JPH05196741A - Radioactive contamination monitor - Google Patents

Abstract

PURPOSE:To realize constantly highly accurate radioactive contamination measurement without being influenced by a position of a subject. CONSTITUTION:A detection sensitivity curve indicating sensitivity characteristics of respective radiation detectors 1a to 1c is obtained from counted values when a moving means 14 for moving a radiation source 13 for calibration to respective positions in a measurement area formed by the plurality of radiation detectors 1a to 1c and the radiation source 13 are placed at the respective positions in the measurement area. A radioactive contamination monitor comprises a calibration constant calculating means 10 for determining a calibration constant corresponding to a ratio of an average value wherein an envelope of the above detection sensitivity curve is averaged with radiation source intensity of the radiation source 13 and a correcting means 10 for correcting the counted value wherein radioactive rays from a subject is detected by the respective radiation detectors la to 1c with the calibration constant determined by the calibration constant calculating means 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive contamination monitor used in nuclear facilities.

[0002]

2. Description of the Related Art Radioactive contamination in which radiation emitted from a contamination source attached to an object is detected, the number of pulses of a pulse signal which is the detection signal is counted, and the degree of radioactive contamination is judged from the magnitude of the counted value. Monitors are known. By the way, since the detector of the radioactive contamination monitor is generally smaller than the subject, a plurality of detectors can simultaneously measure the entire subject.

For example, the radioactive contamination monitor shown in FIG.
It is equipped with three radiation detectors 1a to 1c. The radiation detectors 1a to 1c input the detection signals output by the incidence of radiation to the corresponding measuring devices 2a to 2c.
When the detection signal is input, each of the measuring devices 2a to 2c outputs a pulse signal to the data processing device 3, and the data processing device 3 counts the pulse signal of each detector. Since the radiation detectors 1a to 1c have different detection sensitivities and change with time, it is necessary to periodically calibrate.

Therefore, conventionally, as shown in FIG. 7, a fixing jig 6 holding a calibration radiation source 5 is attached to a radiation detector to be calibrated (1b is a target in the figure). The radiation source 5 is arranged at a position facing the center of the detection surface.

In such a state, the radiation detector 1
The detection signals output from b are counted, and the calibration constant is obtained from the ratio of the count value and the radiation source intensity at that time. Similar sensitivity detection work is performed on each of the radiation detectors 1a to 1c, and the obtained calibration constant is stored in the calibration constant storage unit 4. And at the time of actual measurement, each radiation detector 1a-1
The count value of c is corrected by the calibration constant read from the calibration constant storage unit 4 to determine the accurate contamination degree. By the way, as shown in FIG. 8, the detection sensitivity of the radiation detector is highest at the center of the detection surface and low at the ends.

In the conventional calibration of the radiation detector, the center of the detector having high detection sensitivity is set as the calibration points 1a, 1b, 1c, and the radiation source is fixed at that location to perform the calibration measurement. However, since the subject is not always placed in the center of the detector during the actual measurement of contamination, the measured value may be lower than the actual contamination degree in the above calibration.

[0007]

As described above, in the conventional radioactive contamination monitor, the sensitivity is calibrated with the center of the detector having high detection sensitivity as the calibration point, so the measured value becomes lower than the actual contamination degree. There is a possibility that accurate contamination measurement may not be made.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a radioactive contamination monitor capable of performing highly accurate radioactive contamination measurement regardless of the position of the subject. To aim.

[0009]

In order to achieve the above object, the radioactive contamination monitor according to the first aspect of the present invention arranges a subject in a measurement area formed by a plurality of radiation detectors, A radiation source for calibration in a radioactive contamination monitor that detects emitted radiation by each of the radiation detectors, converts it into a pulse signal, and monitors the radioactive contamination of the subject from the counted value of the pulse signal. A moving means for moving the radiation source to various places in the measurement area, and the sensitivity of each radiation detector from the count value indicated by each radiation detector when the radiation source is arranged at each place in the measurement area by the moving means. Obtaining a detection sensitivity curve showing characteristics, and a calibration constant calculating means for determining the calibration constant of each radiation detector according to the ratio of the average value of the envelope of the detection sensitivity curve and the source intensity of the radiation source, , Covered The count value obtained by detecting the radiation from the body In each of the radiation detectors and configured to anda correction means for correcting the calibration constants determined in the calibration constant calculating means.

Further, in the radioactive contamination monitor according to the second aspect of the invention, the sensitivity characteristic of each radiation detector is obtained from the count value indicated by each radiation detector when the radiation source is arranged at each place in the measurement area by the moving means. Obtain the detection sensitivity curve shown, divide the detection sensitivity curve in a predetermined range, obtain the average value of the detection sensitivity curve in each divided range, the average value of each average value and the radiation source The calibration constant of each radiation detector was determined according to the ratio with the radiation source intensity.

Further, the radioactive contamination monitor according to the third aspect of the present invention shows the sensitivity characteristic of each radiation detector from the count value shown by each radiation detector when the radiation source is arranged at each place in the measurement area by the moving means. Obtaining the detection sensitivity curve, the envelope of the detection sensitivity curve is divided for each radiation detector, according to the ratio of the average value of the envelope in each divided range and the source intensity of the radiation source, The calibration constant was set for each radiation detector.

Further, the radioactive contamination monitor according to the fourth aspect of the present invention shows the sensitivity characteristic of each radiation detector from the count value indicated by each radiation detector when the radiation source is arranged at each place in the measurement area by the moving means. Obtaining a detection sensitivity curve, dividing the detection sensitivity curve for each of the radiation detectors, according to the ratio of the average value of the detection sensitivity curve in each divided range and the source intensity of the radiation source, the radiation detection The calibration constant was set for each instrument.

[0013]

According to the first invention, when the sensitivity of the radiation detector is calibrated, the calibrating radiation source is moved by the moving means to various places in the measurement area, and at this time, the pulse signal output from each radiation detector. Are counted and the respective count values are detected. Then, by the calibration constant calculating means, a detection sensitivity curve showing the sensitivity characteristic of each radiation detector is obtained from each count value, and an average value obtained by averaging the envelopes of the detection sensitivity curve,
The calibration constant of each radiation detector is determined from the ratio of the radiation source to the radiation source intensity.

Next, at the time of measuring the contamination of the subject, the radiation from the subject is detected by each radiation detector, the count value is corrected by the above calibration constant, and the original radioactive contamination degree of the subject is obtained. ..

When the calibration constant is determined using the calibration point with the highest detection sensitivity, there will be a detection error from the maximum value to the minimum value of the detection sensitivity, but in the present invention, the envelope of the detection sensitivity curve is present. By using the average value of the lines, the detection error is reduced to about 1/2. According to the second invention,
Similar to the first aspect of the invention, the radiation source for calibration is moved in the measurement area by the moving means to obtain the detection sensitivity curve of each radiation detector. Then, with respect to the detection sensitivity curve, the average value of the detection sensitivity curve is obtained within each predetermined divided range, and the calibration constant for the entire radiation detector is determined based on the value obtained by further averaging the respective average values. Be done.

According to the third aspect of the invention, similarly to the first aspect of the invention, the radiation source for calibration is moved in the measurement area by the moving means to obtain the detection sensitivity curve of each radiation detector. Then, with respect to the envelope of the detection sensitivity curve, the average value of the envelope corresponding to each radiation detector is obtained, and the calibration constant is determined for each radiation detector based on each average value.

According to the fourth aspect of the invention, similarly to the first aspect of the invention, the radiation source for calibration is moved in the measurement area by the moving means to obtain the detection sensitivity curve of each radiation detector. Then, a division range is determined for each radiation detector with respect to the detection sensitivity curve, and the average value of the envelope of the detection sensitivity curve is obtained within each division range. Then, a calibration constant is determined for each radiation detector based on the respective average values.

[0018]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 shows a functional block of a radioactive contamination monitor according to an embodiment of the present invention. The parts having the same functions as those of the monitor shown in FIG.

The radioactive contamination monitor of this embodiment is equipped with a data processing device 10, and each measuring device 2 in the measuring mode.
It has a function of determining the degree of radioactive contamination of the subject by counting the pulse signals sent from a to 2c, and a function of executing a sensitivity calibration calculation described later in the calibration mode to obtain a calibration constant.

The data processing device 10 is connected to a processing mode changeover switch 11 for inputting the measurement mode / calibration mode changeover signal, and further connected to a measurement start switch 12 for inputting a measurement start timing signal. ing.

Further, in this embodiment, upon receiving a drive control signal from the data processor 10, the calibration radiation source 13 is moved in the vicinity of the measurement area composed of the radiation detectors 1a to 1c, and each position is determined in advance. The radiation source drive device 14 disposed in the position is provided. The calibration radiation source 13 is set so as to be arranged at least at a plurality of positions on the detection surface of one radiation detector.

A position sensor 15 for detecting the position of the radiation source 13 is provided so that the position information of the radiation source 13 is sequentially input to the data processing device 10. Reference numeral 16 is a display unit that displays the degree of radioactive contamination of the subject. Next, four types of calibration constant setting principles will be described with reference to FIGS. 3 and 4.

FIG. 3 shows, as the detection sensitivity, the count value of the detection signals output from the radiation detectors 1a to 1c when the radiation source is moved to the vicinity of the measurement area. The outputs of the radiation detectors 1a to 1c show detection sensitivity curves as shown in FIG.

In this embodiment, each of the radiation detectors 1a-1c is used.
Then, the envelope of each detection sensitivity curve is obtained (curve shown by a solid line in the figure). Then, the calibration constant is determined from the ratio of the average value A1 of the envelope and the source intensity of the source. This calibration constant is used as a calibration constant for the radiation detectors 1a-1c.

Further, the protection range of each radiation detector 1a-1c in the measurement area is preset as shown in FIG. The protection range of the radiation detector 1a is R1, the protection range of the radiation detector 1b is R2, and the protection range of the radiation detector 1c is R3.

The average value of the detection sensitivity curves of the radiation detector 1a in the defensive range R1, the average value of the detection sensitivity curves of the radiation detector 1b in the defensive range R2, and the detection sensitivity curve of the radiation detector 1c in the defensive range R3. , And the average value of each of the defense ranges is further averaged. Then, the calibration constant is determined from the ratio of the value and the source intensity of the source. This calibration constant can also be used as the calibration constant of the radiation detectors 1a to 1c.

Although the above setting principle is for setting a common calibration constant for all the radiation detectors 1a to 1c,
Using the average value of the detection sensitivity curves, each radiation detector 1a-
A specific calibration constant can be set for each 1c.

For example, the average value of the detection sensitivity curve in the range M1 corresponding to the output of the radiation detector 1a having the envelope shown in FIG. 3 is obtained, and similarly, the range M2 corresponding to the respective outputs of the radiation detectors 1b and 1c. , M3 for each detection sensitivity curve. Then, a calibration constant determined from the average value of the range M1 is used for the radiation detector 1a, and similarly, each calibration constant obtained from the average value of the corresponding ranges M2 and M3 is used for the radiation detectors 1b and 1c, respectively.

Further, the calibration constants determined from the average value of the defense range R1 shown in FIG. 4 are used for the radiation detector 1a, and the respective calibration constants determined from the average value of the defense ranges R2 and R3 are used in the radiation detector 1b. , 1c can also be used.

Next, the operation of this embodiment configured as described above will be described with reference to FIG. In this embodiment, when the calibration mode is set by the processing mode changeover switch 11 and then the measurement start timing signal is input from the measurement start switch 12, the data processing device 10 outputs a drive control signal to the radiation source drive device 14. To be done. With this drive control signal, the radiation source driving device 14 sequentially arranges the radiation source 13 in each of the predetermined measurement areas.

At this time, the radiation source 13 may be moved by scanning only one line at the central portion of each of the three radiation detectors 1a to 1c arranged in series, or by scanning a plurality of lines. May be. An accurate detection sensitivity curve can be obtained as the number of scanning lines increases.

In the data processing device 10, the measuring devices 2a-2
While counting the pulse signals sent via c,
The position information of the radiation source 13 sent from the position sensor 15 is taken in and the detection sensitivity curve of each radiation detector is obtained.

When the measurement at all the predetermined measurement points on the measurement area is completed, the calculation calculation of the calibration constant is executed next. This calculation executes one of the above-mentioned four kinds of setting principles based on the count value obtained by the above measurement. For example, the envelope shown in FIG. 3 is obtained from the detection sensitivity curve, and the average value A1 is obtained. Then, the calibration constant is determined from the ratio of the average value A1 and the source intensity.

When the calibration constant is obtained, the value is stored in the calibration constant storage unit 4. In addition, each radiation detector 1a
When the calibration constant is determined for each of the radiation detectors 1c to 1c, the calibration constants are stored for the radiation detectors 1a to 1c.

Next, by switching to the measurement mode by the processing mode changeover switch 11, the radioactive contamination of the subject can be measured. That is, when the measurement start timing signal is input from the measurement start switch 12 in a state where the subject is opposed to the measurement area, each of the radiation detectors 1a to 1c.
The respective detection values are obtained by taking in the detection signals of. Then, the actual contamination amount is calculated by reading the calibration constant stored in the calibration constant storage unit 4 and multiplying it by the count value.

As described above, according to this embodiment, the radiation source driving device 14 is provided so that the calibration radiation source 13 can be freely moved within the measurement area.
1a to 1c, the detection sensitivity curve is further calculated, the envelope of the detection sensitivity curve is further calculated, and the radiation detector 1a is determined by a calibration constant determined based on the ratio between the average value A1 and the source intensity of the radiation source. Since the output of 1c is corrected, the error due to the calibration can be reduced to about 1/2 as compared with the conventional case where the highest detection sensitivity is used as the calibration point.
The measurement accuracy can be improved.

Further, in this embodiment, the protection ranges of the radiation detectors 1a to 1c in the measurement area are set in advance, the average values of the detection sensitivity curves of the radiation detectors in the protection ranges are obtained, and the respective protections are determined. Since the calibration constant is determined by further averaging the average values of the range, the measurement accuracy can be improved in this case as compared with the case where the highest detection sensitivity is used as the calibration point.

Further, in the present embodiment, the average value of the detection sensitivity curve in the range M1 corresponding to the output of the radiation detector 1a of the envelope is obtained, and similarly, it corresponds to each output of the radiation detectors 1b and 1c. The average value of each detection sensitivity curve in the ranges M2 and M3 was calculated, the calibration constant determined from the average value of the range M1 was used for the radiation detector 1a, and similarly the average value of the corresponding ranges M2 and M3 was calculated. Since each calibration constant is used for each of the radiation detectors 1b and 1c, in this case as well, the measurement accuracy can be improved as compared with the case where the highest detection sensitivity is used as the calibration point.

Further, in this embodiment, the calibration constants determined from the average value of the defense range R1 are used for the radiation detector 1a, and the calibration constants determined respectively from the average value of the defense ranges R2 and R3 are used in the radiation detector 1b. , 1c, the measurement accuracy can be improved in this case as compared with the case where the highest detection sensitivity is used as the calibration point.

Further, the source 13 is driven by the source driver 14.
Since it is configured to be moved, there is an advantage that the calibration measurement operation becomes simpler than in the case where a fixing jig is used as in the related art.

In the above embodiment, the radiation detectors 1a ...
Although the example of arranging 1c in series is shown, it is also applicable to those arranged on a plane as shown in FIG. Since the sensitivity characteristic in this case is as shown in FIG.
The calibration radiation source 13 is moved so that the center of each detector is scanned at least once.

Further, as shown in FIG. 6 (a), the radiation detectors 20a to 20d can be applied to a well type arrangement. Since the sensitivity characteristic in this case is as shown in FIG. 7B, the calibration radiation source 13 is moved in a circle as shown in FIG. ..

[0044]

As described above in detail, according to the present invention, it is possible to provide a radioactive contamination monitor that enables reliable reliable measurement of radioactive contamination regardless of the position of the subject.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a radioactive contamination monitor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a calibration measurement operation of the radioactive contamination monitor according to the embodiment.

FIG. 3 is a diagram for explaining the principle of setting calibration constants using the envelope of the output of each radiation measuring device.

FIG. 4 is a diagram for explaining the principle of defining a defensive range on the detection sensitivity curve of each radiation measuring instrument and setting a calibration constant.

FIG. 5 is a diagram showing a radiation detector arranged in a plane and its sensitivity characteristics.

FIG. 6 is a view showing a radiation detector arranged in a well shape and its sensitivity characteristic.

FIG. 7 is a functional block diagram of a conventional radioactive contamination monitor.

FIG. 8 is a diagram for explaining a conventional calibration constant setting principle using a detection sensitivity curve.

[Explanation of symbols]

1a-1c ... Radiation detector, 2a-2c ... Measuring device, 4
... Calibration constant storage unit, 10 ... Data processing device, 13 ... Calibration radiation source, 14 ... Radiation source driving device, 15 ... Position sensor.

Claims (4)

[Claims] 1. A subject is placed in a measurement area formed by a plurality of radiation detectors, the radiation emitted from the subject is detected by each of the radiation detectors and converted into a pulse signal, and the pulse is generated. In a radioactive contamination monitor that monitors the radioactive contamination of the subject from the count value obtained by counting the signals, a moving unit that moves a calibration radiation source to various places in the measurement area, and the radiation source by the moving unit. Obtaining a detection sensitivity curve showing the sensitivity characteristics of each radiation detector from the count value shown by each radiation detector when placed at each position in the measurement area, and an average value obtained by averaging the envelopes of this detection sensitivity curve. A calibration constant calculating means for determining the calibration constant of each radiation detector according to the ratio of the radiation source to the radiation source intensity, and a count value obtained by detecting radiation from a subject with each radiation detector. , The calibration A radioactive contamination monitor, comprising: a correction unit that corrects with a calibration constant determined by the number calculation unit. 2. A subject is placed in a measurement area formed by a plurality of radiation detectors, the radiation emitted from the subject is detected by each of the radiation detectors and converted into a pulse signal, and the pulse signal is generated. In a radioactive contamination monitor that monitors the radioactive contamination of the subject from the count value obtained by counting the signals, a moving unit that moves a calibration radiation source to various places in the measurement area, and the radiation source by the moving unit. Obtaining a detection sensitivity curve showing the sensitivity characteristic of each radiation detector from the count value shown by each radiation detector when arranged at each place in the measurement area, and dividing the detection sensitivity curve in a predetermined range , The calibration constant of each radiation detector is determined according to the ratio of the average value of the detection sensitivity curves in each divided range and the average of the average value and the source intensity of the radiation source. With constant calculation means Radioactivity contamination, comprising: a correction unit that corrects a count value obtained by detecting radiation from a subject with each of the radiation detectors with a calibration constant determined by the calibration constant calculation unit. monitor. 3. A subject is arranged in a measurement area formed by a plurality of radiation detectors, the radiation emitted from the subject is detected by each of the radiation detectors and converted into a pulse signal, and the pulse is generated. In a radioactive contamination monitor for monitoring the radioactive contamination of the subject from the count value obtained by counting the signals, moving means for moving the calibration radiation source to various places in the measurement area, and the radiation source by the moving means. Obtaining a detection sensitivity curve showing the sensitivity characteristic of each radiation detector from the count value shown by each radiation detector when arranged at each place in the measurement area, and the envelope of the detection sensitivity curve for each radiation detector And a calibration constant calculating means for determining a calibration constant for each radiation detector according to a ratio between each average value of the envelope in each divided range and the source intensity of the radiation source, and from the subject. The radiation of A radioactivity, comprising: a correction unit that corrects the count value obtained by detection by each radiation detector with each calibration constant determined by the calibration constant calculation unit, for each radiation detector. Pollution monitor. 4. A subject is placed in a measurement area formed by a plurality of radiation detectors, the radiation emitted from the subject is detected by each of the radiation detectors and converted into a pulse signal, and the pulse signal is generated. In a radioactive contamination monitor that monitors the radioactive contamination of the subject from the count value obtained by counting the signals, a moving unit that moves a calibration radiation source to various places in the measurement area, and the radiation source by the moving unit. Obtaining a detection sensitivity curve showing the sensitivity characteristic of each radiation detector from the count value shown by each radiation detector when arranged at each place in the measurement area, and dividing the detection sensitivity curve for each radiation detector Then
A calibration constant calculating unit that determines a calibration constant for each radiation detector according to the ratio of the average value of the detection sensitivity curve in each divided range and the radiation source intensity of the radiation source, and the radiation from the subject Radioactive contamination, comprising: a correction unit that corrects the count value obtained by detection with the radiation detector, with each calibration constant determined by the calibration constant calculation unit, for each radiation detector. monitor.