Beam source estimation method, dose reduction measure evaluation method, image reproduction method, beam source estimation device and program

Abstract

To provide a method for accurately estimating a beam source.SOLUTION: A beam source estimation method includes the steps of: setting the beam source position, beam source shape, and beam source intensity in a space being an evaluation object; performing radiation distribution analysis on the basis of the set beam source position, beam source shape, and beam source intensity, and generating a reproduction image obtained by imaging the space with a gamma-ray camera by overlaying an image created through radiation flux imaging processing on the basis of the distribution analysis result and an image created through geometry model imaging processing on the basis of the shape information; and reverse-estimating the beam source by comparing the reproduction image with a gamma-ray image obtained by imaging the space with the gamma-ray camera.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a radiation source estimation method, a dose reduction countermeasure evaluation method, an image reproduction method, a radiation source estimation device, and a program. [Background technology]

[0002] In order to safely perform work in a nuclear power plant, it is necessary to implement dose reduction measures and improve the dose in the work environment. Radioactive materials are distributed over a wide area inside a reactor building, and it is difficult to implement effective dose reduction measures with only information on the dose distribution in the work environment. In order to implement effective dose reduction measures, it is necessary to accurately identify the position and intensity of the radiation source (the source generating radiation). Patent Document 1 discloses a method for estimating the intensity and distribution of a radiation source inside a structure.

[0003] Non-Patent Document 1 discloses a technique for visualizing the analysis results of MCNP (A General Monte Carlo N-Particle Transport Code: a three-dimensional Monte Carlo analysis code). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-193817 A [Non-patent literature]

[0005] [Non-Patent Document 1] Erik F. Shores, Clell J. Solomon, John D. Zumbro, Duane P. Flamig and Guillermo Terrones, “Radiographic test problem for MCNP and other mesh-based applications”, Los Alamos National Laboratory, retrieved June 7, 2023, https: / / www.aesj.net / document / pnst004 / 502_506.pdf Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need for a method to estimate the radiation source with high accuracy.

[0007] The present disclosure provides a radiation source estimation method, a dose reduction countermeasure evaluation method, an image reproduction method, a radiation source estimation device, and a program that can solve the above problems. [Means for solving the problem]

[0008] A radiation source estimation method according to the present disclosure includes the steps of: setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity; and generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image showing the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis and a second image showing the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and generating an inverse estimation of a radiation source indicated by the gamma ray image by comparing the reproduction image with the gamma ray image.

[0009] The dose reduction measure evaluation method according to the present disclosure includes the steps of: setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation method described above; calculating a distribution of radiation after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction measure is implemented; and determining whether or not the amount of radiation in the space has reached a predetermined target based on the radiation distribution after the dose reduction measure is implemented.

[0010] The image reproduction method according to the present disclosure includes the steps of acquiring shape information of a space photographed by a gamma ray camera, performing a distribution analysis of radiation in the space based on settings of a radiation source position, a radiation source shape, and a radiation source intensity in the space, and performing a radiation flux imaging process based on a result of the radiation distribution analysis to generate a first image showing the distribution of the radiation in the space, performing a geometry model imaging process based on the shape information to generate a second image showing the shape of the space, and reproducing a gamma ray image of the space photographed by the gamma ray camera by superimposing the first image and the second image.

[0011] The radiation source estimation device according to the present disclosure comprises: means for setting a radiation source position, radiation source shape, and radiation source intensity in a space to be evaluated; means for performing a radiation distribution analysis of the space based on the set radiation source position, radiation source shape, and radiation source intensity, and generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image that shows the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis, and a second image that shows the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and means for comparing the reproduction image with the gamma ray image and determining whether the reproduction image reproduces the gamma ray image.

[0012] The program according to the present disclosure causes a computer to function as: means for setting a radiation source position, radiation source shape, and radiation source intensity in a space to be evaluated; means for performing a radiation distribution analysis of the space based on the set radiation source position, radiation source shape, and radiation source intensity, and generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image showing the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis, and a second image showing the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and means for comparing the reproduction image with the gamma ray image to determine whether the reproduction image reproduces the gamma ray image. Effect of the Invention

[0013] According to the radiation source estimation method, radiation source estimation device, and program of the present disclosure, it is possible to estimate a radiation source with high accuracy. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of a radiation source estimation apparatus according to an embodiment. [Diagram 2] 11 is a flowchart showing an example of a radiation source estimation process and a dose reduction countermeasure evaluation process according to the embodiment. [Diagram 3] FIG. 11 is a diagram illustrating an example of shape information of an evaluation target space according to the embodiment. [Figure 4] FIG. 2 is a diagram showing an example of a gamma ray image according to the embodiment. [Diagram 5] FIG. 11 is a diagram showing an example of a measurement result of a dose rate according to the embodiment. [Figure 6A] FIG. 1 is a first diagram showing an example of a reproduced image according to an embodiment. [Figure 6B] FIG. 2 is a second diagram showing an example of a reproduced image according to the embodiment. [Figure 6C] FIG. 3 is a third diagram showing an example of a reproduced image according to the embodiment. [Figure 6D] FIG. 4 is a fourth diagram showing an example of a reproduced image according to the embodiment. [Figure 6E] FIG. 5 is a diagram showing an example of a reproduced image according to the embodiment. [Figure 7A] FIG. 1 is a first diagram illustrating an example of a method for generating a reproduction image according to an embodiment. [Figure 7B] FIG. 2 is a second diagram illustrating an example of a method for generating a reproduction image according to the embodiment. [Figure 7C] FIG. 3 is a third diagram illustrating an example of a method for generating a reproduction image according to the embodiment. [Figure 7D] FIG. 4 is a fourth diagram illustrating an example of a method for generating a reproduction image according to the embodiment. [Figure 8] FIG. 11 is a diagram showing an example of an analysis procedure of a reproduction analysis of a gamma ray image according to the embodiment. [Figure 9] FIG. 11 is a diagram showing an example of a dose analysis result according to the embodiment. [Figure 10] 11A and 11B are diagrams illustrating a process of setting a radiation source intensity according to an embodiment. [Figure 11] FIG. 2 is a first diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 12] FIG. 2 is a second diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 13] FIG. 13 is a third diagram showing an example of a radiation source position and a measurement position according to the embodiment. [Figure 14] 1 is a diagram illustrating an example of a hardware configuration of a radiation source estimation apparatus according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Embodiment> Hereinafter, the radiation source estimation device of the present disclosure will be described with reference to FIGS. (composition) FIG. 1 is a block diagram showing an example of a radiation source estimation apparatus according to an embodiment. The radiation source estimation device 10 estimates the radiation source by confirming the validity of the position, shape, and intensity of the set radiation source based on the consistency between the analytical value of the dose rate distribution and the measured value. As shown in the figure, the radiation source estimation device 10 includes a gamma ray image acquisition unit 11, a measured value acquisition unit 12, an input reception unit 13, a control unit 14, and a storage unit 15.

[0016] The gamma ray image acquisition unit 11 acquires an image (called a gamma ray image) captured by the gamma ray camera. Here, acquiring a gamma ray image means importing a gamma ray image into the radiation source estimation device 10 (inputting a gamma ray image into the radiation source estimation device 10). The gamma ray camera is a device that acquires information on the relative ratio of the directionality and intensity of radiation using a semiconductor detector, and superimposes and outputs the information on an image captured by the camera, thereby visualizing gamma rays. When the inside or outside of a reactor building is photographed with a gamma ray camera, an image is captured in which radiation sources are superimposed on walls, floors, equipment, ducts, cable trays, etc. inside or outside the building and displayed at their respective distribution positions. The radiation sources are color-coded according to their intensity, and are displayed in colors such as red, yellow, green, and blue. The positions displayed in red indicate high gamma ray doses, and the doses decrease as the colors change to yellow, green, and blue. By referring to a gamma ray image, the position of the radiation source, the distribution shape, and the relative level of the radiation dose can be determined, but the absolute value of the radiation dose cannot be grasped.

[0017] The measurement value acquiring unit 12 acquires gamma ray measurement values ​​measured by a gamma ray measuring device. For example, measuring devices are installed at multiple positions in a reactor building to measure the gamma ray dose rate. The measurement value acquiring unit 12 acquires the measurement values ​​measured at various positions in the building. The gamma ray measurement values ​​acquired by the measurement value acquiring unit 12 are absolute values ​​of the dose rate.

[0018] The input reception unit 13 receives various setting information and instruction information for instructing the start and end of processing, etc., inputted using an input device such as a keyboard, a mouse, a touch panel, a button, etc. For example, the input reception unit 13 receives shape information of the space α to be evaluated. The space α to be evaluated is, for example, a reactor building. The shape information is, for example, CAD data showing the shape of the reactor building at the time of its construction, an image of the inside of the reactor building, and three-dimensional point cloud information measuring the inside of the building with a three-dimensional measuring device. The input reception unit 13 also receives settings of the position, shape (thickness, range), and intensity of the radiation source. The input reception unit 13 records the received information in the storage unit 15, or outputs it to the control unit 14.

[0019] The control unit 14 executes and controls the radiation source estimation process. The control unit 14 includes an image reproduction analysis unit 140, an analysis unit 141, an evaluation unit 142, and an output unit 143. The image reproduction analysis unit 140 generates an image from the analysis result of the dose rate distribution by the analysis unit 141. For example, the image reproduction analysis unit 140 generates an image by superimposing "Image 1", which is an image of the dose rate distribution obtained by radiation flux imaging processing (Radiograph Image Tally), and "Image 2", which is an image of the shape information of the space α obtained by geometry model imaging processing. The image obtained by superimposing "Image 1" and "Image 2" is called a reproduced image. On the other hand, a gamma-ray image taken by a gamma-ray camera is obtained by superimposing an image of a dose rate distribution (color contour on a pixel grid) based on information on the direction of flight from the radiation source to the camera obtained by the measurement principle of a pinhole camera or Compton camera, and an image of an optical camera. In this embodiment, the gamma-ray image is reproduced by generating an image equivalent to the gamma-ray image by superimposing "Image 1" obtained by radiation flux imaging processing and "Image 2" obtained by geometry model imaging processing.

[0020] Both the radiation flux imaging process and the geometry model imaging process are known techniques. For example, by setting the position, direction, angle of view, resolution, etc. of a virtual camera and performing the radiation flux imaging process, it is possible to obtain an image that visualizes the analysis result of the dose rate distribution by the analysis unit 141 (an image that visualizes the distribution of the dose rate in the target space that can be observed when the target space is photographed by the virtual camera from the set position of the virtual camera under the photographing conditions such as the direction, angle of view, and resolution related to the above settings, and corresponds to "the image of the dose rate distribution (color contour on the pixel grid)" in the above description of the gamma ray image). Similarly, by setting the position, direction, angle of view, resolution, etc. of a virtual camera and performing the geometry model imaging process based on the CAD data of the reactor building, it is possible to obtain an image that looks like the inside of the reactor building is photographed by a general camera under the photographing conditions such as the set position (corresponding to "the image of the optical camera" in the above description of the gamma ray image).

[0021] In addition, in this embodiment, when generating the reproduced image, the image reproduction analysis unit 140 sets the position and shooting conditions of a virtual camera in the same way as for an actual gamma-ray camera to generate "image 1" and "image 2", which are then superimposed to generate a "reproduced image", and the gamma-ray image acquired by the gamma-ray image acquisition unit 11 is reproduced by the "reproduced image". The "reproduced image" is compared with the gamma-ray image to verify the reproducibility, thereby verifying whether the position, shape, intensity, etc. of the radiation source that was the premise of "image 1" are appropriate, and the position, shape, intensity, etc. of the radiation source are adjusted until the reproducibility is sufficiently accurate. By reproducing the gamma-ray image with high accuracy, the validity of the position, shape, intensity, etc. of the radiation source that was the premise of "image 1" is confirmed. If sufficient validity is confirmed, the radiation source indicated by the gamma-ray image acquired by the gamma-ray image acquisition unit 11 has been identified.

[0022] The analysis unit 141 analyzes the three-dimensional dose rate distribution in the space α by using a three-dimensional transport calculation code such as MCNP (A General Monte Carlo N-Particle Transport Code: a three-dimensional Monte Carlo analysis code). For example, the analysis unit 141 inputs the shape information of the space α and the information such as the position, shape, and intensity of the radiation source received by the input receiving unit 13 to MCNP or the like, and outputs the dose rate distribution in the space α analyzed by MCNP or the like. The evaluation unit 142 compares the dose rate distribution in the space α analyzed by the analysis unit 141 with the dose rates measured at multiple positions in the space α acquired by the measurement value acquisition unit 12, and evaluates whether the two are consistent. The output unit 143 outputs various information such as shape information of the space α (Figure 3), gamma ray image (Figure 4), distribution of measurement values ​​(Figure 5), reproduced images (Figures 6A to 7D), dose rate distribution analyzed by the analysis unit 141 (Figure 9), and evaluation results by the evaluation unit 142 to a display device, electronic file, etc. The storage unit 15 stores calculation codes such as MCNP, data being processed, and the like.

[0023] (operation) Next, the radiation source estimation process and the dose reduction countermeasure evaluation process of this embodiment will be described. FIG. 2 is a flowchart showing an example of a radiation source estimation process and a dose reduction countermeasure evaluation process according to the embodiment.

[0024] (Radiation source estimation processing) First, the shape information of the space to be evaluated is set (step S11). For example, an analyst inputs CAD data of the space α, and information such as the size and installation position of the equipment to be installed in the space α. The CAD data includes three-dimensional information of the floor and walls of the space α, as well as ducts and cable trays laid in the space α. The input reception unit 13 acquires the shape information and records it in the storage unit 15. An example of the shape information of the space α is shown in FIG. 3. The space α includes equipment 31, equipment 32, piping 33, etc. Position 35 on the floor surface 34 is the position of the gamma ray camera, and dashed line 36 indicates the shooting direction of the gamma ray camera. Position 35 and dashed line 36 do not need to be included in the shape information.

[0025] Next, the gamma ray image acquisition unit 11 acquires a gamma ray image (step S12). The gamma ray image is taken at a predetermined position in the space α (for example, position 35 in FIG. 3). The gamma ray image acquisition unit 11 acquires the input gamma ray image and records it in the memory unit 15. An example of a gamma ray image is shown in FIG. 4. (Information such as "C: Duct 10%" written in FIG. 4 is not included in the gamma ray image. This information will be described later.)

[0026] Next, the measurement value acquiring unit 12 acquires the measurement value of the dose rate (step S13). The measurement value acquiring unit 12 acquires the measurement value of the gamma ray dose rate measured at each point in the space α. The measurement value acquiring unit 12 acquires the input measurement value and records it in the memory unit 15. An example of the measurement value measured at each point is shown in FIG. 5.

[0027] Next, the analyst sets the radiation source position and shape (step S14). For example, when the analyst performs a predetermined operation, the output unit 143 outputs a gamma ray image (for example, FIG. 4) and a three-dimensional model of the space α based on the shape information set in step S11 (for example, FIG. 3) to the display device. The analyst refers to the gamma ray image and identifies a position in the space α corresponding to the image position where a color such as red, yellow, green, or blue is displayed. For example, if a red circle is displayed in a certain part of the gamma ray image, the analyst sets the position corresponding to that part in the shape information of the space α as the radiation source. In addition, the analyst sets the range corresponding to the red circle in a wall, duct, equipment, etc. present at the identified radiation source position and the thickness of the layer of radioactive material attached to that range as the shape of the radiation source. The analyst inputs the position and shape of the radiation source in the set space α to the radiation source estimation device 10. The input receiving unit 13 acquires the input position and shape of the radiation source and records them in the storage unit 15.

[0028] Next, the analyst sets the radiation source intensity (step S15). First, the analyst calculates the contribution rate (contribution rate to the dose rate measured at the position where the gamma ray image was taken) of each radiation source position set in step S14 based on the color displayed in the gamma ray image, and inputs the calculated contribution rate to the radiation source estimation device 10. In the gamma ray image of FIG. 4, red is displayed superimposed on the equipment at position A, red is displayed on the hot spot at position B, green is displayed on the duct at position C, and green is displayed on the pipe at position D. For example, the analyst sets a contribution rate of 40% for positions A and B where red is displayed, and a contribution rate of 10% for positions C and D where green is displayed. Next, the analyst sets a radiation source intensity according to the contribution rate and distance to each radiation source position. For example, as illustrated in FIG. 10, it is assumed that the measured value of the dose rate at position P where the gamma ray image was taken is 10 (mSv / h). If the dose rate of 10 (mSv / h) at position P is allocated according to the above contribution rate, the dose rate of gamma rays arriving at position P from position A is 4 (mSv / h), the dose rate of gamma rays arriving at position P from position B is 4 (mSv / h), the dose rate of gamma rays arriving at position P from position C is 1 (mSv / h), and the dose rate of gamma rays arriving at position P from position D is 1 (mSv / h). Next, the analyst calculates the radiation source strength required for the dose rate allocated to position P to reach the position P according to the distance between position P and each of positions A to D. For example, in consideration of the distance between position P and position A, it is calculated backwards that the radiation source strength at position A must be 100 in order for the dose rate at position P to be 4 (mSv / h). In addition, the analyst calculates backwards the radiation source strength of 10 at position B from the distance between position P and position B and the dose rate at position P of 1 (mSv / h). Similarly, the analyst calculates the radiation source intensity 10 at position C and the radiation source intensity 20 at position D. The analyst inputs the calculated radiation source intensities at positions A to D to the radiation source estimation device 10. The input receiving unit 13 acquires the input radiation source position and radiation source shape, and records them in the memory unit 15.

[0029] The radiation source intensities at the positions A to D may be set by the radiation source estimation device 10. For example, an analyst inputs the measurement value at the position P and the contribution rates of the positions A to D to the radiation source estimation device 10. The control unit 14 then calculates the distances from the position P to the positions A to D from the shape information of the space α, calculates the radiation source intensities at the positions A to D based on the input measurement value (10 (mSv / h)) at the position P, the contribution rates of the positions A to D, and the calculated distances from the position P to the positions A to D, and records the calculated radiation source intensities at the positions A to D in the storage unit 15.

[0030] Next, the image reproduction analysis unit 140 performs a reproduction analysis of the gamma-ray image (step S151). First, the image reproduction analysis unit 140 requests the analysis unit 141 to perform a dose rate distribution analysis by MCNP or the like based on the radiation source position, shape, and intensity set in steps S14 and S15. The image reproduction analysis unit 140 receives the analysis result from the analysis unit 141 and performs a radiation flux imaging process to generate "image 1". At this time, the image reproduction analysis unit 140 matches the position, direction, angle of view, resolution, etc. of the virtual camera used in the radiation flux imaging process to the position, direction, angle of view, resolution, etc. of the gamma-ray camera. In addition, the image reproduction analysis unit 140 performs a geometry model imaging process based on the shape information of the space α acquired in step S11 to generate "image 2". At this time, the image reproduction analysis unit 140 also matches the position, direction, angle of view, resolution, etc. of the virtual camera used in the geometry model imaging process to the position, direction, angle of view, resolution, etc. of the gamma-ray camera. The image reproduction analysis unit 140 generates a "reproduced image" by superimposing "image 1" and "image 2". An example of the reproduced image is shown in Figs. 6A to 6E. Fig. 6A is a reproduced image when it is assumed that there is a radiation source as a hot spot on the surface of the equipment 31 in Fig. 3. Fig. 6B is a reproduced image when it is assumed that there is a radiation source in the pipe 33 in Fig. 3. Fig. 6C is a reproduced image when it is assumed that there is a radiation source in the equipment 32 in Fig. 3. Fig. 6D is a reproduced image when it is assumed that there is a radiation source on the floor surface 34 in Fig. 3. Fig. 6E is a reproduced image obtained by superimposing Figs. 6A to 6D. All of Figs. 6A to 6E are reproduced images generated by assuming that there is a virtual camera at position 35 and that the image is taken in direction 36. For example, if radiation sources are set at certain positions of the equipment 31, the equipment 32, the piping 33, and the floor surface 34 with a predetermined intensity and shape in steps S14 and S15, the analysis unit 141 performs a dose rate distribution analysis for each radiation source, and the image reproduction analysis unit 140 generates image reproductions for each radiation source as illustrated in Figs. 6A to 6D, and combines these (Fig. 6E). By generating reproduction images separated for each radiation source in this way, it becomes easy to compare with a gamma ray image (actual image) and adjust the radiation source position, shape, and intensity. For example, each of Figs. 6A to 6D can be compared with a gamma ray image to help estimate the radiation source.In addition, a reproduced image can be generated by arbitrarily selecting and superimposing two or more of FIGS. 6A to 6D, and this can be used to estimate the radiation source.

[0031] As described above, in this embodiment, the reproduced image is compared with a gamma ray image actually taken by a gamma ray camera to capture the characteristics of the dose rate distribution and inversely estimate the radiation source, but at this time, the following processing is performed so that the characteristics of the dose rate distribution can be grasped. (1) Match the shooting conditions with the actual image (gamma ray image) and align the image format. This is realized by matching the position, direction, angle of view, resolution, etc. of the virtual camera used in the radiation flux imaging process and the geometry model imaging process with the position, direction, angle of view, resolution, etc. of the actual gamma ray camera.

[0032] (2) Using the various operations described below, images are created by combining and separating the radiation source and dose rate components. (a) In the shape information of space α, the walls of the compartment are treated as voids or non-calculation areas (cell importance is set to zero) and a dose rate distribution analysis is performed to generate images of components that exclude only scattered radiation at the walls, or components that exclude all scattered radiation (after the first scattering) from the output of MCNP, etc. By separating direct rays and scattered rays from shielding walls, the areas where the radiation source is present and where the radiation source is not present in the colored area of ​​the gamma ray image are more clearly defined, and the accuracy of identifying the radiation source position is improved. The function of excluding all scattered rays from the output of MCNP and other calculation codes and leaving only direct rays is provided in MCNP and other calculation codes. In addition, although it is possible to separate direct rays from one or more scatterings in the output of MCNP and other codes, if the radiation source is inside a material (shielding), scattering within the self-shielding is also included, and it is not possible to separate direct rays from scattered rays from shielding walls. Therefore, in this example, the direct rays and scattered rays from shielding walls are separated in the analysis by taking the difference between calculations with and without a shielding wall. Figure 7A shows an example of estimating the radiation source position by direct ray component separation. The upper part of Figure 7A is an example of a reproduced image that only direct rays are left, and the lower part of Figure 7A is an example of a reproduced image that includes direct rays and scattered rays.

[0033] (a) Gradually increase the number of radiation sources to generate an image that combines multiple radiation sources. (c) An image is generated by gradually reducing the reproduced image caused by the specified radiation source from the gamma ray image taken by the gamma ray camera. By taking the difference between the image (a) and the gamma-ray image and by checking the image (c), the possibility of estimating the position of the unidentified radiation source is improved. For example, in the case of Figure 7B, the reproduced image in the upper part of Figure 7B contains scattered rays originating from multiple radiation sources, making it difficult to identify each radiation source. In such a case, by reducing the number of radiation sources, the influence of each radiation source can be clarified by the scattered radiation distribution shape, etc. The lower part of Figure 7B shows an example of a reproduced image generated by leaving only the radiation sources located behind (far away) as seen from the gamma-ray camera. For example, by comparing the lower part of Figure 7B with the gamma-ray image, the position, shape, and intensity of the radiation source located behind can be efficiently estimated.

[0034] In addition, in relation to (a), (b), and (c), in cases where differences in scattered radiation distribution shape occur due to the depth conditions of the radiation source, the accuracy of identifying the radiation source depth position can be improved by comparing pattern images with depth conditions. A pattern image is a reproduced image obtained by analyzing how the dose rate distribution is displayed for each radiation source condition. Figures 7C and 7D show examples of reproduced images with different radiation source depth conditions. Figure 7C is a reproduced image when the radiation source is assumed to be present on the surface of the device 1, and Figure 7D is a reproduced image when the radiation source is assumed to be present several centimeters behind the surface of the device 1.

[0035] In addition, in relation to (A), (B), and (C), if there is one-to-one information between radiation source information and a reproduced image with a certain degree of accuracy, the performance of the gamma-ray image (image blur, etc.) can be reproduced, and it is expected that the accuracy of identifying the radiation source shape, etc. can be improved. As shown in Fig. 6A to Fig. 6D, by generating a reproduced image for each radiation source and comparing these with the gamma-ray image in any combination, it is possible to use it for identifying the radiation source shape, etc.

[0036] Next, it is determined whether the reproduced image reproduces the gamma ray image with good accuracy, and whether the reproducibility is good (step S152). For example, when an analyst compares the gamma ray image and the reproduced image and determines that the color distribution positions and ranges of the two images are almost the same, the reproducibility is determined to be good. If there is a difference between the two images, the reproducibility is determined to be not good. The determination in step S152 may be made automatically by the image reproduction analysis unit 140. For example, the image reproduction analysis unit 140 may extract feature points of the reproduced image and the gamma ray image and calculate the similarity of the feature points to determine whether the two are similar. If the two are similar, the image reproduction analysis unit 140 determines that the reproducibility is good, and if the two are not similar, the image reproduction analysis unit 140 determines that the reproducibility is not good.

[0037] If the reproducibility is good (step S152; Yes), proceed to step S16. If the reproducibility is not good (step S152; No), repeat the process from step S14 until the reproducibility is determined to be good. That is, the analyst generates a reproduced image while implementing the techniques (a) to (c) described in relation to the process of step S151, compares the reproduced image with the gamma ray image, and adjusts and sets the radiation source position, shape, and intensity until the reproducibility becomes good (steps S14 to S15). This improves the estimation accuracy of the radiation source shown in the gamma ray image and makes it more efficient.

[0038] Here, the flow of the reproduction analysis of gamma-ray images is shown in FIG. 8. As shown in FIG. 8, in the reproduction analysis of gamma-ray images, the shooting conditions of a virtual camera are matched to those of an actual gamma-ray camera (101). The analyst sets the number, position, shape, intensity, etc. of radiation sources based on actual measurement information, etc. (102). Then, a dose rate distribution calculation is performed for each radiation source (103), and the result is subjected to radiation flux imaging processing (104). Meanwhile, a geometry model imaging processing is performed (105), and the result is integrated with the result of the radiation flux imaging processing to generate a reproduced image of the gamma-ray camera (106). Then, the gamma-ray image is compared with a gamma-ray image measured by a gamma-ray camera (107) (108), and the reproducibility is confirmed. According to the reproduction analysis of gamma-ray images, an actual image is reproduced by superimposing a radiation flux imaging image of multiple radiation sources and a geometry model imaging image, and the characteristics of the dose rate distribution are captured by comparing the actual image and the reproduced image, and the radiation source can be inversely estimated.

[0039] Next, the analysis unit 141 executes a dose rate distribution analysis (step S16). The analysis unit 141 inputs shape information of the space α, radiation source intensity and shape (range, thickness) of radiation source positions A to D, etc., into a calculation code such as MCNP, executes a dose analysis, and calculates a three-dimensional dose rate distribution in the space α. For example, an analysis result of the dose rate distribution shown in Fig. 9 can be obtained (Fig. 9 shows a two-dimensional dose rate distribution diagram as an example).

[0040] Next, the evaluation unit 142 checks the reproducibility of the dose rate (step S17). The reproducibility of the dose rate means whether the distribution of the dose rate calculated by the dose rate distribution analysis reproduces the distribution of the actual dose rate, that is, whether the analysis result of the dose rate distribution matches the measured value of the dose rate measured at each point. The evaluation unit 142 compares the analysis result of the dose rate distribution obtained in step S16 (for example, FIG. 9) with the measured value of the dose rate obtained in step S13 (for example, FIG. 5), and judges whether the analytical value of the dose rate at each position matches the measured value (whether they match or are close to each other). For example, if the difference between the measured value and the analytical value at all measurement positions is within a predetermined range, the evaluation unit 142 judges that the reproducibility of the dose rate is good. If there is a large difference at even one point, the evaluation unit 142 judges that the reproducibility of the dose rate is not good. When the evaluation unit 142 judges that the reproducibility of the dose rate is good (step S18; Yes), the position, shape, and intensity of the radiation source set in steps S14 to S15 are considered to be appropriate. The control unit 14 determines the radiation source defined by the position, shape, and intensity set in steps S14 to S15 as the radiation source distributed in the space α to be evaluated (step S19).

[0041] If the evaluation unit 142 determines that the reproducibility of the dose rate is not good (step S18; No), the output unit 143 outputs a message notifying the user that the reproducibility is low, such as "There is an error in the set radiation source position, shape, and intensity" (step S181), and repeats the processing from step S14 onwards.

[0042] Here, referring to Figs. 11 to 13, factors that reduce the reproducibility of the radiation source position set in steps S14 to S15 will be described. If the hotspot E and the measurement position P of the gamma ray image are in a positional relationship such that direct rays from the radiation source E reach the measurement position P as shown in Fig. 11, radiation source estimation is relatively easy. However, as shown in Fig. 12, when a structure F1 exists between the true radiation source F and the measurement position P of the gamma ray image, and the gamma rays detouring the structure F1 hit the wall F3 and scattered rays reach the measurement position P, the scattering position F2 is displayed in red or yellow in the gamma ray image taken at the measurement position P. When the radiation source position is set with reference to this gamma ray image, F2 is set as the radiation source position. Then, for example, a discrepancy occurs between the actual dose rate measured at a position P1 close to the true radiation source F and the dose rate at the position P1 indicated by the dose rate distribution analyzed with the scattering position F2 as the radiation source position. If there is only a measurement result at one location (for example, position P), even if F2 is set as the radiation source position, an error in the set radiation source position cannot be noticed. However, by comparing the measured dose rate values ​​measured at multiple locations with the analysis value, an error in the radiation source position can be noticed. Also, as illustrated in FIG. 13, when a high-dose device is present on the opposite side of the measurement position P across the wall F3, and a streaming ray that penetrates a part of the wall F3 where the wall thickness is locally thin F4 and reaches the measurement position P is captured by a gamma ray camera, the gamma ray image captured at the measurement position P displays red or yellow at the transmission position F4. If the radiation source position is set with reference to this gamma ray image, the transmission position F4 will be specified as the radiation source position. In this case, too, there is a high possibility that the measured dose rate values ​​measured at locations other than the measurement position P will deviate from the analysis results by MCNP or the like. By comparing the measured dose rate values ​​at multiple locations with the analysis results of the dose rate distribution in this way, an error in the estimated radiation source position, etc. can be noticed. When low reproducibility is output (step S181), the analyst makes an engineering judgment while referring to the shape information of the space α, for example by considering the possibility that the radiation source shown in the gamma ray image is a scattered ray or a streaming ray, resets the radiation source position, radiation source shape, and radiation source intensity, and repeats the process from step S14.

[0043] Note that gamma ray images may be taken at multiple positions within the space α. In this case, gamma ray images taken at multiple positions are acquired in step S12. Then, the processes of steps S14 to S18 are performed for each gamma ray image. In this case, a step of comparing the radiation source position, radiation source shape, and radiation source intensity determined based on each gamma ray image may be further provided, and the radiation source position, etc. may be further adjusted based on the comparison result. Alternatively, an analyst may set the radiation source position, shape, and intensity based on multiple gamma ray images (steps S14 to S15), and the process of checking the reproducibility of this setting (steps S151 to S18) may be repeatedly performed.

[0044] (Dose reduction measures evaluation process) Once the radiation source has been determined by the above process, it becomes possible to execute the process of evaluating dose reduction measures. First, the analyst sets the dose contribution rate for each radiation source (step S20). The analyst sets the contribution rate of each radiation source to each point in the space α while taking into consideration direct rays, scattered rays, and streaming rays from the radiation source. Next, the analyst sets a dose reduction target for each radiation source (step S21). For example, the analyst sets a target to reduce the dose rate of "radiation source 1" present on the floor from 7 (mSv / h) to 0.1 (mSv / h). Next, the analyst sets dose reduction measures (step S22). For example, the analyst sets dose reduction measures for each radiation source determined in step S19, such as taking shielding measures as a measure against "radiation source 2" present in the cable tray, and taking cleaning or wiping measures against "radiation source 3" present in the wall and "radiation source 4" present in the ceiling. Since the radiation source estimation process can accurately estimate the position, shape, and intensity of the radiation source, in step S22, it is possible to appropriately set dose reduction measures based on the estimation results to achieve the goal set in step S21.

[0045] Next, the dose rate distribution after the dose reduction measures are evaluated (step S23). For example, the analyst sets the intensity and shape (range, thickness) of the radiation source after the dose reduction measures set in step S22 are implemented for each radiation source, and inputs these values ​​to the radiation source estimation device 10. The input reception unit 13 acquires the intensity and shape of each input radiation source, and records them in the storage unit 15. Next, the analysis unit 141 inputs the shape information of the space α, the position of each radiation source determined in step S19, the radiation source intensity and shape after the dose reduction measures are implemented, etc., to MCNP, etc., and executes the calculation code. As a result, the dose rate distribution in the space α illustrated in FIG. 9 is obtained. The control unit 14 compares the analysis result by the analysis unit 141 with a predetermined target value and determines whether the dose rate distribution in the space α after the dose reduction measures are implemented has reached the target (step S24). For example, if the analysis result of the dose rate distribution by the analysis unit 141 indicates that the dose rate is equal to or lower than the target value at any position in the space α, the control unit 14 determines that the target has been reached, and if not, determines that the target has not been reached. If the control unit 14 determines that the target has been reached (step S24; Yes), the analyst plans dose reduction countermeasure construction based on the dose reduction countermeasure set in step S22 (step S25).

[0046] When the control unit 14 determines that the target has not been reached (step S24; No), the output unit 143 outputs a message notifying that the dose reduction measures are insufficient and the analysis results of step S23 (step S241), and repeats the processes from step S21 onwards. This makes it possible to formulate dose reduction measures that can achieve the target dose rate.

[0047] (effect) As described above, according to this embodiment, the position, shape, and intensity of a radiation source distributed in a space to be evaluated can be estimated with high accuracy. In particular, by performing a reproduction analysis process on a gamma ray image, the radiation source observed in the dose rate distribution shown in the gamma ray image can be estimated with high accuracy. In addition, effective dose reduction measures can be determined based on the results of radiation source estimation. In the above embodiment, the gamma ray image is reproduced using the dose rate distribution in step S151, but the gamma ray image may be reproduced using the distribution of a quantity other than the dose rate (flux, count rate (CPS, CPM, etc.), etc.) instead of the dose rate distribution. Also, in step S17, etc., the radiation source position, radiation source shape, radiation source intensity, etc. are set so that the analytical value of the dose rate distribution and the measured value of the dose rate are consistent, but in this case, too, the analytical value of the distribution of a quantity other than the dose rate (flux, count rate (CPS, CPM, etc.), etc.) may be applied instead of the analytical value of the dose rate distribution, and the measured value of a quantity other than the dose rate (flux, count rate (CPS, CPM, etc.), etc.) may be used instead of the measured value of the dose rate. In addition, in step S23, etc., it is confirmed whether the dose rate distribution after the dose reduction measures are implemented is equal to or less than the target value. However, it is also possible to determine whether the dose rate distribution is equal to or less than the target value using the distribution of a quantity other than the dose rate (such as flux, counting rate (CPS, CPM, etc.)) instead of the dose rate distribution. Note that a dose rate distribution, a flux distribution, a count rate distribution, etc. that take into account directionality are examples of radiation distributions. A measured dose rate, a measured flux, a measured count rate, etc. that take into account directionality are examples of radiation measurement values.

[0048] FIG. 14 is a diagram illustrating an example of a hardware configuration of the radiation source estimation apparatus. The computer 900 includes a CPU 901 , a main memory device 902 , an auxiliary memory device 903 , an input / output interface 904 , and a communication interface 905 . The radiation source estimation apparatus 10 described above is implemented in a computer 900. Each of the above-mentioned functions is stored in the auxiliary storage device 903 in the form of a program. The CPU 901 reads the program from the auxiliary storage device 903, loads it in the main storage device 902, and executes the above-mentioned processing in accordance with the program. The CPU 901 also reserves a storage area in the main storage device 902 in accordance with the program. The CPU 901 also reserves a storage area in the auxiliary storage device 903 for storing data being processed in accordance with the program.

[0049] In addition, a program for realizing all or part of the functions of the radiation source estimation device 10 may be recorded in a computer-readable recording medium, and the program recorded in the recording medium may be read into a computer system and executed to perform processing by each functional unit. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. In addition, if a WWW system is used, the term "computer system" also includes a homepage providing environment (or display environment). In addition, the term "computer-readable recording medium" refers to a portable medium such as a CD, DVD, or USB, and a storage device such as a hard disk built into a computer system. In addition, when the program is distributed to the computer 900 through a communication line, the computer 900 that receives the program may load the program into the main storage device 902 and execute the above processing. In addition, the above program may be for realizing part of the above-mentioned functions, and may further be capable of realizing the above-mentioned functions in combination with a program already recorded in the computer system.

[0050] As described above, several embodiments according to the present disclosure have been described, but all of these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents as described in the claims, as well as in the scope and gist of the invention.

[0051] <Additional Notes> The radiation source estimation method, the dose reduction countermeasure evaluation method, the image reproduction method, the radiation source estimation device, and the program described in the embodiments can be understood, for example, as follows.

[0052] (1) A radiation source estimation method according to a first aspect includes the steps of: setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; analyzing a radiation distribution in the space (e.g., a dose rate distribution taking into account directivity, a radiation flux distribution, a count rate distribution, etc.) based on the set radiation source position, the radiation source shape, and the radiation source intensity; and generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image showing the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis and a second image showing the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and generating an inverse estimation of a radiation source indicated by the gamma ray image by comparing the reproduction image with the gamma ray image. This allows the radiation source to be estimated with high accuracy.

[0053] (2) A second aspect of the radiation source estimation method is the radiation source estimation method of (1), wherein the first image is an image showing the distribution of radiation in the space when the space is photographed by a first virtual camera, and the second image is an image showing the shape of the space when the space is photographed by a second virtual camera, and in the step of generating the reproduction image, the shooting conditions of the first virtual camera and the second virtual camera are matched to the shooting conditions of the gamma ray camera. This makes it possible to obtain a reproduced image with good reproducibility.

[0054] (3) A radiation source estimation method according to a third aspect is the radiation source estimation method according to (1) to (2), in which the step of generating a reconstruction image generates the reconstruction image for each of the radiation sources. This makes it possible to clarify the radiation source and improve the accuracy and efficiency of radiation source estimation.

[0055] (4) A fourth aspect of the radiation source estimation method is the radiation source estimation method of (3), wherein in the step of generating the reproduction image, the reproduction image is generated by superimposing the reproduction images for the radiation sources, and in generating the reproduction image, the number of the reproduction images to be superimposed is increased or decreased. The radiation source estimation method according to claim 3. This makes it possible to clarify the radiation source and improve the accuracy and efficiency of radiation source estimation.

[0056] (5) A radiation source estimation method according to a fifth aspect is the radiation source estimation method according to any one of (1) to (4), wherein the step of generating a reproduction image generates the reproduction image of only direct rays. This makes it possible to clarify the radiation source and improve the accuracy and efficiency of radiation source estimation.

[0057] (6) A sixth aspect of the radiation source estimation method is a radiation source estimation method according to any one of (1) to (5), wherein in the step of generating the reproduction image, the reproduction image is generated in which scattered radiation due to a wall surface of the space is removed. This makes it possible to clarify the radiation source and improve the accuracy and efficiency of radiation source estimation.

[0058] (7) A radiation source estimation method according to a seventh aspect is a radiation source estimation method according to any one of (1) to (6), in which in the step of generating the reconstruction image, a distribution analysis of the radiation is performed by a three-dimensional transport calculation code. This makes it possible to calculate the distribution of radiation (eg, dose rate distribution, flux distribution, count rate distribution, etc.).

[0059] (8) A radiation source estimation method according to an eighth aspect is the radiation source estimation method of any one of (1) to (7), further comprising the steps of: setting, at the radiation source position, a radiation source intensity calculated based on a contribution rate of the radiation source based on the gamma ray image and the measurement value of the radiation at a predetermined measurement position in the space; performing a radiation distribution analysis based on the shape information, the radiation source position, the radiation source shape, and the radiation source intensity to calculate the radiation distribution in the space; comparing a result of the calculation of the radiation distribution with the measurement value of the radiation; and correcting at least one of the radiation source position, the radiation source shape, and the radiation source intensity based on a result of the comparison, wherein the correcting step, the calculating step of the radiation distribution, and the comparing step are repeated until the calculation result of the radiation distribution by the radiation distribution analysis and the measurement value of the radiation are consistent with a predetermined target accuracy. This allows the radiation source to be estimated with high accuracy.

[0060] (9) A ninth aspect of the radiation source estimation method is the radiation source estimation method of (8), wherein, when setting the radiation source intensity, a measurement value of the radiation measured at the same position as the shooting position of the gamma ray image is allocated to the radiation source position based on the contribution rate, and the radiation source intensity is set based on the allocated value and the distance between the shooting position and the radiation source position. This allows a specific value of the radiation source intensity to be set.

[0061] (10) A radiation source estimation method according to a tenth aspect is the radiation source estimation method of (9), wherein in the step of comparing the calculation result of the radiation distribution with the measurement value of the radiation, the measurement values ​​of the radiation at a plurality of positions are compared with the calculation result of the radiation distribution, and the correction step, the calculation step of the radiation distribution, and the comparison step are repeated until the measurement values ​​of the radiation at each of the plurality of positions and the calculation result of the radiation distribution are consistent with the target accuracy. This makes it possible to check the validity of the initially set radiation source position, radiation source shape, and radiation source strength. If the calculated radiation distribution results differ from the radiation measurement values ​​at each location (e.g., dose rate measurement, radiation flux measurement, count rate measurement, etc.), the settings of the radiation source position, etc. are corrected. This makes it possible to estimate the radiation source position with high accuracy.

[0062] (11) A radiation source estimation method according to an eleventh aspect is the radiation source estimation method according to (10), further comprising a step of notifying that there is an error in any of the radiation source position, the radiation source shape, and the radiation source intensity if there is any inconsistent position as a result of comparing the radiation measurement values ​​at the multiple positions with the calculation result of the radiation distribution. This makes it possible to notice an error, for example, when a radiation source is set erroneously due to the influence of scattered radiation, streaming radiation, or the like.

[0063] (12) A radiation source estimation method according to a twelfth aspect is a radiation source estimation method according to any one of (8) to (11), further comprising a step of notifying whether or not the comparison results in a match at the target accuracy. This makes it possible to determine whether the set radiation source position, radiation source shape, and radiation source intensity are appropriate.

[0064] (13) A radiation source estimation method according to a thirteenth aspect is a radiation source estimation method according to any one of (8) to (11), comprising the steps of: for each of gamma ray images taken at a plurality of positions in the space, setting the radiation source position and the radiation source shape, setting the radiation source intensity, calculating the radiation distribution, comparing the calculation result of the radiation distribution with the radiation measurement values, the correcting step, and repeating the correcting step, the calculating step of the radiation distribution in the space, and the comparing step until the calculation result of the radiation distribution by the radiation distribution analysis and the radiation measurement values ​​are consistent with the target accuracy, and further comprising a step of comparing the radiation source position, the radiation source shape, and the radiation source intensity obtained based on each of the gamma ray images. This allows the position, shape, and intensity of the radiation source to be calculated based on multiple gamma-ray intensity distribution images, and the results can be compared.If there is a discrepancy in the radiation source position or dose within the same area, the possibility of scattering or streaming can be considered and the exact source position can be estimated.

[0065] (14) A radiation source estimation method according to a fourteenth aspect is a radiation source estimation method according to any one of (8) to (13), wherein in the step of calculating the distribution of radiation, the radiation is analyzed using a three-dimensional transport calculation code capable of reproducing the behavior of gamma rays. This makes it possible to calculate the distribution of radiation (eg, dose rate distribution, flux distribution, count rate distribution, etc.).

[0066] (15) A dose reduction countermeasure evaluation method according to a fifteenth aspect includes the steps of: setting a dose reduction countermeasure for each of the radiation source positions estimated by the radiation source estimation method according to any of (8) to (14); calculating a distribution of the radiation after the dose reduction countermeasure is implemented based on the radiation source strength and the radiation source shape for each of the radiation source positions after the dose reduction countermeasure is implemented; and determining whether or not the amount of the radiation in the space has reached a predetermined target based on the radiation distribution after the dose reduction countermeasure is implemented. This allows for planning dose reduction measures that will achieve the goal.

[0067] (16) An image reproduction method according to a sixteenth aspect includes the steps of acquiring shape information of a space photographed by a gamma ray camera, performing a distribution analysis of radiation in the space based on settings of a radiation source position, a radiation source shape, and a radiation source intensity in the space, and performing a radiation flux imaging process based on a result of the radiation distribution analysis to generate a first image showing the distribution of the radiation in the space, performing a geometry model imaging process based on the shape information to generate a second image showing the shape of the space, and reproducing a gamma ray image of the space photographed by the gamma ray camera by superimposing the first image and the second image. This allows a gamma ray image to be reconstructed.

[0068] (17) A radiation source estimation device according to a seventeenth aspect includes: means for setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; means for performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity, and generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image that shows the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis, and a second image that shows the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and means for comparing the reproduction image with the gamma ray image and determining whether the reproduction image reproduces the gamma ray image.

[0069] (18) A program according to an eighteenth aspect causes a computer 900 to function as: a means for setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; a means for performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity, and for generating a reproduction image that reproduces a gamma ray image of the space captured by a gamma ray camera by superimposing a first image showing the radiation distribution in the space generated by performing a radiation flux imaging process based on a result of the radiation distribution analysis and a second image showing the shape of the space generated by performing a geometry model imaging process based on shape information of the space; and a means for comparing the reproduction image with the gamma ray image to determine whether the reproduction image reproduces the gamma ray image. [Explanation of symbols]

[0070] 10...Radiation source estimation device 11 Gamma ray image acquisition unit 12 Measurement acquisition section 13 Input reception section 14. Control section 140...Image reproduction analysis section 141...Analysis Department 142...Evaluation section 143 Output section 15...Storage section 900...Computer 901···CPU 902...Main memory 903...Auxiliary storage device 904 Input / Output Interface 905 Communication Interface

Claims

1. A step of setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity, and generating a reproduced image that reproduces a gamma ray image captured by a gamma ray camera of the space by superimposing a first image showing the radiation distribution in the space, the first image being generated by performing a radiation flux imaging process based on the result of the radiation distribution analysis, and a second image showing the shape of the space, the second image being generated by performing a geometry model imaging process based on shape information of the space; a step of inversely estimating a radiation source indicated by the gamma ray image by comparing the reconstruction image with the gamma ray image; The radiation source estimation method has the following structure:

2. the first image is an image showing a distribution of the radiation in the space when the space is photographed by a first virtual camera, and the second image is an image showing a shape of the space when the space is photographed by a second virtual camera, In the step of generating the reproduced image, imaging conditions of the first virtual camera and the second virtual camera are made to coincide with imaging conditions of the gamma ray camera. The radiation source estimation method according to claim 1 .

3. In the step of generating the reconstructed image, the reconstructed image is generated for each of the radiation sources. The radiation source estimation method according to claim 1 or 2.

4. In the step of generating the reproduction image, the reproduction image is generated by superimposing the reproduction images for the respective radiation sources; In generating the reproduction image, the reproduction images to be superimposed are increased or decreased. The radiation source estimation method according to claim 3.

5. In the step of generating the reproduced image, the reproduced image is generated using only direct rays. The radiation source estimation method according to claim 1 or 2.

6. In the step of generating the reproduced image, the reproduced image is generated from which scattered radiation due to a wall surface of the space has been removed. The radiation source estimation method according to claim 1 or 2.

7. In the step of generating the reconstruction image, a distribution analysis of the radiation is performed using a three-dimensional transport calculation code. The radiation source estimation method according to claim 1 or 2.

8. a step of setting a radiation source intensity at the radiation source position, the radiation source intensity being calculated based on a contribution rate of the radiation source based on the gamma ray image and a radiation measurement value at a predetermined measurement position in the space; performing a distribution analysis of the radiation based on the shape information, the radiation source position, the radiation source shape, and the radiation source intensity, and calculating a distribution of the radiation in the space; comparing the calculated radiation distribution with the measured radiation; modifying at least one of the source position, the source shape, and the source intensity based on a result of the comparison; and repeating the correction step, the calculation step of the radiation distribution, and the comparison step until the calculation result of the radiation distribution by the radiation distribution analysis matches the measured radiation values ​​with a predetermined target accuracy. The radiation source estimation method according to claim 1 or 2.

9. When setting the radiation source intensity, the radiation measurement value measured at the same position as the gamma ray image capturing position is allocated to the radiation source position based on the contribution rate; setting the radiation source intensity based on the allocated value and a distance between the imaging position and the radiation source position; The radiation source estimation method according to claim 8.

10. In the step of comparing the calculation result of the radiation distribution with the measured value of the radiation, comparing the measured radiation levels at a plurality of positions with the calculated distribution of the radiation levels; repeating the correction step, the calculation step of the radiation distribution, and the comparison step until the radiation measurement value at each of the plurality of positions and the calculation result of the radiation distribution match with the target accuracy. The radiation source estimation method according to claim 9.

11. a step of notifying that there is an error in any of the radiation source position, the radiation source shape, and the radiation source intensity, if there is any inconsistent position as a result of comparing the radiation measurement values ​​at the multiple positions with the calculation result of the radiation distribution; The radiation source estimation method according to claim 10, further comprising:

12. notifying whether the comparison results in a match at the target accuracy; The radiation source estimation method according to claim 8, further comprising:

13. For each of the gamma ray images taken at a plurality of positions in the space, setting the radiation source position and the radiation source shape; setting the radiation source intensity; calculating a distribution of the radiation; comparing the calculated radiation distribution with the measured radiation; the modifying step; repeating the correction step, the calculation step of the radiation distribution in the space, and the comparison step until the calculation result of the radiation distribution by the radiation distribution analysis and the measured radiation values ​​match with the target accuracy; Run further comprising a step of comparing the radiation source position, the radiation source shape, and the radiation source intensity obtained based on each of the gamma ray images; The radiation source estimation method according to claim 8, further comprising:

14. In the step of calculating the distribution of the radiation, a distribution analysis of the radiation is performed using a three-dimensional transport calculation code capable of reproducing the behavior of gamma rays. The radiation source estimation method according to claim 8.

15. A step of setting a dose reduction measure for each of the radiation source positions estimated by the radiation source estimation method according to claim 8; calculating a distribution of the radiation after the dose reduction measure is implemented based on the radiation source strength and the radiation source shape for each radiation source position after the dose reduction measure is implemented; determining whether the amount of radiation in the space has reached a predetermined target based on the distribution of the radiation after the dose reduction measure has been implemented; A method for evaluating dose reduction measures.

16. A step of acquiring shape information of a space photographed by a gamma ray camera; performing a radiation distribution analysis in the space based on settings of a radiation source position, a radiation source shape, and a radiation source intensity in the space, and performing a radiation flux imaging process based on a result of the radiation distribution analysis to generate a first image indicating the radiation distribution in the space; performing a geometry model imaging process based on the shape information to generate a second image showing a shape of the space; reproducing a gamma ray image of the space captured by a gamma ray camera by superimposing the first image and the second image; The image reproduction method according to claim 1,

17. A means for setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; a means for performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity, and for generating a reproduced image by superimposing a first image showing the radiation distribution in the space, which is generated by performing a radiation flux imaging process based on the result of the radiation distribution analysis, and a second image showing the shape of the space, which is generated by performing a geometry model imaging process based on shape information of the space; and means for comparing said reproduced image with said gamma ray image to determine whether said reproduced image reproduces said gamma ray image; A radiation source estimation device having the above structure.

18. Computer, A means for setting a radiation source position, a radiation source shape, and a radiation source intensity in a space to be evaluated; a means for performing a radiation distribution analysis of the space based on the set radiation source position, the radiation source shape, and the radiation source intensity, and for generating a reproduced image by superimposing a first image showing the radiation distribution in the space, which is generated by performing a radiation flux imaging process based on the result of the radiation distribution analysis, and a second image showing the shape of the space, which is generated by performing a geometry model imaging process based on shape information of the space; and means for comparing said reproduced image with said gamma ray image to determine whether said reproduced image reproduces said gamma ray image; A program to function as a

Images