ranges from 1.2 to 2. The surface area of the stainless steel base is increased by means of the above arrangements to increase a bonding strength between the stainless steel base and the engineering plastic layer, and the area of the concave-convex surface refers to a superficial area of the concave-convex surface. The concave-convex surfaces are positioned on the upper surface of the stainless steel base and the lower surface of the stainless steel base respectively, wherein the thickness of the engineering plastic layer on the concave-convex surface positioned on the upper surface of the stainless steel base is 2 to 15 mm, and the thickness of the engineering plastic layer on the concave-convex surface positioned on the lower surface of the stainless steel base is 0.5 to 5 mm. The concave-convex surface is positioned on the upper surface of the stainless steel base, and the thickness of the engineering plastic layer is 2 to 15 mm. The convex surface of the concave-convex surface is provided with rough face. The rough face is obtained by a treatment method which including the following three methods or a combination of the following three methods: (1) performing a knurling treatment with knurling wheel, a knurling pitch being about 0.3 to 1.5 mm; (2) forming criss-cross grooves which are 0.5 to 1.5 mm wide and 0.2 to 0.8 mm depth through mechanical machining, or machining grooves which are staggered longitudinally and transversely with an angle of 30° to 90° and a depth of 0.2 to 0.8 mm; and (3) performing a roughening treatment, such as surface sandblasting, etc. The stainless steel base is sector-shaped or circular; the concave surface of the concave-convex surface is composed of a plurality of annular grooves, the shape of the annular grooves being matched with the outer edge of the stainless steel base, the plurality of the annular grooves being arranged at equal intervals, the distance between the adjacent annular grooves being 6 to 10 mm, the width of a rabbet of the annular groove being 4 to 12 mm, the width of a bottom of the annular groove being 0.5 to 1 mm larger than the width of a rabbet of the annular groove, and the depth of the annular groove being 1 to 5 mm. The stainless steel base is sector-shaped or circular; the concave surface of the concave-convex surface is composed of a plurality of transverse grooves and a plurality of longitudinal grooves, the plurality of transverse grooves being arranged at equal intervals, the distance between the adjacent transverse grooves being 6 to 10 mm, the width of a rabbet of the transverse groove being 4 to 12 mm, the width of a bottom of the transverse groove being 0.5 to 1 mm larger than the width of a rabbet of the transverse groove, and the depth of the transverse groove being 1 to 5 mm; the plurality of longitudinal grooves being arranged at equal intervals, the distance between the adjacent longitudinal grooves being 6 to 10 mm, the width of a rabbet of the longitudinal groove being 4 to 12 mm, the width of a bottom of the longitudinal groove being 0.5 to 1 mm larger than the width of a rabbet of the longitudinal groove, and the depth of the longitudinal groove being 1 to 5 mm. The stainless steel base is sector-shaped; the concave surface of the concave-convex surface is composed of a plurality of arc-shaped grooves, the shape of the arc-shaped groove being matched with an arc of the sector, the plurality of the arc-shaped grooves being arranged at equal intervals along a radius direction of the sector, the distance between the adjacent arc-shaped grooves being 6 to 10 mm, the width of a rabbet of the arc-shaped groove being 4 to 12 mm, the width of a bottom of the arc-shaped groove being 0.5 to 1 mm larger than the width of a rabbet of the arc-shaped groove, and the depth of the arc-shaped groove being 1 to 5 mm. The stainless steel base is sector-shaped or circular, and the concave surface of the concave-convex surface is composed of a plurality of blind holes that are arranged in order, the distance between the adjacent blind holes being 6 to 10 mm, the diameter of an opening of the blind hole being 4 to 10 mm, the diameter of a bottom of the blind hole being 0.5 to 1 mm larger than the diameter of an opening of the blind hole, and the depth of the blind hole being 1 to 5 mm. The blind holes arranged in order means that the blind holes may be arranged in square, rectangle, rhombus, triangle or matrix form, etc. The engineering plastic layer is a single-layer engineering plastic layer or a composite engineering plastic layer, and the composite engineering plastic layer comprises a modified layer and a non-modified layer, the modified layer being connected to the concave-convex surface via the non-modified layer; the single-layer engineering plastic layer being made of modified polyether ether ketone powder or modified Polyphthalazinone ether sulfone ketone (PPESK) powder, the modified layer being made of modified polyether ether ketone powder or modified poly phthalazinone ether sulfone ketone powder, and the non-modified layer being made of pure resin powder. The pure resin powder refers to non-modified polyether ether ketone powder or non-modified poly phthalazinone ether sulfone ketone powder. If the modified layer is made of modified polyether ether ketone powder, the pure resin powder is pure polyether ether ketone powder; if the modified layer is made of modified poly ether sulfone powder, the pure resin powder is poly phthalazinone ether sulfone ketone powder. The thickness of the modified layer is ⅔-⅘ of the thickness of the composite engineering plastic layer. The non-modified layer is added between the stainless steel base and the modified layer to improve the adhesiveness therebetween due to the decrease in the bonding property after the modification. The concave-convex surface and the engineering plastic layer are combined through the concave surface and the convex surface of the concave-convex surface and the bonding property obtained after fusion of the rough face and the engineering plastic layer, thereby forming a reliable composite thrust bearing that is physically connected into a whole. The engineering plastic layer positioned on the upper surface of the stainless steel base is a working surface friction layer of the thrust bearing, and the engineering plastic layer on the lower surface of the stainless steel base is a heat resistant layer of the thrust bearing. The thermoplastic compound molding has the following steps: (1) the mould of the thermoplastic compound molding is made of heat-resistant stainless steel, the shape and size of a concave mold cavity of the mould are designed, processed and matched according to the geometrical shape and size of the outer edge of a workblank of the stainless steel base, and the mould is arranged exhaust channels; (2) drying the modified polyether ether ketone resin powder or the modified poly phthalazinone ether sulfone ketone resin powder at 120° C. for 8 hours or more before molding, and when the engineering plastic layer is a composite engineering plastic layer, drying a certain amount of non-modified pure resin powder according to the same drying condition; (3) putting the stainless steel base in the concave mold of the mould; (4) when the engineering plastic layer is a composite engineering plastic layer, wherein the thickness of the composite engineering plastic layer, ⅔ to ⅘ of which is the modified polyether ether ketone resin powder or the modified poly phthalazinone ether sulfone ketone resin powder, and ⅕ to ⅓ of which is pure resin powder. Calculating and weighing the amount of the used materials according to the different thicknesses, uniformly putting the pure resin powder onto the stainless steel base in a concave mold cavity and striking off first, and then uniformly putting the modified resin powder into the concave mold cavity of the mould, striking off and closing the mould; when the engineering plastic layer is a single-layer engineering plastic layer, weighing the mount of the material according to the thickness of the single-layer engineering plastic layer, uniformly putting the modified resin powder in a concave mold cavity of the mould, striking off and closing the mould; (5) applying a pressure of 30 to 80 MPa to the mould on a press; (6) putting the whole mould in an air circulating heating furnace, and heating to 350 to 410° C., such that the powder is molten completely, wherein the heating time depends on the specification of the workpiece and the size of the mould; (7) putting the mould on the press after heating, applying a pressure of 30 to 60 MPa while maintaining the pressure, and cooling at a cooling rate of 30 to 60° C./h, demoulding after the temperature of the mould drops to below 70° C., and taking the workpiece out; and (8) performing mechanical machining to form the water lubricated composite material thrust bearing. When the concave-convex surfaces are positioned on the upper surface of the stainless steel base and the lower surface of the stainless steel base respectively, in the above step (4), the amounts of powder required for the engineering plastic layers positioned on two parts, i.e., the upper and lower surfaces of the stainless steel base need to be calculated and weighed first respectively, and then, the powder required for the engineering plastic layer positioned on the lower surface of the stainless steel base is uniformly put in the mould, struck-off and then put in the stainless steel base. Compared with the prior art, the working surface friction layer of the present invention is the engineering plastic layer, which is a kind of elastic and plastic material, has favorable impact resistance and compliance, and effectively overcomes the defect that a graphite bearing is easy to break. The concave-convex surface and the engineering plastic layer are combined through the concave surface and the convex surface of the concave-convex face and the bonding property obtained after fusion of the rough face and the engineering plastic layer, thereby forming a reliable composite thrust bearing that is physically connected into a whole. Since the present invention is of a composite structure in which metal and nonmetal are combined into a whole firmly, respective advantages of metal and nonmetal can be brought into play. The thickness of the engineering plastic layer can be greatly reduced, not only improves the bearing capability, but also the size of the bearing still has good stability under the effect of pressure and temperature during operating, which is conductive to establishment of a stable safe lubrication water film; and the water lubricated composite thrust bearing of the present invention is a safe and reliable novel water lubricated composite thrust bearing with resistance to nuclear radiation. The water lubrication composite thrust bearing disclosed by the present invention has the characteristics of impact resistance, abrasion resistance, low friction, self-lubricating, compliance and self-adjusting in addition to good resistance to radiation and water lubrication. The present invention may be widely promoted in the fields of thrust bearings and the like for the above-mentioned reasons. As shown in FIGS. 1 to 10, a water lubricated composite thrust bearing of a nuclear main pump comprises a stainless steel base 1 and an engineering plastic layer 2, wherein the stainless steel base 1 is provided with concave-convex surfaces 3 connected to the engineering plastic layer 2; the concave-convex surfaces 3 and the engineering plastic layer 2 are compositely formed by means of thermoplastic compound molding; a ratio of the area of the concave-convex surface 3 to the area of an orthographic projection of the concave-convex surface 3 on the stainless steel base 1 ranges from 1.2 to 2. The concave-convex surface 3 is positioned on the upper surface of the stainless steel base 1, or the concave-convex surfaces 3 are positioned on the upper surface of the stainless steel base 1 and the lower surface of the stainless steel base 1 respectively, the thickness of the engineering plastic layer 2 on the concave-convex surface 3 positioned on the upper surface of the stainless steel base 1 is 2 to 15 mm, and the thickness of the engineering plastic layer 2 on the concave-convex surface 3 positioned on the lower surface of the stainless steel base 1 is 0.5 to 5 mm. The convex surface of the concave-convex surface 3 is provided with rough face 4. When the stainless steel base 1 is sector-shaped or circular, the concave surface of the concave-convex surface 3 is composed of a plurality of annular grooves 5, the shape of the annular grooves 5 are matched with the outer edge of the stainless steel base 1, the plurality of the annular grooves 5 are arranged at equal intervals, the distance between the adjacent annular grooves 5 is 6 to 10 mm, the width of a rabbet of the annular groove 5 is 4 to 12 mm, the width of a bottom of the annular groove 5 is 0.5 to 1 mm larger than the width of a rabbet of the annular groove 5, and the depth of the annular groove 5 is 1 to 5 mm. Alternatively, the concave surface of the concave-convex surface 3 is composed of a plurality of transverse grooves 6 and a plurality of longitudinal grooves 7, the plurality of transverse grooves 6 are arranged at equal intervals, the distance between the adjacent transverse grooves 6 is 6 to 10 mm, the width of a rabbet of the transverse groove 6 is 4 to 12 mm, the width of a bottom of the transverse groove 6 is 0.5 to 1 mm larger than the width of a rabbet of the transverse groove 6, and the depth of the transverse groove 6 is 1 to 5 mm; the plurality of longitudinal grooves 7 are arranged at equal intervals, the distance between the adjacent longitudinal grooves 7 is 6 to 10 mm, the width of a rabbet of the longitudinal groove 7 is 4 to 12 mm, the width of a bottom of the longitudinal groove 7 is 0.5 to 1 mm larger than the width of a rabbet of the longitudinal groove 7, and the depth of the longitudinal groove 7 is 1 to 5 mm. Alternatively, the concave surface of the concave-convex surface 3 is composed of a plurality of blind holes 9 that are arranged in order, the distance between the adjacent blind holes is 6 to 10 mm, the diameter of a hole opening of the blind hole 9 is 4 to 10 mm, the diameter of a hole bottom of the blind hole 9 is 0.5 to 1 mm larger than the diameter of a hole opening of the blind hole 9, and the depth of the blind hole 9 is 1 to 5 mm. When the stainless steel base 1 is sector-shaped, the concave surface of the concave-convex surface 3 is composed of a plurality of arc-shaped grooves 8, the shape of the arc-shaped groove 8 is matched with the arc of the sector, the plurality of the arc-shaped grooves 8 are arranged at equal intervals along a radius direction of the sector, the distance between the adjacent arc-shaped grooves 8 is 6 to 10 mm, the width of a rabbet of the arc-shaped groove 8 is 4 to 12 mm, the width of a bottom of the arc-shaped groove 8 is 0.5 to 1 mm larger than the width of a rabbet of the arc-shaped groove 8, and the depth of the arc-shaped groove 8 being 1 to 5 mm. The engineering plastic layer 2 is a single-layer engineering plastic layer or a composite engineering plastic layer, the composite engineering plastic layer comprises a modified layer and a non-modified layer, and the modified layer is connected to the concave-convex surface 3 via the non-modified layer. The single-layer engineering plastic layer is made of modified polyether ether ketone powder or modified Polyphthalazinone ether sulfone ketone powder, the modified layer is made of modified polyether ether ketone powder or modified poly phthalazinone ether sulfone ketone powder, and the non-modified layer is made of pure resin powder. The thickness of the modified layer is ⅔-⅘ of the thickness of the composite engineering plastic layer. The present invention will now be further described by way of embodiments. As shown in FIGS. 1, 2 and 4, a water lubricated composite thrust bearing of a nuclear main pump comprises a stainless steel base 1 and an engineering plastic layer 2, wherein the stainless steel base 1 is sector-shaped and has a concave-convex surface 3 connected to the engineering plastic layer 2, the concave-convex surface 3 is positioned on the upper surface of the stainless steel base 1, and the thickness of the engineering plastic layer 2 is 2 to 15 mm. The engineering plastic layer 2 is a composite engineering plastic layer. The composite engineering plastic layer comprises a modified layer and a non-modified layer, the modified layer is connected to the concave-convex surface 3 via the non-modified layer, the modified layer is made of modified polyether ether ketone powder or modified Polyphthalazinone ether sulfone ketone powder, and the non-modified layer is made of pure resin powder. The thickness of the modified layer is ⅔ of the thickness of the composite engineering plastic layer. The concave surface of the concave-convex surface 3 is composed of a plurality of annular grooves 5, the shape of the annular groove 5 is matched with the outer edge of the stainless steel base 1, the plurality of the annular grooves 5 are arranged at equal intervals, the distance between the adjacent annular grooves 5 is 10 mm, the width of a rabbet of the annular groove 5 is 5 mm, the width of a bottom of the annular groove 5 is 5.5 mm, the depth of the annular groove 5 is 1 mm, i.e. the cross section of the annular groove 5 is swallowtail shape. The annular groove 5 positioned near the outer edge of the stainless steel tile 1 is spaced 5 mm from the outer edge of the stainless steel base 1. A ratio of the area of the concave-convex surface 3 to the area of an orthographic projection of the concave-convex surface 3 on the stainless steel base 1 is 1.2. The convex surface of the concave-convex surface 3 is provided with rough face 4. The rough face 4 is obtained by a knurling treatment with a knurling wheel, and a knurling pitch is about 0.9 mm. The concave-convex surface 3 and the engineering plastic layer 2 are formed by thermoplastic compound molding. The thermoplastic compound molding compounding has the following steps: (1) a thermoplastic compound molding mould is made of heat-resistant stainless steel, the shape and size of a concave mold cavity of the mould are designed, processed and matched according to the geometrical shape and size of the outer edge of a workblank of the stainless steel base 1, and the mould is arranged exhaust channels; (2) drying the modified polyether ether ketone resin powder or the modified poly phthalazinone ether sulfone ketone resin powder at 120° C. for more than 8 hours before molding, and drying a certain amount of non-modified pure resin powder according to the same drying condition; (3) putting the stainless steel base 1 in the concave mold of the mould; (4) according to the thickness of the engineering plastic layer 2, ⅔ of which is the modified polyether ether ketone resin powder or the modified Polyphthalazinone ether sulfone ketone resin powder, and ⅓ of which is pure resin powder; calculating and weighing the amount of the used materials according to the different thicknesses, uniformly putting the pure resin powder onto the stainless steel base in a concave mold cavity and striking off first, and then uniformly putting the modified resin powder into the concave mold cavity of the mould, striking off and closing the mould; (5) applying a pressure of 30 to 80 MPa to the mould on a press; (6) putting the whole mould in an air circulating heating furnace, and heating to 385° C. to melt the powder completely, wherein the heating time depends on the specification of the workpiece and the size of the mould; (7) putting the mould on the press after heating, applying a pressure of 30 MPa while maintaining the pressure, and cooling at a cooling rate of 30 to 60° C./h, demoulding after the temperature of the mould drops to below 70° C., and taking the workpiece out; and (8) performing mechanical machining to form the water lubricated composite material thrust bearing. As shown in FIGS. 3 and 4, compared with the water lubricated composite thrust bearing of the nuclear main pump disclosed in embodiment 1, the present embodiment has the following distinguishing features: both the upper surface of the stainless steel base 1 and the lower surface of the stainless steel base 2 are provided with the concave-convex surface 3 disclosed in embodiment 1; in the step (4) disclosed in Embodiment 1, the amounts of the polyether ether ketone resin powder or the modified Polyphthalazinone ether sulfone ketone resin required for the engineering plastic layers 2 positioned on two parts, i.e., the upper and lower surfaces of the stainless steel base 1, as well as the amount of the pure resin powder need to be calculated and weighed first respectively; and then, the polyether ether ketone resin powder or the modified Polyphthalazinone ether sulfone ketone resin required for the engineering plastic layer positioned on the lower surface of the stainless steel base 1 and the pure resin powder are uniformly put in the mould, struck-off and then put in the stainless steel base 1. The contents described above are merely preferred detailed embodiments of the present invention without limiting the protection scope of the present invention in any way. That person skilled in the art can make equivalent replacements or changes to the present invention, which according to the technical solutions and inventive concepts within the disclosed technical scope of the present invention, shall fall into the protection scope of the present invention. |
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abstract | A control rod/fuel support grapple is provided which is capable of pulling up simultaneously a control rod and a fuel support from a reactor and also uncoupling the control rod and control rod drive mechanism. The control rod/fuel support grapple comprises a control rod holding unit for holding a control rod""s hoist handle, a fuel support holding unit for holding a fuel support, and a coupling releasing unit or uncoupling the control rod and the control rod drive mechanism, coupled by virtue of a spud coupling. These three units are attached to a main body frame which is lowered into a reactor pressure vessel. |
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048428108 | abstract | A nuclear power plant with a high temperature reactor located eccentrically in a prestressed concrete pressure vessel with spherical fuel elements for a capacity of 100-300 MWth intended primarily for power generation. The plant is inherently safe even in extreme accidents due to special devices for removal of decay heat. It is provided that upon a failure of the operational decay heat removal devices, decay heat is removed through a liner cooling system of the prestressed concrete pressure vessel. The liner cooling system is connected to a water-filled elevated reservoir by an external circulation loop. The elevated reservoir is connected to a further heat sink through a recooling circulation loop. It is possible to feed water into the elevated reservoir. |
abstract | The invention provides a magnetic lens for generating a magnetic imaging field to focus charged particles emitted from a sample, the lens comprising a central pole piece and an outer pole piece disposed about the central pole piece, wherein the lens comprises a magnetic moveable element for movement relative to at least one of the pole pieces, whereby a focal length of the lens is variable by said movement of the magnetic moveable element, thereby enabling a zoom facility for changing the magnification of an image. The movement of the moveable element preferably changes the magnetic circuit between the pole pieces. Also provided is a method of focusing charged particles emitted from a sample and a charged particle energy analyzer, such as an imaging photoelectron spectroscopy system. |
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053944488 | abstract | The activated elements (4) comprise two constituents having different magnetic characteristics. The first constituent has high activity and the second constituent substantially lower activity. The activated elements (4) are ground to obtain unit fragments, each consisting mainly of the first or of the second constituent. The fragments consisting of the first constituent are separated and sent towards a first discharge and storage station (18, 19, 20), and the fragments consisting mainly of the second constituent are separated and sent towards a conveyor (21). Detection of fragments of the first constituent is carried out on the conveyor, and the fragments deposited on the conveyor (21) are removed to the second discharge and packaging station (24, 25, 26) in the event that fragments of the first constituent are not detected on the conveyor (21). |
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description | This application claims the benefit of Chinese Patent Application No. 200910134856.7 filed Apr. 9, 2009, which is hereby incorporated by reference in its entirety. Embodiments of the present invention relates to a blade device and an X-ray imaging apparatus. Particularly, embodiments of the present invention are concerned with a blade device comprising four blade members to form a hollow cone having both open ends, as well as an X-ray imaging apparatus having the blade device. An X-ray imaging apparatus has a collimator for adjusting an irradiation field. On an inlet side of the collimator there is disposed a blade device for excluding an off-focal radiation, i.e., X-ray radiated from outside an X-ray focal point. In the blade device, a hollow cone having both open ends is formed using four X-ray impermeable blade members. The tip of the cone is directed to an X-ray focal point lest X-ray radiated from outside the X-ray focal point should get into the collimator. The blade device is constructed such that the shape of the cone is adjusted in interlock with the irradiation field adjustment performed by the collimator to always permit optimal exclusion of an off-focal radiation irrespective of whether the irradiation field is large or small (see, for example, column 7 line 66 to column 9 line 19, FIG. 6, FIG. 7, of U.S. Pat. No. 4,246,488). In the blade device which adjusts the shape of a cone in interlock with the irradiation field adjustment performed by the collimator, the number of parts increases due to a complicated construction of the device. Consequently, the blade device is difficult to be reduced in size and the cost thereof becomes high. Accordingly, embodiments of the present invention provide a blade device simple in construction and easy to be reduced in size, as well as an X-ray imaging apparatus having such a blade device. In a first aspect of the present invention as means for solving the problem there is provided a blade device for forming a hollow cone-like radiation, comprising: a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to the axis of the cone; a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone and also perpendicular to the first direction; a pair of lever members fixed respectively at one ends thereof to faces of the pair of second blade members on the side opposite to the mutually confronting side; and lever actuating unit for pivoting the pair of lever members about respective support shafts. In a second aspect of the present invention as means for solving the problem there is provided, in combination with the above first aspect, a blade device wherein the lever actuating unit includes: a pair of shaft members supported axially movably and unrotatably, and having outer peripheries formed with thread grooves respectively and being engaged at front end portions thereof with opposite end portions of the pair of lever members respectively; a pair of wheels supported axially unmovably and rotatably, having inner peripheries formed with thread grooves respectively and being threadedly engaged with the pair of shafts respectively; a common entraining member engaged with the pair of wheels; and a driving wheel for driving the entraining member. In a third aspect of the present invention as means for solving the problem there is provided, in combination with the above second aspect, a blade device wherein the lever actuating unit includes a pair of springs for urging the opposite end portions of the pair of lever members toward the pair of shaft members respectively. In a fourth aspect of the present invention as means for solving the problem there is provided, in combination with the above second aspect, a blade device wherein the lever actuating unit includes a tension imparting device for imparting tension to the entraining member. In a fifth aspect of the present invention as means for solving the problem there is provided, in combination with the above fourth aspect, a blade device wherein the tension imparting device includes an idler wheel engaged with the entraining member and a spring for urging the axis of the idler wheel in a direction to expand a loop of the entraining member. In a sixth aspect of the present invention as means for solving the problem there is provided, in combination with the above fifth aspect, a blade device wherein the wheels are toothed wheels and the entraining member is a toothed belt. In a seventh aspect of the present invention as means for solving the problem there is provided, in combination with the above first aspect, a blade device wherein the lever actuating unit includes a ring capable of rotating coaxially with the axis of the cone and a pair of cam members formed on an end face of the ring so as to engage opposite end portions of the pair of lever members. In an eighth aspect of the present invention as means for solving the problem there is provided, in combination with the above seventh aspect, a blade device wherein the lever actuating unit includes a pair of springs for urging the opposite end portions of the pair of lever members toward the cam members respectively. In a ninth aspect of the present invention as means for solving the problem there is provided, in combination with the above eighth aspect, a blade device wherein the springs are leaf springs. In a tenth aspect of the present invention as means for solving the problem there is provided an X-ray imaging apparatus having an X-ray tube, a blade device for excluding an off-focal radiation, a collimator for adjusting an irradiation field, and an X-ray receiver, the blade device being adapted to form a hollow cone-like radiation, comprising: a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to the axis of the cone; a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone and also perpendicular to the first direction; a pair of lever members fixed respectively at one ends thereof to faces of the pair of second blade members on the side opposite to the mutually confronting side; and lever actuating unit for pivoting the pair of lever members about respective support shafts. According to the first aspect of the present invention, since the blade device for forming a hollow cone-like radiation comprises a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to the axis of the cone, a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone and also perpendicular to the first direction, a pair of lever members fixed respectively at one ends thereof to faces of the pair of second blade members on the side opposite to the mutually confronting side, and lever actuating unit for pivoting the pair of lever members about respective support shafts, the blade device is simple in construction and easy to be reduced in size. According to the tenth aspect of the present invention, in the X-ray imaging apparatus having an X-ray tube, a blade device for excluding an off-focal radiation, a collimator for adjusting an irradiation field and an X-ray receiver, since the blade device is adapted to form a hollow cone-like radiation and comprises a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to the axis of the cone, a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone and also perpendicular to the first direction, a pair of lever members fixed at one ends thereof to faces of the pair of second blade members on the side opposite to the mutually confronting side, and lever actuating unit for pivoting the pair of lever members about respective support shafts, the X-ray imaging apparatus is simple in construction and easy to be reduced in size. According to the second aspect of the present invention, since the lever actuating unit includes: a pair of shaft members supported axially movably and unrotatably, the pair of shaft members having outer peripheries formed with thread grooves respectively and being engaged at front end portions thereof with opposite end portions of the pair of lever members respectively; a pair of wheels supported axially unmovably and rotatably, the pair of wheels having inner peripheries formed with thread grooves respectively and being threadedly engaged with the pair of shafts respectively; a common entraining member engaged with the pair of wheels; and a driving wheel for driving the entraining member, it is possible to simplify the construction of the lever actuating unit. According to the third aspect of the present invention, since the lever actuating unit includes a pair of springs for urging the pair of lever members toward the pair of shaft members respectively, it is possible to facilitate reciprocative pivoting motions of the pair of lever members with advance and retreat of the pair of shaft members. According to the fourth aspect of the present invention, since the lever actuating unit includes a tension imparting device for imparting tension to the entraining member, it is possible to ensure engagement between the entraining member and each wheel. According to the fifth aspect of the present invention, since the tension imparting unit includes an idler wheel engaged with the entraining member and a spring for urging the axis of the idler wheel in a direction to expand a loop of the entraining member, it is possible to impart tension appropriately to the entraining member. According to the sixth aspect of the present invention, since the wheels are toothed wheels and the entraining member is a toothed belt, it is possible to ensure engagement between each wheel and the entraining member. According to the seventh aspect of the present invention, since the lever actuating unit includes a ring capable of rotating coaxially with the axis of the cone and a pair of cam members formed on an end face of the ring so as to engage opposite end portions of the pair of lever members, it is possible to simplify the construction of the lever actuating unit. According to the eighth aspect of the present invention, since the lever actuating unit includes a pair of springs for urging the opposite end portions of the pair of lever members toward the cam members respectively, it is possible to facilitate reciprocative motions of the pair of lever members with rotation of the ring. According to the ninth aspect of the present invention, since the springs are leaf springs, it is possible to attain the simplification of construction. Embodiments of the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments described herein. FIG. 1 shows schematically the construction of an X-ray imaging apparatus. This apparatus is an example of the mode for carrying out the invention. With the construction of this apparatus, there is shown an example of the mode for carrying out the invention related to the X-ray imaging apparatus. As shown in FIG. 1, the X-ray imaging apparatus includes an X-ray tube 1, a blade device 3 for excluding an off-focal radiation, a collimator 5 for adjusting an irradiation field, and an X-ray receiver 9. The X-ray tube 1 is an example of the X-ray tube defined in the present invention. The blade device 3 is an example of the blade device defined in the present invention. The collimator 5 is an example of the collimator defined in the present invention. The X-ray receiver 9 is an example of the X-ray receiver defined in the present invention. The X-ray tube 1 includes an anode 101 and a cathode 103. X-ray is emitted from a collision point (focal point) of electrons which are released from the cathode 103 toward the anode 101. The X-ray emitted from the X-ray tube 1 is radiated to an object 7 to be radiographed through the blade device 3 and the collimator 5. The X-ray which has passed through the object 7 is received by the X-ray receiver 9. In the blade device, a hollow cone having both open ends is formed using four X-ray impermeable blade members. The blade device is disposed on an inlet side of the collimator 5 with the cone tip facing the X-ray focal point. The collimator 5 includes a blade 501 constructed of an X-ray impermeable material, e.g., lead. An X-ray irradiation field V depends on an aperture defined by the blade 501. The aperture of the blade 501 is variable, whereby the irradiation field V of X-ray can be adjusted. In interlock with adjustment of the irradiation field V, the blade device 3 adjusts the shape of the cone. In interlock with expansion of the irradiation field V, the blade device 3 expands the opening at the cone tip, while in interlock with contraction of the irradiation field V, the blade device 3 narrows the cone tip opening. FIGS. 2A-2C show an example of construction of the blade device 3. The blade device 3 is an example of the mode for carrying out the present invention. With the construction of the blade device 3, there is shown an example of the mode for carrying out the invention related to the blade device. FIG. 2A is a perspective view, FIG. 2B is an elevation, and FIG. 2C is an exploded diagram. FIG. 2C shows, in order from above, a top structure, a middle structure and a bottom structure, of the blade device 3. As shown in FIGS. 2A-2C, the blade device 3 includes four blade members 302, 304, 306 and 308. For example, the blade members 302, 304, 306 and 308 are trapezoidal plate members constructed of an X-ray impermeable material, e.g., lead. The blade members 302, 304, 306 and 308 form a hollow cone. The blade members 302 and 304 confront each other symmetrically with respect to the axis of the cone and at a fixed inclination angle. The blade members 302 and 304 are an example of the pair of blade members defined in the present invention. The blade members 306 and 308 confront each other symmetrically with respect to the axis of the cone and at a variable inclination angle in a direction orthogonal to the mutually confronting direction of the blade members 302 and 304. The blade members 306 and 308 are an example of the second pair of blade members. The blade device 3 includes a top base member 310a and a bottom base member 310b. For example, the top base member 310a and the bottom base member 310b are each a circular plate member constructed of an X-ray impermeable material, e.g., lead. The top base member 310a and the bottom base member 310b are connected in parallel with each other through four columnar spacers 312a, 312b, 312c and 312d. The top base member 310a is formed, at it's center, with a quadrangular aperture for X-ray passage, while the bottom base member 310b is formed, at it's center, with a circular aperture for X-ray passage. The top base member 310a supports the blade members 302, 304, 306 and 308. The blade members 302 and 304 are supported by a surface of the top base member 310a. The blade members 306 and 308 are supported by a back surface of the top base member 310a and project to the surface side through the aperture of the top base member 310a. Base portions of the blade members 302 and 304 are mounted to the surface of the top base member 310a along a pair of opposed sides of the quadrangular aperture. One longitudinal ends of lever members 316 and 318 formed by bars are fixed to back surfaces of the top base member 310a, namely, to the sides opposite to the confronting sides, of the blade members 306 and 308, and shafts 326 and 328 of the lever members 316 and 318 are supported by bearings 336 and 338 respectively which are disposed on the back surface of the top base member 310a. That is, the blade members 306 and 308 are supported on the back surface of the top base member 310a through the shafts 326 and 328 of the lever members 316 and 318 and also through the bearings 336 and 338. Therefore, the blade members 306 and 308 are made variable in inclination angle by pivoting about the shafts 326 and 328. The tip of a drive section 400 and one ends of leaf springs 416 and 418 come into abutment respectively from below and from above against end portions of the lever members 316 and 318 on the side opposite to the blade members 306 and 308 with respect to the shafts 326 and 328. The lever members 316 and 318 are an example of the pair of lever members defined in the present invention. The drive section 400 is an example of the lever actuating unit defined in the present invention. The leaf springs 416 and 418 are an example of the pair of springs defined in the present invention. The tip of the drive section 400 moves up and down, causing the blade members 306 and 308 to pivot about the shafts 326 and 328 respectively through the lever members 316 and 318 and thereby causing the inclination angle of the blade members to change. The leaf springs 416 and 418 push the lever members 316 and 318 against the tip of the drive section 400 to keep them in contact. FIGS. 3A-3D show a disassembled state of the blade device 3 is shown in terms of a perspective view. FIG. 3A is an exploded view of the whole of the blade device, FIG. 3B is an exploded view of a middle structure, FIG. 3C is an exploded view of a blade member, and FIG. 3D is an exploded view of the drive section. As shown in FIGS. 3A-3D, the drive section 400 includes a pair of shafts 606 and 608. Thread grooves are formed in outer peripheries respectively of the shafts 606 and 608. The shafts 606 and 608 are an example of the pair of shaft members defined in the present invention. The shafts 606 and 608 are supported axially movably and unrotatably by a pair of parallel guide shafts 616 and 618. Base portions of the guide shafts 616 and 618 are fixed to bottom base members 310b. A pair of wheels 626 and 628 having thread grooves formed in inner peripheries thereof are threadedly engaged with the shafts 606 and 608 respectively. The wheels 626 and 628 are toothed wheels having teeth formed on outer peripheries thereof The wheels 626 and 628 are supported axially unmovably and rotatably by the bottom base member 310b. The wheels 626 and 628 are an example of the pair of wheels defined in the present invention. Together with a driving wheel 622 and an idler wheel 624, the wheels 626 and 628 form a square which surrounds the aperture over the bottom base member 310b. The driving wheel 622 and the idler wheel 624 are also toothed wheels. The wheels 626 and 628, as well as the driving wheel 622 and the idler wheel 624, are each in a relation of a kinematic pair in the square. Rotary shafts of the four wheels are parallel to one another. An entraining member 630 is entrained on the four wheels 622, 624, 626 and 628 in an endless manner. Rotation of a motor 634 is transmitted to the driving wheel 622 through a reduction gear 632. A tensile force of a coil spring 640 is applied to the rotary shaft of the idler wheel 624 in a direction away from the driving wheel 622, with tension applied to the entraining member 630, whereby a belt drive device for the wheels 626 and 628 is constituted. The entraining member 630 is an example of the entraining member defined in the present invention. The driving wheel 622 is an example of the driving wheel defined in the present invention. The idler wheel 624 and the coil spring 640 are an example of the tension imparting device defined in the present invention. The idler wheel 624 is an example of the idler wheel defined in the present invention. The coil spring 640 is an example of the spring defined in the present invention. The entraining member 630 is not limited to the toothed belt. It may be any other suitable entraining member, e.g., chain, V belt, flat belt, or steel wire. The wheels 622, 624, 626 and 628 may also be wheels having an outer periphery structure matching the entraining member. FIGS. 4A-4E a relation among the shaft 606 (608), guide shaft 618 (618) and wheel 626 (628). FIG. 4A is a perspective view showing an assembled state, FIG. 4B is a perspective view showing a disassembled state, FIG. 4C is an elevation showing the disassembled state, FIG. 4D is a sectional view showing a state of operation, and FIG. 4E is an elevation showing the state of operation. As shown in FIGS. 4A-4E, the shaft 606 (608) is supported by the guide shaft 616 (618) which is an eccentric shaft, and the wheel 626 (628), which are axially unmovable and rotatable, is threadedly engaged with the shaft 606 (608). In such a construction, when the wheel 626 (628) rotates, the shaft 606 (608) moves linearly along the guide shaft without rotation. The moving direction of the shaft 606 (608) depends on the rotating direction of the wheel 626 (628). For example, the shaft 606 (608) advances with forward rotation of the wheel 626 (628) and retreats with reverse rotation of the wheel 626 (628). FIGS. 5A and 5B show in what manner the blade members 306 and 308 change in inclination angle with advance and retreat of the shafts 606 and 608. In FIG. 5A, the shafts 606 and 608 are in the most retreated state, in which the blade members 306 and 308 tilt so that the cone tip aperture becomes maximum. In FIG. 5B, the shafts 606 and 608 are in the most advanced state, in which the blades 306 and 308 tilt so that the cone tip aperture becomes minimum. In FIGS. 6A-6C there is shown another example of construction of a blade device 3. The blade device 3 is an example of the mode for carrying out the present invention. With the construction of the blade device 3, there is shown an example of the mode for carrying out the invention related to the blade device. FIG. 6A is an elevation, FIG. 6B is a sectional view, and FIG. 6C is an exploded view. FIG. 6C shows, in order from above, a top structure, a middle structure and a bottom structure, of the blade device 3. The exploded view of FIG. 6C is of the sectional view of FIG. 6B. As shown in FIGS. 6A-6C, the blade device 3 includes four blade members 702, 704, 706 and 708. For example, the blade members 702, 704, 706 and 708 are trapezoidal plate members constructed of an X-ray impermeable material, e.g., lead. The blade members 702, 704, 706 and 708 form a hollow cone. The blade members 702 and 704 confront each other symmetrically with respect to the axis of the cone and at a fixed inclination angle. The blade members 702 and 704 are an example of the first pair of blade members defined in the present invention. The blade members 706 and 708 confront each other symmetrically with respect to the axis of the cone and at a variable inclination angle in a direction orthogonal to the mutually confronting direction of the blade members 702 and 704. The blade members 706 and 708 are an example of the second pair of blade members defined in the present invention. The blade device 3 includes a base member 710a, a slide ring 710b and a base ring 710c. For example, the base member 710a is a stepped short cylinder constructed of an X-ray impermeable materials, e.g., lead. The base member 710a has a quadrangular aperture of X-ray passage formed at a center of an end face of an upper-step portion. Also, the base member 710a has a groove 712a formed throughout the whole circumference of a lower-step portion thereof The depth direction of the groove 712a corresponds to the radial direction of the base member 710a. The base member 710a supports the blade members 702, 704, 706 and 708. The blade members 702 and 704 are supported on a surface side of an end face of the base member 710a. The blade members 706 and 708 are supported on a back side of the end face of the base member 710a and project to the surface side through the aperture of base member 710a. Base portions of the blade members 702 and 704 are mounted to the surface of the base member 710a along a pair of opposed sides of the quadrangular aperture. On the back side of the base member 710a, one longitudinal ends of lever members 716 and 718 formed by bars are fixed to back surfaces, namely, to the sides opposite to the confronting sides, of the blade members 706 and 708, and shafts 726 and 728 of the lever members 716 and 718 are supported respectively by bearings 736 and 738 disposed on the back surface of the base member 710a. That is, the blade members 706 and 708 are supported on the back surface of the base member 710a through the shafts 726 and 728 of the lever members 716 and 718 and further through the bearings 736 and 738. Therefore, the blade members 706 and 708 are made variable in inclination angle by pivoting about the shafts 726 and 728. The slide ring 710b is a thin plate-like ring. An inside portion of the slide ring 710b is loosely fitted in the groove 712a, while an outside portion thereof protrudes from the groove 712a. The base ring 710c is a plate-like ring having a diameter larger than the outside diameter of the base member 710a. The aperture of the ring serves as an X-ray passing aperture. An upwardly raised, concentric rib 712c is formed on an end face of the base ring 710c, and the protruding portion of the ring 710b is connected to the rib 712c. As a result, the base ring 710c is rotatable coaxially with respect to the base member 710a. The base ring 710c is an example of the ring defined in the present invention. The base ring 710c includes a pair of cams 716c and 718c formed on the end face of the base ring at positions inside the rib 712c. However, the cam 718c is positioned on this side of the section and is therefore not shown. The cams 716c and 718c are inverted V-shaped projections projecting upward from the end face of the base ring 710c and inclined in the circumferential direction of the base ring 710c. The base ring 710c having the cams 716c and 718c constitutes a drive section 800. The drive section 800 is an example of the lever actuating unit defined in the present invention. The cams 716c and 718c are an example of the pair of cam members defined in the present invention. The base ring 710c is a gear having a toothed outer periphery and is driven by a motor 804 through a gear 802 meshing with the base ring gear. The operation of the base ring 710c by the motor 804 may be done by utilizing friction of a roller or a belt instead of the engagement between the gears. The cams 716c and 718c of the drive section 800 are abutted from below against end portions of the lever members 716 and 718 respectively on the side opposite to the blade members 706 and 708 with respect to the shafts 726 and 728, while one ends of leaf springs 816 and 818 are abutted from above against the end portions. The leaf springs 816 and 818 push the lever members 716 and 718 against the cams 716c and 718c respectively to keep both in contact with each other. The lever members 716 and 718 are an example of the pair of lever members defined in the present invention. The leaf springs 816 and 818 are an example of the pair of leaf springs defined in the present invention. FIGS. 7A and 7B show the disassembled state of the blade device 3 in terms of a perspective view. FIG. 7A is an exploded view of the whole of the blade device and FIG. 7B is an exploded view of a blade member. As shown in FIGS. 7A and 7B, the base ring 710c has a pair of cams 716c and 718c. The height of the cams 716c and 718c for lifting the opposite end sides of the lever members 716 and 718 changes with rotation of the base ring 710c. That is, the base ring 710c provided with the cams 716c and 718c constitute a so-called scroll cam device, and the amount of rotation of each of the lever members 716 and 718 is changed by the change in height of each of the cams 716c and 718c which results from rotation of the base ring 710c. FIGS. 8A and 8B show a change in inclination angle of the blade members 706 and 708 with rotation of the base ring 710c. FIG. 8A shows a state in which the base ring 510c has rotated so that the height of each of the cams 716c and 718c becomes the lowest. In this state, the blade members 706 and 708 tilt so that the cone tip aperture becomes maximum. FIG. 8B shows a state in which the base ring 710c has rotated so that the height of each of the cams 716c and 718c becomes the highest. In this state, the blade members 706 and 708 tilt so that the cone tip aperture becomes minimum. |
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045405123 | summary | BACKGROUND OF THE INVENTION Nuclear wastes containing large amounts of boric acid are generated during the operation of pressurized water reactor (PWR) electrical generating plants. Other sources of such wastes are low level burial sites which have either intercepted and stored run-off from the burial trenches or received unacceptable, unsolidified boric acid waste. The most popular method for solidifying low level waste in power plants is to concentrate the waste to 12% boric acid in waste evaporators, then mix the waste with concrete. Alternatively, a bitumen or a water expandable polymer may be mixed with the waste to produce a solid mass. While methods for reducing the volume of the waste have been devised, the volume of the waste is still large, and the high concentrations of boric acid in the waste may interfere with the setting of concrete. Also, boric acid is a very leachable substance in concrete and as it leaches out, it leaves pores through which the radionuclides can escape. SUMMARY OF THE INVENTION We have discovered a process for separating and recovering boric acid from water containing nuclear wastes and boric acid. The process of this invention lowers the volume and mass of nuclear waste that must be solidified up to about eight times less than it would be if the boric acid were present. The resulting cement containing the nuclear waste without boric acid present is stronger and less susceptible to leaching of the radionuclides. An added advantage of the process of this invention is that the boric acid is recovered and can be reused in the nuclear reactor. The process of this invention is relatively uncomplicated and inexpensive to implement. RELEVANT ART The 53rd Edition of the CRC Handbook of Chemistry and Physics, page D-29, shows that an azeotrope is formed of 27.0% methanol and 73.0% trimethylborate which boils at 54.0.degree. C. U.S. Pat. No. 4,086,325 discloses a process for drying solutions containing boric acid by the addition of an oxidizing agent, such as hydrogen peroxide. The boric acid solution is first neutralized with sodium hydroxide. The sodium borate is then oxidized to an insoluble perborate by the addition of hydrogen peroxide. U.S. Pat. Nos. 4,225,390 and 4,073,683 both disclose boron control systems for a nuclear power plant which include an evaporative boric acid recovery apparatus. U.S. Pat. No. 4,314,877 discloses a method and apparatus for drawing radioactive waste for the concentrates from evaporators in order to reduce the volume on the resultant waste. U.S. Pat. No. 4,257,912 discloses a process for encapsulating spent nuclear fuel into concrete. |
claims | 1. A material for the absorption and attenuation of neutrons, characterized by having the following volume composition: alumina cement between 4% and 5%, water between 17% and 18%, anhydrous calcium sulfate between 5% and 5.5%, colemanite between 72% and 73.5%, and approximately 0.02% of additives. |
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claims | 1. An irradiation target handling device having an isotope production cable assembly comprising:a drive cable configured for use with an existing nuclear reactor drive mechanism for cable drive systems configured to insert and withdraw sensors within nuclear reactor cores, wherein an interior of the drive cable comprises a signal lead; a self-powered radiation detector, wherein the self-powered radiation detector is spirally wound and wrapped around an axial length of the drive cable, wherein the self-powered radiation detector is located on the drive cable proximate one end of the drive cable that is designed to be inserted into a flux thimble in a core of a nuclear reactor, wherein the self-powered radiation detector comprises a length configured to provide a preselected signal output with a minimal axial length from end to end of the spiral such that the self-powered radiation detector provides an output indicative of reactor flux at a position of the self-powered radiation detector position in a reactor core to optimize an axial position of a target material supported by and proximate the one end of the drive cable;a one of a female end or male end of a quick disconnect coupling attached to the one end of the drive cable; anda target holder element cable assembly having another of the female end or male end of the quick disconnect coupling at one end of the target holder element cable assembly, configured to attach to and detach from the one of the female or male end attached to the one end of the drive cable, the target holder element cable assembly having a target material holder configured to hold the target material as the drive cable is inserted and withdrawn through the flux thimble. 2. The irradiation target handling device of claim 1 wherein the target holder element cable assembly comprises a hollow cylinder of metal mesh having a length configured to hold the target material within the confines of the flux thimble. 3. The irradiation target handling device of claim 2 wherein the target holder element assembly is constructed from a material having substantially no cobalt. 4. The irradiation target handling device of claim 2 wherein the metal mesh is configured to support the target material in traveling through the flux thimble. 5. The irradiation target handling device of claim 2 wherein the hollow cylinder comprises the quick disconnect coupling at one end and a cap at another end. 6. The irradiation target handling device of claim 5 wherein the cap is secured in place with a ring clamp. 7. The irradiation target handling device of claim 1 wherein the quick disconnect coupling is a ball clasp coupling. 8. The irradiation target handling device of claim 1 wherein the drive cable is constructed for use with a drive mechanism that is part of an existing in-core moveable detector system. 9. The irradiation target handling device of claim 1 wherein the self-powered radiation detector further comprises a signal output lead routed axially through an opening in the drive cable. |
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042657075 | description | DETAILED DESCRIPTION As shown in the drawings, the apparatus for carrying out the process of the invention comprises a dust container 1 of the hopper type, having its outlet 2 leading into a pneumatic feed line 3. One end of the feed line 3 is connected to equipment for supplying gas under pressure that includes a reducing valve 4 for setting the gas pressure in the feed line and, also, a compressed gas storage tank 5 which can be filled with compressed gas after opening of a gate cock 6 between the tank 5 and a compressor 7. In the illustrated example, air is used as the compressed gas. It is also possible, however, to connect gas storage tanks filled with inert gas, especially nitrogen tanks, to the suction pipe 8 of the compressor 7, for use in order to prevent dust explosions when combustible dusting powder is used. In the illustrated example, fire estinguishing powders are stored in the dust hopper 1, such materials having very little danger of explosion. The equipment for supplying compressed gas is installed outside the reactor building. In FIGS. 1 and 2, the illustration of the reactor building itself is limited merely to a portion of the outer pre-stressed concrete wall structure 9 having a liner 10 provided on its internal side. Within the reactor building, there is located a gas-cooled high-temperature nuclear reactor that is not shown in the drawing. The pneumatic feed line 3 leads through the pre-stressed concrete wall structure 9 and ends in the internal space 11 of the reactor building. At this end of the feed line 3, a dust dispersion nozzle 12 is provided through which the dusting material, carried through the feed line 3 by compressed gas, issues in fine dispersion into the internal space. The gas pressure in the feed line 3 is set at a value that depends on the pressure in the internal space 11. For this purpose, the pressure reduction valve 4 is in operative connection with a pressure-sensing box or enclosure 13 located in the internal space 11. In order to prevent or mitigate undersired effects of overpressure occurring in the internal space of the reactor building, particularly pressure shocks produced by the contingency in question, on the pneumatic feed line 3 and the dust hopper 1, a check valve 14 is inserted in the feed line downstream, in the direction of feed, of the outlet 2 of the dust hopper. The orifice of the outlet 2 of the dust hopper 1 in the feed line 3 is conventiently constituted as a tube opening out in the feed direction, so that the dusting powder stored in the hopper 1 can be drawn out by the gas flowing in the feed line 3, completely and without disturbance. In order to make it possible to introduce additional quantities of dusting powder, beyond the amount left over from the last charge, at any particular time, and to furnish the same to the space within the reactor building, an input device 15 is provided at the top of the dusting powder hopper container 1. In the illustrated example, the dusting powder hopper 1 is conveniently located outside of the reactor building. The dusting powder hopper can, however, also be provided inside the reactor building. FIG. 2, which is a bottom view of the equipment shown in FIG. 1, shows that the equipment 5,6,7,8 for supplying compressed gas feeds a number of feed pipes 3a, 3b, 3c connected in parallel. In the illustrated example, only three branches are shown but, of course, a branching manifold could be provided taking care of many more such parallel feed lines. Each of the feed lines 3a, 3b, 3c is connected with an individual dusting powder hopper 1a, 1b, 1c. Each feed pipe leads into the internal space 11 of the reactor building and there is at least one dust dispersion nozzle, and generally more than one. Thus, the powder hopper 1b feeds power into the line 3b which is sprayed out by the nozzles 12' and 12" shown in FIG. 2 and others not shown in the drawing. The provision of several independent systems, each with its own supply hopper for the dust or powder particles, for introducing the particles into the internal reactor space is, of course, an advantage from the point of view of security and reliability. The distribution of the dusting nozzles 12' 12" over the ceiling surface 16 in the internal space 11 of the reactor building is illustrated in FIG. 2. The spacing between the dusting nozzles 12' and 12" as well as between these and the adjacent dusting nozzles on the adjacent feed lines is determined with regard to magnitude of the dusting radius provided for the dusting powder particles, in such a way that a distribution of the dust particles that is to a great extent homogeneous is produced in the gas atmosphere in the internal space of the reactor building. The amount of dust or powder to be blown into that space is determined by the desired reaction of the content of fission and activation products after dusting of the gas atmosphere by blowing in the dust particles. FIG. 3 shows that at least 500 kg of dusting particles of an average grain size d'=0.5 .mu.m should be injected for 50.10.sup.3 m.sup.3 of volume of the enclosed gas atmosphere, in order to knock down the content of fission and activation products from 1% to 1.multidot.10.sup.-4 % within a period of 100 hours. Shorter periods for the reduction of the fission and activation products in the gas atmosphere can be obtained by dispensing larger quantities of dusting powder. If 40 tons of dusting particles of the same average grain size d'=0.5 .mu.m are introduced in a space having a volume of 50.multidot.10.sup.3 m.sup.3, the content of fission and activation products falls from 1% of to a value of 1.multidot.10.sup.-4 % after only approximately one hour. Although the invention has been described with reference to a particular illustrative example, it will be understood that modifications and variations are possible within the inventive concept. |
055966187 | abstract | An exposure apparatus includes a holder for holding a substrate to be exposed, and a movable shutter movable across a path of exposure light, having an intensity distribution in a predetermined direction, and in a direction intersecting the predetermined direction, wherein the movable shutter has an edge with a protruded portion being protruded in the movement direction and having a shape and size determined on the bases of the intensity distribution of the exposure light. |
description | The method of the present invention is a beam modulation-based technique for a SEM system that creates a charging map by selectively scanning a sample, discriminating between charging and non-charging areas in charging samples to reduce contrast artifacts and facilitate the restoration of dynamic range of the image so that sample features can be more easily interpreted. A charging map is defined herein as data in any form that indicates the charging and/or non-charging characteristic of areas on a sample. Areas that have insulative properties tend to accumulate charge, while areas that are conductive dissipate charge. It is generally known that conventional raster scanning of samples with insulative properties under certain conditions introduces charging artifacts due to the relatively high intensity of the electron dose. Simply raster scanning a sample does not provide any compensation for the charge state of points being irradiated. The present invention provides a method wherein a map of a sample is prepared, indicating areas having insulative properties, i.e. areas that will accumulate charge. This map is then used to selectively deposit electrons by modulating the intensity of the electron beam so as to compensate for insulative/charging areas of the sample for the purpose of allowing the SEM to more accurately display the topography of the sample. Although the preferred embodiment of the present invention is applied using a conventional scanning electron microscope with a PC connection, the method also applies to other particle beam imaging devices such as imaging devices using an ion beam. The method of creating a xe2x80x9ccharging mapxe2x80x9d according to the present invention will now be described. This method is able to generate charging maps indicating the areas of the sample that exhibit secondary electron contrast artifacts. As noted above, these areas are generally those having an electrically insulative property. Consider a SEM detector with pixel locations (x, y) representing corresponding locations on a sample. The signal level from the pixel at a time t can be expressed as F(x,y,t)=I(x,y,t)+C(x,y,t)xe2x80x83xe2x80x83(1) Where F(x, y, t)=final resultant signal at detector output I(x, y, t)=signal due to inherent contrast mechanism of the sample C(x, y, t)=signal due to local charging at the scan point of the sample For a constant operating condition, i.e. constant beam voltage, beam current and specimen geometry relative to the electron beam, I(x, y, t) does not change with time t. F(x,y,t)=I(x,y,0)+C(x,y,t)xe2x80x83xe2x80x83(2) where t=0 in I(x, y, t) denotes time-invariance. By recording the changes in F(x, y, t) as t changes, we can therefore isolate the charging component C(x, y, t). Isolating C(x, y, t) using image-based subtraction techniques requires at least two scans of a sample, yielding dissimilar images. The difference between the images is due to a longer scan time for one scan relative to the other, causing a difference in charge storage between the two scans. Another condition is that the differences between the images must be due to charging artifacts alone, i.e. only the C(x, y, t) component is changing. In practice, the change in C(x, y, t) can be obtained simply by subtracting consecutive frames/scans. However, the presence of noise in the images introduces noise in the resultant difference image. Hence, a lower bound on the magnitude of the pixel difference, i.e. a predetermined threshold, has to be included to minimize the effects of noise. In order to generate adequately different images, according to the preferred embodiment of the present invention the sample is scanned at a first rate to generate a first image, and then at a second rate to generate a second image. With a constant electron beam strength, the two images are significantly different if the first and second scan rates are adequately different. The slower scan rate delivers a higher electron dosage to the sample, causing larger collection of charge in the charging areas of the sample. Alternate embodiments of the invention include different electron beam strengths for the two scans, or a combination of different beam strengths and different scan rates. The steps for generating the charging map are shown in the block diagram of FIG. 1. In step 10, the image is checked for saturation. In step 12, a xe2x80x9cfast scanxe2x80x9d of the sample is performed where the first frame is taken at the maximum scan rate that the system is capable of, which is about 1.5 seconds per frame in the current implementation. In step 14, a xe2x80x9cslow scanxe2x80x9d is performed where the frame is acquired in about 23 seconds. Note that the absolute frame times are not important and will vary depending on the particular implementation of a system, but rather it is the relative frame time which is critical, i.e. one frame time being much longer than the other frame. The frames are acquired using digital technology to detect the secondary electron signals and display the result on a digital display. Having acquired and stored two significantly different images, the two frames are then subtracted pixel-by-pixel, providing data indicating the charging characteristic of the sample (step 16). A lower bound on the pixel intensity is used in the comparison to reduce noise effects. If the difference between the two scans exceeds the lower bound, determined using histogram analysis of the images, the data is accepted, i.e., pixel data is recorded/marked. After the pixel-by-pixel comparison, the resultant data is stored or displayed for use (step 18). In step 19, the charging regions are identified for use in the selective deposition. In the preferred embodiment, the comparison involves subtracting the values of corresponding pixel intensities of two scans, where the two scans are performed at different scan rates. The present invention also includes other comparisons than simple subtraction, and other ways of performing two different scans. For example, two scans can be distinguished by having different beam intensities as well as or rather than a different scan rate. The selective deposition process for charging reduction basically varies the dosage on a sample based on the charging map of the sample. For the non-charging areas, i.e. the dark areas on the charging map, irradiation by the electron beam occurs at every frame. Averaging is also performed at every frame to minimize the noise and maximize the S/N ratio for the non-charging areas. For the charging areas, i.e. the bright patches on the charging map, irradiation only occurs every selected number of frames. As this technique selectively scans the sample to reduce electron dose in charging areas, it is named the selective deposition charging-control technique. The flowchart of FIG. 2 shows the steps in the Selective Deposition process for charging reduction. In step 20, the charging map is generated, as described in reference to FIG. 1. According to the present invention, the areas indicated as xe2x80x9cchargingxe2x80x9d areas in the charging map are exposed to a reduced level of exposure to the electron beam during a series of scans, i.e. frames. The present invention includes various ways this can be done which will be apparent to those skilled in the art. Step 22 of FIG. 2 represents the operation of setting the degree of exposure. According to the preferred embodiment, the charging areas are exposed to the beam only during a selected percentage of the scans, i.e., a duty cycle is set for the charging areas. The duty cycle for a charging area is set by determining an interleave factor x. This factor x controls the number of frames that expose the charging areas to the particle beam. The factor x is determined by the charge decay time of the sample under a given scanning condition, i.e. the beam current, beam voltage, pixel dwell time and sample-election beam geometry. Because different areas may have different charging characteristics, a different factor x is maintained for the two regions to provide an optimum electron dose for each area. In step 24, a pass counter is incremented to keep track of the number of passes or frames. In step 26, it is determined whether a whole frame should be scanned, or only the non-charging areas. This is set by the interleave factor x. For example, a factor x of 10 could indicate that the entire frame is to be scanned (which includes both the charging and non-charging areas), step 28, in only one frame out of ten frames; for the other nine frames, only the non-charging areas are scanned, as indicated by step 30. Finally, the results of a number of adjoining pixels are averaged to maximize the S/N ratio according to step 32. The process is repeated, as indicated by line 33, until the selected number of frames have been exposed. The sequence is preferably controlled by software running on a PC coupled to the SEM. Also implemented is a frame by frame capture function to store the results. The frame capture and averaging are done using image buffers stored in the PC memory to eliminate the need for unnecessary scans of the sample. The above process is based on the following principle. The presence of charge-dissipation paths in a real and finitely-insulating sample allow the sample to return to the initial uncharged state after being given an electron dose. This is shown in samples that self-discharge after the primary electron beam is turned off. This means that a charge dissipation rate constant, fd, can be defined for any point irradiated by an electron beam. If the rate of charge injection finj at a particular pixel exceeds fd, then a net gain in charge occurs, and the pixel charges up negatively in the case of irradiation by an electron beam. Conversely, charging can be avoided if the time between successive doses is increased to allow for the excess charge to be dissipated, i.e. fd greater than finj. Note that fd is dependent on parameters such as beam energy, specimen geometry, sample composition and surface condition. Evaluation of the charge dissipation rate constant fd requires a charge monitor. Monitoring/determining fd can be done with the use of a histogram of the image. According to this method, successive frames are captured at the highest possible scan rate to minimize charging. A histogram of each frame is prepared, and the histograms of these frames are continuously compared. A waiting period, i.e. a time between scans when the sample is not being irradiated, termed an inter-frame delay time, is then gradually increased until the histograms obtained reach equilibrium. At this point, a steady-state scanning rate is achieved where the charge injection by the electron beam is fully compensated by adequate charge dissipation time, resulting in zero net charge build-up. This procedure is performed only on the charging portions of the sample selected from the charging map of the sample. The remaining non-charging portions are given maximum exposure to the electron beam to obtain the best S/N ratio for these areas. In summary, the charging maps of moderately charging insulators are prepared according to the method described in reference to FIG. 1 involving calculations based on measurements done on scans performed at different rates. A process of selective deposition is then used to reduce charging in the charging areas/insulating areas of a sample, these areas indicated by the charging map. The method of selective deposition uses the intrinsic decay mechanism present in moderate insulators. By varying the exposure of the charging areas to the electron beam, the charging effects can be reduced in the insulating areas without sacrificing resolution and S/N performance in the non-charging areas. This technique provides a more optimized imaging of partially-charging samples compared with conventional beam blanking techniques which do not differentiate between charging and non-charging areas. The method of the present invention involves generating a charging map for a sample, and then using this map to selectively irradiate the sample to compensate for the charging areas. The method described above for generating the charging map and for selective deposition is set forth as the preferred embodiment. Upon reading this disclosure, other methods of preparing a charging map and of selective deposition will be apparent to those skilled in the art, and these are to be included in the spirit of the present invention. An alternative method of preparing a charging map will now be described that uses a xe2x80x9ccharge balancexe2x80x9d concept and provides a more direct indicator of the charge condition on the sample. The charge balance in a specimen being scanned by an electron beam is derived from the principle of universal conservation of charge. It can be used to generate a 2-dimensional map of the sample showing sections where the charge balance condition is violated and hence charging could be present. This method utilizes the specimen current and the emission images which are obtained from the electrical current through the sample and the emitted charged particles from the sample respectively. After normalizing the dynamic range of the specimen current and the emission images, the next step in applying the Charge Balance condition is to add the specimen current image and the emission image together. If the Charge Balance condition holds, a perfect monotone image is obtained. A monotone image is one having only a single gray level, i.e. without any gray level variations. It can be evaluated using a histogram profile of the image, which would show only one gray level. Any deviation from the monotone indicates that charging is present. Darkened portions of the summed image indicate that the sample is charging negatively in the case of an electron beam system. Conversely, brighter spots indicate positive charging. The flow diagram in FIG. 3 illustrates the steps for generating a charging map based on the charge balance principle described above. Referring to FIG. 3, in step 34, the dynamic range of the specimen current image and the emission image is normalized. In step 36, the images corresponding to the emission and specimen current are prepared. The specimen current and the emission images are obtained from the electrical current through the sample and the emitted charged particles from the sample respectively. In step 38, the emission image and specimen current image are added together by doing a pixel-by-pixel addition of each pixel of the emission image with a corresponding pixel of the current image. In step 40 the areas of the summed image which are not monotone are marked or noted to indicate the charging areas. In step 42, the finished charging map is created submitting the data of block 38 to morphological enhancements such as those described for the preferred map generation method mentioned above. The term xe2x80x9cmorphological enhancementxe2x80x9d is a general term in image processing used to refer to the family of image-processing functions used to improve the continuity of image features. Although generally an SEM system can be used to generate the charge balance map described herein, a few components need to be added to detect the different currents, if the SEM system does not already come with these facilities. Mainly, the SEM system should have a detector for detecting and amplifying the secondary emission current, the backscattered emission current, and the specimen current which is connected to a common PC or some other computing apparatus. This technique has been shown to provide useful insights into the fundamental charge state of the sample. It is able to discriminate between real and false features. As it measures the rate of charge flow, it is particularly applicable in cases where the additional charging current is non-zero. Finally, it is also dependent on precise alignment between the emission and the specimen current image. This condition means that this method is best suited for samples with relatively large features and minimal edge features at the magnification of interest. The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein. |
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summary | ||
051715155 | abstract | A process for inhibiting corrosion caused by the presence of coolant water passing through a pressurized water nuclear reactor by the addition of an effective amount of an aqueous solution of zinc borate to the reactor coolant water. The transport of corrosion products and radioactive cobalt ions through the reactor primary circuit, as well as levels of radioactivity within the primary circuit, are reduced. |
040509842 | abstract | In a nuclear power plant, a gas cooled nuclear reactor is located within a prestressed concrete pressure tank which is enclosed within a safety tank. The main components of the plant are positioned within the pressure tank and include a gas turboset arranged in a horizontally extending tunnel spaced below the nuclear reactor. The main components of the plant include heat exchange equipment which is positioned in vertically extending shafts disposed in an annular arrangement within the pressure tank about the nuclear reactor. The gas coolant flows in a closed cycle through the plant from the nuclear reactor to the turbine in the turboset and then into the heat exchange equipment which includes recuperators, precoolers and intermediate coolers disposed in symmetrically arranged groups located in the vertically extending shafts. |
051986787 | summary | Cross-reference to related U.S. patents, the disclosures of which are incorporated by reference: U.S. Pat. No. 3,712,984, LEINHARD U.S. Pat. No. 4,127,898, FISCHER U.S. Pat. No. 4,839,521, OPPAWSKY FIELD OF THE INVENTION The present invention relates to a polymerization device for treating plastic dental parts, having an irradiation space in an irradiation chamber, the space being accessible via at least one pivotable or displaceable wall, and having a light conductor and a radiation source unit; the light conductor feeds the radiation from the radiation source into the irradiation space of the irradiation chamber and forms a releasable connection between the irradiation chamber and the radiation source unit. BACKGROUND A polymerization device of this type is known from the Kulzer brochure "Translux, Hochleistungshandlichtgerate fur Praxis und Labor" (German version No. 155188/D 185 sk; English version: "Translux EC: High efficiency hand-held light unit"). One of the radiation source units shown is a tabletop unit that has a connection for a light conductor. The light conductor that can be connected to it is long and flexible and has a grip element by which the light conductor is guided about the patient's mouth by the dentist. A curved light exit end is attached to the front end of the grip element. An irradiation chamber, of the kind known from German Patent 37 08 204, can also be attached to the connection for the light conductor. The irradiation chamber rests directly on the tabletop unit and is supported by the table. This polymerization device, comprising the tabletop unit and the irradiation chamber connected to it, is dependent on the availability of a tabletop unit as the radiation source unit. Besides these tabletop units, hand-held polymerization units, the housings of which contain not only the grip element but also operation and display elements, along with the light source and the fan, and stationary polymerization units, which contain an irradiation chamber and are used predominantly in dental laboratories, are also in use. Dentists' offices, however, often have only hand-held polymerization units on hand for treating plastic dental elements; such units are used exclusively inside the patient's mouth. THE INVENTION It is accordingly the object of the present invention to create a polymerization device that makes it possible to operate an irradiation chamber for curing plastic dental elements by using a hand-held polymerization unit, and to assure easy conversion of such a hand-held polymerization unit to a stationary one. Briefly, the radiation source unit is a hand-held polymerization unit, which is retained by its housing part on a first support, disposed on a support plate of a support frame; external sheathing of the light conductor is guided in a second support of the support plate; and the irradiation chamber is supported and optionally fixed on a part of the support frame. By combining an irradiation chamber and a hand-held polymerization unit, which is achieved by means of the support frame, it is possible to use a hand-held polymerization unit as a stationary one, in combination with an irradiation chamber. Hand-held polymerization units suitable for such use are known from German Patent Disclosure Documents DE-OS 26 27 249 and DE-OS 22 01 308, or from German Patent 34 11 996. The hand-held polymerization units include a radiation source, a fan, and operation and display elements. A socket by which various light conductors can be secured to the hand-held polymerization unit is mounted on the front of the hand-held polymerization unit. The housing part of this kind of hand-held polymerization unit is fixed in a recess in the first support. The external sheathing of the light conductor is guided through an opening in the second support, is held securely and firmly, for instance by form-fitting engagement with this opening, and is fastened in the irradiation chamber. The irradiation chamber is supported on the support frame. The polymerization device according to the invention enables fast, uncomplicated conversion and stable coupling of a hand-held polymerization unit to an irradiation chamber, so that even in dentists' offices in which only a hand-held polymerization unit is available, plastic dental elements can be irradiated, cured and tempered in stationary fashion. An especially practical embodiment of the support frame provides that the first support is a platform-like part that has an opening for receiving the hand-held polymerization unit. The housing part of the hand-held polymerization unit can be inserted into this opening and held securely and firmly by form-fitting engagement with it. In a simple embodiment of the support frame, the supports are fastened vertically to the support plate. The support frame may comprise plastic, such as acrylic glass, or sheet aluminum. To simplify converting a hand-held polymerization unit to a stationary unit, the first support is slit from the opening to the outside; this assures accurate adjustment when the hand-held polymerization unit is mounted on the light conductor of the irradiation chamber. This slit can also offer the advantage that the entire hand-held polymerization unit need not be removed through the opening; instead, it suffices to pull out the housing and to run the light conductor to the outside through the slit. This simplifies the assembly and disassembly of the hand-held polymerization unit and irradiation chamber. With a view to ease of connection or disconnection, the external sheathing of the light conductor can be connected interlockingly to the irradiation chamber and/or the hand-held polymerization unit. This assures fixation of the relative position of the hand-held polymerization unit and the irradiation chamber, and assures that constant radiation conditions prevail for the plastic dental element to be treated. Advantageously, the irradiation chamber rests on the side of the second support remote from the hand-held polymerization unit, and external sheathing of the light conductor, by its face end, firmly clamps the second support in place between it and the irradiation chamber, in the interlocked state of the light conductor. This assures a stable connection between the irradiation chamber, the support frame and the hand-held polymerization unit, so that the entire polymerization device is intrinsically stable. In another advantageous arrangement, the irradiation chamber along with the light conductor is fixed by resting on the second support from the side of this support remote from the hand-held polymerization unit. Additionally, the irradiation chamber along with the externally sheathed light conductor can be secured to the support plate of the support frame. In particular, this prevents torsion of the irradiation chamber relative to the optical axis of the beam of light. Simple clamping is effected by providing the base of the irradiation chamber with two lateral ribs that partly enclose the outer contour of the support plate. To increase the stability of the polymerization device still further, it is practical to retain the hand-held polymerization unit in the first support in a manner fixed against relative rotation. This prevents the components of the polymerization device from changing position on their own, and thereby altering irradiation conditions in the irradiation chamber or impairing the polymerization process as a result of jarring caused by twisting of the hand-held polymerization unit in the support frame. The use of the polymerization device is also simplified by the torsionally fixed arrangement, because the operating or display elements on the hand-held polymerization unit, for instance, are always located at the same place and do not have to be searched for first. In the event that the hand-held polymerization unit has a protrusion on its housing serving for instance to receive a display element or a cable lead, the torsionally fixed arrangement can be attained by engagement of this protrusion with an existing slit in the first support, without requiring any special components for the purpose. To make for the simplest possible use, it is practical to fix the hand-held polymerization unit in the support frame in such a way that an activation switch on the housing is located on a side remote from the support plate. This not only makes the switch easily accessible, but also assures that the switch is always located at the same place and thus is always easy for the dentist using the unit to find. To make the construction of the support plate as simple as possible, this component is at the same time embodied as the base plate of the support frame. To make the structural design simple, the polymerization device is embodied such that the axis of the light conductor extends approximately parallel to the support plate. The device can be secured to a wall, for instance with the aid of holes located in the support plate, or can be used as a stand-alone unit, in which case the light conductor is aligned with its axis extending horizontally. An exemplary embodiment of the invention will be described in detail below, in conjunction with the drawing. |
claims | 1. A shielding assembly for a system that generates and infuses radiopharmaceuticals, the shielding assembly comprising:a sidewall that defines a plurality of compartments and provides a radioactive radiation barrier for the compartments;a first compartment of the plurality of compartments, the first compartment being defined by a first portion of the sidewall that surrounds a first space configured to contain a radioisotope generator that generates radiopharmaceuticals via elution;a second compartment of the plurality of compartments, the second compartment being defined by a second portion of the sidewall that surrounds a second space configured to hold a portion of an infusion circuit of the system, the portion of the infusion circuit including an eluate line, a waste line, and a patient line;a third compartment of the plurality of compartments, the third compartment being defined by a third portion of the sidewall that surrounds a third space configured to accommodate a waste bottle of the infusion system, the third portion of the sidewall extending upward relative to the second portion of the sidewall;a first passageway formed in the sidewall and extending between the first compartment and the second compartment, the first passageway being configured to receive the eluate line so that, when the generator is contained within the first compartment and the eluate line is coupled to the generator, the eluate line extends through the sidewall via the first passageway; anda second passageway formed in the third portion of the sidewall, the second passageway being configured to receive at least one of the waste line and the patient line so that, when the portion of the infusion circuit that includes the waste line and the patient line is held in the second compartment, the at least one of the waste line and the patient line received in the second passageway extends upward with respect to ground on an opposite side of the third portion of the sidewall from a side facing the space configured to accommodate the waste bottle. 2. The shielding assembly of claim 1, wherein the first portion of the sidewall extends about a perimeter to define an opening into the first compartment. 3. The shielding assembly of claim 1, wherein the second passageway extends to an upper surface of the third portion of the sidewall, the upper surface of the third portion extending about a perimeter to define an opening into the third compartment. 4. The shielding assembly of claim 1, further comprising a retaining member mounted within the second passageway to hold the at least one of the waste line and the patient line in place within the second passageway. 5. The shielding assembly of claim 1, further comprising a third passageway formed in the second portion of the sidewall, the third passageway being configured to receive an eluant line from an eluant source positioned outside of the shielding assembly so that, when the portion of the infusion circuit is held within the second compartment, the eluant line extends from outside of the shielding assembly into the second compartment via the third passageway. 6. The shielding assembly of claim 5, further comprising a fourth passageway formed in the sidewall and extending between the first compartment and the second compartment, the fourth passageway being configured to receive another eluant line from the eluant source so that, when the generator is contained within the first compartment, the another eluant line extends through the sidewall via the fourth passageway. 7. The shielding assembly of claim 1, further comprising a third passageway formed in the sidewall and extending between the first compartment and the second compartment, the third passageway being configured to receive the eluant line so that, when the generator is contained within the first compartment and the eluant line is coupled to the generator, the eluant line extends through the sidewall via the third passageway. 8. The shielding assembly of claim 7, wherein the third passageway extends alongside the first passageway. 9. A shielding assembly for a system that generates and infuses radiopharmaceuticals, the shielding assembly comprising:a sidewall that defines a plurality of compartments and provides a radioactive radiation barrier for the compartments;a first compartment of the plurality of compartments, the first compartment being defined by a first portion of the sidewall that surrounds a first space configured contain a radioisotope generator that generates radiopharmaceuticals via elution;a second compartment of the plurality of compartments, the second compartment being defined by a second portion of the sidewall that surrounds a second space configured to hold a portion of an infusion circuit of the system, the second compartment being located extending immediately adjacent to the first compartment with the sidewall separating the first compartment from the second compartment, and the portion of the infusion circuit including an eluate line, a waste line, and a patient line, anda first passageway formed in the sidewall and extending between the first compartment and the second compartment, the first passageway being configured to receive the eluate line so that, when the generator is contained within the first compartment and the eluate line is coupled to the generator, the eluate line extends through the sidewall via the first passageway. 10. The shielding assembly of claim 9, further comprising a second passageway formed in the second portion of the sidewall, the second passageway being configured to receive an eluant line from an eluant source positioned outside of the shielding assembly so that, when the portion of the infusion circuit is held in the second compartment, the eluant line extends from outside of the shielding assembly into the second compartment via the second passageway. 11. The shielding assembly of claim 10, further comprising a third passageway formed in the sidewall and extending between the first compartment and the second compartment, the third passageway being configured to receive another eluant line from the eluant source so that, when the generator is contained within the first compartment, the another eluant line extends through the sidewall via third passageway. 12. The shielding assembly of claim 9, further comprising a second passageway formed in the sidewall and extending between the first compartment and the second compartment, the second passageway being configured to receive the eluant line so that, when the generator is contained within the first compartment and the eluant line is coupled to the generator, the eluant line extends through the sidewall via the second passageway. |
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