JPH1039033A - Nuclide analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a counting rate without exchanging a specimen table and retrying the measurement even when the specimen to be measured has a high counting rate. SOLUTION: There is disclosed a nuclide analyzer that measures an energy spectrum of radiation and analyzes a nuclide included in a specimen to be measured based on the energy spectrum. It comprises a counting rate attenuation means 10 that adjusts an apparent counting rate detected by a radiation detector 2, a pre-measuring means that pre-measures the counting rate of the radiation emitted from the specimen S to be measured, an adjustment instruction means that instructs the counting rate attenuation means 10 to attenuate the counting rate when the counting rate obtained by the pre-measurement is beyond the acceptable range of the counting rate and an automatic calibration means that calibrates a detection efficiency of the radiation detector 2 on the calculation of the analysis of the nuclide corresponding to the attenuated apparent counting rate when the attenuation of the counting rate is instructed by the adjustment instruction means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclide analyzer used for analyzing nuclides contained in a measurement sample in a nuclear power plant or a processing facility handling radioactive materials.

[0002]

2. Description of the Related Art γ released from a measurement sample or an environmental sample
There is a nuclide analyzer that measures the spectrum of a line and analyzes nuclides contained in a sample. FIG. 8 shows a configuration example of a nuclide analyzer. In the nuclide analyzer shown in FIG. 1, a Ge detector 2 is arranged in close proximity to a measurement sample S placed on a sample stage 1 so that the measurement sample is not affected by the background (BG) of the measurement environment. The periphery of S is covered with a shield 3. The Ge detector 2 converts the ionization current generated by the ionization effect accompanying the incidence of the γ-ray into a measurement signal having energy information and transmits the measurement signal to the measurement unit.

The measuring unit is an MCA (Multi Chanell Analize)
r) 4 as a main component, and includes a high-voltage power supply, a linear amplifier, an AD converter, a process memory, and the like. In this measuring section, the digital signal value indicated by the measurement signal is stored in a process memory divided into energy channels corresponding to nuclides.

[0004] The data processing device 5 reads out the measurement values stored in the process memory of the MCA 4 and performs nuclide analysis using analysis software built in the data processing device 5 so that the measurement value is stored in the measurement sample S. The nuclide that has been determined is determined. Information such as an analysis result is output in a form from a printer 6 connected to the data processing device 5.

FIG. 9 shows the entire flow of the measurement operation of the above nuclide analyzer. By mounting the measurement sample S on the sample table 1, the measurement sample S and the Ge detector 2 are arranged at a predetermined distance from each other. Measurement conditions such as a sample name, a sample amount, an ashing rate, and a measurement time are input to the data processing device 5, and measurement is started. Since the γ-ray measurement is measured in the form of a count rate, the count rate data is stored in the corresponding energy channel of the process memory. The nuclide analysis is performed based on the count rate data and the energy channel.

Incidentally, when the measurement sample S has a high counting rate (10
(kcps or more), the Ge detector 2 may fall into a kind of saturation state and cause a so-called suffocation phenomenon of the detector. If the detector has suffocated, it cannot be measured or the error will be significant.

Therefore, if the count rate taken out of the process memory is too high, it is determined that measurement is impossible due to the suffocation phenomenon, and measurement is resumed after waiting for a change in the sample position. The change of the sample position is performed by replacing the current sample stage 1 with a higher sample stage having a different height. By using a sample stage higher than the current one, the distance between the measurement sample S and the Ge detector 2 can be made farther than now, so that the counting rate measured even for the same measurement sample is reduced. be able to. In the case of a measurement sample that is expected to have a high dose rate in advance, it is replaced with a prepared tall sample stage in order to increase the distance between the measurement sample S and the Ge detector 2.

[0008]

As described above, in the conventional nuclide analyzer, the sample table must be replaced each time after the suffocation of the detector occurs or when the suffocation is expected. The operation is cumbersome, and when it is determined that the suffocation phenomenon has occurred after the measurement has been performed once, the measurement must be performed again, which causes a reduction in work efficiency.

The present invention has been made in view of the above circumstances, and accurately measures the counting rate without replacing the sample table and re-measuring even a sample having a high counting rate. It is an object of the present invention to provide a nuclide analyzer capable of improving the reliability of a nuclide analysis result and reducing the time required for nuclide analysis.

[0010]

In order to achieve the above object, the present invention takes the following measures. The present invention detects radiation emitted from a measurement sample with a radiation detector,
The pulse signal output from the radiation detector is counted for each energy channel, an energy spectrum indicated by a count rate for each energy channel is measured, and nuclides contained in the measurement sample are analyzed based on the energy spectrum. In the nuclide analyzer, a count rate attenuating means for adjusting an apparent count rate as viewed from the radiation detector, a pre-measurement means for pre-measuring the count rate of radiation emitted from the measurement sample, and a pre-measurement obtained by the pre-measurement. If the count rate indicates that the count rate exceeds the permissible count rate range, an adjustment command means for instructing the count rate attenuating means to decrease the count rate; and Comprises automatic calibration means for calibrating the detection efficiency of the radiation detector in the calculation of nuclide analysis in accordance with the attenuated apparent count rate.

According to the present invention, the counting rate of the radiation emitted from the measurement sample is pre-measured, and if the counting rate obtained in the pre-measurement indicates that the counting rate exceeds the allowable range of the counting rate, the counting rate attenuating means is used. On the other hand, the count rate is instructed to decrease, and the apparent count rate viewed from the radiation detector is adjusted in accordance with the instruction. On the other hand, the count rate measured after the apparent count rate is adjusted so that the count rate obtained in the pre-measurement falls within the count rate allowable range is used for actual nuclide analysis. When the apparent count rate is adjusted by the count rate attenuation instruction, the detection efficiency is calibrated according to the attenuated apparent count rate in the calculation of the nuclide analysis.
Therefore, the apparent count rate is repeatedly attenuated by the count rate attenuating means until the count rate measured by the pre-measuring means does not exceed the allowable range of the count rate even for a sample having a high count rate. The measurement will be performed in a good condition that does not exceed the allowable range.

The count rate attenuating means is calibrated by a collimator mechanism for adjusting an apparent count rate by selectively disposing a plurality of collimator holes having different hole diameters on the detection surface of the radiation detector. As the hole diameter of the collimator hole disposed on the detection surface of the radiation detector decreases, the apparent count rate of the radiation detector decreases.

The counting rate attenuating means is constituted by a moving mechanism for adjusting the apparent counting rate by automatically moving the measurement position of the radiation detector away from the measurement sample. As the measurement position of the radiation detector moves away from the measurement sample, the apparent count rate seen from the radiation detector decreases.

According to the present invention, since the pre-measurement is performed, the measurement can be performed after confirming that the apparent count rate seen from the radiation detector falls within the allowable range of the count rate. Is eliminated, and the counting rate can be accurately measured even with a measurement sample having a high counting rate.

[0015]

Embodiments of the present invention will be described below. (First Embodiment) FIG. 1 shows the structure of a nuclide analyzer according to a first embodiment. This nuclide analyzer includes a collimator mechanism 10 capable of adjusting an apparent count rate measured by the Ge detector 2 in a plurality of stages. The collimator mechanism 10 includes a collimator plate 11, a rising screw 12, a rotating motor 13, a controller 14, and the like.

FIG. 2 is a plan view of the collimator plate 11.
As shown in the figure, the collimator plate 11 has a fan shape as a whole, and a plurality of collimator holes 11a to 10e having different hole diameters are continuously formed on the same circumference around the rotation axis O. A horizontal line is formed between the measurement sample S and the detection surface of the Ge detector 2 so that the continuous formation line of the collimator holes 11a to 10e passes through the region corresponding to the center of the measurement sample S and the Ge detector 2 facing each other. Has been partially inserted. The rotation axis of the collimator plate 11 is fixed to a rising screw 12 for rotation, which is vertically arranged on the side of the sample table 1. The collimator holes 11 a to 10 e disposed between the measurement sample S and the detection surface of the Ge detector 2 can be switched by rotating the rotation screw 12 by the rotation motor 13. The control of the rotation motor 13 is performed by the controller 14 which receives a rotation command from the data processing device 15.

Here, the relationship between the hole diameters of the collimator holes 11a to 10e and the apparent count rate of the Ge detector 2 will be described. If the dose rate and facing distance of the measurement sample S are constant, the detection efficiency of the Ge detector 2 is proportional to the size of the effective detection area of the Ge detector 2. Therefore, the apparent count rate can be adjusted by changing the effective detection area of the Ge detector 2 by changing the collimator holes 11a to 11e. If the collimator holes 11a to 11e are reduced to reduce the effective detection area of the Ge detector 2, the apparent count rate of the Ge detector 2 can be attenuated.

For example, the diameters of the collimator holes 11a to 10e are multiplied by the collimator holes 11a to 10e so that the hole diameters are gradually reduced, and the collimator hole 11a having the largest hole diameter is set to be effective for the Ge detector 2. Diameter (effective detection area)
To the same size as. Based on this, the effective diameter is gradually reduced until the counting rate does not fall within the asphyxiation range.

The data processing device 15 includes the collimator plate 11
A detection efficiency table for managing the correspondence between the hole numbers of the collimator holes 11a to 10e and the detection efficiency correction value at each collimator hole position is prepared. When the measurement is performed using the collimator plate 11, the count value obtained from the Ge detector 2 is an apparent count rate obtained with the adjusted detection efficiency. Needs to be converted to a true count. Therefore, the detection efficiency correction value corresponding to the collimator stop position is extracted by using the detection efficiency table, and can be used for a process of converting an apparent count value into a true count value.

The operation of the nuclide analyzer configured as described above will be described with reference to the flowchart of FIG. The measurement sample S is mounted on the upper surface of the sample table 1 at a predetermined position above the Ge detector 2, and then measurement conditions are input to the data processing device 15. The measurement conditions include a sample name, a collection date, a collection place, a sample amount, an ashing rate, a collection efficiency, an energy calibration, an efficiency calibration, a height correction, a BG correction, a measurement time setting, and the like.

Next, the count rate of a specific nuclide is pre-measured. The rotation of the collimator plate 11 is controlled so that a collimator hole 11a equal to the effective diameter (effective detection area) of the Ge detector 2 is arranged between the measurement sample S and the detector.
The specific nuclide generally refers to a specific nuclide contained in a large amount in a measurement sample, and specifically, 137Cs, 60Co
And so on. The measurement of the count rate for these specific nuclides is performed for a short time (for example, 30 seconds), and the count rate when the measurement of the count rate of the measurement sample S is continued for the measurement time set in the measurement condition is predicted and calculated.

Based on the result of the prediction calculation, if the measurement is continued until the set time, it is determined whether or not the counting rate may exceed the suffocation range. When the counting rate of the specific nuclide contained in the measurement sample S indicates a possibility of exceeding the asphyxiation range,
A rotation command is given from the data processing device 15 to the controller 14 so that the collimator hole 11b having a smaller hole diameter by one stage than the current position is arranged between the measurement sample S and the detector. Perform pre-measurement with collimator hole 11b,
The count rate prediction calculation is performed again. Until the counting rate of the specific nuclide contained in the measurement sample S shows no possibility of exceeding the suffocation range, the same process is repeated by sequentially reducing the diameter of the collimator holes.

By repeating the pre-measurement, if a collimator hole suitable for the measurement of the counting rate of the measurement sample S can be specified, an appropriate position arrival signal is transmitted. When transmitting the proper position arrival signal, the data processing device 15 shifts the processing to a normal measurement. That is, the hole number of the collimator hole from which the proper position arrival signal has been transmitted is determined from the position detection signal sent from the controller 14. The position detection signal is obtained by detecting the actual amount of rotation of the rotation motor 13 or a detector (not shown) by detecting the current collimator hole.
This is a signal that indicates the current collimator hole position generated based on the signal input to. The data processing device 15 acquires the detection efficiency correction value registered for the current hole number of the collimator hole determined from the position detection signal using the detection efficiency table. Specifically, the detection efficiency correction value itself corresponding to the collimator stop position is managed in the form of an efficiency calibration file, and only the file number corresponding to the collimator hole number is registered in the detection efficiency table.

Next, when the measurement is started and the measurement set time previously input as the measurement condition has elapsed, the digital signal value of the count rate is read from the process memory of the MCA 4. Here, the principle of nuclide analysis in this embodiment will be briefly described. A nuclide emits radiation and changes to another nucleus, but the energy at which radiation is emitted varies depending on the nuclide. When a pulse signal output from a detector used for nuclide analysis such as a Ge detector is detected according to the amount of energy (signal level of the pulse signal), a different peak is shown for each nuclide. actually,
Since the pulse signal for radiation detection falls within the range of 0 to 2 MeV, this energy range is divided into, for example, 4000 channels. It becomes 0.5 KeV per channel. Then, the dimension corresponding to the digital value of the signal level of the pulse signal is plotted on the horizontal axis (energy range is 400
The horizontal axis is divided into 0 channels), and the number of pulses of each energy channel is plotted on the vertical axis. This makes it possible to determine the nuclide based on the number of pulses of each energy channel counted during the measurement set time. The process memory of the MCA 4 functions as storage means for adding and storing the number of pulses of the pulse signal converted into a digital signal by the AD converter for each energy channel.

The data processing device 15 takes out the measured values accumulated during the measurement set time from the process memory of the MCA 4 and issues an analysis instruction to analysis software for nuclide analysis. This analysis software has already determined the position detection signal and corrected the measurement value using the detection efficiency correction value extracted from the file, then calculated the true counting rate from the corrected measurement value and performed nuclide analysis I do.

According to such an embodiment, it is necessary to replace the sample table 1 by providing the collimator mechanism 10 capable of adjusting the apparent measured value of the Ge detector 2 in multiple steps. In addition, it is possible to adjust the apparent measured value of the Ge detector 2 to a state in which the suffocation phenomenon does not occur, and it is possible to reduce troublesome work such as replacing the sample table.

According to this embodiment, the actual measurement is started after the hole position of the collimator plate 11 is set to the collimator hole where the suffocation does not occur by the pre-measurement. Even if the ratio is the same, there is no need to repeat the measurement, and an accurate measured value can be obtained.

(Second Embodiment) This embodiment is different from the first embodiment in that
This is a nuclide analyzer provided with an elevating mechanism for automatically elevating and lowering the measurement sample S to a height at which the detector does not cause the suffocation phenomenon based on the pre-measurement. FIG. 4 shows the configuration of the nuclide analyzer according to the second embodiment. The nuclide analyzer includes a lifting fork 21, a lifting screw 22, and a rotating motor 23.
And a lifting mechanism including a controller 24 and the like. This elevating mechanism places the measurement sample S on an elevating fork 21 whose height can be freely adjusted, instead of on the sample table 1 having a fixed height, and moves the elevating fork 21 to the side of the measurement sample S. It is screwed to a lifting screw 22 arranged in the vertical direction. That is, by holding the elevating fork 21 movably in the up and down direction by a holding member (not shown), when the elevating screw 22 is rotated, the elevating fork 21 relatively moves up and down. The rotation motor 23 drives the lifting screw 22 to rotate, and the controller 24 receives a movement command from the data processing device 15 to control the rotation motor 23.

In the data processing device 15, a detection efficiency table is set in which the relative distance between the Ge detector 2 and the measurement sample S and the detection efficiency correction value information correspond. Since the Ge detector 2 is fixed, a detection efficiency correction value at each height with respect to the detection efficiency at the reference position is registered with a certain height of the elevating fork 21 on which the measurement sample S is placed as a reference position. . The height of the elevating fork 21 is divided into a plurality of stages within a range in which the same detection efficiency can be considered.

FIG. 5 is a flowchart showing the operation of the nuclide analyzer constructed as described above. In this nuclide analyzer, after setting the lifting / lowering fork 21 at the reference position, a pre-measurement is performed on the counting rate for a specific nuclide, and a prediction calculation is performed. to decide. If the counting rate exceeds the suffocation range, the elevating fork 21 is used to reduce the detection efficiency.
Command to move the controller 2 to the next height range
Give to 4. Again, the counting rate is pre-measured and the prediction calculation is performed. This pre-measurement is repeated until the count rate does not exceed the suffocation range, and finally an appropriate position reaching signal is generated at a height position where the count rate does not exceed the suffocation range.

The file in which the detection efficiency correction value is stored at the appropriate position is automatically selected using the detection efficiency table, and actual measurement is started. Subsequent processing is the same as in the above-described first embodiment.

According to such an embodiment, since the detector is provided with an elevating mechanism for automatically elevating and lowering the measurement sample S to a height at which the detector does not cause the suffocation phenomenon based on the pre-measurement, the measurement sample having a high counting rate is provided. Even in this case, the work of exchanging the sample table can be reduced, and an accurate measured value can be obtained without performing the measurement again.

(Third Embodiment) This embodiment is similar to the third embodiment.
This is an example in which the collimator mechanism described in the first embodiment and the elevating mechanism described in the second embodiment are provided side by side. FIG. 6 shows a configuration of a nuclide analyzer according to the third embodiment. Since the collimator mechanism and the elevating mechanism have already been described in detail, the use of both mechanisms will be described here. The pre-measurement is started by inputting the measurement conditions, and the measurement of the counting rate is performed only for a short time for a specific nuclide that is contained in a large amount in a normal measurement sample. Performing a prediction calculation of the counting rate of the measurement sample from the measurement result is the same as in the above-described embodiments.

From the result of the prediction calculation, it is determined whether or not the counting rate exceeds the suffocation range. If it is determined that the counting rate may exceed the suffocation range, first, the data processing device 15 sends a command to the controller 14. By giving a rotation command, an attempt is made to attenuate the counting rate due to the collimator hole diameter of the collimator plate 11. The pre-measurement is performed again, and if there is a possibility that the counting rate may still exceed the suffocation range, the data processing device 1
From 5, a movement command is given to the controller 24 to try to attenuate the count rate due to movement in the height range. Again, a pre-measurement is performed to determine whether the count rate exceeds the suffocation range.

The pre-measurement by the collimator mechanism and the elevating mechanism as described above is alternately repeated until the counting rate finally does not exceed the suffocation range. According to such an embodiment, the adjustment amount of the counting rate can be subdivided depending on the combination of the collimator hole diameter of the collimator plate 11 and the division setting of the height range of the lifting mechanism. In addition, by setting the amount of adjustment by the collimator hole diameter roughly and setting the height range by the elevating mechanism finely, or by setting the reverse combination, the time of pre-measurement until the start of constant measurement Can also be shortened.

In the above description, a Ge detector is used to detect radiation emitted from the measurement sample. However, any other type of detector may be used as long as the energy information of the pulse signal appears in the detection signal. good. The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0037]

As described above in detail, according to the present invention, it is possible to accurately measure a counting rate without exchanging a sample table and re-measuring even a sample having a high counting rate. And improve the reliability of the nuclide analysis results.
A nuclide analyzer that can reduce the time required for nuclide analysis can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a nuclide analyzer according to a first embodiment.

FIG. 2 is a plan view of a collimator plate provided in the nuclide analyzer according to the first embodiment.

FIG. 3 is a flowchart for counting rate measurement and nuclide analysis in the first embodiment.

FIG. 4 is a configuration diagram of a nuclide analyzer according to a second embodiment.

FIG. 5 is a flowchart for counting rate measurement and nuclide analysis in the second embodiment.

FIG. 6 is a configuration diagram of a nuclide analyzer according to a third embodiment.

FIG. 7 is a flowchart for counting rate measurement and nuclide analysis in the third embodiment.

FIG. 8 is a configuration diagram of a conventional nuclide analyzer.

FIG. 9 is a flowchart for counting rate measurement and nuclide analysis in a conventional nuclide analyzer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sample stand 2 ... Ge detector 3 ... Shield 4 ... MCA 6 ... Printer 10 ... Collimator mechanism 11 ... Collimator plate 11a-11e ... Collimator hole 12,22 ... Rising screw 13,23 ... Rotating motor 14, 24 ... Controller 15 ... Data processing device 1 21 ... Elevating fork

Claims (3)

[Claims] 1. A radiation detector detects radiation emitted from a measurement sample, counts a pulse signal output from the radiation detector for each energy channel, and calculates an energy spectrum indicated by a count rate for each energy channel. In a nuclide analyzer for measuring and analyzing nuclides contained in the measurement sample based on the energy spectrum, a counting rate attenuating means for adjusting an apparent counting rate viewed from the radiation detector; Pre-measuring means for pre-measuring the counting rate of the radiation to be performed, and instructing the counting rate attenuating means to attenuate the counting rate if the counting rate obtained in the pre-measurement indicates that the counting rate exceeds an allowable range. When there is an instruction to decay the count rate by the adjustment command means,
An nuclide analyzer comprising: an automatic calibration means for calibrating the detection efficiency of the radiation detector in the calculation of nuclide analysis in accordance with the attenuated apparent count rate. 2. The nuclide analyzer according to claim 1, wherein the counting rate attenuating means is apparently arranged by selectively arranging a plurality of collimator holes having different hole diameters on a detection surface of the radiation detector. A nuclide analyzer comprising a collimator mechanism for adjusting the counting rate of the nuclide. 3. The nuclide analyzer according to claim 1, wherein the counting rate attenuating means adjusts an apparent counting rate by automatically moving a measurement position of the radiation detector away from the measurement sample. A nuclide analyzer comprising a mechanism.