JP2013088380A - Portable radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a portable radiation detector for achieving temperature compensation means by a relative simple constitution.SOLUTION: A portable radiation detector 1 includes: a scintillator 11 for emitting light when radiation is applied; a photodetector 12 for converting light emitted from the scintillator 11 into an electric signal; and a power supply part 20 including a battery 21 for supplying bias voltage to the photodetector 12 and connecting a temperature sensor 25 for changing a current value in accordance with a temperature change between the battery 21 and the photodetector 12.

Description

  The present invention relates to a portable radiation detector.

  A radiation detector having a dosimeter for detecting radiation has a unique temperature characteristic depending on its type. Therefore, in order to measure radiation with stable accuracy, it is necessary to perform temperature compensation on the temperature characteristics of the radiation detector, and various methods have been considered and put into practical use.

  For example, there is a technique described in Patent Document 1. In this technique, the preamplifier used for converting the output current pulse of the radiation detector into a voltage pulse has a temperature compensation function. More specifically, the negative feedback capacitor of the preamplifier has a negative temperature characteristic to compensate for the temperature characteristic of the radiation detector.

  Further, there is a technique described in Patent Document 2. In this technique, temperature measuring means for measuring the ambient temperature of the photomultiplier tube is provided, and the ambient temperature and the bias voltage of the photomultiplier tube for obtaining a predetermined dose rate detection sensitivity at each ambient temperature are 1 Remember one-on-one. When the temperature measuring means measures the ambient temperature, the bias voltage of the photomultiplier tube corresponding to the ambient temperature is read, and the bias voltage is applied to the photomultiplier tube.

Japanese Examined Patent Publication No. 4-12048 JP 2003-35779 A

  In the technique described in Patent Document 1, a negative temperature coefficient appearing in the peak value of the output voltage pulse of the preamplifier is compensated by the negative feedback capacitance of the negative temperature coefficient provided in the preamplifier due to the temperature characteristics of the radiation detector. Therefore, there is a problem that a negative temperature coefficient appears in the pulse width, and the compensation is reduced by the gain-frequency characteristic of the main amplifier provided for amplifying the output voltage pulse of the preamplifier.

  Further, in the case of the technique described in Patent Document 2, it is necessary to realize a means for storing the temperature and the bias voltage in association with each other and a means for performing a predetermined calculation process by, for example, a microcomputer, so that the circuit design is complicated. In addition, problems such as increased cost burden and hindering downsizing of the radiation detector may occur.

  An object of the present invention is to provide a portable radiation detector that realizes temperature compensation means with a relatively simple configuration.

  According to the present invention, there is provided a scintillator that emits light when exposed to radiation, a photodetector that converts light emitted by the scintillator into an electrical signal, and a battery that supplies a bias voltage to the photodetector, There is provided a portable radiation detector having a power supply unit connected with a temperature sensor that changes a current value according to a temperature change between a battery and the photodetector.

  According to the present invention, there is provided a portable radiation detector that realizes temperature compensation means with a relatively simple configuration.

It is an example of the functional block diagram of the portable radiation detection of this embodiment. It is a figure for demonstrating the effect of the portable radiation detector of this embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  FIG. 1 is an example of a functional block diagram of a portable radiation detector 1 of the present embodiment. As shown in FIG. 1, the portable radiation detector 1 of the present embodiment includes a radiation sensor unit 10, a power supply unit 20, an analog signal processing circuit 30, and an output unit 40. Hereinafter, each component will be described.

  The radiation sensor unit 10 includes a scintillator 11 and a photodetector 12. The scintillator 11 emits light when exposed to radiation. In the present embodiment, any conventional scintillator can be employed. The photodetector 12 converts the light emitted from the scintillator 11 into an electrical signal (voltage pulse signal), and then inputs the voltage pulse signal to the analog signal processing circuit 30. The photodetector 12 can be, for example, a silicon photomultiplier, a high electron multiplier, or the like, but considering the downsizing of the portable radiation detector 1, it is preferably a silicon photomultiplier. Since such a radiation sensor unit 10 can be realized in accordance with the prior art, a detailed description thereof is omitted here.

  The power supply unit 20 includes a battery 21 for supplying a bias voltage to the photodetector 12, and a temperature sensor 25 whose current value changes according to a temperature change is connected between the battery 21 and the photodetector 12. doing.

  The temperature value of the temperature sensor 25 changes according to the temperature change. For example, a temperature transducer can be employed as the temperature sensor 25. Such a temperature sensor 25 is known to have linearity in changes in temperature and current value.

  The power supply unit 20 of the present embodiment connects the temperature sensor 25 between the battery 21 and the photodetector 12 to linearly change the value of the bias voltage supplied to the photodetector 12 according to the temperature. It is configured as follows. And the portable radiation detector 1 of this embodiment is provided with such a power supply part 20, and is a temperature compensation means which compensates the negative temperature coefficient which appears in the peak value of the voltage pulse signal which the photodetector 12 outputs. Is realized. Hereinafter, an example of the configuration of such a power supply unit 20 will be described with reference to FIG.

  The power supply unit 20 illustrated in FIG. 1 includes a booster circuit 22, a voltage regulator 23, a voltage correction resistor 24, a voltage follower 26, and a voltage adjustment circuit 27 in addition to the battery 21 and the temperature sensor 25.

  According to such a power supply unit 20, the voltage supplied from the battery 21 is boosted to a voltage necessary for the operation of the photodetector 12 by the booster circuit 22, and then converted into an appropriate voltage by the voltage adjustment circuit 27. , And input to the anode or cathode of the photodetector 12. Further, the voltage input to the voltage regulator 23 after being boosted to an appropriate voltage by the booster circuit 22 is reduced to a constant pressure by reducing the absolute value of the voltage by a predetermined amount by the voltage regulator 23, and then is supplied to the voltage correction resistor 24. It is input to the cathode or anode of the photodetector 12 via the voltage follower 26. The temperature sensor 25 is connected between the voltage correction resistor 24 and the voltage follower 26 and is connected to the ground 28.

Here, the voltage input to the voltage correction resistor 24 is V ₀ , the voltage output from the voltage follower 26 and input to the photodetector 12 is V (−), the current value flowing from the temperature sensor 25 is I, and the voltage correction is performed. When the resistance of the resistor 24 is R, these are represented by the following formula (1).

  As described above, the temperature value of the temperature sensor 25 changes according to the temperature change. Therefore, if the change in temperature is ΔT, the temperature coefficient of the temperature sensor 25 is a, and the change in the current value flowing from the temperature sensor 25 is ΔI, these are expressed by the following equation (2).

  From the relationship of the above equations (1) and (2), the change ΔV (−) corresponding to the temperature change of the voltage output from the body follower 26 and input to the photodetector 12 is expressed by the following equation (3). Represented.

  Based on the above relationship, ΔV (−) is multiplied by a negative coefficient with respect to the gain temperature dependency of the radiation sensor unit 10, whereby the temperature dependency of the peak value of the voltage pulse signal output from the radiation sensor unit 10 is increased. Less.

  Note that the configuration of the power supply unit 20 shown in FIG. 1 is merely an example, and other modes can be used as long as desired temperature compensation means can be realized. That is, the aspect of connecting the temperature sensor 25 between the battery 21 and the photodetector 12 may be changed, or a plurality of other components (22, 23, 24, 26, 27) shown in FIG. 1 may not be included, or other parts not shown in FIG. 1 may be included.

  A voltage pulse signal output from the radiation sensor unit 10 is input to the analog signal processing circuit 30. Since the analog signal processing circuit 30 acquires only the voltage pulse signal output from the photodetector 12, a DC component is removed by the preceding circuit. After that, a certain voltage threshold is provided for the voltage pulse signal, only the signal exceeding the threshold is accumulated in the capacitor, and the accumulated voltage value is output from the analog signal processing circuit 30 and input to the output unit 40. The

  The output unit 40 outputs a radiation detection result using the signal input from the analog signal processing circuit 30. For example, the output unit 40 may output a 1 cm dose equivalent according to the radiation dose input to the radiation sensor unit 10. The output means by the output unit 40 is not particularly limited, and can be realized by using any output device such as a display, a speaker, and a printing device.

<< Example >>
<Example 1>
<Configuration of radiation measurement device>
The radiation sensor unit 10 was configured using a cerium-activated gadolinium gallium garnet for the scintillator 11 and a silicon photomultiplier for the photodetector 12. In this case, the temperature dependence of the gain of the radiation sensor unit 10 has a negative dependence of about −5% / ° C.

The power supply unit 20 has the configuration shown in FIG. The temperature coefficient a of the temperature sensor 25 is 1 × 10 ⁻⁶ , the voltage V ₀ input to the voltage correction resistor 24 is 23.3 V, and the resistance R of the voltage correction resistor 24 is 56 kΩ. In this case, based on the above formulas (2) and (3), the change ΔV in the voltage input to the photodetector 12 is about −0.05 V / ° C.

<Comparative Example 1>
<Configuration of radiation measurement device>
Except that the power supply unit 20 does not have the temperature sensor 25, the configuration is the same as that of the first embodiment.

<Comparative example 2>
<Configuration of radiation measurement device>
Instead of the temperature sensor 25, the power supply unit 20 has the same configuration as that of the first embodiment except that the power supply unit 20 has a thermistor whose resistance value changes according to the temperature.

<Measurement>
The radiation measuring apparatus of Example 1, Comparative Example 1 and Comparative Example 2 is an environment in which the surrounding radiation environment does not change greatly, specifically, JIS_z_04333_2006, the surrounding γ-ray background is 1 cm dose equivalent rate of 0.25 or less Cover the radiation measurement device with a shielding material such as lead, and place a 10MBq cesium standard radiation source so that the ambient radiation is negligible. The ambient temperature of the radiation measurement device is -25 ° C to 50 ° C. The change of the radiation measurement result was observed while changing between. Then, using the indicated value at 20 ° C. as a reference, the percentage of the value obtained by subtracting the reference value from the indicated value at each ambient temperature with respect to the reference value was obtained.

  The results are shown in Table 1.

  Moreover, the result of having plotted these data on the graph is shown in FIG. The vertical axis represents the change rate of the indicated value, and the horizontal axis represents the ambient temperature of the radiation measuring apparatus.

  From Table 1 and FIG. 2, it can be seen that the rate of change in Comparative Example 1 and Comparative Example 2 fluctuates greatly according to the temperature change. On the other hand, it can be seen that Example 1 is almost unaffected by temperature changes and can output a substantially constant measurement result. Furthermore, it can be seen that in Example 1, the change rate of the measurement result can be suppressed to within 10% in the range where the ambient temperature is −25 ° C. or more and 50 ° C. or less.

  Here, the temperature range of -25 ° C or more and 50 ° C or less is based on the standard of X-ray and γ-ray dose equivalent rate survey meter specified in JIS_z_04333_2006, and is assumed to be used at extremely high or very low temperatures. Yes. In such a temperature range, the change rate of the measurement result is preferably within 50%, preferably within 20%, and more preferably within 10%. When it is suppressed to 50% or less, it conforms to the standard for the dose equivalent rate survey meter for special outdoor X-rays and γ-rays stipulated in JIS_z_04333_2006, and can be used at extremely high or very low temperatures. When the temperature is kept within 20%, the rate of change equivalent to the standard of dose equivalent rate survey meter for outdoor X-rays and γ-rays specified in JIS_z_04333_2006 can be achieved at extremely high or very low temperatures. There is a merit that enables highly accurate measurement. If it is kept within 10%, the rate of change equivalent to the standard of indoor X-ray and γ-ray dose equivalent rate survey meter defined in JIS_z_04333_2006 can be achieved at extremely high or very low temperatures. There is an advantage that more accurate measurement is possible.

  According to the radiation measuring apparatus of the present embodiment described above, a portable radiation detector that is not easily affected by the ambient temperature is realized.

  Further, the radiation measuring apparatus of the present embodiment has a relatively simple configuration in which a temperature sensor 25 whose current value changes according to a temperature change is connected between the battery 21 and the photodetector 12, and the temperature compensation means. Is realized. That is, the temperature compensation means can be realized without requiring expensive parts such as a microcomputer and many other parts. As a result, the circuit design is facilitated, the cost burden can be reduced, and the radiation measuring apparatus can be further downsized.

DESCRIPTION OF SYMBOLS 1 Portable radiation detector 10 Radiation sensor part 11 Scintillator 12 Photodetector 20 Power supply part 21 Battery 22 Booster circuit 23 Voltage regulator 24 Voltage correction resistor 25 Temperature sensor 26 Voltage follower 27 Voltage adjustment circuit 28 Ground 30 Analog signal processing circuit 40 Output section

Claims (3)

A scintillator that emits light when exposed to radiation,
A photodetector that converts light emitted by the scintillator into an electrical signal;
A power supply unit having a battery for supplying a bias voltage to the photodetector, and connecting a temperature sensor whose current value changes according to a temperature change between the battery and the photodetector;
A portable radiation detector. The portable radiation detector according to claim 1, wherein
A portable radiation detector in which a temperature-dependent change of an electric signal output from the photodetector is within 50% in a range of −25 ° C. to 50 ° C. The portable radiation detector according to claim 1 or 2,
The photodetector is a portable radiation detector which is a silicon photomultiplier.

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