JP5523407B2 - Radiation detection apparatus and detection method - Google Patents

Description

  The present invention relates to a radiation detection apparatus and detection method used in, for example, a nuclear power plant, and more particularly to a radiation detection apparatus and detection method suitable for multi-nuclide analysis under a high background.

  Conventionally, analysis of radionuclides in reactor water at nuclear power plants has been conducted after sampling reactor water in a plastic container or the like and leaving it for about a day to attenuate short half-life nuclides (nitrogen 13, oxygen 19, etc.) The analysis was performed using a germanium semiconductor detector.

  To save labor and reduce exposure to radionuclide analysis in reactor water, online is desired. However, because the strength of nitrogen 13 and oxygen 19, which are the main radionuclides in reactor water, is strong, It was difficult to measure radionuclides such as cobalt 58 and 60, manganese 54 and 56, iodine 131 and 133, cesium 134 and 137, etc. online with high accuracy.

  As an on-line radionuclide monitor at a nuclear power plant, a high-sensitivity off-gas monitor using a germanium semiconductor detector has been commercialized, and two units installed in the 180 ° direction are used to suppress the background nitrogen 13. An anti-coincidence method using the above detectors and a Compton suppression method in which one detector is surrounded by another detector are applied.

  However, this method can suppress the nitrogen 13 but cannot accurately measure other nuclides. The high-sensitivity off-gas monitor uses gamma-ray emitting nuclides with low energy, so a thin plate-shaped germanium semiconductor detector is applied so that the measurement sensitivity of low-energy gamma rays is relatively high. However, high-energy gamma-ray measurements cannot be applied to the analysis of radionuclides in reactor water.

  Various leaked radiation detection monitors using NaI (sodium iodide) scintillation detectors are used as on-line radiation monitors at nuclear power plants. However, accurate nuclide analysis is difficult due to insufficient energy resolution. It is. In addition, an area monitor using a silicon semiconductor detector, a main vapor dose monitor using an ion chamber, and the like are used. It is difficult.

  In addition to nuclear power, for example, in the medical field, a detector is disposed at a position opposite to the object to be measured with respect to the object to be measured for the purpose of efficiently detecting gamma rays from the nuclide to be measured, or a non-facing position. It is known from Patent Document 1, Patent Document 2, Patent Document 3, and the like to arrange a detector in the above.

Japanese translation of PCT publication No. 2002-511930 Japanese National Patent Publication No. 11-514742 Japanese National Patent Publication No. 11-508048

  As described above, in the analysis of radionuclides in reactor water at nuclear power plants, it is desired that multinuclide analysis can be performed on a high background and can be brought online. In this regard, detector placement techniques in the medical field such as Patent Document 1, Patent Document 2, and Patent Document 3 can be applied to the analysis of radionuclides in reactor water at nuclear power plants, but under high background. In order to achieve the requirements such as certain points, the ability to perform multi-nuclide analysis, and the ability to go online, further ingenuity is required.

  An object of the present invention is to provide a radiation detection apparatus and a detection method suitable for multi-nuclide analysis on which measurement is possible in a high background environment such as a nuclear power plant.

  The feature of the present invention for achieving the above-described object is that it comprises at least one set of detectors that are provided around a measurement object and performs gamma ray measurement, and a pulse signal detected by the detector is used for time and peak value. A radiation detector comprising a peak value and time measuring device obtained as information and a processing device for processing a signal from the detector, wherein the processing device detects two of the pulse signals from each detector. Extraction step for extracting only peak value information whose detection time difference is within a predetermined time width, and the number of pulse values from the extraction step with a pulse-shaped signal having a predetermined peak value as a true counting area Measuring step, measuring the number of other pulsed signals as background area, the count rate of the true counting area of the measuring step and the counting rate of the background area The time width for determining the predetermined time width when the ratio of the count rate of the true count area and the count ratio of the background area is maximized by changing the predetermined time width of the count rate calculating step and the extraction step Including a setting step.

  In addition, a predetermined time width when the ratio between the count rate of the true count area and the count rate of the background area is maximized is determined for each true count area of each detector, and is determined for each true count area. The pulsed signal is measured with the predetermined time width.

  The predetermined time width when the ratio between the count rate of the true count area and the count rate of the background area is maximized is appropriately determined as time passes, and is reflected in the measurement.

  In addition, at least one set of detectors is provided at a position opposed to the measurement object, and a gamma ray measurement is provided at a position opposed to the measurement object. And a second set of detectors.

  Also, one or two of the set of detectors is a semi-doughnut-shaped detector, and the detector is covered in a semicircular shape in the circumferential direction of a cylindrical pipe-shaped measurement object. Install.

  Further, in a region where a plurality of true counting regions on the two-dimensional peak value spectrum overlap, the number of the overlapping portions is divided by the ratio of the counting in the plurality of true counting regions in the non-overlapping region in the vicinity of the region.

  In addition, the true count rate in the coincidence determination time width at the count rate obtained from the measurement data of the two-dimensional peak value spectrum is calculated based on the database of the true count rate for the coincidence determination time width created in advance. By correcting, the true count rate is evaluated.

As the detector, a germanium semiconductor detector, a LaBr ₃ (Ce) scintillation detector, or a NaI detector is used.

  The feature of the present invention for achieving the above-described object is that a first detector set that performs gamma ray measurement is provided at an opposing position sandwiching the measurement object, and a non-opposing position with respect to the measurement object. A second detector group that performs gamma ray measurement, a peak value and time measuring device that obtains a pulse-like signal detected by the detector as time and peak value information, and a processing device that processes a signal from the detector; The processing device is an extraction device that extracts only peak value information in which a difference in detection time between two detectors is within a predetermined time width for a pulse signal from each detector set. Step, the number of pulse values from the extraction step is measured by using a pulsed signal having a predetermined peak value as a true counting region, and the number of other pulsed signals is measured by using a background region as a background region. The counting rate calculation step for calculating the ratio of the counting rate of the true counting area and the counting rate of the background area in the measuring step, and the counting rate and back of the true counting area by changing the predetermined time width of the extraction step A time width setting step for determining a predetermined time width when the ratio of the count rates of the ground area is maximized.

  A feature of the present invention for achieving the above object is that a pulse signal detected by a set of detectors provided around a measurement object is obtained as time and peak value information, and radiation is used by using this information. A radiation detection method for measuring, wherein only information on a crest value whose detection time difference is within a predetermined time width is extracted from a continuous pulse signal from a set of detectors. Measure the number of pulsed signals with high values of a predetermined magnitude as a true count area and count the number of other pulsed signals as a background area, and count the number of true count areas and the background area. The ratio of the counting rate is calculated, and the predetermined time width is changed to determine the predetermined time width when the ratio of the counting rate of the true counting area and the counting rate of the background area is maximized.

  The feature of the present invention for achieving the above-described object is that a first detector set that performs gamma ray measurement is provided at an opposing position sandwiching the measurement object, and a non-opposing position with respect to the measurement object. A radiation detection method in which a pulse-like signal detected by a second detector set provided for gamma ray measurement is obtained as time and peak value information, and radiation is measured using this information, and a pulse from each detector set is obtained. For the signal, only information on the crest value in which the difference in detection time between the two detectors is within a predetermined time width is extracted, and the number of the pulse-shaped signals with the extracted crest value having a predetermined size is set as a true count area. Measure and count the number of other pulsed signals as the background area, determine the ratio of the count ratio of the true count area to the count ratio of the background area, change the predetermined time width and perform the true count Total area The ratio of the count rate of incidence and background areas to determine the predetermined time width when the maximum.

  ADVANTAGE OF THE INVENTION According to this invention, the measurement in a high background environment like a nuclear power plant is attained, Furthermore, the radiation detection apparatus and detection method suitable for a multi-nuclide analysis can be provided.

The figure which shows the structural example of the radiation detection apparatus which concerns on one suitable Example of this invention. The figure which shows an example of the waveform measured in the peak value and the detection time measuring device 6. FIG. The figure which shows the processing content in the personal computer 7 for data collection and control. The figure which shows the example of the three-dimensional graph calculated | required about the detector groups 2a and 2b of opposing arrangement | positioning. The figure which expressed the relationship of true count rate on the vertical axis | shaft with the simultaneous coefficient time width | variety (DELTA) t on the horizontal axis. The figure which traced the maximum value of the true count rate and displayed it as a trend graph. The figure which shows the measuring device arrangement example using a half donut-shaped detector. The figure which shows the measuring device arrangement example using a half donut-shaped detector.

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

  A configuration of a radiation detection apparatus according to a preferred embodiment of the present invention will be described with reference to FIG.

  In this embodiment, a plurality of (two or more, 2a, 2b, 2c in the illustrated example) radiation detectors 2 for detecting gamma rays are installed around the detection target 1 in a predetermined positional relationship. Among a plurality of detectors 2 (2a, 2b, 2c), 2a and 2b are installed at opposing positions across the inspection object 1, and 2a and 2c are installed at non-opposing positions around the inspection object 1. . Note that the detector sets installed at the non-opposing positions may be 2b and 2c.

  Here, in the case of a detector group arranged oppositely, it is possible to detect a nuclide such as N-13 (nitrogen 13) that simultaneously emits two gamma rays in the 180 ° direction, and a detector group arranged non-oppositely. In this case, it is possible to detect a nuclide that simultaneously emits two gamma rays in the 4π direction in a cascade such as Co-60 (cobalt 60).

  In order to achieve the effect of multi-nuclide analysis in the present invention, it is best to provide both a counter-arranged detector group and a non-opposite-arranged detector group. Since multiple gamma rays with the same radioactive tendency are detected, the effect of multi-nuclide analysis can be achieved.

  Signals from the radiation detectors 2 (2a, 2b, 2c) are amplified and detected by the preamplifiers 3 (3a, 3b, 3c), respectively. The output S1 of the preamplifier 3 (3a, 3b, 3c) is a signal that suddenly changes in a pulse shape at the time of radiation detection, and this is led to the amplifier 4 (4a, 4b, 4c) that shapes the waveform. The amplifier 4 generates and outputs a rectangular signal S2 every time a pulse signal is generated.

  Further, the output S1 of the preamplifier 3 (3a, 3b, 3c) is guided to the wave height discriminator 5 (5a, 5b, 5c), and a signal corresponding to the wave height value h and the detection time each time a pulse signal is generated. S3 is determined.

  The peak value and detection time measuring device 6 includes a signal S2 from an amplifier 4 (4a, 4b, 4c) provided for each radiation detector 2 (2a, 2b, 2c), and a wave height discriminator 5 (5a, 5b). , 5c) are input in pairs. Obtaining this input, in the peak value and detection time measuring device 6, the peak value and detection time of the signal detected by the radiation detector 2a, and the peak value and detection time of the signal detected by the radiation detector 2b are detected. The peak value and detection time of the signal detected by are recognized as a set of signals.

  FIG. 2 shows an example of a waveform obtained by the above detector configuration and measured by the peak value and detection time measuring device 6. In the illustrated example, the signal S3 from the wave height discriminator 5 (5a, 5b, 5c) is shown in the upper part, the wave height value detected by the detector 5a is ha, and the wave height value detected by the detector 5b is hb, It is assumed that the peak value detected by the detector 5c is hc. Further, in the figure, the signal S2 from the amplifier 4 (4a, 4b, 4c) is shown in the lower part, and it is assumed that a pulse signal is detected in the order of the detectors 4a, 4c, 4b. Assume that these detection times are ta, tb, and tc, respectively.

  Information on the peak value h and detection time t of the signal detected by each radiation detector 2 obtained by the peak value and detection time measuring device 6 is given to the data collection / control personal computer 7. The data collection / control personal computer 7 executes a series of processes shown in FIG. In addition, since the pulsed signals thus captured include those depending on the measurement target nuclide and others, the data collection / control personal computer 7 uses only gamma rays from the measurement target nuclide. Performs processing to enable highly accurate detection and measurement that is not affected by the background.

  In the series of processing of FIG. 3, after the measurement is started, batch measurement by the apparatus of FIG. 1 is executed in step S100, and the crest value and measurement time data at an arbitrary time are accumulated in step S101. As the amount of data stored here is richer, the accuracy of statistical processing to be performed thereafter improves.

  Using these accumulated data, in step S102, a three-dimensional graph is created based on the peak value and time data of two detector groups that have arrived within a preset time width. FIG. 4 is an example of a three-dimensional graph obtained for the oppositely arranged detector sets 2a and 2b described above as two detector sets. A three-dimensional graph is also created for the detector sets 2a and 2c. This graph may be a two-dimensional graph.

  Each of the three-dimensional graphs is created according to the following procedure, which will be described with reference to the example of the wave series in FIG. As a premise for explanation, it is assumed that a considerable number of waveform sequences as shown in FIG. 2 are accumulated. Of these wave series, when creating a three-dimensional graph for the detector groups 2a and 2b arranged oppositely, attention is paid to the outputs from the amplifiers 4a and 4b and the wave height discriminators 5a and 5b.

  First, for the time signal t, all time differences Δtab between the detection time ta on the detector 2a side and the detection time tb on the detector 2b side are extracted from the accumulated waveform sequence. After that, only peak values whose time difference Δtab is within a predetermined time width Δt are extracted. In the case of FIG. 2, Δtab is equal to or greater than Δt, so that the two peak values ha and hb are not extracted. Only the two extracted peak values are used to create a three-dimensional graph.

  This determination is based on a certain time width as a reference for determining whether or not pulse trains as shown in FIG. 2 obtained in succession are simultaneously measured. For example, if the pulse train arrives within a certain time width, it is determined as “simultaneous”. When the detection time when measured by one detector is considered as the base point, if the other detector measures within a certain time width, the measurement on the other is Judged as simultaneous measurement.

  In the three-dimensional graph of FIG. 4, the magnitude of the peak value ha detected by the detector 2a on the X axis and extracted by simultaneous determination, and the peak value hb detected by the detector 2b on the Y axis and extracted by simultaneous determination. Is taking the size of. On the two-axis plane, the intersection of two peak values ha and hb extracted by simultaneous determination is plotted. Furthermore, the number of intersection points on the biaxial plane is shown on the Z axis.

  In FIG. 2, for convenience of description, the description will be made in two dimensions of the X axis and the Y axis, but the intersections of two peak values ha and hb are plotted in a wide area on this plane. Many of these intersections are in the background, but there are regions where the intersections are noticeably concentrated. On the detector 2a side, many intersection points occur before and after the peak values ha1 and ha2, while on the detector 2b side, many intersection points occur before and after the peak values hb1 and hb2. From this result, an L-shaped region Z1 determined by the peak value ha1 on the detector 2a side and the peak value hb1 on the detector 2b side appears as a densely intersecting region. Similarly, an L-shaped region Z2 defined by the peak value ha2 on the detector 2a side and the peak value hb2 on the detector 2b side appears as a densely intersecting region.

  Here, the specific peak values ha1 and ha2 or hb1 and hb2 that are measured in large numbers are each of a peculiar size to the nuclide, and the pulse-like signals included in the regions Z1 and Z2 are from the measurement nuclide. There are signals and signals from other backgrounds. For this reason, highly accurate measurement is possible by efficiently excluding signals from the background.

  In FIG. 4, the number of intersections constituting the L-shaped areas Z1 and Z2 is hereinafter simply referred to as counting, and the L-shaped areas Z1 and Z2 are referred to as counting areas. The counting areas Z1 and Z2 are respectively specified. It is composed of many gamma rays from nuclides. For example, in the case of opposing detector sets 2a and 2b, the counting region Z1 contains many gamma rays from nuclides that simultaneously emit two gamma rays in the 180 ° direction, such as N-13 (nitrogen 13). The counting region Z2 is configured to include many gamma rays from other specific nuclides that simultaneously emit two gamma rays in the 180 ° direction. Thus, the count areas Z1 and Z2 that appear prominently differ depending on the nuclide.

  Here, the reason why the counting regions Z1 and Z2 are “configured to include a large amount of gamma rays from the specific nuclide” is because the background includes the background in addition to the gamma rays from the specific nuclide. However, since this region is considered to contain a large amount of gamma rays from a specific nuclide, in the following description, these regions Z1 and Z2 will be referred to as true counting regions. On the other hand, the other area can be called a background area.

  The data included in the true counting areas Z1 and Z2 are extracted by the above-described procedure. However, since the background is included in these, the present invention is devised to further increase the detection accuracy. .

  For this purpose, in the embodiment of FIG. 3, in step S103, the count rates of the background area and the true counting area designated in advance are calculated. Here, a region Z3 in FIG. 4 is set as a background region designated in advance.

  In step S103, for the true count areas Z1 and Z2 and the background area Z3, the count values included in the respective areas are added and divided by the measurement time to calculate the count rate for each area (and thus for each nuclide). In this case, the counting of the overlapping region Z21 in which the true counting regions Z1 and Z2 are overlapped is distributed using the count value in the region of the same area of the adjacent region (Z1 or Z2).

  In step S104, the ratio between the count rate in the true count areas Z1 and Z2 and the count rate in the background area Z3 is obtained. Further, the above-described series of processing (from step S100 to S104) is repeatedly executed by changing the predetermined time width Δt in FIG.

  Hereinafter, the predetermined time width Δt for determining simultaneous measurement is expressed as “simultaneous coefficient time width”. FIG. 5 shows the relationship of the true count rate on the vertical axis when the simultaneous coefficient time width Δt is on the horizontal axis. Here, the true count rate indicates a ratio (S + N) / N of the count rate (S + N) in the true count regions Z1 and Z2 and the count rate N in the background region Z3. This result (S + N) / N is obtained by the processing in step S104 because the true count and the background are measured in the true count areas Z1 and Z2, as shown in FIG. 4, and in the background area Z3 It is clear from the background being measured.

  In this true count rate (S + N) / N, as shown in FIG. 5, there is a simultaneous coefficient time width Δt (horizontal axis) that maximizes the true count rate (vertical axis). Thus, the fact that the true count rate (S + N) / N has the maximum value will be described. First, when the time width Δt for simultaneous count determination is set to be small, the true count is reduced by counting down the true count, but the background count is also reduced at the same time. In this case, the tendency of counting down is more remarkable in the true count, and the ratio (S + N) / N of the count rates of the true count rate areas Z1, Z2 and the background area Z3 becomes smaller.

  On the other hand, as the time width of the coincidence counting is increased, the true count is not counted down and the true count takes a constant value, but the background count increases. For this reason, even if the time width of the coincidence counting is increased, the ratio (S + N) / N of the count rates of the true count rate areas Z1, Z2 and the background area Z3 is reduced.

  As a result, the ratio (S + N) / N of the count rate of the true count rate and the background region has a maximum value ((S + N) / N) m. Therefore, by setting the coincidence determination time width Δt to this maximum value ((S + N) / N) m and setting it to Δtm, the S / N ratio is improved and the nuclide analysis performance is improved.

  In step S105, there is a relationship shown in FIG. 5 between a plurality of coincidence determination time widths Δt obtained in the above-described series of processing (steps S100 to S104) and the ratio (S + N) / N of the count rate at that time. From this, the optimum value Δtm of the coincidence counting determination time width when the ratio (S + N) / N of the counting rate is maximized is obtained. The optimum value Δtm of the coincidence determination time width is obtained for each true count area in FIG. Further, not only the true counting area in the case of the counter-arranged detector set, but also the true counting area in the case of the non-opposing detector set is obtained.

  In step S106, the true count rate obtained in this way is evaluated. It is verified and confirmed that the true count rate obtained by the optimum value Δtm of the coincidence determination time width shows a better numerical value than the true count rate under other conditions of Δt.

  In this way, the optimum value Δtm of each coincidence determination time width is obtained for all the true count areas, and this result is reflected in the measurement of each true count area. As a result, in the case of the detector set in the opposite arrangement, high-precision detection can be performed for nuclides such as N-13 (nitrogen 13), and in the case of the detector set in the non-opposition arrangement, Co-60 (cobalt). 60) and the like can be detected with high accuracy.

  Note that the true count rate is not an invariable constant value but varies with time. For this reason, when realizing the apparatus configuration of FIG. 1, it is preferable to always trace the optimum true count rate and reflect it in the processing of FIG.

  In step S107, the maximum value of the true count rate that fluctuates with time is traced and displayed as a trend graph for nuclide measurement as shown in FIG.

  As described above, in the processing of the present invention, first, the crest value and measurement time data at an arbitrary time are accumulated. Next, a two-dimensional graph based on the peak value and time data of the two detector groups is created using a preset time width. Next, the count rates of the background area and the true counting area designated in advance are calculated. Next, the ratio between the true count area and the background area is calculated using the time width as a parameter. The time width is set so that this ratio is maximized, and the true count rate is evaluated based on the database of the true count rate with respect to the time width. Trend graph data is created and displayed using the evaluated count rate.

  According to the embodiment of the present invention described above, it is possible to provide a radiation detector and a detection method suitable for multi-nuclide analysis in a high background environment, which is a problem to be solved by the present invention. Since the detection accuracy (count ratio (S + N) / N) in each true counting region obtained from the opposingly arranged detector group and the non-facingly arranged detector group can be increased, Not only is it difficult to be affected, but it also enables measurement of multiple types of nuclides (multi-nuclide analysis) with a single measurement.

  The above-described effect of the present invention is largely due to the arrangement configuration of the detector groups arranged opposite to each other and the detector groups arranged not to face each other. Next, the structural example of the radiation detector in the Example of this invention is demonstrated based on FIG.7 and FIG.8. Here, the measuring object 1 has a pipe shape. One or two of the two detector groups 2a and 2b is a half-doughnut-shaped detector obtained by removing a small-radius semi-cylinder from a large-radius semi-cylinder. In FIG. 7, 2b is a detector, and in FIG. 8, 2a and 2b are half-doughnut-shaped detectors. By using this detector 2 and installing the detector 2 so as to cover the measurement object 1 in a semicircular shape, gamma rays from the measurement object 1 can be measured efficiently.

  The modification of the present invention may be configured as follows.

Using multiple detectors (three or more) detectors (germanium semiconductor detector, LaBr ₃ (Ce) scintillation detector, etc.), among the detectors, detections installed at opposite positions around the object to be inspected It has a detector set installed at a position that is not opposed to the set. Each detector has a function to measure the measurement time and peak value of gamma rays, and the detector set at the opposite position and the non-opposing position by measuring the measurement time and peak value of the gamma ray at each detector The coincidence counting and the non-coincidence counting are respectively performed by the detected detector sets.

  The output signal from the preamplifier is split into two, one is measuring the peak value through the amplifier, the other is converting to a pulse signal containing time information through the pulse height discriminator, and the rise time of the pulse signal is Use to measure time. When a scintillation detector is used, an output signal of a photomultiplier tube installed at a subsequent stage of the scintillation element may be used without using a preamplifier.

  If gamma rays are detected by a plurality of detectors within a predetermined time range or a time range adjusted during measurement, it is determined that simultaneous counting has been performed, and otherwise, it is determined that non-simultaneous counting has been performed. Time width adjustment, coincidence counting, and non-coincidence determination are performed by software after the peak value data and detection time data of each detector are taken into a personal computer.

  According to the detector to be used, the true count rate data of the two detector sets with respect to the time width is acquired and stored as a database. The background is considered to change over time because it varies greatly depending on the installation environment.

  In a two-dimensional peak value graph of two detector groups, the ratio of the count rate of the true count rate to the count rate of the background region (S + N) / N is obtained in a timely manner, and the time width is set so that the value becomes the highest. Set.

  When the time width of the coincidence determination is set to be small, the true count is reduced but the background count is also reduced by counting off the true count. As the time width of the coincidence determination is increased, the true count is not counted down and the true count becomes a constant value. However, since the background count increases, the true count rate area and the back count are increased. The ratio of the count ratio of the ground area (S + N) / N becomes small.

  Thus, the ratio (S / N) of the count rate of the true count rate and the background region has a maximum value. Accordingly, by setting the coincidence determination time width to this maximum value, the S / N is improved and the nuclide analysis performance is improved.

  Further, in the two-dimensional peak value graph, since the region indicating the Compton scattering amount of one detector and the total absorption peak of the other detector can be determined as one nuclide region, there are a plurality of regions having a true count rate. In some cases, the nuclides overlap. In that case, by dividing the overlapping portion by the ratio of the counting rates of the adjacent non-overlapping portions, the identification accuracy of each nuclide is improved and the nuclide analysis performance is improved.

  According to the present invention, since multi-nuclide analysis can be realized in a short time, it is preferably applied to measurement in a nuclear power plant.

1: Detection object 2: Radiation detector 3: Preamplifier 4: Amplifier 5: Wave height discriminator 6: Wave height value and time measuring device 7: Personal computer for data collection 8: Database of true count rate

Claims (11)

From at least one set of detectors that are provided around the measurement object and that measures gamma rays, and that obtains a pulse signal detected by the detector as time and peak value information, and a detector A radiation detection device comprising a processing device for processing the signal of
For the pulse signal from each detector, the processing device extracts only the information of the peak value whose detection time difference between the two detectors is within a predetermined time width, and the peak value from the extraction step A measurement step of measuring the number of pulsed signals having a peak value of a predetermined magnitude as a true counting region, and measuring the number of pulses of other pulsed signals as a background region, the true counting of the measuring step A count rate calculation step for obtaining a ratio between the count rate of the area and the count rate of the background area; and a ratio between the count rate of the true count area and the count ratio of the background area by changing a predetermined time width of the extraction step And a time width setting step for determining the predetermined time width when the maximum value becomes a maximum. The radiation detection apparatus according to claim 1,
The predetermined time width when the ratio of the count rate of the true count area to the count rate of the background area is maximized is determined for each true count area of each detector, and for each true count area A radiation detection apparatus that measures a pulse signal with a predetermined time width. The radiation detection apparatus according to claim 1 or 2,
The predetermined time width when the ratio of the count rate of the true count region to the count rate of the background region is maximized is appropriately determined as time passes, and is reflected in the measurement. Radiation detection device. In the radiation detection apparatus in any one of Claims 1-3,
The at least one set of detectors is provided at a position opposed to the measurement object and performs gamma ray measurement, and is provided at a position not opposed to the measurement object and performs gamma ray measurement. A radiation detection apparatus comprising: a second detector group to perform. The radiation detection apparatus according to any one of claims 1 to 4,
One or two of the set of detectors is a semi-doughnut-shaped detector, and the detector is installed in the circumferential direction of a cylindrical pipe-shaped measurement object so as to cover it in a semicircular shape. A radiation detection apparatus. The radiation detection apparatus according to any one of claims 1 to 5,
In a region where a plurality of true counting regions on the two-dimensional peak value spectrum overlap, a count distribution of overlapping portions is performed at a ratio of counts in a plurality of true counting regions in a non-overlapping region in the vicinity of the region. Radiation detection device. The radiation detection apparatus according to any one of claims 1 to 6,
The true count rate in the coincidence determination time width at the count rate obtained based on the measurement data of the two-dimensional peak value spectrum is corrected based on the database of the true count rate for the coincidence determination time width created in advance. A radiation detection apparatus characterized by evaluating a true count rate. The radiation detection apparatus according to any one of claims 1 to 6,
A radiation detection apparatus using a germanium semiconductor detector, a LaBr ₃ (Ce) scintillation detector, or a NaI detector as a detector. A first detector group that is provided at a position facing the measurement object and that measures gamma rays; and a second detector group that is provided at a position not facing the measurement object and that performs gamma ray measurement; A pulse detection signal detected by the detector as a time and peak value information, a pulse height and time measuring device, and a radiation detection device configured to process a signal from the detector,
The processing device extracts, for the pulse-like signal from each detector set, only the information of the peak value whose detection time difference between the two detectors is within a predetermined time width, the peak value from the extraction step Measuring step of measuring the number of pulsed signals having a peak value as a true counting region and measuring the number of other pulsed signals as a background region, the true value of the measuring step A count rate calculation step for obtaining a ratio between the count rate of the count region and the count rate of the background region, and changing the predetermined time width of the extraction step to change the count rate of the true count region and the count rate of the background region And a time width setting step for determining the predetermined time width when the ratio is maximized. A radiation detection method for obtaining a pulsed signal detected by a set of detectors provided around a measurement object as time and peak value information, and measuring radiation using the pulsed signal,
For a continuous pulse signal from a set of detectors, only information on the peak value whose detection time difference is within a predetermined time width is extracted, and for the extracted peak value, the pulse value has a predetermined magnitude. Measure the number of signals in the true count area and measure the number of pulses in the other pulse signals as the background area to obtain the ratio of the count ratio of the true count area to the count ratio of the background area. The predetermined time width is changed to determine the predetermined time width when the ratio of the count rate of the true count region to the count rate of the background region is maximized. A first detector group that is provided at an opposing position with respect to the measurement object and performs gamma ray measurement, and a second detector group that is provided at a non-opposing position with respect to the measurement object and performs gamma ray measurement. It is a radiation detection method for obtaining a detected pulse signal as time and peak value information, and measuring radiation using this,
For the pulsed signal from each detector set, only information on the peak value whose detection time difference between the two detectors is within a predetermined time width is extracted, and a pulsed signal whose extracted peak value has a predetermined size is extracted. The number is measured as a true counting area and the number of other pulsed signals is measured as a background area, and the ratio between the counting rate of the true counting area and the counting ratio of the background area is obtained, The radiation detection method, wherein the predetermined time width when the ratio of the count rate of the true count area to the count ratio of the background area is maximized by changing the time width is determined.

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