Radiation detection device, radionuclide detection device, and radionuclide distribution measurement method

Abstract

To detect a specific radionuclide even when the multiple radionuclides exist in a mixed manner by recognizing information about energy of the radiation when recognizing a distribution of the radionuclides with detection of the radiation.SOLUTION: Light detectors 21A, 21B that detect light on the respective ends are provided on both ends of a liquid light guide 10. In a MCA 26, a time difference of detection timing in the light detectors 21A, 21B can be recognized for a single light emission when charged particles are incident on the liquid light guide 10. In a detection intensity distribution obtained by a radiation detection device 1, reflection peaks based on the second detection light (light reflected at the end surface) are formed at both ends, and non-reflection peaks based on the first detection light (light not reflected at the end surface) are formed between them. When detecting Cherenkov light due to the charged particles, an intensity ratio of these peaks varies with the energy of the charged particles.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiation detection device for measuring radiation intensity, a radionuclide detection device using the same, and a method for measuring radionuclide distribution. [Background technology]

[0002] Techniques for measuring the spatial distribution of radioactive nuclides are important in evaluating environments contaminated with radioactive materials. As a technique for this purpose, Non-Patent Document 1 describes a technique in which an optical fiber or liquid light guide that functions as a scintillator is laid, light emission is detected at both ends of the guide, and the light emission position (incident position of radiation) is calculated from the time difference between the light reception timings. In this technique, optical fibers or the like can be laid in a desired form in the area to be measured, and this makes it possible to measure the one-dimensional and two-dimensional distribution of the radioactive nuclides.

[0003] When the radiation dose is low, this technique can accurately calculate the radiation incidence position, but when the dose is high, the number of detected emissions increases, making it difficult to identify the combination of emission outputs for which the time difference should be detected, making it difficult to accurately calculate the radiation incidence position. In response to this, Patent Document 1 describes a technique for recognizing the radiation incidence position by measuring the spectrum of the emission with a spectroscope provided at the end of an optical fiber. With this technique, the distribution of the nuclide that emitted the radiation can be measured even when the dose is high.

[0004] These techniques can measure the spatial distribution of radioactive nuclides (radionuclides) that emit radiation using simple equipment configurations. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] M. Hayashi, J. Kawarabayashi, K. Asai, H. Iwai, Yuri Nakagawa, and T. Iguchi, "Position-Sensitive Radiation Detector with Flexible Light Guide and Liquid Organic Scintillator to Monitor Distributions of Radioactive Isotopes", Journal of Nuclear Science and Technology, Vol. 45 (sup. 6), p. 81 (2008) [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-32627 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above technology, the position (spatial distribution) of a radionuclide can be measured by identifying the position of the light emission. On the other hand, when identifying what this radionuclide is, or when measuring the distribution of a specific radionuclide and distinguishing it from other radionuclides, information about the energy of the detected radiation is required. In the above technology, it was difficult to obtain information about the energy of this radiation while measuring the distribution of the radiation (or the nuclide that emitted it).

[0008] For this reason, there has been a demand for technology that, when detecting radiation to recognize the distribution of radioactive nuclides, can also recognize information regarding the energy of this radiation, thereby making it possible to detect specific radioactive nuclides even when multiple radioactive nuclides are mixed.

[0009] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an invention that solves the above problems. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following configuration. The radiation detection apparatus of the present invention is a radiation detector that detects incident charged particles by detecting Cherenkov light generated by the charged particles, the radiation detection apparatus comprising: a light guiding member that generates light that is the Cherenkov light, propagates the light towards both end portions in a longitudinal direction, and reflects a part of the light at each end portion; and a first detection light that is light that has reached one of the end portions without being reflected at the end portion from a generation point of the Cherenkov light in the light guiding member, and a second detection light that is light that has reached one of the end portions after being reflected at the end portion from the generation point of the Cherenkov light through the reflection at the end portion, the first detection light being light that has reached one of the end portions through the reflection at the end portion of the light guiding member. the first detection light is incident on one end of the light guide member and the second detection light is incident on the other end of the light guide member, and an analysis unit that corresponds a time difference between combinations of light detection in the first detection light detector and the second detection light detector to a position in the longitudinal direction of the light guide member, and recognizes a detection intensity distribution that is a measurement result of the dependence of the count number of the combination on the position, the detection intensity distribution having a non-reflective peak that is a peak formed other than on the end end sides due to the first detection light, and a reflective peak that is a peak formed on the end end sides due to the second detection light, and detects the charged particles having different energies from the detection intensity distribution. In the radiation detection device of the present invention, the charged particles that generate Cherenkov light in the light-guiding member are Compton electrons generated by gamma rays, and the analysis unit detects the gamma rays by detecting the charged particles. The radionuclide detection device of the present invention is a radionuclide detection device that detects radiation that is a charged particle or a radionuclide that emits radiation that generates charged particles in a measurement target region, characterized in that the radiation detection device is used, the light-guiding member is laid in the measurement target region, and the analysis unit recognizes the presence of the radionuclide to be measured in the measurement target region, distinguishing it from other radionuclides, on the basis of the detection intensity distribution. In the radionuclide detection device of the present invention, the analysis section recognizes the distribution of the radionuclide to be measured within the measurement target region as a distribution along the longitudinal direction of the light-guiding member. In the radionuclide detection device of the present invention, the analysis unit sets two types of nuclides that generate the charged particles with different energies as the radioactive nuclides to be measured, divides the position in the longitudinal direction of the light-guiding member into three or more sections including regions corresponding to both end sides, and recognizes the distribution of each of the two types of nuclides along the longitudinal direction of the light-guiding member from the detection intensity distribution obtained for the measurement target region using a response coefficient calculated from the count number in each of the sections in a reference detection intensity distribution, which is the detection intensity distribution when each of the two types of nuclides is present in each of the sections. In the radionuclide detection device of the present invention, the analysis unit recognizes the reflective peaks as peaks on both ends of the light-guiding member in the longitudinal direction and the non-reflective peaks as peaks on the central side in the longitudinal direction in the detection intensity distribution, and recognizes the presence of the radionuclide to be measured in the measurement target region, distinguishing it from the other radionuclides, from the intensity ratio between the reflective peak and the non-reflective peak. In the radionuclide detection device of the present invention, the radionuclide to be measured includes 90 Sr or 90 It is characterized in that it contains Y. In the radionuclide detection device of the present invention, the two types of nuclides are 90 Sr or 90 Y, 137 It is characterized by being Cs. The radionuclide distribution measurement method of the present invention detects radiation that is the charged particle or radiation that generates the charged particle by detecting Cherenkov light generated by an incident charged particle, and measures the distribution within a measurement target region by distinguishing the radionuclide that emits the radiation and is the measurement target from other radionuclides, the method comprising the steps of: generating light that is the Cherenkov light; propagating the light toward both end portions in a longitudinal direction; and laying a light guiding member in the measurement target region that reflects a part of the light at each end portion; receiving a first detection light that is light that reaches one of the end portions without being reflected at the end portions in the light guiding member from a point where the Cherenkov light is generated within the light guiding member; a first photodetector and a second photodetector for detecting, at each of the two end sides of the light-guiding member, a second detection light, which is light that has been reflected by a first photodetector and reached one of the two end sides, and a time difference between a combination of light detections in the first photodetector and the second photodetector is made to correspond to a position in the longitudinal direction of the light-guiding member, and a detection intensity distribution is recognized as a measurement result of the dependency of the count number of the combination on the position, the detection intensity distribution having a non-reflection peak which is a peak formed at a position other than the two end sides due to the first detection light and a reflection peak which is a peak formed at the two end sides due to the second detection light, and a distribution of the radioactive nuclide to be measured is recognized from the detection intensity distribution while being separated from distributions of the other radioactive nuclide. The radionuclide distribution measuring method of the present invention is characterized in that a position in the longitudinal direction of the light-guiding member is divided into three or more sections including regions corresponding to both end sides, and a distribution of each of the radionuclide to be measured and the other radionuclide along the longitudinal direction of the light-guiding member is recognized from the detection intensity distribution obtained for the measurement target region by using a response coefficient calculated from the count number in each of the sections in a reference detection intensity distribution, which is the detection intensity distribution when the radionuclide to be measured and the other radionuclide are present in each of the sections. In the method for measuring radionuclide distribution of the present invention, the radionuclide to be measured and the other radionuclide are each 90 Sr or90 Y, 137 It is characterized by being Cs. Effect of the Invention

[0011] Since the present invention is configured as described above, it is possible to simultaneously recognize the spatial distribution of radiation and information about the energy of this radiation, or to use this technique to measure the distribution of a specific radioactive nuclide even when multiple radioactive nuclides are mixed. [Brief description of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of a radiation detection apparatus according to an embodiment of the present invention; [Diagram 2] 4 is an example of a detection intensity distribution obtained for 90Sr (90Y) by the radiation detection device according to the embodiment of the present invention. [Diagram 3] 4 is an example of a detection intensity distribution obtained for 137Cs by the radiation detection device according to the embodiment of the present invention. [Figure 4] FIG. 10 is a diagram illustrating a schematic distribution of measured detection intensity. [Diagram 5] FIG. 1 shows a schematic diagram of the propagation of Cherenkov light generated in a liquid light guide from the emission position to the end face when the radiation source is 90Sr (90Y) (a) and when the radiation source is 137Cs (b). [Figure 6] FIG. 1 shows a schematic diagram of the propagation state of Cherenkov light generated in a liquid light guide after it is reflected at the end face when the radiation source is 90Sr (90Y) (a) and when the radiation source is 137Cs (b). [Figure 7] This is the result of calculating the dependence of the radiation angle of Cherenkov light on the electron energy. [Figure 8] The ratio of non-reflected to reflected peak intensity in the detection intensity distribution was calculated for each position of the radiation source when the radiation source was 90Sr (90Y) or 137Cs. [Figure 9]1A shows a detection intensity distribution, (b) a 90Sr / 90Y distribution, and (c) a 137Cs distribution actually obtained for a first sample by a radionuclide detection device according to an embodiment of the present invention. [Figure 10] 1A shows a detection intensity distribution, (b) a 90Sr / 90Y distribution, and (c) a 137Cs distribution actually obtained for a second sample by a radioactive nuclide detection device according to an embodiment of the present invention. [Figure 11] FIG. 13 is a diagram showing a modified example of a radionuclide detection device according to an embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing a schematic diagram of a detection intensity distribution obtained by a modified example of the radionuclide detection device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A radiation detection device according to an embodiment of the present invention will be described below. This radiation detection device detects radionuclides that emit detected radiation, and also functions as a radionuclide detection device that measures the spatial distribution of the detected radiation. FIG. 1 is a diagram showing the configuration of this radiation detection device (radionuclide detection device) 1. This radiation detection device 1 also uses a liquid light guide (light guiding member) 10, as in the technology described in Non-Patent Document 1. The liquid light guide 10 can be considered as an optical fiber with a liquid core, and can propagate light along its length.

[0014] The refractive index n of the liquid in this liquid light guide 10 is greater than 1, and the propagation speed of the light propagating through it is c / n (<c) where the speed of light in a vacuum is c. In such a case, when a high-speed charged particle (for example, an electron) is incident on this liquid, if the speed of this charged particle in this liquid is v, v > c / n can hold, and in this case, light (Cherenkov light) is emitted due to the Cherenkov effect. In this case, the Cherenkov light is emitted directionally only in a conical region within an angle θ determined by cosθ = c / (n·v) around the direction of travel of the charged particle. When this light propagates along the extending direction (longitudinal direction) of the liquid light guide 10 and reaches both ends, similar to the technique described in Non-Patent Document 1, if the time difference at which this light emission is detected at both ends of the liquid light guide 10 is recognized, the emission position (the incident position of the charged particle beam) in the longitudinal direction of the liquid light guide 10 can be recognized from this time difference.

[0015] Here, for example 90 Sr undergoes β decay 90 to become Y, 90 and electrons (β rays) with a maximum energy of 2.28 MeV are emitted from Y, and electrons with this energy can generate Cherenkov light within the liquid light guide 10. Also, since the range of β rays is short, 90 if Sr ( 90 Y) is brought close to the above liquid light guide 10, 90 the presence of Sr ( 90 Y), or the position of Sr ( 90 Y) along the longitudinal direction of the liquid light guide 10 90 can be recognized by the above method.

[0016] On the other hand, for example 137 Cs undergoes β decay and γ decay, but the energy of the emitted β rays is 90 lower than that of Sr ( 90 Y). Also, although γ rays themselves do not generate Cherenkov light, low-energy electrons (Compton electrons) are generated by Compton scattering between γ rays and electrons in the substance (liquid), and these Compton electrons can generate Cherenkov light. Therefore, 137The existence and location of Cs can be determined by the same principle. 90 Sr( 90 Y) can be recognized in the same way.

[0017] 1, a photodetector (first photodetector) 21A and a photodetector (second photodetector) 21B for detecting light at each end are provided at both ends (upper and lower sides in the figure) of the liquid light guide 10. Photomultiplier tubes are particularly preferably used as the photodetectors 21A and 21B because high sensitivity and high time resolution are required when detecting weak Cherenkov light, as described below.

[0018] The outputs (pulse outputs) of the photodetectors 21A and 21B are input to the amplifiers 22A and 22B, respectively, and amplified, and then the timings are compared. For this reason, the configuration behind the photodetectors 21A and 21B is a well-known TOF (Time of Flight) circuit for recognizing the time difference between these outputs. First, these outputs are input to CFD (Constant Fraction Discriminators) 23A and 23B, and even if the wave heights of the output pulses are different, the timings are output as timing pulses whose timings are properly recognized, and after a certain delay time is given to the output of the CFD 23A by the delay unit 24, the recognized time difference is converted into a voltage and output by the TAC (Time to Amplitude Converter) 25. This output allows the multichannel analyzer (MCA) 26 to recognize the time difference between the detection timings of the photodetectors 21A and 21B for one light emission when a charged particle is incident on the liquid light guide 10.

[0019] The output from the MCA 26 is input to the analysis unit 30, which is a computer. In the TAC 25, a combination of light detections with close detection timings in the photodetectors 21A and 21B can be presumed to be caused by a single light emission. Therefore, the analysis unit 30 can recognize the position of the light emission (the incident position of the radiation) in the liquid light guide 10 from the recognized time difference. As described above, 90 Sr( 90Y) and 137 By bringing Cs close to the liquid light guide 10, the position along the extension direction can be recognized. In practice, the above results are obtained every time radiation (electron beam, gamma ray) is detected, so the analysis unit 30 can obtain a detection intensity distribution, which is a position-dependent distribution of the detection intensity (count number) of radiation, across the extension direction of the liquid light guide 10. The position of the peak in this detection intensity distribution corresponds to the position of the radioactive nuclide.

[0020] The above content is the same as the technology described in Non-Patent Document 1. In the radiation detection device (radionuclide detection device) 1 according to the embodiment of the present invention, analysis other than the time difference of the detection timing as described above can be performed to obtain information on the energy of the detected charged particles, or the radioactive nuclide that is the source of the charged particles can be identified using this information. The operation of such a device or the method of measuring the distribution of radioactive nuclides will be described below.

[0021] First, the analysis unit 30 recognizes the number of counts (corresponding to the emission intensity) of the combination of light detection by the light detectors 21A and 21B as described above, as a histogram (detection intensity distribution) with the vertical axis representing the number of counts and the horizontal axis representing the position in the liquid light guide 10. In fact, in the configuration of FIG. 1, the length of the liquid light guide 10 is set to 5 m, 90 Sr( 90 Y), 137 The results of actually measuring the detected intensity distribution (histogram) of the above-mentioned radiation when each of Cs was placed at a certain position (1.5 m, 2.5 m, 3.5 m from one end) in the extension direction of liquid light guide 10 will be described.

[0022] Figure 2 shows a 100 kBq source. 90 Sr( 90 Y), Figure 3 shows the results of 137These are the measurement results when using Cs. In both cases, as described above, a distribution with a peak at the position where the line source is installed is obtained, and from this, it is clear that the position of the line source can be recognized in both cases. On the other hand, in both Figures 2 and 3, peaks can also be recognized on both end sides (0 m, 5 m sides). Although the intensity of this peak changes according to the position of the line source, this peak exists at any position. Furthermore, when comparing the intensity of this peak with the intensity of the original peaks (at positions 1.5 m, 2.5 m, 3.5 m) corresponding to the position of the line source, in the case of Figure 2 ( 90 Sr( 90 Y)), it is smaller than in the case of Figure 3 ( 137 Cs).

[0023] Figure 4 is a diagram schematically showing, in a simplified manner, the characteristics having the three peaks obtained here in the detection intensity distribution. The central peak P0 is the peak corresponding to the light emission position as described above, and the position of the apex of this peak corresponds to the light emission position (the incident position of the radiation). That is, the combination of the outputs of the photodetectors 21A and 21B constituting the peak P0 corresponds to the combination of the light that has traveled to the left and right end sides respectively and been detected in one emission at the light emission position. This is as described in Non-Patent Document 1.

[0024] Here, when the light emitted by the incidence of one radiation (electron) propagates to one end, this light may be detected by the photodetector on this end side, or may not be detected on this end side and be reflected by this end face and propagate to the other end side. Also, as described above, since the Cherenkov light is emitted at a radiation angle of a certain angle θ, in the same light emission, light propagating to the opposite side (the other end side) is also generated simultaneously, and similarly on this side, it may be detected by the photodetector on this end side or may be reflected by this end face. The combination of the photodetections constituting the peak P0 corresponds to the combination of the light detected on one end side without passing through reflection at this end face and the light detected on the other end side without passing through reflection at this end face in the same way.

[0025] Here, we consider the propagation state after the particularly directional Cherenkov light is generated at a certain point in the liquid light guide 10. Figures 5(a) and (b) show schematic diagrams of the propagation state of the Cherenkov light generated by the incidence of an electron (charged particle) to both ends in the liquid light guide 10. In Figure 5(a), 90 Sr( 90 Y) (when the detected radiation is β radiation (electrons)), in Fig. 5(b), the radiation source is 137 Cs (where the detected radiation is gamma rays) are shown. In reality, electrons do not necessarily travel in a straight line inside the liquid light guide 10, and the light emission process is more complicated, but here it is described in a simplified manner as light being emitted from a certain point (light emission position P).

[0026] As mentioned above, Cherenkov light is emitted in a cone-shaped region within an angle (radiation angle) θ around the electron's traveling direction at the emission position P. In FIG. 5(a), 90 Sr( 90 Electrons emitted from the liquid light guide 10 pass through the lower outer wall W from below and enter the liquid light guide 10, where they emit Cherenkov light. The maximum energy of the electrons is about 2.28 MeV. 137 The 0.662 MeV gamma rays emitted from Cs do not generate Cherenkov light, but these gamma rays are Compton scattered in the liquid light guide 10 to generate Compton electrons of up to about 0.48 MeV, and these Compton electrons (electrons) generate Cherenkov light at the emission position P, as in Figure 5(a). However, compared to the case of Figure 5(a), the energy of these Compton electrons is lower (the aforementioned v is smaller), so the radiation angle θ of the Cherenkov light is smaller.

[0027] Here, in order for light to propagate in the length direction within the liquid light guide 10, the light is required to be reflected between the upper and lower outer walls W, and the light needs to be totally reflected by the outer walls W. The angle of incidence (based on the normal direction of the outer walls W) with respect to the upper and lower outer walls W in the figure is large and close to π / 2 (close to horizontal in the figure), that is, it is required to be obliquely incident on the outer walls W. For this reason, for example, in FIG. 5(a), the light of L1 and L2 propagates within this liquid light guide 10 and reaches the left end face LF and the right end face RF, respectively, but the light of L3, which is close to normal incidence with respect to the outer wall W, cannot propagate within the liquid light guide 10 and does not reach either end face. In this case, the combination of the light detection D1 of the light of L1 at the left end face LF and the light detection D2 of the light of L2 at the right end face RF constitutes the above-mentioned peak P0. Since the time difference between the light detection D1 and the light detection D2 depends on the light emission position P in the length direction, the light emission position P can be calculated from the peak position of the peak P0, as described in Non-Patent Document 1.

[0028] On the other hand, in FIG. 5(b), the light of L4 corresponding to L1 in FIG. 5(a) reaches the left end face LF like L1, but the light of L5 corresponding to L2 is close to normal incidence on the outer wall W like the light of L3, does not reach either end face, and is not detected. For this reason, in the case of FIG. 5(b), the light detection D3 of the light of L4 is recognized, but the light detection of the light of L5 that is paired with it (D4 in the figure) is not recognized, so the light detection D3 caused by the light of L4 is not included in the combination that constitutes the peak P0. In FIG. 5(b), the light of L5 is emitted toward the upper left side, but the same is true when it is emitted toward the upper right side. In this way, when the energy of the electrons is low and the radiation angle θ is small, the proportion of light that does not reach the end face increases, so the number of combinations of light detection that constitute the peak P0 decreases, and the intensity (peak value or integral value) of the peak P0 decreases compared to when the energy is high.

[0029] On the other hand, as mentioned above, among the light that reaches each end face, there is a component that is not detected by the photodetector, but is reflected from this end face and reaches the opposite end face. Figures 6(a) and (b) show the path of the light that reaches each end face in Figures 5(a) and (b) after it is reflected. Here, the dotted line shows the path of the light that first propagated to the left (right after reflection) after reflection in Figures 5(a) and (b), and the dashed line shows the path of the light that first propagated to the right (left after reflection) after reflection. As mentioned above, the latter light does not exist in Figure 6(b).

[0030] In Fig. 6(a), the light detection D5 on the left side is the output of the light L2 in Fig. 5(a) that is reflected by the right end face RF and detected by the left photodetector. Therefore, the time difference between the light detection D2 in Fig. 5(a) and the light detection D5 in Fig. 6(a) corresponds to the length of the liquid light guide 10, and this combination constitutes the above-mentioned peaks P1 and P2. The light detection D1 in Fig. 5(a) and the light detection D6 in Fig. 6(a) are similar except that the light propagation directions are opposite.

[0031] On the other hand, in Fig. 6(b), the light detection D7 on the right side is the output of the light component of L4 in Fig. 5(b) reflected by the left end face LF, detected by the right photodetector. Therefore, the time difference between light detection D3 in Fig. 5(b) and light detection D7 in Fig. 6(b) also corresponds to the length of the liquid light guide 10, and this combination also constitutes the above-mentioned peaks P1 and P2. Therefore, the light of L4 in Fig. 5(b) does not contribute at all to peak P0, but contributes to peaks P1 and P2.

[0032] That is, peak P0 in FIG. 4 is a peak (non-reflection peak) based on the first detection light, which is light that reaches either of the two end portions without being reflected by the end face, and peaks P1 and P2 in FIG. 4 are considered to be peaks (reflection peaks) based on the second detection light, which is light that is reflected by the end face and reaches either of the two end portions.

[0033] As described above, when the electron energy is low and θ is small, the light components that are obliquely incident on the upper outer wall W are reduced, and the light that travels from the light emission position P toward the left and right end faces is reduced, and the number of combinations that constitute peak P0 is reduced. Accordingly, the number of reflected lights (the number of combinations that constitute peaks P1 and P2) that are generated at the end faces is also reduced. However, there is also light that generates combinations that do not contribute to peak P0 at all but contribute to peaks P1 and P2, such as the light L4 in Fig. 5(b) and Fig. 6(b). Therefore, compared to when θ is large, when θ is small, the intensity of peaks P0 to P2 is reduced, but the reduction rate of peaks P1 and P2 is smaller than the reduction rate of peak P0. Therefore, when considering the ratio of the intensity of peak P0 to the intensity of peak P1 or P2 (non-reflected-reflected peak intensity ratio), this ratio is small when θ is small. In other words, peaks P0, P1, and P2 are formed in the same way regardless of the magnitude of θ (high or low electron energy), but this ratio differs depending on θ (electron energy).

[0034] That is, in the detection intensity distribution obtained by the radiation detection device 1, reflection peaks P1 and P2 are formed on both end sides based on the second detection light (light reflected at the end face), and a non-reflection peak P0 is formed between them based on the first detection light (light not reflected at the end face). The intensity ratio of these peaks changes depending on the energy of the detected charged particles (electrons). Using this, the energy of the detected charged particles can be estimated. Alternatively, the radiation source that emitted the charged particles as radiation, or the radiation source that emitted the radiation that generated the charged particles, can be detected, and in particular the position or distribution of the radiation source in the longitudinal direction of the liquid light guide 10 can be calculated.

[0035] Figure 7 shows the results of calculating the electron energy dependence of the radiation angle θ of Cherenkov light in the range of 0 to 1 MeV. Here, two types of liquid (medium) were assumed in the liquid light guide 10: quartz and water. From this result, it can be confirmed that there is a large decrease in θ below 1 MeV, and it is clear that the situation in Figures 5(a) and (b) actually holds true.

[0036] In addition, as shown in FIG. 90 Sr( 90 Y), Fig. 3( 137 Figure 8 shows the results of calculating the non-reflected / reflected peak intensity ratio for each position of the radiation source from the results of Cs. Here, the intensity of the reflected peaks on the left and right (P1, P2) may not be equal, but here the sum of the two was used. As shown here, this ratio is constant regardless of the position of the radiation source, and as mentioned above, 90 Sr( 90 Y) uniformly 137 It can be confirmed that the ratio is larger than Cs. This ratio is determined by θ, and ultimately by the energy of the electrons. In other words, the energy of the detected electrons (charged particles) can be recognized from the non-reflected to reflected peak intensity ratio. If the relationship between the electron energy and the non-reflected to reflected peak intensity ratio is experimentally determined in advance, the analysis unit 30 can also calculate the energy of the detected electrons.

[0037] For this reason, for example, in the case where two types of radioactive nuclides that generate different energies of electrons are to be measured, based on the measurement results corresponding to Figs. 2 and 3 using the device of Fig. 1 (the results of measuring the detection intensity for each position for each position of the radiation source, and determining the results for two types of radiation sources), it is possible to calculate the distribution of each radioactive nuclides when these two types of radioactive nuclides are mixed in a sample by the unfolding method as in Patent Document 1.

[0038] An example of a calculation method for this purpose will be specifically described below. Here, the positions (horizontal axis) in the results (detection intensity distribution) of Figures 2 and 3 are simplified into five sections (ROIs) of (-0.5m to 0.5m), (1.0m to 2.0m), (2.0m to 3.0m), (3.0m to 4.0m), and (4.5m to 5.5m). 1 ~ROI 5 The actual counts and the distribution of each radiation source to be recognized are defined according to this division. 1 , ROI 5 contains the reflective peaks as described above, but does not contain non-reflective peaks, and ROI 2~ROI 4 The ROI contains non-reflective peaks and does not contain reflective peaks. 1 ~ROI 5 All results are taken into account, but the location of the actual radionuclides is within the ROI 2 ~ROI 4 In addition, the radionuclides to be measured as described above are as follows: 90 Sr( 90 Y) for nuclide 1, 137 Cs is nuclide 2.

[0039] ROI when measuring the sample to be measured (measurement area) 1 ~ROI 5 The number of counts (detection intensity) at each 1 ~S 5 Then, S 1 ~S 5 is expressed by equation (1), where X 2 ~X j (j=4) are the ROIs for nuclide 1, respectively. 2 ~ROI 4 is the abundance in Y 2 ~Y j (j=4) are the ROIs for nuclide 2 2 ~ROI 4 These are the amounts to be calculated. 1,2 ~R i,j is the response factor when only nuclide 1 is present, and C 1,2 ~C i,j is the response factor when only nuclide 2 is present.

[0040]

number

[0041] Here, in the characteristic of FIG. 2, (X 2 ~X j ) and (S 1 ~S 5 ) are recognized, and Y 2 ~Y jis always zero, so that R in Eq. (1) 1,2 ~R i,j Similarly, in the characteristic of FIG. 3, (Y 2 ~Y j ) and (S 1 ~S 5 ) are recognized, as well as X 2 ~X j is always zero, so that C in Eq. (1) 1,2 ~C i,j In other words, by obtaining the measurement results shown in Figures 2 and 3 in advance, the response coefficient R 1,2 ~R i,j , C 1,2 ~C i,j That is, each of the two nuclides can be determined as ROI. 2 ~ROI 4 The ROI in the detection intensity distributions (reference detection intensity distributions) in Figures 2 and 3, which are the detection intensity distributions when each of 1 ~ROI 5 The response coefficient can be calculated from the detected intensity of the reflected peak. The response coefficient calculated here is determined based on Figures 2 and 3, taking into account the effect of the reflected peak as described above.

[0042] Therefore, the S obtained for the actual sample 1 ~S 5 Using equation (1), X 2 ~X j , Y 2 ~Y j Specifically, the least squares method is applied to the left and right sides of equation (1), and X is calculated so that Δ defined by equation (2) is minimized. 2 ~X j , Y 2 ~Y j Here, σ Sk is the measured value S k is the error.

[0043]

number

[0044] The above method actually detects a given intensity nuclide 1( 90 Sr( 90 Y)), nuclide 2( 137 Cs) is the ROI 2 ~ROI 4 The actual intensity (Bq) and the intensity calculated by the above method were measured and the results are described below. Here, a product name LLG3-8H (manufactured by Thorlab) (core diameter 3.0 mmΦ, length 5 m) was used as the liquid light guide 10, and photomultiplier tubes (product name H10721P-01 (manufactured by Hamamatsu Photonics) were used as the photodetectors 21A and 21B.

[0045] 9 and 10 show the measurement results for two types of samples (first sample and second sample) in this case. In Fig. 9 and 10, (a) shows the actually measured detection intensity distribution (number of counts for each recognized position), (b) shows the nuclide 1 ( 90 Sr / 90 Distribution of (X) and (Y) 2 ~X 4 ) and the actual distribution, (c) is the calculated distribution of nuclide 2 ( 137 Cs) distribution (Y 2 ~Y 4 As shown here, the distributions of nuclides 1 and 2 can be measured with high accuracy even for completely different distributions.

[0046] In contaminated environments caused by nuclear accidents, etc., 90 Sr( 90 It is required to measure the distribution of β-ray-emitting nuclides such as β-ray ... 137 Conventionally, this measurement was difficult in environments with high gamma radiation doses due to the presence of a mixture of nuclides that emit gamma rays, such as Cs. 90 Sr( 90 The distribution of γ can be measured.

[0047] In the above example, the distribution is measured in three sections (five including the end sections for recognizing the reflection peaks), but by increasing the number of sections, the position resolution of the measurement can be improved. However, if one section is shortened, the number of counts detected within this section will decrease, and σ in equation (2) will decrease. Sk becomes large and the measurement accuracy decreases, so the width of this section is set appropriately taking into consideration the position resolution and measurement accuracy. In the above example, the distribution of each nuclide was measured using equations (1) and (2), but this distribution can also be calculated using other methods as appropriate, taking into consideration such accuracy.

[0048] In the above example, the position was measured in a one-dimensional direction along the extension direction of the liquid light guide 10. However, similar to the technology described in Patent Document 1, if the bendable liquid light guide 10 is bent and laid in a two-dimensional region, it is also possible to measure the two-dimensional distribution of nuclides in this two-dimensional region as a one-dimensional distribution along the extension direction of the liquid light guide 10.

[0049] Conversely, by setting only one measurement section and providing sections at both ends to recognize the peaks of reflected light, making a total of three sections, it is possible to measure the abundances of nuclide 1 and nuclide 2 in the measurement section more simply and with higher accuracy.

[0050] 11 is a diagram showing a configuration (modification) corresponding to FIG. 1 in this case. Here, the components subsequent to the photodetectors 21A and 21B in FIG. 1 are omitted. In this case, the liquid light guide 10 is wound and placed so as to overlap two-dimensionally within the measurement target area AA, and the region within the measurement target area AA is the ROI in the liquid light guide 10. 2 ~ROI 4 is recognized as an integrated RO, and the ROs on both sides 1 , R.O. 5are similar, liquid light guide 10 is divided into these three sections in the longitudinal direction. Since liquid light guides 10 are placed in a two-dimensionally overlapping state in this manner, the detection efficiency of radiation emitted by nuclides within measurement area AA by liquid light guide 10 is increased.

[0051] In this case, the measurement results for each section are recognized as three sections, as shown in Fig. 12. In this case, the measurement results are symmetric around RO, so the sections RO on both ends are 1 , R.O. 5 The counts (detection intensities) of the two sections are equal to Z1, and the counts of the central section RO are Z0.

[0052] In this case, as mentioned above, the count 137 In the case of gamma rays from Cs, the influence of the reflection peak is large, so Z0 / Z1 becomes small and the count 90 Sr( 90 Y), the effect of the reflected peak is small and Z0 / Z1 is large. 137 In an environment where the dose of gamma rays from Cs is high 90 Sr( 90 In order to recognize the presence or absence of a target object (Y), a threshold is set for Z0 / Z1. If Z0 / Z1 exceeds this threshold, 90 Sr( 90 Y) can be recognized to exist. That is, within the measurement area AA 90 Sr( 90 Y) can be easily and accurately recognized. Conversely, when Z0 / Z1 is small, 137 It can be determined that Cs is dominant.

[0053] If the liquid light guide 10 is flexible as described above, it is possible to use such a configuration, or to realize a configuration for measuring one-dimensional or two-dimensional distribution of radioactive nuclides as described above using a common liquid light guide 10.

[0054] In the above example, a liquid light guide was used to detect Cherenkov light, but any optical fiber (light guide member) that can generate Cherenkov light and transmit this light to the end side can be used in the same way. For example, if a medium that generates Cherenkov light greater than 1 is filled in the outer wall made of a material with a refractive index greater than this, it can be used in the same way. In this case, based on the results in Figure 7, it is preferable that the refractive index of this medium is smaller than that of quartz.

[0055] In addition, for example, by constructing the outer wall from a material with a refractive index very close to 1 and using a material with a refractive index slightly higher than that of the outer wall, v can be set large (close to c) to satisfy the condition for emitting Cherenkov light (v>c / n), and the energy of the electrons can be increased. 90 Sr( 90 Y) produces only Cherenkov light, 137 It is possible to prevent the generation of Cerenkov light by Cs. In this case, selectively 90 Sr( 90 Y) can be detected.

[0056] Also, in the above example 90 Sr( 90 Y) and 137 Although it has been assumed that Cs is detected separately, in principle, the above radiation detection device (radioactive nuclide detection device) can detect two types of charged particles that generate Cherenkov light separately if the charged particles have different energies. Therefore, it is also possible in principle to detect two nuclides that emit beta rays with different energies, or two nuclides that emit gamma rays with different energies and therefore generate Compton electrons with different energies.

[0057] In addition, when a configuration capable of measuring the time difference between light detections at both ends of the light-guiding member other than the configuration in Fig. 1 is used, the same measurement can be performed and the same results can be obtained. For example, a photodetector other than a photomultiplier tube can be used. In addition, a radionuclide distribution measurement method (a method for calculating the amount of nuclide present in each section) can be used in the same way as long as the relationship between the reflection peak and the non-reflection peak as described above is taken into consideration. [Explanation of symbols]

[0058] 1. Radiation detection device (radionuclide detection device) 10 Liquid light guide (light guiding member) 21A Photodetector (First Photodetector) 21B Photodetector (second photodetector) 22A, 22B Amplifier 23A, 23B CFD(Constant Fraction Discriminator) 24 Delay section 25 TAC(Time to Amplitude Converter) 30 Analysis Department LF, RF end face P Light emitting point P0 Non-reflective peak P1, P2 reflection peaks W Exterior wall

Claims

1. A radiation detector that detects an incident charged particle by detecting Cherenkov light generated by the charged particle, comprising: a light guide member that generates light that is the Cherenkov light, propagates the light toward both end portions in a longitudinal direction, and reflects a part of the light at each end surface of the both end portions; a first photodetector and a second photodetector for detecting, at each of both end portions of the light guiding member, a first detection light, which is light that has reached either of both end portions from a generation point of the Cherenkov light in the light guiding member without being reflected at the end surface, and a second detection light, which is light that has reached either of the both end portions from the generation point of the Cherenkov light after being reflected at the end surface; an analysis unit that corresponds a time difference between a combination of light detections in the first photodetector and the second photodetector to a position in the longitudinal direction of the light-guiding member, recognizes a detection intensity distribution that is a measurement result of the dependency of the count number of the combination on the position, the detection intensity distribution having a non-reflection peak that is a peak formed on a side other than the two ends due to the first detection light, and a reflection peak that is a peak formed on the two ends due to the second detection light, and detects the charged particles having different energies from the detection intensity distribution; A radiation detection device comprising:

2. 2. The radiation detection device according to claim 1, wherein the charged particles that generate Cherenkov light in the light-guiding member are Compton electrons generated by gamma rays, and the analysis unit detects the gamma rays by detecting the charged particles.

3. A radionuclide detection device that detects radiation that is a charged particle or a radionuclide that emits radiation that generates a charged particle in a measurement target area, Using the radiation detection device according to claim 1, The light guide member is laid in the measurement target area, The radionuclide detection device according to claim 1, wherein the analysis unit recognizes the presence of the radionuclide to be measured in the measurement region from the detection intensity distribution, by distinguishing it from other radionuclides.

4. 4. The radionuclide detection device according to claim 3, wherein the analysis unit recognizes a distribution of the radionuclide to be measured within the measurement target region as a distribution along the longitudinal direction of the light-guiding member.

5. The analysis unit is Two types of nuclides that generate the charged particles having different energies are set as the radioactive nuclides to be measured; The position of the light guide member in the longitudinal direction is divided into three or more sections including regions corresponding to both end sides, 5. The radionuclide detection device according to claim 4, characterized in that a distribution of each of the two types of nuclides along the longitudinal direction of the light-guiding member is recognized from the detection intensity distribution obtained for the measurement target region by using a response coefficient calculated from the count number in each of the sections in a reference detection intensity distribution, which is the detection intensity distribution when each of the two types of nuclides is present in each of the sections.

6. 4. The radionuclide detection device according to claim 3, wherein the analysis unit recognizes, in the detection intensity distribution, the reflection peaks as peaks on both ends in the longitudinal direction of the light-guiding member and the non-reflection peak as a peak on the central side in the longitudinal direction, and recognizes the presence of the radionuclide to be measured in the measurement target region, distinguishing it from the other radionuclides, from an intensity ratio between the reflection peak and the non-reflection peak.

7. The radionuclides to be measured include ９０ Sr or ９０ 7. The radionuclide detection device according to claim 3, further comprising Y.

8. The two types of nuclides are ９０ Sr or ９０ Y. １３７ 6. The radioactive nuclide detection device according to claim 5, characterized in that the radioactive nuclide is 3Cs.

9. A radionuclide distribution measurement method for detecting radiation that is a charged particle or radiation that generates the charged particle by detecting Cherenkov light generated by an incident charged particle, and measuring the distribution of a radionuclide that emits the radiation and is a measurement target in a measurement target region by distinguishing the radionuclide from other radionuclides, comprising: a light guide member is provided in the measurement target area to generate light that is the Cherenkov light, propagate the light toward both end portions in a longitudinal direction, and reflect a part of the light at each end surface of the both end portions; a first detection light, which is light that has traveled from a generation point of the Cherenkov light in the light guiding member to one of the two end portions without being reflected by the end surface, and a second detection light, which is light that has traveled from the generation point of the Cherenkov light to one of the two end portions after being reflected by the end surface, are detected at each of the two end portions of the light guiding member by using a first photodetector and a second photodetector, a time difference between a combination of light detections by the first photodetector and the second photodetector is made to correspond to a position in the longitudinal direction of the light-guiding member, and a detection intensity distribution is recognized as a measurement result of the dependency of the count number of the combination on the position, the detection intensity distribution having a non-reflection peak which is a peak formed at a side other than both ends due to the first detection light, and a reflection peak which is a peak formed at both ends due to the second detection light; A method for measuring a distribution of a radioactive nuclide, comprising: recognizing a distribution of the radioactive nuclide to be measured separately from distributions of the other radioactive nuclide from the detection intensity distribution.

10. The position of the light guide member in the longitudinal direction is divided into three or more sections including regions corresponding to both end sides, 10. The method for measuring a radionuclide distribution according to claim 9, further comprising the steps of: recognizing a distribution of each of the radionuclide to be measured and the other radionuclides along the longitudinal direction of the light-guiding member from the detection intensity distribution obtained for the measurement target region by using a response coefficient calculated from the count number in each of the sections in a reference detection intensity distribution, which is the detection intensity distribution when the radionuclide to be measured and the other radionuclides are each present in each of the sections.

11. The radioactive nuclide to be measured and the other radioactive nuclide are, respectively, ９０ Sr or ９０ Y. １３７ The method for measuring distribution of a radioactive nuclide according to claim 10, characterized in that the radioactive nuclide is 3Cs.

Images