A method of processing a proportional counter

Abstract

The application relates to the technical field of radioactivity measurement, and provides a processing method of a proportional counter, which comprises the following steps: introducing standard tritium gas into the proportional counter to obtain a target pulse signal of the standard tritium gas; obtaining a first charge integral, a second charge integral and a target shape discrimination factor according to the target pulse signal; and obtaining a discrimination line according to the first charge integral and the target shape discrimination factor, wherein the target shape discrimination factor is located below the discrimination line. The processing method of the proportional counter can reduce the background count rate in the proportional counter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radioactivity measurement, and particularly relates to a processing method of a proportional counter. BACKGROUND

[0002] As a kind of radionuclide, tritium can emit low-energy beta rays with average energy of 5.9 keV and maximum energy of 18.6 keV. Tritium is widely present in effluent of nuclear power plants. With the increasing development of nuclear energy utilization, the influence of tritium on environment and human health is also increasingly concerned. Therefore, it is of great significance to monitor the activity of tritium in air.

[0003] A proportional counter is selected as a radiation detector in a tritium gas measuring device with low activity level. In the related technology, the proportional counter adopts a pulse amplitude analysis method, and pulses with signal amplitude within a set threshold range are all recorded as effective signals. Since most of the pulse amplitudes of background signals generated by environmental gamma rays and cosmic rays in the proportional counter are the same as or similar to those of tritium signals, the lower limit of detection of the proportional counter is increased, which cannot meet the needs of actual environmental monitoring. SUMMARY

[0004] Therefore, embodiments of the present application aim to provide a processing method of a proportional counter, which can reduce the background count rate in the proportional counter.

[0005] To achieve the above object, the technical scheme of the embodiments of the present application is as follows:

[0006] The embodiments of the present application disclose a processing method of a proportional counter, which comprises:

[0007] passing standard tritium gas into the proportional counter to obtain target pulse signals of the standard tritium gas;

[0008] obtaining a first charge integral, a second charge integral and a target shape discrimination factor according to the target pulse signals;

[0009] obtaining a discrimination line according to the first charge integral and the target shape discrimination factor, wherein the target shape discrimination factor is located below the discrimination line.

[0010] In an embodiment, the processing method comprises:

[0011] passing to-be-measured tritium gas into the proportional counter, and determining a pulse signal corresponding to a to-be-determined shape discrimination factor of the to-be-measured tritium gas as an effective pulse signal in a case where the to-be-determined shape discrimination factor is located below the discrimination line;

[0012] obtaining an activity value of the to-be-measured tritium gas according to the effective pulse signal.

[0013] In one embodiment, the step of obtaining the first charge integration and the second charge integration comprises:

[0014] According to the target pulse signal, a long gate time window and a short gate time window are set, and the first charge integration in the long gate time window and the second charge integration in the short gate time window are obtained.

[0015] In one embodiment, the target shape discrimination factor is equal to the ratio of the difference between the first charge integration and the second charge integration to the first charge integration.

[0016] In one embodiment, before obtaining the first charge integration, the second charge integration and the target shape discrimination factor according to the target pulse signal, the processing method comprises:

[0017] The target pulse signal is amplified by a preamplifier.

[0018] In one embodiment, the type of the preamplifier is current sensitive.

[0019] In one embodiment, after amplifying the target pulse signal by the preamplifier, the processing method comprises:

[0020] The amplified target pulse signal is digitally converted.

[0021] In one embodiment, the digital conversion is performed by a waveform acquisition card.

[0022] In one embodiment, the pulse amplitude of the digitized target pulse signal is determined to be within a first preset interval.

[0023] In one embodiment, the ratio between the activity value of the standard tritium gas and the activity value of the background of the proportional counter is not less than two orders of magnitude.

[0024] In one embodiment, the first charge integration, the second charge integration and the target shape discrimination factor are obtained by a signal processing circuit.

[0025] In one embodiment, according to the first charge integration and the target shape discrimination factor, the step of obtaining a discrimination line comprises:

[0026] A relationship chart of the target shape discrimination factor and the first charge integration is constructed, the number of the first charge integration and the target shape discrimination factor is greater than a first preset value, and each first charge integration and a corresponding target shape discrimination factor form a target coordinate.

[0027] A line is set as the discrimination line in the relation chart, so that all the target coordinates are below the discrimination line.

[0028] The embodiment of the present application discloses a processing method of a proportional counter. The target pulse signal of standard tritium gas is acquired, and the first charge integral, the second charge integral and the target shape discrimination factor are acquired according to the target pulse signal. Finally, the discrimination line is acquired through the first charge integral and the target shape discrimination factor. The target shape discrimination factor is below the discrimination line, that is, all the target shape discrimination factors below the discrimination line correspond to the pulse signals of standard tritium gas. In this way, on one hand, when measuring the activity of the to-be-measured tritium gas, the same discrimination line can be used to only count and calculate the pulse signals corresponding to the target shape discrimination factors below the discrimination line, so that most of the background signals can be discriminated without losing the activity measurement efficiency of the tritium gas, thereby effectively reducing the background count rate, lowering the detection lower limit of the proportional counter and meeting the needs of actual environmental monitoring. On the other hand, the proportional counter itself is not modified, so that different specifications of proportional counters can be selected for different measurements, and the flexibility is high. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The pulse amplitude distribution diagram of the background signal and the tritium signal;

[0030] Figure 2 The flowchart of the processing method of the proportional counter provided by the embodiment of the present application;

[0031] Figure 3 The connection diagram of the proportional counter, the preamplifier, the waveform acquisition card and the signal processing circuit;

[0032] Figure 4 The pulse signal shape diagram of the standard tritium gas provided by another embodiment of the present application;

[0033] Figure 5 The pulse shape spectrum diagram of the standard tritium gas provided by still another embodiment of the present application, wherein the discrimination line is located at the upper left of the pulse shape spectrum;

[0034] Figure 6 The pulse signal shape diagram of the background provided by still another embodiment of the present application;

[0035] Figure 7 The pulse shape spectrum diagram of the background provided by still another embodiment of the present application, wherein the discrimination line in the discrimination line is used for discrimination. Figure 5

[0036] REFERENCE SIGNS

[0037] ​A proportional counter 1; a preamplifier 2; a waveform acquisition card 3; a signal processing circuit 4. DETAILED DESCRIPTION

[0038] It should be noted that the embodiments in the present application and the technical features in the embodiments can be combined with each other without conflict, and the detailed description in the specific embodiments should be understood as the explanation and description of the purpose of the present application, and should not be regarded as improper limitation on the present application.

[0039] The present application will be described in further detail below with reference to the accompanying drawings and specific embodiments. The "first", "second", and the like in the embodiments of the present application are only for the purpose of description, and should not be understood as indicating or implying relative importance or implicitly including at least one feature. In the description of the embodiments of the present application, the meaning of "a plurality of" is at least two, for example, two, three, and the like, unless otherwise explicitly specified.

[0040] In the related art, as shown in Figure 1 , Figure 1 are pulse amplitude distributions of the background signal and the tritium signal, wherein the solid points represent the tritium signal, the amplitude range is between 0 and 180, the hollow points represent the background signal, and most of the distribution is between 0 and 180. Therefore, when the pulse amplitude is analyzed, the lower limit of detection of the proportional counter is increased, which cannot meet the needs of actual environmental monitoring.

[0041] Therefore, the present application provides a processing method of a proportional counter, please refer to Figure 2 and Figure 3 , the processing method comprises:

[0042] S1, standard tritium gas is introduced into the proportional counter to obtain a target pulse signal of the standard tritium gas.

[0043] In this way, the standard tritium gas ionizes the working gas in the proportional counter 1 and generates a target pulse signal.

[0044] It should be noted that the standard tritium gas described herein is tritium gas with a set activity value, wherein the set activity value of the standard tritium gas is greater than the activity value of the background.

[0045] S2, according to the target pulse signal, a first charge integral, a second charge integral and a target shape discrimination factor are obtained;

[0046] S3, according to the first charge integral and the target shape discrimination factor, a discrimination line is obtained, wherein the target shape discrimination factor is located below the discrimination line.

[0047] The embodiment obtains the target pulse signal of the standard tritium gas, and obtains the first charge integral, the second charge integral and the target shape discrimination factor according to the target pulse signal. Finally, the discrimination line is obtained through the first charge integral and the target shape discrimination factor. The target shape discrimination factor is below the discrimination line. That is, all the target shape discrimination factors below the discrimination line correspond to the pulse signals of the standard tritium gas. In this way, on the one hand, when measuring the activity of the to-be-measured tritium gas, the same discrimination line can be used to only count and calculate the pulse signals corresponding to the target shape discrimination factors below the discrimination line. In this way, without losing the activity measurement efficiency of the tritium gas, most of the background signals can be discriminated to effectively reduce the background count rate, so that the detection lower limit of the proportional counter 1 is reduced to meet the needs of actual environmental monitoring. On the other hand, the proportional counter 1 itself is not modified. In this way, different specifications of the proportional counter 1 can be selected for different measurements, which is highly flexible.

[0048] In an embodiment, the processing method comprises: S4, passing the to-be-measured tritium gas into the proportional counter. If the to-be-determined shape discrimination factor of the to-be-measured tritium gas is below the discrimination line, it is determined that the pulse signal corresponding to the to-be-determined shape discrimination factor is an effective pulse signal.

[0049] S5, obtaining the activity value of the to-be-measured tritium gas according to the effective pulse signal.

[0050] In this way, when measuring the activity of the to-be-measured tritium gas, the to-be-measured tritium gas can be passed into the proportional counter 1 to obtain the to-be-determined pulse signal of the to-be-measured tritium gas. The to-be-determined shape discrimination factor is obtained according to the to-be-determined pulse signal. It is determined that the pulse signal below the discrimination line is an effective pulse signal. The activity value of the to-be-measured tritium gas can be calculated through the effective pulse signal. In this way, the measured activity value of the to-be-measured tritium gas can be more accurate, the detection lower limit of the proportional counter 1 can be reduced, the sensitivity can be high, and the error can be small.

[0051] In an embodiment, the ratio between the activity value of the standard tritium gas and the activity value of the background of the proportional counter 1 is not less than two orders of magnitude. For example, the activity value of the standard tritium gas can be 300000 Bq / m 3 , and the activity value of the background of the proportional counter 1 can be 6000 Bq / m 3 . In this way, it can be ensured that most of the obtained target pulse signals are pulse signals of tritium gas. In this way, the accuracy of the subsequent obtained discrimination line can be improved. It should be noted that the activity value of the background is not fixed. The background has different activity values at different places. Therefore, the corresponding activity value of the tritium gas needs to be selected according to the activity value of the background to ensure that most of the obtained target pulse signals are pulse signals of tritium gas.

[0052] In an embodiment, the step of obtaining the first charge integral and the second charge integral includes: S21, setting a long gate time window and a short gate time window according to the target pulse signal, and obtaining the first charge integral in the long gate time window and the second charge integral in the short gate time window.

[0053] For example, refer to Figure 4 and Figure 6 The proportional counter 1 can be cleaned with a working gas without tritium for a period of time so that the count rate returns to the background level, and then the pulse signal thereof is obtained, that is, the pulse signal with a pulse amplitude that fluctuates greatly is measured, and then the duration of the pulse amplitude that fluctuates greatly is taken as the long gate time window by observing the pulse signal shape, for example, the long gate time window can be 100 ns to 600 ns, and then the long gate time window is set on the target pulse signal, and the first charge integral is the area surrounded by the long gate time window and the corresponding pulse amplitude. The proportional counter 1 is filled with tritium gas with a certain activity value, and then the pulse signal thereof is obtained, and since the activity value of the tritium gas is much greater than the activity value of the background, it can be determined that the obtained pulse signal is almost the pulse signal of the tritium gas, and then the duration of the pulse amplitude that fluctuates greatly is taken as the short gate time window by observing the pulse signal shape, for example, the short gate time window can be 100 ns to 300 ns, and then the short gate time window is set on the target pulse signal, and the second charge integral is the area surrounded by the short gate time window and the corresponding pulse amplitude.

[0054] In an embodiment, the target shape discrimination factor is equal to the ratio of the difference between the first charge integral and the second charge integral to the first charge integral. In this way, the pulse shape spectrum of the standard tritium gas can be obtained, which provides data support for subsequent acquisition of the discrimination line.

[0055] In an embodiment, before S2, the processing method includes:

[0056] S6, amplifying the target pulse signal by the preamplifier.

[0057] For example, refer to Figure 3 The preamplifier 2 is electrically connected to the proportional counter 1, and can amplify the pulse signal output by the proportional counter 1 to obtain a better signal-to-noise ratio, so that the amplification of the weak pulse signal can be realized, and the subsequent processing of the pulse signal is facilitated.

[0058] In an example, the preamplifier 2 can amplify the to-be-determined pulse signal. On one hand, the weak pulse signal can be amplified to facilitate subsequent pulse signal processing. On the other hand, the preamplifier 2 has a fast time characteristic, and thus the shape difference between the pulse signal of the tritium gas and the pulse signal of the background can be preserved, which facilitates subsequent differentiation.

[0059] In an example, the preamplifier 2 is of a current-sensitive type. In this way, the pulse signal shape after amplification by the preamplifier 2 is similar to the pulse signal shape output by the proportional counter 1, so as to reduce distortion and improve the accuracy of the first charge integral, the second charge integral, and the target shape discrimination factor.

[0060] In an example, after the target pulse signal is amplified by the preamplifier, the processing method comprises:

[0061] S7, digitizing the amplified target pulse signal.

[0062] In this way, the first charge integral, the second charge integral, and the target shape discrimination factor of the target pulse signal can be obtained.

[0063] In an example, the digitization is performed by the waveform acquisition card 3. For example, the waveform acquisition card 3 is connected to the side of the preamplifier 2 away from the proportional counter 1, so that the target pulse signal amplified by the preamplifier 2 can be digitized by the high-speed AD conversion circuit, and the acquisition rate is fast and the acquisition precision is high. Figure 3

[0064] In an example, the pulse amplitude of the digitized target pulse signal is in a first preset interval. It should be noted that the energy of tritium emission is between 0 keV and 18.6 keV, and the emission energy of the background is between 0 keV and 2600 keV, and the energy is in a corresponding relationship with the pulse amplitude. Therefore, by processing the target pulse signal with the pulse amplitude in the first preset interval, it can be ensured that the processed target pulse signal is almost entirely the pulse signal of the tritium gas. On one hand, the interference of the background signal on the measurement can be further reduced, and the accuracy of the subsequent acquisition of the first charge integral, the second charge integral, and the target shape discrimination factor can be improved. On the other hand, by discriminating the signals outside the first preset interval, the subsequent calculation pressure can be reduced.

[0065] In an example, the first preset interval can be 0-180, 1-180, 2-180, 3-180, 4-180, or 5-180. It should be noted that the pulse amplitude of 180 corresponds to an energy of about 20 keV. In this way, by using a suitable first preset interval, most of the background signals can be discriminated.​

[0066] In one embodiment, the first charge integration, the second charge integration and the target shape discrimination factor are obtained by the signal processing circuit 4. For example, referring to Figure 3 , the signal processing circuit 4 is connected with the waveform acquisition card 3. First, the signal processing circuit 4 judges whether the pulse amplitude of the digitized target pulse signal is in the first preset interval. Then, the signal processing circuit 4 stores the digitized target pulse signal in the first preset interval into the cache. Subsequently, the long gate time window and the short gate time window are set. Then, the signal processing circuit 4 calculates the first charge integration in the long gate time window and the second charge integration in the short gate time window based on the digitized target pulse signal in the cache. The target shape discrimination factor is calculated based on the first charge integration and the second charge integration.

[0067] In one embodiment, S3, the step of obtaining the discrimination line based on the first charge integration and the target shape discrimination factor, comprises:

[0068] S31, a relationship chart of the target shape discrimination factor and the first charge integration is constructed. The number of the first charge integration and the target shape discrimination factor is greater than the first preset value. Each of the first charge integration and the corresponding target shape discrimination factor constitutes a target coordinate.

[0069] S32, a line is set as the discrimination line in the relationship chart, so that all the target coordinates are below the discrimination line.

[0070] For example, referring to Figure 5 , the horizontal axis is energy, which is the first charge integration, and the vertical axis is the shape discrimination factor. The curve in the chart is the pulse shape spectrum of the tritium signal, which is composed of a plurality of target coordinates. As shown in the chart, the distribution of the signal shape of the tritium is very concentrated, and the target shape discrimination factor is relatively low. Then, a straight line which is substantially the same as the extension direction of the pulse shape spectrum can be made as the discrimination line based on the pulse shape spectrum of the tritium signal. For example, the discrimination line can be located at the upper left of the pulse shape spectrum, so that all the target coordinates are below the discrimination line. Figure 5

[0071] For example, in one embodiment, the discrimination line is verified. Referring to Figure 7 , the proportional counter 1 is cleaned with the working gas without tritium for a period of time, so that the counting rate returns to the background level. The digitized pulse signal is observed again. As shown in Figure 7 , the duration of the emission energy of the background is much longer than that of the tritium because the radiation ability of the background is higher. Then, the same long gate time window and the short gate time window as those when the standard tritium gas is measured are set. After a period of time, the pulse shape spectrum of the background is obtained, as shown in​Figure 7 As shown in the figure, it can be seen that the background signal shape distribution is relatively dispersed, and there is a small peak in the area with relatively high shape discrimination factor. In this way, by using the discrimination line, most of the background signals can be discriminated without losing the efficiency of tritium gas measurement, so as to effectively reduce the background count rate. For example, by using the processing method of the present application, the background count rate of the proportional counter 1 can be reduced from 22 s -1 to 2.7 s -1 Under the condition that the proportional counter 1 adopts lead shielding, the background count rate can be reduced from 3.0 s -1 to 0.34 s -1 . According to ISO11929, at this background level, the detection limit of the proportional counter 1 can be reduced to 100 Bq / m 3 below after 1 hour of measurement.

[0072] In an embodiment, the first preset value can be 10000. In this way, by setting a suitable first preset value, the discrimination accuracy of the discrimination line can be ensured to be high, and the discrimination range can be large.

[0073] The above is only a preferred embodiment of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application is included in the protection scope of the present application.

Claims

1. A processing method of a proportional counter, characterized by, The processing method comprises: passing standard tritium gas into a proportional counter to obtain a target pulse signal of the standard tritium gas, wherein a ratio between an activity value of the standard tritium gas and an activity value of a background of the proportional counter is not less than two orders of magnitude; setting a long gate time window and a short gate time window according to the target pulse signal, obtaining a first charge integral in the long gate time window, a second charge integral in the short gate time window and a target shape discrimination factor, wherein the proportional counter is cleaned with working gas without tritium so that a count rate returns to a background level, a pulse signal of the background is obtained, a duration of fluctuation of a pulse amplitude of the pulse signal of the background is taken as the long gate time window, and a duration of fluctuation of a pulse amplitude of the target pulse signal is taken as the short gate time window; obtaining a discrimination line according to the first charge integral and the target shape discrimination factor, wherein the target shape discrimination factor is below the discrimination line.

2. The treatment method according to claim 1, characterized in that, The processing method comprises: passing the to-be-tested tritium gas into the proportional counter, and determining a pulse signal corresponding to a to-be-determined shape discrimination factor of the to-be-tested tritium gas as an effective pulse signal in a case where the to-be-determined shape discrimination factor is below the discrimination line; obtaining an activity value of the to-be-tested tritium gas according to the effective pulse signal.

3. The treatment method of claim 1, wherein The target shape discrimination factor is equal to a ratio between a difference between the first charge integral and the second charge integral and the first charge integral.

4. The treatment method of claim 1, wherein Before obtaining the first charge integral, the second charge integral and the target shape discrimination factor according to the target pulse signal, the processing method comprises: amplifying the target pulse signal through a preamplifier.

5. The treatment method according to claim 4, characterized in that, The preamplifier is of a current-sensitive type.

6. The treatment method of claim 4, wherein After amplifying the target pulse signal through the preamplifier, the processing method comprises: digitally converting the amplified target pulse signal.

7. The treatment method according to claim 6, characterized in that, The digital conversion is performed through a waveform acquisition card.

8. The treatment method according to claim 7, characterized in that, It is determined that a pulse amplitude of the digitized target pulse signal is within a first preset interval.

9. The treatment method of claim 1, wherein, The first charge integral, the second charge integral and the target shape discrimination factor are obtained through a signal processing circuit.

10. The treatment method of claim 1, wherein, The step of obtaining the discrimination line according to the first charge integral and the target shape discrimination factor comprises: constructing a relationship chart of the target shape discrimination factor and the first charge integral, a number of the first charge integral and a number of the target shape discrimination factor are both greater than a first preset value, each of the first charge integral and a corresponding one of the target shape discrimination factor form a target coordinate; setting a line in the relationship chart as the discrimination line so that all the target coordinates are below the discrimination line.

Images