JP2009133748A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector capable of reducing the influence of the background component by cosmic rays, using a simple constitution. <P>SOLUTION: This detector has a constitution, equipped with the first flat radiation detection part 2 for emitting light by interaction with each of the first radiation and the second radiation; the second flat radiation detection part 3, provided in parallel with the back side of the first radiation detection part 2, having different time responsiveness from the first radiation detection part 2, for emitting light by interaction with the second radiation penetrating the first radiation detection part 2; a photodetection part 4 for detecting each emission from the first radiation detection part 2 and the second radiation detection part 3, and converting it into an electrical signal; a digital conversion part 5 for converting digitally the electrical signal output from the photodetection part 4; and a waveform discriminating part 6 for discriminating a numerically-expressed electrical signal waveform output from the digital conversion part 5 into a result, based on the interaction only by the first radiation detection part 2 and a result, based on the interaction by both the first radiation detection part 2 and the second radiation detection part 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a planar radiation detector that requires radiation measurement in particular with low background.

Planar radiation detectors used in surface contamination inspection equipment that inspects radioactive contamination in clothes and articles, etc., increase the background as the sensitive area increases, thereby degrading the detection limit. . And, the proportion of the cosmic ray component in the background component is large, and in particular, the μ particle that continuously imparts energy has an intensity of about 0.02 particles / second / cm ^2, so that it is about 2000 cm ² . A planar radiation detector having a sensitive area results in a background count of about 400 counts / second. On the other hand, since this background component increases in proportion to the sensitive area of the radiation detector, the larger the sensitive area, the worse the detection limit of the radiation detector.

  For this reason, multiple radiation detectors are placed so as to surround the measurement target, and the background component is reduced by removing the background by anticoincidence using the detection pulse signal of each radiation detector. (For example, refer to Patent Document 1). However, since it is anti-coincidence between the radiation detectors arranged at a relatively large interval, the gap is large and the solid angle is large, and the probability of generating coincidence must be small, and the efficiency is not always sufficient. .

In addition, two radiation detectors each having high sensitivity to different radiation are provided in the same radiation inspection apparatus, and the background is removed by anticoincidence using electrical pulses generated in each radiation detector. There is one in which components are reduced (for example, see Patent Document 2). However, it is necessary to provide each radiation detector with a light collection system that captures light emitted by interaction with radiation.
Japanese Patent Laid-Open No. 11-44766 Japanese Patent Laid-Open No. 06-18669

  The present invention has been made in view of the situation as described above. The object of the present invention is to provide a radiation detector capable of reducing the influence of, for example, cosmic rays on the background component of the radiation to be detected with a simple configuration. Is to provide.

  The radiation detector of the present invention includes a flat plate-like first radiation detection unit that emits light by interaction with each of the first radiation and the second radiation, and a back surface side of the first radiation detection unit. A flat plate-like second radiation detection unit that is provided and has a time response different from that of the first radiation detection unit and emits light by interaction with the second radiation penetrating the first radiation detection unit A light detection unit that detects each light emission of the first radiation detection unit and the second radiation detection unit and converts the light emission into an electrical signal, and a digital conversion unit that digitally converts the electrical signal output from the light detection unit. The result of the electrical signal waveform output from the digital conversion unit based on the interaction of only the first radiation detection unit and both the first radiation detection unit and the second radiation detection unit Results based on interaction with It is characterized in that it comprises a waveform discrimination unit to discriminate.

  Further, the radiation detector of the present invention includes a flat plate-like first radiation detector that emits light by the interaction of the first radiation and the second radiation, and a back side of the first radiation detector. A flat plate-like second radiation that is provided in parallel, has a time response different from that of the first radiation detection unit, and emits light by interaction with the second radiation penetrating the first radiation detection unit. A detection unit, a plurality of light detection units that detect each light emission of the first radiation detection unit and the second radiation detection unit and convert them into electrical signals, and an electrical signal output from the plurality of light detection units, respectively A plurality of digital conversion units for digital conversion, an addition unit for adding each digitized electric signal waveform output from the plurality of digital conversion units, and a numerical addition electric signal waveform output from the addition unit, Said first radiation detection A waveform discriminating unit for discriminating between a result based only on an interaction and a result based on an interaction between both the first radiation detection unit and the second radiation detection unit. is there.

  According to the present invention, while having a simple configuration, it is possible to reduce the influence of, for example, cosmic rays, which are background components, and to improve the detection accuracy of radiation to be detected.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, a first embodiment will be described with reference to FIGS. FIG. 1 is a configuration diagram, FIG. 2 is a schematic diagram showing an output waveform of the light detection unit, FIG. 2 (a) is a schematic diagram of an output waveform by beta rays, and FIG. 2 (b) is an output waveform by cosmic rays. FIG. 3 is a schematic diagram, and FIG. 3 is a configuration diagram showing a modified embodiment.

  In FIG. 1, 1 is a radiation detector. The radiation detector 1 emits fluorescence by the interaction of the first radiation and the second radiation, and has a predetermined thickness that allows the first radiation to penetrate and the second radiation to penetrate. The first radiation detection unit 2 and a second radiation detection in the form of a plate that is provided in parallel to the back side of the first radiation detection unit 2 and has a predetermined thickness for emitting fluorescence by interaction with the second radiation. Part 3 is provided.

  Furthermore, the radiation detector 1 detects the fluorescence emitted by the first radiation detection unit 2 and the second radiation detection unit 3 on the back side of the second radiation detection unit 3, converts it to an electrical signal, and outputs it. For example, a photosensor 4a constituting the photodetecting unit 4 having a sufficiently fast time response such as a photomultiplier tube (PMT) is provided. In addition to the optical sensor 4a, the optical detection unit 4 includes an amplifier 4b that amplifies the output of the optical sensor 4a and outputs the amplified electrical signal.

  Still further, the radiation detector 1 includes a digital conversion unit 5 that outputs an electrical signal waveform output by the analog / digital conversion of the electrical signal output from the light detection unit 4 and a digitized electrical signal output from the digital conversion unit 5. Waveform discrimination for discriminating a signal waveform into a result based on the interaction only in the first radiation detection unit 2 and a result based on the interaction in both the first radiation detection unit 2 and the second radiation detection unit 3 A portion 6 is provided. The waveform discriminating unit 6 that discriminates a plurality of quantified electric signal waveforms may be configured as shown in, for example, Japanese Patent No. 3980451, which is a known technique.

The first radiation detection unit 2 has a surface portion on which radiation is incident from the outside, for example, several nanoseconds (3 to 5 × 10 ⁻⁹ seconds) due to beta rays of the first radiation and cosmic rays of the second radiation. The light guide plate 2b, which is formed of a thin plastic scintillator 2a that emits light for a certain light emission time, and is formed of a transparent material that absorbs less light with respect to the emitted light as the support, is provided on the back surface portion. Yes. The second radiation detection unit 3 emits light by cosmic rays of the second radiation, and has a light emission time of about several hundred nanoseconds (3 × 10 ⁻⁷ seconds), which is significantly different from the plastic scintillator 2a NaI (Tl). ) A scintillator 3a is provided on the back side of the first radiation detection unit 2, and a light guide plate 3b formed of a transparent material having little light absorption with respect to the emitted light, which is also a support, on the back side of the NaI (Tl) scintillator 3a. Is provided.

  And in what was comprised as mentioned above, the beta ray 7 of the 1st radiation radiated | emitted from test | inspection objects, such as clothes and articles | goods contaminated radioactively, for example to the plastic scintillator 2a of the 1st radiation detection part 2 is carried out. Incidence and interaction occur, for example, as shown schematically, fluorescence is emitted at the light emission position 8, and since the penetrating power is weak, it is absorbed by the first radiation detection unit 2 and disappears, and the second radiation detection unit 3 is not reached. On the other hand, for example, the cosmic ray 9 coming from the outside as the second radiation has a strong penetrating force. Therefore, the cosmic ray 9 first enters the plastic scintillator 2a of the first radiation detection unit 2 to cause an interaction, for example, schematically Thus, fluorescence is emitted at the light emitting position 10a. Further, after penetrating the first radiation detection unit 2, it enters the second radiation detection unit 3 to cause an interaction, and emits fluorescence at a light emission position 10 b as schematically shown, for example.

  The light emitted from the first radiation detection unit 2 and the second radiation detection unit 3 by the beta rays 7 and the light emitted from the second radiation detection unit 3 by the cosmic rays 9 are each transparent to the emitted light. The detection output is amplified by the amplifier 4b and output as an electrical signal. Subsequently, the analog electrical signal output from the light detection unit 4 is analog / digital converted by the digital conversion unit 5 and output as a digitized electrical signal waveform.

  Thereafter, the digitized electric signal waveform is input to the waveform discriminating unit 6, the result based on the interaction only with the first radiation detection unit 2, the first radiation detection unit 2, and the second radiation detection unit 3. It is distinguished from the result based on the interaction between the two. As shown in FIG. 2, the output waveform of the beta ray 7 rises as shown in FIG. 2 (a). As shown in FIG. Since the output waveform of the cosmic ray 9 is composed of a fast rising component and a slow rising component as shown in FIG. 2 (b), analog / digital conversion of the electric signals having such differences is performed as numerical data. By doing so, the waveform can be discriminated. Although not shown in the drawing, the output of the waveform discriminating unit 6 is selectively output by only the signal due to the interaction with the beta ray 7, so that only one optical sensor 4 a is provided. The influence of the background component can be reduced, and the detection of the beta ray 7 of the radiation to be detected can be accurately performed.

  In the above-described embodiment, the first radiation detection unit 2 has a configuration in which the transparent light guide plate 2b is provided as a support on the back surface portion of the thin plastic scintillator 2a, but the back surface portion of the plastic scintillator 2a includes: The NaI (Tl) scintillator 3a of the second radiation detection unit 3 may be provided directly so as to serve also as a support for the plastic scintillator 2a. Further, at this time, the second radiation detection unit 3 may be configured by only the NaI (Tl) scintillator 3a without providing the light guide plate 3b.

  Moreover, in said embodiment, although the optical sensor 4a of the photon detection part 4 was provided in the back side of the 2nd radiation detection part 3, you may comprise like the modification shown in FIG. Hereinafter, the same reference numerals are given to the same portions as those in the above embodiment, and the description thereof will be omitted, and the configuration of this modified embodiment different from the above embodiment will be described.

  That is, in FIG. 3, 11 is a radiation detector. The radiation detector 11 emits fluorescence by the interaction between the first radiation and the second radiation, and is a flat plate-like first radiation detector that allows the first radiation to pass through and the second radiation to pass through. 12 and a flat plate-like second radiation detection unit 13 that is provided in parallel with the back side of the first radiation detection unit 12 and emits fluorescence by interaction with the second radiation.

  Then, the first radiation detection unit 12 forms a surface portion on which radiation is incident from the outside with a thin plastic scintillator 2a that emits light by, for example, beta rays of the first radiation and cosmic rays of the second radiation, A light guide plate 12a made of a transparent material that absorbs little light with respect to emitted light is provided as a support on the back surface portion. Further, unlike the second radiation detection unit 3 of the above embodiment, the second radiation detection unit 13 is formed on the back side of the first radiation detection unit 12 with NaI (e.g., emitted by cosmic rays of the second radiation). Tl) Only the scintillator 3a is provided, and the light guide plate is not provided on the back surface portion.

  Further, the radiation detector 11 includes, for example, a light guide plate of the first radiation detection unit 12 between the plastic scintillator 2a of the first radiation detection unit 12 and the NaI (Tl) scintillator 3a of the second radiation detection unit 13. Time responsiveness in which the fluorescence emitted from the plastic scintillator 2a of the first radiation detection unit 12 and the NaI (Tl) scintillator 3a of the second radiation detection unit 13 is detected and converted into an electrical signal and output to the 12a portion. Is provided with a light sensor 4a that constitutes a sufficiently fast light detection unit 4. In addition to the optical sensor 4a, the optical detection unit 4 includes an amplifier 4b that amplifies the output of the optical sensor 4a and outputs the amplified electrical signal.

  Still further, the radiation detector 11 includes a digital conversion unit 5 that outputs the electrical signal output from the light detection unit 4 as an analog / digital converted digital signal waveform, and a digitalized electrical signal output from the digital conversion unit 5. Waveform discrimination for discriminating a signal waveform into a result based on an interaction only in the first radiation detection unit 12 and a result based on an interaction in both the first radiation detection unit 12 and the second radiation detection unit 13 A portion 6 is provided.

  And in the modified form comprised in this way, the effect similar to the said embodiment can be acquired with a simpler structure.

  Next, a second embodiment will be described with reference to FIGS. FIG. 4 is a block diagram, and FIG. 5 is a block diagram showing a modification. In addition, the same code | symbol is attached | subjected to the same part as 1st Embodiment, description is abbreviate | omitted, and the structure of this embodiment different from 1st Embodiment is demonstrated.

  In FIG. 4, 21 is a radiation detector. The radiation detector 21 emits fluorescence by the interaction between the first radiation and the second radiation, and the first radiation detection unit has a flat plate shape that does not penetrate the first radiation and penetrates the second radiation. 2 and a flat second radiation detection unit 3 that is provided in parallel to the back side of the first radiation detection unit 12 and emits fluorescence by interaction with the second radiation.

  The first radiation detection unit 2 is formed of a thin plastic scintillator 2a that emits light, for example, by beta rays of the first radiation and cosmic rays of the second radiation. The light guide plate 2b transparent to the emitted light is provided. The second radiation detection unit 3 is provided with a NaI (Tl) scintillator 3a that emits light by cosmic rays of the second radiation on the back side of the first radiation detection unit 2, and further transparent to the emitted light on the back side. The light guide plate 3b is provided.

  Furthermore, the radiation detector 21 includes a plurality of, for example, two light detection units 22a and 22b so as to detect fluorescence emitted by the first radiation detection unit 2 and the second radiation detection unit 3. Since each of the light detection units 22a and 22b detects emitted light, for example, photosensors 23a and 23b such as a photomultiplier tube (PMT) are provided on the back side of the second radiation detection unit 3 with a sufficiently fast time response. The amplifiers 24a and 24b are arranged with a predetermined interval, and further amplify the outputs of the optical sensors 23a and 23b and output the amplified signals as electric signals.

  Furthermore, since the radiation detector 21 outputs the electrical signal output from the amplifiers 24a and 24b of the light detection units 22a and 22b as analog / digital converted and digitized electrical signal waveforms, it corresponds to a plurality of light detection units. For example, two digital conversion units 25a and 25b are provided, and an addition unit 26 for adding and calculating the digitized electric signal waveforms output from the digital conversion units 25a and 25b is provided. The result of the electrical signal waveform digitized and output by the addition operation in the unit 26 is obtained based on the interaction of only the first radiation detection unit 2 and both the first radiation detection unit 2 and the second radiation detection unit 3. The waveform discriminating unit 6 is provided for discriminating the result based on the interaction in FIG.

  Further, a calibration light source 27 is provided on the back side of the second radiation detection unit 3 at a substantially equal distance from the optical sensors 23a and 23b of the respective light detection units 22a and 22b. The gain can be adjusted by a gain adjustment signal from the gain adjustment unit 28. At the same time, the gain adjustment unit 28 adjusts the calibration light source 27 and corrects variations in characteristics of the optical sensors 23a and 23b in the outputs of the digital conversion units 25a and 25b that are added by the addition unit 26. The weighting factor to be multiplied by is calculated based on the output response values of the respective light detection units 22a and 22b obtained using the calibration light source 27, and stored.

  In the configuration as described above, prior to the inspection of radioactive contamination, the weighting coefficient to be multiplied to correct the variation in the characteristics of each of the optical sensors 23a and 23b stored in the gain adjustment unit 28 is calculated. Done.

  In calculating the weighting factor, first, the gain adjustment unit 28 is operated at a constant period, or a calibration mode signal is input from the outside to start the pulsed light emission of the calibration light source 27. The pulsed light emitted from the calibration light source 27 is detected by the optical sensors 23a and 23b, and the detected outputs are amplified by the amplifiers 24a and 24b and output as electrical signals. Subsequently, the analog electrical signals output from the respective light detection units 22a and 22b are subjected to analog / digital conversion by the respective digital conversion units 25a and 25b, and are output as digitized electrical signal waveforms. Outputs from the digital conversion units 25 a and 25 b are input to the addition unit 26. After that, the gain adjusting unit 28 obtains a digitized electrical signal waveform that is an output of each of the digital conversion units 25a and 25b from the adding unit 26, detects a difference between the digitized electrical signal waveforms, and determines the detected difference. Based on this, a weighting factor by which the output is multiplied is calculated and stored so that the outputs of both the digital conversion units 25a and 25b are the same.

  After the weighting factor is obtained in this way, a predetermined radioactive contamination inspection is started. For example, the beta ray 7 of the first radiation emitted from the inspection object, such as a radioactively contaminated clothing or article, It enters the plastic scintillator 2 a of the radiation detection unit 2 and interacts therewith, for example, emits fluorescence at the light emission position 8 and does not reach the second radiation detection unit 3. On the other hand, since the cosmic ray 9 which is the second radiation coming from the outside has a strong penetrating force, it first enters the plastic scintillator 2a of the first radiation detector 2 and causes an interaction, for example, fluorescence at the light emitting position 10a. Then, the light passes through the first radiation detection unit 2 and enters the second radiation detection unit 3 to cause an interaction. For example, fluorescence is emitted at the light emission position 10b.

  The light emitted from the first radiation detection unit 2 and the second radiation detection unit 3 by the beta ray 7 and the light emitted from the second radiation detection unit 3 by the cosmic ray 9 are transmitted through the respective parts transparent to the emitted light. It is simultaneously detected by the optical sensors 23a and 23b of the light detection units 22a and 22b, and the detection outputs are amplified by the amplifiers 24a and 24b and output as electrical signals. Subsequently, the analog electrical signals output from the light detection units 22a and 22b are analog / digital converted by the digital conversion units 25a and 25b, and output as digitalized electrical signal waveforms.

  Thereafter, the two digitized electrical signal waveforms are input to the adding unit 26 and multiplied by the weighting factor stored and stored in the gain adjusting unit 28 by the adding unit 26 to correct variations in characteristics of the optical sensors 23a and 23b. Then, the addition operation is performed. Further, the digitized summed electric signal waveform output from the adding unit 26 is input to the waveform discriminating unit 6, the result based on the interaction only with the first radiation detecting unit 2, the first radiation detecting unit 2 and the first radiation detecting unit 2. And the result based on the interaction between the two radiation detection units 3.

  The adding unit 26 is configured not to output the addition calculation result to the waveform discriminating unit 6 unless there is simultaneous output from both the digital converting units 25a and 25b, and there are three or more photodetecting units. In addition, when there are the same number of digital conversion units, the addition operation result is not output to the waveform discrimination unit 6 unless there are simultaneous outputs from at least two digital conversion units.

  Then, the result of only the signal due to the interaction with the beta ray 7 (not shown) is selectively outputted from the waveform obtained by discriminating the added electric signal waveform digitized as described above by the waveform discriminator 6. The influence of the background component due to the cosmic rays 9 can be reduced, and the detection of the beta rays 7 of the radiation to be detected can be accurately performed.

  Further, normally, an optical sensor includes a noise component due to thermal noise or the like, but a signal due to such a noise component is an independent event in each optical sensor. On the other hand, signals based on radiation-induced events are emitted simultaneously from both photosensors. Therefore, it is possible to remove a noise component caused by thermal noise or the like by determining the synchronism of the optical sensor. However, there is a variation in the optical / electrical conversion efficiency of each photosensor, and the variation may cause a time variation.

  In such a situation, by configuring as in the present embodiment, it is possible to correct variations in the optical / electrical conversion efficiency of the optical sensors 23a and 23b with a simple configuration. The digitized waveform data of the added electric signal waveform does not depend on the characteristic variation of the optical sensors 23a and 23b, and the waveform discrimination unit 6 and the result based on the interaction only with the first radiation detection unit 2 are used. Thus, it is possible to accurately discriminate between the result based on the interaction in both the first radiation detection unit 2 and the second radiation detection unit 3.

  In the above-described embodiment, the first radiation detection unit 2 has a configuration in which the transparent light guide plate 2b is provided as a support on the back surface portion of the thin plastic scintillator 2a, but the back surface portion of the plastic scintillator 2a includes: The NaI (Tl) scintillator 3a of the second radiation detection unit 3 may be provided directly so as to serve also as a support for the plastic scintillator 2a.

  In the above-described embodiment, the optical sensors 23a and 23b and the calibration light source 27 of the light detection units 22a and 22b are provided on the back side of the second radiation detection unit 3. However, as in the modification shown in FIG. You may comprise. Hereinafter, the same reference numerals are given to the same portions as those in the above embodiment, and the description thereof will be omitted, and the configuration of this modified embodiment different from the above embodiment will be described.

  That is, in FIG. 5, 31 is a radiation detector. The radiation detector 31 emits fluorescence by the interaction between the first radiation and the second radiation, and the first radiation detection unit has a flat plate shape that does not penetrate the first radiation and penetrates the second radiation. 32 and a flat second radiation detection unit 33 that is provided in parallel to the back side of the first radiation detection unit 32 and emits fluorescence by interaction with the second radiation.

  Then, the first radiation detection unit 32 forms a surface portion on which radiation is incident from the outside, for example, with a thin plastic scintillator 2a that emits light by the beta rays of the first radiation and the cosmic rays of the second radiation, A light guide plate 32a formed of a transparent material that absorbs little light with respect to emitted light as a support is provided on the back surface portion. Also, unlike the second radiation detection unit 3 of the above embodiment, the second radiation detection unit 33 is formed on the back side of the first radiation detection unit 32 with, for example, NaI (light emitted by cosmic rays of the second radiation). Tl) Only the scintillator 3a is provided, and the light guide plate is not provided on the back surface portion.

  Further, the radiation detector 31 is, for example, a light guide plate of the first radiation detection unit 32 between the plastic scintillator 2a of the first radiation detection unit 32 and the NaI (Tl) scintillator 3a of the second radiation detection unit 33. 12a portion detects the fluorescence emitted from the plastic scintillator 2a of the first radiation detection unit 32 and the NaI (Tl) scintillator 3a of the second radiation detection unit 33, converts it into an electrical signal, and outputs it. Are arranged at predetermined intervals. The photosensors 23a and 23b constituting the photodetecting portions 22a and 22b are sufficiently fast. In addition to the optical sensors 23a and 23b, the optical detectors 22a and 22b include amplifiers 24a and 24b that amplify the outputs of the optical sensors 23a and 23b, respectively, and output the amplified electrical signals.

  Still further, the radiation detector 31 includes digital converters 25a and 25b that output the electric signals output from the amplifiers 24a and 24b of the light detectors 22a and 22b as analog / digital converted digital signals, An adder unit 26 for adding and calculating the digitized electric signal waveforms output from the digital conversion units 25a and 25b is provided. Further, the digitized electric signal waveform added and calculated by the adder unit 26 is output as the first electric signal waveform. A waveform discriminating unit 6 is provided that discriminates a result based on the interaction only in the radiation detection unit 32 and a result based on the interaction in both the first radiation detection unit 32 and the second radiation detection unit 33.

  In addition, between the first radiation detection unit 32 and the second radiation detection unit 33, the light emission is gain adjustment unit 28 at a position approximately equidistant from the optical sensors 23a and 23b of the respective light detection units 22a and 22b. A calibration light source 27 that is adjusted by the above is provided. In addition to the adjustment of the calibration light source 27, the gain adjustment unit 28 multiplies the output of each digital conversion unit 25a, 25b, which is added by the addition unit 26, in order to correct variations in characteristics of the respective optical sensors 23a, 23b. The weighting coefficient is calculated and stored based on the output response value of each of the light detection units 22a and 22b obtained using the calibration light source 27.

  In the configuration as described above, as in the above-described embodiment, prior to the inspection of radioactive contamination, the weighting coefficient to be multiplied to correct the variation in characteristics of each of the optical sensors 23a and 23b is calculated. However, the calibration light source 27 emits light in pulses. The pulsed light emitted from the calibration light source 27 is detected by the optical sensors 23a and 23b, amplified by the amplifiers 24a and 24b, and output as an electrical signal.

  The analog electrical signals output from the light detection units 22a and 22b are analog / digital converted by the digital conversion units 25a and 25b, and are output as digitized electrical signal waveforms. Further, the outputs from the digital conversion units 25 a and 25 b are input to the addition unit 26. Thereafter, the gain adjusting unit 28 obtains the digitized electric signal waveforms of the outputs of the digital conversion units 25a and 25b from the adding unit 26, detects the difference between the digitized electric signal waveforms, and based on the detected difference. The weighting coefficient by which the output is multiplied is calculated and stored so that the outputs of both the digital conversion units 25a and 25b are the same.

  After the weighting factor is obtained in this way, a predetermined radioactive contamination inspection is started. For example, the beta ray 7 of the first radiation emitted from the inspection object, such as a radioactively contaminated clothing or article, The light enters the plastic scintillator 2 a of the radiation detection unit 32 and interacts therewith, for example, emits fluorescence at the light emission position 8 and does not reach the second radiation detection unit 33. On the other hand, since the cosmic ray 9 which is the second radiation coming from the outside has a strong penetrating force, it first enters the plastic scintillator 2a of the first radiation detector 32 and causes an interaction, for example, fluorescence at the light emitting position 10a. Then, the light passes through the first radiation detection unit 32 and is incident on the second radiation detection unit 33 to cause an interaction. For example, fluorescence is emitted at the light emission position 10b.

  The light emitted from the first radiation detection unit 32 and the second radiation detection unit 33 by the beta ray 7 and the light emitted from the second radiation detection unit 33 by the cosmic ray 9 are respectively emitted from the light detection units 22a and 22b. It is simultaneously detected by the optical sensors 23a and 23b, amplified by the amplifiers 24a and 24b, and output as an electrical signal. Subsequently, the analog electrical signals output from the light detection units 22a and 22b are analog / digital converted by the digital conversion units 25a and 25b, and output as digitalized electrical signal waveforms.

  Thereafter, the two digitized electrical signal waveforms are input to the adding unit 26 and multiplied by the weighting factor stored and stored in the gain adjusting unit 28 by the adding unit 26 to correct variations in characteristics of the optical sensors 23a and 23b. Then, the addition operation is performed. Furthermore, the digitized summed electric signal waveform output from the adding unit 26 is input to the waveform discriminating unit 6, the result based on the interaction only with the first radiation detecting unit 32, the first radiation detecting unit 32, and the first radiation detecting unit 32. And the result based on the interaction between the two radiation detection units 33.

  And although not shown in figure, the influence of the background component by the cosmic ray 9 is reduced by selectively outputting only the signal by interaction with the beta ray 7 as the output of the waveform discriminating unit 6, and the detection target The detection of the beta rays 7 of the radiation to be performed can be performed accurately and accurately with a simpler configuration.

It is a block diagram which shows the 1st Embodiment of this invention. FIG. 2A is a schematic diagram showing an output waveform of a light detection unit in the first embodiment of the present invention, FIG. 2A is a schematic diagram of an output waveform by a beta ray, and FIG. 2B is a schematic diagram of an output waveform by a cosmic ray. It is. It is a block diagram which shows the modification of the 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of this invention. It is a block diagram which shows the modification of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... 1st radiation detection part 3 ... 2nd radiation detection part 4 ... Optical detection part 5 ... Digital conversion part 6 ... Waveform discrimination part

Claims (9)

  A flat plate-like first radiation detection unit that emits light by interaction with each of the first radiation and the second radiation, and provided in parallel on the back side of the first radiation detection unit, the first radiation A flat second radiation detector that emits light by interaction with the second radiation penetrating the first radiation detector and having a time response different from that of the detector; and the first radiation detection Output from the light detection unit that detects each light emission of the first and second radiation detection units and converts them into an electrical signal, a digital conversion unit that digitally converts the electrical signal output from the light detection unit, and the digital conversion unit The numerical electrical signal waveform obtained from the result based on the interaction only in the first radiation detection unit and the result based on the interaction in both the first radiation detection unit and the second radiation detection unit Waveform discrimination part Radiation detector characterized by.   A flat plate-like first radiation detection unit that emits light by interaction with each of the first radiation and the second radiation, and provided in parallel on the back side of the first radiation detection unit, the first radiation A flat second radiation detector that emits light by interaction with the second radiation penetrating the first radiation detector and having a time response different from that of the detector; and the first radiation detection A plurality of light detection units that detect each light emission of the first and second radiation detection units and convert them into electrical signals, and a plurality of digital conversion units that respectively convert the electrical signals output from the plurality of light detection units, An adder for adding each digitized electrical signal waveform output from the plurality of digital converters, and a digitized added electrical signal waveform output from the adder for the first radiation detector only Results based on interactions Radiation detector characterized by comprising a waveform discriminator to discriminate on the results based on the interaction of both of the second radiation detector and the first radiation detector.   The radiation detector according to claim 2, further comprising a calibration light source for correcting outputs of the plurality of light detection units.   The radiation detector according to claim 2, wherein the addition unit performs an addition operation by inputting outputs from at least two of the plurality of light detection units.   5. The radiation detection according to claim 2, wherein the adding unit multiplies the outputs from the plurality of light detecting units by respective weighting factors calculated in advance, and then performs an addition operation. vessel.   6. The radiation according to claim 5, wherein a weighting factor to be multiplied by outputs of the plurality of light detection units is calculated based on an output response value of each light detection unit obtained using the calibration light source. Detector.   The radiation detector according to claim 1, wherein the light detection unit or the plurality of light detection units is provided on a back side of the second radiation detection unit.   The said light detection part or these light detection part is provided between the said 1st radiation detection part and the said 2nd radiation detection part, The Claim 1 or Claim 2 characterized by the above-mentioned. Radiation detector.   The radiation detector according to claim 1 or 2, wherein the first radiation is a beta ray, and the second radiation is a cosmic ray.

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