Radiation source estimation device and radiation source estimation method

Abstract

This method accurately estimates the radiation source distribution of a measurement target whose physical properties are unknown and access is limited. [Solution] The radiation source estimation device of the present invention comprises a radiation detector that measures the energy spectrum of radiation emitted from an object to be measured; a position measurement unit that measures the position information of the radiation detector and the object to be measured; a physical property measurement unit that measures the surface properties and depth information of the object to be measured; a data matching unit that compares assumed physical property data of the object to be measured with the information measured by the physical property measurement unit; a response function creation unit that inputs the physical property data matched with the position information and creates a response function; and a distribution estimation unit that estimates the intensity of the radiation source based on the detection result of the radiation detector. The response function creation unit is characterized by meshing the inside of the object to be measured and assigning the physical property data matched by the data matching unit to the corresponding mesh from the information measured by the physical property measurement unit.

Description

Technical Field

[0001] The present invention relates to a source estimation device and a source estimation method.

Background Art

[0002] Structures such as melt containing nuclear fuel and concrete deposited in the building at the Fukushima Daiichi Nuclear Power Plant are in a state where their source distributions are unknown. For safe removal work, it is necessary to accurately grasp the three-dimensional distribution of sources such as radioactivity or radioactivity concentration. It is required to grasp the source distribution of the object to be measured, such as fuel debris, by non-contact or only small-scale processing rather than by investigations involving large-scale processing operations such as excavation and sampling of the object to avoid criticality.

[0003] As a general method for obtaining the source distribution of the object to be measured, there is a method of specifying the direction of arrival of gamma rays by measuring gamma rays emitted from the object to be measured using a device such as a gamma camera or a Compton camera. Furthermore, by utilizing the fact that the energy of gamma rays is unique for each nuclide, the nuclide can be identified, and the intensity of the radioactive substance contained in the object to be measured can be measured based on the number of detected gamma rays.

[0004] However, the above-described method cannot obtain the distribution in the depth direction of the object to be measured. Therefore, a technique for grasping the source distribution in the depth direction has been proposed. Patent Document 1 describes a method of measuring the energy distribution of radiation emitted from an object to be measured and inversely estimating the source from a response function created for each detector position based on the positional relationship between the detector and the object to be measured.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The radiation source estimation method described in Patent Document 1 utilizes reference data on the thickness and density of the object being measured, such as the human body, to create the response function. However, if the thickness and density of the object being measured, such as the aforementioned fuel debris, are unknown, and the accessible locations are limited, it may not be possible to create a response function. Alternatively, the measurement data necessary for inverse estimation may be insufficient, potentially leading to a decrease in estimation accuracy.

[0007] The object of the present invention is to provide a radiation source estimation device and a radiation source estimation method that can accurately estimate the radiation source distribution of an object to be measured whose physical properties are unknown and access is limited. [Means for solving the problem]

[0008] The radiation source estimation device of the present invention comprises a radiation detector that measures the energy spectrum of radiation emitted from an object to be measured; a position measurement unit that measures the position information of the radiation detector and the object to be measured; a physical property measurement unit that measures the surface properties and depth information of the object to be measured; a data matching unit that compares assumed physical property data of the object to be measured with the information measured by the physical property measurement unit; a response function creation unit that inputs the physical property data matched with the position information and creates a response function; and a distribution estimation unit that estimates the intensity of the radiation source based on the detection result of the radiation detector, wherein the response function creation unit meshes the inside of the object to be measured and assigns the physical property data matched by the data matching unit to the corresponding mesh from the information measured by the physical property measurement unit.

[0009] Furthermore, the radiation source estimation method of the present invention is characterized by measuring the energy spectrum of radiation emitted from an object to be measured with a radiation detector, acquiring positional information of the radiation detector and the object to be measured, acquiring surface properties and depth information of the object to be measured, comparing the assumed physical property data of the object to be measured with the surface properties and depth information, creating a response function from the physical property data compared with the positional information, and estimating the intensity of the radiation source based on the detection result of the radiation energy spectrum. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a radiation source estimation device and a radiation source estimation method that can accurately estimate the radiation source distribution of a measurement target whose physical properties are unknown and whose access is limited. [Brief explanation of the drawing]

[0011] [Figure 1] This is an overall configuration diagram of the radiation source estimation device according to Example 1. [Figure 2] This is a conceptual diagram showing the relationship between the detector and the object being measured according to Example 1. [Figure 3] This is a conceptual diagram showing the process for creating a response function from surface information and depth information of the object to be measured according to Example 1. [Figure 4] This is a flowchart of the process for estimating the radiation source distribution according to Example 1. [Figure 5] This is an example of an energy spectrum obtained by the detector according to Example 2. [Figure 6] This is an example of measuring the energy spectrum of an object to be measured according to Example 3 using a detector from multiple angles. [Modes for carrying out the invention]

[0012] Embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate. Hereinafter, embodiments of the present invention will be described based on the drawings. [Examples]

[0013] Example 1 will be explained using Figures 1 to 4. Figure 1 is an overall configuration diagram of the radiation source estimation device according to Example 1.

[0014] The radiation source estimation device includes a radiation detector 1 that measures the energy spectrum of radiation emitted from the measurement object, a signal processing unit 2, a position measurement unit 3 that measures the position information of the radiation detector 1 and the measurement object, a physical property measurement unit 4 that measures the surface properties and thickness of the measurement object, a measurement value DB 5 that is a database of measurement values, a physical property DB 6 that is a database of various physical property values, a data matching unit 7, a physical property data input unit 8, a response function creation unit 9, and a distribution estimation unit 10. The radiation source estimation device may further include a display unit (not shown) as an interface for outputting the distribution estimation result and inputting physical property data. Further, the radiation source estimation device may further include a moving mechanism (not shown) for moving the radiation detector 1 and the physical property measurement unit 4 respectively. Further, the radiation detector 1 may further include a shielding structure (not shown) for shielding radiation that becomes noise from outside the measurement target area.

[0015] In the radiation source estimation device, the radiation detector 1 detects radiation at a plurality of positions with respect to the measurement object. The detected output signal is signal-processed by the signal processing unit 2 to obtain an energy spectrum, which is stored in the measurement value DB 5.

[0016] The position measurement unit 3 measures the position information of the radiation detector 1 and the measurement object. Also, the position where the radiation detector 1 measures radiation is measured and stored in the measurement value DB 5.

[0017] The physical property measurement unit 4 measures the surface properties and thickness (depth information) of the measurement object. The surface properties are, for example, as surface information, color, shape, magnetic properties, thermal properties, constituent elements, etc. In the thickness information, as depth information, depth, shape, etc. These are measured and stored in the measurement value DB 5.

[0018] In the physical property DB 6, various physical property values of constituent members that are assumed to constitute the measurement object in advance are stored.

[0019] The data matching unit 7 matches the surface information and depth information, which are the information measured by the physical property measurement unit 4, with the physical property data stored in the physical property DB 6.

[0020] Figure 2 is a conceptual diagram showing the relationship between the detector according to Example 1 and the measurement object. It shows the positional relationship between the radiation detector 1 of the radiation source estimation device and the measurement object. In the response function creation unit 9, as shown in Figure 2, a virtual region is created by geometrically dividing the measurement object into elements (meshes) having a very small volume from the position information of the measurement object and the radiation detector 1. The shape of the mesh shown in Figure 2 is a cube, but the mesh shape in this method may be any shape.

[0021] Based on the result collated by the data collation unit 7 and the position information measured by the position measurement unit 3, the physical property data input unit 8 assigns physical property values to the meshes created by the response function creation unit 9. The response function creation unit 9 creates a response function considering the distance from each mesh of the measurement object to the detector and the shielding effect of the structures on the path. From the information measured by the physical property measurement unit 4, the physical property data collated by the data collation unit 7 is assigned to the corresponding mesh.

[0022] The distribution estimation unit 10 can estimate the radiation source by solving an inverse problem from the response function and the energy spectrum measured by the radiation detector 1.

[0023] The radiation detector 1 detects the radiation emitted from the measurement object. The radiation includes alpha rays, beta rays, gamma rays, neutrons, etc. In this example, the configuration for detecting gamma rays will be described, but it is not limited to this.

[0024] The means for the radiation detector 1 to detect gamma rays may be composed of, for example, a scintillator and a photoelectric converter that converts the light emitted from the scintillator into an electronic signal. As the scintillator, for example, LaBr3, GSO, LYSO, BGO, etc. may be used, or a radiation-emitting element with a different composition may be used. As the photoelectric converter, for example, a photomultiplier tube, a photodiode, etc. can be used. Also, instead of a scintillator, a semiconductor detector such as Ge, CdTe, or CZT may be used. In this case, the radiation detector 1 uses a preamplifier instead of a photoelectric converter.

[0025] Gamma rays interact with the sensitive part of the radiation detector 1, transferring all or part of the radiation's energy to the sensitive part of the radiation detector 1. As a result, the radiation detector 1 outputs a voltage pulse with a height proportional to the energy transferred to the sensitive part. The voltage pulse is amplified and its pulse height is analyzed by the signal processing unit 2, and the energy spectrum is stored in the measured value DB5.

[0026] The radiation detector 1 may consist of a single detection element, or it may consist of multiple detection elements arranged in an array. If the radiation detector 1 consists of a single detection element, the measurement point relative to the object to be measured is measured by the position measurement unit 3 and stored in the measurement value DB5. If there are multiple detection elements, the position and energy spectrum of each detection element are stored in the measurement value DB5.

[0027] The position measuring unit 3 measures the measurements of the radiation detector 1 and the physical property measuring unit 4 (described later) on the object to be measured. The means by which the position measuring unit 3 measures the measurement position may be, for example, calculated from shape data measured by a position measuring device such as an encoder or GPS, or by an externally mounted optical camera or laser measuring instrument. The means for measuring the measurement position is not limited to this, and any configuration that can measure the measurement points of the radiation detector 1 and the physical property measuring unit 4 on the object to be measured is acceptable.

[0028] The physical property measurement unit 4 consists of either a surface information measurement unit 4a that measures surface information, or a deep information measurement unit 4b that acquires deep information, or a combination thereof.

[0029] The surface information measurement unit 4a measures surface information of the object to be measured as seen from the physical property measurement unit 4 (color, shape, optical image, point cloud data, particle size, magnetic properties, thermal properties, constituent elements, etc.). At least one of the optical image, point cloud data, magnetic properties, and thermal properties is measured. Means for measuring color as surface information include, for example, an optical camera. Means for measuring shape and particle size include, for example, a laser, stereo camera, or infrared camera. Means for measuring magnetic properties include, for example, eddy current measurement using a coil. Means for measuring thermal properties include, for example, thermography or thermocouples. Means for measuring constituent elements include, for example, laser-induced breakdown spectroscopy. Furthermore, as a means of directly acquiring surface information, sampling of the surface to be measured is performed. In this case, for example, a sampling jig attached to the tip of an arm of a remote-controlled robot can be used.

[0030] The deep information measurement unit 4b measures at least one of the following information about the object being measured in the depth direction: depth (thickness), shape of the sediment, sound velocity (speed of sound propagation), particle size, and constituent elements. Examples of means for measuring depth, shape, and sound velocity include ultrasonic measurement. Ultrasonic measurement may be configured with a single element for transmission and reception, or with multiple elements. Geometric information in the depth direction of the constituent materials can be obtained by receiving ultrasonic waves reflected at points with different acoustic impedances along the ultrasonic wave propagation path.

[0031] The surface information and depth information measured by the physical property measurement unit 4 are stored in the measurement value DB 5 along with the position information measured by the position measurement unit 3.

[0032] The Physical Properties DB6 stores and stores the expected physical properties and characteristics of the object to be measured. Even if the physical properties of the object to be measured are unknown, it stores the expected physical properties. Examples of physical properties and characteristics include color, shape, particle size, magnetic properties, thermal properties, constituent elements, sound velocity (speed of sound propagation), and density. The physical properties may be general values, or they may be constructed and calculated from simulation data that constitutes the object to be measured, or they may be derived from tests using a simulated object.

[0033] The physical properties database 6 may include a physical properties database update unit (not shown) for updating pre-stored physical properties. The means for updating physical properties may include, for example, adopting measurement results of surface and depth information measured by the physical properties measurement unit as newly acquired physical properties. Furthermore, if physical properties are calculated from a simulation rayon, the results obtained by inputting surface or depth information measured by the physical properties measurement unit into the simulation conditions may be adopted as physical properties. By including a physical properties database update unit, physical properties can be updated and corrected, leading to improved accuracy.

[0034] The data matching unit 7 compares the physical property information measured in the measurement value DB5 with the physical property information stored in the physical property DB6 and determines the physical property value for each region of the object being measured. The method for matching the physical property data may, for example, be to calculate the similarity of multiple physical property values, or it may be determined only from the physical property values ​​of representative features.

[0035] The physical property data input unit 8 assigns physical property values ​​to each mesh in the mesh formed by the object to be measured. The physical property values ​​to be assigned are, for example, the constituent elements and density.

[0036] Next, an example of a means for assigning physical properties to a mesh will be described. Figure 3 is a conceptual diagram showing the process for creating a response function from surface information and depth information of a measurement target according to Example 1. Surface information and depth information are assigned to the meshed region of the measurement target. For the region 31 on the xy plane to which the measured surface information corresponds, a mesh region 32 in the z direction with the same physical properties as region 31 is identified from the depth information, and physical properties are assigned to it. By doing this for the entire area of ​​the measurement target, physical properties are assigned to all mesh regions of the measurement target. By assigning assumed physical properties in this way, the radiation source distribution of a measurement target whose physical properties are unknown and whose access is limited can be estimated with high accuracy.

[0037] The response function creation unit 9 uses geometric information from each mesh of the object to be measured, to which physical property values ​​have been assigned by the physical property data input unit 8, to calculate the contribution of radiation from each mesh to the radiation detector 1. The means for calculating the contribution includes, for example, assigning constituent elements and density as physical property values, and calculating the path from each mesh to the radiation detector 1. This path is calculated by determining the distance to other meshes traversed when a straight line is drawn from any mesh to the radiation detector 1. The gamma ray attenuation effect is calculated from the constituent elements, density, and distance of the radiation passing through each path. By calculating the attenuation effect from all meshes to the radiation detector 1 and summing them to 1, the relative contribution ratio of gamma rays reaching the radiation detector from each mesh can be calculated. This calculation is performed for all measurement positions of the radiation detector 1 to obtain the response matrix.

[0038] The distribution estimation unit 10 estimates the distribution of radiation generated in each mesh by solving an inverse problem using the response function created by the response function creation unit 9 and the energy spectrum measured by the radiation detector 1.

[0039] The data matching unit 7, physical property data input unit 8, response function creation unit 9, and distribution estimation unit 10 each have a calculation unit, which can be configured by a computer equipped with a processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit) and memory.

[0040] The CPU implements the functions of the arithmetic unit through software by reading and executing computer programs stored in memory. The arithmetic unit may implement some or all of its functions through hardware. For example, the arithmetic unit may be configured using a custom IC such as an ASIC (Application Specific Integrated Circuit) or a programmable IC such as an FPGA (Field Programmable Gate Array), and the circuit design may be carried out to implement its functions.

[0041] Figure 4 is a flowchart of the process for estimating the radiation source distribution according to Example 1. It shows the process for estimating the radiation source. At the start, the energy spectrum detected by the radiation detector 1 and the surface information and depth information measured by the physical property measurement unit 4 are stored in the measurement value DB 5.

[0042] The measurement range of the object to be measured is divided (meshed) into arbitrary minute regions (S41). The surface information and depth information stored in the measurement value DB5 and the physical property values ​​stored in the physical property DB6 are compared in the data matching unit 7 to determine the physical property values ​​(S42). The physical property values ​​matched from the surface information on the xy plane are assigned to the mesh in the depth direction using the depth information (S43). The path from each mesh to the radiation detector 1 is calculated, the contribution ratio from each mesh is calculated, and a response function is created for each measurement position (S44). The distribution within the object to be measured is inversely estimated from the energy spectrum and response function for each measurement point of the radiation detector 1 (S45).

[0043] Specifically, by measuring the energy spectrum of radiation emitted from the object to be measured with the radiation detector 1, acquiring the position information of the radiation detector 1 and the object to be measured, acquiring the surface properties and depth information of the object to be measured, comparing the assumed physical property data of the object to be measured with the surface properties and depth information, creating a response function from the physical property data compared with the position information, and estimating the intensity of the radiation source based on the detection result of the energy spectrum of the radiation, it is possible to accurately estimate the source distribution of an object to be measured whose physical properties are unknown and access is limited.

[0044] Thus, the radiation source estimation device according to this embodiment can provide a radiation source estimation device and radiation source estimation method that can accurately estimate the radiation source distribution of an object to be measured whose physical properties are unknown and whose access is limited. Furthermore, according to this embodiment, the radiation source distribution of a radiation source whose physical properties (composition, density, shape) of the object to be measured are unknown can be estimated with high accuracy. [Examples]

[0045] Example 2 will be explained using Figure 5. In the following examples, including this one, the differences from Example 1 will be described in particular. In Example 2, a method for estimating the radiation source using an energy spectrum with multiple energy peaks obtained by the radiation detector 1 will be explained.

[0046] Figure 5 shows an example of an energy spectrum obtained by the detector according to Example 2. It shows an energy spectrum with multiple energy peaks (E1, E2, E3) obtained by radiation detector 1. The energy of the gamma rays is determined by the emitted radioactive nuclide. The height of the energy peaks and the shape of the Compton continuum in the energy spectrum are determined by the characteristics of the detector and the position and shape of the radioactive material. Therefore, the count value of the energy peak of a particular radioactive nuclide is determined by the amount of that radioactive nuclide present and the attenuation effect due to the path from its position to the radiation detector.

[0047] When the same species emits multiple energy peaks E1, E2, and E3, the degree of attenuation is smaller at higher energies and larger at lower energies. Therefore, the depth can be estimated from the ratio of the count values ​​of energy peaks E1, E2, and E3.

[0048] The response function creation unit 9 may also include a physical property shape estimation unit. The physical property shape estimation unit can create a response function for each of the multiple energy bands of radiation and determine the layer density from the attenuation of multiple energy peaks from the same nuclide.

[0049] By using the response function created in the response function creation unit 9, and the response function for each energy peak calculated to show the attenuation effect at multiple energies, along with the count value for each energy peak, inverse estimation becomes possible for the same nuclide that emits multiple gamma-ray energies. [Examples]

[0050] Example 3 will be explained using Figure 6. Figure 6 shows an example of measuring the energy spectrum of the object to be measured according to Example 3 using a detector from multiple angles.

[0051] The radiation detector 1 has a sensitivity characteristic in the angular direction relative to the object being measured. Although not shown, a shielding body that limits the field of view of the detector may also be used to create a sensitivity distribution in the angular direction. In this embodiment, measurements are taken at multiple inclinations such that the radiation detector 1 includes the same location on the object being measured. Figure 6 shows an example where the central axis 1a, which is the orientation of the radiation detector 1, is tilted at angles +θ and -θ, and measurements are taken at three inclinations. A response function is created by the response function creation unit 9 from the geometric information of the radiation detector and the object being measured at each inclination, as well as the angular characteristics of the detector. The angular sensitivity characteristic of the radiation detector 1 is determined in advance. Subsequently, the source position can be estimated using the method shown in Example 1.

[0052] In this embodiment, measurements are taken at the same location on the target object by changing the angle of the field of view of the radiation detector 1, and a response function is created for each angle to estimate the distribution in the depth direction. By measuring the same location from multiple angles, the estimation accuracy for overlapping fields of view can be improved, or the number of measurement points can be reduced.

[0053] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0054] 1...Radiation detector, 2...Signal processing unit, 3...Position measurement unit, 4...Physical property measurement unit, 5...Measurement value DB, 6...Physical property DB, 7...Data matching unit, 8...Physical property data input unit, 9...Response function creation unit, 10...Distribution estimation unit, 21...Mesh, 31...Region on the xy plane, 32...Region in the z direction.

Claims

1. A radiation detector that measures the energy spectrum of radiation emitted from an object being measured, The aforementioned radiation detector and a position measuring unit that measures the position information of the object to be measured, A physical property measurement unit that measures the surface properties and depth information of the object to be measured, A data matching unit compares the assumed physical property data of the object to be measured with the information measured by the physical property measurement unit, A response function creation unit that inputs the physical property data matched with the position information and creates a response function, The system includes a distribution estimation unit that estimates the intensity of the radiation source based on the detection results of the radiation detector, The radiation source estimation device is characterized in that the response function creation unit meshes the inside of the object to be measured, and assigns the physical property data, which has been matched by the data matching unit, to the corresponding mesh based on the information measured by the physical property measurement unit.

2. In the radiation source estimation device according to claim 1, A radiation source estimation device characterized by having a physical properties database that stores the physical properties data of the assumed object to be measured.

3. In the radiation source estimation device according to claim 2, The radiation source estimation device is characterized in that the aforementioned physical property database includes a physical property database update unit that updates the physical property data using measurement results.

4. In the radiation source estimation device according to claim 2, The radiation source estimation device is characterized in that the aforementioned physical property database is composed of simulation data constituting the object to be measured.

5. In the radiation source estimation device according to claim 1, The radiation source estimation device is characterized in that the material property measurement unit comprises a surface information measurement unit that measures at least one of optical images, point cloud data, magnetic properties, and thermal properties.

6. In the radiation source estimation device according to claim 1, The radiation source estimation device is characterized in that the physical property measurement unit comprises a deep information measurement unit that measures at least one of the shape, thickness, sound velocity, particle size, and constituent elements of the sediment of the object to be measured.

7. In the radiation source estimation device according to claim 1, The radiation source estimation device is characterized in that the response function creation unit creates the response function for each of the multiple energy bands of the radiation and includes a physical property shape estimation unit that determines the density of the layer from the decay amounts of multiple energy peaks from the same nuclide.

8. In the radiation source estimation device according to claim 1, A radiation source estimation device characterized by measuring the same location on the object to be measured by changing the angle of the field of view of the radiation detector, creating the response function for each angle, and estimating the distribution in the depth direction.

9. The energy spectrum of radiation emitted from the object being measured is measured using a radiation detector. The positional information of the radiation detector and the object to be measured is acquired, The surface properties and depth information of the object to be measured are acquired, The physical property data of the object to be measured is compared with the surface properties and the depth information. A response function is created from the physical property data compared with the position information. A radiation source estimation method characterized by estimating the intensity of a radiation source based on the detection results of the energy spectrum of the aforementioned radiation.

10. In the source estimation method according to claim 9, A radiation source estimation method characterized by creating the response function by meshing the interior of the object to be measured, and assigning the physical property data, matched to the corresponding mesh, from the surface properties and depth information of the object to be measured.

11. In the source estimation method according to claim 9, A radiation source estimation method characterized by creating the response function for each of the multiple energy bands of the radiation, and determining the density of the layer from the decay rate of multiple energy peaks from the same nuclide.

12. In the source estimation method according to claim 9, A radiation source estimation method characterized by measuring the same location on the object to be measured by changing the angle of the field of view of the radiation detector, creating the response function for each angle, and estimating the distribution in the depth direction.

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