JP7019521B2 - Gamma camera - Google Patents

Description

The present application relates to a gamma camera capable of measuring the direction of arrival of gamma rays and obtaining the distribution of contamination by radioactive substances.

If radioactive material leaks due to an accident at a nuclear power plant, it will be necessary to proceed with decontamination after understanding the radioactive material contamination range and the spatial distribution of radioactive level. In order to measure the spatial distribution of radioactive substances, a gamma camera that can measure the distribution of radioactive substances over a wide range at once is generally used (see, for example, Patent Documents 1 to 9). ).

The gamma camera is a radiation detector that measures the direction of arrival of gamma rays, and a pinhole method, a Compton method, or the like is adopted. In either method, in order to obtain the incident vector of gamma rays, it is necessary to obtain information on the position where the gamma rays interact with a scintillator, a semiconductor detector, or the like.

As a method of obtaining position information with a gamma camera, a method using a pixel type semiconductor detector (see, for example, Patent Document 1), a method using a scintillator arranged in a pixel shape (see, for example, Patent Document 2), and a scintillator. A method of obtaining a light emitting position of a scintillator by combining a microlens array with a scintillator (see, for example, Patent Document 3) is known.

Further, in order to obtain not only the planar distribution in the incident direction of the radiation source but also the three-dimensional distribution including the depth, a method of using a parallax with a compound eye using a plurality of gamma cameras (see, for example, Patent Document 4). A method has been devised in which the arrangement of radiation detection elements is devised in one Compton camera and a three-dimensional distribution is obtained by a maximum likelihood estimation expected value maximization operation using the parallax (see, for example, Patent Document 2). ..

Japanese Unexamined Patent Publication No. 2017-26524 Japanese Unexamined Patent Publication No. 2011-85418 Japanese Unexamined Patent Publication No. 2016-223997 Japanese Unexamined Patent Publication No. 2017-26526 Japanese Patent Application Laid-Open No. 2003-130919 International Publication No. 2009/051053 Japanese Unexamined Patent Publication No. 2004-85250 Japanese Unexamined Patent Publication No. 2016-20832 Japanese Unexamined Patent Publication No. 2014-122861

The challenges of these gamma cameras are as follows. In the case of the pinhole camera method, the incident direction of the gamma ray is limited to the direction of the pinhole when viewed from the radiation detector, so that the viewing angle of the gamma camera is determined by the geometric relationship between the radiation detector and the pinhole. This viewing angle is limited to the front due to the nature of the pinhole type gamma camera.

On the other hand, in the case of the Compton method, since the scattering of gamma rays in the gamma camera is used, the pinhole becomes unnecessary and it is possible to obtain a wider viewing angle than the pinhole camera. However, since two types of radiation detection elements, one for an absorber and the other for a scatterer, are used in one gamma camera, the viewing angle is limited by the geometrical arrangement of the radiation detection elements.

For these reasons, the viewing angle of the camera is limited even in the Compton type gamma camera. Therefore, when observing the distribution of the radiation source over all directions around the gamma camera, for example, it is necessary to repeat the measurement while rotating the gamma camera.

This application has been made to solve the above-mentioned problems in the gamma camera. That is, it is to provide a gamma camera capable of measuring the incident direction of gamma rays in all directions without measuring while rotating the gamma camera.

The gamma camera according to the present application is based on a gamma ray detector having a first scintillator unit, a second scintillator unit, a third scintillator unit, and a fourth scintillator unit, and an output from the gamma ray detector. A light emitting amount calculation device for obtaining the light emission amount of the incident gamma ray in the fourth scintillator unit from the first scintillator unit, a light emission amount of the incident gamma ray obtained by the light emission amount calculation device, and detection of the primary gamma ray 1 From the position of the secondary scintillator unit and the position of the secondary scintillator unit that detected the secondary gamma ray, the gamma ray incident direction calculation device for obtaining the incident direction of the incident gamma ray and the incident gamma ray obtained by the emission amount calculation device. The first scintillator unit includes a radioactive contamination distribution calculation device that obtains a radiation concentration distribution of a radioactive substance from the amount of light emitted and the incident direction of the incident gamma rays obtained by the gamma ray incident direction calculation device. The first scintillator, the second scintillator of the second scintillator unit, the third scintillator of the third scintillator unit, and the fourth scintillator of the fourth scintillator unit are regular tetrahedrons. It is placed at the apex .

The gamma camera according to the present application is based on a gamma ray detector having a first scintillator unit, a second scintillator unit, a third scintillator unit, and a fourth scintillator unit, and an output from the gamma ray detector. A light emitting amount calculation device for obtaining the light emission amount of incident gamma rays from the first scintillator unit to the fourth scintillator unit, a light emission amount of incident gamma rays obtained by the light emission amount calculation device, and detection of primary gamma rays 1 From the position of the secondary gamma ray unit and the position of the secondary gamma ray that detected the secondary gamma ray, the gamma ray incident direction calculation device that obtains the incident direction of the incident gamma ray and the incident gamma ray obtained by the emission amount calculation device. The first scintillator unit includes a radioactive contamination distribution calculation device for obtaining a radiation concentration distribution of a radioactive substance from the amount of light emitted and the incident direction of the incident gamma ray obtained by the gamma ray incident direction calculation device. The first scintillator, the second scintillator included in the second scintillator unit, the third scintillator included in the third scintillator unit, and the fourth scintillator included in the fourth scintillator unit are regular tetrahedrons. Since it is arranged at the apex, it is not necessary to rotate the gamma camera when measuring, and it is possible to obtain the incident direction of the gamma ray in all directions.

It is a figure which shows the whole structure of the gamma camera which concerns on Embodiment 1. FIG. It is a figure which shows the structure of the scintillator unit which concerns on Embodiment 1. FIG. It is a figure for demonstrating the role of the light emission amount calculation apparatus. It is a figure for demonstrating the relationship between the energy of an incident gamma ray (primary gamma ray), and the energy of a scattered gamma ray (secondary gamma ray) in Compton scattering. It is a flow chart which shows the procedure when the arithmetic unit 70 obtains the incident direction of a gamma ray in all directions. It is a 1st schematic diagram which shows how the gamma ray incident on the 1st scintillator s1 causes Compton scattering. It is a 2nd schematic diagram which shows how the gamma ray incident on the 1st scintillator s1 causes Compton scattering. In order to explain the incident direction of the gamma ray incident on the 1st scintillator s1, it is the figure which combined the 1st cone f (g1) and the 2nd cone f (g2). In order to explain the incident direction of the gamma ray incident on the 2nd scintillator s2, it is the figure which combined the 1st cone f (g1) and the 2nd cone f (g2). It is a figure which shows the whole structure of the gamma camera which concerns on Embodiment 2. FIG. It is a figure which shows the structure of the scintillator unit which concerns on Embodiment 2. It is a figure which shows the whole structure of the gamma camera which concerns on Embodiment 3. FIG. It is a figure which shows the structure of the scintillator unit which concerns on Embodiment 3.

The gamma camera according to the embodiment of the present application will be described below with reference to the drawings. In each figure, the same or similar components are designated by the same reference numerals, and the sizes and scales of the corresponding components are independent of each other. For example, when illustrating the same component that has not been changed between cross-sectional views in which a part of the structure is changed, the size and scale of the same component may be different. In addition, the gamma camera is actually provided with a plurality of members, but for the sake of simplicity, only the parts necessary for the explanation are described, and the other parts are omitted.

Embodiment 1.
FIG. 1 is a diagram showing the configuration of the gamma camera 100 in the first embodiment. The gamma camera 100 in the present embodiment includes a gamma ray detector 10, an arithmetic unit 70, and the like. The gamma ray detector 10 is composed of a first scintillator unit su1, a second scintillator unit su2, a third scintillator unit su3, a fourth scintillator unit su4, a light-shielding case 50, and the like. The arithmetic unit 70 includes a light emission amount arithmetic unit 61, a gamma ray incident direction arithmetic unit 62, a radioactive contamination distribution arithmetic unit 63, a storage device 64, a CPU (Central Processing Unit) 65, and the like.

The first scintillator unit su1 is composed of a first scintillator s1, an optical fiber cable 31, a light receiving element 51, and a signal cable 45. The second scintillator unit su2 is composed of a second scintillator s2, an optical fiber cable 32, a light receiving element 52, and a signal cable 46. The third scintillator unit su3 is composed of a third scintillator s3, an optical fiber cable 33, a light receiving element 53, and a signal cable 47. The fourth scintillator unit su4 is composed of a fourth scintillator s4, an optical fiber cable 34, a light receiving element 54, and a signal cable 48.

The optical fiber cable 31 to the optical fiber cable 34 transmit the scintillation light emitted by the corresponding first scintillators s1 to the fourth scintillator s4 to the light receiving element. The light receiving element 51 to the light receiving element 54 receive the scintillation light transmitted by the corresponding optical fiber cable 31 to the optical fiber cable 34, and output an electric signal through the signal cable. The light emission amount calculation device 61 obtains the light emission amount inside the corresponding scintillator by calculation based on the outputs from the first scintillator unit su1 to the fourth scintillator unit su4 (light receiving element 51 to light receiving element 54). .. Further, the light emission amount calculation device 61 detects which scintillator emits light based on the outputs from the first scintillator unit su1 to the fourth scintillator unit su4, and obtains the light emission position.

The gamma ray incident direction arithmetic unit 62 determines the gamma ray incident direction from the light emission amount of the first scintillator unit su1 to the fourth scintillator unit su4 and the geometric conditions of the first scintillator unit su1 to the fourth scintillator unit su4. Ask for. The radioactive contamination distribution calculation device 63 obtains the radioactive concentration distribution of the radioactive substance to be measured from the incident direction of the gamma ray. Since the scintillator is used as the radiation detection element, the first scintillator unit su1 to the fourth scintillator unit su4 are fixedly arranged inside the light-shielding light-shielding case 50, and the optical fiber cable 31 to the optical fiber cable 34 are also light-shielded. It is covered with a covered coating. Although only four scintillators are shown in the figure, in the present embodiment, at least four scintillators may be used, and the number may be five or more.

The function of the arithmetic unit 70 is realized by software, firmware, or a combination of software and firmware. The software and firmware are described as programs and stored in the storage device 64. The CPU 65 (processing circuit) realizes the functions of each part by reading and executing the program stored in the storage device 64. That is, the arithmetic unit 70 includes a storage device 64 for storing a program in which each step is to be executed as a result.

Further, it can be said that these programs cause a computer to execute the procedure and method of the arithmetic unit 70. Here, the storage device 64 is, for example, a RAM (Random).
Access Memory), ROM (Read-Only Memory), Flash Memory, EPROM (Erasable Programmable ROM), EEPROM (Electrically Erasable Programmable R)
Non-volatile or volatile semiconductor memories such as OM), magnetic disks, flexible disks, optical disks, compact disks, mini disks, DVDs, and the like fall under this category.

FIG. 2 shows the configuration of the gamma ray detector 10 in the present embodiment. A gamma camera is configured by combining four or more scintillator units. It is desirable that the first scintillator s1, the second scintillator s2, the third scintillator s3, and the fourth scintillator s4 are arranged at the vertices of the regular tetrahedron because later calculations are facilitated. In the present embodiment, the scintillation light is transmitted from the first scintillator s1 to the fourth scintillator s4 to the corresponding optical fiber cable 31 to the optical fiber cable 34. The first scintillator s1 to the fourth scintillator s4 serve as scintillators in the first scintillator unit su1 to the fourth scintillator unit su4.

Next, the basic operation of the gamma camera according to the first embodiment will be described with reference to FIG. The figure shows that Compton scattering occurs in the first scintillator s1 and photoelectric absorption occurs in the second scintillator s2. Hereinafter, the first scintillator s1 to which the gamma ray (primary gamma ray) coming from the outside first enters is the primary scintillator (or the incident side scintillator), and the scattered gamma ray 3 (or the secondary gamma ray) generated by the incident gamma ray 2 The incident second scintillator s2 is referred to as a secondary side scintillator (or a scattering side scintillator). When the gamma rays emitted from the radioactive substance 1 are incident on the first scintillator s1, Compton scattering occurs.

As a result of Compton scattering, energy is applied to the first scintillator s1 (primary scintillator), so that scintillation light is generated. The energy is applied to the scintillator by the rebounding electrons generated by Compton scattering traveling in the scintillator and the electrons applying energy to the scintillator. In general, the range of electrons inside a solid (scintillator) is sufficiently short compared to the size of the scintillator, so that all the energy of the electrons is applied to the inside of the scintillator (solid).

The scintillation light generated by the first scintillator s1 (primary side scintillator) is transmitted through the optical fiber cable 31 and incident on the light receiving element 51, and is converted into an electric signal according to the amount of light by the light receiving element 51. On the other hand, the scintillation light generated by the second scintillator s2 (secondary scintillator) is transmitted to the light receiving element 52 through the optical fiber cable 32, and is converted into an electric signal according to the amount of light by the light receiving element 52. The electric signal output from each light receiving element is input to the light emitting amount calculation device 61 via the signal cable.

The scintillation light generated by the first scintillator unit su1 (primary side scintillator unit or incident side scintillator unit) is larger than the scintillation light generated by the second scintillator unit su2 (secondary side scintillator unit or scattering side scintillator unit). The scintillation light can be considered to reach the same time because the difference is very small, although the light emission amount calculation device 61 is reached quickly. Here, since the amount of light emitted from the first scintillator s1 to the fourth scintillator s4 is proportional to the energy of the gamma ray applied to the scintillator, the magnitude of the electric signal output from the light receiving element is given to each scintillator. It is proportional to the energy of the gamma rays.

The output of the light emission amount calculation device 61 is input to the gamma ray incident direction calculation device 62. The gamma ray incident direction arithmetic unit 62 calculates the incident direction of the incident gamma ray 2 that has flown to the first scintillator s1 (primary side scintillator) based on the theoretical formula of Compton scattering. The calculation in the gamma ray incident direction calculation device 62 is a calculation performed in a general Compton camera (see, for example, Patent Document 1). FIG. 4 shows the relationship between the energy of gamma rays and the scattering angle θ of Compton scattering.

Equation (1) in the figure shows the energy of the incident gamma ray 2, the energy of the scattered gamma ray 3 (secondary gamma ray), and the Compton when the gamma ray causes Compton scattering in the primary side scintillator (first scintillator s1). It shows the relationship between the scattering angle θ and the scattering. Of these, the energy of the scattered gamma rays 3 (secondary gamma rays) is obtained from the energy imparted by the secondary scintillator (second scintillator s2), and the energy of the incident gamma rays 2 is the energy imparted by the first scintillator s1 and the second. It is obtained from the total energy applied to the scintillators s2. Therefore, since variables other than the scattering angle θ of Compton scattering are known, the scattering angle θ of Compton scattering can be obtained from Eq. (1).

FIG. 5 is a flow chart showing a procedure when the arithmetic unit 70 obtains the incident direction of gamma rays in all directions. When a gamma ray arrives at the gamma ray detector 10, light is emitted from the first scintillator to somewhere in the fourth scintillator (step ST01). Based on the signals from each scintillator, the light emission amount calculation device 61 calculates the light emission amount (gamma ray energy) (step ST02). The gamma ray incident direction calculation device 62 obtains a primary side scintillator and a secondary side scintillator based on the calculation result of the light emission amount calculation device 61 (step ST03). The gamma ray incident direction calculation device 62 further obtains the scattering angle of Compton scattering from the energy of the incident gamma ray detected by the primary side scintillator unit and the energy of the scattered gamma ray detected by the secondary side scintillator unit. The incident direction of the incident gamma ray is obtained based on the scattering angle of Compton scattering (step ST04). The radioactive contamination distribution calculation device obtains the radioactive concentration distribution of the radioactive substance from the emission amount of the incident gamma ray obtained by the light emission amount calculation device 61 and the incident direction of the incident gamma ray obtained by the gamma ray incident direction calculation device 62 (step). ST05).

Next, how to obtain the incident direction of the incident gamma ray will be described in detail. FIG. 6 shows a first cone related to the incident direction of gamma rays, which is obtained by calculation. It is assumed that the first scintillator s1 and the second scintillator s2 illuminate when the first event occurs. Since the first scintillator s1 and the second scintillator s2 emit light at the same time, the scintillator having the smaller light emission amount (energy) is used as the primary side scintillator (incident side scintillator), and the light emission amount (energy) is larger. The other scintillator is a secondary side scintillator (scattering side scintillator). When the first scintillator s1 is the primary scintillator and the second scintillator s2 is the secondary scintillator, the incident direction of the gamma ray g1 is on the conical surface of the cone f (g1).

FIG. 7 shows a second cone related to the incident direction of gamma rays, which is obtained by calculation. It is assumed that the first scintillator s1 and the third scintillator s3 illuminate when the second event occurs. As shown in the figure, depending on the size of the incoming gamma rays 2, the first scintillator s1 is the primary side scintillator (incident side scintillator), and the third scintillator s3 is the secondary side scintillator (scattering side). It becomes a scintillator). In this case, the incident direction of the gamma ray g2 is on the conical surface of the cone f (g2) 2. The apex angle of the cone f (g1) and the apex angle of the cone f (g2) are equal to the scattering angle θ of Compton scattering.

FIG. 8 is a diagram in which the cone f (g1) shown in FIG. 6 and the cone f (g2) shown in FIG. 7 are combined. Since the two cones representing the incident direction of the gamma ray ideally touch each other in one straight line, the direction of this straight line is the incident direction of the incident gamma ray. In this way, the gamma camera in the present embodiment can determine the incident direction of the incident gamma ray. Next, in the radioactive contamination distribution calculation device 63, the radioactivity in the measurement target is obtained from the emission amount of the incident gamma ray obtained by the emission amount calculation device 61 and the incident direction of the incident gamma ray obtained by the gamma ray incident direction calculation device 62. Find the concentration distribution.

On the other hand, since the gamma camera in the present embodiment does not have a shield such as a collimator and a pinhole, the second scintillator s2 may be a primary side scintillator (incident side scintillator) as shown in FIG. Occur. Also in this case, the incident direction of the incident gamma ray 2 can be obtained by using any scintillator other than the second scintillator s2 as the secondary side scintillator (scattering side scintillator). That is, here, when the second scintillator s2 is the primary scintillator and the first scintillator s1 is the secondary scintillator, the incident direction of the gamma ray g1 is on the conical surface of the cone f (g1). Will be. On the other hand, when the second scintillator s2 is the primary scintillator and the fourth scintillator s4 is the secondary scintillator, the incident direction of the gamma ray g2 is on the conical surface of the cone f (g2) 2. At this time, since the two cones representing the incident direction of the incident gamma ray are ideally in contact with each other in one straight line, the direction of this straight line is the incident direction of the incident gamma ray.

As described above, in the gamma camera of the present embodiment, any one of the four or more scintillators constituting the gamma camera can be the primary side scintillator (incident side scintillator). Further, any one of them can be a secondary side scintillator (scattering side scintillator). The viewing angle per primary scintillator is limited by the geometrical conditions of the first scintillator and the second scintillator. Since the primary scintillator can be freely selected from four or more scintillators, the incident direction of gamma rays can be obtained in all directions without rotating the gamma ray detector 10 (gamma camera). In other words, since the combination of the scintillator that causes Compton scattering and the scintillator that causes total energy absorption can be freely selected, it is not necessary to measure while rotating the gamma ray detector 10 (gamma camera), and the incident direction of gamma rays. Can be obtained in all directions.

That is, in order to transmit the scintillator emitted by four or more scintillators, the gamma camera according to the present embodiment receives the optical fiber cable optically coupled to the scintillator and the scintillation light transmitted by the optical fiber cable. A light-receiving element that outputs an electric signal, a light-emitting amount calculation device that obtains the amount of light emitted in each scintillator by calculation based on the output from each scintillator, and a gamma-ray incident direction from the light-emitting position of each scintillator. Equipped with a gamma-ray incident direction calculation device and a radioactive contamination distribution calculation device that obtains the radiation concentration distribution of radioactive substances in the measurement target from the gamma-ray incident direction, and gamma-ray detection by freely selecting the combination of scintillator and absorber. It is characterized in that the incident direction of gamma rays can be obtained in all directions without rotating the device 10 (gamma camera).

According to the gamma camera according to the present embodiment, any one of the scintillators constituting the gamma camera can be a scatterer. The viewing angle per scatterer is limited by the geometrical conditions of the scatterer (primary scintillator) and the absorber (secondary scintillator), but since the scatterer can be freely selected, a gamma camera The incident direction of gamma rays can be obtained in all directions without rotating. By freely selecting a combination of a gamma ray scatterer and an absorber from a plurality of scintillators constituting the gamma camera, the incident direction of the gamma ray can be obtained in all directions without rotating the gamma camera.

Therefore, the gamma camera according to the present application is based on a gamma ray detector having a first scintillator unit, a second scintillator unit, a third scintillator unit, and a fourth scintillator unit, and an output from the gamma ray detector. Then, a light emitting amount calculation device for obtaining the light emission amount of the incident gamma ray in the fourth scintillator unit from the first scintillator unit, a light emission amount of the incident gamma ray obtained by the light emission amount calculation device, and a primary gamma ray are detected. A gamma ray incident direction calculation device that obtains the incident direction of the incident gamma ray from the geometric position of the primary side scintillator unit and the geometric position of the secondary side gamma ray that detected the secondary gamma ray, and the emission amount calculation. It is equipped with a radioactive contamination distribution calculation device that obtains the radioactivity concentration distribution of radioactive substances from the emission amount of incident gamma rays obtained by the device and the incident direction of the incident gamma rays obtained by the gamma ray incident direction calculation device. Is.

Embodiment 2.
FIG. 10 is a diagram showing the configuration of the gamma camera 100 in the second embodiment. The gamma camera 100 in the present embodiment includes a gamma ray detector 10, an arithmetic unit 70, and the like. The gamma ray detector 10 is composed of a first scintillator unit su1, a second scintillator unit su2, a third scintillator unit su3, a fourth scintillator unit su4, a light-shielding case 50, and the like. The arithmetic unit 70 includes a light emission amount arithmetic unit 61, a gamma ray incident direction arithmetic unit 62, a radioactive contamination distribution arithmetic unit 63, a storage device 64, a CPU 65, and the like.

The first scintillator unit su1 is composed of a first scintillator s1, a light guide 21, an optical fiber cable 31, a light receiving element 51, and a signal cable 45. The second scintillator unit su2 is composed of a second scintillator s2, a light guide 22, an optical fiber cable 32, a light receiving element 52, and a signal cable 46. The third scintillator unit su3 is composed of a third scintillator s3, a light guide 23, an optical fiber cable 33, a light receiving element 53, and a signal cable 47. The fourth scintillator unit su4 is composed of a fourth scintillator s4, a light guide 24, an optical fiber cable 34, a light receiving element 54, and a signal cable 48.

The light guide 21 to the light guide 24 and the optical fiber cable 31 to the optical fiber cable 34 transmit the scintillation light emitted by the corresponding first scintillators s1 to the fourth scintillator s4 to the light receiving element. The light receiving element 51 to the light receiving element 54 receive the scintillation light transmitted by the corresponding optical fiber cable 31 to the optical fiber cable 34, and output an electric signal via the signal cable. The light emission amount calculation device 61 obtains the light emission amount in the corresponding scintillator by calculation based on the outputs from the first scintillator unit su1 to the fourth scintillator unit su4 (light receiving element 51 to light receiving element 54). Further, the light emission amount calculation device 61 detects which scintillator emits light based on the outputs from the first scintillator unit su1 to the fourth scintillator unit su4, and obtains the light emission position.

The gamma ray incident direction arithmetic unit 62 determines the gamma ray incident direction from the light emission amount of the first scintillator unit su1 to the fourth scintillator unit su4 and the geometric conditions of the first scintillator unit su1 to the fourth scintillator unit su4. Ask. The radioactive contamination distribution calculation device 63 obtains the radioactive concentration distribution of the radioactive substance to be measured from the incident direction of the gamma ray. Since the scintillator is used as the radiation detection element, the first scintillator s1 to the fourth scintillator s4 and the light guides 21 to 24 are arranged inside the light-shielding light-shielding case 50, and the optical fiber cable 31 to the optical fiber cable are arranged. 34 is also covered with a light-shielded coating. Although only four scintillators are shown in the figure, in the present embodiment, at least four scintillators may be used, and the number may be five or more.

FIG. 11 shows the configuration of the gamma ray detector 10 in the present embodiment. A gamma camera is configured by combining four or more scintillator units. It is desirable that the first scintillator s1, the second scintillator s2, the third scintillator s3, and the fourth scintillator s4 are arranged at the vertices of the regular tetrahedron because later calculations are facilitated. In the present embodiment, the scintillation light when a gamma ray is incident on the scintillator and causes an interaction is transmitted to an optical fiber cable via the corresponding light guides 21 to 24. The first scintillator s1 to the fourth scintillator s4 serve as scintillators in the first scintillator unit su1 to the fourth scintillator unit su4. The functions of the arithmetic unit 70 (light emission amount arithmetic unit 61, gamma ray incident direction arithmetic unit 62, radioactive contamination distribution arithmetic unit 63, storage device 64, and CPU 65) are the same as those in the first embodiment.

Embodiment 3.
FIG. 12 is a diagram showing the configuration of the gamma camera 100 in the third embodiment. The gamma camera 100 in the present embodiment includes a gamma ray detector 10, an arithmetic unit 70, and the like. The gamma ray detector 10 is composed of a first scintillator unit su1, a second scintillator unit su2, a third scintillator unit su3, a fourth scintillator unit su4, a light-shielding case 50, and the like. The arithmetic unit 70 includes a light emission amount arithmetic unit 61, a gamma ray incident direction arithmetic unit 62, a radioactive contamination distribution arithmetic unit 63, a storage device 64, a CPU 65, and the like.

The first scintillator unit su1 is composed of a first scintillator s1, a photomultiplier tube 41, and a signal cable 45. The second scintillator unit su2 is composed of a second scintillator s2, a photomultiplier tube 42, and a signal cable 46. The third scintillator unit su3 is composed of a third scintillator s3, a photomultiplier tube 43, and a signal cable 47. The fourth scintillator unit su4 is composed of a fourth scintillator s4, a photomultiplier tube 44, and a signal cable 48.

The photomultiplier tube 41 to the photomultiplier tube 44 convert the scintillation light when gamma rays are incident on the scintillator and cause an interaction into an electric signal. The signal cable 45 to the signal cable 48 transmit the electric signal output from the corresponding photomultiplier tube 41 to the photomultiplier tube 44 to the light emission amount calculation device 61. The light emission amount calculation device 61 calculates light emission in the corresponding scintillator based on the output from the first scintillator unit su1 to the fourth scintillator unit su4 (photomultiplier tube 41 to photomultiplier tube 44). Find the quantity. Further, the light emission amount calculation device 61 detects which scintillator emits light based on the outputs from the first scintillator unit su1 to the fourth scintillator unit su4, and obtains the light emission position.

The gamma ray incident direction arithmetic unit 62 determines the incident direction of the incident gamma ray from the light emission amount of the first scintillator unit su1 to the fourth scintillator unit su4 and the geometric conditions of the first scintillator unit su1 to the fourth scintillator unit su4. Ask for. The radioactive contamination distribution calculation device 63 obtains the radioactive concentration distribution of the radioactive substance to be measured from the incident direction of the incident gamma ray. Since the scintillator is used as the radiation detection element, the first scintillator s1 to the fourth scintillator s4 are arranged inside the light-shielding light-shielding case 50. Although only four scintillators are shown in the figure, in the present embodiment, at least four scintillators may be used, and the number may be five or more.

FIG. 13 shows the configuration of the scintillator unit according to the present embodiment. A gamma camera is configured by combining four or more scintillator units. It is desirable that the first scintillator s1, the second scintillator s2, the third scintillator s3, and the fourth scintillator s4 are arranged at the vertices of the regular tetrahedron because later calculations are facilitated. In this embodiment, a photomultiplier tube is optically coupled to the scintillator. The amount of light of the scintillation light when a gamma ray is incident on the scintillator and causes an interaction is converted into an electric signal by a photomultiplier tube and input to the light emission amount calculation device 61. The first scintillator s1 to the fourth scintillator s4 serve as scintillators in the first scintillator unit su1 to the fourth scintillator unit su4. The functions of the arithmetic unit 70 (light emission amount arithmetic unit 61, gamma ray incident direction arithmetic unit 62, radioactive contamination distribution arithmetic unit 63, storage device 64, and CPU 65) are the same as those in the first embodiment.

Generally, in a gamma camera, the viewing angle is limited because the gamma ray scatterer and absorber are predetermined among the multiple scintillators constituting the gamma camera, and the gamma ray incident direction is once omnidirectional. Could not be measured. Since the gamma camera according to the present embodiment does not transmit the scintillation light by the optical fiber cable, there is an advantage that the loss of the light collection efficiency is small. Since there is an advantage that the energy resolution is improved in the energy measurement of gamma rays, it is possible to improve the measurement accuracy in the incident direction of gamma rays.

The gamma camera according to the present embodiment is characterized in that a scintillator and a photomultiplier tube are optically coupled to transmit an electric signal according to the amount of light emitted. Since the scintillation light is not transmitted by the optical fiber cable, there is an advantage that the loss of focusing efficiency is small, and there is an advantage that the energy resolution in the energy measurement of gamma rays is improved. This makes it possible to improve the measurement accuracy of the incident direction of gamma rays.

Although the present application describes various exemplary embodiments and examples, the various features, embodiments, and functions described in one or more embodiments are applications of a particular embodiment. It is not limited to, but can be applied to embodiments alone or in various combinations. Therefore, innumerable variations not exemplified are envisioned within the scope of the techniques disclosed in the present application. For example, it is assumed that at least one component is modified, added or omitted, and further, at least one component is extracted and combined with the components of other embodiments.

1 Radioactive material, 2 Incident gamma ray, 3 Scattered gamma ray, 10 Gamma ray detector, 21 Light guide, 22 Light guide, 23 Light guide, 24 Light guide, 31 Optical fiber cable, 32 Optical fiber cable, 33 Optical fiber cable, 34 Optical fiber cable, 41 Optical fiber multiplying tube, 42 Optical electron multiplying tube, 43 Optical electron multiplying tube, 44 Photoelectron multiplying tube, 45 signal cable, 46 signal cable, 47 signal cable, 48 signal cable, 50 shading case, 51 light receiving element, 52 light receiving element , 53
Light receiving element, 54 light receiving element, 61 light emitting amount calculation device, 62 gamma ray incident direction calculation device, 63 radiation pollution distribution calculation device, 64 storage device, 65 CPU, 70 calculation device, 100 gamma camera, s1 first scintillator, s2 2nd scintillator, s3 3rd scintillator, s4 4th scintillator, su1 1st scintillator unit, su2 2nd scintillator unit, su3 3rd scintillator unit, su4 4th scintillator unit, θ Compton scattering scattering Horn

Claims (6)

A gamma ray detector having a first scintillator unit, a second scintillator unit, a third scintillator unit, and a fourth scintillator unit,
An emission amount calculation device for obtaining the emission amount of incident gamma rays from the first scintillator unit to the fourth scintillator unit based on the output from the gamma ray detector.
From the emission amount of the incident gamma ray obtained by the light emission amount calculation device, the position of the primary side scintillator unit that detected the primary gamma ray, and the position of the secondary side scintillator unit that detected the secondary gamma ray, the incident gamma ray A gamma-ray incident direction arithmetic unit that calculates the incident direction,
A radioactive contamination distribution calculation device that obtains the radioactive concentration distribution of a radioactive substance from the emission amount of the incident gamma ray obtained by the light emission amount calculation device and the incident direction of the incident gamma ray obtained by the gamma ray incident direction calculation device. Be prepared ,
The first scintillator of the first scintillator unit, the second scintillator of the second scintillator unit, the third scintillator of the third scintillator unit, and the fourth scintillator of the fourth scintillator unit. The scintillator is a gamma camera located at the apex of a regular tetrahedron . The gamma ray incident direction arithmetic unit is
When the incident of gamma rays is detected in two scintillator units at the same time among the fourth scintillator units from the first scintillator unit.
The gamma according to claim 1, wherein the scintillator unit that detects the gamma ray having the smaller energy is the primary side scintillator unit, and the scintillator unit that detects the gamma ray having the larger energy is the secondary scintillator unit. camera. The gamma ray incident direction arithmetic unit is
The scattering angle of Compton scattering was obtained from the energy of the primary gamma ray detected by the primary side scintillator unit and the energy of the secondary gamma ray detected by the secondary side scintillator unit.
The gamma camera according to claim 2, wherein the incident direction of the incident gamma ray is obtained based on the scattering angle of the Compton scattering. The first scintillator unit, the second scintillator unit, the third scintillator unit, and the fourth scintillator unit each have a scintillator, an optical fiber cable, and a light receiving element. The gamma camera according to any one of claims 1 to 3, wherein the gamma camera is characterized. The first scintillator unit, the second scintillator unit, the third scintillator unit, and the fourth scintillator unit each have a scintillator, a light guide, an optical fiber cable, and a light receiving element. The gamma camera according to any one of claims 1 to 3, wherein the gamma camera is characterized by the above. The first scintillator unit, the second scintillator unit, the third scintillator unit, and the fourth scintillator unit are characterized by having a scintillator and a photomultiplier tube, respectively. The gamma camera according to any one of claims 1 to 3.

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