JP6654819B2 - Radiation detector and radiation detection method - Google Patents

Description

  The present invention relates to a radiation detector and a radiation detection method.

  Patent Literatures 1 to 4 are known as techniques relating to a radiation detector and a radiation detection method. For example, Patent Literature 1 describes a positron CT apparatus. This positron CT apparatus has a detection unit including a scintillator bundle in which columnar scintillator elements are bundled, and a position detecting photodetector coupled to both ends of the scintillator bundle. By arranging the detection units in a ring shape, the gamma ray absorption position in the scintillator is three-dimensionally detected.

Japanese Patent Publication No. 6-5290 Republished Patent No. 2012-105292 JP 2013-140024 A Patent No. 5585094

  In the detection unit as described in Patent Literature 1, the one-dimensional absorption position in the direction in which the scintillator extends and the two-dimensional absorption position in a plane intersecting the direction in which the scintillator extends are acquired by different processing. . Since the detection unit has a pair of position detecting light detectors, the outputs of the two position detecting light detectors can be used to obtain a two-dimensional absorption position. In the field of such technology, it is desired to improve the position separation characteristics in detecting the position of scintillation light.

  Therefore, an object of the present invention is to provide a radiation detector and a radiation detection method capable of improving position separation characteristics.

  One embodiment of the present invention is a radiation detector. The radiation detector generates scintillation light by absorbing radiation and extends in a predetermined direction, and a first emission surface orthogonal to the predetermined direction and emitting first light caused by the scintillation light. A scintillator having a second emission surface formed to be spaced apart from the first emission surface in a predetermined direction and emitting second light caused by the scintillation light; A first position-detecting photodetector that outputs a first signal corresponding to the first light and is optically coupled to a second exit surface; A second position detection type photodetector that outputs a second signal corresponding to the following, and a position acquisition unit that acquires a position of the scintillator at which radiation has been absorbed using the first signal and the second signal. , And the position obtaining unit outputs the first signal Has a two-dimensional position obtaining unit that obtains a two-dimensional position where radiation is absorbed on a plane orthogonal to a predetermined direction by using the other signal having a signal strength greater than one signal in the second signal .

  In this radiation detector, when radiation enters the scintillator, the scintillator absorbs the radiation and generates scintillation light. The scintillation light is incident on the first position detecting light detector as first light, and is incident on the second position detecting light detector as second light. This scintillation light is diffused before reaching the position detection type photodetector. The degree of the diffusion depends on the distance from the position where the scintillation light is emitted to the position detecting photodetector. When the distance from the light emitting position to the position detecting photodetector is large, the degree of diffusion also increases. When scintillation light having such a large degree of diffusion is incident on the position detection type photodetector, the signal obtained from the position detection type photodetector has a relatively small signal intensity and a small difference in intensity between the signals. There can be. The result of the center-of-gravity calculation using such a plurality of signals has a large fluctuation in the result, and the position of the center of gravity tends to be closer to the center of the scintillator. On the other hand, when the distance from the light emitting position to the position detecting light detector is small, the degree of diffusion is small. Then, contrary to the above-described case, a plurality of signals obtained from the position detection type photodetector may have a large difference in intensity between the signals. Since the fluctuation of the center of gravity calculation result using such a plurality of signals is small, good separation characteristics can be obtained. Therefore, in the radiation detector, the position acquisition unit compares the signal intensities of the first signal and the second signal, and uses the signal with the larger signal intensity. Therefore, by using the signal having the larger signal strength, the influence of light diffusion is suppressed, and the position separation characteristics can be improved.

  The position acquisition unit may further include a one-dimensional position acquisition unit that acquires a one-dimensional position at which radiation in a predetermined direction is absorbed between the first emission surface and the second emission surface. According to this configuration, the two-dimensional position where the radiation is absorbed is acquired by the two-dimensional position acquisition unit, and the one-dimensional position where the radiation is absorbed is acquired by the one-dimensional position acquisition unit. Therefore, by combining the two-dimensional position where the radiation is absorbed and the one-dimensional position, the three-dimensional position where the radiation is absorbed can be obtained.

  The position acquisition unit uses the first signal to calculate a first position on the first emission surface where the radiation is absorbed, and uses the second signal to calculate a first position. And a second calculation unit that calculates a second position where the radiation is absorbed on the emission surface of the second unit, and the two-dimensional position acquisition unit uses the one-dimensional position to obtain the first signal or In the second signal, the other signal having a signal strength greater than that of one signal is selected, and one of the first position or the second position calculated from the selected signal is obtained as a two-dimensional position. Good. According to this configuration, the position acquisition unit calculates the first position in the first calculation unit after converting the input first signal into a digital signal. In addition, the position obtaining unit converts the input second signal into a digital signal, and then calculates the second position in the second calculating unit. Then, since the length of the transmission line through which the analog signal is transmitted can be shortened, it is possible to simplify the configuration for noise suppression for the analog signal. Therefore, the configuration of the radiation detector can be simplified.

  According to another aspect of the present invention, there is provided a scintillator portion that absorbs radiation to generate scintillation light and extends in a predetermined direction, and a first light that is orthogonal to the predetermined direction and emits first light resulting from the scintillation light. Radiation is absorbed in a scintillator having a first emission surface and a second emission surface formed to be spaced apart from the first emission surface in a predetermined direction and emitting second light caused by the scintillation light. This is a radiation detection method for acquiring the position of the radiation. In this detection method, a first signal is obtained from a first position detecting photodetector that is optically coupled to a first emission surface and outputs a first signal corresponding to the first light. A first step, obtaining a second signal from a second position detecting photodetector optically coupled to the second exit surface and outputting a second signal corresponding to the second light; And a third step of using the first signal and the second signal to obtain a position of the scintillator at which the radiation has been absorbed, wherein the third step includes the first step. A fourth step of obtaining a two-dimensional position where radiation is absorbed on a plane orthogonal to the predetermined direction by using the other signal having a signal strength greater than one signal in the second signal or the second signal. Including.

  This radiation detection method can obtain the same effect as the above-described radiation detector. That is, in the third step, the signal strength of the first signal and the signal strength of the second signal are compared, and the signal having the larger signal strength is used. Therefore, by using the signal having the larger signal strength, the influence of light diffusion is suppressed, and the position separation characteristics can be improved.

  The third step may further include a fifth step of obtaining a one-dimensional position where the radiation has been absorbed along the predetermined direction between the first emission surface and the second emission surface. According to these steps, in the fourth step, the two-dimensional position where the radiation is absorbed is obtained, and in the fifth step, the one-dimensional position where the radiation is absorbed is obtained. Therefore, by combining the two-dimensional position where the radiation is absorbed and the one-dimensional position, a three-dimensional position where the radiation is absorbed can be obtained.

  The third step is a step of calculating a first position on the first exit surface where the radiation has been absorbed using the first signal, and a step of calculating the first position using the second signal. And a seventh step of calculating a second position where the radiation is absorbed on the exit surface of the second signal. In the fourth step, the first signal or the second signal is calculated using the one-dimensional position. The other signal having a greater signal strength than one of the signals is selected, and one of the first position or the second position calculated from the selected signal is obtained as a two-dimensional position. According to these steps, by the processing in the first or second step, the analog signal output from the first or second position detecting photodetector is shifted to the first or second position, which is a digital signal. Is converted. Then, since the length of the transmission line through which the analog signal is transmitted can be shortened, the configuration for reducing the noise with respect to the analog signal can be simplified. Therefore, the configuration of the radiation detector can be simplified.

  ADVANTAGE OF THE INVENTION According to the radiation detector which concerns on one form of this invention, and the radiation detection method which concerns on another form of this invention, the separation characteristic of the position where radiation was absorbed can be improved.

It is a figure showing composition of a radiation detector concerning an embodiment. FIG. 2 is an exploded perspective view showing the detection unit of FIG. 1 in an exploded and enlarged manner. It is a figure for explaining processing which acquires a position where radiation was absorbed using a signal outputted from a detection unit. It is a figure for explaining processing which acquires a position where radiation was absorbed using a signal outputted from a detection unit. It is a figure showing the main steps of the radiation detection method concerning an embodiment. It is a figure showing composition of a radiation detector concerning a comparative example. FIG. 3 is a diagram for explaining a relationship between diffusion of scintillation light and detection accuracy. FIG. 3 is a diagram for explaining a relationship between diffusion of scintillation light and detection accuracy. It is a figure showing a detection unit with which a radiation detector concerning a modification is provided. It is a figure showing the light scattering surface with which the radiation detector concerning a modification is provided.

  Hereinafter, embodiments for carrying out the present invention will be described in detail 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.

  As shown in FIG. 1, the radiation detector 1 includes a detection unit 2 and a position acquisition unit 3. The detection unit 2 generates scintillation light corresponding to the dose of the radiation H by absorbing the radiation H such as a gamma ray. The detection unit 2 converts the scintillation light into an electric signal and outputs the electric signal to the position acquisition unit 3. The position acquisition unit 3 outputs information on the position where the radiation H is absorbed (hereinafter, also simply referred to as “radiation absorption position”) using the electric signal input from the detection unit 2. Therefore, according to the radiation detector 1, information on the radiation absorption position can be obtained.

  The detection unit 2 has a scintillator array (scintillator) 4, a photodetector 6A (first position detection type photodetector), and a photodetector 6B (second position detection type photodetector). The pair of photodetectors 6A and 6B are optically coupled to both ends of the scintillator array 4 so as to sandwich the scintillator array 4. The detection unit 2 having such a configuration is called a double-end detection type. The scintillator array 4 generates scintillation light by absorbing the radiation H. The photo detectors 6A and 6B generate an electric signal corresponding to the intensity of the scintillation light.

  As shown in FIG. 2, the scintillator array 4 includes a first emission surface 4a, a second emission surface 4b, and a plurality of light emission surfaces 8 divided by a light scattering surface 8 so as to extend in the Z direction (predetermined direction). And a scintillator unit 7 of the above. The first emission surface 4a is one end surface of the scintillator array 4 orthogonal to the Z direction. The second emission surface 4b is the other end surface of the scintillator array 4 orthogonal to the Z direction. Note that the plurality of scintillator sections 7 may be divided by air layers instead of the light scattering surfaces 8. In addition, the scintillator may have a monolithic configuration that is not divided by the light scattering surface 8 or the air layer.

  The scintillator array 4 has a side surface 4c extending between the first emission surface 4a and the second emission surface 4b. The light reflection layer 5 is provided on the side surface 4c. That is, the scintillation light is emitted from the scintillator array 4 from at least one of the first emission surface 4a and the second emission surface 4b, and is not emitted from the side surface 4c. The light reflection layer 5 is made of, for example, a material such as Teflon tape (Teflon is a registered trademark), barium sulfate, aluminum oxide, titanium oxide, an ESR (Enhanced Specular Reflector) film, or a polyester film.

The scintillator array 4 is a crystal mass that generates scintillation light at a radiation absorption position. The intensity of the scintillation light corresponds to the absorbed dose of the radiation H. The crystal mass is, for example, Bi ₄ Ge ₃ O ₁₂ (BGO), Lu ₂ SiO ₅ (LSO) doped with Ce, Lu _{2 (1-X)} Y _2X SiO ₅ (LYSO), Gd ₂ SiO ₅ (GSO) ), Pr-doped LuAG (Lu ₃ Al ₅ O ₁₂ ), Ce-doped LaBr ₃ (LaBr ₃ ), Ce-doped LaCl ₃ (LaCl ₃ ), or Ce-doped Lu _0.7 Y _{0.3 It} is composed of crystals such as AlO ₃ (LuYAP) and Luttetium Fine Silicate (LFS).

  The scintillator unit 7 has, for example, a regular prism shape. The scintillator units 7 are two-dimensionally arranged along an XY plane orthogonal to the Z direction. The light scattering surface 8 extends from the first emission surface 4a to the second emission surface 4b, and the plurality of light scattering surfaces 8 are combined in a grid when viewed from the Z direction. The light scattering surface 8 is formed by modifying (for example, amorphizing) a part of a crystal lump constituting the scintillator array 4. This modification is performed by laser light irradiation. More specifically, a laser beam having optical transparency is condensed on the crystal mass constituting the scintillator array 4. Then, the focal point of the laser beam is relatively moved along a predetermined surface of the crystal lump. Thereby, light absorption occurs at the focal point of the laser beam in the crystal lump, and a modified region is formed along a predetermined surface of the crystal lump. For example, when the laser light is a pulsed laser light, one modified spot is formed by irradiation of one pulse of the laser light. Then, a plurality of modified spots are formed along a predetermined surface of the crystal lump to form a planar modified region. The modified spot does not block or absorb the scintillation light. Therefore, even if the modified spot is formed on the entire surface of the light scattering surface 8, a part of the incident scintillation light is transmitted. The light scattering surface 8 has different transmittance of the scintillation light depending on the incident angle of the scintillation light.

  The position detection type photodetector 6A is optically coupled to the first emission surface 4a via, for example, an optical adhesive. The photodetector 6A detects the intensity of the first light L1 (see FIG. 4) emitted from the first emission surface 4a, and outputs an electric signal having a magnitude corresponding to the detected value. The position detection type photodetector 6B is optically coupled to the second emission surface 4b via, for example, an optical adhesive. The photodetector 6B detects the intensity of the second light L2 (see FIG. 4) emitted from the second emission surface 4b, and outputs an electric signal having a magnitude corresponding to the detected value. The photodetectors 6A and 6B are, for example, semiconductor photodetectors using a photomultiplier tube, an avalanche photodiode (APD), an MPPC (Multi-Pixel Photon Counter), or the like. The MPPC is a photon counting device including a plurality of Geiger mode APD pixels.

  As shown in FIGS. 3 and 4, the photodetector 6A has a plurality of photodetectors 11A and an output extraction unit 12A. The light detection unit 11A is optically coupled to an end surface of the scintillator unit 7 included in the first emission surface 4a. The number of the light detection units 11A is the same as the number of the scintillator units 7 or smaller than the number of the scintillator units 7. In the present embodiment, the number of the light detection units 11A is the same as the number of the scintillator units 7. Then, one scintillator unit 7 is coupled to one light detection unit 11A. The output extraction unit 12A has a resistance chain and an output terminal. In the resistance chain, the photodetectors 11A adjacent to each other in the X direction are electrically connected via a resistor (see FIG. 3). In the resistance chain, the photodetectors 11A adjacent to each other in the Y direction are electrically connected via a resistor (see FIG. 4). The output extracting unit 12A outputs, as a first signal, a first combined signal AM (= A1 + A2 + A3 + A4) obtained by adding the signals A1, A2, A3, A4 and the signals A1, A2, A3, A4 (FIG. 2). reference). These signals are analog signals.

  The light detector 6B has the same configuration as the light detector 6A. The light detector 6B includes a light detection unit 11B and an output extraction unit 12B. The light detection unit 11B is optically coupled to an end face of the scintillator unit 7 included in the second emission surface 4b. The output extracting unit 12B outputs a second combined signal BM (= B1 + B2 + B3 + B4) obtained by adding the signals B1, B2, B3, and B4 and the signals B1, B2, B3, and B4 as the second signal (FIG. 2). reference). These signals are analog signals.

  As shown in FIG. 1, the position acquisition unit 3 outputs information indicating a radiation absorption position using the first signal and the second signal input from the photodetectors 6A and 6B. This position information is information indicating a three-dimensional position in the scintillator array 4. The position acquisition unit 3 is realized by, for example, predetermined software that processes the first signal and the second signal. When this software is executed by a personal computer, the personal computer functions as the position acquisition unit 3. The position acquiring unit 3 may be realized by hardware (for example, FPGA: Field-Programmable Gate Array) on which a desired logic circuit can be mounted.

  The position acquisition unit 3 includes a one-dimensional position acquisition unit 13, a first calculation unit 14A, a second calculation unit 14B, a two-dimensional position acquisition unit 16, and an analog-digital conversion unit as functional components. .

The one-dimensional position acquisition unit 13 calculates a radiation absorption position in the Z direction using the first combined signal AM and the second combined signal BM. That is, the position information calculated by the one-dimensional position acquisition unit 13 is one-dimensional position information. The first synthesized signal AM and the second synthesized signal BM are converted into digital signals by analog-digital conversion processing in an analog-digital conversion unit, and are input to the one-dimensional position acquisition unit 13. The one-dimensional position acquisition unit 13 outputs information on the radiation absorption position in the Z direction to the outside of the position acquisition unit 3 and to the two-dimensional position acquisition unit 16. The center of gravity calculation processing in the one-dimensional position acquisition unit 13 will be described. First, the one-dimensional position acquisition unit 13 calculates the ratio R1 using Expression (1).
R1 = BM / (AM + BM) (1)
here,
AM: signal value of the first combined signal (= A1 + A2 + A3 + A4)
BM: signal value of the second synthesized signal (= B1 + B2 + B3 + B4)
It is. Next, the radiation absorption position (light emission position) in the Z direction is specified using the ratio R1.

  The first calculation unit 14A calculates the radiation absorption position on the first emission surface 4a as the first position using the first signals A1, A2, A3, and A4. That is, the first position is two-dimensional position information. The first signals A1, A2, A3, and A4 are converted into digital signals by being subjected to analog-to-digital conversion processing in the analog-to-digital conversion unit, and are input to the first calculation unit 14A. The first calculation unit 14A performs a gravity center calculation for calculating a radiation absorption position in the X direction and a gravity center calculation for calculating a radiation absorption position in the Y direction. Then, the first calculation unit 14A outputs information indicating the two-dimensional position where the radiation H has been absorbed to the two-dimensional position acquisition unit 16.

The operation of the first calculator 14A will be described. The first calculation unit 14A calculates a radiation absorption position in the X direction. Specifically, first, the first calculation unit 14A calculates the ratio R2 by using Expression (2).
R2 = (A1 + A3) / AM (2)
Next, the radiation absorption position in the X direction is specified by associating the ratio R2 with the value shown on the horizontal axis of the histogram G2 (see FIG. 3).

The operation of the first calculator 14A will be further described. The first calculator 14A calculates a radiation absorption position in the Y direction. Specifically, first, the first calculation unit 14A calculates the ratio R4 using Expression (3).
R4 = (A1 + A2) / AM (3)
Next, the radiation absorption position in the Y direction is specified by associating the ratio R4 with the value shown on the horizontal axis of the histogram G4 (see FIG. 4).

  By using the radiation absorption position in the X direction and the radiation absorption position in the Y direction obtained by the above operation, the two-dimensional position (first position) where the radiation H is absorbed on the first exit surface 4a is used. ) Is obtained.

  The second calculation unit 14B calculates the radiation absorption position on the second emission surface 4b as the second position using the second signals B1, B2, B3, and B4. That is, the second position is two-dimensional position information. The second signals B1, B2, B3, and B4 are subjected to analog-to-digital conversion processing in an analog-to-digital conversion unit, so that they are converted into digital signals and input to the second calculation unit 14B. The second calculation unit 14B performs a gravity center calculation for calculating a radiation absorption position in the X direction and a gravity center calculation for calculating a radiation absorption position in the Y direction. Then, the second calculation unit 14B outputs information indicating the two-dimensional position where the radiation H has been absorbed to the two-dimensional position acquisition unit 16.

The operation of the second calculator 14B will be described. The second calculator 14B calculates the radiation absorption position in the X direction. Specifically, first, the second calculation unit 14B calculates the ratio R3 using Expression (4).
R3 = (B1 + B3) / BM (4)
Next, the radiation absorption position in the X direction is specified by associating the ratio R3 with the value indicated on the horizontal axis of the histogram G3 (see FIG. 3).

The operation of the second calculator 14B will be further described. The second calculator 14B calculates a radiation absorption position in the Y direction. Specifically, first, the second calculating unit 14B calculates the ratio R5 using the equation (5).
R5 = (B1 + B2) / BM (5)
Next, the radiation absorption position in the Y direction is specified by associating the ratio R5 with the value indicated on the horizontal axis of the histogram G5 (see FIG. 4).

  By using the radiation absorption position in the X direction and the radiation absorption position in the Y direction obtained by the above operation, the two-dimensional position (second position) where the radiation H is absorbed on the second exit surface 4b is used. ) Is obtained.

  The two-dimensional position acquisition unit 16 determines which of the first signal output from the photodetector 6A and the second signal output from the photodetector 6B is used. In other words, the two-dimensional position acquisition unit 16 selects one of the first position and the second position as the radiation absorption position on the XY plane. In this process, the ratio R1 between the first signal output from the photodetector 6A and the second signal output from the photodetector 6B, or the first combined signal AM and the first combined signal AM / D By comparing the magnitude relationship between the two combined signals BM, the photodetector having a shorter distance from the radiation absorption position to the photodetector is determined. Then, the position information calculated from the specified signal of the photodetector is selected, and the position information is output.

  Subsequently, a radiation detection method will be described with reference to FIG. This method is performed by the radiation detector 1.

  First, a step of acquiring a first signal is performed (first step: S1). Step S1 is performed by the photodetector 6A. In step S1, as described above, the photodetector 6A acquires the signals A1, A2, A3, A4 and the first combined signal AM (= A1 + A2 + A3 + A4) as the first signals. Then, the photodetector 6 </ b> A outputs the first signal to the position acquisition unit 3.

  Next, a step of acquiring a second signal is performed (second step: S2). Step S2 is performed by the photodetector 6B. In step S2, as described above, the photodetector 6B acquires the signals B1, B2, B3, and B4 and the second combined signal BM (= B1 + B2 + B3 + B4) as the second signals. Then, the photodetector 6B outputs the second signal to the position acquisition unit 3.

  Next, a step of acquiring a radiation absorption position is performed (third step: S3). Step S3 is performed by the position acquisition unit 3. In step S3, information indicating the position where the radiation H is absorbed in the scintillator array 4 is acquired using the first signal and the second signal. Hereinafter, this step S3 will be described in detail.

  First, a radiation absorption position in the Z direction is obtained (fifth step: S4). Step S4 is performed by the one-dimensional position acquisition unit 13. In step S4, the ratio R1 is calculated using equation (1). Using the ratio R1, the radiation absorption position (light emission position) in the Z direction is specified.

  Next, a step of acquiring the first position using the first signal is performed (sixth step: S5). Step S5 is performed by the first calculation unit 14A. In step S5, the radiation absorption position in the X direction is specified by the center-of-gravity calculation using equation (2). Further, in step S5, the radiation absorption position in the Y direction is specified by the center-of-gravity calculation using equation (3). Then, using the radiation absorption positions in the X direction and the Y direction, the two-dimensional position (first position) on the first emission surface 4a where the radiation H has been absorbed is specified. The signal indicating the two-dimensional position is a digital signal.

  Next, a step of acquiring a second position using the second signal is performed (seventh step: S6). Step S6 is performed by the second calculator 14B. In step S6, the radiation absorption position in the X direction is specified by the center-of-gravity calculation using equation (4). Further, in step S6, the radiation absorption position in the Y direction is specified by the center of gravity calculation using equation (5). Then, using the radiation absorption positions in the X direction and the Y direction, the two-dimensional position (second position) on the second emission surface 4b where the radiation H has been absorbed is specified. The signal indicating the two-dimensional position is a digital signal.

  Next, a step of obtaining a radiation absorption position is performed (fourth step: S7, S8, S9). Steps S7, S8, and S9 are performed by the two-dimensional position acquisition unit 16. In step S7, the first combined signal AM obtained from the photodetector 6A is compared with the second combined signal BM obtained from the photodetector 6B, and the other having the signal strength larger than the one signal strength is obtained. Identify the signal.

  In step S7, for example, it is determined whether the first synthesized signal AM is larger than the second synthesized signal BM. If this determination criterion is satisfied (step S7: YES), the first position obtained from the first signal is selected as the radiation absorption position on the XY plane (step S8). On the other hand, if the criterion is not satisfied (step S7: NO), the second position obtained from the second signal is selected as the radiation absorption position on the XY plane (step S9).

  By executing the above steps S1 to S9, the three-dimensional position where the radiation H is absorbed is specified in the scintillator array 4.

  Hereinafter, the operation and effect of the radiation detector 1 will be described in comparison with the operation and effect of the radiation detector 100 according to the comparative example. As illustrated in FIG. 6, the radiation detector 100 according to the comparative example includes a detection unit 102 and a position acquisition unit 103. The detection unit 102 has the same configuration as the detection unit 2. The position acquisition unit 103 includes a one-dimensional position acquisition unit 113, a signal addition unit 114, and a two-dimensional position acquisition unit 116. The one-dimensional position acquisition unit 113 has the same configuration as the one-dimensional position acquisition unit 13 and performs the same operation. The two-dimensional position acquisition unit 116 acquires a radiation absorption position on the XY plane using the first and second signals. However, the acquisition differs from the two-dimensional position acquisition unit 16 of the radiation detector 1 in that the signal addition unit 114 uses a combined signal obtained by adding the second signal to the first signal.

  Here, the relationship between the emission position of the scintillation light and the separation characteristics will be described with reference to FIGS. FIGS. 7A and 7B and FIGS. 8A and 8B show light emission positions in the scintillator array 4, intensities of a plurality of signals acquired by the respective light detection units 11A, and a plurality of signals. The figure shows the result of the center-of-gravity calculation calculated by using this. FIG. 7A illustrates an example in which the distance from the light emission position to the light detection unit 11A is large. FIG. 7B is an example in the case where the distance from the light emission position to the light detection unit 11B is small.

  First, as shown in FIG. 7A, the scintillation light is diffused before reaching the light detection unit 11A. The degree of the diffusion depends on the distance from the light emission position to the light detection unit 11A. In the example of FIG. 7A, since the distance from the light emission position to the light detection unit 11A is large, the degree of diffusion is also large. Such scintillation light having a large degree of diffusion enters the plurality of light detection units 11A. Then, a plurality of signals obtained from the plurality of photodetectors 11A may have relatively small signal intensities and a small difference in intensity between the signals. The result of the center-of-gravity calculation using such a plurality of signals has a large fluctuation in the result, and the position of the center of gravity tends to be closer to the center of the scintillator array 4. Further, as shown in FIG. 8A, when the distance from the light emitting position to the light detecting unit 11A is large and the scintillator unit 7 whose light emitting position is located on the outside, the separation characteristic is also obtained for the same reason. May occur.

  On the other hand, as shown in FIG. 7B, when the distance from the light emission position to the light detection unit 11A is small, the degree of diffusion is small. Then, contrary to the above-described example, a plurality of signals obtained from the plurality of light detection units 11A may have a large difference in intensity between the signals. Since the fluctuation of the center of gravity calculation result using such a plurality of signals is small, good separation characteristics can be obtained. Further, as shown in FIG. 8B, even in the case of the scintillator unit 7 whose light emission position is located outside, when the distance from the light emission position to the light detection unit 11A is small, good results are obtained for the same reason. Separation characteristics are obtained.

  Therefore, the separation characteristic tends to decrease as the distance between the light emission position and the light detection units 11A and 11B increases. Therefore, in the radiation detector 1 of the present embodiment, the position acquisition unit 3 compares the signal intensities of the first signal and the second signal, and uses the signal with the larger signal intensity. Therefore, by using the signal having the larger signal intensity, the influence of light diffusion is suppressed, and therefore, a decrease in separation characteristics can be suppressed. In the radiation detector 1 and the radiation detection method according to the present embodiment, the scintillation light L reaches the photodetectors 6A and 6B in a configuration in which the scintillator units 7 are not completely optically separated from each other (light scattering surface 8). This is particularly effective in the case where it is spread by the time it is performed.

  The position acquisition unit 3 further includes a one-dimensional position acquisition unit 13 that acquires a one-dimensional position where the radiation H in the Z direction is absorbed between the first emission surface 4a and the second emission surface 4b. According to this configuration, the two-dimensional position at which the radiation H is absorbed is acquired by the two-dimensional position acquisition unit 16, and the one-dimensional position at which the radiation H is absorbed is acquired by the one-dimensional position acquisition unit 13. Therefore, by combining the two-dimensional position where the radiation H is absorbed and the one-dimensional position, a three-dimensional position where the radiation H is absorbed can be obtained.

The position acquisition unit 3 uses a first signal to calculate a first position on the first emission surface 4a where the radiation H is absorbed, using the first signal, and uses a second signal. And a second calculator 14B for calculating a second position on the second emission surface 4b where the radiation H is absorbed. Using the one-dimensional position, the two-dimensional position acquisition unit 16 selects the other signal having a signal strength greater than the one signal in the first signal or the second signal, and is calculated from the selected signal. One of the first position and the second position is acquired as a two-dimensional position.
According to this configuration, the position obtaining unit 3 calculates the first position in the first calculation unit 14A after converting the input first signal into a digital signal. Further, the position acquisition unit 3 calculates the second position in the second calculation unit 14B after converting the input second signal into a digital signal. Then, since the length of the transmission line through which the analog signal is transmitted can be shortened, it is possible to simplify the configuration for noise suppression for the analog signal. Therefore, the configuration of the radiation detector 1 can be simplified.

  As described above, the radiation detector 1 and the radiation detection method of the present invention have been described, but the present invention is not limited to the above embodiment.

  For example, as shown in FIG. 9, the scintillator array 4A of the detection unit 2A may have a light scattering surface 9 different from the light scattering surface 8. The plurality of light scattering surfaces 9 are formed at intervals from each other along the Z direction. The light scattering surface 9 is a surface orthogonal to the Z direction. The light scattering surfaces 9 have the same shape as the end face of the scintillator part 7 (see FIG. 10A), and are formed so as to overlap each other when viewed from the Z direction. The scintillator section 7 is divided by the light scattering surface 9 into a plurality of segment areas. For example, the segment region has a cubic shape. The light scattering surface 9 attenuates the intensity of the scintillation light by scattering part of the scintillation light passing through the light scattering surface 9. Note that the light scattering surface 9 is not limited to the same shape as the end face of the scintillator part 7, but can take various shapes. For example, when the scintillator portion 7 is viewed from the Z direction, the light scattering surface 9A may have a light-scattering portion having an outline shape formed along the edge portion of the scintillator portion 7 (FIG. 10 (b)). )reference).

  According to the scintillator array 4A having the light scattering surface 9, the light scattering surface 9 makes it possible to distribute the amount of light for each segment region. As shown in the histogram G6, setting the magnitude relationship between the count numbers in each segment region. Can be. By using such a histogram G6, it is determined which value on the horizontal axis of the histogram G6 the ratio R1 calculated by the equation (1) corresponds to, thereby specifying the segment area where the scintillation light has occurred. It becomes possible. For example, when the ratio R1 corresponds to the third mountain portion of the histogram G6, it is determined that the scintillation light L has occurred in the third segment area 7A 'from the left.

  In short, according to the scintillator array 4A having the light scattering surface 9, since laser processing is performed in a direction perpendicular to the axial direction (Z direction) of the scintillator array 4A, optical area division is performed. When the center of gravity calculation is performed in the same manner as that not performed, a clear distribution corresponding to each region is obtained.

DESCRIPTION OF SYMBOLS 1 ... Radiation detector, 2 ... Detection unit, 3 ... Position acquisition part, 4 ... Scintillator array, 4a ... First emission surface, 4b ... Second emission surface, 6A ... Photodetector (1st position detection type) Photodetector), 6B photodetector (second position detection type photodetector), 7 scintillator part, 8 light scattering surface, 11A, 11B photodetector, 12A, 12B output output part, 13 ... one-dimensional position acquisition unit, 14A ... first calculation unit, 14B ... second calculation unit, 16 ... two-dimensional position acquisition unit, H ... radiation, L ... scintillation light, L1 ... first light, L2 ... Two lights.

Claims (2)

A scintillator section that absorbs radiation to generate scintillation light and extends in a predetermined direction; a first emission surface orthogonal to the predetermined direction and emitting first light caused by the scintillation light; A scintillator having a second emission surface formed to be spaced apart from the first emission surface in the predetermined direction and emitting second light caused by the scintillation light;
A first position detecting photodetector optically coupled to the first exit surface and outputting a first signal corresponding to the first light;
A second position detecting photodetector optically coupled to the second exit surface and outputting a second signal corresponding to the second light;
Using the first signal and the second signal, a position acquisition unit that acquires a position of the scintillator at which the radiation is absorbed,
The position acquisition unit has a signal strength greater than one signal in the first signal or the second signal and uses the other signal with a small degree of diffusion, on a surface orthogonal to the predetermined direction. A two-dimensional position acquisition unit that acquires a two-dimensional position at which the radiation has been absorbed ,
Between the first exit surface and the second exit surface, a one-dimensional position acquisition unit that acquires a one-dimensional position where the radiation is absorbed in the predetermined direction;
A first calculator that calculates a first position on the first emission surface at which the radiation is absorbed, using the first signal;
A second calculation unit that calculates a second position on the second emission surface at which the radiation has been absorbed, using the second signal,
The two-dimensional position acquisition unit uses the one-dimensional position to select another signal having a signal strength greater than one signal in the first signal or the second signal, and selects the selected signal. It is acquired as the two-dimensional position one of the calculated first position or the second position from, ray detector release. A scintillator section that absorbs radiation to generate scintillation light and extends in a predetermined direction; a first emission surface orthogonal to the predetermined direction and emitting first light caused by the scintillation light; Obtaining a position where the radiation is absorbed in a scintillator having a second emission surface formed to be spaced apart from the first emission surface in the predetermined direction and emitting second light caused by the scintillation light. Radiation detection method,
Obtaining a first signal from a first position detecting photodetector optically coupled to the first exit surface and outputting a first signal corresponding to the first light; Process and
Acquiring a second signal from a second position detecting photodetector that is optically coupled to the second exit surface and outputs a second signal corresponding to the second light; Process and
Using the first signal and the second signal to obtain a position of the scintillator where the radiation is absorbed, and
In the third step, the first signal or the second signal has a larger signal strength than one of the signals and uses the other signal having a small degree of diffusion, and uses a surface orthogonal to the predetermined direction. A fourth step of obtaining a two-dimensional position where the radiation has been absorbed above ;
A fifth step of obtaining a one-dimensional position where the radiation is absorbed in the predetermined direction between the first exit surface and the second exit surface;
A sixth step of using the first signal to calculate a first position on the first exit surface where the radiation has been absorbed;
Using the second signal to calculate a second position on the second exit surface where the radiation has been absorbed, comprising:
In the fourth step, using the one-dimensional position, the first signal or the second signal is used to select another signal having a larger signal strength than one signal, and from the selected signal, A radiation detection method , wherein one of the calculated first position or the second position is acquired as the two-dimensional position .

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