JP5525916B2 - Radiation monitor - Google Patents

Description

  The present invention relates to a radiation monitor having a sensitivity adjustment function.

  As shown in FIG. 7, the conventional radiation monitor is composed of a radiation source 1 for calibration, a radiation detection unit 2, a high voltage power source 3, a signal amplification unit 4, a wave height discrimination unit 5, and a calculation unit 6. Used in an environment where the radiation dose is below the measurement range.

In such a radiation monitor, the measurement accuracy may deteriorate due to a very slight change in sensitivity over a long period of time. Therefore, in order to check the measurement accuracy of the radiation monitor, periodically adjust the sensitivity of the radiation monitor. I'm doing it. In the radiation monitor shown in FIG. 7, the radiation detection unit 2 is irradiated with radiation from the radiation source 1 at the time of calibration, and sensitivity adjustment is performed by readjusting various setting values such as a pulse height discrimination level based on the output signal. (Patent Document 1).
As a calibration irradiation means, a sensitivity adjustment means using an optical pulse irradiation means having a wave height distribution as shown in a or b of FIG. 6 has also been proposed (Patent Document 1).

JP 2006-84345 A

The conventional calibration means described above requires a great deal of time for sensitivity adjustment, and there is a problem that radiation cannot be measured during that time.
Further, in the case of using an optical pulse for confirmation of normal operation, if the wave height discrimination level is in the wave height distribution as in the light pulse a in FIG. 6, a rapid change occurs due to a slight change in the wave height value, or FIG. If the wave height discrimination level is far from the wave height distribution as in the light pulse b, the indicated value does not change even if the wave height value changes. In addition, there is a problem that a light emission amount drifts in the light source itself or an electrical failure occurs.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a radiation monitor capable of automatically performing sensitivity adjustment with high accuracy while continuously performing radiation measurement.

In order to solve the above-described problems, the present invention provides a calibration radiation source, a radiation detection unit that converts radiation from the calibration radiation source and radiation to be monitored into an electrical signal, and a high detection level for the radiation detection unit. A high-voltage power supply for supplying voltage, a signal amplifying unit for amplifying a signal from the radiation detection unit, a pulse height discriminating unit for discriminating the amplified signal from noise, and the signal discriminated by two different time constants. A radiation monitor having a calculation unit that performs calculation processing at the same time and a gain control unit that automatically adjusts the gain of the signal amplification unit based on the correction value calculated by the calculation unit, wherein the wave height discrimination unit is a wave height discrimination level. was set within the pulse height distribution range of the radiation source for the calibration, the arithmetic unit, by calculation process using the time constant of the smaller of the two different time constants to calculate the command value of the radiation source, And calculates the correction value to be used for automatic adjustment of the radiation sensitivity calculation processing using the time constant of the hearing side.

  According to the present invention, it is possible to automatically adjust the sensitivity of a radiation monitor with high accuracy while continuously performing radiation measurement.

The lineblock diagram of the radiation monitor concerning a 1st embodiment. The lineblock diagram of the radiation monitor concerning a 2nd embodiment. The lineblock diagram of the radiation monitor concerning a 3rd embodiment. The lineblock diagram of the radiation monitor concerning a 4th embodiment. The wave height distribution map which concerns on 4th Embodiment. Wave height distribution map by radiation source and light pulse. The block diagram of the conventional radiation monitor.

Hereinafter, embodiments of a radiation monitor according to the present invention will be described with reference to the drawings.
[First Embodiment]
A radiation monitor according to a first embodiment of the present invention will be described with reference to FIGS.

(Constitution)
The radiation monitor according to the first embodiment includes a calibration radiation source 1, a radiation detection unit 2, a high voltage power supply 3, a signal amplification unit 4, a pulse height discrimination unit 5, a calculation unit 6, and a gain control unit 7. Is done.

  Usually, in an environment where the radiation dose to be monitored is below the measurement range, the radiation detector 2 is irradiated with radiation from the radiation source 1 for calibration in order to confirm that the radiation monitor is operating normally. As the radiation source 1 for calibration, a β-ray source made of, for example, Sr-90 having a wide wave height distribution as shown in FIG.

  The radiation detection unit 2 uses, for example, a semiconductor element, detects radiation, and converts it into an electrical signal. The high voltage power supply 3 supplies a high voltage to the radiation detection unit 2. The signal amplifier 4 amplifies the signal output from the radiation detection unit 2 and sends it to the wave height discrimination unit 5. The pulse height discriminating unit 5 discriminates a noise component and a signal component by outputting a corresponding pulse signal only when a signal having a peak value equal to or higher than a set peak height discrimination level is input.

  The calculation unit 6 counts and calculates the pulse signal output from the pulse height discrimination unit 5 to calculate a measurement value and a correction value used for automatic correction of radiation sensitivity. The gain control unit 7 adjusts the gain of the signal amplifier 4 based on the correction value calculated by the calculation unit 6.

(Function)
In the radiation monitor configured as described above, since the radiation detection signal from the calibration radiation source 1 has a wide wave height distribution as shown in FIG. 6c, the wave height discrimination level is set within the range of the wave height distribution. Thus, even a slight change in the detection signal peak value that causes the sensitivity change can be detected as a change in the indicated value. Further, since the radiation source 1 irradiates the radiation detection unit 2 while measuring the radiation dose to be monitored, the radiation source 1 is sufficiently lower than the radiation dose to be monitored and has a certain instruction. It has been adjusted to show the value.

  However, since there is a demand for response time in the radiation monitor and the time constant cannot be made extremely long, the indication value from the radiation source 1 at the normal time has a statistical fluctuation of about several percent.

  Therefore, in the calculation unit 6, the time constant used for the normal measurement is Ta, the time constant used for calculating the correction value is Tb, and Tb is larger than Ta, for example, Tb = 100 × Ta. When the time constant Tb is set to, and calculation is performed using Tb for calculation of the correction value, a value with which the relative standard deviation becomes 1/10 of the normal instruction value is obtained. As a result, a calculation result with a fast response speed but a large statistical fluctuation and a calculation result with a low response speed but a small statistical fluctuation can be obtained at the same time. The calculation value with small statistical fluctuation is compared with the reference value, and the correction value is calculated with high accuracy.

In addition, when calculating the correction value, the attenuation due to the half-life of the radiation source 1 is corrected, so that the sensitivity adjustment is erroneously performed as a decrease in sensitivity for the decrease in the instruction value due to the attenuation of the radiation source. Can be prevented.
The gain control unit 7 changes the gain setting of the signal amplification unit 4 based on the correction value obtained by the calculation unit 6 so as to obtain an optimum gain.

  Since the correction value is stable after about three times the time constant, this sensitivity adjustment may be performed periodically once a month as long as the correction value is stable. Alternatively, the correction value may be constantly monitored, and the sensitivity adjustment may be performed when the correction value becomes constant.

  When high reliability is required, the gain control unit 7 may perform only the adjustment for increasing the gain and may not perform the adjustment for decreasing the gain. Thereby, since the sensitivity is adjusted only in the increasing direction, it is possible to perform a highly reliable evaluation on the safe side compared to the case where the conventional adjustment is not performed.

In addition, when the indicated value of normal measurement exceeds a certain level, the data while it exceeds the certain level is not used for the correction value calculation, or the correction value calculation is stopped while it exceeds the certain level. Then, the sensitivity adjustment is performed after about 3 times the time constant after restarting the correction value calculation below a certain level, so that the data when the radiation dose is increased is excluded from the correction value calculation. be able to.
In this embodiment, the time constant Tb is set so that Tb = 100 × Ta. However, the present invention is not limited to this, and the multiplication factor may be changed as appropriate.

  As described above, according to the first embodiment, the calibration radiation source having a wide wave height distribution is used, and signal processing is performed using different time constants, thereby greatly increasing the configuration of the conventional radiation monitor. Without making any changes, it is possible to automatically perform high-precision sensitivity adjustment while continuously performing radiation measurement without interrupting radiation measurement for sensitivity adjustment. This also improves the reliability of measurement during long-time continuous measurement.

[Second Embodiment]
A radiation monitor according to the second embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure similar to 1st Embodiment, and the overlapping description is abbreviate | omitted.
The radiation monitor according to the second embodiment includes a radiation source 1, a radiation detection unit 2, a high voltage power supply 3, a signal amplification unit 4, a wave height discrimination unit 5, a calculation unit 6, and a high voltage power supply control unit 8.

  This is obtained by replacing the gain control unit 7 of the first embodiment with a high-voltage power supply control unit 8, and the high-voltage power supply control unit 8 has an optimum voltage based on the correction value from the calculation unit 6. The high voltage power supply 3 is adjusted.

  In addition, when high reliability is required, the high voltage power supply control unit 8 may only perform adjustment to increase the voltage, and may not perform adjustment to decrease the voltage. Thereby, since the sensitivity is adjusted only in the increasing direction, it is possible to perform a highly reliable evaluation on the safe side compared to the case where the conventional adjustment is not performed.

  According to the second embodiment, the high-voltage power supply control unit 8 optimally adjusts the voltage of the high-voltage power supply 3 based on the correction value from the calculation unit 6 to automatically perform radiation measurement continuously. High-precision sensitivity adjustment can be performed.

[Third Embodiment]
A radiation monitor according to the third embodiment will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure similar to the said embodiment, and the overlapping description is abbreviate | omitted.

  The radiation monitor according to the third embodiment includes a radiation source 1, a radiation detection unit 2, a high voltage power supply 3, a signal amplification unit 4, a wave height discrimination unit 5, a calculation unit 6, and a wave height discrimination level control unit 9. The

  In this embodiment, the gain control unit 7 is replaced with a wave height discrimination level control unit 9 in the first embodiment, and the wave height discrimination level control unit 9 determines the optimum wave height based on the correction value from the calculation unit 6. The wave height discriminating unit 5 is adjusted so as to be at the discrimination level.

  Further, when high reliability is required, the wave height discrimination level control unit 9 may perform only the adjustment for lowering the wave height discrimination level and may not perform the adjustment for increasing the wave height discrimination level. Thereby, since the sensitivity is adjusted only in the increasing direction, it is possible to perform a highly reliable evaluation on the safe side compared to the case where the conventional adjustment is not performed.

  According to the third embodiment, the wave height discrimination control unit 9 optimally adjusts the discrimination level of the wave height discrimination unit 5 on the basis of the correction value from the calculation unit 6 to automatically perform radiation measurement continuously. The sensitivity can be adjusted with high accuracy and safety side.

[Fourth Embodiment]
A radiation monitor according to the fourth embodiment will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the structure similar to the said embodiment, and the overlapping description is abbreviate | omitted.

The radiation monitor according to the fourth embodiment includes a radiation source 1, a radiation detection unit 2, a high voltage power supply 3, a signal amplification unit 4, a plurality of wave height discrimination units 5-1 to 5-3, a calculation unit 6, and a gain. It is comprised from the control part 7. This is a plurality of wave height discriminating sections in the first embodiment.
The gain control unit 7 may be replaced with the high-voltage power supply control unit 8 or the wave height discrimination level control unit 9 as shown in the second or third actual form.

  In the present embodiment configured as described above, the wave height discriminating units 5-1 to 5-3, as shown in FIG. 5, have a normal wave height discriminating level Vo and a Compton edge of environmental γ rays (d in FIG. 5). And two wave height discrimination levels Va and Vb between the total absorption peaks. And only the signal of the radiation source 1 exists by using the count calculated | required in the calculation of the correction value in the calculating part 6 (the count above the wave height discrimination level Va)-(the count above the wave height discrimination level Vb). Since pulses having a peak value within a certain range can be counted, sensitivity can be adjusted with higher accuracy using this.

In the present embodiment, an example in which three wave height discriminating units are used has been described. However, more wave height discriminating units and wave height measuring means using an A / D converter may be used.
According to the fourth embodiment, by using a plurality of wave height discriminating units, it is possible to perform sensitivity adjustment with higher accuracy while continuously performing radiation measurement.

  DESCRIPTION OF SYMBOLS 1 ... Radiation source, 2 ... Radiation detection part, 3 ... High voltage power supply, 4 ... Signal amplification part, 5, 5-1 to 5-3 ... Wave height discrimination part, 6 ... Calculation part, 7 ... Gain control part, 8 ... High pressure Power control unit, 9... Wave height discrimination level control unit.

Claims (6)

A radiation source for calibration, a radiation detector that converts radiation from the radiation source for calibration and radiation to be monitored into an electrical signal, a high-voltage power supply that supplies a high voltage to the radiation detector, and the radiation detector A signal amplifying unit for amplifying the signal from the signal, a wave height discriminating unit for discriminating the amplified signal from noise, an arithmetic unit for simultaneously calculating the discriminated signal with two different time constants, and the arithmetic unit A radiation monitor having a gain control unit that automatically adjusts the gain of the signal amplification unit based on the calculated correction value;
The wave height discrimination unit sets a wave height discrimination level within the wave height distribution range of the radiation source for calibration, and the calculation unit performs the radiation by the calculation process using the smaller time constant of the two different time constants. A radiation monitor characterized by calculating an instruction value of a source and calculating the correction value used for automatic adjustment of radiation sensitivity by a calculation process using a larger time constant.   2. The radiation monitor according to claim 1, wherein instead of the gain control unit, a high-voltage power source control unit that automatically adjusts the voltage of the high-voltage power source based on a correction value obtained by the calculation unit is used.   2. The radiation monitor according to claim 1, wherein a pulse height discrimination level control unit that automatically adjusts a wave height discrimination level of a wave height discrimination unit based on a correction value obtained by the calculation unit is used instead of the gain control unit. .   The radiation monitor according to claim 1, wherein the calculation unit performs attenuation correction of the radiation source when calculating a correction value.   The radiation monitor according to any one of claims 1 to 4, wherein the calculation unit excludes the correction value from being calculated when an instruction value of the radiation monitor becomes a predetermined value or more.   The wave height discriminating unit has a plurality of wave height discriminating units having different discrimination levels, and the calculation unit calculates the correction value based on a pulse count value in a predetermined range in which only a signal from a calibration radiation source exists. The radiation monitor according to claim 1, wherein:

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