JP5487173B2 - Radionuclide analyzer and its coincidence coincidence suppression method - Google Patents

Description

  The present invention relates to a radionuclide analyzer that suppresses coincidence coincidence and a method for suppressing coincidence coincidence when analyzing radionuclides from pulse signals output from a plurality of radiation detectors using a radionuclide analyzer.

  The radionuclide analyzer measures the radiation energy emitted by the radionuclide, and identifies and quantifies the radionuclide. For radiation energy measurement, radiation is converted into an electrical signal using a general-purpose radiation detector such as a NaI (Tl) scintillation detector, Ge (Li) semiconductor detector, etc., and a photomultiplier tube, charge sensitive type A radiation energy distribution is generated and analyzed by a general-purpose radiation measuring device such as a preamplifier, a pulse shaping amplifier, a DSP (Digital Signal Processor) to which a trapezoidal filter is applied, and a multichannel wave height analyzer.

  Nuclear facilities, medical facilities that use accelerators or radioisotopes, research accelerator facilities, and the space environment have situations and places where the atmospheric dose rate is very high, and the trace amount to be measured in a very severe high background environment Radioactivity measurement may be required.

  As an example, in a nuclear reactor containment vessel during operation of a nuclear power plant, the dose rate in the nuclear reactor containment vessel is a short half-life nuclide [N-16, N-13, F-18, O- 19 etc.] from several mSv / h to several hundred mSv / h, and from several μSv / h to several mSv / h depending on the measurement nuclide [Co-60, Co-58 etc.] adhering to the inner wall of the pipe at the time of periodic inspection It is known to be very high compared to the dose rate of the degree.

  In order to measure the target nuclide in this environment, there is a monitoring method that combines two radiation detectors, coincidence counting method, and energy discrimination method using the fact that the measuring nuclide emits cascade γ rays. Yes (Patent Document 1). However, when the coincidence method is used, an event that two photons accidentally enter two detectors or an accidental coincidence event that is scattered by one detector and detected by another detector occurs. In the signal processing, erroneous counting occurs. Since accidental coincidence occurs with a certain probability, miscounting increases at high atmospheric dose rates. Therefore, with the conventional coincidence device, the measurement of trace radioactivity that emits cascade γ-rays in a high background of a nuclear power plant or the like deteriorates the SN ratio and is difficult to measure.

  If accidental coincidence can be suppressed, trace radioactivity can be measured by cascade gamma ray coincidence method in a high background, and quantification of measurement objects that could not be measured conventionally can be realized.

  Patent Document 2 is a γ-ray coincidence method in a nuclear medicine diagnostic apparatus equipped with a coincidence circuit in a radiation measurement technique related to a nuclear medicine diagnostic apparatus, and is simultaneously performed in accordance with the amount of radiopharmaceutical administered to a subject. The length of the gate time window of the counting circuit is varied.

  Patent Document 3 is a radiation measurement technique related to a nuclear medicine diagnostic apparatus. A first coincidence circuit to which three signals are input, and two of the three signals are delayed by different delay times, A second coincidence circuit to which a signal is input, and a difference between the counts of the two coincidence circuits is a true count.

JP-A-8-101275 Japanese Patent No. 4681487 Japanese Patent No. 2629872

  In order to realize trace radioactivity measurement that emits cascade γ-rays in a high background, a new means for suppressing accidental coincidence is necessary.

  In Patent Document 1, a main detector and a gate detector are provided, the gate detector signal is subjected to energy discrimination, and a gate signal of only predetermined energy γ rays is input to the non-simultaneous counting circuit. However, there is no mention of improving measurement accuracy in a high background.

  In Patent Document 2, the length of the gate time window of the coincidence circuit is varied depending on the amount of radiopharmaceutical administered to the subject. However, in order to operate the configuration of Patent Document 1 or the like in a high background of a nuclear power plant or the like, it is essential to shorten the gate time window. It is difficult to realize trace radioactivity measurement that emits cascade γ rays in the background.

  In Patent Document 3, by making the difference between the counts of the two coincidence circuits a true count, accidental triple coincidence is removed and only true triple coincidence is counted. However, Patent Document 3 is a technique applicable only to a multi-channel radiation detector having three or more channels used in a nuclear medicine diagnostic apparatus, and is not applicable to an apparatus using two radiation detectors. Also, there is no mention of means for avoiding accidental coincidence in the two radiation detectors. Therefore, in Patent Document 3, it is difficult to realize a trace amount radioactivity measurement that emits cascade γ rays with high background.

  If accidental coincidence can be suppressed, trace radioactivity can be measured by cascade gamma ray coincidence method in a high background, and quantification of measurement objects that could not be measured conventionally can be realized.

  An object of the present invention is to provide a radionuclide analyzer and a method for suppressing incidental coincidence for realizing trace radioactivity measurement by cascade gamma ray coincidence counting in a high background that solves the problems described above. .

  The present invention relates to a radionuclide analyzer that analyzes radionuclides from a plurality of radiations emitted from a specific radionuclide, detects coincidence values by cascaded gamma rays emitted from the radionuclide while suppressing accidental coincidence. A plurality of radiation detectors for detecting radionuclide radiation, a plurality of coincidence counting circuits having different coincidence gate time widths for counting all outputs from the plurality of radiation detectors, and processing results of the coincidence counting circuit A simultaneous counting processing circuit for deriving the clock value, wherein the simultaneous counting gate time widths in at least two of the multiple counting circuits are δt1 and δt2 (δt1 <δt2), Based on this, the processing circuit detects the same clock value by the cascade gamma ray by subtracting the two clock values by the two coincidence circuits. The features.

  In the radionuclide analyzer, a counter for counting the output of the coincidence counting circuit is provided.

  In the radionuclide analyzer, three or more radiation detectors are provided, and the same number of coincidence circuits for inputting a combination of the outputs of the radiation detectors are provided in the subsequent stage of the radiation detectors as many as the radiation detectors.

  In the radionuclide analyzer, the radiation from the radionuclide to be measured is used as annihilation gamma rays.

  In the radionuclide analyzer, the coincidence gate time widths δt1 and δt2 are set to 1000 ns or less.

  In the radionuclide analyzer, the coincidence gate time width ratio δt1 / δt2 is set to 1/150 or less.

  Further, the radionuclide analyzer is characterized in that the difference between the clock values is made as a relative value based on one of the clock values obtained with the coincidence gate time widths δt1 and δt2.

  In the radionuclide analyzer, any one of Si, Ge, CdTe, GaAs, TlBr, HgI2, and CZT, which is a semiconductor, is used as a radiation detector.

  In the radionuclide analyzer, NaI (Tl), BGO, LaBr3 (Ce), LaCl3 (Ce), LSO (Ce), YAG, LBO (Cu), YAP used as a scintillator for γ rays as a radiation detector Any one of (Ce), GSO (Ce), PWO, CeF2, LuAG (Pr), and LuAG (Ce) is used.

  Moreover, in the radionuclide analyzer, a plurality of coincidence counting circuits are configured from an energy discrimination type coincidence circuit, and an output of the energy discrimination type coincidence circuit is input to an energy analysis circuit that calculates γ-ray energy for each radiation count, The coincidence gate time widths in at least two energy discrimination type coincidence circuits among the plurality of energy discrimination type coincidence circuits are δt1 and δt2 (δt1 <δt2), and the coincidence gate time widths δt1 and δt2 generated by the energy analysis circuit Based on the γ-ray energy information based on the energy distribution in, the processing circuit detects at least two clock values by the energy discrimination type coincidence circuit and detects the clock values by the cascade γ-ray.

  In addition, the radionuclide is analyzed from the pulse signals output from multiple radiation detectors that have detected radiation, and the coincidence counting of radiation nuclides is suppressed by suppressing the coincidence of radiation and detecting the same clock value by cascade gamma rays. In the method, a plurality of radiations output from the radionuclide are counted with different coincidence gate time widths, the same clock value is derived from the counting results, and at least two coincidence gate time widths are set as δt1 and δt2 (δt1 <δt2). Based on the coincidence gate time width, the two clock values are differentiated to detect the clock value by the cascade γ-ray.

  Furthermore, in the method for suppressing incidental coincidence counting of radionuclides, the radiation of the radionuclide to be measured is used as annihilation gamma rays.

  Furthermore, in the method for suppressing incidental coincidence counting of radionuclides, the coincidence counting gate time widths δt1 and δt2 are set to 1000 ns or less.

  Furthermore, in the incidental coincidence counting suppression method for radionuclides, the coincidence gate time width ratio δt1 / δt2 is set to 1/150 or less.

  Furthermore, in the method for suppressing coincidence coincidence counting of radionuclides, the difference between the clock values as a relative value is performed with reference to one of the clock values obtained with the coincidence gate time widths δt1 and δt2.

  Further, in the method for suppressing incidental coincidence counting of radionuclides, based on the γ-ray energy information based on the energy distribution generated by the coincidence gate time widths δt1 and δt2, two clock values are subtracted to generate a clock using cascade γ-rays. It is characterized by detecting numerical values.

  The present invention analyzes a radionuclide from a plurality of radiations radiated from a specific radionuclide as described above, suppresses coincidence coincidence, and detects a clock value by cascade γ rays emitted from the radionuclide. In a nuclide analyzer, a plurality of radiation detectors for detecting radionuclide radiation, a plurality of coincidence circuits having different coincidence gate time widths for counting all outputs from the plurality of radiation detectors, and a coincidence circuit And a coincidence counting processing circuit for deriving the same clock value from the processing result of the above, and the coincidence gate time width in at least two coincidence circuits among the plural coincidence circuits is set to δt1 and δt2 (δt1 <δt2). Based on the gate time width, the processing circuit calculates the difference between the two clock values by the two coincidence circuits and the clock value by the cascade gamma ray. By detecting, it is possible to count only coincidence coincidence with a coincidence circuit having a long coincidence gate time width, and therefore coincidence coincidence based on the same clock value obtained with two coincidence gate time widths. It is possible to extract the coincidence component due to the cascade γ rays. Therefore, it is possible to realize a minute radioactivity measurement that emits cascade γ rays in a high background in a nuclear power plant or the like with high accuracy.

1 is a block diagram showing a configuration of a radionuclide analyzer of Example 1 of the present invention. 4 is a time chart showing signals in the coincidence counting circuit 3 of the first embodiment. 3 is a graph showing a relationship between a gate time window and coincidence counting in Example 1. FIG. 6 is a block diagram showing a configuration of an energy discrimination type radionuclide analyzer of Example 2. The graph which shows the energy spectrum after the simultaneous count of Example 2. FIG. The graph which shows the energy spectrum by the different gate time window of Example 2. FIG.

  The present invention provides various methods that can be realized even in a high background of a nuclear power plant, etc., for a radionuclide analyzer for measuring a minute amount of radioactivity in a high background and a method for suppressing the coincidence coincidence thereof. It was made based on new knowledge obtained through examination.

  In this knowledge, it can be assumed that the cascade γ-rays to be measured are simultaneously emitted when viewed from the measurement circuit, the clock value is constant regardless of the length of the coincidence gate time width, and the coincidence gate Using the fact that the coincidence coincidence fluctuates linearly with the length of the time width, the coincidence circuit and the coincidence coincidence by the cascade γ-ray are counted by the coincidence counting circuit with a short coincidence gate time width, and the coincidence gate time Compared with accidental coincidence with a long coincidence circuit, the coincidence component due to cascade γ rays can be relatively ignored, and it can be considered that only coincidence coincidence is counted. Based on the same clock value obtained in step 1, it is possible to suppress the contribution of the coincidence coincidence and to extract the coincidence component due to the cascade γ rays. Therefore, it is possible to realize a trace radioactivity measurement that emits cascade γ rays in a high background in a nuclear power plant or the like.

  The preferred embodiments of the radiation measuring apparatus and method according to the present invention will be described in detail below with reference to the drawings.

  A radionuclide analyzer of Embodiment 1 which is a preferred embodiment of the present invention and its coincidence coincidence suppression method will be described with reference to FIGS. The radionuclide analyzer RA according to the first embodiment includes radiation detectors 1 and 2, coincidence circuits 3 and 4, counters 5 and 6, and a processing circuit 7. The output of the radiation detector 1 is branched and connected to the coincidence counting circuits 3 and 4. The output of the radiation detector 2 is also branched and connected to the coincidence counting circuits 3 and 4. The coincidence circuit 3 is connected to the radiation detectors 1 and 2 and is connected to the counter 5 at the subsequent stage. The coincidence circuit 4 is connected to the radiation detectors 1 and 2 and is connected to the counter 6 at the subsequent stage. The processing circuit 7 is connected to the counter 5 and the counter 6.

  The radiation detectors 1 and 2 detect radiation emitted from the radionuclide 8. It is assumed that the radionuclide 8 emits cascade gamma rays 9 and 9 'simultaneously. As the radiation detectors 1 and 2, scintillation detectors and semiconductor detectors are generally used when performing quantitative analysis and energy analysis of radionuclides. As the counter detector, an organic scintillation detector and a gas detector are used in addition to the above detector.

  Here, an example of a detector used in the radiation detectors 1 and 2 will be given. Typical scintillators include NaI (Tl), BGO, GSO, LSO, YAP, LuAG (Pr), LaCl3 (Ce), LaBr3 (Ce), CsI, PWO and the like. In particular, when used in a high count rate and high dose rate environment, a scintillator with a short emission decay time is required, and as a scintillator having an emission decay time of 100 ns or less, LaBr3 (Ce), LaCl3 (Ce), and LSO (Ce). YAG, LBO (Cu), YAP (Ce), GSO (Ce), PWO, CeF2, LuAG (Pr), LuAG (Ce), and the like. Typical semiconductor elements include Si, Ge, CdTe, GaAs, TlBr, HgI2, and CZT. Some diamond detectors are not semiconductors but exhibit similar behavior.

  FIG. 2 shows signal processing in the coincidence counting circuit 3. The coincidence circuit 3 transmits a logic signal to the subsequent stage when two consecutive inputs are within the overlapping range of the respective gate time windows 10. Here, the gate time width of the gate time window 10 opened for a predetermined time by the signal input of the radiation detectors 1 and 2 in the coincidence circuit 3 is assumed to be δt1.

  Similarly, the coincidence circuit 4 has a time width δt2 of a gate time window and counts coincidence with the same logic. In the present invention, δt1 and δt2 are set to different values, and in the first embodiment, description will be made assuming that δt1 <δt2.

FIG. 3 shows the relationship between the gate time window and coincidence counting. Here, if the coincidence coincidence is a count when two different γ-rays enter the two radiation detectors, the coincidence coincidence N _BG is represented by the product of the count rate n and the measurement time tm. Here, when δt is the gate time width of the coincidence counting circuit 3 or 4, and the signal input to the coincidence circuit early among the signals of the radiation detectors 1 and 2 is a start signal, the gate opening time is 2 × δt. I can express. Since the respective count rates φ1 and φ2 of the radiation detectors 1 and 2 are input within the gate open time, the random coincidence count _NBG can be expressed by the following equation.

  Since the radiation time interval of the cascade γ-rays is very short, it can be considered that they are emitted almost simultaneously as seen from the coincidence counting circuit, and since the frequency of their occurrence is low, there is no change in the count value due to the gate time width. Accordingly, it is desirable to set a gate time window as small as possible in order to suppress the coincidence coincidence, and to optimize the same clock value by the cascade γ ray and the SN ratio by the coincidence coincidence.

  On the other hand, when the gate time window is set to be long, the coincidence count due to the cascade γ-ray is relatively small compared to the coincidence coincidence and can be ignored, so that the count value can be regarded as the coincidence coincidence. .

The counters 5 and 6 output the count values in the coincidence circuits 3 and 4 at a predetermined measurement time. The processing circuit 7 performs random coincidence count reduction processing based on the count values input from the counters 5 and 6. In the coincidence counting circuit 3 having the gate time width δt1, δt1 is set to a gate time width in which the S / N ratio of the same clock value and the coincidence coincidence by the cascade γ ray is optimized. Further, in the coincidence counting circuit 3 having the gate time width δt2, δt2 is set to the gate time width in which the SN ratio of the same clock value and the coincidence coincidence by the cascade γ-ray is the worst. Count values N1 and N obtained by δt1 and δt2 in a predetermined measurement time are expressed by equations (2) and (3).
N1 = Ns + N _BG 1 (2)
N2 = Ns + N _BG 2 (3)
N1 is the same clock value obtained by the coincidence counting circuit 3, Ns is the same clock value by the cascade γ-ray, and N _BG 1 is an accidental coincidence. Similarly, N2 is the same clock value obtained by the coincidence counting circuit 4, Ns is the same clock value by the cascade γ ray, and N _BG 2 is the coincidence coincidence. In order to standardize and compare these N1 and N2, the clock value N2 obtained at δt2 is multiplied by δt1 / δt2. This is because the ratio of coincidence coincidence is proportional to the gate time width as shown in FIG.

  A clock value N obtained by subtracting two clock values obtained by this processing can be expressed by clock values Ns, δt1, and δt2 based on cascade γ rays as shown in Expression (4).

N = N1-N2 × δt1 / δt2
= (Ns + N _GB 1)-(Ns + N _GB 2 × δt1 / δt2)
_{= (1-δt1 / δt2)} Ns + (N GB 1-N GB 2 × δt1 / δt2)
(4)
The first term of Equation (4) represents the cascaded γ-ray coincidence component, the second term represents the accidental coincidence component, and finally converges to zero. Therefore, it is possible to extract the same clock value Ns based on the cascade γ ray from the equation (4).

  As described above, in the radionuclide analysis apparatus RA of the first embodiment, the radionuclide analysis is performed by effectively applying the radiation detectors 1 and 2, the coincidence counting circuits 3 and 4, the counters 5 and 6, and the processing circuit 7. Suppressing coincidence coincidence of the device can be realized, and accurate trace radioactivity detection in a high background such as a nuclear power plant can be realized.

  A radionuclide analyzer according to Embodiment 2 which is another embodiment of the present invention and a method for suppressing incidental coincidence will be described. In the second embodiment, γ-ray energy information is added to the time information based on the coincidence count to effectively suppress the coincidence coincidence.

  FIG. 4 shows a configuration diagram of an energy discrimination type radionuclide analyzer RA2. The energy discrimination type coincidence circuits 12 and 13 are coincidence circuits capable of discriminating an arbitrary range of radiation energy levels based on the peak value level and the integral value level of the input electric signal.

  The energy analysis circuits 14 and 15 are circuits for calculating γ-ray energy for each count, and generally a multi-channel analyzer is used. The processing circuit 16 introduces and outputs an algorithm for removing coincidence coincidence by combining time information and energy information.

  FIG. 5 shows the energy spectrum after coincidence counting. Here, the γ-ray source to be measured is Co-60, and the configuration is such that 1.17 MeV and 1.33 MeV cascade γ-rays are detected. The energy discrimination region 17 set by the energy discrimination type coincidence circuits 12 and 13 is within the range of the photoelectric peak due to the two cascaded γ rays.

  In a high background environment, there is an energy spectrum due to interfering nuclides 20. Here, as an example, it is assumed that the interfering nuclides 20 exist at a high energy level and a low energy level as compared with the energy of the Co-60 cascade γ-ray. As a high energy background component in a nuclear power plant, there is N-16 which emits 6.13 MeV gamma rays. As a low energy background component, there is N-13 that emits 511 keV gamma rays.

  Since the coincidence count based on the count outside the range of the energy discrimination region 17 is removed by the energy discrimination type coincidence circuits 12 and 13, the spectrum 19 after the energy discrimination can effectively extract the coincidence component by Co-60. .

  FIG. 6 shows energy spectra of the energy discrimination type coincidence circuits 12 and 13 with different gate time widths δt1 and δt2. In a high background environment, particularly when the γ-ray energy of the interfering nuclide is higher than the γ-ray energy to be measured, the Compton component due to the interfering nuclide is counted in the energy discrimination region 17, and the algorithm provided in the processing circuit 16 It is necessary to reduce the coincidence coincidence count. Here, as an example, the measurement target is Co-60, and the interfering nuclide is N-16.

  In FIG. 6, reference numeral 21 denotes an energy distribution related to the gate time width δt1 output from the energy analysis circuit 14. Reference numeral 22 denotes an energy distribution related to the gate time width δt2 output from the energy analysis circuit 15.

  When measuring a small amount of radioactivity (several tens of nSv / h) in an environment with a strong background (several tens of μSv / h), only Co-60 can be obtained using only the energy distribution (δt1) 21 obtained by applying the gate time width δt1. It is difficult to discriminate photoelectric peaks by counting. Therefore, the energy distribution (δt2) 22 by the coincidence coincidence obtained with the gate time width δt2 is used. The energy distribution 23 before application of the difference shows a comparison between the energy distribution (δt1) 21 and the energy distribution obtained by multiplying the energy distribution (δt2) 22 by δt1 / δt2. If the two distributions are differentiated, it is possible to effectively extract the coincidence component by the Co-60 cascade γ rays using the energy distribution 24 after the difference application.

  By applying the second embodiment, effective coincidence coincidence suppression can be realized in the radionuclide analyzer by combining time information by the coincidence counting circuit and gamma ray energy information by the energy analyzing circuit.

  A radionuclide analyzer according to Embodiment 3 which is another embodiment of the present invention and a method for suppressing incidental coincidence will be described.

  In the third embodiment, the simultaneous counting component extraction by the cascade γ rays is optimized by setting the ratio δt1 / δt2 of the coincidence gate time width in the first and second embodiments to 1/150 or less. Equation (5) indicates a statistical error, and is based on the same clock value N and σ (N) obtained by Equation (4) by setting the coincidence gate time width ratio δt1 / δt2 to 1/150 or less. Moreover, the deterioration of the relative standard error can be reduced to 1% or less. As an example, δt1 = 200 ns and δt2 = 30 μs may be set. By using this method, effective coincidence reduction can be realized.

  By appropriately combining Example 1 to Example 3 described above, it is possible to realize an optimum trace radioactivity measurement by cascade γ rays in a high background environment.

  In the present invention, as described above, since the cascade γ-rays to be measured can be regarded as being simultaneously emitted when viewed from the measurement circuit, the clock value is constant regardless of the length of the coincidence gate time width, and the gate time By using the fact that the coincidence coincidence fluctuates linearly with the length of the width, the coincidence circuit and the coincidence coincidence by the cascade gamma ray are counted by the coincidence circuit with a short gate time width, and the coincidence with a long gate time width is counted. Compared with accidental coincidence in the circuit, the coincidence component due to cascade γ rays can be relatively ignored and it is possible to count only coincidence coincidence, so it was obtained with two coincidence gate time widths Based on the clock value, it is possible to suppress the contribution of the coincidence coincidence and extract the coincidence component due to the cascade γ-ray. Therefore, it is possible to realize a minute radioactivity measurement that emits cascade γ rays in a high background in a nuclear power plant or the like with high accuracy.

  Further, by providing three or more radiation detectors and providing a measurement circuit in the subsequent stage according to the combination of the radiation detectors, detection efficiency can be improved and measurement time can be shortened by the increase in the number of channels.

  Also, by comparing the two clock values by the two energy discrimination type coincidence circuits based on the γ-ray energy information by the energy distribution generated with the gate time widths δt1 and δt2, it is compared with the energy of the cascade γ-rays. Therefore, the coincidence component due to a sufficiently high energy component or a low energy component can be removed. Therefore, high-accuracy coincidence counting based on the γ-ray energy of the measurement object can be realized.

  Moreover, since the radiation to be measured is paired annihilation gamma rays, the paired annihilation gamma rays radiate gamma rays having energy of 511 keV in the direction of 180 °, so that time is information for suppressing coincidence coincidence counting. In addition to information and energy information, it is possible to suppress coincidence coincidence counting based on radiation direction information.

  Further, by setting the coincidence gate time widths δt1 and δt2 to 1000 ns or less, it is possible to effectively suppress accidental coincidence in a high background.

  Further, by setting the ratio δt1 / δt2 of the coincidence gate time width to 1/150 or less, the same clock value by the cascade γ ray in the coincidence circuit having δt2 can be ignored as compared with the accidental clock value. Suppressing coincident coincidence counting can be realized.

  In addition, the derivation of the clock value with the contribution due to the coincidence coincidence suppressed by performing the difference of the clock value as a relative value on the basis of one of the clock values obtained with the coincidence gate time widths δt1 and δt2. Can be realized.

  Furthermore, by using Si, Ge, CdTe, GaAs, TlBr, HgI2, and CZT, which are semiconductors, as the radiation detector, the detector portion can be easily reduced in size and multi-channeled.

  Furthermore, NaI (Tl), BGO, LaBr3 (Ce), LaCl3 (Ce), LSO (Ce), YAG, LBO (Cu), YAP (Ce), GSO (used as a scintillator for γ rays as a radiation detector By using Ce), PWO, CeF2, LuAG (Pr), LuAG (Ce), etc., it is possible to easily improve detection sensitivity and increase the number of channels.

DESCRIPTION OF SYMBOLS 1, 2 ... Radiation detector 3, 4 ... Simultaneous counting circuit 5, 6 ... Counter 7, 16 ... Processing circuit 8 ... Radionuclide 9, 9 '... Cascade gamma ray 10 ... Gate time window 12, 13 ... Energy discrimination type simultaneous Count circuit 14, 15 ... Energy analysis circuit 17 ... Energy discrimination region 18 ... Spectrum before energy discrimination 19 ... Spectrum after energy discrimination 20 ... Interfering nuclide 21 ... Energy distribution (δt1)
22 ... Energy distribution (δt2)
23: Distribution before difference application 24 ... Distribution RA after difference application, RA2: Radionuclide analyzers δt1, δt2: Gate time width

Claims (14)

In a radionuclide analyzer that analyzes a radionuclide from a plurality of radiations emitted from a specific radionuclide, detects coincidence values by cascade gamma rays emitted from the radionuclide while suppressing coincidence coincidence,
A plurality of radiation detectors for detecting the radiation of the radionuclide, a plurality of coincidence counting circuits having different coincidence gate time widths for counting all outputs from the plurality of radiation detectors, and processing of the coincidence counting circuit A coincidence counting processing circuit for deriving the same clock value from the result, wherein the coincidence gate time width in at least two coincidence circuits among the plural coincidence circuits is δt1 and δt2 (δt1 <δt2), and the coincidence counting A radionuclide analysis apparatus characterized in that, based on a gate time width, the processing circuit detects a clock value by a cascade γ-ray by subtracting two clock values by two coincidence circuits.   2. The radionuclide analyzer according to claim 1, further comprising a counter that counts an output of the coincidence circuit.   3. The radionuclide analyzer according to claim 1, wherein the radiation detector includes three or more radiation detectors, and the coincidence circuit that inputs a combination of outputs of the radiation detectors is disposed in a stage subsequent to the radiation detector. A radionuclide analyzer characterized in that the same number of detectors are provided.   The radionuclide analyzer according to claim 1 or 2, wherein the coincidence gate time widths δt1 and δt2 are set to 1000 ns or less.   3. The radionuclide analyzer according to claim 1, wherein the coincidence gate time width ratio δt1 / δt2 is 1/150 or less.   The radionuclide analyzer according to claim 1 or 2, wherein a difference between the clock values as a relative value is performed based on one of the clock values obtained with the coincidence gate time widths δt1 and δt2. Characteristic radionuclide analyzer.   3. The radionuclide analyzer according to claim 1, wherein any one of Si, Ge, CdTe, GaAs, TlBr, HgI2, and CZT, which is a semiconductor, is used as the radiation detector. . In the radionuclide analyzer according to claim 1 or 2, NaI (Tl), BGO, LaBr3 (Ce), LaCl3 (Ce), LSO (Ce) used as a scintillator for γ rays as the radiation detector, A radionuclide analyzer using any one of YAG, LBO (Cu), YAP (Ce), GSO (Ce), PWO, CeF2, LuAG (Pr), and LuAG (Ce).   2. The radionuclide analyzer according to claim 1, wherein the plurality of coincidence counting circuits are configured by an energy discrimination type coincidence counting circuit, and an output of the energy discrimination type coincidence counting circuit is used to calculate γ-ray energy for each radiation count. The coincidence gate time width in at least two energy discrimination type coincidence circuits among the plurality of energy discrimination type coincidence circuits is set as δt1 and δt2 (δt1 <δt2), and the energy analysis circuit Based on the generated γ-ray energy information based on the energy distribution in the coincidence gate time widths δt1 and δt2, at least two of the same clock values obtained by the energy discrimination type coincidence circuit are differentiated by the processing circuit and cascaded γ-rays are obtained. Radiation characterized by detecting the same clock value by Seed analyzer. Method for suppressing accidental coincidence counting of radionuclides by analyzing radionuclides from pulse signals output from a plurality of radiation detectors that have detected radiation and suppressing coincidence counting of said radiation to detect the same clock value by cascade gamma rays In
Counting a plurality of radiations output from the radionuclide with different coincidence gate time widths, deriving the same clock value from the counting results, and setting at least two coincidence gate time widths as δt1 and δt2 (δt1 <δt2), A method for suppressing coincidence coincidence counting of radionuclides, wherein two simultaneous clock values are differentiated based on the coincidence gate time width to detect the same clock value by a cascade γ-ray. The radionuclide random coincidence coincidence suppression method according to claim 10 , wherein the coincidence gate time widths δt1 and δt2 are set to 1000 ns or less. 11. The method for suppressing incidental coincidence counting of radionuclides according to claim 10 , wherein the coincidence gate time width ratio [delta] t1 / [delta] t2 is 1/150 or less. 11. The method of suppressing coincidence coincidence counting of radionuclides according to claim 10 , wherein a difference between the clock values is made as a relative value based on any one of the clock values obtained at the coincidence gate time widths δt1 and δt2. A method for suppressing incidental coincidence counting of radionuclides. The method of suppressing coincidence coincidence counting of radionuclides according to claim 10 , wherein two simultaneous clock values are differentiated based on γ-ray energy information by energy distribution generated in the coincidence gate time widths δt1 and δt2. A method for suppressing coincidence coincidence counting of radionuclides, comprising detecting the same clock value by cascade γ-rays.

Images