JPH0651069A - Radiation sensor - Google Patents

Abstract

PURPOSE:To provide a radiation sensor which is embodied in a simple structure and which has an enhanced position resolution in the depth direction without causing drop of the energy resolution. CONSTITUTION:Two scintillators 111a, 111b made of the same material in sole substance composition are coupled with photo-sensors 120a, 120b in 1:1 proportion and bundled with air interposed. The joint surface of the scintillators each other 111a, 111b is specular finished in one region on the photo-sensor side and coarse finished in the other region while the boundary is laid at the middle point in the depth direction. As a result, the photo-transmittance between the two scintillators has a two-value discrete distribution over the depth direction. A reflecting agent 130 is applied over except the joint surfaces of scintillators 111a, 111b and the joint surfaces of the photo-sensors 120a, 120b so that the scintillation light generated inside of either scintillator is hindered from radiating to outside of the radiations sensor concerned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector for detecting gamma rays.

[0002]

2. Description of the Related Art A reagent labeled with a radioisotope is put into an object to be measured, and a pair of photons (γ rays) generated by pair annihilation of a positron emitted from the radioisotope and an electron in a normal substance A positron CT device (or PET (Positron E) that measures and measures the internal substance distribution of the measured object.
(mission tomography) device) is drawing attention. In this case, pair annihilation occurs in the state where kinetic energy of both positron and electron is sufficiently smaller than mass energy,
At that time, each photon energy in the two-photon production mode, which is the transition mode with the highest probability, is almost the same as the mass energy (0.511 Mev) of the positron or electron. In addition, since almost positrons and electrons also undergo pair annihilation in a stationary state, two photons are emitted in opposite directions according to the conservation law of momentum.
The substance distribution is measured by measuring the characteristic photon pairs as described above, estimating the positron-electron pair annihilation occurrence position, and obtaining the pair annihilation frequency near each point in the measured object.
In consideration of the energy of each photon and the current measuring means, a measurement system is generally used in which scintillation light emission in the γ-ray detection element is caused by the photon and then the scintillation light is detected by a photodetector.

Such a PET device is composed of a γ-ray detecting element (for example, a BGO scintillator) and a photodetector.
A large number of line detectors are arranged in a multilayer ring with respect to a predetermined axis. Two photons of the above specific energy (0.511Mev)
The line detector simultaneously recognizes that positron-electron pair annihilation has occurred, and spatially connects the scintillation emission positions in the scintillator caused by each photon incidence to estimate the position of pair annihilation. . The resolution of the PET device depends on the resolution of this scintillation emission position.

In the original PET device, wherever scintillation light emission occurs in the same γ-ray detection element, the representative point of the γ-ray detector (for example, the center point of the detector entrance surface) is set as the scintillation emission position. I was thinking
That is, the resolution of the scintillation light emission position matched the size of the γ-ray detection element. In recent years, in order to improve the resolution, the γ-ray detection element has been reduced in diameter, and the position detection resolution in the generatrix direction and the circumferential direction of the multilayer ring has been improved. The position resolution is also improved in the radial direction (hereinafter referred to as the depth direction), which is difficult to shorten in order to maintain the photon detection efficiency.

The necessity of improving the position resolution in the depth direction is shown in FIG.
Will be described with reference to. FIG. 6 is a conceptual diagram of a cross section of the PET apparatus. A radiation detector 300 including a scintillator 310 and a photodetector 320 is arranged in a ring shape, and an object to be measured 350 is installed in the ring. Point P near the center of the field of view
The γ-ray generated by the pair annihilation in 1 is the γ-ray detector 3
Even if it hits 00, the γ-ray detector 3
The deviation between the line connecting the representative points of 00 and the line connecting the actual scintillation emission positions is within the incident surface of the γ-ray detection element 310, and therefore the error is relatively small. However, since the γ-rays generated in the peripheral part of the visual field (for example, the point P2) are inclined and incident from the direction perpendicular to the incident surface of the γ-ray detection element 310, the incident γ-ray detector 310 emits scintillation light emission. The other γ-ray detection element 310 that transmits without causing it
May emit scintillation light. In the pair annihilation example at the point P2 shown in FIG. 6, the γ-ray detectors A and B are transmitted, and the γ-ray detector C emits scintillation light emission. In this case, if the γ-ray detector does not have the resolution in the depth direction, the line connecting the γ-ray detectors will connect the representative points of the γ-ray detectors, and as shown in the figure, the actual The positional deviation from the line connecting the light emitting points becomes larger than that in the above case. Therefore, if the depth direction positional resolution of each radiation detector is improved, the spatial resolution of the peripheral part of the visual field can be improved as a PET device.

As a typical example of this trial, there is one in which the structure of the detecting element is devised as shown in FIG. Figure 5 (a)
Shows a main part of a radiation position detector according to an embodiment disclosed in Japanese Patent Application No. 62-117885 (hereinafter, referred to as Conventional Example 1). In this radiation position detector, one plate-shaped scintillator 210 provided with a plurality of grooves 211 and 212 is
It is coupled to a photomultiplier tube 220 (for example, a multi-anode type photomultiplier tube or a single anode type photomultiplier tube group) provided with a photodetection segment for each region divided by the groove 212. Groove 21 dug from the photon entrance surface
1 and the groove 2 dug from the surface connecting the photomultiplier tube 220
The photomultiplier tubes 22 are arranged in a staggered manner.
The scintillator surface and the groove 211 excluding the 0 bonding surface,
212 includes a reflector 230 for scintillation light.
Has been applied. This radiation position detector has a photomultiplier tube 22 if the number of the above-mentioned segments in which light is detected is one.
It is judged that scintillation light emission has occurred on the side of the coupling surface with 0, and on the other hand, if there are two or more light-detecting segments, it is judged that scintillation light emission has occurred on the side of the photon incident surface, and the position of the scintillator in the depth direction The resolution is improved.

FIG. 5B shows a main part of a radiation position detector according to an embodiment disclosed in Japanese Patent Application No. 63-57233 (hereinafter, referred to as Conventional Example 1). In this radiation position detector, a plurality of plate-like or columnar scintillators 250 are bundled into two layers, and each layer is arranged with a shift of one half of the scintillator interval, and the layers are optically coupled, and one layer is formed. It is coupled to the photomultiplier tube 220. Each of the scintillators in the same layer is coated with a reflector 230 except for the multi-layer and the joint surface with the photomultiplier tube 220.
Is provided with a photodetection segment for each scintillator of the layers to be joined (eg, a multi-anode photomultiplier tube or a group of single-anode photomultiplier tubes). Similar to the above-mentioned radiation position detector, this radiation position detector determines that scintillation light emission has occurred on the coupling surface side with the photomultiplier tube 220 if there is only one segment from which light is detected, If there are two or more light-detected segments, it is determined that scintillation light emission has occurred on the photon incident surface side, and the position resolution in the depth direction of the scintillator is improved.

Further, a plurality of types of scintillators having different emission decay times are arranged in layers in the depth direction to detect the depth of the emission position from the difference in the decay time (WHWong: Designing
a Stratified Detection System for PET Cameras: IEE
E Trans Nucl Sci vol.33, No.1 (1986) 591; hereinafter referred to as Conventional Example 3; not shown), three-dimensionally measures the scintillation emission position by combining a semiconductor position detector and a photomultiplier tube. Device (SEDrenzo et al .: Initial Cha
racterization of a Position-Sensitive Photodiode / B
GO Detector for PET: IEEE Trans Nucl Sci vol.36, N
o.1 (1989) 1084; hereinafter referred to as Conventional Example 4; not shown) has been proposed and manufactured.

[0009]

In the conventional radiation detector, the position resolution in the depth direction is improved as described above, but in the conventional examples 1 to 3, the structure of the scintillator which is the detection element is complicated. However, in Conventional Example 4, the structure of the γ-ray detector was inevitably complicated due to the necessity of coexisting different measurement methods. Further, in the conventional examples 1 and 2, since the reflection layer is finely divided, the probability of absorption of scintillation light in the reflection layer is increased, so that the amount of light reaching the photodetector is decreased, and as a result, the energy resolution is lowered and the γ-rays are reduced. I had to take measurements.
Further, in Conventional Example 4 as well, since the scintillation light is guided to the semiconductor position detector installed separately from the photodetector, the amount of light reaching the photodetector is reduced, and as a result, the energy resolution is reduced and γ-ray measurement is performed. I had to.

The present invention has been made to solve the above problems, and has a simple structure, and a radiation detector having an improved position resolution in the depth direction without lowering the energy resolution. The purpose is to provide.

[0011]

One of the radiation detectors of the present invention is a radiation detector in which two photodetectors are joined to two scintillators joined at the scintillator joining surface by a photodetector joining surface. The two scintillators and the two photodetectors are connected in a one-to-one manner, the light transmittance between the scintillators is changed in the direction perpendicular to the photodetector coupling surface, and the scintillator bonding surface and the photodetector coupling surface are excluded. It is characterized in that a reflection agent is applied to form a scintillator and the light emission position in the scintillator is detected. In this case, the scintillators are bundled together via air, and the light transmittance of the joint surface is changed continuously or discretely. As one method of changing this light transmittance,
It may be due to the surface roughness of the bonding surface. When the change in the light transmittance between the scintillators is a binary discrete distribution, the scintillator joint surfaces may have a two-region structure of an air region and a reflection region corresponding to the light transmittance.

Another radiation detector of the present invention is a radiation detector in which two photodetectors are coupled to each other at a photodetector coupling surface to two scintillators which are coupled at a scintillator bonding surface. The scintillator and the two photodetectors are combined in a one-to-one manner, the two scintillators are bundled via air, and the reflection direction randomness of the surface opposite to the scintillator joint surface is perpendicular to the photodetector joint surface. The scintillator joint surface and the photodetector joint surface are changed to be coated with a reflecting agent, and the light emission position in the scintillator is detected. In this case, the reflection direction randomness change on the surface opposite to the scintillator joining surface is changed continuously or discretely. One method of forming the randomness is considered to be surface roughness.

[0013]

Since one radiation detector of the present invention is configured as described above, the scintillation light generated by the incidence of γ-rays is proportional to the light transmittance between the bonding surfaces near the depth of the light emitting position. Are distributed to adjacent scintillators and reach the photodetector. By comparing the output of each detector with respect to the arriving light, it is possible to identify the scintillator in which the scintillator light emission has occurred and to measure the depth of the light emission generation position. Since the arrangement of the reflection layer that absorbs the scintillation light was minimized, the total amount of light that reached each photodetector accurately reflected the energy of the incident γ-rays. Therefore, gamma ray measurement can be performed with good energy resolution by taking the sum of the output electric signals of the photodetectors.

Further, since the other radiation detector of the present invention is constructed as described above, the scintillation light generated by the incidence of the high-energy γ-rays is on the opposite side of the junction surface near the depth of the scintillation emission position. The light is distributed to the adjacent scintillators at a rate according to the randomness of the reflection direction on the surface and reaches the photodetector. Also in this radiation detector,
By comparing the output of each detector with respect to the arriving light, it is possible to identify the scintillator in which scintillation light emission has occurred and to measure the depth of the light emission generation position. Since the arrangement of the reflection layer that absorbs the scintillation light was minimized, the total amount of light that reached each photodetector accurately reflected the energy of the incident γ-rays. Therefore, gamma ray measurement can be performed with good energy resolution by taking the sum of the output electric signals of the photodetectors.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(First Embodiment) FIG. 1 is an explanatory view of a radiation detector according to the first embodiment of the present invention. Figure 1 (a)
The structure of this radiation detector is shown. Two scintillators 111a and 111b made of the same single material have two photodetectors 1.
It is connected to 20a and 20b in a one-to-one manner and is bundled via air. Regarding the joint surface between the scintillators 111a and 111b, one region on the photodetector side is mirror-finished and the other region is rough-finished with the middle point in the depth direction as a boundary. As a result, the light transmissivity between the two scintillators has a discrete distribution of the two peaks in the depth direction as shown in FIG.
Photodetector 120 and junction surface of scintillators 111a and 111b
A reflection agent 130 is applied except for the coupling surfaces of a and b, and blocks the emission of scintillation light generated inside either of the scintillators 111a and 111b to the outside of the radiation detector.

When γ-rays are incident on one of the scintillators 111a and 111b to cause scintillation light emission, the amount of light distributed according to the light transmittance at the depth of the light emission position is the photodetector 12.
Reach 0a, b. The photodetectors 120a and 120b convert and output an electric signal having an intensity proportional to the amount of light that has arrived.
The intensity of each output electric signal with respect to the depth of the light emission position when scintillation light emission occurs in the scintillator 111a is shown in the graph of FIG. When scintillation light emission occurs in the scintillator 111b, a graph in which (output a) and (output b) in FIG. Since air is present between the two scintillators 111a and 111b and does not absorb light, the sum of the two output electric signal intensities accurately reflects the energy of γ-rays which is the cause of light emission. Also,
Since the two scintillators 111a and 111b are made of the same material, the emission decay time is the same, and the energy of the incident γ-ray can be identified from the signal obtained by simply superimposing the output electric signals.

Therefore, according to this radiation detector, by comparing the output electric signal intensities of the respective photodetectors, the scintillator in which the light emission has occurred is identified and the difference (or ratio) between the output electric signal intensities determines the emission position. It is possible to discriminate whether the depth is near or far from the photodetector.
In addition, energy identification is possible by crest analysis of the signals that are simply superposed of the two output electrical signals.

Although the above functions sacrifice the energy resolution to some extent, even if the scintillator surface is made to have a constant finish, the scintillators may be formed of an air region and a reflection region so as to correspond to the light transmittance between the scintillators. realizable.

(Second Embodiment) FIG. 2 is an explanatory view of a radiation detector according to the second embodiment of the present invention. Figure 2 (a) shows
The structure of this radiation detector is shown. Two scintillators 112a and 112b made of the same single material have two photodetectors 1
It is connected to 20a and 20b in a one-to-one manner and is bundled via air. As for the joint surface between the scintillators 112a and 112b, an area obtained by dividing each joint surface into three equal parts in the depth direction is subjected to polishing finish in the order from the area on the photodetector side to the mirror surface, slightly rough surface, and rough surface. As a result, the light transmissivity between the two scintillators has a discrete distribution of the three-valued peaks in FIG. 2B in the depth direction. Except for the bonding surface of the scintillators 112a and 112b and the bonding surface of the photodetectors 120a and 120b, the reflecting agent 130 is applied to the outside of the radiation detector of the scintillation light generated inside either of the scintillators 112a and 112b. Is blocking the radiation of.

When γ-rays are incident on one of the scintillators 112a and 112b to cause scintillation light emission, the amount of light distributed according to the light transmittance at the depth of the light emission position is the photodetector 12.
Reach 0ab. The photodetectors 120a and 120b convert and output an electric signal having an intensity proportional to the amount of light that has arrived. The graph of FIG. 2C shows the respective output electric signal intensities with respect to the depth of the light emission position when scintillation light emission occurs in the scintillator 112a. When scintillation light emission occurs in the scintillator 112b, a graph in which (output a) and (output b) in FIG. Since air is present between the two scintillators 112a and 112b and does not absorb light, the sum of the two output electric signal intensities accurately reflects the energy of γ-rays which is the cause of light emission. Further, since the two scintillators 112a and 112b are made of the same material,
The emission decay time is the same, and the energy of the incident γ-ray can be identified from the signal obtained by simply superimposing the output electric signals.

Therefore, according to this radiation detector, by comparing the output electric signal intensities of the respective photodetectors, the scintillator in which the light emission has occurred is identified, and the emission position is determined from the difference (or ratio) in the output electric signal intensity. It is possible to discriminate which region of the three-divided region it belongs to in accordance with the light transmittance between the scintillators. In addition, energy identification is possible by crest analysis of the simple superimposed signal of the two output electrical signals.

(Third Embodiment) FIG. 3 is an explanatory diagram of a radiation detector according to a third embodiment of the present invention. Figure 3 (a) shows
The structure of this radiation detector is shown. Two scintillators 1
13a and 13b are connected to the two photodetectors 120a and 120b in a one-to-one manner and are bundled via air. Scintillator 1
The joint surfaces of 13a and 13b are polished to have a continuous roughness in the depth direction. As a result, the light transmittance between the two scintillators is shown in FIG.
It has a continuous distribution as shown in (b). Except for the bonding surface of the scintillators 113a and 113b and the bonding surface of the photodetectors 120a and 120b, the reflecting agent 130 is applied to the outside of the radiation detector of the scintillation light generated inside one of the scintillators 113a and 113b. Is blocking the radiation of.

When γ-rays are incident on one of the scintillators 113a and 113b to cause scintillation light emission, the amount of light distributed according to the light transmittance at the depth of the light emission position is the photodetector 12.
Reach 0ab. The photodetectors 120a and 120b convert and output an electric signal having an intensity proportional to the amount of light that has arrived. The intensity of each output electric signal with respect to the depth of the light emitting position when scintillation light emission occurs in the scintillator 113a is shown in the graph of FIG. When scintillation light emission occurs in the scintillator 113b, a graph in which (output a) and (output b) in FIG. Since air is present between the two scintillators 113a and 113b and does not absorb light, the sum of the two output electric signal intensities accurately reflects the energy of γ-rays which is the cause of light emission. Further, since the two scintillators 113a and 113b are made of the same material,
The emission decay time is the same, and the energy of the incident γ-ray can be identified from the signal obtained by simply superimposing the output electric signals.

Therefore, according to this radiation detector, by comparing the output electric signal intensities of the respective photodetectors, the scintillator in which the light emission has occurred is identified and the difference (or ratio) in the output electric signal intensity indicates the emission position. Depth identification is possible. In addition, energy identification is possible by crest analysis of the simple superimposed signal of the two output electrical signals.

(Fourth Embodiment) FIG. 4 is an explanatory diagram of a radiation detector according to a fourth embodiment of the present invention. Figure 4 (a)
The structure of this radiation detector is shown. Two scintillators 114a and 114b made of the same single material have two photodetectors 1
It is connected to 20a and 20b in a one-to-one manner and is bundled via air. The surface of the scintillators 114a and 114b opposite to the bonding surface is mirror-finished in one area on the photodetector side with the middle point in the depth direction as a boundary, and roughened in the other area. As a result, the degree of randomness in the reflection direction of these surfaces has a discrete distribution of the ridge binary values shown in FIG. 4 (b) in the depth direction. Except for the bonding surface of the scintillators 114a and 114b and the bonding surface of the photodetectors 120a and 120b, the reflection agent 130 is applied to the outside of the radiation detector of scintillation light generated inside either of the scintillators 114a and 114b. Is blocking the radiation of.

When γ-rays are incident on one of the scintillators 114a and 114b to cause scintillation light emission, the amount of light distributed according to the reflection direction randomness at the depth of the light emission position reaches the photodetector 120ab. The photodetectors 120a and 120b convert and output an electric signal having an intensity proportional to the amount of light that has arrived. The graph of FIG. 4C shows each output electric signal intensity with respect to the depth of the light emission position when scintillation light emission occurs in the scintillator 114a. Scintillator 114b
If scintillation emission occurs in Fig. 4,
This is a graph in which (output a) and (output b) in (c) are exchanged. Since air is present between the two scintillators 111a and 111b and does not absorb light, the sum of the two output electric signal intensities accurately reflects the energy of γ-rays which is the cause of light emission. Further, since the two scintillators 111a and 111b are made of the same material, the emission decay time is the same, and the energy of the incident γ-ray can be identified from the signal obtained by simply superimposing the output electric signals.

Therefore, according to this radiation detector, by comparing the output electric signal intensities of the respective photodetectors, the scintillator in which the light emission has occurred is identified, and the difference (or ratio) between the output electric signal intensities determines the light emission position. It is possible to discriminate whether the depth is near or far from the photodetector.
In addition, energy identification is possible by crest analysis of the simple superimposed signal of the two output electrical signals.

By setting the polishing roughness of the surface on the side opposite to the bonding surface between the scintillators in the fourth embodiment to two or more steps or continuous, the second and the first embodiments can be obtained.
As in the third embodiment, the depth direction resolution of the light emitting position can be increased.

[0030]

As described above in detail, according to the present invention, two sets of scintillators and photodetectors made of a single material bonded in a one-to-one manner are used, and the polishing degree of only the scintillator bonding surface is adjusted. Since the radiation detector is configured by applying a reflecting agent to the outside, it is possible to provide a radiation detector having a simple structure suitable for mass production and having accurate energy resolution and position resolution in the depth direction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a radiation detector according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a radiation detector according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a radiation detector according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram of a radiation detector according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory diagram of a conventional radiation detector.

FIG. 6 is an explanatory diagram of the necessity of depth direction position resolution in a PET device.

[Explanation of symbols]

111, 112, 113, 114, 210, 250, 3
10 ... Scintillator, 120, 220, 320 ... Photodetector, 130, 230 ... Reflecting agent, 211, 212 ... Groove, 3
00 ... γ-ray detector, 350 ... Object to be measured.

Claims (8)

[Claims] 1. A radiation detector in which two photodetectors are coupled to each other at a photodetector coupling surface to two scintillators arranged such that the scintillator bonding surfaces face each other, wherein the two scintillators and the two scintillators are provided. 1 to 1 photo detector
And changing the light transmittance between the scintillators in the direction perpendicular to the photodetector coupling surface, and by applying a reflector except the scintillator coupling surface and the photodetector coupling surface, A radiation detector characterized by detecting a light emission position in a scintillator. 2. An air layer is interposed between the scintillator bonding surfaces, and the light transmittance is continuously changed by continuously changing the polishing roughness of the scintillator surface. The radiation detector according to claim 1. 3. An air layer is interposed between the scintillator joint surfaces, and the change in light transmittance is made discrete by discretely changing the polishing roughness of the scintillator surface. The radiation detector according to claim 1. 4. The radiation detection according to claim 1, wherein a change in light transmittance is made discrete by forming a two-region structure of an air layer region and a reflection layer region between the scintillator joint surfaces. vessel. 5. A radiation detector in which two photodetectors are coupled at the photodetector coupling surface to two scintillators arranged such that the scintillator bonding surfaces face each other, wherein the two scintillator and the scintillator are coupled to each other. Two photo detectors one to one
The scintillator bonding surface and the reflection direction randomness of the surface on the side opposite to the scintillator bonding surface are changed in the direction perpendicular to the photodetector bonding surface, and a reflection agent is applied except the scintillator bonding surface and the photodetector bonding surface. And a radiation detector configured to detect the light emission position in the scintillator. 6. The radiation detector according to claim 5, wherein an air layer is interposed between the scintillator bonding surfaces. 7. The variation in the reflection direction randomness of the opposite surface is continuously made by continuously changing the polishing roughness of the surface opposite to the scintillator joining surface. The radiation detector according to claim 5. 8. The scattering roughness of the surface on the opposite side of the scintillator joint surface is discretely changed, so that the reflection direction randomness change of the surface on the opposite side is discrete. The radiation detector according to claim 5.