Design method of wide-range NaI (T1) detector

Abstract

The invention belongs to the technical field of radiation monitoring, and particularly relates to a design method of a wide-range NaI (T1) detector, which comprises the following steps of: 1, connecting all lines of the NaI (T1) detector, and opening a multi-channel analyzer; 2, a 137Cs radioactive source is adopted, different preamplifier electronic gains are adjusted, the relation between the high voltage and the channel position where the characteristic energy of the 137Cs radioactive source is located is established, and energy spectrum data are output; 3, according to the output energy spectrum data, preamplifier electronic gain and linear amplifier high voltage needed by the detector are determined; and 4, under the determined preamplifier electronic gain required by the detector and the high voltage condition of the linear amplifier, different radioactive sources are adopted to carry out energy calibration on the detector, and whether digital gain needs to be adjusted is determined according to the energy calibration. According to the method, the measuring range of the sodium iodide gamma-ray spectrometer can be expanded, so that the sodium iodide gamma-ray spectrometer can cover high-energy radiation monitoring of 3MeV-10MeV or above.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radiation monitoring, and particularly relates to a design method of a wide-range NaI(Tl) detector. BACKGROUND

[0002] A sodium iodide gamma spectrometer is an indispensable device in the fields of nuclear physics research and radioactivity monitoring. It is mainly composed of a sodium iodide crystal detector, a photomultiplier tube, and a series of signal processing components, including a preamplifier, a main amplifier, a multichannel analyzer, and a data processing system. The sodium iodide crystal detector is the core of the device, which uses its unique scintillation characteristics to convert the received gamma ray energy into visible light signals. These light signals are then captured by the photomultiplier tube and converted into electrical signals. The electrical signals are amplified by the preamplifier and the main amplifier to ensure that the signal strength is sufficient for subsequent analysis. The multichannel analyzer is responsible for energy analysis of the amplified electrical signals, classifying them according to energy size. Finally, the data processing system records and processes the data output by the multichannel analyzer to generate energy spectrum graphs for researchers to analyze and interpret in depth.

[0003] Most current sodium iodide gamma spectrometers have a linear measurement range of 35keV to 3MeV, but the upper limit of the measurement range limits its application in higher energy gamma ray monitoring. In some nuclear physics experiments, radioactive waste treatment, and nuclear accident emergency response, monitoring high-energy radiation above 3MeV is crucial. However, the sodium iodide crystal has low detection efficiency for high-energy gamma rays, and its energy resolution decreases significantly with increasing energy, making it difficult to accurately distinguish high-energy radiation sources. Therefore, the existing technology cannot meet the needs of these specific applications, and it is urgent to expand the measurement range of the sodium iodide gamma spectrometer to cover high-energy radiation monitoring above 3MeV. SUMMARY

[0004] The purpose of the present application is to provide a design method of a wide-range NaI(Tl) detector, which can expand the measurement range of the sodium iodide gamma spectrometer to cover high-energy radiation monitoring above 3MeV to 10MeV. The sodium iodide gamma spectrometer with expanded measurement range will be able to better serve the fields of nuclear physics research, radioactivity monitoring, and nuclear safety, and meet more extensive application needs.

[0005] The technical solution to achieve the purpose of the present application is as follows:

[0006] A design method of a wide-range NaI(Tl) detector, comprising:

[0007] Step 1: Connect all the lines of the NaI(Tl) detector, and turn on the multichannel analyzer;

[0008] Step 2: Adjust different preamplifier electronic gains by using a 137Cs radioactive source, establish the relationship between high voltage and channel position of the characteristic energy of the 137Cs radioactive source, and output the energy spectrum data;

[0009] Step 3: Determine the required preamplifier electronic gain and linear amplifier high voltage of the detector according to the output energy spectrum data;

[0010] Step 4: Under the condition of the determined preamplifier electronic gain and linear amplifier high voltage required by the detector, use different radioactive sources to calibrate the energy of the detector, and determine whether the digital gain needs to be adjusted according to the energy calibration.

[0011] Further, the channel position of the multichannel analyzer in step 1 is set to 4096 channels.

[0012] Further, step 2 includes:

[0013] Step 2.1: Adjust the electronic gain of the preamplifier of the detector to the minimum electronic gain;

[0014] Step 2.2: Place the 137Cs radioactive source under the detector to start testing, and record the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, the linear amplifier high voltage, and the digital gain at this time;

[0015] Step 2.3: When the preamplifier electronic gain is the minimum electronic gain, gradually change the linear amplifier high voltage of the detector, record the change of the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, and establish the relationship between the linear amplifier high voltage and the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source. At the same time, calculate the maximum energy that can be measured by the energy spectrum of the detector at this time and output the energy spectrum;

[0016] Step 2.4: Adjust the preamplifier electronic gain to different data, repeat steps 2.2-2.3, and output the energy spectrum; until the preamplifier electronic gain cannot output normal energy spectrum data after adjustment.

[0017] Further, in step 2.3, the maximum energy that can be measured by the energy spectrum of the detector at this time is calculated and the energy spectrum is output, which is specifically: according to the established relationship between the linear amplifier high voltage and the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, the set linear amplifier high voltage is calculated; keep the preamplifier electronic gain as the minimum electronic gain, adjust the linear amplifier high voltage to the set linear amplifier high voltage, start measurement, and output the energy spectrum.

[0018] Further, step 3 includes:

[0019] Step 3.1: According to the output spectrum data, the total count rate of the output spectrum in steps 2.3-2.4 is calculated, and the total count rate at different electronic gains under the same detector range is compared;

[0020] Step 3.2: The electronic gain with the minimum total count rate under the same detector range is selected as the electronic gain of the preamplifier, and the high voltage is set to the required range of high voltage.

[0021] Further, in step 4, whether the digital gain needs to be adjusted according to the energy calibration is determined, specifically: if the energy calibration is a linear relationship, the digital gain does not need to be adjusted; if the energy calibration is a nonlinear relationship, the digital gain needs to be adjusted.

[0022] Further, in step 4, the different radioactive sources include Cs-137, Co-60, and Th-232.

[0023] The beneficial technical effects of the present application are:

[0024] 1. The design method of the wide-range NaI(Tl) detector provided by the present application adopts five different high voltages corresponding to the channel addresses of the Cs-137 radioactive source, fits and calculates the corresponding relationship between the linear amplifier high voltage and the channel address, so as to quickly calculate the high voltage corresponding to the channel address position of the characteristic energy of the Cs-137 radioactive source under the required range.

[0025] 2. The design method of the wide-range NaI(Tl) detector provided by the present application is a selection method of different preamplifier gains under the optimal condition, which is to compare the minimum background count rate collected by more than 3MeV energy.

[0026] 3. The design method of the wide-range NaI(Tl) detector provided by the present application can use digital gain to fine-tune the range when the energy calibration of the detector is not linear or the error between the required range and the actual measured range is small. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a measurement principle diagram of a sodium iodide detector;

[0028] Figure 2 It is a multi-channel analyzer display interface diagram in the embodiment of the present application;

[0029] Figure 3 It is a measured spectrum diagram under different high voltages when the preamplifier electronic gain is 1100 in the embodiment of the present application.

[0030] Figure 4 It is a multi-channel analyzer display interface diagram when the preamplifier electronic gain is 430 in the embodiment of the present application;

[0031] Figure 5 The measured energy spectrum diagram of the preamplifier electronic gain of 430 at different high voltages in the embodiment of the present application is shown in the following table:

[0032] Figure 6 The multi-channel analyzer display interface diagram of the preamplifier electronic gain of 3400 in the embodiment of the present application is shown in the following table:

[0033] Figure 7 The measured energy spectrum diagram of the preamplifier electronic gain of 3400 at different high voltages in the embodiment of the present application is shown in the following table:

[0034] Figure 8 The energy calibration diagram of the wide-range NaI(Tl) detector in the embodiment of the present application is shown in the following table. DETAILED DESCRIPTION

[0035] The present application will be further described in detail below in combination with the drawings and embodiments.

[0036] The measurement principle of the NaI(Tl) detector is shown in the following table: Figure 1 It is mainly based on the scintillation characteristics of NaI(Tl). When gamma rays interact with the sodium iodide crystal, scintillation light is generated, and these light signals are then converted into electrical signals by a photomultiplier tube (PMT). After amplification and processing, the pulse amplitude spectrum corresponding to the energy of the gamma rays can be obtained.

[0037] The detector mainly includes a sodium iodide crystal, a photomultiplier tube, a signal processing circuit (amplifier, discriminator, multi-channel analyzer), a data recording and analysis system.

[0038] The design method of the wide-range NaI(Tl) detector provided by the present application is based on the 0.662 MeV pulse signal generated by a Cs-137 radioactive source. By changing the high voltage of the linear amplifier, the pulse amplitude of the input signal is changed, so that the pulse of the photon with the maximum energy can fall within the voltage of the discrimination domain of the pulse amplitude analyzer, and is output through the anticoincidence circuit. When the pulse amplitude of the photon with the maximum range energy exceeds the upper discrimination domain and is recorded, it falls in the last channel of the multi-channel analyzer. As shown in the following table, the output pulse amplitude is divided into 512 channels, 1024 channels, 2048 channels, etc. according to different measurement needs using a multi-channel analyzer. Each channel can measure the pulse intensity within each narrow channel width, realizing wide-range measurement of the same sodium iodide detector. Figure 2

[0039] Specifically, the present application provides a design method of a wide-range NaI(Tl) detector, including the following steps:

[0040] ​Step 1: Connect all lines of NaI (Tl) detector, turn on the multichannel analyzer, and set the channel address of the multichannel analyzer to 4096 channels.

[0041] Step 2: Use 137Cs radioactive source to adjust different preamplifier electronic gains, establish the relationship between high voltage and channel address position of characteristic energy of 137Cs radioactive source, and output energy spectrum data

[0042] Step 2.1: Adjust the electronic gain of the preamplifier of the detector to the minimum (EG1) that the detector can adjust, that is, allow the pulse to reach the lower discrimination voltage of the pulse amplitude analyzer.

[0043] Step 2.2: Place the 137Cs radioactive source under the detector to start testing, record the channel address position of the characteristic energy 0.662 MeV of the 137Cs radioactive source at this time, record it as N1, and record the high voltage of the linear amplifier at this time as V1 and the digital gain as DG1.

[0044] Step 2.3: When the electronic gain of the preamplifier is EG1, gradually change the high voltage of the linear amplifier of the detector, record the change of the channel address position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, and establish the relationship between the high voltage of the linear amplifier and the channel address position N1 of the characteristic energy 0.662 MeV of the 137Cs radioactive source. At the same time, calculate the maximum energy that the detector can measure at this time and output the energy spectrum: according to the established relationship between the high voltage of the linear amplifier and the channel address position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, calculate the set high voltage of the linear amplifier; keep the electronic gain of the preamplifier as the minimum electronic gain, adjust the high voltage of the linear amplifier to the set high voltage of the linear amplifier, start measuring, and output the energy spectrum.

[0045] Step 2.4: Adjust the electronic gain of the preamplifier to different data, repeat steps 2.2-2.3, and output the energy spectrum; until the preamplifier electronic gain adjustment cannot output normal energy spectrum data.

[0046] Step 3: According to the output energy spectrum data, determine the required preamplifier electronic gain and linear amplifier high voltage of the detector

[0047] Step 3.1: According to the output energy spectrum data, calculate the total count rate of the output energy spectrum in steps 2.3-2.4, and compare the total count rate at the same detector range under different electronic gains. Reduce the influence of noise generated by electronic circuit on the energy spectrum.

[0048] Step 3.2: Select the electronic gain with the smallest total count rate at the same detector range as the electronic gain of the preamplifier of the detector, and set the high voltage to the required range of the high voltage.

[0049] Step 4: Under the conditions of the required preamplifier electronic gain of the detector and the high voltage of the linear amplifier, energy calibration of the detector is performed using different radioactive sources, and whether the digital gain needs to be adjusted is determined according to the energy calibration: if the energy calibration is a linear relationship, the digital gain does not need to be adjusted; if the energy calibration is a nonlinear relationship, the digital gain needs to be adjusted.

[0050] Step 3: Under the conditions of the required preamplifier electronic gain of the detector and the high voltage of the linear amplifier, energy calibration of the detector is performed using different radioactive sources, and whether the digital gain needs to be adjusted is determined according to the energy calibration: if the energy calibration is a linear relationship, the digital gain does not need to be adjusted; if the energy calibration is a nonlinear relationship, the digital gain needs to be adjusted. The digital gain can be adjusted through the Digital Gain in the multichannel analyzer, so that the detector can perform wide-range measurement.

[0051] Embodiment

[0052] Taking an example that the maximum range of the NaI(Tl) detector is adjusted from 3 MeV to 12 MeV and the energy calibration of the detector is linear, the embodiment provides a design method of a wide-range NaI(Tl) detector, which specifically comprises the following steps:

[0053] Step 1: Connect all the lines of the NaI(Tl) detector, turn on the multichannel analyzer, and set the channel address of the multichannel analyzer to 4096 channels, as shown in FIG. 1. Figure 2

[0054] Step 2: Record the electronic gain of the preamplifier as 1100, the high voltage of the linear amplifier as 1129.99, the digital gain as 6293.50, and the channel address of the 137Cs radioactive source (0.662 MeV) as 883.

[0055] Step 3: Keep the preamplifier electronic gain unchanged, and adjust the high voltage of the linear amplifier to 1100, 1050, 1000 and 950 step by step, output the measured data spectrum as shown in FIG. 2, and calculate the channel address position of the 137Cs radioactive source (0.662 MeV) energy under different high voltages. Figure 3 Figure 3 According to the relationship between the linear amplifier high voltage and the channel address position of the 137Cs radioactive source (0.662 MeV) energy obtained in Steps 2 and 3, nonlinear fitting is performed, and a fitting relationship is obtained as shown in Formula 1.

[0056] ​​H = 3 × 10 -7 N 3 -0.0008N 2 +0.9442N+696.82 (1)

[0057] In the formula,

[0058] N: Indicates the location of the 137Cs radioactive source (0.662 MeV);

[0059] H: indicates the high voltage of the detector linear amplifier.

[0060] Step 4: When the detector energy scale is linear, the energy of channel 4096 should be 12 MeV, and the channel address where the 137Cs radioactive source (0.662 MeV) energy is located should be channel 225.96. According to Equation 1, the set linear amplifier high voltage is calculated to be 872.79.

[0061] Step 5: Keep the preamplifier electronic gain at 1100, adjust the set linear amplifier high voltage to 872.79, start the measurement for 10 minutes, and output the energy spectrum.

[0062] Step 6: Adjust the preamplifier gain to 430, as shown below. Figure 4 As shown, the detector's linear amplifier high voltage is 1360, the digital gain is 6293.50, and the channel address of the 137Cs radioactive source (0.662MeV) is channel 906.2.

[0063] Step 7: Keeping the preamplifier gain at 430, gradually adjust the linear amplifier high voltage to 1300, 1250, 1200, and 1150, and output the measured data spectrum as shown. Figure 5 As shown, the location of the 137Cs radioactive source (0.662 MeV) energy at different high voltages was calculated, and the calculated locations at each high voltage were 717.2, 585.35, 473.59, and 381.73. A nonlinear fitting was performed based on the relationship between the linear amplifier high voltage and the location of the 137Cs radioactive source (0.662 MeV) energy, and the fitting relationship is shown in Equation 2.

[0064] H = 3 × 10 -7 N 3 -0.0009N 2 +1.1266N+832.39 (2)

[0065] Step 8: When the detector energy scale is linear, the energy of channel 4096 should be 12 MeV, and the channel address where the 137Cs radioactive source (0.662 MeV) energy is located should be channel 225.96. According to Equation 2, the set linear amplifier high voltage is calculated to be 1044.46.

[0066] Step 9: Keep the preamplifier electronic gain as 430, set the linear amplifier high voltage as 1044.46, start measuring for 10 min, and output the energy spectrum.

[0067] Step 10: Adjust the preamplifier gain to 3400, as shown in the figure, record the linear amplifier high voltage of the detector at this time as 1000, the digital gain as 6293.50, and the channel address of the 137Cs radioactive source (0.662 MeV) as 1441.41 channels. Figure 6

[0068] Step 11: Keep the preamplifier gain as 3400, adjust the linear amplifier high voltage to 950, 900, 850, and 800 step by step, output the measured data spectrum as shown in the figure, and calculate the channel address position of the 137Cs radioactive source (0.662 MeV) energy at different high voltages. The calculated channel addresses at different high voltages are 1112.5, 836.4, 609.13, and 441.37 respectively. According to the relationship between the linear amplifier high voltage and the channel address of the 137Cs radioactive source (0.662 MeV) energy, a nonlinear fitting is performed, and the fitting relationship is shown in equation 3. Figure 7

[0069] H = 1 × 10 -7 N 3 -0.0005N 2 + 0.7039N + 570.8 (3)

[0070] Step 12: When the energy scale of the detector is linear, the energy of the 4096th channel should be 12 MeV, and the channel address of the 137Cs radioactive source (0.662 MeV) energy should be 225.96 channels. According to equation 3, the set linear amplifier high voltage is calculated as 705.47.

[0071] Step 13: Keep the preamplifier electronic gain as 430, set the linear amplifier high voltage to 705.47, start measuring for 10 min, and output the energy spectrum.

[0072] Step 14: According to the energy spectrum output in steps 5, 9, and 13, calculate the total count rate of energy greater than 3 MeV. When the maximum range of the detector is the same, the total count rate of energy greater than 3 MeV at each gain is 3.33, 4.00, and 3.42 respectively. Select the preamplifier electronic gain corresponding to the minimum count rate as the required gain of the detector. The final preamplifier electronic gain in this example is 1100.

[0073] ​​Fifteenth step: when the preamplifier electronic gain is 1100, the linear amplifier high voltage is 872.79, the detector is scaled by Cs-137, Co-60, K-40 and Th-232, and the energy scale is as shown in the figure Figure 8 From the figure, it can be seen that the detector energy scale is linear, and according to the calculation Figure 8 , the 4096th energy theoretical value should be 12.59 MeV, and the required energy is 12 MeV, which meets the use requirements, and does not need to be adjusted by adjusting the digital gain.

[0074] The above describes the present application in detail in combination with the drawings and examples, but the present application is not limited to the above examples, and various changes can be made within the knowledge possessed by those skilled in the art without departing from the purpose of the present application. The contents not described in detail in the present application can adopt the existing technology.

Claims

1. A method of designing a wide-range NaI(Tl) detector, characterized in that, The application relates to a method for setting up a NaI (Tl) detector. Step 1: connecting all lines of the NaI (Tl) detector, and turning on a multi-channel analyzer; Step 2: using a 137Cs radioactive source, adjusting different preamplifier electronic gains, establishing the relationship between high voltage and the channel position of the characteristic energy of the 137Cs radioactive source, and outputting energy spectrum data; Step 3: determining the required preamplifier electronic gain and linear amplifier high voltage of the detector according to the output energy spectrum data; Step 4: under the condition of the determined preamplifier electronic gain and linear amplifier high voltage of the detector, using different radioactive sources to perform energy calibration on the detector, and determining whether the digital gain needs to be adjusted according to the energy calibration.

2. The method of designing a wide-range NaI(TI) detector according to claim 1, wherein, In step 1, the channel position of the multi-channel analyzer is set to 4096 channels.

3. The method of designing a wide-range NaI(TI) detector according to claim 2, wherein, Step 2 includes: Step 2.1: adjusting the electronic gain of the preamplifier of the detector to the minimum electronic gain; Step 2.2: placing the 137Cs radioactive source under the detector to start testing, and recording the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, the linear amplifier high voltage and the digital gain at this time; Step 2.3: when the electronic gain of the preamplifier is the minimum electronic gain, gradually changing the linear amplifier high voltage of the detector, recording the change of the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, establishing the relationship between the linear amplifier high voltage and the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, and calculating the maximum energy that can be measured by the energy spectrum of the detector at this time and outputting the energy spectrum; Step 2.4: adjusting the electronic gain of the preamplifier to different data, repeating steps 2.2-2.3, and outputting the energy spectrum; until the preamplifier electronic gain cannot output normal energy spectrum data after adjustment.

4. The method of designing a wide-range NaI(TI) detector according to claim 3, wherein, In step 2.3, the calculation of the maximum energy that can be measured by the energy spectrum of the detector at this time and the output of the energy spectrum are specifically as follows: according to the established relationship between the linear amplifier high voltage and the channel position of the characteristic energy 0.662 MeV of the 137Cs radioactive source, the set linear amplifier high voltage is calculated; the electronic gain of the preamplifier is kept as the minimum electronic gain, the linear amplifier high voltage is adjusted to the set linear amplifier high voltage, measurement is started, and the energy spectrum is output.

5. The method of designing a wide-range NaI(TI) detector according to claim 4, wherein, Step 3 includes: Step 3.1: according to the output energy spectrum data, calculating the total count rate of the output energy spectrum in steps 2.3-2.4, and comparing the total count rate at different electronic gains under the same detector range; Step 3.2: selecting the electronic gain with the minimum total count rate under the same detector range as the electronic gain of the preamplifier of the detector, and setting the high voltage as the required high voltage of the range.

6. The method of designing a wide-range NaI(TI) detector according to claim 5, wherein, In step 4, the determination of whether the digital gain needs to be adjusted according to the energy calibration is specifically as follows: if the energy calibration is a linear relationship, the digital gain does not need to be adjusted; if the energy calibration is a nonlinear relationship, the digital gain needs to be adjusted.

7. The method of designing a wide-range NaI(TI) detector according to claim 6, wherein, In step 4, the different radioactive sources include Cs-137, Co-60 and Th-232.

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