Measuring range adjusting method of sodium iodide gamma-ray spectrometer

Abstract

The invention relates to a measuring range adjusting method of a sodium iodide gamma-ray spectrometer. The measuring range adjusting method comprises the following steps: S1, determining an adjusting direction of a measuring range; s2, setting the channel number of the multi-channel pulse analyzer, and recording the initial high voltage and the electronic gain at the moment; s3, continuously changing the electronic gains, and recording the initial high voltage corresponding to each electronic gain; s4, keeping the electronic gain unchanged, changing the high voltage according to the adjustment direction, recording the channel address where the known radioactive source is located, and establishing the relationship between the high voltage and the channel address; s5, calculating a theoretical channel address of the known radioactive source, and calculating a theoretical high voltage according to the relationship between the high voltage and the channel address; s6, keeping the electron gain unchanged, measuring the known radioactive source according to the theoretical high voltage, and outputting an energy spectrum; s7, changing the electronic gain, and repeating the steps S4-S6; s8, circularly executing the step S7, calculating the total counting rate when the energy spectrum energy is greater than or smaller than the initial range, and selecting the corresponding high voltage and electronic gain when the total counting rate is minimum. According to the invention, by establishing the relationship between the high voltage and the channel address, the target measuring range is accurately adjusted.

Description

Technical Field

[0001] The present invention relates to a method for adjusting the measurement range, and more particularly to a method for adjusting the measurement range of a sodium iodide gamma spectrometer. Background Art

[0002] A sodium iodide gamma spectrometer is an indispensable device in the fields of nuclear physics research and radioactive monitoring. As Figure 1 shown, it mainly consists of a sodium iodide crystal detector, a photomultiplier tube, and a series of signal processing components. The signal processing components mainly include a preamplifier, a linear amplifier, a pulse amplitude analyzer, a multi-channel pulse analyzer, and a data processing system, etc. The sodium iodide crystal detector is the core of this device. It 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 linear amplifier to ensure that the signal intensity is sufficient for subsequent analysis. The high-voltage power supply provides the working voltage for the linear amplifier. As Figure 2 shown, the pulse amplitude analyzer is used to process the signals transmitted from the preamplifier. It determines the energy of radioactive events based on the amplitude of the signals (i.e., the pulse height). The scintillation detector can convert the energy of incident particles into voltage pulse signals, and the signal amplitude is proportional to the energy of the incident particles. Therefore, as long as the number of pulses with different amplitudes is measured, the number of particles with different energies can be obtained. The multi-channel analyzer is responsible for performing energy analysis on the amplified electrical signals and classifying them according to their energy magnitudes. Finally, the data processing system records and processes the data output by the multi-channel analyzer to generate a spectrum diagram for researchers to conduct in-depth analysis and interpretation.

[0003] Currently, the measurement range of most sodium iodide gamma spectrometers is 35 keV to 3 MeV. The upper limit of its measurement range restricts its application in monitoring higher-energy gamma rays. When monitoring an unknown radiation source, since the energy of the radiation is unknown and the radiation source cannot be determined, it is crucial to monitor high-energy radiation above 3 MeV. However, most of the current sodium iodide gamma spectrometers on the market can only achieve energy monitoring below 3 MeV.

[0004] Under specific experimental conditions, it is necessary to adjust the range of a sodium iodide gamma spectrometer to an accurate value. Although the prior art can adjust the range of the sodium iodide gamma spectrometer by adjusting the gain of the sodium iodide gamma spectrometer and the high voltage of the linear amplifier, to adjust to the accurate range, it is often necessary to repeatedly consider and finely adjust the gain of the preamplifier multiple times to gradually become accurate. For experienced operators, adjusting the range of the sodium iodide gamma spectrometer is relatively simple. For inexperienced operators, it is not easy to accurately adjust the range of the sodium iodide gamma spectrometer, and even need to frequently replace the components of the sodium iodide gamma spectrometer, consuming a large amount of working costs. Summary of the Invention

[0005] The object of the present invention is to provide a method for adjusting the range of a sodium iodide gamma spectrometer to solve the problem of consuming a large amount of working costs when adjusting the sodium iodide gamma spectrometer using the prior art.

[0006] The object of the present invention is achieved as follows:

[0007] A method for adjusting the range of a sodium iodide gamma spectrometer includes the following steps:

[0008] S1. Determine the target range of the sodium iodide gamma spectrometer; according to the initial range and the target range of the sodium iodide gamma spectrometer, determine the range adjustment direction, and according to the adjustment direction, determine the adjustment direction of the high voltage of the linear amplifier;

[0009] S2. Set the number of channels of the multi-channel pulse analyzer, place a known radiation source under the sodium iodide detector to start testing, record the initial channel address N where the characteristic energy of the known radiation source is located 10 , and record the initial high voltage V of the linear amplifier at this time 10 and the electronic gain EG of the preamplifier 1 ;

[0010] S3. Change the electronic gain EG of the preamplifier i at least three times, and record the initial channel address N where the characteristic energy of the known radiation source is located each time the change is made i0 and the initial high voltage V of the linear amplifier i0 ;

[0011] S4. Keep the electronic gain EG of the preamplifier 1 unchanged, take the corresponding initial high voltage V 10 as the starting value, according to the adjustment direction of the high voltage, change the high voltage of the linear amplifier at least four times, and record the channel address where the characteristic energy of the known radiation source is located each time the high voltage is changed; establish the relationship between the high voltage of the linear amplifier and the channel address where the characteristic energy of the known radiation source is located;

[0012] S5. Calculate the theoretical channel address of the characteristic energy of the known radiation source according to the target range; and calculate the theoretical high voltage of the linear amplifier according to the calculated theoretical channel address by using the established relationship between the high voltage and the channel address.

[0013] S6. Keep the electronic gain EG of the preamplifier 1 , set the high voltage of the linear amplifier to the theoretical high voltage, place the known radiation source under the sodium iodide detector and start measuring for 10 min, and output the energy spectrum.

[0014] S7. Change the electronic gain EG of the preamplifier 1 to the electronic gain EG in step S3 i , repeat steps S4 - S6 with the corresponding initial high voltage V i0 as the starting value, continuously change the high voltage of the linear amplifier according to the adjustment direction of the high voltage, record the channel address where the characteristic energy of the known radiation source is located each time the high voltage is changed; establish the relationship between the high voltage of the linear amplifier corresponding to each changed electronic gain and the channel address where the characteristic energy of the known radiation source is located; calculate the theoretical channel address of the characteristic energy of the known radiation source according to the target range; and calculate the theoretical high voltage of the linear amplifier according to the calculated theoretical channel address by using the established relationship between the high voltage and the channel address; keep the electronic gain EG of the preamplifier i , set the high voltage of the linear amplifier to the theoretical high voltage, place the known radiation source under the sodium iodide detector and start measuring for 10 min, and output the energy spectrum.

[0015] S8. Loop through step S7 until the changed electronic gain EG in step S3 i is traversed, calculate the total count rate of the energy spectrum output each time the energy of the energy spectrum is greater than or less than the initial range, select the high voltage selected during the energy spectrum measurement with the smallest total count rate, and the electronic gain of the preamplifier as the parameters for the sodium iodide gamma spectrometer to achieve the target range.

[0016] Further, when the adjustment direction of the range of the sodium iodide gamma spectrometer is to decrease the range, the adjustment direction of the high voltage of the linear amplifier is to increase the high voltage; when the adjustment direction of the range of the sodium iodide gamma spectrometer is to increase the range, then the adjustment direction of the high voltage of the linear amplifier is to decrease the high voltage.

[0017] Further, the specific method for establishing the relationship between the high voltage of the linear amplifier and the channel address where the characteristic energy of the known radiation source is located in step S4 is:

[0018] S3 - 1. Establish the relationship formula between the high voltage and the channel address:

[0019] H = aN 3 + bN 2 + cN + d

[0020] Wherein, H is the high voltage of the linear amplifier, N is the channel address where the characteristic energy of the known radiation source is located, and a, b, c, and d are all coefficients;

[0021] S3-2. Substitute the obtained high voltage and its corresponding channel address into the relationship formula between the high voltage and the channel address to calculate the values of a, b, c, and d;

[0022] S3-3. Substitute the values of a, b, c, and d into the relationship formula between the high voltage and the channel address to obtain the relationship between the high voltage and the channel address.

[0023] Further, the specific method for calculating the theoretical channel address of the characteristic energy of the known radiation source is:

[0024] Determine the energy corresponding to each channel according to the target range and the total number of channels; calculate the theoretical channel address according to the energy corresponding to each channel and the characteristic energy of the known radiation source.

[0025] The present invention can quickly change the range of the sodium iodide gamma spectrometer by adjusting the electronic gain of the preamplifier and the high voltage of the linear amplifier according to the task requirements during work, which is very helpful for application scenarios that require quick feedback. At the same time, there is no need to frequently replace components or use expensive consumables, thereby reducing the working cost.

[0026] For each electronic gain, the present invention calculates the channel address where the characteristic energy of the known radiation source is located under at least five different high voltages, and fits the relationship between the high voltage of the linear amplifier and the channel address where the characteristic energy of the known radiation source is located according to the different channel addresses corresponding to different high voltages, so as to quickly calculate the high voltage corresponding to the channel address where the characteristic energy of the known radiation source should be located under the target range. The present invention can not only expand the range of the sodium iodide gamma spectrometer, but also reduce the range of the sodium iodide gamma spectrometer, and flexibly control the range of the sodium iodide gamma spectrometer.

[0027] The present invention also tests the known radiation source by using the high voltage corresponding to the channel address where the characteristic energy of the known radiation source is located under different electronic gains for the target range, and obtains the energy spectrum according to the combination of each electronic gain and high voltage. Select the energy spectrum with the minimum count rate according to the adjustment direction of the range, and use the combination of the electronic gain and high voltage corresponding to the minimum energy spectrum as the parameters of the sodium iodide gamma spectrometer, thereby reducing the noise of the sodium iodide gamma spectrometer. Description of the Drawings

[0028] Figure 1 is the measurement schematic diagram of the sodium iodide gamma spectrometer.

[0029] Figure 2 is the working principle of the pulse amplitude analyzer.

[0030] Figure 3It is the measured graph when the electronic gain of the preamplifier is 1100 and the range is 3 MeV.

[0031] Figure 4 It is the measured graph when the electronic gain of the preamplifier is 430 and the range is 3 MeV.

[0032] Figure 5 It is the measured graph when the electronic gain of the preamplifier is 3400 and the range is 3 MeV.

[0033] Figure 6 It is the measured energy spectrum graph under different high voltages when the electronic gain of the preamplifier is 1100.

[0034] Figure 7 It is the measured energy spectrum graph under different high voltages when the electronic gain of the preamplifier is 430.

[0035] Figure 8 It is the measured energy spectrum graph under different high voltages when the electronic gain of the preamplifier is 3400.

[0036] Figure 9 It is the energy calibration of the wide-range sodium iodide gamma spectrometer. Specific implementation mode

[0037] The present invention will be further described in detail below.

[0038] The method for adjusting the range of the sodium iodide gamma spectrometer provided by the present invention includes the following steps:

[0039] S1. Determine the target range of the sodium iodide gamma spectrometer; according to the initial range and the target range of the sodium iodide gamma spectrometer, determine the range adjustment direction, and determine the adjustment direction of the high voltage of the linear amplifier according to the adjustment direction.

[0040] The target range is the range to be obtained. Each sodium iodide gamma spectrometer has an initial range. The present invention adjusts the range on the basis of the existing sodium iodide gamma spectrometer. When the adjustment direction of the range of the sodium iodide gamma spectrometer is to decrease the range, the adjustment direction of the high voltage of the linear amplifier is to increase the high voltage; when the adjustment direction of the range of the sodium iodide gamma spectrometer is to increase the range, the adjustment direction of the high voltage of the linear amplifier is to decrease the high voltage.

[0041] When the target range is less than the initial range, the adjustment direction of the range is to decrease the range, and vice versa, it is to increase the range.

[0042] S2. Set the number of channels of the multi-channel pulse analyzer, place the known radiation source under the sodium iodide detector to start the test, record the initial channel address N where the characteristic energy of the known radiation source is located 10 , and record the initial high voltage V of the linear amplifier at this time 10 and the electronic gain EG of the preamplifier1 。

[0043] The sodium iodide gamma spectrometer 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 the electrical signals are amplified and processed, a pulse amplitude spectrum corresponding to the energy of the gamma rays can be obtained. The sodium iodide gamma spectrometer mainly includes a sodium iodide crystal, a photomultiplier tube, a signal processing circuit (amplifier, discriminator, multichannel analyzer), a data recording and analysis system, etc.

[0044] In the present invention, by changing the high voltage of the linear amplifier, the pulse amplitude of the input signal is adjusted so that the pulse of the photon with the maximum energy can fall within the voltage of the discrimination region on the pulse amplitude analyzer, and is output through an anticoincidence circuit. When the pulse amplitude generated by a photon exceeding the maximum range energy exceeds the upper discrimination region and is recorded, it will uniformly fall into the last channel of the multichannel analyzer.

[0045] Using a multichannel analyzer, the output pulse amplitude is evenly divided into 512 channels, 1024 channels, 2048 channels, etc. according to different measurement requirements. Each channel can be measured simultaneously, and the pulse intensity within each narrow channel width can be measured, realizing wide-range measurement of the same sodium iodide gamma spectrometer.

[0046] In the present invention, the same known radiation source is used each time.

[0047] The present invention uses 137 Cs as the known radiation source. The initial range of the sodium iodide gamma spectrometer is 3 MeV. Taking the target range of 12 MeV as an example, the method for adjusting the range of the sodium iodide gamma spectrometer is described.

[0048] Connect all the lines of the sodium iodide gamma spectrometer, turn on the multichannel analysis controller, and the present invention sets the channel address of the multichannel analyzer to 4096 channels. Place 137 the Cs radiation source under the sodium iodide detector to start the test. Figure 3 The peak with the largest full-energy peak intensity in 137 is the position where the characteristic energy of the Cs radiation source is located. Record the position of 137 the characteristic energy 0.662 MeV of the Cs radiation source and record N 1 as 883 channels, and record the high voltage V 1 at this time as 1129.99, the electronic gain EG of the preamplifier 1 as 1100, and the digital gain DG of the main amplifier of the sodium iodide gamma spectrometer 1 as 6293.50.

[0049] S3. Change the electronic gain EG of the preamplifier iAt least three times, record the initial channel address N where the characteristic energy of the known radiation source is located each time a change occurs i0 and the initial high voltage V of the linear amplifier i0 .

[0050] For some sodium iodide gamma spectrometers, the electronic gain of the preamplifier is several fixed values for users to select according to their needs; for some sodium iodide gamma spectrometers, users can continuously adjust the electronic gain of the preamplifier

[0051] For a sodium iodide gamma spectrometer with a fixed electronic gain, when changing the electronic gain of the preamplifier, it is necessary to traverse all the preset fixed electronic gain parameter options of the preamplifier; for a sodium iodide gamma spectrometer that can continuously adjust the electronic gain of the preamplifier, determine the electronic gain EG of the preamplifier in step S2 1 within the range where, when the electronic gain EG 1 is less than or equal to 500, when changing the electronic gain, double and triple the initial electronic gain respectively; when the electronic gain EG 1 is greater than 500 and less than 3000, when changing the electronic gain, double and reduce the initial electronic gain by one-half respectively; when the electronic gain EG 1 is greater than or equal to 3000, when changing the electronic gain, reduce the initial electronic gain by one-half and five-sixths respectively

[0052] The reduction and increase amounts of the electronic gain can be set by users according to their needs

[0053] The present invention changes the electronic gain to 430 and 3400 respectively

[0054] As Figure 4 shown, adjust the electronic gain of the preamplifier to 430, place the 137 Cs radiation source under the sodium iodide detector to start testing. The high voltage of the linear amplifier is 1360, and the digital gain of the main amplifier is 6293.50 137 The channel address where the Cs radiation source is located is 906.2 channels

[0055] As Figure 5 shown, adjust the electronic gain of the preamplifier to 3400, place the known radiation source under the sodium iodide detector to start testing. At this time, the high voltage of the linear amplifier is 1000, and the digital gain is 6293.50 137 The channel address where the characteristic energy of the Cs radiation source is located is 1441.41 channels

[0056] S4. Keep the electronic gain EG of the preamplifier 1 unchanged, and use the corresponding initial high voltage V 10Take [[ID=]] as the starting value. According to the adjustment direction of the high voltage, change the high voltage of the linear amplifier at least four times. Record the channel address where the characteristic energy of the known radiation source is located each time the high voltage is changed; establish the relationship between the high voltage of the linear amplifier and the channel address where the characteristic energy of the known radiation source is located.

[0057] Round down the high voltage of the linear amplifier at the beginning of the measurement to the nearest hundred. Each time the high voltage of the linear amplifier is changed later, lower or raise the previous high voltage. The difference in changing the high voltage can be set by the technician. In the present invention, each time the high voltage of the linear amplifier is changed by one-tenth or one-twentieth of the previous high voltage.

[0058] Set the high voltage of the linear amplifier to 1100. At this time 137 The channel address where the characteristic energy of the Cs radiation source is 0.662 MeV is 776.63.

[0059] As Figure 6 shown, round down the high voltage of the linear amplifier to the nearest hundred and lower it by 50 each time to get 1050, 1000, and 950. Measure the Cs radiation source respectively using different high voltages of the linear amplifier 137 and output the measurement data spectrum. According to Figure 6 the measurement data spectrum in, calculate that when the high voltage of the linear amplifier is 1050, 137 the channel address where the energy of the Cs radiation source is located is 600.98; when the high voltage of the linear amplifier is 1000, 137 the channel address where the energy of the Cs radiation source is located is 465.08; when the high voltage of the linear amplifier is 950, 137 the channel address where the energy of the Cs radiation source is located is 357.67. A total of 5 groups of data are output.

[0060] Perform a non-linear fitting on the relationship between the high voltage and the channel address:

[0061] First, establish the relationship formula between the high voltage and the channel address:

[0062] H 1 = a 1 N 1 3 + b 1 N 1 2 + c 1 N 1 + d 1

[0063] Among them, H 1 is the high voltage of the linear amplifier corresponding to the electronic gain of the preamplifier obtained for the first time, N 1 is the channel address where the characteristic energy of the known radiation source is located corresponding to the electronic gain of the preamplifier obtained for the first time, a 1 、b 1, c 1 and d 1 are both coefficients.

[0064] Secondly, substitute the obtained high - voltage set and its corresponding channel addresses into the relationship formula between high - voltage and channel addresses to obtain a 1 , b 1 , c 1 and d 1 values.

[0065] Finally, substitute the values of a 1 , b 1 , c 1 and d 1 into the relationship formula between high - voltage and channel addresses to obtain the fitting relationship between high - voltage and channel addresses: H 1 = 3×10 -7 N 1 3 - 0.0008N 1 2 + 0.9442N 1 + 696.82.

[0066] S5. According to the target range, calculate the theoretical channel address of the known radioactive source characteristic energy; and according to the calculated theoretical channel address, use the established relationship between high - voltage and channel addresses to calculate the theoretical high - voltage of the linear amplifier.

[0067] When the target range is 12 MeV, when the energy scale of the sodium iodide gamma - ray spectrometer is linear, the energy of the 4096th channel should be 12 MeV, and it is calculated that the energy of each channel should be 0.00293 MeV; according to 137 the characteristic energy of the Cs radioactive source is 0.662 MeV, calculate 137 the theoretical channel address of the Cs radioactive source energy is 225.96 channels.

[0068] Calculate the theoretical high - voltage corresponding to the theoretical channel address in the relationship between high - voltage and channel addresses, that is, 872.79.

[0069] S6. Keep the electronic gain EG 1 of the pre - amplifier, set the high - voltage of the linear amplifier to the high - voltage calculated in step S5, place the known radioactive source under the sodium iodide detector and start measuring for 10 min, and output the energy spectrum.

[0070] Keep the electronic gain EG 1 of the pre - amplifier as 1100, set the high - voltage of the linear amplifier to 872.79, place the 137 Cs radioactive source under the sodium iodide detector and start measuring for 10 min, and output the energy spectrum.

[0071] S7. Change the electronic gain EG of the pre - amplifier1 is the electronic gain EG in step S3 i , repeat steps S4 - S6 with the corresponding initial high voltage V i0 as the starting value, continuously change the high voltage of the linear amplifier according to the adjustment direction of the high voltage, and record the channel address where the characteristic energy of the known radiation source is located each time the high voltage is changed; establish the relationship between the high voltage of the linear amplifier corresponding to the electronic gain changed each time and the channel address where the characteristic energy of the known radiation source is located; calculate the theoretical channel address of the characteristic energy of the known radiation source according to the target range; and according to the calculated theoretical channel address, use the established relationship between the high voltage and the channel address to calculate the theoretical high voltage of the linear amplifier; keep the electronic gain EG of the preamplifier i , set the high voltage of the linear amplifier to the theoretical high voltage, place the known radiation source under the sodium iodide detector and start measuring for 10 min, and output the energy spectrum.

[0072] Keep the electronic gain of the preamplifier at 430, adjust the high voltage of the linear amplifier to 1300, and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 717.2.

[0073] As Figure 7 shown, change the high voltage 4 times in total and output 5 groups of high voltages and their corresponding channel addresses. Adjust the high voltage to 1250 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 585.35; adjust the high voltage to 1200 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 473.59; adjust the high voltage to 1150 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 381.73.

[0074] Establish the relationship formula between the high voltage and the channel address:

[0075] H i = a i N i 3 + b i N i 2 + c i N i + d i

[0076] where i is the i-th time of changing the electronic gain of the preamplifier.

[0077] Substitute the obtained set of high voltages and their corresponding set of channel addresses into the relationship formula between the high voltage and the channel address, and the relationship between the high voltage and the channel address is: H 2 = 3×10 -7 N 2 3-0.0009 N 2 2 +1.1266 N 2 +832.39

[0078] Known in step S5 137 The theoretical channel address of the Cs radiation source energy is 225.96 channels. Substituting the theoretical channel address into the relationship between the high voltage and the channel address obtained when the gain of the preamplifier is changed for the second time, the theoretical high voltage of the linear amplifier corresponding to the theoretical channel address is 1044.46

[0079] Keep the electronic gain of the preamplifier at 430 and the high voltage of the linear amplifier set at 1044.46. Place 137 the Cs radiation source under the sodium iodide detector and start measuring for 10 min to output the energy spectrum

[0080] S8. Loop and execute step S7 until the electronic gain EG changed in step S3 i is traversed. Calculate the total count rate of each output energy spectrum greater than or less than the initial range. Select the high voltage and the electronic gain of the preamplifier selected during the energy spectrum measurement with the smallest total count rate as the parameters for the sodium iodide gamma spectrometer to achieve the target range

[0081] Change the electronic gain of the preamplifier to 3400. At this time, the high voltage of the linear amplifier is 1000. Gradually adjust the high voltage of the linear amplifier to 950, 900, 850, 800. Place 137 the Cs radiation source under the sodium iodide detector and test it with different high voltages respectively

[0082] As Figure 8 shown, adjust the high voltage to 950 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 1112.5; adjust the high voltage to 900 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 836.4; adjust the high voltage to 850 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 609.13; adjust the high voltage to 800 and measure 137 the channel address where the characteristic energy of the Cs radiation source is located is 411.37

[0083] Substitute the adjusted high voltage and the channel address corresponding to the high voltage into the established relationship formula between the channel address and the high voltage, and the relationship between the high voltage and the channel address is: H 3 =1×10 -7 N 3 3 -0.0005 N 3 2 +0.7039 N 3+570.8。

[0084] Substitute 137 the theoretical channel address 225.96 where the characteristic energy of the Cs radiation source is located into the relationship between the high voltage and the channel address corresponding to an electronic gain of 3400, and the theoretical high voltage of the linear amplifier is obtained as 705.47. Keep the electronic gain of the preamplifier at 3400, adjust the high voltage of the linear amplifier to 705.47, start measuring for 10 min, and output the energy spectrum.

[0085] When the adjustment direction is to decrease the range, calculate the total count rate of energies less than the initial range. When the adjustment direction is to increase the range, calculate the total count rate of energies greater than the initial range. Take the electronic gain corresponding to the energy spectrum with the minimum count rate as the electronic gain of the preamplifier when the NaI gamma-ray spectrometer achieves the target range, and take the high voltage corresponding to the energy spectrum with the minimum count rate as the high voltage of the linear amplifier when the NaI gamma-ray spectrometer achieves the target range.

[0086] The present invention calculates the total count rate of energies greater than 3 MeV. When the electronic gain of the preamplifier is different and the maximum range of the NaI gamma-ray spectrometer is the same, when the electronic gain of the preamplifier is 1100, the total count rate of energies greater than 3 MeV is 3.33. When the electronic gain of the preamplifier is 430, the total count rate of energies greater than 3 MeV is 4.00. When the electronic gain of the preamplifier is 3400, the total count rate of energies greater than 3 MeV is 3.42. Select the electronic gain of the preamplifier corresponding to the minimum count rate as the required gain for detecting the NaI gamma-ray spectrometer. Finally, the electronic gain of the preamplifier in this example is 1100.

[0087] As Figure 9 shown, when the electronic gain of the preamplifier is 1100 and the high voltage of the linear amplifier is 872.79, use 137 Cs, 6 0Co, 232 Th and 40 K to perform energy calibration on the NaI gamma-ray spectrometer. It can be seen from Figure 9 that the energy calibration of the NaI gamma-ray spectrometer is a linear relationship, and the theoretical value of the energy of the 4096th channel should be 13.42 MeV. The required energy of 12 MeV meets the usage requirements and does not need to be adjusted by adjusting the digital gain. Among them, Figure 9 in R 2 is the linear correlation degree between the channel address and the energy.

[0088] When the maximum measured energy is slightly less than the maximum energy of the required detection range, the range can be changed by finely adjusting the digital gain. When the maximum measured energy is greater than the maximum energy of the required detection range, there is no need to adjust the digital gain.

Claims

1. A range adjustment method for a sodium iodide gamma spectrometer, characterized in that: The steps include: S1. Determine the target range of the sodium iodide gamma spectrometer; determine the range adjustment direction according to the initial range and target range of the sodium iodide gamma spectrometer, and determine the adjustment direction of the linear amplifier high voltage according to the adjustment direction; S2. Set the number of channels of the multi-channel pulse analyzer, place the known radioactive source under the sodium iodide detector and start the test, and record the initial channel address N where the characteristic energy of the known radioactive source is located. 10 , and record the initial high voltage V of the linear amplifier at this time 10 and the electronic gain EG1 of the preamplifier; S3. Change the electronic gain EG of the preamplifier i At least three times, record each change, the initial track address N where the characteristic energy of the known radiation source is located i0 and the initial high voltage V of the linear amplifier i0 ; S4. Keep the electronic gain EG1 of the preamplifier unchanged, with the corresponding initial high voltage V 10 As the starting value, change the high voltage of the linear amplifier at least four times according to the adjustment direction of the high voltage, and record the channel address where the characteristic energy of the known radiation source is located each time the high voltage is changed; establish the relationship between the high voltage of the linear amplifier and the channel address where the characteristic energy of the known radiation source is located; S5. Calculate the theoretical channel address of the characteristic energy of the known radiation source according to the target range; and calculate the theoretical high voltage of the linear amplifier according to the calculated theoretical channel address by using the established relationship between the high voltage and the channel address; S6. Maintain the electronic gain EG1 of the preamplifier, set the high voltage of the linear amplifier to the theoretical high voltage, place the known radioactive source under the sodium iodide detector, start measuring for 10 minutes, and output the energy spectrum; S7. Change the electronic gain EG1 of the preamplifier to the electronic gain EG in step S3. i Repeat steps S4-S6 with the corresponding initial high voltage V i0 As the starting value, the high voltage of the linear amplifier is continuously changed according to the adjustment direction of the high voltage, and the channel address of the characteristic energy of the known radiation source is recorded each time the high voltage is changed; the relationship between the high voltage of the linear amplifier corresponding to each change of the electronic gain and the channel address of the characteristic energy of the known radiation source is established; according to the target range, the theoretical channel address of the characteristic energy of the known radiation source is calculated; and according to the calculated theoretical channel address, the theoretical high voltage of the linear amplifier is calculated using the established relationship between the high voltage and the channel address; the electronic gain EG of the preamplifier is maintained i , set the high voltage of the linear amplifier to the theoretical high voltage, place the known radioactive source under the sodium iodide detector and start measuring for 10 minutes, and output the energy spectrum; S8. Execute step S7 repeatedly until the electronic gain EG changed in step S3 is i After the traversal is completed, the total count rate of each output energy spectrum energy greater than or less than the initial range is calculated, and the high voltage selected during the energy spectrum measurement with the smallest total count rate and the electronic gain of the preamplifier are selected as parameters for the sodium iodide gamma spectrometer to achieve the target range.

2. The range adjustment method of the sodium iodide gamma spectrometer according to claim 1, characterized in that: If the adjustment direction of the range of the sodium iodide gamma spectrometer is to reduce the range, the adjustment direction of the high voltage of the linear amplifier is to increase the high voltage; if the adjustment direction of the range of the sodium iodide gamma spectrometer is to increase the range, the adjustment direction of the high voltage of the linear amplifier is to reduce the high voltage.

3. The range adjustment method of the sodium iodide gamma spectrometer according to claim 1, characterized in that: The specific method of establishing the relationship between the high voltage of the linear amplifier and the address of the characteristic energy of the known radiation source in step S4 is: S4-1. Establish the relationship between high voltage and address: H=aN 3 +bN 2 +cN+d Where H is the high voltage of the linear amplifier, N is the channel address where the characteristic energy of the known radiation source is located, and a, b, c and d are all coefficients; S4-2. Substitute the obtained high voltage and its corresponding channel address into the relationship formula between high voltage and channel address to calculate the values ​​of a, b, c and d; S4-3. Substitute the values ​​of a, b, c and d into the relationship formula between high voltage and track address to obtain the relationship between high voltage and track address.

4. The range adjustment method of the sodium iodide gamma spectrometer according to claim 1, characterized in that: The specific method for calculating the theoretical address of the characteristic energy of a known radiation source is: The energy corresponding to each channel is determined based on the target range and the total number of channel addresses; the theoretical channel address is calculated based on the energy corresponding to each channel and the characteristic energy of the known radiation source.

Images