JP2018013439A - Radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation measuring device capable of directly measuring a radiation incoming direction, holding down an increase in costs, and easily measuring spatial intensity distribution of radiation and the like.SOLUTION: A radiation measuring device 100 comprises a detection window part 20, a first detecting unit 40, a second detecting unit 50, and a control device 70. The first detecting unit 40 is connected to one end side of a scintillator part 22, and detects a light signal from the scintillator part 22 as distribution of a two-dimensional light signal. The second detecting unit 50 is connected to the other end side of the scintillator part 22, and detects a light signal from the scintillator part 22. The radiation measuring device can narrow down a passage position of electromagnetic radiation RR in a scintillation rod unit 22a by using detection results from the first detecting unit 40 and the second detecting unit 50.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation measurement apparatus that enables measurement of the direction of radiation and the like, measurement of the spatial intensity distribution of radiation, and the like.

  As a radiation measurement device, in order to measure the radiation direction of radiation, etc., a collimator that limits the incident direction of radiation, and a sensor array comprising a large number of scintillation rods arranged in parallel at equal intervals adjacent to the collimator A radiation measuring apparatus is known which detects a light signal from the detection unit as a two-dimensional light signal distribution (see Patent Document 1).

  However, when the spatial intensity distribution of radiation is measured by the radiation measuring apparatus as described above, the collimator gives directivity related to the radiation direction of radiation, so the detection direction corresponding to the directivity of the collimator is set. Scanning measurement is required to perform measurement while changing, and the time required for measurement increases.

  As another method for detecting the direction of radiation, there is a Compton method using Compton scattering (see Non-Patent Documents 1 and 2). Specifically, for example, a scatterer detector that causes Compton scattering with respect to radiation and an absorber detector that photoelectrically absorbs photons after scattering are provided, and the scattering angle based on the scattering or absorption position and applied energy in each. And a method of determining the arrival of radiation from the same calculation for a plurality of radiations. In the Compton camera in which the Compton method is put into practical use, expensive thallium activated sodium iodide (NaI), thallium activated cesium iodide (CsI) or the like is used, or expensive semiconductor sensors are mounted at high density. It is not easy to increase sensitivity at low cost.

International Publication No.2013 / 147277

V. Schonfelder, A. Hirner, and K. Schneider, Nuclear Instruments and Methods 107, 385 (1973). R. W. Todd, J. M. Nightingale, and D. B. Everett, Nature 251, 132 (1974).

  An object of the present invention is to provide a radiation measuring apparatus that can directly measure the direction of radiation radiation and can easily measure the spatial intensity distribution of radiation while suppressing an increase in cost.

  In order to achieve the above object, a radiation measuring apparatus according to the present invention includes a three-dimensional sensor array in which a plurality of linear scintillator elements extending in a predetermined direction are two-dimensionally arranged in a direction perpendicular to the predetermined direction, and a sensor array A first detector connected to one end of the sensor array to detect the optical signal from the sensor array as a two-dimensional optical signal distribution; and connected to the other end of the sensor array in the predetermined direction from the sensor array. Detection information including a plurality of arrival positions corresponding to specific electromagnetic radiation and a second detection portion that detects the optical signal of the first and second electromagnetic wave arrival positions based on the detection results of the first and second detection portions. And an information processing device for obtaining flight information related to the incident direction of the specific electromagnetic radiation.

  In the radiation measuring apparatus of the present invention, since the three-dimensional sensor array and the first detection unit are used, electromagnetic radiation flying in a relatively wide space can be captured as two-dimensional image information corresponding to the arrangement of scintillator elements. This makes it possible to detect electromagnetic radiation at a reduced cost. Further, by using the detection results of the first and second detection units, it is possible to narrow down the passing position of electromagnetic radiation in the scintillator element, and to determine the generation position of a series of Compton scattering and the like caused by the arrival of specific electromagnetic radiation. It can be detected as a plurality of radiation arrival positions, and the flying direction or incident direction of electromagnetic radiation can be directly measured.

  In a specific aspect or viewpoint of the present invention, the radiation measurement apparatus further includes an azimuth restriction unit that azimuthally restricts the incidence of electromagnetic radiation to the sensor array. In this case, the background electromagnetic radiation can be restricted, and extraction of the target electromagnetic radiation is facilitated.

  In another aspect of the present invention, the azimuth restricting portion is disposed to face a planar incident portion set in a predetermined region between the one end side and the other end side of the sensor array, and includes a plurality of shielding plates. At least one collimator arranged close to each other. In this case, the azimuth limiter can be made relatively lightweight. In addition, the collimator can limit the incident direction or the incident direction of electromagnetic radiation to the sensor array at least in the incident part or the vicinity thereof, and can easily identify the incident direction of the target electromagnetic radiation, The reliability of the flight information obtained increases. The flat plates of the plurality of shields can be arranged in parallel with each other, for example, but can also be arranged so as to be inclined so as to gather toward a specific distance.

  In another aspect of the present invention, the orientation restriction unit includes two collimators whose restriction orientations intersect each other. In this case, the incident direction of electromagnetic radiation can be limited in two directions, and flight information can be obtained with high accuracy.

  In still another aspect of the present invention, the information processing apparatus determines the energy of scattered electrons derived from specific electromagnetic radiation based on the intensity of the optical signal in units of scintillator elements detected by the first detection unit. This energy can be used to specify the direction of radiation or the direction of incidence of radiation.

  In yet another aspect of the present invention, the information processing apparatus synchronizes the optical signal detected by the first detection unit in units of scintillator elements and the optical signal detected by the second detection unit, and generates specific electromagnetic radiation. Determine that it is incident. Thus, it can be determined whether Compton scattering occurring at one place is caused by the arrival of one event.

  In still another aspect of the present invention, the arrival position of the specific electromagnetic radiation in the linear scintillator element from the relative intensity relationship between the optical signal detected by the first detection unit and the optical signal detected by the second detection unit. To decide. In this case, it is possible to ensure the determination of the passing position of the electromagnetic radiation in the specific scintillator element.

  In still another aspect of the present invention, the information processing apparatus generates Compton scattering and photoelectric absorption or complex Compton scattering by specific electromagnetic radiation by synchronizing optical signals obtained by a plurality of linear scintillator elements. Judge that. As a result, it is possible to make an association for determining whether Compton scattering or the like generated at two places is caused by the arrival of one event.

  In still another aspect of the present invention, the sensor array has a plurality of scintillation rods doped with a fluorescent material as a plurality of sensor portions. In this case, the sensor array can be reduced in weight at low cost, and the occupied space of the sensor array can be easily expanded.

It is a notional block diagram explaining the radiation measuring device of one embodiment concerning the present invention. It is a conceptual front view of a detection window part. It is a conceptual diagram explaining the structure of the scintillation rod unit which comprises a scintillator part. (A)-(C) are the figures explaining the simulation result regarding a detection principle. It is a conceptual perspective view explaining detection operation. It is a flowchart explaining operation | movement of a radiation measuring device.

  Hereinafter, the structure and operation of the radiation measuring apparatus according to the embodiment of the present invention will be described in detail.

  The radiation measurement apparatus 100 shown in FIG. 1 detects gamma rays flying from the front direction of the detection window 20 and the vicinity thereof as electromagnetic radiation RR. The radiation measurement apparatus 100 includes a detection window unit 20, a bundle unit 30, a first detection unit 40, a second detection unit 50, and a control device 70. Here, the detection window part 20, the bundle part 30, the 1st detection part 40, the 2nd detection part 50, etc. are accommodated in the case 11 for radiation shielding with the support structure or frame member which is not shown in figure.

  The detection window portion 20 includes a two-dimensional collimator portion 21 provided so as to be exposed to the opening 11a of the case 11, and a scintillator portion 22 disposed behind the two-dimensional collimator portion 21 and having a rectangular parallelepiped shape. .

  The two-dimensional collimator unit 21 functions as an azimuth restricting unit that restricts the flying direction or incident direction of the electromagnetic radiation RR to a predetermined local area (measurement azimuth area DA) extending around the reference line BL. The first collimator 21a extending in a layered manner and the second collimator 21b extending in a layered manner are laminated. The two-dimensional collimator unit 21 is disposed so as to face a planar incident unit 22i set in a rectangular predetermined region corresponding to one side surface (a surface parallel to the XY plane) of the rectangular parallelepiped scintillator unit 22.

  The first collimator 21a limits the incident direction of the electromagnetic radiation RR with respect to the Y direction, and the limiting direction is the Y direction. The first collimator 21a has a plurality of radiation shielding plates 21c, which are long and thin flat shields, arranged in parallel in the Y direction at equal intervals in a state where the detection window portion 20 faces the -Z direction of the front. (See FIG. 2). Each radiation shielding plate 21c has the X-direction as a longitudinal direction and the Y-direction as a normal direction in a state where the detection window portion 20 faces the -Z direction of the front. Each radiation shielding plate (flat plate of the shielding body) 21c is a lead plate having a thickness of, for example, about 0.5 to 1 mm and a width of 2 cm or more (specifically, about 4 cm) in the Z direction. The shielding plates 21c are spaced apart from each other with a gap GA of about 1 to 5 mm (specifically 2 mm). With the first collimator 21a, when the electromagnetic radiation RR is detected by the detection window unit 20, a gentle focus function or directivity in the Y direction can be provided, and a vertical line that extends in parallel to the X axis intersects the reference line BL. Only the electromagnetic radiation RR from the belt-like azimuth region including the axis can be detected preferentially or selectively.

  The second collimator 21b limits the incident direction of the electromagnetic radiation RR with respect to the X direction, and the limiting direction is the X direction. The second collimator 21b is configured by arranging a large number of elongated shielding plates 21d, which are parallel to the X direction, in parallel in the X direction with the detection window portion 20 facing in the -Z direction on the front. (See FIG. 2). Each radiation shielding plate 21d has the Y direction as a longitudinal direction and the X direction as a normal direction in a state where the detection window portion 20 faces the -Z direction of the front. Each radiation shielding plate (flat plate of the shielding body) 21d has a thickness of, for example, about 0.5 to 1 mm and a width of 2 cm or more (specifically, about 4 cm) in the Z direction, like the radiation shielding plate 21c. It is a lead plate, and is spaced apart from each other with a gap GA of about 1 to 5 mm. With this second collimator 21b, when the electromagnetic radiation RR is detected by the detection window part 20, it is possible to give a loose focus function or directivity in the X direction, and it extends in parallel to the Y axis across the reference line BL. Only the electromagnetic radiation RR from the belt-like azimuth region including the axis can be detected preferentially or selectively. As a result, the first and second collimators 21a and 21b can limit the incident direction of the electromagnetic radiation RR to an intended angle of view range around the reference line BL, that is, the measurement azimuth area DA. The directivity in the −Z direction can be given to the part 22 or the detection window part 20.

  The directivity by the two-dimensional collimator unit 21 can be adjusted by setting the gap GA and the width of the first and second collimators 21a and 21b. In addition, the first and second collimators 21a and 21b are provided with posture adjusting units 21i and 21j made of stepping motors, etc., so that the postures of the individual radiation shielding plates 21c and 21d can be changed. The unit 21 can function as a focal system. Specifically, each radiation shielding plate 21c can be rotated around a rotation axis parallel to the X axis by the attitude adjustment unit 21i, and each radiation shielding plate 21d can be rotated in parallel to the Y axis by the attitude adjustment unit 21j. A function of focusing on the finite distance or the infinity with respect to the X direction and the Y direction by directing these radiation shielding plates 21c and 21d to one point of the finite distance or the infinity of the reference line BL. Can be given.

  When the posture adjusting units 21i and 21j for the radiation shielding plates 21c and 21d are provided, a scanning function can be provided instead of the focus function. Specifically, by adjusting the inclination angle of each radiation shielding plate 21c with respect to the reference line BL by the attitude adjustment unit 21i and gradually changing the inclination angle, the first collimator 21a can perform scanning in the Y direction. . In addition, by adjusting the inclination angle of each radiation shielding plate 21d with respect to the reference line BL by the attitude adjustment unit 21j and gradually changing the inclination angle, the second collimator 21b can perform scanning in the X direction.

  As will be described later, the incident direction of the electromagnetic radiation RR can be specified by detecting the electromagnetic radiation RR at a plurality of locations in the scintillator unit 22, but the two-dimensional collimator unit 21 provides directivity as described above. As a result, the frequency of the electromagnetic radiation RR incident on the scintillator unit 22 can be reduced and the amount of data can be suppressed, so that the burden of signal processing on the output of the scintillator unit 22 can be reduced. Further, by operating the scintillator unit 22 and adjusting the postures of the collimators 21a and 21b, it is possible to perform scanning that changes the azimuth and distance of measurement by the radiation measuring apparatus 100. In addition, by using the radiation shielding plates 21c and 21d, it becomes possible to eliminate the background signal that uniformly enters from the surroundings in the region adjacent to the radiation shielding plates 21c and 21d, so that the case 11 itself has radiation shielding properties. Is not required.

  The scintillator unit 22 is a three-dimensional sensor array. The size of the scintillator 22 is about 50 cm on a side in a specific embodiment. The scintillator section (sensor array) 22 has a large number of long and thin linear scintillation rod units 22a (that is, scintillator elements) extending in the Y direction, which are regularly spaced in two dimensions in the X and Z directions at a pitch of 3 to 5 mm, for example. They are arranged in close proximity and fill a cube-shaped space. The scintillator section 22 is filled with, for example, 100 × 100 to 170 × 170 scintillation rod units (scintillator elements) 22a. Thus, by making the scintillator 22 three-dimensional, it is possible to increase the sensitivity to the electromagnetic radiation RR, and to accurately measure the radiation dose from unknown radiation sources including weak ones. When electromagnetic radiation RR is incident on the scintillation rod unit 22a and Compton scattering or photoelectric absorption associated with the Compton scattering occurs, fluorescence due to scintillation light emission corresponding to Compton scattering is emitted from both ends of the scintillation rod unit 22a. The

  As shown in FIG. 3, the scintillation rod unit 22a is a linear scintillator element, and includes a prismatic rod body (scintillation rod) 25a, a cylindrical sheath portion 25b, and connector portions 25c and 25d. The rod body (scintillation rod) 25a is formed from a single material by injection molding, and converts the radiation that has passed through the two-dimensional collimator unit 21 into an optical signal. Specifically, the rod body 25a is a non-coated structure in which a core of an optical fiber is exposed, which is a member of polystyrene, acrylic or other plastics doped with a phosphor. That is, the side surface of the rod body 25a is a mirror surface with almost no optical loss. The size of the rod body 25a is, for example, about 2 × 2 mm in cross section and about several tens cm to 1 m in length. The rod body 25a is an active index for gamma rays. In a specific example, the rod body 25a scatters, for example, 0.622 MeV gamma rays originating from cesium 137, and outputs scintillation light emission generated by Compton electrons as detection light. The sheath portion 25b is an outer cylinder portion having a mirror 26b on the inner surface, and is a mirror 26b made of Al or the like on the inner surface of a mylar film 26a that is thin enough to ignore the scattering of electrons (for example, a thickness of several tens to several hundreds μm). It is obtained by preparing a sheet formed by vapor deposition or the like, and cutting the sheet appropriately and then bonding the seam in a state of being wound in a cylindrical shape. On the one hand, the sheath part 25b is fitted to the outer periphery of the support member 25g fixed to one end of the rod body 25a and joined to the connector part 25c, and on the other hand, the support fixed to the other end of the rod body 25a. It fits on the outer periphery of the member 25g and is joined to the connector portion 25d. One connector portion 25 c is composed of a lens, a light guide, and the like, and is connected to or coupled to one end of an optical fiber 31 that is supported by a frame member (not shown) and constitutes the bundle portion 30. The detection light from the rod body 25a is guided to the optical fiber 31 by the connector portion 25c. The other connector portion 25d is connected or coupled to the incident surface of the second detection portion 50 via optical grease or the like. The detection light from the rod body 25a is guided to the second detection unit 50 by the connector unit 25d. The connector part 25d provided corresponding to all the scintillation rod units 22a constitutes the connection part 28 (see FIG. 1) as a whole. Each scintillation rod unit 22a is supported in an aligned state by a plurality of mesh-like supports (not shown) that are fixed in the case 11 and extend in a direction orthogonal to the scintillation rod unit 22a.

  When scintillation light (fluorescence due to scintillation light emission phenomenon) generated in the rod body 25a is incident on the inner surface 25h of the rod body 25a at an angle θ1 that is equal to or greater than the critical angle of total reflection (that is, in the case of light L1), the efficiency is small. Propagation. At this time, since the rod body 25a is bare and does not have a clad, the critical angle of total reflection can be made as small as possible, and the conditions for total reflection of the scintillation light are relaxed, so that the transmission efficiency of the scintillation light is increased. be able to. Further, when the total reflection condition is not satisfied, that is, when the light is incident on the inner surface 25h of the rod body 25a at an angle θ2 equal to or less than the critical angle of total reflection (that is, in the case of the light L2), the light is reflected by the mirror 26b on the inner surface of the sheath portion 25b. Since propagation is possible, loss of scintillation light can be further reduced.

  Returning to FIG. 1, the bundle unit 30 is a collection of many optical fibers 31 for guide. One end of the optical fiber 31 is coupled to the output end of each scintillation rod unit 22a constituting the scintillator section 22 via a connector board 27 in which a large number of connector sections 25c shown in FIG. 3 are assembled, and the other end of the optical fiber 31 is connected to the connector board. It is positioned and fixed so as to oppose the lattice point of the light receiving part 41a of the photoelectric imaging tube part 41 provided in the first detection part 40 via (not shown). The bundle unit 30 transmits an optical signal to the light receiving unit 41 a of the photoelectric imaging tube unit 41 while maintaining the arrangement relationship of the scintillation rod units 22 a constituting the scintillator unit 22.

  The first detection unit 40 is connected to one end side of the scintillator unit (sensor array) 22 via the bundle unit 30 and detects an optical signal from the scintillator unit 22 as a two-dimensional optical signal distribution. That is, the first detection unit 40 converts an optical signal emitted to one side of the scintillator unit 22 into an electrical signal corresponding to a two-dimensional optical signal distribution (specifically, a distribution of detected charges corresponding to light intensity). ). The first detection unit 40 includes a photoelectric imaging tube unit 41 and a reading unit 43, and detects and amplifies a pixel pattern that maintains the lattice-like arrangement of the scintillation rod units 22a constituting the scintillator unit 22 as they are. Thereby, the scintillation light generated in each scintillation rod unit 22a can be detected together with the position information in the XZ plane. The photoelectric imaging tube portion 41 has a structure housed in a vacuum vessel, and a detailed description is omitted, but a light receiving portion 41a that is an input portion for photoelectric conversion and incident electrons are converted into light. An electrostatic converging system (not shown) for converging electrons after photoelectric conversion is provided between the output unit 41c that forms an image. Here, the light receiving unit 41a has an optical window made of glass, and a photoelectric conversion surface is formed inside the optical window by vapor deposition of a photoelectric conversion material having predetermined characteristics. The output unit 41c has a phosphor screen coated with a phosphor having a predetermined characteristic on the incident side, and a micro channel plate (MCP) for multiplying the fluorescence image from the phosphor screen is arranged on the emission side. You can also

  The reading unit 43 includes a relay optical system 43a, a fine imaging unit 43b, and the like. The relay optical system 43a is a projection optical system that projects the image of the output unit 41c of the photoelectric imaging tube unit 41 on the imaging surface of the fine imaging unit 43b at approximately the same magnification. The fine imaging unit 43b includes, for example, a solid-state imaging device that is a CMOS type imaging device and a drive circuit that causes the solid-state imaging device to perform an imaging operation, and causes the solid-state imaging device to perform an imaging operation. The fine imaging unit 43b converts a fine image of weak light formed on the output unit 41c of the photoelectric imaging tube unit 41 into a pixel digital signal at a video rate and outputs it. Although not shown, a coarse image capturing unit such as a multi-anode type photomultiplier is provided on the optical path branched from the relay optical system 43a, and the fine imaging unit 43b performs an imaging operation. A trigger signal is given to the drive circuit that performs the above.

  The 2nd detection part 50 is connected with the other end side of the scintillator part (sensor array) 22, and detects the optical signal from the scintillator part 22 per division. That is, the second detection unit 50 converts an optical signal emitted to the other side of the scintillator unit 22 into an electrical signal (specifically, an optical signal corresponding to an optical signal obtained by batching a plurality of scintillation rod units 22a in the partition. Detected as a detected charge corresponding to the incident light intensity). The second detection unit 50 includes a plurality of block-like photomultiplier tubes 51 arranged in a two-dimensional matrix along the XZ plane. For example, about 17 × 17 to 10 × 10 constituting the scintillator unit 22. The electric signals corresponding to the optical signals from the unit group 22g composed of the group of scintillation rod units 22a set to are collectively detected and amplified. Thereby, scintillation light generated by the plurality of scintillation rod units 22a constituting the unit group 22g can be detected in a lump. Each photomultiplier tube 51 has a structure in which a photocathode, a secondary electron multiplier electrode, an anode, and the like are enclosed in a vacuum vessel.

  Although it depends on the incidence frequency of the electromagnetic radiation RR, since the scintillation light emitted from one end of the specific scintillation rod unit 22a is detected together with the position information by the first detection unit 40, the second detection unit 50 performs the first detection. When the scintillation light is detected simultaneously with the unit 40, if there is a scintillation rod unit 22a common to both the detection units 40 and 50, it is determined that the same event, that is, the scintillation light caused by the same electromagnetic radiation RR is detected. It is no longer necessary to detect accurate position information by the two detectors 50. The number of scintillation rod units 22a constituting the unit group 22g is appropriately set in consideration of the type of radiation source, the use of the radiation measuring apparatus 100, and the like. Note that the second detection unit 50 may include a photoelectric imaging tube unit 41, a reading unit 43, and the like, like the first detection unit 40. In this case, complete position information can be obtained independently by the first detector 40 and the second detector 50.

  The control device 70 is an information processing device, monitors the image signal and the intensity signal output from the first and second detection units 40 and 50, and outputs them to the outside while keeping them in the storage device. Specifically, when the electromagnetic radiation RR from the target radiation source is incident on the detection window unit 20, that is, when scintillation light is detected, the control device 70 is based on the trigger output from the first detection unit 40. The address or position in the XZ plane of the scintillation rod unit 22a that has detected the light emission is specified. Further, the control device 70 is generated in the scintillation rod unit 22a based on the signal intensity from the first and second detection units 40 and 50 (specifically, the corrected intensity value obtained by calibrating the detected charge). The position of the scintillation light in the Y-axis direction is specified. Thereby, the production | generation position of the scintillation light in the scintillator part 22 is detectable as three-dimensional information. Further, the control device 70 estimates the intensity of each scintillation light and the energy of Compton scattering or photoelectric absorption based on the signal intensity from the first and second detection units 40 and 50. When such scintillation light is detected at approximately two locations at substantially the same time, the incident direction of the electromagnetic radiation RR can be narrowed down along with the type of radiation source based on their emission positions and scattered energy, as will be described later. Can be clearly specified in the incident direction of the electromagnetic radiation RR. Further, by adjusting the postures of the radiation shielding plates 21c and 21d using the posture adjusting units 21i and 21j, it is possible to perform precise radiation measurement by changing the measurement azimuth area DA over a wide range.

  4A to 4C are diagrams for specifically explaining the principle of radiation detection in the scintillator section 22. FIG. 4A shows a side view of a track (white solid line) of 100 gamma rays shot at the same point from one direction on a plastic scintillator made of the same material as the rod body 25a of the scintillation rod unit 22a using simulation. Show. The 0.622 MeV gamma rays emitted from cesium (Cs) 137 mainly cause Compton scattering in the material. Scattering occurs at the point where the direction is changed in the track of the gamma rays in FIG. 4A, and the electrons are recoiled. This energy gamma ray repeatedly undergoes Compton scattering in the material, and eventually disappears due to the photoelectric absorption reaction while losing energy. That is, in a cube filled with a scintillation rod unit 22a having a depth of about 0.5 m, that is, in a 0.5 m cube plastic scintillator, 0.622 MeV gamma rays pass almost all of their energy to electrons and come out. It has been completely absorbed. From this, it can be considered that the average output value from the scintillation rod unit 22a arranged on the back side farthest from the two-dimensional collimator unit 21 in the scintillation rod unit 22a represents the background level. The output value of the scintillation rod unit 22a can be used for S / N separation.

  The scattered electrons cause an ionization reaction while running in a 0.5 m cubic plastic scintillator, and emit fluorescence by a scintillation emission phenomenon. An electron generated by Compton scattering that occurs first when 0.622 MeV gamma rays are incident travels about 1 mm and emits light during that time. As shown in FIG. 4 (B), only a track of electrons of 10 keV or more generated from the previous gamma-ray irradiation simulation example is shown by a white point, and as shown in FIG. 4 (C), the previous gamma-ray irradiation simulation example Only the tracks of electrons of 100 keV or more generated from the above are shown by white dots. As can be seen from the figure, when electrons of 100 keV or higher are selected, electrons are more concentrated in the arrival direction of gamma rays and generated in a straight line. That is, if a light emission point of about 1 mm corresponding to 100 keV or more is selected, electrons due to Compton scattering caused by gamma rays are detected first, and electrons due to the next Compton scattering induced by this may be detected. It becomes relatively easy. As a result, it is possible to specify the gamma rays coming from cesium 137 and to specify the orientation of the cesium 137.

With reference to FIG. 5, the incident direction of the electromagnetic radiation RR and the measurement principle of energy will be specifically described. The direction and distance of the measurement target are limited by the two-dimensional collimator unit 21. In this state, for example, electromagnetic radiation RR, which is a gamma ray radiated from Cs 137 with energy E _g = 0.662 MeV, enters one scintillation rod unit 22 a in the scintillator section (sensor array) 22 as an incident photon GR. In the scintillation rod unit 22a, the incident photons GR is cause recoil electrons undergo Compton scattering, the energy of recoil electrons is assumed to be E _1. Further, the scattered photon GR2 generated due to the Compton scattering of the incident photon GR is incident on the scintillation rod unit 22a at another position. Within this scintillation rod unit 22a, the photoelectric absorption electron energy E ₂ occurs released by scattered photons GR2. Here, it is assumed that the light attenuation function f (y) representing the light attenuation at the position y in the Y direction in the rod body 25a (see FIG. 3) of the full length LSR constituting the scintillation rod unit 22a is obtained in advance by actual measurement. . On the first detection unit 40 side, e ₁ = f (y ₁ ) and e ₂ = f, where E ₁ and E ₂ are energy released by scattering and photoelectric absorption at the positions y ₁ and y ₂ of the scintillation rod unit 22a. It is assumed that photometry is performed as (y ₂ ), and photometry is performed as e ′ ₁ = f (LSR−y ₁ ) and e ′ ₂ = f (LSR−y ₂ ) on the second detection unit 50 side. From the measured values e ₁ , e ₂ , e ′ ₁ , e ′ ₂ and the light attenuation function f (y) in such an event, emission positions (arrival positions) y ₁ , y ₂ due to scattering of two electrons, etc., The energy E ₁ and E ₂ can be reconstructed and obtained. That is, the optical signal detected by the first detection unit 40 or the measured values e ₁ and e ₂ and the optical signal detected by the second detection unit 50 while considering the sensitivity difference between the first and second detection units 40 and 50. Alternatively, the arrival positions of the incident photon GR and the scattered photon GR2 in the corresponding two scintillation rod units 22a can be determined based on the relative intensity relationship with the measured values e ′ ₁ and e ′ ₂ . At that time, the energies E ₁ and E _{2 of} the incident photon GR and the scattered photon GR2 can also be estimated. Then, using techniques conventional Compton camera, Motomari Compton scattering angle theta ₁₂ of the incident photons GR, emission position (destination position) corresponding to the scattering y _1, opening angle about an axis AX1 determined from y ₂ theta The radiation source of incident photons GR is limited on ₁₂ cones. Note that cone of the opening angle theta ₁₂ is adapted to include a shaft AX0 corresponding to the incident direction of the electromagnetic radiation RR.

  In the actual visualization of the direction distribution, directivity by the two-dimensional collimator unit 21 (that is, the effect of restricting the focal field), background events coming from other than the measurement target, errors in each measurement value, and the like are also taken into consideration. Further, the likelihood or probability density function as a function of direction is estimated for each case or event, and the density distribution of Cs137 or the like as the radiation source is calculated based on the overlap of the probability density function due to many cases or events and the calibration data. Derived and visualized. Here, the case of two scattered electrons has been described as an example of explanation, but an event caused by multiple times of Compton scattering or the like can be similarly analyzed and reconstructed. Conventionally, plastic scintillators (using a phosphor-doped plastic as the rod body 25a) are not suitable for energy measurement because of their low atomic number and poor photoelectric absorption efficiency despite their cost efficiency and high processability. I came. In the scintillation detection using the scintillator unit 22 having a large sensitive volume of, for example, 0.5 m × 0.5 m × 0.5 m as in the present embodiment, the original gamma ray is derived from all the electron energies detected in the detector. Since the energy and direction of the photon, that is, the incident photon GR can be accurately reconstructed, the problem of the low atomic number of the plastic scintillator can be overcome.

In the above, in the second detection unit 50, the common photomultiplier tube 51 is used for the unit group 22g including the group of scintillation rod units 22a. When Compton scattering or the like occurs in the vicinity, the photomultiplier tube 51 is used. The energy of the two incident photons GR cannot be distinguished. That is, when Compton scattering or the like occurs close to a predetermined value or more, the measured values e ′ ₁ and e ′ ₂ due to the two incident photons GR are not independent and the sum e ′ ₁₂ = e ′ ₁ + e ′ ₂ Is measured by the photomultiplier tube 51, but the measured values e ₁ and e ₂ resulting from the two incident photons GR can be separated and recognized from the resolution by the photoelectric imaging tube unit 41 of the first detection unit 40. Although the accuracy is lowered, the energy E ₁ , E ₂ and the Compton scattering angle θ ₁₂ can be estimated in light of other detection information. Therefore, it is possible to measure without waste even when Compton scattering etc. is close, and the probability density function for each direction of the radioactive material obtained from the likelihood can be accurately calculated, contributing to the determination of the radiological examination. To get.

  Hereinafter, an outline of the operation of the radiation measuring apparatus 100 shown in FIG. 1 will be described with reference to FIG. First, the first detection unit 40 and the second detection unit 50 are operated in parallel to start a measurement operation for detecting the incidence of electromagnetic radiation RR or incident photons GR on the scintillator unit 22 (step S11).

  The control device 70 detects the light signal in units of the scintillation rod unit 22a detected by the first detection unit 40 and the light intensity signal (specifically, an electric signal corresponding to the light intensity) detected by the second detection unit 50. Threshold processing is performed while synchronizing, and it is determined that specific electromagnetic radiation RR (incident photon GR) that is the same event is incident (step S12).

  Next, the control device 70 detects the light intensity signal detected by the first detection unit 40 (specifically, a value obtained by correcting the detected charge) and the light intensity signal detected by the second detection unit 50 (specifically, detection). And determining the incident position or the arrival position of the specific electromagnetic radiation RR (incident photon GR) in the Y direction based on the corrected charge), the three-dimensional incident position of the specific electromagnetic radiation RR or The light emission position is determined (step S13). The incident position or arrival position of the electromagnetic radiation RR in the XZ direction is specified by the vertical / horizontal position or address of the scintillation rod unit 22a that has detected the optical signal.

  In parallel with this, the control device 70 detects the scattered photon GR2 resulting from the incidence of the specific electromagnetic radiation RR (incident photon GR), which is the same event obtained in step S12 (step S14). That is, the control device 70 performs threshold processing while synchronizing the optical signal in units of the scintillation rod unit 22 a detected by the first detection unit 40 and the optical signal detected by the second detection unit 50, thereby performing scattering. The detection of the photon GR2 is determined. Whether or not the scattered photon GR2 is detected can be determined whether or not there is a correlation by synchronizing with the optical signal obtained in step S12. That is, it is possible to determine that Compton scattering and photoelectric absorption have occurred due to the specific electromagnetic radiation RR by performing measurement while synchronizing optical signals obtained by the plurality of scintillation rod units 22a. Specifically, when the incident photon GR and the scattered photon GR2 are detected substantially simultaneously in the order of picoseconds, the scattered photon GR2 is generated due to the incident photon GR, and the Compton scattering due to the specific electromagnetic radiation RR, etc. Specifically, it is determined that Compton scattering fluorescence due to the incident photon GR and photoelectric absorption due to the scattered photon GR2 are sequentially generated.

  Next, the control device 70 determines the incident position or the arrival position of the scattered photon GR2 in the Y direction based on the optical signal detected by the first detection unit 40 and the optical signal detected by the second detection unit 50. Thus, the three-dimensional incident position or light emission position of the scattered photon GR2 is determined (step S15). The incident position or the arrival position of the scattered photon GR2 in the XZ direction is specified by the vertical / horizontal position or address of the scintillation rod unit 22a that detects the optical signal.

Next, based on the incident position and light intensity obtained in step S12 and the incident position and light intensity obtained in step S14, the control device 70 determines the energy of the incident photon GR that is the electromagnetic radiation RR and the Compton scattering angle θ. ₁₂ is determined (step S16).

  By repeating the above steps S11 to S16, it is possible to detect the incidence of a plurality of electromagnetic radiations RR corresponding to a plurality of events, and the control device 70 can accurately identify the incident direction of the electromagnetic radiation RR. Incidence frequency can also be measured. The control device 70 performs background correction processing on such a result, further performs statistical processing to increase accuracy, and integrates processing such as processing into a two-dimensional distribution map by data visualization. Is performed (step S17). As a result, it is possible to perform information processing for converting a radiation dose from an unknown radiation source into a probability density function for each direction while specifying a radiation substance.

  Here, the background correction processing will be briefly described. Regarding the background, it is conceivable to use (1) measurement at the same time in different directions and (2) use measurement at the same time in different directions. In the case of the same direction at different times, the scintillator unit 22 can be rotated, for example, in the horizontal azimuth direction, and the amount of background can be measured by directing the scintillator unit 22 toward the direction where there is no gamma ray radiation source. Specifically, after the measurement is started and after the measurement is started, the scintillator unit 22 is rotated by about 90 °, for example, so that the measurement target region is swung out of the measurement visual field of the two-dimensional collimator unit 21. Good. In the case of different orientations at the same time, while measuring and counting gamma rays incident on a shallow area close to the two-dimensional collimator unit 21, the scintillator unit 22 is close to three surfaces adjacent to the surface facing the two-dimensional collimator unit 21. Counts and counts gamma rays incident on shallow areas simultaneously. By correcting the relative ratio of the obtained results for each azimuth to increase the attenuation effect of gamma rays by the two-dimensional collimator unit 21, the background can be corrected. The attenuation effect of gamma rays by the two-dimensional collimator unit 21 can be accurately predicted by simulation if the incident direction distribution is obtained by actual measurement.

  According to the radiation measurement apparatus 100 of the above embodiment, since the radiation measurement apparatus 100 uses the three-dimensional scintillator unit (sensor array) 22 and the first detection unit 40, the electromagnetic radiation RR flying in a relatively wide space is detected. It can be regarded as two-dimensional image information corresponding to the arrangement of scintillation rod units (scintillator elements) 22a, and electromagnetic radiation can be detected with reduced costs. In addition, by using the detection results of the first and second detection units 40 and 50, the passing position of the electromagnetic radiation RR in the scintillation rod unit 22a can be narrowed down, and a series of Comptons resulting from the arrival of the specific electromagnetic radiation RR Generation positions such as scattering can be detected as a plurality of arrival positions of the electromagnetic radiation RR, and the flying direction or the incident direction of the electromagnetic radiation RR can be directly measured.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and can be implemented in various modes without departing from the gist thereof. Such modifications are also possible.

  That is, the rod body 25a is not limited to a prismatic shape but can be a cylindrical shape, and the sheath portion 25b can be omitted. In the case where the sheath portion 25b is omitted, a thin light shield can be disposed instead. The arrangement density, arrangement space, and the like of the scintillation rod unit 22a can be changed as appropriate according to the application. Further, it is possible to arrange so that a gap is provided between the scintillation rod units 22a within a range in which the influence on the detection capability is allowed.

  The two-dimensional collimator unit 21 can be omitted. In the two-dimensional collimator unit 21, only one of the first and second collimators 21a and 21b can be omitted.

  A mount for directing the radiation measuring apparatus 100 in a desired direction can be added, and a driving means is attached to the base to perform scanning in the measuring direction by the radiation measuring apparatus 100 to widen the angle of view and range of measurement. You can also.

  AX0, AX1 ... axis, BL ... reference line, DA ... measurement azimuth region, GR ... incident photon, GR2 ... scattered photon, RR ... electromagnetic radiation, 11 ... case, 20 ... detection window part, 21 ... dimensional collimator part, 21a , 21b ... Collimator, 21c, 21d ... Radiation shielding plate, 21i, 21j ... Posture adjustment unit, 22 ... Scintillator unit, 22a ... Scintillation rod unit, 22g ... Unit group, 22i ... Incident unit, 25a ... Rod body, 25b ... Sheath part, 25c ... Connector part, 25d ... Connector part, 25g ... Support member, 25h ... Inner surface, 26a ... Mylar film, 26b ... Mirror, 27 ... Connector substrate, 30 ... Bundle part, 30 ... Bundle part, 31 ... Optical fiber, 40: first detection unit, 41: photoelectric imaging tube unit, 41a: receiving Department, 41c ... output unit, 43 ... reading unit, 43 b ... definition imaging unit, 50 ... second detector, 51 ... photomultiplier tube, 70 ... controller, 100 ... radiation measurement instrumentation

Claims (9)

A three-dimensional sensor array in which a plurality of linear scintillator elements extending in a predetermined direction are two-dimensionally arranged in a direction perpendicular to the predetermined direction;
A first detector connected to one end of the sensor array in the predetermined direction and detecting an optical signal from the sensor array as a two-dimensional optical signal distribution;
A second detection unit connected to the other end of the sensor array in the predetermined direction to detect an optical signal from the sensor array;
The arrival position of electromagnetic radiation is determined based on the detection results of the first and second detection units, and the incident direction of the specific electromagnetic radiation is determined based on detection information including a plurality of arrival positions corresponding to the specific electromagnetic radiation. A radiation measurement apparatus comprising: an information processing apparatus that obtains flight information related to the.   The radiation measurement apparatus according to claim 1, further comprising an azimuth restriction unit that azimuthally restricts the incidence of electromagnetic radiation on the sensor array.   The azimuth restricting portion is arranged to face a planar incident portion set in a predetermined region between the one end side and the other end side of the sensor array, and closes flat plates of a plurality of shields. The radiation measuring apparatus according to claim 2, wherein the radiation measuring apparatus has at least one collimator arranged.   The radiation measurement apparatus according to claim 3, wherein the orientation restriction unit includes two collimators whose restriction orientations intersect each other.   The said information processing apparatus determines the energy of the scattered electron derived from the said specific electromagnetic radiation based on the intensity | strength of the optical signal per scintillator element detected by the said 1st detection part. The radiation measuring apparatus according to one item.   The information processing apparatus is configured to detect the incidence of the specific electromagnetic radiation by synchronizing the optical signal detected by the first detection unit in units of scintillator elements and the optical signal detected by the second detection unit. The radiation measuring apparatus according to claim 1, wherein the radiation measuring apparatus is determined.   The arrival position of the specific electromagnetic radiation in the linear scintillator element is determined from a relative intensity relationship between the optical signal detected by the first detection unit and the optical signal detected by the second detection unit. Item 7. The radiation measurement apparatus according to Item 6.   The information processing apparatus determines that Compton scattering and photoelectric absorption or complex Compton scattering is caused by the specific electromagnetic radiation by synchronizing optical signals obtained by the plurality of linear scintillator elements. Item 8. The radiation measurement apparatus according to any one of Items 6 and 7.   The radiation measurement apparatus according to claim 1, wherein the sensor array includes a plurality of scintillation rods doped with a fluorescent material as the plurality of sensor units.

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