Patent Publication Number: US-2012025086-A1

Title: Radiation detection device

Description:
TECHNICAL FIELD 
     The present invention relates to a dual-energy type radiation detection device that detects radiation such as X-rays in two different energy ranges. 
     BACKGROUND ART 
     A dual-energy type radiation detection device (for example, X-ray detection device) is a device to be used for detecting radiation (for example, X-rays) in a low-energy range, and radiation in a high-energy range transmitted through an inspection object (refer to, for example, Patent Documents 1 and 2). With such a radiation detection device, a radiation image in a low-energy range and a radiation image in a high-energy range can be simultaneously obtained. 
     Based on these radiation images in different energy ranges, by preparing an image applied with a predetermined processing (for example, a weighted subtraction, superimposition, or the like), for example, in an in-line non-destructive inspection of an inspection object that is conveyed by a belt conveyor, various measurements such as measurement of distribution of a plurality of mixed components, detection of a foreign substance that is hardly provided with contrast, or measurement of a weight before cutting, can be realized with high accuracy. 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Patent Application Laid-Open No. 2000-298198 
     Patent Document 2: Japanese Patent Application Laid-Open No. H4-2907 
     SUMMARY OF INVENTION 
     Technical Problem 
     As a configuration of such a dual-energy type radiation detection device, for example, a two-stage configuration including a radiation detector that is positioned on the upstream side with respect to a radiation incident direction in which radiation from a radiation source is supplied and detects radiation in a low-energy range, and a radiation detector that is positioned on the downstream side and detects radiation in a high-energy range, can be considered. In such a configuration, there is a distance between an imaging element included in the detector on the upstream side and an imaging element included in the detector on the downstream side, so that images acquired with the respective imaging elements deviate from each other. Such deviations between the images cause deterioration in the accuracy of measurement in a non-destructive inspection, etc., of an inspection object to be conducted by using the radiation detection device. 
     The present invention has been made in order to solve the above-described problem, and an object thereof is to provide a dual-energy type radiation detection device capable of reducing deviations between images respectively acquired with two-stage radiation detectors. 
     Solution to Problem 
     In order to achieve such an object, a radiation detection device according to the present invention is a radiation detection device for detecting radiation in a first energy range and radiation in a second energy range higher than the first energy range, made incident in a radiation incident direction, including: (1) a first radiation detector positioned on the upstream side of the radiation incident direction and used for detecting radiation in the first energy range; and (2) a second radiation detector positioned on the downstream side of the radiation incident direction and used for detecting radiation in the second energy range, wherein (3) the first radiation detector includes a first scintillator layer that extends along an image detecting direction and converts an image of the radiation in the first energy range into an optical image, and a first imaging element that includes a plurality of pixels arrayed along the image detecting direction and acquires a first image by the optical image converted in the first scintillator layer, (4) the second radiation detector includes a second scintillator layer that extends along the image detecting direction and converts an image of the radiation in the second energy range into an optical image, and a second imaging element that includes a plurality of pixels arrayed along the image detecting direction and acquires a second image by the optical image converted in the second scintillator layer, (5) a first pixel width p 1  in the image detecting direction of each of the plurality of pixels in the first imaging element and a second pixel width p 2  in the image detecting direction of each of the plurality of pixels in the second imaging element are set to be different in width from each other, and (6) the plurality of pixels in the first imaging element are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, the plurality of pixels in the second imaging element are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, a second pixel unit width w 2  of each of the plurality of pixel units in the second imaging element is set to be larger than a first pixel unit width w 1  of each of the plurality of pixel units in the first imaging element. 
     In the above-described radiation detection device, the detection device includes the first radiation detector for radiation in a low-energy range, positioned on the upstream side with respect to the radiation incident direction, and the second radiation detector for radiation in a high-energy range, positioned on the downstream side. The pixel width p 1  of the imaging element in the first radiation detector and the pixel width p 2  of the imaging element in the second radiation detector are set to be different in width from each other (p 1 &lt;p 2  or p 1 &gt;p 2 ). With such a configuration, it becomes possible to perform high-accuracy measurement of a radiation image with the dual-energy detection device by reducing deviations between images respectively acquired with the imaging element of the first radiation detector and the imaging element of the second radiation detector. The pixel widths p 1  and p 2  of the above-described imaging elements are preferably set by considering the distance Δd between the first imaging element and the second imaging element. 
     Further, in the above-described radiation detection device, it is thus configured such that the pluralities of pixels in the first and second imaging elements are divided into pluralities of pixel units, respectively, and the second pixel unit width w 2  in the second imaging element is set to be larger than the first pixel unit width w 1  in the first imaging element. By setting the widths of pixel units that serve as substantial pixels in image acquisition with the imaging elements to satisfy w 1 &lt;w 2  as described above, it becomes possible to preferably reduce deviations between images respectively acquired with the first and second imaging elements. 
     Advantageous Effects of Invention 
     According to a radiation detection device of the present invention, the detection device includes a first radiation detector for a low-energy range, positioned on the upstream side of the radiation incident direction, and a second radiation detector for a high-energy range, positioned on the downstream side, the pixel width p 1  of the imaging element in the first radiation detector and the pixel width p 2  of the imaging element in the second radiation detector are set different in width from each other, the pluralities of pixels in the first and second imaging elements are respectively divided into pluralities of pixel units, and the pixel unit width w 2  in the second imaging element is set to be larger than the pixel unit width w 1  in the first imaging element, and accordingly, deviations between images acquired with the first and second imaging elements are reduced, and it becomes possible to perform high-accuracy measurement of a radiation image by a dual-energy type detection device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a figure including (a) a sectional side view and (b) a sectional front view, showing a configuration of an embodiment of an X-ray detection device. 
         FIG. 2  is a figure including (a) a side view and (b) a front view, showing an example of configurations of an X-ray detection device and an X-ray detection system. 
         FIG. 3  is a figure including (a) a sectional side view and (b) a sectional front view, showing a configuration of another embodiment of an X-ray detection device. 
         FIG. 4  is a figure including (a) a side view and (b) a front view, showing another example of configurations of an X-ray detection device and an X-ray detection system. 
         FIG. 5  includes views showing examples of pixel structures in a second imaging element. 
         FIG. 6  is a diagram showing a variation example of the X-ray detection device shown in  FIG. 4 . 
         FIG. 7  is a view showing an example of a specific configuration of imaging elements in the X-ray detection device. 
         FIG. 8  is a view showing a correspondence relationship between pixel units in the imaging elements shown in  FIG. 7 . 
         FIG. 9  is a view showing another example of a specific configuration of imaging elements in the X-ray detection device. 
         FIG. 10  is a view showing a correspondence relationship between pixel units in the imaging elements shown in  FIG. 9 . 
         FIG. 11  is a view showing a correspondence relationship between pixel units in the imaging elements shown in  FIG. 9 . 
         FIG. 12  includes views showing pixel structures in the imaging elements to be used in the X-ray detection device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of a radiation detection device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same components are denoted with the same reference symbols, and overlapping description will be omitted. The dimensional ratios in the drawings are not always equal to those in the description. 
       FIG. 1  is a figure including views showing a configuration of an embodiment of an X-ray detection device, which is a radiation detection device, and (a) in  FIG. 1  shows a sectional side view, and (b) in  FIG. 1  shows a sectional front view. Hereinafter, X-rays are assumed as radiation to be detected by the detection device, and a configuration of an X-ray detection device, which is a kind of radiation detection device, will be described. Such an X-ray detection device can be preferably applied to a non-destructive inspection or the like of an inspection object described above. 
     An X-ray detection device  1 A of the present embodiment is a dual-energy type detection device that detects X-rays in a first energy range (low-energy range) and X-rays in a second energy range (high-energy range) higher than the first energy range of X-rays made incident in a predetermined X-ray incident direction (radiation incident direction, the vertical direction in the drawing). This X-ray detection device  1 A has a two-stage configuration including a first X-ray detector (first radiation detector)  10  that is positioned on the upstream side of the X-ray incident direction and is used for detecting X-rays in the low-energy range, and a second X-ray detector (second radiation detector)  20  that is positioned on the downstream side and is used for detecting X-rays in the high-energy range. 
     The first X-ray detector  10  includes a first support substrate  15  and a first imaging element  12  and a first scintillator layer  11  placed on the support substrate  15 , and is disposed so that the first scintillator layer  11  is on the upstream side with respect to the X-ray incident direction. The first scintillator layer  11  is made of a predetermined scintillator material, extends along an X-ray image detecting direction (horizontal direction in (b) in  FIG. 1 ) perpendicular to the X-ray incident direction so that its longitudinal direction is along the image detecting direction, and converts an image of X-rays in the low-energy range out of X-rays made incident on the detection device  1 A into an optical image. 
     To the surface on the downstream side of the scintillator layer  11 , the first imaging element  12  is optically connected. The imaging element  12  includes a plurality of pixels  13  one-dimensionally arrayed along the image detecting direction, and by acquiring a first image caused by the optical image converted in the scintillator layer  11 , acquires a first X-ray image in the low-energy range. The image detecting direction in the first X-ray detector  10  matches the longitudinal direction of the pixel array of the first imaging element  12  in the present embodiment. 
     The second X-ray detector  20  includes a second support substrate  25  and a second imaging element  22  and a second scintillator layer  21  placed on the support substrate  25 , and is disposed so that the second scintillator layer  21  is on the upstream side with respect to the X-ray incident direction. The second scintillator layer  21  is made of a predetermined scintillator material, extends along the X-ray image detecting direction so that its longitudinal direction is along the image detecting direction, and converts an image of X-rays in the high-energy range out of the X-rays made incident on the detection device  1 A into an optical image. 
     To the surface on the downstream side of the scintillator layer  21 , the second imaging element  22  is optically connected. The imaging element  22  includes a plurality of pixels  23  one-dimensionally arrayed along the image detecting direction, and by acquiring a second image caused by the optical image converted in the scintillator layer  21 , acquires a second X-ray image in the high-energy range. The image detecting direction in the second X-ray detector  20  matches the longitudinal direction of the pixel array of the second imaging element  22  in the present embodiment. 
     Between the first support substrate  15  of the first X-ray detector  10  and the second scintillator layer  21  of the second X-ray detector  20 , a filter  18  is installed. The filter  18  is a filter for selecting energy components of X-rays that pass through from the first X-ray detector  10  to the second X-ray detector  20 , and is disposed or changed as appropriate when selecting or changing an energy range of X-rays desired to be detected by the second X-ray detector  20 . 
     Further, in the X-ray detection device  1 A of the present embodiment, a first pixel width p 1  in the image detecting direction of each of the plurality of pixels  13  in the first imaging element  12  positioned on the upstream side and a second pixel width p 2  of each of the plurality of pixels  23  in the second imaging element  22  positioned on the downstream side are set to be different in width from each other (p 1 &lt;p 2  or p 1 &gt;p 2 ) by considering the distance Ad between the first and second imaging elements  12  and  22  (refer to (b) in  FIG. 1 ). 
     A specific configuration of the X-ray detection device  1 A shown in  FIG. 1  will be further described with reference to  FIG. 2 .  FIG. 2  is a figure including schematic views showing an example of configurations of an X-ray detection device and an X-ray detection system including the detection device, and (a) in  FIG. 2  shows a side view, and (b) in  FIG. 2  shows a front view. Here, in  FIG. 2 , concerning the configuration of the X-ray detection device  50 , only the structures of the pixels  13  and  23  in the imaging elements  12  and  22  in each of the first and second X-ray detectors are shown. Configurations of other parts of the X-ray detection device  50  are the same as, for example, those in the X-ray detection device  1 A shown in  FIG. 1 . 
     The X-ray detection system of this configuration example is configured as an inspection system for performing a non-destructive inspection of an inspection object  56  that is conveyed by a belt conveyor  55 . Above the belt conveyor  55 , an X-ray source  52  as a radiation source that supplies X-rays (radiation) for inspection to the inspection object  56  is disposed. Below the belt conveyor  55 , a dual-energy X-ray detection device  50  that detects an X-ray image in a low-energy range and an X-ray image in a high-energy range of X-rays that passed through the inspection object  56  is disposed. 
     Hereinafter, for convenience of description, as shown in  FIG. 2 , a conveying direction of the inspection object  56  by the belt conveyor  55  is defined as a y-axis direction (horizontal direction in (a) in  FIG. 2 ), an X-ray incident direction from the X-ray source  52  to the detection device  50 , perpendicular to the y-axis direction, is defined as a z-axis direction (vertical direction in (a) and (b) in  FIG. 2 ), and an image detecting direction (array direction of the pixels  13 ,  23 ) in the imaging elements  12  and  22  of the detection device  50 , perpendicular to the y-axis direction and the z-axis direction, is defined as an x-axis direction (horizontal direction in (b) in  FIG. 2 ). Thus, when the X-ray detection device  50  is applied to an inspection object conveyed in a predetermined conveying direction, it is preferable that the image detecting direction in the X-ray detector is a direction perpendicular to the conveying direction of the inspection object. 
     In this configuration example, as pixel units that serve as substantive pixels for acquiring first and second images by the imaging elements  12  and  22  in the X-ray detection device  50 , the plurality of pixels  13  in the first imaging element  12  are divided into a plurality of pixel units each consisting of one pixel as a unit, and one pixel simply corresponds to one pixel unit. On the other hand, the plurality of pixels  23  in the second imaging element  22  are divided into a plurality of pixel units each consisting of one pixel as a unit, and similar to the first imaging element  12 , one pixel simply corresponds to one pixel unit. 
     In such a configuration, a second pixel unit width w 2  (=p 2 ) of the pixel unit in the imaging element  22  on the downstream side is set to be larger than a first pixel unit width w 1  (=p 1 ) of the pixel unit in the imaging element  12  on the upstream side (w 1 &lt;w 2 ). Preferably, when the distance from the X-ray source  52  that supplies X-rays to the detection device  50  to the imaging element  12  is defined as d 1 , and the distance to the imaging element  22  is defined as d 2 =d 1 +Δd, the second pixel unit width w 2  is set to become substantially equal to w 2 =w 1 ×d 2 /d 1  with respect to the first pixel unit width w 1 . Accordingly, as viewed from the X-ray source  52 , each pixel unit (one pixel  13 ) in the imaging element  12  corresponds to each pixel unit (one pixel  23 ) in the imaging element  22 : 
     Effects of the X-ray detection device and the X-ray detection system according to the above-described embodiment will be described. 
     In the X-ray detection devices  1 A and  50  shown in  FIG. 1  and  FIG. 2 , the detection device includes the first X-ray detector  10  for X-rays in the low-energy range, positioned on the upstream side with respect to the X-ray incident direction, and the second X-ray detector  20  for X-rays in the high-energy range, positioned on the downstream side. The pixel width p 1  of the pixel  13  of the imaging element  12  in the first X-ray detector  10  and the pixel width p 2  of the pixel  23  of the imaging element  22  in the second X-ray detector  20  are set to be different in width from each other. 
     With such a configuration, by preferably setting the pixel widths p 1  and p 2  in the imaging elements  12  and  22 , deviations between first and second images respectively acquired by the imaging element  12  of the first X-ray detector  10  and the imaging element  22  of the second X-ray detector  20  are reduced, and it becomes possible to perform high-accuracy measurement of an X-ray image with the dual-energy type detection device. It is preferable that the pixel widths p 1  and p 2  of the imaging elements are set by considering the distance Δd between the first imaging element  12  and the second imaging element  22 . 
     Here, in Patent Document 1, it is described that correction is applied so that sizes of a plurality of radiation image data become equal to each other. However, in such a configuration, image processing takes time because image data correction is performed by software, and it is difficult to apply this to the field in which high-speed image processing is required as in the case of, for example, a non-destructive inspection of an inspection object. On the other hand, the X-ray detection device according to the above-described embodiment reduces deviations between images by hardware by means of the pixel structures of the imaging elements, and accordingly realizes high-speed measurement of X-ray images. 
     As specific pixel structures in the imaging elements  12  and  22 , according to the above-described embodiment, the plurality of pixels  13  in the first imaging element  12  are divided into a plurality of pixel units each consisting of one pixel as a unit, and the plurality of pixels  23  in the second imaging element  22  are also divided into a plurality of pixel units each consisting of one pixel as a unit. The second pixel unit width w 2  (=pixel width p 2 ) in the second imaging element  22  is set to be larger than the first pixel unit width w 1  (=pixel width p 1 ) in the first imaging element  12 . By thus setting the widths of pixel units which serve as substantive pixels in image acquisition by the imaging elements to satisfy w 1 &lt;w 2  (p 1 &lt;p 2 ), it becomes possible to preferably reduce the deviations between images respectively acquired with the first and second imaging elements  12  and  22 . 
     As specified settings of the pixel unit widths, when the position of the radiation source with respect to the detection device is assumed or set, as described above with reference to  FIG. 2 , when the distance from the assumed position of the X-ray source  52  to the imaging element  12  is defined as d 1  and the distance to the imaging element  22  is defined as d 2  (=d 1 +Δd), the second pixel unit width w 2  is preferably set to be substantially equal to w 2 =w 1 ×d 2 /d 1  with respect to the first pixel unit width w 1 . Accordingly, according to the position of the X-ray source, deviations between images respectively acquired by the first and second imaging elements can be reliably reduced and the accuracy of measurement can be improved. Even when the second pixel unit width w 2  does not completely satisfy the above-described relation equation, it is possible to reduce the deviations between the images. 
     Pixel widths and pixel unit widths in the first and second imaging elements  12  and  22  are set to be constant entirely in the image detecting direction in the configurations of  FIG. 1  and  FIG. 2 . These pixel widths may be set so that the pixel unit width w 2  (pixel width p 2 ) in the second imaging element  22  increases (the pixel width increases) from the central portion toward the peripheral portion in the image detecting direction in which the plurality of pixel units are arrayed. With such a configuration, influences, etc., of the X-ray incident angle that increases from the central portion toward the peripheral portion can be reduced. 
     The pixel widths in the direction (y-axis direction) perpendicular to the image detecting direction in the first and second imaging elements  12  and  22  may be set to be equal to both of the imaging elements  12  and  22  as shown in (a) in  FIG. 2 . Alternatively, it may also be configured such that the pixel width in the y-axis direction in the second imaging element  22  is set to be larger than the pixel width in the first imaging element  12 . 
     The entire configuration of the X-ray detection device is not limited to the configuration shown in  FIG. 1 , and specifically, various configurations can be used. An example of such configurations of the X-ray detection device is shown in  FIG. 3 . 
       FIG. 3  is a figure including views showing a configuration of another embodiment of an X-ray detection device, which is a radiation detection device, and (a) in  FIG. 3  shows a sectional side view, and (b) in  FIG. 3  shows a sectional front view. The X-ray detection device  1 B according to the present embodiment includes a first X-ray detector  10  that is positioned on the upstream side of the X-ray incident direction and is used for detecting X-rays in the low-energy range, and a second X-ray detector  20  that is positioned on the downstream side and is used for detecting X-rays in the high-energy range. The configuration of the second X-ray detector  20  out of these detectors is the same as the configuration shown in  FIG. 1 . 
     The first X-ray detector  10  includes a first support substrate  15  and a first imaging element  12  and a first scintillator layer  11  placed on the support substrate  15 , and opposite to the configuration shown in  FIG. 1 , the first support substrate  15  is on the upstream side with respect to the X-ray incident direction. Further, in the present embodiment, between the first scintillator layer  11  of the first X-ray detector  10  and the second scintillator layer  21  of the second X-ray detector  20 , a filter or the like is not installed. 
     In the X-ray detection device  1 B of the present embodiment, similar to the X-ray detection device  1 A shown in  FIG. 1 , the first pixel width p 1  in the image detecting direction of the pixels  13  in the first imaging element  12  and the second pixel width p 2  of the pixels  23  in the second imaging element  22  are set to be different in width from each other by considering the distance Δd between the first and second imaging elements  12  and  22 . Thus, specifically, as the entire configuration of the X-ray detection device, various configurations can be used. 
     A specific configuration of the X-ray detection device will be further described.  FIG. 4  is a figure including schematic views showing another example of configurations of an X-ray detection device and an X-ray detection system including the detection device, and (a) in  FIG. 4  shows a side view, and (b) in  FIG. 4  shows a front view. In this configuration example, the configuration except for the structure of the pixels  23  in the imaging element  22  in the second X-ray detector is the same as the configuration shown in  FIG. 2 . 
     In this configuration example, the plurality of pixels  13  in the first imaging element  12  are divided into a plurality of pixel units each consisting of one pixel as a unit, and one pixel simply corresponds to one pixel unit. On the other hand, the plurality of pixels  23  in the second imaging element  22  are divided into a plurality of pixel units each consisting of a plurality (specifically, two in  FIG. 4 ) of pixels as a unit, and two pixels correspond to one pixel unit. 
     In such a configuration, the second pixel unit width w 2  (= 2 ×p 2 ) of the pixel unit in the imaging element  22  on the downstream side is set to be larger than the first pixel unit width w 1  (=p 1 ) of the pixel unit in the imaging element  12  on the upstream side (w 1 &lt;w 2 ). Preferably, as in the same case with  FIG. 2 , when the distance from the X-ray source  52  to the imaging element  12  is defined as d 1 , and the distance to the imaging element  22  is defined as d 2 =d 1 +Δd, the second pixel unit width w 2  is set to be substantially equal to w 2 =w 1 ×d 2 /d 1  with respect to the first pixel unit width w 1 . Further, the respective pixels  13  and  23  of the imaging elements  12  and  22  are set so that the second pixel width p 2  of the pixel  23  in the imaging element  22  is smaller than the first pixel width p 1  (p 1 &gt;p 2 ). Accordingly, as viewed from the X-ray source  52 , each pixel unit (one pixel  13 ) in the imaging element  12  and each pixel unit (two pixels  23 ) in the imaging element  22  correspond to each other. 
     Thus, as the pixel structure of the second imaging element  22  in the X-ray detector on the downstream side, it may also be configured such that the plurality of pixels  23  are divided into a plurality of pixel units each consisting of a plurality of pixels as a unit, and each pixel unit corresponds to the pixel of the first imaging element  12 , and the second pixel width p 2  is set to be smaller than the first pixel width p 1 . If necessary, the pixel structure of the first imaging element  12  on the upstream side may also be similarly configured so that the plurality of pixels  13  are divided into a plurality of pixel units each consisting of a plurality of pixels as a unit. 
     As the configurations of the first and second imaging elements  12  and  22 , preferably, generally, the plurality of pixels  13  in the first imaging element  12  are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, and the plurality of pixels  23  in the second imaging element  22  are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, the second pixel unit width w 2  of each of the plurality of pixel units in the second imaging element  22  is set to be larger than the first pixel unit width w 1  of each of the plurality of pixel units in the first imaging element  12 . Thus, by setting the widths of the pixel units so as to satisfy w 1 &lt;w 2 , it becomes possible to preferably reduce deviations between images respectively acquired with the first and second imaging elements  12  and  22 . 
     As the pixel structures in the imaging elements  12  and  22 , in the above-described configuration example, in the image detecting direction (x-axis direction), the pixel structure is segmented into a plurality of pixels  13 ,  23  arrayed one-dimensionally. On the other hand, in the direction (y-axis direction) perpendicular to the image detecting direction, the pixel structure consists of a single pixel. 
     In such a pixel structure, it is also possible that pixels are segmented into two or more pixels in the y-axis direction as appropriate.  FIG. 5  includes views showing examples of pixel structures in the second imaging element, and (a) in  FIG. 5  is a front view showing a pixel structure in the second imaging element  22 , (b) in  FIG. 5  is a top view (viewed from the X-ray source side) showing a first example of the pixel structure in the second imaging element, and (c) in  FIG. 5  is a top view showing a second example of the pixel structure. In each of the first and second examples, the pixel structure viewed from the front is the same as shown in (a) in  FIG. 5 . 
     In the first example shown in (b) in  FIG. 5 , pixels are not segmented in the y-axis direction perpendicular to the image detecting direction, and the plurality of pixels  23  are one-dimensionally arrayed in one row in the pixel structure (strip type). On the other hand, in the second example shown in (c) in  FIG. 5 , pixels are segmented into two in the y-axis direction, and the plurality of pixels  23  are one-dimensionally arrayed in two rows in the pixel structure (lattice type). 
     Thus, as pixel structures of the first and second imaging elements  12  and  22  to be used in X-ray detectors, generally, a configuration of a one-dimensional imaging element including a plurality of pixels one-dimensionally arrayed in one row along the image detecting direction, or a configuration of a two-dimensional imaging element including a plurality of pixels segmented into two or more also in the direction perpendicular to the image detecting direction and arrayed in a plurality of rows along the image detecting direction can be used. Further, in such a configuration, the image detecting directions in the first and second X-ray detectors respectively match the pixel array directions of the first and second imaging elements  12  and  22 . Specifically, when the imaging element is the one-dimensional imaging element, the longitudinal direction of the pixel array serves as the image detecting direction. When the imaging element is the two-dimensional imaging element, one of the pixel array directions, preferably, the longitudinal direction serves as the image detecting direction. 
     As shown in  FIG. 4 , in the second imaging element  22 , when the plurality of pixels  23  thereof are used divided into a plurality of pixel units each consisting of a plurality of pixels as a unit, such pixel units can be realized, for example, by binning processing including performing summing, etc., of detection signals on a pixel-unit basis, for the detection signals acquired by the pixels  23 . In this case, for the plurality of pixels  23  of the second imaging element  22 , a pixel unit control section for controlling binning processing according to the number of pixels in the set pixel unit is preferably provided. Accordingly, it becomes possible for the pixel unit in the imaging element  22  to be preferably set or changed as appropriate. 
       FIG. 6  is a diagram showing a variation example of the X-ray detection device shown in  FIG. 4 . In this configuration example, as the same with  FIG. 4 , the plurality of pixels  13  in the imaging element  12  are divided into a plurality of pixel units each consisting of one pixel as a unit. Also, the plurality of pixels  23  in the imaging element  22  are divided into a plurality of pixel units each consisting of a plurality of pixels as a unit. In  FIG. 6 , according to setting of the plurality of pixels  23  as a pixel unit in the second imaging element  22 , a pixel unit control section  30  is provided for the imaging element  22 . By this pixel unit control section  30 , binning processing in the imaging element  22  can be preferably performed according to the number of pixels in the set pixel unit. 
     Further, for the pixel unit control section  30 , a distance information input section  31  and a pixel unit setting section  32  are provided. The distance information input section  31  is used for inputting distance information from the X-ray source  52  to the X-ray detectors in the X-ray detection system (refer to  FIG. 4 ). Distance information in this case is, for example, the distance d 1  from the position of the X-ray source  52  to the first imaging element  12  or the distance d 2  from the position of the X-ray source  52  to the second imaging element  22 . 
     The pixel unit setting section  32  performs settings of the number of pixels which a pixel unit should consist of in the second imaging element  22  or pixel arrangement of those pixels, based on distance information input from the input section  31 . The pixel unit control section  30  controls binning processing in the imaging element  22  based on information on the pixel unit set in this setting section  32 . With such a configuration, even when, for example, the position of the X-ray source  52  and the distance from the X-ray source  52  to the X-ray detector are newly set or changed in the X-ray detection system, it becomes possible to variably set or change the configuration of the pixel units in the second imaging element  22  correspondingly. 
     In the configuration example shown in  FIG. 6 , image signals output from the imaging elements  12  and  22  of the X-ray detection device are input to an image acquisition section  33 . Then, in this image acquisition section  33 , data of a first image imaged with the imaging element  12  corresponding to an X-ray image in the low-energy range and data of a second image imaged with the imaging element  22  corresponding to an X-ray image in the high-energy range are acquired. 
     To these data of the first and second images, predetermined arithmetic processing, for example, a weighted subtraction, superimposition operation, or the like is applied in an image processing section  34 . An image finally obtained through this arithmetic processing (for example, an inspection image in a non-destructive inspection system) is displayed on an image display section  35  to an operator as appropriate. These image acquisition section  33 , image processing section  34 , and image display section  35 , etc., can also be applied to the configuration shown in  FIG. 2  in the same manner. 
     Further, in the first imaging element  12  of the first X-ray detector, when the plurality of pixels  13  thereof are divided into a plurality of pixel units each consisting of a plurality of pixels as a unit, similar to the above-described pixel unit control section  30  for the second imaging element  22 , a pixel unit control section may be provided for the plurality of pixels  13  of the first imaging element  12 . 
     The X-ray detection device according to the above-described embodiments will be further described along with an example of a specific pixel array structure thereof. 
       FIG. 7  is a view showing an example of specific pixel structures of the imaging elements  12  and  22  in the X-ray detection device.  FIG. 8  is a view showing a correspondence relationship between pixel units in the imaging elements  12  and  22  shown in  FIG. 7 . This example corresponds to a specific example of the configuration shown in  FIG. 2 . 
     In the present example, in the first imaging element  12 , one pixel  13  simply corresponds to one pixel unit. Similarly, in the second imaging element  22 , one pixel  23  simply corresponds to one pixel unit. In the present example, the first pixel width p 1  in the first imaging element  12  is set to 0.8 mm, and the second pixel width p 2  in the second imaging element  22  is set to 0.9 mm. In this case, similarly, the pixel unit widths in the imaging elements  12  and  22  are w 1 =p 1 =0.8 mm and w 2 =p 2 =0.9 mm, respectively. 
     Thus, by configuring the imaging elements  12  and  22  so that the pixel unit widths satisfy w 1 &lt;w 2  (pixel widths satisfy p 1 &lt;p 2 ), it becomes possible to prevent pixel deviations between the first and second images respectively acquired with the imaging element  12  of the first X-ray detector and the imaging element  22  of the second X-ray detector. Here, in such a configuration, the correspondence relationship between the pixel units of the imaging elements  12  and  22  is fixed, therefore, the distance between the X-ray source and the X-ray detection device must also be substantially fixed. 
       FIG. 9  is a view showing another example of the specific pixel structures of the imaging elements  12  and  22  in the X-ray detection device.  FIG. 10  and  FIG. 11  respectively show correspondence relationships between pixel units of the imaging elements  12  and  22  shown in  FIG. 9 . The present example corresponds to a specific example of the configuration shown in  FIG. 4 . 
     In the present example, in the first imaging element  12 , one pixel  13  simply corresponds to one pixel unit. In the second imaging element  22 , four pixels  23  correspond to one pixel unit. In the present example, the first pixel width p 1  in the first imaging element  12  is set to 0.8 mm, and the second pixel width p 2  in the second imaging element  22  is set to 0.225 mm. In this case, the pixel unit widths in the imaging elements  12  and  22  are w 1 =p 1 =0.8 mm and w 2 =4×p 2 =0.9 mm, respectively. 
     Thus, by configuring the imaging elements  12  and  22  so that the pixel unit widths satisfy w 1 &lt;w 2  (pixel widths satisfy p 1 &gt;p 2 ), it becomes possible to prevent pixel deviations between the first and second images respectively acquired with the imaging element  12  of the first X-ray detector and the imaging element  22  of the second X-ray detector. 
     Further, in such a configuration, even when the distance between the X-ray source and the X-ray detection device is changed, by changing the setting and the control method of the pixel units in the second imaging element  22  by binning processing, response to the change in distance is possible. As a method for changing the setting of the pixel unit, specifically, for example, there is a method in which the number of pixels constituting the pixel unit is changed. Alternatively, there is a method in which the positions of pixels constituting the pixel unit are shifted. 
       FIG. 10  and  FIG. 11  show an example of such a method for changing the setting of the pixel units. In this example, for two positions  52   a  and  52   b  of the X-ray source different from each other in the distances d 1  and d 2  to the imaging elements  12  and  22  of the X-ray detection device, the number of pixels constituting each of the pixel units  1  to  11  in the second imaging element  22  is fixed to 4. Concerning positions of the pixels constituting the pixel unit, in the pixel units  4  to  8  in a central portion with small pixel deviations, the constituent pixels are the same for both the positions  52   a  and  52   b  of the X-ray source. On the other hand, in the pixel units  1  to  3  and  9  to  11  in the peripheral portions where pixel deviations become large, the constituent pixels are set shifted by one between the positions  52   a  and  52   b  of the X-ray source. With such a configuration, it becomes possible to variably prevent and reduce pixel deviations between the first and second images acquired by the imaging elements  12  and  22  according to the distance from the X-ray source to the detection device. 
       FIG. 12  includes views showing pixel structures in the first and second imaging elements to be used in the X-ray detection device. In each of the three configuration examples (a) to (c) shown in  FIG. 12 , only one pixel unit in the first imaging element  12  on the upstream side and a corresponding one pixel unit in the second imaging element  22  on the downstream side are shown. 
     The example of the pixel structure shown in (a) in  FIG. 12  corresponds to the configuration shown in  FIG. 7 , and the pixel  13  in the first imaging element has a square shape with a pixel width of p 1 =0.8 mm. The pixel  23  in the second imaging element has a square shape with a pixel width of p 2 =0.9 mm. 
     The example of the pixel structure shown in (b) in  FIG. 12  corresponds to the configuration shown in  FIG. 9 , and the pixel  13  in the first imaging element has a square shape with a pixel width of p 1 =0.8 mm. The pixel  23  in the second imaging element has a rectangular shape with a pixel width of p 2 =0.9/4=0.225 mm in the image detecting direction and a pixel width of q 2 =0.9 mm in the direction perpendicular to the image detecting direction. 
     The example of the pixel structure shown in (c) in  FIG. 12  indicates an example of a configuration in which a pixel unit in the first imaging element also consists of a plurality of pixels. In this example, in both first and second imaging elements, pixels are segmented in the direction perpendicular to the image detecting direction as well. Specifically, in this configuration, the pixel  13  in the first imaging element has a rectangular shape with a pixel width of p 1 =0.8/4=0.2 mm in the image detecting direction and a pixel width of q 1 =0.8/2=0.4 mm in the direction perpendicular to the image detecting direction. The pixel  23  in the second imaging element has a rectangular shape with a pixel width of p 2 =0.9/4=0.225 mm in the image detecting direction and a pixel width of q 2 =0.9/2=0.45 mm in the direction perpendicular to the image detecting direction. 
     As shown in these (a) to (c) in  FIG. 12 , as the configurations of the pixel structures and pixel units in the first and second imaging elements, various configurations and combinations can be used, specifically. Generally, as described above, each of the first imaging element and the second imaging element is preferably a one-dimensional imaging element including a plurality of pixels one-dimensionally arrayed in a row along the image detecting direction, or a two-dimensional imaging element including a plurality of pixels arrayed in a plurality of rows along the image detecting direction. 
     The radiation detection device according to the present invention is not limited to the above-described embodiments and configuration examples, but can be modified in many ways. For example, the above-described embodiments describe an X-ray detection device configured by assuming X-rays as radiation to be detected, however, the above-described configurations can also be applicable to a radiation detection device for detecting radiation other than X-rays. As configurations of the first and second radiation detectors, various configurations such as, for example, a configuration in which the support substrate is omitted from the configuration of  FIG. 1 , can be specifically used. Generally, any configurations can be used as long as each of the first and second radiation detectors includes a scintillator layer that extends along the image detecting direction and converts a radiation image into an optical image and an imaging element that includes a plurality of pixels arrayed in one or a plurality of rows along the image detecting direction and acquires an image by the optical image converted in the scintillator layer. 
     Here, the radiation detection device according to the above-described embodiment is a radiation detection device that detects radiation in a first energy range and radiation in a second energy range higher than the first energy range, made incident in a radiation incident direction, and includes (1) a first radiation detector that is positioned on the upstream side with respect to the radiation incident direction and is used for detecting radiation in the first energy range; and (2) a second radiation detector that is positioned on the downstream side with respect to the radiation incident direction and is used for detecting radiation in the second energy range, wherein (3) the first radiation detector includes a first scintillator layer that extends along an image detecting direction and converts an image of the radiation in the first energy range into an optical image, and a first imaging element that includes a plurality of pixels arrayed along the image detecting direction and acquires a first image corresponding to the optical image converted by the first scintillator layer, (4) the second radiation detector includes a second scintillator layer that extends along the image detecting direction and converts an image of the radiation in the second energy range into an optical image, and a second imaging element that includes a plurality of pixels arrayed along the image detecting direction and acquires a second image corresponding to the optical image converted by the second scintillator layer, (5) a first pixel width p 1  in the image detecting direction of each of the plurality of pixels in the first imaging element and a second pixel width p 2  in the image detecting direction of each of the plurality of pixels in the second imaging element are set to be different in width from each other, and (6) the plurality of pixels in the first imaging element are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, the plurality of pixels in the second imaging element are divided into a plurality of pixel units each consisting of one or a plurality of pixels as a unit, a second pixel unit width w 2  of each of the plurality of pixel units in the second imaging element is set to be larger than a first pixel unit width w 1  of each of the plurality of pixel units in the first imaging element. 
     In the above-described configuration, in the case where the position of the radiation source with respect to the detection device is assumed or set, when the distance from the assumed position of the radiation source that supplies radiation to the first and second radiation detectors to the first imaging element is defined as d 1 , and the distance from the assumed position of the radiation source to the second imaging element is defined as d 2 =d 1 +Δd, the second pixel unit width w 2  is preferably set to be substantially equal to w 2 =w 1 ×d 2 /d 1  with respect to the first pixel unit width w 1 . By thus setting the pixel unit widths, according to the assumed position of the radiation source, deviations between images respectively acquired with the first and second imaging elements can be reliably reduced and the accuracy of measurement can be improved. 
     The second pixel unit width w 2  (or the second pixel width p 2 ) in the second imaging element may be set so as to increase (the pixel width increase) from the central portion toward the peripheral portion in the image detecting direction in which a plurality of pixel units are arrayed. With such a configuration, influences of the radiation incident angle that increases from the central portion toward the peripheral portion can be reduced. 
     As a specific configuration of the first and second imaging elements, a configuration in which the plurality of pixels in the first imaging element are divided into the plurality of pixel units each consisting of one pixel as a unit, and the plurality of pixels in the second imaging element are divided into the plurality of pixel units each consisting of one pixel as a unit, and the second pixel width p 2  is set to be larger than the first pixel width p 1  (p 1 &lt;p 2 ) can be used. 
     Alternatively, as a configuration of the imaging elements, a configuration in which the plurality of pixels in the first imaging element are divided into the plurality of pixel units each consisting of one pixel as a unit, the plurality of pixels in the second imaging element are divided into the plurality of pixel units each consisting of a plurality of pixels as a unit, and the second pixel width p 2  is set to be smaller than the first pixel width p 1  (p 1 &gt;p 2 ) can be used. 
     When the plurality of pixels in the second imaging element are divided into a plurality of pixel units each consisting of a plurality of pixels, etc., for such pixel unit setting, a pixel unit control section is preferably provided for controlling binning processing according to the number of pixels in the set pixel unit for the plurality of pixels in the second imaging element. Accordingly, it becomes possible for the pixel unit in the second imaging element to be preferably set or changed as appropriate. 
     Each of the first imaging element and the second imaging element is preferably a one-dimensional imaging element including a plurality of pixels one-dimensionally arrayed in a row along the image detecting direction, or a two-dimensional imaging element including a plurality of pixels arrayed in a plurality of rows along the image detecting direction. In such a configuration, the image detecting directions in the first and second radiation detectors match the pixel array directions of the first and second imaging elements, respectively. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used as a dual-energy type radiation detection device capable of reducing deviations between images respectively acquired with two-stage radiation detectors. 
     REFERENCE SIGNS LIST 
       1 A,  1 B—X-ray detection device (radiation detection device),  10 —first X-ray detector (first radiation detector),  11 —first scintillator layer,  12 —first imaging element,  13 —pixel,  15 —first support substrate,  20 —second X-ray detector (second radiation detector),  21 —second scintillator layer,  22 —second imaging element,  23 —pixel,  25 —second support substrate,  18 —filter,  30 —pixel unit control section,  31 —distance information input section,  32 —pixel unit setting section,  33 —image acquisition section,  34 —image processing section,  35 —image display section,  50 —X-ray detection device,  52 —X-ray source,  55 —belt conveyor,  56 —inspection object.