CN102830420A - Method and system for calibrating working voltage of nuclear radiation detector - Google Patents

Abstract

The invention belongs to the technical field of nuclear radiation measurement, and in particular relates to a method and system for calibrating the working voltage of a nuclear radiation detector. On the basis of obtaining the pulse amplitude spectrum, the method firstly determines the time constant of the main amplifier, then determines the optimal operating voltage of the nuclear radiation detector under this time constant, and then determines the amplification factor of the amplifier and the threshold value of the discriminator under the optimal operating voltage of the detector . The plateau curve is measured under the condition that the discriminator threshold, amplifier magnification, time constant and other parameters are fixed, and the influence of high voltage fluctuation on the measurement data is determined by calculating the plateau slope. The invention helps prolong the service life of the detector, improves the gamma signal suppression ability, reduces the high-voltage discharge phenomenon, and avoids the situation that the plateau curve cannot be measured by random setting of parameters.

Description

Method and system for calibrating working voltage of nuclear radiation detector

technical field

The invention belongs to the technical field of nuclear radiation measurement, and in particular relates to a method and system for calibrating the working voltage of a nuclear radiation detector.

Background technique

The measurement of nuclear radiation intensity is one of the routine tasks in the field of nuclear research. The hardware structure of the measurement system is shown in Figure 1. The nuclear radiation detector converts the nuclear signal into an electrical signal for subsequent processing by the nuclear electronics system. The nuclear radiation detector must be applied with high voltage to work normally. As shown in Figure 1, the high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier. The size of the high voltage affects the actual performance of the nuclear radiation detector, which must be calibrated through experiments. On the one hand, the calibration of the working voltage of the nuclear radiation detector is to determine its optimal working voltage, and on the other hand, it is to determine the influence of high voltage fluctuations on the measurement data. The plateau curve measurement method is a traditional method for calibrating the working voltage of nuclear radiation detectors, and its hardware structure is shown in Figure 2. Under the condition that the discriminator threshold, amplifier magnification, time constant and other parameters are constant, after loading the radiation source, adjust the applied voltage of the detector from small to large, read the count rate (or count at a fixed measurement time) through the scaler, and measure the count Rate (or fixed measurement time count) versus applied voltage. The measured counting curve has an obvious counting plateau area, so it is called the plateau curve, as shown in Figure 3. The best working voltage is set in the ping, as shown by the downward arrow in Figure 3. In the counting ping area, the counting rate (or counting at a fixed measurement time) still increases with the increase of the working voltage, showing a slope of the ping, which is called a slope, which refers to the counting rate (or counting at a fixed measurement time) for every increase of 100V The percentage increase, which is calculated as:

$\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; \&times;</span>\frac{\mathrm{<span\; class="notranslate">\; 100</span>}}{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

V and N represent the voltage value and count value respectively. The slope represents the relative change in the count rate (or counting at a fixed measurement time) caused by high-voltage fluctuations. The smaller the slope, the smaller the impact of high-voltage fluctuations on the measurement data, and vice versa.

The plateau curve measurement is carried out under the condition that the discriminator threshold, amplifier magnification, and time constant are constant, and the working voltage determined by the plateau curve is under the current working conditions (discriminator threshold, amplifier magnification, time constant and other parameters are fixed. ) The best working voltage of the detector. The operating voltage of various types of nuclear radiation detectors has an interval. If the discriminator threshold, amplifier magnification, and time constant are properly selected, the plateau curve can be measured, and the optimum operating voltage determined by the plateau curve falls within this interval. In fact, the threshold value of the discriminator and the magnification of the amplifier have a great influence on the measurement of the plateau curve. The plateau curves measured by different discriminator thresholds and amplifier magnifications are different, and the determined operating voltages are also different. If the threshold value of the discriminator and the magnification of the amplifier are not selected properly, even the plateau curve cannot be measured, and the optimal working voltage cannot be determined. However, there is no reasonable method for the selection of the threshold value of the discriminator, the magnification of the amplifier, and the time constant, and there is a lot of randomness.

Because any point in the working voltage range of the detector can meet the measurement requirements, and the low working voltage helps to prolong the service life of the detector, improve the gamma signal suppression ability, and reduce the high-voltage discharge phenomenon, so the optimal working voltage of the present invention is The lower limit of the detector's operating voltage range. In order to measure the lower limit of the working voltage range of the detector, it is necessary to eliminate the influence of the threshold value of the discriminator, the magnification of the amplifier, and the time constant on the measurement. The traditional plateau curve measurement method can no longer meet the requirements.

Contents of the invention

The object of the present invention is to aim at the defect of prior art, provide a kind of nuclear radiation detector operating voltage calibration method and system based on pulse amplitude spectrum, this method under the condition of determined time constant, amplifier magnification, discriminator threshold value, measure Plateau curve, avoiding the situation that the plateau curve cannot be measured if the parameters are set arbitrarily.

The technical scheme of the present invention is as follows: a method for calibrating the working voltage of a nuclear radiation detector comprises the following steps:

(1) Adjust the applied high voltage of the nuclear radiation detector to any point within the estimated operating voltage range, and measure the pulse amplitude spectrum output by the main amplifier connected to the nuclear radiation detector through a multi-channel pulse amplitude analyzer. The abscissa of the amplitude spectrum is the channel number of the multi-channel pulse amplitude analyzer, and the ordinate is the count of the multi-channel pulse amplitude analyzer;

(2) Adjust the micro and integral time constants of the main amplifier, and select the time constant with high resolution in the pulse amplitude spectrum, resolution = main peak half maximum width / main peak address;

(3) Under the time constant selected in step (2), determine the optimal operating voltage of the nuclear radiation detector, the optimal operating voltage is the lower limit of the operating voltage range of the nuclear radiation detector, and determine the optimal The magnification of the main amplifier under the working voltage;

(4) Determine the optimal threshold value of the discriminator according to the pulse amplitude spectrum corresponding to the measured optimal working voltage and adjust the threshold value of the discriminator to the optimal value;

(5) When the discriminator threshold, amplifier magnification, and time constant are fixed, load the radiation source measurement plateau curve, and determine the influence of high voltage fluctuations on the measurement data by calculating the plateau slope.

Further, in the method for calibrating the working voltage of the nuclear radiation detector as described above, in step (2), while adjusting the micro and integral time constants of the main amplifier, use an oscilloscope to observe the shape of the output pulse of the main amplifier to ensure that its peak shape is not distorted .

Furthermore, in the method for calibrating the working voltage of the nuclear radiation detector as described above, in step (2), in the case of the same resolution in the pulse amplitude spectrum, a relatively small time constant is selected.

Further, in the method for calibrating the operating voltage of the nuclear radiation detector as described above, in step (3), the method for determining the optimal operating voltage of the nuclear radiation detector is: when the radiation source is loaded, the externally applied voltage of the nuclear radiation detector Adjust the high voltage from small to large, measure the pulse amplitude spectrum output by the main amplifier, adjust the magnification of the main amplifier to change the width of the pulse amplitude spectrum, and adjust the pulse amplitude spectrum until a counting valley with a certain width appears to achieve the discrimination between nuclear signals and noise signals It is required that the count valley refers to a region of low count between the nuclear signal and the noise signal in the pulse amplitude spectrum.

Further, in the method for calibrating the operating voltage of the nuclear radiation detector as described above, in step (4), the method for determining the optimal threshold of the discriminator is: determining the point M corresponding to the discrimination threshold in the pulse amplitude spectrum, and the M The point is located at the bottom of the counting valley of the pulse amplitude spectrum; the abscissa address m' of the multi-channel pulse amplitude analyzer corresponding to the discrimination threshold M point is substituted into the multi-channel pulse amplitude analyzer address and voltage value conversion formula A=pm+A ₀ , find the optimal threshold A', where m is the track address, A is the voltage value corresponding to m, p is a coefficient, and A ₀ is a constant.

Furthermore, in the method for calibrating the working voltage of the nuclear radiation detector as described above, in step (4), the method of adjusting the threshold of the discriminator to the optimum value is: use a signal generator to input a square wave pulse signal to the main amplifier, and use an oscilloscope to Observe the output of the main amplifier, adjust the amplitude of the square wave pulse signal, so that the main amplifier outputs a pulse signal with an amplitude of A'; use an oscilloscope to observe the output of the discriminator connected to the main amplifier, and adjust the threshold of the discriminator from small to large until the discriminant Just until there is no pulse signal output from the discriminator, at this time the actual threshold of the discriminator has been adjusted to the optimal threshold A'.

Further, in the method for calibrating the working voltage of the nuclear radiation detector as described above, in step (5), the method of measuring the plateau curve is: after loading the radiation source, adjust the nuclear radiation detector from small to large and apply high voltage, and read the count through the calibrator Counting rate or fixed measurement time counting, the curve of measuring counting rate or fixed measuring time counting with the change of high voltage applied to the nuclear radiation detector.

A nuclear radiation detector operating voltage calibration system, comprising a time constant determining device, an optimal operating voltage determining device, a discriminator threshold adjusting device, and a plateau curve measuring device, wherein the time constant determining device and the optimal operating voltage determining The device adopts the same hardware structure, including nuclear radiation detectors. The nuclear radiation detectors are connected to the preamplifier and the main amplifier in sequence. The high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier. The multi-channel pulse amplitude analyzer is connected to the computer; the discriminator threshold adjustment device includes a signal generator, the signal generator is connected to the main amplifier, the main amplifier is respectively connected to the amplitude discriminator and the oscilloscope, and the amplitude discriminator is connected to the oscilloscope ; The plateau curve measuring device includes a nuclear radiation detector, the nuclear radiation detector is connected to the preamplifier and the main amplifier in sequence, the high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier, and the main amplifier is connected to the amplitude discriminator , the amplitude discriminator is connected to the scaler.

Further, in the nuclear radiation detector working voltage calibration system as described above, the main amplifier of the time constant determining device is also connected to an oscilloscope.

The beneficial effects of the present invention are as follows: the present invention carries out the calibration of nuclear radiation detector operating voltage based on the pulse amplitude spectrum measurement method, compared with the plateau curve measurement method of the prior art, the selection of time constant, amplifier magnification, and discriminator threshold value is much better. Arbitrary again, the pulse amplitude spectrometry method provides a complete set of methods for the selection of these parameters. The optimal operating voltage of the nuclear radiation detector determined by the pulse amplitude spectrum method is the lower limit of the operating voltage range of the detector, which is the minimum operating voltage for the detector to work normally, which is smaller and lower than the optimal operating voltage of the detector determined by the plateau curve measurement method. The working voltage helps to prolong the service life of the detector, improve the gamma signal suppression ability, and reduce the high-voltage discharge phenomenon. Under the conditions of time constant, amplifier magnification and discriminator threshold value determined by the pulse amplitude spectrum measurement method, the plateau curve is measured, which avoids the situation that the plateau curve cannot be measured by random setting of parameters.

Description of drawings

Fig. 1 is a schematic diagram of the hardware structure of the nuclear radiation intensity measurement system;

Fig. 2 is a schematic diagram of the hardware structure of the platen curve measuring method;

Fig. 3 is a schematic diagram of a flat curve;

Fig. 4 is method flowchart of the present invention;

Fig. 5 is the hardware structure schematic diagram that the present invention determines time constant;

Fig. 6 is a schematic diagram of the hardware structure of the present invention to determine the optimal working voltage of the detector;

FIG. 7 is a schematic diagram of the hardware structure of the discriminator threshold adjustment of the present invention;

Figure 8 is a schematic diagram of the pulse amplitude spectrum;

Fig. 9 is when applied voltage 1150V in the embodiment ³ He proportional counter pulse amplitude spectrum;

(a) Integral and integral of the main amplifier are 4 μs each, (b) Integral of the main amplifier is 2 μs and differential is 4 μs;

Fig. 10 is the pulse amplitude spectrum of He ^proportional counter tube under different applied voltages in the embodiment;

(a) 1150V, (b) 1250V;

Fig. 11 is two plateau curves measured with the same discriminator threshold value and other experimental conditions (magnification, time constant, etc.) in the embodiment; (a) 0.46V, (b) 1.46V.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The hardware structure of the nuclear radiation detector operating voltage calibration system provided by the present invention includes a time constant determining device, an optimal operating voltage determining device, a discriminator threshold adjusting device, and a plateau curve measuring device, wherein the time constant determining device The structure is shown in Figure 5, and the structure of the optimal working voltage determination device is shown in Figure 6. The two devices use basically the same hardware structure, including nuclear radiation detectors, which are connected to preamplifiers and main amplifiers in sequence. The high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier, the main amplifier is connected to the multi-channel pulse amplitude analyzer, and the multi-channel pulse amplitude analyzer is connected to the computer. The main amplifier of the time constant determining device is also connected to an oscilloscope, and the shape of the output pulse of the main amplifier is observed through the oscilloscope to ensure that the peak shape is not distorted.

The structure of the discriminator threshold adjustment device is shown in Figure 7, including a signal generator, the signal generator is connected to the main amplifier, the main amplifier is respectively connected to the amplitude discriminator and the oscilloscope, and the amplitude discriminator is connected to the oscilloscope.

Described plateau curve measurement device as shown in Figure 2, comprises nuclear radiation detector, and nuclear radiation detector is connected preamplifier and main amplifier in sequence, and high-voltage power supply is transferred on the nuclear radiation detector by preamplifier, and main amplifier It is connected with the amplitude discriminator, and the amplitude discriminator is connected with the scaler.

As shown in Figure 4, the nuclear radiation detector working voltage calibration method provided by the present invention, on the basis of obtaining the pulse amplitude spectrum, first determines the time constant of the main amplifier, and then determines the optimal working voltage of the nuclear radiation detector under the time constant , and then determine the amplifier magnification and the discriminator threshold under the optimal working voltage of the detector. Under this condition (discriminator threshold, amplifier magnification, time constant and other parameters are fixed), the plateau curve is measured, and the impact of high voltage fluctuations on the measured data is determined by calculating the plateau slope. Specifically include the following steps:

(1) Since the working voltage range of the same type of nuclear radiation detectors will not differ too much, adjust the applied high voltage of the nuclear radiation detector to any point within the estimated working voltage range, and measure and nuclear The pulse amplitude spectrum that the main amplifier output that radiation detector is connected, as shown in Figure 8, the abscissa of described pulse amplitude spectrum is the channel number of multi-channel pulse amplitude analyzer, and the ordinate is the count of multi-channel pulse amplitude analyzer .

(2) Adjust the micro and integral time constants of the main amplifier, and select the time constant with high resolution in the pulse amplitude spectrum, resolution = main peak half-height width/main peak address, the hardware structure is shown in Figure 5; when measuring the pulse amplitude spectrum , it is also necessary to use an oscilloscope to observe the shape of the output pulse of the main amplifier to ensure that it is not distorted; for the same nuclear radiation detector, since the larger the time constant is, the wider the output pulse of the main amplifier is, and the higher the leakage count rate is, so in the same pulse amplitude spectrum In order to reduce the missing count rate under the premise of resolution, choose a small time constant.

(3) Under the time constant selected in step (2), determine the optimal working voltage of the nuclear radiation detector. The hardware structure is shown in Figure 6; the method is to load the radiation source and adjust the high voltage from small to large (according to the actual Generally, the starting point of voltage adjustment is 100V, of course, it can also be adjusted from 0V), measure the output pulse amplitude spectrum of the main amplifier, adjust the magnification of the main amplifier to adjust the pulse amplitude spectrum to a suitable width, until the pulse amplitude spectrum appears as shown in Figure 8 Shown is a counting valley with a certain width (reaching the requirements of the nuclear signal and noise signal screening), the counting valley refers to a low count area between the nuclear signal and the noise signal in the pulse amplitude spectrum, and the counting valley width can be The output pulse amplitude spectrum of the main amplifier covers 1/10 of the width of the multi-channel interval. The applied voltage at this time is the best working voltage of the detector and the lower limit of the working voltage range of the detector. The magnification of the amplifier at this time is the amplifier under the best working voltage. gain.

(4) According to the measured pulse amplitude spectrum (the main amplifier amplification factor and time constant are fixed, and the pulse amplitude spectrum corresponding to the optimal working voltage) the optimal threshold of the discriminator is determined and the threshold of the discriminator is adjusted to the optimal value. The pulse amplitude spectrum is measured as shown in Figure 8. The nuclear signal is located on the right side of the spectrum, and the noise is located on the left side of the spectrum. There is a low count area between the nuclear signal and the noise, which is called the count valley. The threshold is set at the bottom of the counting valley, that is, the place where the count is the smallest, generally located in the middle of the counting valley, as shown at point M in Figure 8. The determined discrimination threshold M point corresponds to the abscissa address m' of the multi-channel pulse amplitude analyzer, and the address m' is substituted into the address and voltage value conversion formula A=pm+A ₀ of the multi-channel pulse amplitude analyzer (the formula is given by The specification of the multi-channel pulse amplitude analyzer is given; m is the channel address, A is the voltage value corresponding to m, p is the coefficient, and A ₀ is a constant), and the optimal threshold value A' is obtained. To get the optimal threshold A', it is necessary to adjust the threshold of the discriminator to this value. The hardware structure is shown in Figure 7. The threshold adjustment of the discriminator requires the help of a signal generator and an oscilloscope. The parameters such as the amplification factor and time constant of the main amplifier remain unchanged. Use a signal generator to input a square wave pulse signal to the main amplifier, use an oscilloscope to observe the output of the main amplifier, and adjust the amplitude of the square wave pulse signal so that the main amplifier outputs a pulse with an amplitude of A' Signal. Use an oscilloscope to observe the output of the discriminator, and adjust the threshold of the discriminator from small to large until there is no pulse signal output from the discriminator, indicating that the actual threshold of the discriminator has been adjusted to the optimal threshold A'.

计算出坪斜。(5) When the threshold value of the discriminator, the magnification of the amplifier, and the time constant are fixed, load the measurement plateau curve of the radiation source, and determine the influence of high-voltage fluctuations on the measurement data by calculating the plateau slope. The hardware structure is shown in Figure 2; Under the condition that the discriminator threshold, amplifier magnification, time constant and other parameters are constant, after loading the radiation source, adjust the applied voltage of the detector from small to large, read the count rate (or count at a fixed measurement time) through the scaler, and measure the count rate (or fixed measurement time counting) curves as a function of applied voltage. Measure the flat curve shown in Figure 3, according to the flat slope calculation formula

Calculate the slope.

Example

The nuclear radiation detector uses ³ He proportional counter tube, and the radiation source uses ²⁴¹ Am-Be isotope neutron source. The time constant is determined using the pulse amplitude spectrum measurement method, and its hardware structure is shown in Figure 5. The working voltage of the ³ He proportional counter tube is generally between 1000 and 1500V. During the experiment, the applied voltage of the ³ He proportional counter tube was adjusted to 1150V. Under this high voltage, the resolution of the pulse amplitude spectrum is high and the output of the main amplifier is not distorted. The minimum time constant is 2 μs for the integration of the main amplifier and 4 μs for the differential. As shown in Figure 9, the main peak of the pulse amplitude spectrum of the main amplifier with 4 μs of differentiation and integration (the situation in Figure 9(a)) splits, and the resolution is obviously worse than that of the main amplifier integration at 2 μs and differential at 4 μs (in the case of Figure 9(b) ) of the pulse amplitude spectrum resolution.

Under the time constant of main amplifier integration 2μs and differential 4μs, the best working voltage of the detector is determined by pulse amplitude spectrum measurement method, the hardware structure is shown in Figure 6, and the measurement results are shown in Figure 10. ³ The optimal working voltage of the He proportional counter tube (that is, the minimum working voltage, the lower limit of the working voltage range) is 1250V, and the magnification of the main amplifier under the best working voltage is 30.

According to the measured pulse amplitude spectrum shown in Figure 10(b), the optimal threshold value of the discriminator is determined to be 0.46V by using the "Method for Determining the Discrimination Threshold of the Pulse Amplitude Discriminator", and the threshold value of the discriminator is adjusted to this value.

Parameters such as discriminator threshold, amplifier magnification, and time constant are fixed, and the neutron source measurement plateau curve is loaded, and the results are shown in Fig. 11(a). Ping length 200V (1150～1350V), Ping slope 1.6%/100V.

The amplification factor and time constant of the amplifier are fixed, the threshold value of the discriminator is adjusted from 0.46V to 1.46V, and the neutron source measurement plateau curve is loaded. The results are shown in Figure 11(b), no plateau curve with counting plateaus was detected, which verifies that the selection of the discriminator threshold has a great influence on the plateau curve measurement, and if the selection is inappropriate, plateau curves cannot even be measured.

The preamplifier model QF07 used in this embodiment, the main amplifier model BH1218, the multi-channel pulse amplitude analyzer model 2048, the signal generator model SU5102, the amplitude discriminator model BH1299A, the oscilloscope model TDS2024, and the scaler model BH1220N.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (9)

1. A method for calibrating the operating voltage of a nuclear radiation detector, comprising the steps of: (1) Adjust the applied high voltage of the nuclear radiation detector to any point within the estimated operating voltage range, and measure the pulse amplitude spectrum output by the main amplifier connected to the nuclear radiation detector through a multi-channel pulse amplitude analyzer. The abscissa of the amplitude spectrum is the channel number of the multi-channel pulse amplitude analyzer, and the ordinate is the count of the multi-channel pulse amplitude analyzer; (2) Adjust the micro and integral time constants of the main amplifier, and select the time constant with high resolution in the pulse amplitude spectrum, resolution = main peak half maximum width / main peak address; (3) Under the time constant selected in step (2), determine the optimal operating voltage of the nuclear radiation detector, the optimal operating voltage is the lower limit of the operating voltage range of the nuclear radiation detector, and determine the optimal The magnification of the main amplifier under the working voltage; (4) Determine the optimal threshold value of the discriminator according to the pulse amplitude spectrum corresponding to the measured optimal working voltage and adjust the threshold value of the discriminator to the optimal value; (5) When the discriminator threshold, amplifier magnification, and time constant are fixed, load the radiation source measurement plateau curve, and determine the influence of high voltage fluctuations on the measurement data by calculating the plateau slope. 2. The method for calibrating the working voltage of the nuclear radiation detector according to claim 1, characterized in that: in step (2), while adjusting the differential and integral time constants of the main amplifier, use an oscilloscope to observe the shape of the output pulse of the main amplifier, Make sure that its peak shape is not distorted. 3. The method for calibrating the working voltage of nuclear radiation detectors according to claim 2, characterized in that in step (2), a relatively small time constant is selected when the resolution in the pulse amplitude spectrum is the same. 4. The method for calibrating the working voltage of the nuclear radiation detector according to any one of claims 1-3, characterized in that: in step (3), the method for determining the optimum working voltage of the nuclear radiation detector is: In the case of radiation sources, adjust the applied high voltage of the nuclear radiation detector from small to large, measure the pulse amplitude spectrum output by the main amplifier, adjust the magnification of the main amplifier to change the width of the pulse amplitude spectrum, and adjust the pulse amplitude spectrum to a certain width Up to the counting valley of the pulse amplitude spectrum, the requirement of nuclear signal and noise signal screening is met. The counting valley refers to a region with a low count between the nuclear signal and the noise signal in the pulse amplitude spectrum. 5. The method for calibrating the working voltage of nuclear radiation detectors according to claim 4, characterized in that: in step (4), the method of determining the optimal threshold of the discriminator is: determining the corresponding discriminant threshold in the pulse amplitude spectrum The point M is located at the bottom of the counting valley of the pulse amplitude spectrum; the abscissa address m' of the multi-channel pulse amplitude analyzer corresponding to the discrimination threshold M point is substituted into the address and voltage value conversion of the multi-channel pulse amplitude analyzer Formula A=pm+A ₀ , find the best threshold A', Among them, m is the track address, A is the voltage value corresponding to m, p is a coefficient, and A ₀ is a constant. 6. The method for calibrating the operating voltage of nuclear radiation detectors as claimed in claim 5, characterized in that: the method for adjusting the discriminator threshold to the optimum value is: use a signal generator to input a square wave pulse signal to the main amplifier, and use an oscilloscope to Observe the output of the main amplifier, adjust the amplitude of the square wave pulse signal, so that the main amplifier outputs a pulse signal with an amplitude of A'; use an oscilloscope to observe the output of the discriminator connected to the main amplifier, and adjust the threshold of the discriminator from small to large until the discriminant Just until there is no pulse signal output from the discriminator, at this time the actual threshold of the discriminator has been adjusted to the optimal threshold A'. 7. The method for calibrating the working voltage of the nuclear radiation detector according to claim 6, wherein in step (5), the method of measuring the plateau curve is: after loading the radiation source, adjusting the nuclear radiation detector from small to large and applying high voltage, Read the count rate or fixed measurement time count through the scaler, and measure the curve of the change of the count rate or fixed measurement time count with the high voltage applied to the nuclear radiation detector. 8. A nuclear radiation detector operating voltage calibration system, characterized in that: it includes a time constant determining device, an optimal operating voltage determining device, a discriminator threshold adjusting device, and a plateau curve measuring device, wherein the time constant determining device It adopts the same hardware structure as the optimal working voltage determination device, including nuclear radiation detectors. The nuclear radiation detectors are connected to the preamplifier and the main amplifier in sequence. The high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier. The main amplifier It is connected with a multi-channel pulse amplitude analyzer, and the multi-channel pulse amplitude analyzer is connected with a computer; the discriminator threshold adjustment device includes a signal generator, and the signal generator is connected with a main amplifier, and the main amplifier is respectively connected with an amplitude discriminator and an oscilloscope, and the amplitude The discriminator is connected with the oscilloscope; the plateau curve measuring device includes a nuclear radiation detector, and the nuclear radiation detector is connected to the preamplifier and the main amplifier in sequence, and the high-voltage power supply is transferred to the nuclear radiation detector through the preamplifier, and the main amplifier The amplifier is connected to the amplitude discriminator, and the amplitude discriminator is connected to the scaler. 9. The nuclear radiation detector operating voltage calibration system according to claim 8, characterized in that: the main amplifier of the time constant determining device is also connected to an oscilloscope.

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