JP2014215145A - Photon detection device and radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photon detection device and a radiation measuring device attaining miniaturization and capable of improving a spatial resolution further than before.SOLUTION: A photon which hits a photon absorption film 6 among photons generated inside a scintillator 5 is absorbed into the photon absorption film 6. The photon which transmits from a pin hole 7 is detected by a SPAD 17 located in a direction to which the photon flies, and therefore, the photon does not repeat reflection inside the scintillator 5, and by that much, an analysis for estimating a location where the photon is generated becomes easier than before, and a space resolution can be improved. Further, the photon having transmitted from the pin hole 7 is detected by a plurality of SPADs 17, and the location where the photon is generated can be estimated based on a distribution state of the presence or absence of a detection of the photon by each SPAD 17. Therefore, a plurality of types of scintillators 5 having different characteristics or a photo multiplier for multiplying photons can be dispensed with, thus attaining simplified device structure and miniaturization of the device.

Description

  The present invention relates to a photon detection device and a radiation measurement device equipped with the photon detection device, and is suitable for application to, for example, specifying an electron trajectory generated when a γ-ray enters a scintillator.

  In recent years, as a radiation detection device that detects the direction of γ-ray arrival, for example, there is a radiation detection device in which three types of scintillators having a fan shape with a central angle of 120 degrees and different characteristics are housed in a cylindrical container separated by a metal plate. It is known (for example, refer nonpatent literature 1). In such a radiation detection apparatus, a photomultiplier tube is provided at the end of a cylindrical container, and light emitted when gamma rays are incident on each scintillator is converted into electrons by a photoelectric effect by the photomultiplier tube. Thus, the electrons can be amplified. The radiation detection device identifies the scintillator side from which the γ-rays come from by comparing the amount of electrons that change for each scintillator, with the measurement value of the light emitted by each of the divided scintillators changing according to the direction of γ-ray flight. It is made to be able to do.

  However, in such a radiation detection apparatus, it is necessary to use three types of scintillators having different characteristics and to provide a photomultiplier tube for amplifying electrons. There was a problem that.

  Therefore, development of a radiation detection apparatus that is downsized while maintaining the sensitivity of γ rays is desired. For example, a radiation detection apparatus as shown in Non-Patent Document 2 is considered. This radiation detection apparatus has a 1.6 × 16 × 16 microscopic scintillator made of LGSO (lutetium gadolinium silicate) single crystal or LYSO (lutetium yttrium silicate) single crystal, for example, fixed by an optical adhesive. A [mm] square scintillator block is provided, and semiconductor light-receiving elements are bonded to all six surfaces of the scintillator block.

  The semiconductor light receiving element provided on the surface of the scintillator block is provided with a light receiving portion at a predetermined interval, a reflective material is provided in the gap between the light receiving portions, and light emitted from the scintillator block is reflected by the reflective material. The light is prevented from leaking out of the scintillator block. Thus, in the semiconductor light receiving element, even if it is weak light emitted in the scintillator block, the light is reflected in the scintillator block without leaking from the gap between the light receiving parts by the reflecting material, and the light is received in the light receiving part. Therefore, it is possible to reliably receive light.

  Thereby, in the radiation detection apparatus, when radiation is incident on the scintillator block, the positions where photons are generated in the scintillator block are detected in all of the vertical direction, the horizontal direction, and the thickness direction, and these detections are obtained. By analyzing the results, it is possible to estimate the direction in which γ rays come.

“Succeeded in developing a gamma-ray detector that understands the direction and energy of incoming radiation” [Online], July 16, 2008, Japan Science and Technology Agency, Vol. 539 (searched April 19, 2013), Internet <URL : Http://www.jst.go.jp/pr/info/info539/ ＞ “Development of three-dimensional radiation detectors to achieve PET resolution approaching theoretical limits” [Online], October 5, 2011, National Institute of Radiological Sciences (searched April 19, 2013), Internet <URL: http://www.nirs.go.jp/news/press/2011/10_05.shtml>

  However, in the radiation detection apparatus using such a scintillator block, since the reflective material is provided in the gap between the light receiving parts, the light generated in the scintillator block repeatedly reflects in the scintillator block, Therefore, the analysis for estimating the position where the photon is generated becomes complicated, and the spatial resolution may be lowered.

  Therefore, the present invention has been made in consideration of the above points, and an object of the present invention is to propose a photon detection device and a radiation measurement device capable of reducing the size and improving the spatial resolution as compared with the prior art.

  The photon detection device according to claim 1 of the present invention is a polyhedral scintillator that generates photons upon incidence of radiation, and a plurality of pinholes that are attached to each surface of the scintillator and formed in an array. A photon absorption film for exposing the scintillator to the outside, and a plurality of light receiving portions arranged in an array, the photon absorption film being arranged to face each surface of the scintillator with the photon absorption film interposed therebetween, and the pin And a photon detection element capable of detecting the photons transmitted through the holes by the light receiving portions.

  Moreover, the radiation measuring apparatus of Claim 5 of this invention is connected to the photon detection apparatus of any one of Claims 1-4, and the said photon detection apparatus, The detection of the said photon in each said light-receiving part A signal processing unit that receives detection result data indicating presence / absence from the photon detection device, the signal processing unit identifies each position in the scintillator by three-dimensional coordinates, and emits a predetermined number of photons from one coordinate Assuming that the light receiving unit has detected the probability of detecting photons by the probability distribution, a probability distribution data table obtained from all coordinates is stored in advance, and the radiation is transmitted to the scintillator. When the detection result data is received from all the light receiving units, the probability distributions corresponding to the light receiving units that have detected the photons are all added for each database. An estimated probability distribution is calculated for each database.

  According to the present invention, among the photons generated in the scintillator, the photons that hit the photon absorption film are absorbed by the photon absorption film, and the photons that have passed through the pinhole are detected by the light receiving unit in the flying direction. Thus, the photon does not repeatedly reflect, and accordingly, the analysis for estimating the position where the photon is generated becomes easier than before, and the spatial resolution can be improved. In addition, since the photons transmitted from the pinhole can be detected by a plurality of light receiving units, and the position where the photons are generated can be estimated based on the distribution state of the photon detection in each light receiving unit. Since a plurality of types of scintillators having different characteristics and photomultiplier tubes for amplifying electrons are not required, the apparatus configuration can be simplified and the size can be reduced.

It is the schematic which shows the structure of the radiation measuring device by this invention. It is the schematic which shows the structure of a photon detection apparatus. It is the schematic where it uses for description of the phenomenon when a gamma ray injects into a photon detection apparatus. It is the schematic which shows the mode of the movement of the photon emitted from the certain light source in a scintillator. It is the schematic where it uses for description of the Monte Carlo method. It is the schematic where it uses for description of the reflection in a boundary surface, and permeation | transmission. It is a flowchart which shows a database production | generation process procedure. It is the schematic which shows the structure of photodetection data, and the structure of a probability distribution data table, and the schematic where it uses for description of the calculation method of estimated probability distribution. It is a flowchart which shows the light source estimation processing procedure. It is the schematic which shows the mode of a light source position estimation image. It is the schematic where it uses for description of an estimation electronic locus. It is a graph which shows the database in a light source (5,5,5). It is a graph which shows the database in a light source (1,1,1). It is the table | surface which showed the various design conditions at the time of simulating changing the number of pinholes. It is a graph which shows error distribution when changing the number of pinholes. It is a graph which shows an error rate when changing the number of pinholes. It is a graph which shows the relationship between spatial resolution and the number of pinholes. It is the table | surface which showed various design conditions at the time of simulating changing the total area of a pinhole. It is a graph which shows error distribution when changing the total area of a pinhole. It is a graph which shows an error rate when changing the total area of a pinhole. It is a graph which shows the relationship between a spatial resolution and the total area of a pinhole. It is a table | surface which shows the various design conditions at the time of performing a simulation by changing the design conditions of SPAD. It is a graph which shows error distribution when changing the design conditions of SPAD. It is a graph which shows an error rate when the design conditions of SPAD are changed. It is a graph which shows the relationship between the spatial resolution and the center distance of SPAD.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Radiation Measurement Device In FIG. 1, reference numeral 1 denotes a radiation measurement device, which is composed of a photon detection device 2 and a signal processing unit 3, and γ rays are incident on the photon detection device 2. The generated photons are detected by the photon detection device 2, and based on the detection results, the signal processing unit 3 can estimate the electron trajectory (line light source) due to the γ rays generated by the photon detection device 2, and the arrival of γ rays. The direction can also be estimated.

In the case of this embodiment, the photon detection device 2 includes a scintillator 5 made of CaF ₂ (Eu) formed in a hexahedral shape, and when γ rays are incident on the scintillator 5, Gamma rays can cause Compton scattering and emit photons. Although all six surfaces of the scintillator 5 are covered with a photon absorption film 6 such as a multi-coat material, γ rays flying from the outside can pass through the photon absorption film 6 and enter the inside.

  Here, the photon absorption film 6 is attached to the outer surface so as not to form a gap with the surface of the scintillator 5, and is formed so as to cover the entire scintillator 5. The photon absorption film 6 absorbs photons generated in the scintillator 5 when it hits the wall surface, and suppresses photon reflection at the photon absorption film 6 and transmission of photons from the photon absorption film 6. Has been made to get.

In addition, in the photon absorption film 6, a plurality of pinholes 7 penetrating through the thickness of the wall portion are formed in an array (a state where they are arranged at equal intervals in the vertical and horizontal directions). The scintillator 5 is exposed to the outside. As a result, some of the photons generated in the scintillator 5 are transmitted (passed) through the pinhole 7 of the photon absorption film 6, and SPAD (single-photon) arranged opposite to the photon absorption film 6.
avalanche diode) can be detected by SPAD of array element 9 (not shown in FIG. 1).

  In practice, in this photon detection device 2, plate-like SPAD array elements 9 are arranged opposite to each other on the six surfaces (each surface) of the scintillator 5 with a predetermined distance. The surface of the SPAD array element 9 is formed in a quadrilateral shape, and each side is selected to be approximately the same as the length of the side of the scintillator, for example. SPAD array element 9 as a light detection element has a configuration in which SPAD is arranged in an array on the surface opposed to scintillator 5, for example, rod-like support portions 11 provided at four corners of photon absorption film 6 Can be fixed at the four corners. As a result, the SPAD array element 9 can be disposed so that the surface on which the SPAD is provided faces the plane of the photon absorption film 6 with a predetermined distance from the support 11 so as to be parallel to the plane.

  Each SPAD array element 9 is electrically connected to the signal processing unit 3 through a wiring, and can detect whether or not a photon detected by each SPAD is sent to the signal processing unit 3 as detection result data. Yes. When the signal processing unit 3 acquires detection result data from all SPADs obtained from all the SPAD array elements 9, the signal processing unit 3 can collectively store these detection result data as light detection data.

  Here, the signal processing unit 3 includes a calculation unit 14 that executes a light source estimation process, which will be described later, and the calculation result obtained by the calculation unit 14 is displayed on the display unit 15 and visually displayed to the user. It is designed to be notified. Actually, the calculation unit 14 stores a probability distribution data table generated in advance according to the database generation process described later, and compares the photodetection data obtained from the photon detection device 2 with the probability distribution data table to generate photons. It is possible to estimate at which position in the scintillator 5 the electron trajectory is made, and to calculate the flying direction of γ rays incident on the scintillator 5 using the estimated electronic trajectory obtained thereby. .

  Here, the calculation unit 14 sets one vertex of the eight vertices of the scintillator 5 as the origin O, and the longitudinal direction z, the lateral direction y, and the thickness that are orthogonal to each other along the side of the scintillator 5 around the origin O. Each position in the scintillator 5 can be specified by three-dimensional coordinates in the direction x. As a result, the calculation unit 14 can identify the position in the scintillator 5 where the electronic locus is located using the coordinates. The display unit 15 displays information indicating the position of the estimated electronic locus calculated by the calculation unit 14, information indicating the estimated flying direction of the γ-ray (for example, a Compton cone described later in FIG. 3), for example, the scintillator 5 It can be displayed superimposed on the simulated three-dimensional stereoscopic image and recognized by the user.

  Next, the detailed configuration of the photon detection device 2 will be described with reference to FIG. In the case of this embodiment, as shown in FIG. 2, the scintillator 5 is formed in, for example, a cubic shape having a side H of 10 [mm], and a total of 4 × 4 by photon absorption films 6 on each surface. Sixteen circular pinholes 7 are formed at equal intervals. For example, the pinholes 7 all have the same shape and the same dimensions, the diameter D1, the center-to-center distance W1 between adjacent pinholes 7, and the total area of all the pinholes 7 in one area ER1 The position of the light source in the scintillator 5 can be estimated more accurately by appropriately adjusting the number of pinholes 7 in the region L1 in which the pinholes 7 are arranged in a row between opposing sides on one surface.

  In this embodiment, the case where all the pinholes 7 are formed with the same shape and the same dimensions has been described.However, the present invention is not limited to this, and for example, a plurality of pins positioned around the central portion on one surface of the scintillator 5 are used. A pinhole is formed in a small diameter, a plurality of pinholes arranged so as to surround the small diameter pinhole are formed in a large diameter, a pinhole group around the center portion on one surface of the scintillator 5, and a pinhole in the vicinity of the side The diameter may be different for each group.

  Further, in this embodiment, the center-to-center distance W1 of all the pinholes 7 is selected at equal intervals, but the present invention is not limited to this, and the pinholes in the vicinity of the center part and in the vicinity of the side are not limited to this. The degree of congestion may be changed. For example, the distance W1 between the centers of the pinholes 7 increases in the one surface of the scintillator 5 from the center to the side, and the pinhole group around the center of one surface of the scintillator 5 is more than the pinhole group near the side. May also be crowded.

  The SPAD array element 9 is selected so that the distance W between the photon absorption film 6 is, for example, 1 [mm] or more and is separated from the photon absorption film 6 in which the pinhole 7 is formed by a predetermined distance W, thereby transmitting the pinhole 7. Thus, a photon from a light source emitted at a predetermined angle can be detected by SPAD 17 in the direction in which the photon flew. The SPAD array element 9 has a plurality of circular SPADs 17 arranged at equal intervals, for example, on the surface opposed to the scintillator 5, and the diameter D2 of the SPAD 17 and the center-to-center distance W2 between the adjacent SPAD 17 The scintillator 5 can be adjusted by appropriately adjusting the number of SPADs 17 in a region L2 in which SPADs 17 are arranged in a row between opposing sides on one side (only a part of the region between the sides is omitted in FIG. 2). Photons emitted through the pinhole 7 from the inside can be detected by the SPAD 17 in the direction in which the photons flew. Note that a region ER2 in FIG. 2 is an enlargement of a partial region of the SPAD array element 9.

  Next, focusing on the two pinholes 7 of the photon absorption film 6 as shown in FIG. 3, the phenomenon that occurs when the γ-ray Gr enters the scintillator 5 will be described below. In FIG. 3, for convenience of explanation, two pinholes 7 are provided in the photon absorption film 6 and the front photon absorption film 6 is omitted. Here, γ rays Gr are incident on the scintillator 5 through the photon absorption film 6 from the incident point P 1 ′ on the surface of the scintillator 5. Thus, in the scintillator 5, Compton scattering occurs with a certain probability at the scattering point P2 ′, a part of the energy of the γ-ray Gr is given to the electrons, and γ-ray SGr scattered in a predetermined direction from the scattering point P2 ′ is generated. And can then be absorbed. On the other hand, the electrons that have obtained energy travel in the scintillator 5 while emitting light (scintillation light), and an electronic locus ET1 is generated in which the traveled portion appears to shine like a locus.

  At this time, the radiation measuring apparatus 1 estimates the electron locus ET1 generated in the scintillator 5 based on the light detection data obtained from the photon detector 2 by the signal processing unit 3, and the length (scattering) of the electron locus ET. It is the distance from the point P2 ′ until the electron stops, which is also called the range). As a result, the radiation measuring apparatus 1 can obtain the energy given to the electrons by the γ-ray Gr from a well-known equation that is generally given as an empirical equation of the range, and the obtained energy and general Compton scattering can be obtained. Therefore, it can be estimated that the source position of the γ-ray Gr is within the Compton cone (conical surface) of the arrival angle 2θ ′. In the radiation measuring apparatus 1, the radiation source position can be specified more accurately by calculating and overlapping a plurality of such Compton cones.

  For the empirical equation of the range used when obtaining the energy given to the electrons by the γ-ray Gr and the relational equation of Compton scattering for obtaining the angle of arrival 2θ ′ using the obtained energy, see “Shinichi Sasaki Radiation Measurement Fundamentals”. High energy accelerator research organization Radiation Science Center (Internet: URL http://accwww2.kek.jp/oho/OHOtxt/OHO-2011/7_oho11_sasaki_20110822.pdf) To do.

  Here, the light generated in the scintillator 5 is determined by the number of photons emitted by the scintillator 5 and the energy of the γ-ray Gr. It is thought that photons are emitted randomly from the light source in the scintillator 5 in all directions. At this time, some photons pass through, for example, two pinholes 7 and are ahead of the SPAD array element. 9 SPAD 17 (not shown in FIG. 3) can be detected.

  When the SPAD array element 9 detects one photon at the SPAD 17, it causes a breakdown at the SPAD 17, and by measuring the pulse voltage at that time, the SPAD 17 that has detected the photon can be identified among the plurality of SPAD 17 . For example, one photon emitted from a position of the electron trajectory ET1 in the scintillator 5 passes through the path SL1 and passes through one pinhole 7, and can be detected by the SPAD 17 of the SPAD array element 9 on the path SL1. Further, the other photons emitted from the same position as described above pass through the path SL2 different from the path SL1 and pass through the other pinhole 7, and can be detected by the SPAD 17 of the SPAD array element 9 on the path SL2.

  In the SPAD array element 9, as shown in FIG. 3, the SPAD 17 for detecting photons differs depending on the location (the position in the electron trajectory ET1) where the photons in the scintillator 5 are emitted. In the present invention, using such a phenomenon, first, it is assumed that there is a light source at one coordinate in the scintillator 5, and which SPAD 17 of the SPAD array element 9 may detect a photon. A database represented by probability distribution for each SPAD 17 is obtained by simulation for every coordinate in the scintillator 5, and this is stored in advance in the signal processing unit 3 (for example, the calculation unit 14) as a probability distribution data table.

(2) Database Generation Processing Here, when generating a database at a certain coordinate P3 ′, as shown in FIG. 4, a predetermined number of photons emitted from the coordinate P3 ′ are traced one by one. For example, the photon of the path SL3 flies toward a certain pinhole 7, passes through the pinhole 7 as it is, and is detected by a predetermined SPAD 17 (not shown in FIG. 4) of the SPAD array element 9. The photons in the path SL4 fly toward the wall surface of the photon absorption film 6 and are absorbed by the photon absorption film 6. In addition, although the photons in the path SL5 fly toward a certain pinhole 7, they are reflected at the interface between the scintillator 5 and the outside air without passing through the pinhole 7, and pass through the other pinhole 7 in the reflection direction. The light is transmitted and detected by a predetermined SPAD 17 of the SPAD array element 9. On the other hand, although the photons in the path SL6 are also reflected in the pinhole 7, they hit the wall surface of the photon absorption film 6 in the reflection direction and are absorbed by the photon absorption film 6.

In performing a simulation for tracking such a photon one by one, photons randomly emitted from a certain coordinate in all directions are simulated using the Monte Carlo method. Generating photons in all directions is equivalent to uniformly distributing photons on the surface of a unit sphere as shown in FIG. Therefore, by determining the variables so that the function representing the minute surface area dS is proportional to the minute surface area dS, the function can be uniformly distributed on the surface of the unit sphere.
Here, when spherical coordinates (1, θ, φ) are set, the minute surface area dS can be expressed by the following equation.

  In this equation, it is expressed as a function of θ, φ, but since the minute surface area dS is proportional to sinθ, if these two variables are used as they are, they will not be distributed uniformly on the sphere surface. Perform variable conversion using.

  As a result, the following equation is obtained, and in the simulation for generating a database with coordinates, photons uniformly distributed on the sphere surface can be randomly generated in all directions by generating random numbers for z and φ.

The generated photons always enter the wall surface of the photon absorption film 6 or the pinhole 7 as shown in FIG. As shown in FIG. 6, reflection and transmission at the interface between the scintillator 5 and air formed in the pinhole 7 are obtained by changing the refractive index of the scintillator 5 made of, for example, CaF ₂ (Eu) to n ₁ (the scintillator 5 is CaF). ₂ (Eu), n ₁ is 1.47), the refractive index of air is n ₂ (1.000), the incident angle θ _i , and the refraction angle θ _t , from Snell's law, n ₁ sinθ _i = n ₂ sinθ _t . In this case, since n ₁ > n ₂ , sin θ _i <sin θ _t holds.

Therefore, when the incident angle θ _i is increased, the refraction angle θ _t reaches 90 degrees at a certain point. Further, when the incident angle θ _i is increased, the above-described equation does not hold due to sin θ _t <1. The critical angle θ _c that is the limit value of the incident angle θ _i can be calculated by the following equation.

Therefore, when the scintillator 5 is formed of CaF ₂ (Eu), if a photon is incident on the pinhole 7 at an angle of 42.9 degrees or more, it is totally reflected, and the photon reflected by the pinhole 7 is the wall surface of the photon absorption film 6. Or enter one of the other pinholes 7. When entering the pinhole 7 again, it is calculated again whether the photon is reflected or transmitted. On the other hand, in this simulation, when the incident angle θ _i is equal to or _smaller than the critical angle θ _c , the photon is reflected or transmitted at the boundary surface of the pinhole 7.

However, when light is incident on the boundary surface, it has properties of S wave and P wave. The S wave is an electromagnetic wave whose electric field component is perpendicular to the incident surface, and the P wave is an electromagnetic wave whose electric field component is parallel to the incident surface. The probability of reflection and transmission is determined by the power reflectance and the power transmittance, and this value is different between the S wave and the P wave. If the power reflectance of the S wave is R _S and the power reflectance of the P wave is R _P , it can be expressed as the following equation.

また、S波のパワー透過率をT_S、P波のパワー透過率をT_Pとすると、下記の式のように表すことができる。

Further, when the power transmittance of the S wave is T _S and the power transmittance of the P wave is T _P , it can be expressed as the following equation.

Therefore, even if the refractive indexes n ₁ and n ₂ are the same value, the light having different S wave and P wave ratios has different reflectance and transmittance. Here, if the ratio including the S wave is P _S and the ratio including the P wave is P _P , the true power reflectance R and the power transmittance T can be expressed as follows.

In this case, P _S + P _P = 1, R + T = 1 holds, and in the simulation when generating the database, the ratio of S wave and P wave is assumed to be 0.5 each. When a database is generated using a certain coordinate as a light source by simulation, whether a photon that hits the pinhole 7 is reflected or transmitted is determined from the calculated power reflectance R and power transmittance T. In the simulation when generating the database, when the power reflectance value is larger than the power transmittance value, photons are reflected by the pinhole 7, while the power transmittance value is larger than the power reflectance value. Is larger, photons pass through the pinhole 7.

  In the simulation for generating a database at a certain coordinate, the position of the light source in the scintillator 5, the position of the pinhole 7 of the photon absorption film 6, and the position of the SPAD 17 arranged in the SPAD array element 9 are specified by the coordinates. In the simulation for generating the database, using the Monte Carlo method described above and the calculation results of the power reflectance R and the power transmittance T, and assuming that the light source is at a predetermined coordinate in the scintillator 5, the SPAD 17 A database can be generated that shows the probability distribution of the probability distribution. Such a database is generated at all coordinates in the scintillator 5, and the databases generated for each coordinate are collectively stored in the calculation unit 14 as a probability distribution data table.

  Next, a database generation processing procedure for generating such a database will be described with reference to the flowchart shown in FIG. In the case of this embodiment, the case where the database generation process is executed by the signal processing unit 3 will be described below. However, the present invention is not limited to this, and the database generation process is executed by another information processing apparatus. A probability distribution data table generated by the apparatus may be stored in the signal processing unit 3.

  In this case, as shown in FIG. 7, the signal processing unit 3 enters from the start step of the routine RT1, and in step SP1, selects one of the coordinates in the scintillator 5 and determines this coordinate as the location of the light source. Then, the process proceeds to the next step SP2.

In step SP2, the signal processing unit 3 generates photons in random directions from the coordinates selected in step SP1 using the Monte Carlo method, and proceeds to the next step SP3. In this simulation, 1.00 × 10 ⁸ photons are generated in one event. First, one photon is generated in a random direction, and the place where the photon hits is calculated in step SP3.

  In step SP4, the signal processing unit 3 determines whether or not the pinhole 7 has a coordinate in the direction in which the photon flies, that is, whether or not the photon strikes the pinhole 7. Here, if a negative result is obtained, this means that there is no coordinate of the pinhole 7 in the direction in which the photon flew, that is, the photon hits the wall surface of the photon absorption film 6 without hitting the pinhole 7. At this time, the signal processing unit 3 proceeds to the next step SP5.

In step SP5, the signal processing unit 3 determines whether or not the number of photons generated in step SP2 has been repeated a specified number of times (1.00 × 10 ⁸ times). That is, in step SP5, 1.00 × 10 ⁸ photons are generated in one event, set as the specified number of times, and it is determined whether the number of photons generated in step SP2 has been repeated the specified number of times.

For example, in the scintillator 5 made of CaF ₂ (Eu), about 1.25 × 10 ⁴ photons are emitted in one event. Therefore, it is necessary to specify the place where the photons hit these plural photons. Therefore, in this database generation process, by executing a simulation with a number of photons (for example, 1.00 × 10 ⁸ ) larger than the number of photons determined by the material of the scintillator 5 (about 1.25 × 10 ⁴ ), photons enter which SPAD17 The probability distribution indicating whether it is easy can be generated more accurately.

  If a negative result is obtained in step SP5, this indicates that photons are not generated in a random direction a predetermined number of times. At this time, the signal processing unit 3 returns to step SP2 again, and the Monte Carlo method is used. Photons are generated in random directions, and the above-described processing is repeated.

On the other hand, if a positive result is obtained in step SP4 described above, this indicates that the coordinates of the pinhole 7 are in the direction in which the photon flew, that is, the photon hits the pinhole 7, and signal processing is performed at this time. Part 3 moves to the next step SP6. In step SP6, the signal processing unit 3 calculates the incident angle θ _{i of} the photon with respect to the pinhole 7, the true power reflectivity R, and the power transmittance T, and the photon is reflected by or transmitted through the pinhole 7. Is stochastically determined, and the process proceeds to the next step SP7.

  In step SP7, the signal processing unit 3 determines whether or not the photon is determined probabilistically to pass through the pinhole 7 in step SP6. If a negative result is obtained here, this means that the photon is reflected without passing through the pinhole 7, and at this time, the signal processing unit 3 returns to step SP3 again to determine the place where the reflected photon hits. The calculation is repeated, and the above process is repeated until a negative result is obtained in step SP4 or a positive result is obtained in step SP7.

  On the other hand, if a positive result is obtained in step SP7, this indicates that the photon has passed through the pinhole 7, and at this time, the signal processing unit 3 proceeds to the next step SP8. In step SP8, the signal processing unit 3 determines whether or not the coordinate of the SPAD 17 of the SPAD array element 9 exists in the direction in which the photon transmitted through the pinhole 7 flies, that is, whether or not the photon hits the SPAD 17.

  Note that photons are refracted when they pass through the pinhole 7, and SPAD 17 is selected to be circular, and if a photon enters somewhere within the circle indicated by coordinates, the photon hits SPAD 17 . Here, if a positive result is obtained in step SP8, this means that the coordinate of SPAD17 is in the direction in which the photon flew, that is, that the photon has hit SPAD17. Move on to step SP9.

  In step SP9, the signal processing unit 3 adds 1 to the number of SPADs hit by photons, and proceeds to the next step SP5. Also, if a negative result is obtained in step SP8 described above, this means that there is no SPAD17 coordinate in the direction in which the photon flew, that is, the photon transmitted through the pinhole 7 did not hit SPAD17, Also at this time, the signal processing unit 3 proceeds to the next step SP5.

  In step SP5, the signal processing unit 3 generates photons in a random direction until the specified number of times is reached, repeats steps SP2 to SP9 described above, and obtains a positive result when the number of generated photons reaches the specified number of times. Move on to step SP10.

In step SP10, the signal processing unit 3 divides all the SPAD17 counts by the specified number of times, and when there is a light source at the coordinates selected in step SP1, a database that indicates the probability that each SPAD17 will hit a photon Is moved to the next step SP11, and the database generation processing procedure is terminated. Here, the probability distribution obtained for each SPAD 17 is normalized by the number of photons (for example, 1.25 × 10 ⁴ ) that is supposed to be generated in one event.

  In this way, the signal processing unit 3 selects all the coordinates in the scintillator 5 as the light source locations, generates a database for each coordinate, and for each of these coordinates, as shown in the middle part of FIG. , M (1 to M indicate simple numbers assigned to the database) are stored as a probability distribution data table T100.

(3) Light Source Estimation Processing In the radiation measurement apparatus 1 according to the present invention, when the probability distribution data table T100 generated in this way is stored in the calculation unit 14, actually γ rays are incident on the photon detection apparatus 2. The electron trajectory ET1 generated in the scintillator 5 by the γ rays can be estimated by executing a light source estimation process described later. In practice, the photon detection device 2 detects photons generated by the incidence of γ-rays in the scintillator 5 by each SPAD 17, and sends detection result data obtained from all SPADs 17 to the calculation unit 14, respectively. Result data can be stored as light detection data in the calculation unit 14.

  The upper part of FIG. 8 shows photodetection data indicating the detection results of photons in each SPAD17 when the total number of SPAD17 of the six SPAD array elements 9 provided in the photon detector 2 is N. Binary digital codes “0” and “1” are associated with bit numbers 1 to N assigned to identify SPAD 17 in accordance with photon detection result data. Here, the light detection data is the same as the SPAD17 in the same position as the SPAD17 assumed in the simulation when the databases 1 to M are generated, but the same bit numbers 1 to N as the bit numbers 1 to N of the SPAD17 of the databases 1 to M Is attached.

  In the case of this embodiment, for example, a SPAD 17 that has detected a photon is assigned a digital code of “1”, and a SPAD 17 that has not detected a photon is assigned a digital code of “0”. In the detection data, no photon is detected in each SPAD 17 of bit numbers 1, 3,..., N−1, and each digital code is “0”. On the other hand, in the bit numbers 2,..., N-2, N, each SPAD 17 detects a photon, and each digital code is “1”.

Then, the signal processing unit 3 can calculate the estimated probability distributions P _{1 to} P _M indicating the possibility of the light source by executing the light source estimation process described later by the calculation unit 14. In this case, the calculation unit 14 pays attention to the SPAD 17 in which the digital code of the light detection data is “1”. For example, in the database 1, the bit number 2 in which the digital code of the light detection data is “1”. .., N-2, N can be calculated as an estimated probability distribution P ₁ obtained by adding all probability distributions P ₁₂ ,..., P _1N-2 , P _1N having the same bit numbers 2 _,.

Further, the calculation unit 14 also applies to the database M of the probability distribution data table T100, for example, the same as the bit numbers 2,..., N-2, N where the digital code of the photodetection data is “1”, as described above. An estimated probability distribution P _M obtained by adding all probability distributions P _M2 ,..., P _MN-2 , P _MN of bit numbers 2 _,. In this way, the calculation unit 14 calculates the estimated probability distributions P _{1 to} P _M for all the databases _{1 to M} in the probability distribution data table T100, and for example, coordinates associated with the databases _{1 to M} are used as the estimated probability distribution P _1. It is possible to visually identify coordinates where a light source may exist by color-coding for each numerical value of ~ P _M and plotting on three-dimensional coordinates.

  Next, such light source estimation processing will be described below with reference to the flowchart shown in FIG. In this case, the calculation unit 14 proceeds from start step RT2 to step SP21, acquires photodetection data indicating the photon detection results in all SPADs 17 of the photon detection device 2, and proceeds to next step SP22.

  In step SP22, the calculation unit 14 refers to the database m (where m is an initial value 1 and 1 ≦ m ≦ M), and proceeds to the next step SP23. In step SP23, the calculation unit 14 determines whether or not the digital code of the bit number n of the light detection data is “1”, that is, whether or not the SPAD 17 of the bit number n has detected a photon. If a positive result is obtained here, this means that the digital code of the bit number n of the photodetection data is “1”, that is, the SPAD 17 of the bit number n is detecting a photon. The time calculating unit 14 proceeds to the next step SP24.

  In step SP24, the calculation unit 14 adds the value of the probability distribution associated with the bit number n in the database m to the sum value (initial value 0) that finally becomes the estimated probability distribution, and proceeds to the next step SP25. . On the other hand, if a negative result is obtained in step SP23 described above, this means that the digital code of bit number n of the photodetection data is “0”, that is, SPAD17 of bit number n has not detected a photon. In this case, the body calculation unit 14 proceeds to the next step SP25.

  In step SP25, the calculation unit 14 determines whether or not all the digital codes having the bit numbers 1 to N of the light detection data have been confirmed. If a negative result is obtained here, this means that all the digital codes of the bit numbers 1 to N of the photodetection data have not been confirmed, and at this time, the calculation unit 14 proceeds to the next step SP26.

  In step SP26, the calculation unit 14 sets n indicating the bit number to n = n + 1, returns to step SP23 again, and determines whether or not the digital code of the next bit number (n + 1) is “1”. Then, the above-described processing is repeated until a positive result is obtained in step SP25 (until all digital codes of bit numbers 1 to N of the photodetection data are confirmed).

  On the other hand, if an affirmative result is obtained in step SP25, this means that all digital codes of bit numbers 1 to N of the photodetection data have been confirmed, that is, of the photodetection data among the bit numbers 1 to N in the database m. This indicates that an estimated probability distribution is calculated by adding up all probability distributions of the same bit number as the bit number having the digital code “1”. At this time, the calculation unit 14 proceeds to the next step SP27.

In step SP27, the calculation unit 14 compares all the databases _{1 to M} with the light detection data to determine whether or not the estimated probability distributions P _{1 to} P _M have been calculated. As a result, if a negative result is obtained, this means that all the databases _{1 to M} are not yet compared with the photodetection data, that is, the estimated probability distributions P _{1 to} P _M are calculated for all the databases _{1 to M.} In this case, the calculation unit 14 proceeds to the next step SP28. In step SP28, the calculation unit 14 sets m = m + 1, returns to step SP22, refers to the next database (m + 1), and repeats the above-described processing until an affirmative result is obtained in step SP27.

On the other hand, if a positive result is obtained in step SP27, this means that all the databases _{1 to M} have been compared with the light detection data, that is, the estimated probability distributions P _{1 to} P _M are calculated for all the databases _{1 to M.} At this time, the calculation unit 14 proceeds to the next step SP29. The estimated probability distributions P _{1 to} P _M generated in this way have higher values as the coordinates of the light source are more likely to exist, and based on these values, the light source in which photons are generated can be estimated.

In step SP29, the calculation unit 14 plots the estimated probability distributions P _{1 to} P _M obtained from the databases _{1 to M} at the coordinates indicated by the databases _{1 to M} , for example, the estimated probability distribution P on three-dimensional coordinates. generates a light source position estimation image data shown in different colors ₁ to P _M, it moves to the next step SP30, and ends the light source estimation processing.

  When the display unit 15 receives the light source position estimation image data generated in this way from the calculation unit 14, the display unit 15 displays a light source position estimation image as shown in FIGS. 10A and 10B based on the light source position estimation image data. Can do. 10A shows the light source position estimation image on the three-dimensional coordinates of the x axis, the y axis, and the z axis, and FIG. 10B shows the y axis at the position of the coordinate 5 of the x axis in FIG. 10A. It is a light source position estimation image on the two-dimensional coordinate of the z axis.

Incidentally, in the case of this embodiment, for example, the calculation unit 14 assumes that the estimated probability distribution having the highest value among the estimated probability distributions P _{1 to} P _M is 1, and adjusts the values of the other estimated probability distributions together. Then, it is possible to generate light source position estimation image data whose density changes as the maximum value 1 is lowered. Thus, the user can recognize the estimated light source position instantaneously from the light / dark difference by visually recognizing the light source position estimated image displayed on the display unit 15.

  For example, in FIG. 10A, a light source position estimation image in which light and shade changes in a spherical shape with a certain coordinate as the center, and the position of the light source can be estimated from the light and shade difference. Further, in FIG. 10B, a light source position estimation image in which the light and shade changes in a circular shape centered on a certain coordinate, and the position of the light source can be estimated from the light and shade difference.

  In the photon detection device 2, considering the speed of light, all photons emitted from each position in time series from the start point to the end point of the electron trajectory ET1 extending linearly as shown in FIG. Detection can be performed by the SPAD 17 at a time, and a plurality of SPAD 17 can be broken down at the same time to generate detection result data indicating whether each SPAD 17 has detected a photon with respect to the electron trajectory ET1.

  Therefore, in the signal processing unit 3, when the light source estimation process described above is executed based on the light detection data obtained from the linear electron trajectory ET1 generated in such a scintillator, an elliptical shape in which the light and shade distribution spreads in an elliptical shape is obtained. A light source position estimation image having a state probability distribution region can be obtained. Next, the signal processing unit 3 uses the calculation unit 14 to obtain the estimated electronic trajectory ET2 from the elliptical probability distribution region ER3 having a high estimated probability distribution value along the central axis. Assuming a straight line passing through the region ER3, a straight line passing through a region with a high estimated probability distribution value is calculated as the estimated electronic locus ET2 by the least square method, and this estimated electronic locus ET2 is estimated as the electron locus ET1 generated in the scintillator 5. Can do.

  Since the signal processing unit 3 can estimate the electron trajectory ET1 in the scintillator 5 as the estimated electronic trajectory ET2 as described above, as described above in “(1) Configuration of the radiation measurement apparatus”, Using the formula given as an empirical formula, the energy given to the electrons by the γ-ray Gr can be obtained from the estimated electron trajectory ET2, and it arrives based on this calculated energy and the general formula for Compton scattering. Since the angle 2θ can also be obtained, it can be estimated that the source position of the γ ray Gr is within the Compton cone (conical surface) of the arrival angle 2θ.

(4) Verification test Next, each side of the scintillator 5 is 10 [mm], the diameter D1 of the pinhole 7 is 25 [μm], the center-to-center distance W1 of the pinhole 7 is 150 [μm], and one row of pins The number of holes is 64, the total area of the pinhole 7 is 0.8 ² x πmm ² , the diameter D2 of SPAD17 is 10 [μm], the center-to-center distance W2 of SPAD is 20 [μm], and one row of SPAD in SPAD array element 9 The number (hereinafter also referred to as the length of the SPAD array) is 500, the distance between the pinhole 7 and the SPAD array element 9 is 1 [mm], and the coordinates of the light source are (5,5,5) or (1,1 , 1) and a simulation was performed to generate a database of coordinates (5,5,5) and (1,1,1).

  Here, the coordinate value of the light source is based on mm, and the origin 0 is set to the apex of the scintillator 5. Accordingly, the coordinates (5, 5, 5) are the center of the scintillator 5, and the coordinates (1, 1, 1) are near the vertex of the scintillator 5. Since the center distance W2 of the SPAD 17 is 20 [μm], 500 × 500 SPAD 17 are provided on one surface. Then, the database of coordinates (5, 5, 5) and (1, 1, 1) was obtained according to the procedure of “(2) Database generation process” described above.

  As a result, a database as shown in FIGS. 12A to 12C was obtained when the light source was arranged at coordinates (5, 5, 5). 12A to 12C, the horizontal axis indicates the bit number of SPAD17, and the vertical axis indicates the numerical value of the probability distribution. FIG. 12C is a graph in which a part of FIG. 12B is enlarged, and FIG. 12B is a graph in which a part of FIG. 12A is enlarged. With the light source (5, 5, 5), as shown in FIGS. 12A to 12C, a database showing a probability distribution with a high probability that a photon enters the SPAD 17 near the center could be generated.

  On the other hand, when the light source was arranged at the coordinates (1,1,1), the databases as shown in FIGS. 13A to 13C were obtained. 13A to 13C, the horizontal axis indicates the bit number of SPAD 17, and the vertical axis indicates the numerical value of the probability distribution. FIG. 13C is a graph obtained by enlarging a part of FIG. 13B, and FIG. 13B is a graph obtained by enlarging a part of FIG. 13A. In the light source (1, 1, 1), as shown in FIGS. 13A to 13C, unlike the light source (5, 5, 5), a database in which one vertex portion has a high probability distribution could be generated.

Next, after performing a simulation to generate a database for all coordinates in the scintillator (hereinafter also referred to as a database generation simulation), a simulation to generate light detection data assuming that γ rays are actually incident on the scintillator Went. However, unlike the database generation simulation, in the simulation for generating the photodetection data composed of the digital code (hereinafter also referred to as the photodetection data generation simulation), the number of photons is transferred to the scintillator 5 composed of CaF ₂ (Eu). There was a 1.25 × 10 ⁴ cells actually generated in one event when the incident without further dividing the number of photons impinging photon number SPAD17, "1 SPAD17 bit number of striking at least once ", And the bit number of SPAD17 that was never hit was set to" 0 ", and photodetection data composed of digital codes" 1 "and" 0 "was generated.

  Here, in both the database generation simulation and the light detection data generation simulation, only the design conditions for the number of pinholes are changed while the design conditions are the same as the simulation conditions obtained for the results of FIGS. 12 and 13 described above. Then, the spatial resolution at that time was examined. However, the total area of the pinhole 7 was made constant. Here, the reason for making the total area of the pinhole 7 constant is that the number of photons determined by one event is skipped in a random direction, so the total area of the pinhole 7 changes to the pinhole 7 This is because if the probability of entering changes and the number of photons entering the pinhole 7 changes, the number of photons entering the SPAD 17 will naturally change.

  As shown in FIG. 14, four patterns of Example 1 to Example 4 having different pinhole number conditions are prepared. Since the total pinhole area is constant here, the diameter D1 of the pinhole 7 and the pinhole The center distance W1 of 7 was also changed. Note that Example 4 has exactly the same conditions as the simulations that obtained the results of FIGS. Then, the database generation simulation and the light detection data generation simulation were performed with the coordinates of the light source as (5, 5, 5) and (1, 1, 1).

  It should be noted that the database is ideally simulated by dividing the coordinates into infinitesimal sizes, but here, the first and second embodiments are 25 [μm], and the third and fourth embodiments are 5 [μm]. ], And compared with a digital code of light detection data.

  Then, using the light detection data obtained by the light detection data generation simulation, the above-described “(3) light source estimation process” was executed to estimate the position of the light source. Next, the estimated position of the light source and the actual position of the light source were compared. The results at this time are shown in FIGS. 15A to 15D and FIGS. 16A to 16D.

  15A to 15D show the distance (error distance) between the actual light source position and the light source position estimated by the light source estimation process (hereinafter also simply referred to as the estimated light source position) on the horizontal axis. The estimated frequency is shown on the vertical axis. Therefore, it can be said that the spatial resolution is better as the distribution is concentrated on the left side. 15A to 15D were compared, it was found that as the number of pinholes increased, the difference between the actual light source position and the estimated light source position gradually decreased.

  16A to 16D show the distance from the actual light source position to the estimated light source position on the horizontal axis and the error rate on the vertical axis. Here, the error rate is the probability that the estimated light source position is away from the actual light source position. Also, if an acceptable error rate is determined, the maximum distance for the error rate is the spatial resolution.

  Here, from FIGS. 16A to 16D, when the number of pinholes is small, the spatial resolution when the coordinates of the light source are set to (5,5,5) rather than when (1,1,1) is set. On the other hand, when the number of pinholes is large, the spatial resolution was better when the light source coordinates were (1,1,1) than when the light source coordinates were (5,5,5). .

  FIG. 17 shows the relationship between such spatial resolution and the number of pinholes, and shows the spatial resolution when the error rate is 1 [%] (0.01). From FIG. 17, it was found that when the number of pinholes in one row is 64 × 64, a high spatial resolution of 30 [μm] or less can be realized.

  Next, while setting the same design conditions as those described above, only the condition of the total area of the pinhole 7 was changed, and the spatial resolution at that time was examined. Here, with respect to Example 1 and Example 4 to Example 8 shown in FIG. 18, the above-described database generation simulation and photodetection data generation simulation are performed, and the above-described photodetection data obtained by the photodetection data generation simulation is used. The “(3) light source estimation process” was executed, and the position of the light source was estimated.

  Then, when the distance (error distance) between the actual light source position and the estimated light source position was examined, and the frequency with which the distance was estimated was also examined, the results shown in FIGS. 19A to 19D were obtained. It was. Further, when the relationship between the distance from the actual light source position to the estimated light source position and the error rate was also examined, the results shown in FIGS. 20A to 20D were obtained.

  Based on these results, the place where the error rate is 1 [%] is defined as spatial resolution, and when the relationship between this spatial resolution and the total area of the pinhole 7 is examined, the result shown in FIG. 21 is obtained. Obtained. From FIG. 21, the change of the spatial resolution due to the change of the total area of the pinhole 7 is not large, but the diameter D1 and the number of pinholes 7 and the arrangement state are selected and the total area of the pinhole 7 is adjusted. It was confirmed that the spatial resolution can be reduced.

  Next, the design conditions of SPAD17 were changed while setting the same design conditions as those described above, and the spatial resolution at that time was examined. Here, with respect to Example 4 and Example 9 to Example 11 shown in FIG. 22, the above-described database generation simulation and photodetection data generation simulation are performed, and the above-described photodetection data obtained by the photodetection data generation simulation is used. The “(3) light source estimation process” was executed, and the position of the light source was estimated.

  Then, when the distance (error distance) between the actual light source position and the estimated light source position was examined, and the frequency with which the distance was estimated was also examined, the results shown in FIGS. 23A to 23D were obtained. It was. Further, when the relationship between the distance from the actual light source position to the estimated light source position and the error rate was also examined, the results shown in FIGS. 24A to 24D were obtained.

  In this case, if the center-to-center distance W2 of the SPAD17 is reduced, the diameter of the SPAD17 is also reduced. On the other hand, the larger the distance W2 between the centers of SPAD17, the higher the aperture ratio.

  From FIG. 23A, it was confirmed that when the center-to-center distance W2 of the SPAD 17 is reduced and the aperture ratio (occupation ratio of the SPAD 17) is reduced, the distribution is spread over a wide range and the spatial resolution is deteriorated. On the other hand, as shown in FIG. 23D, it was confirmed that when the center-to-center distance W2 of the SPAD 17 is increased and the aperture ratio increases, the distribution increases on the left side and the spatial resolution is improved.

  Here, based on these results, the place where the error rate is 1 [%] is defined as spatial resolution, and the relationship between this spatial resolution and the center-to-center distance W2 of SPAD 17 is examined. As shown in FIG. Results were obtained. From FIG. 25, it was confirmed that, when the design conditions of the pinhole 7 were made constant, the spatial resolution was improved by increasing the center distance W2 of the SPAD 17 and increasing the aperture ratio. This is presumably because if the center-to-center distance W2 of the SPAD 17 is reduced to reduce the aperture ratio, the number of photons that do not strike the SPAD 17 increases, and the photon detection probability in the SPAD 17 decreases.

(5) Action and Effect In the above configuration, the photon detection device 2 is attached to each surface of the scintillator 5 having a polyhedral shape in which photons are generated when gamma rays are incident, and the scintillator 5 is arranged in an array. A photon absorption film 6 for exposing the scintillator 5 to the outside from the plurality of formed pinholes 7 and a SPAD array element 9 in which a plurality of SPADs 17 are arranged in an array are provided. In the photon detection device 2, the SPAD array element 9 is disposed opposite to each surface of the scintillator 5 with the photon absorption film 6 interposed therebetween, and the photons transmitted through the pinhole 7 can be detected by each SPAD 17.

  As a result, in the photon detection device 2, among the photons generated in the scintillator 5, the photon that hits the photon absorption film 6 is absorbed by the photon absorption film 6, and the photons that have passed through the pinhole 7 are in the direction in which the photons flew. Therefore, the photon is not repeatedly reflected in the scintillator 5, and accordingly, the analysis for specifying the position where the photon is generated becomes easier and the spatial resolution can be improved.

  Further, in the photon detection device 2, photons transmitted from the pinhole 7 can be detected by a plurality of SPADs 17, and the position where the photons are generated can be estimated based on the distribution state of the presence or absence of photon detection in each SPAD 17. Since the conventional scintillator with different characteristics and photomultiplier tubes that amplify electrons are not required, the device configuration can be simplified and the size can be reduced. It is possible to propose a photon detection device 2 that can improve the spatial resolution as compared with the prior art.

  In this case, in the photon detection device 2, each SPAD array element 9 is connected to the signal processing unit 3, and detection result data indicating the presence or absence of photon detection in each SPAD 17 is sent to the signal processing unit 3. Here, the signal processing unit 3 identifies each position in the scintillator 5 by three-dimensional coordinates, and assuming that a predetermined number of photons are emitted from one coordinate, each SPAD 17 has a possibility of detecting each photon. A probability distribution data table T100 in which the databases 1 to M indicated by the probability distribution are obtained for every coordinate is stored in advance.

Thereafter, when actually measuring γ rays, the signal processing unit 3 receives the detection result data from all SPADs 17 when the γ rays are incident on the scintillator 5, and detects the photons based on these detection result data. And the probability distributions corresponding to the specified SPAD 17 are all added for each of the databases _{1 to M} to calculate the estimated probability distributions P _{1 to} P _M for each of the databases _{1 to M.}

As a result, the signal processing unit 3 can obtain estimated probability distributions P _{1 to} P _M whose values are higher as the coordinates of the light source are more likely, and the scintillator is based on the values of these estimated probability distributions P _{1 to} P _M. The position where the photon is generated within 5 can be estimated.

Incidentally, the signal processing unit 3 can calculate a straight line passing through a region having a high value of the estimated probability distributions P _{1 to} P _M as an estimated electronic trajectory ET2 according to the regression analysis method by the least square method. By considering the electron trajectory ET1 generated in the scintillator 5, the energy given to the electrons by the γ-ray Gr is obtained from the estimated electron trajectory ET2 using the formula given as the empirical formula of the range, and this calculation is further performed. The angle of arrival 2θ 'can be obtained from the relational expression of the energy and general Compton scattering, and thus the source position of the γ-ray Gr is in the Compton cone (conical surface) of the angle of arrival 2θ'. You can also.

(6) Other Embodiments The present invention is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present invention. The light receiving unit detects photons. Other than the SPAD 17 may be applied, and the shape of the pinhole 7 may be other various shapes such as a quadrangular shape other than a circular shape, a triangular shape, and the like. Furthermore, X-rays other than γ rays may be applied as radiation.

  Furthermore, in the above-described embodiment, the case where the scintillator 5 having a cubic shape is applied has been described, but the present invention is not limited thereto, and various other hexahedral scintillators such as a rectangular parallelepiped shape may be applied. Further, scintillators having various polyhedron shapes such as a tetrahedron shape such as a triangular pyramid and a pentahedron shape such as a quadrangular pyramid may be applied. In this case, the SPAD array element can be arranged to face each surface of the scintillator.

Furthermore, in the above-described embodiment, the case where the scintillator 5 made of CaF ₂ (Eu) is applied has been described, but the present invention is not limited thereto, and various other scintillators such as BGO and ZnS (Ag) are used. You may apply. However, as the scintillator used in the present invention, it is desirable that the photon is refracted at the expected refractive index and the photon is detected by the assumed SPAD 17.

Further, in the present invention, since there is a distance from the scintillator 5 to the SPAD array element 9, a scintillator having a low refractive index is desirable because a photon may be detached from the SPAD array element 9 when the refractive index is high. Furthermore, in order to measure the electron trajectory, a scintillator that can observe the electron trajectory as long as possible is appropriate. From these conditions, CaF ₂ (Eu) can be used as the scintillator 5.

Furthermore, in the above-described embodiment, the case where the light source position estimated image is generated by plotting all the grayscale images corresponding to the values of the estimated probability distributions P _{1 to} P _M for each coordinate has been described. The present invention is not limited to this, and only the estimated probability distribution having the largest value among the estimated probability distributions P _{1 to} P _M may be plotted on the three-dimensional coordinates to be estimated as the estimated light source.

In this case, the signal processing unit 3 calculates the estimated probability distributions P _{1 to} P _M every time the photodetection data is obtained, selects only the estimated probability distribution with the largest value among them, and plots it on the three-dimensional coordinates. Thus, a plurality of estimated light sources may be obtained, a straight line close to the plurality of estimated light sources may be calculated by the least square method according to the regression analysis method, and the straight line may be used as the estimated electronic locus ET2.

  Furthermore, in the above-described embodiment, the case where the SPAD array element 9 is fixed to the photon absorption film 6 with a predetermined distance by the rod-like support portion 11 has been described, but the present invention is not limited to this. For example, the SPAD array element 9 may be fixed at a predetermined distance from the photon absorption film 6 by an optical adhesive that can transmit photons. In this case, the optical adhesive is formed, for example, by providing a predetermined thickness on the outer surface of the photon absorption film 6 so as to cover the entire photon absorption film 6, and allows the photons transmitted through the pinhole 7 to reach the SPAD array element 9. obtain.

1 Radiation measurement equipment
2 Photon detector
3 Signal processor
5 Scintillator
6 Photon absorption film
7 pinhole
9 SPAD array element (light detection element)
17 SPAD (receiver)

Claims (6)

A polyhedral scintillator that generates photons upon incidence of radiation; and
A photon absorption film that is attached to each surface of the scintillator and exposes the scintillator from a plurality of pinholes formed in an array;
A plurality of light receiving portions are arranged in an array, and are arranged to face each surface of the scintillator with the photon absorption film interposed therebetween, and the photons transmitted through the pinholes are detected by the light receiving portions. A photon detection device comprising: a possible photon detection element. The photon detection device according to claim 1, wherein the photon detection element acquires detection result data indicating whether or not the photon is detected by the light receiving unit from all the light receiving units. The photon detection device according to claim 1, wherein the photon detection element is disposed at a predetermined distance from the photon absorption film. The scintillator has a hexahedron shape, and the four-sided photon detection elements are arranged to face each other of the scintillator with the photon absorption film interposed therebetween. The photon detection device according to item. The photon detection device according to any one of claims 1 to 4,
A signal processing unit connected to the photon detection device and receiving detection result data indicating the presence or absence of detection of the photon in each light receiving unit from the photon detection device;
The signal processing unit
A database showing the probability distribution that each light receiving unit detects a photon in a probability distribution when each position in the scintillator is specified by three-dimensional coordinates and a predetermined number of photons are emitted from one coordinate. , A probability distribution data table obtained for all coordinates is stored in advance,
When the radiation is incident on the scintillator and the detection result data is received from all the light receiving units, the probability distributions corresponding to the light receiving units that have detected the photons are all added for each of the databases. A radiation measurement apparatus characterized by calculating an estimated probability distribution. Each database is assumed to have a probability distribution indicating that each photodetection unit may detect a photon, assuming that more photons than the number of photons determined from the material of the scintillator are emitted from the one coordinate. The radiation measuring apparatus according to claim 5.

Images