A low-energy gamma-ray spectrum measurement method based on the law of ray attenuation

Abstract

The present application relates to a kind of gamma-ray measurement method, to solve the problem of low efficiency or the demand equipment complexity or timeliness and safety is poorer existing gamma spectrum method measurement low-energy characteristic peak, and provide a kind of low-energy gamma-ray spectrum measurement method based on the law of radioactive decay.The present application includes the following steps:1) using three-dimensional position sensitive cadmium zinc telluride detector to carry out gamma-ray detection to radioactive sample;2) according to the anode signal intensity and electron carrier drift time in three-dimensional position sensitive cadmium zinc telluride detector, obtain the three-dimensional coordinates (x, y, z) of the position where gamma-ray and three-dimensional position sensitive cadmium zinc telluride detector interact;3) calculate the attenuation amount ΔR curve of gamma-ray at different depths of three-dimensional position sensitive cadmium zinc telluride detector;4) energy statistics is carried out to the gamma-ray deposited in all depths corresponding to the attenuation amount ΔR less than the set threshold value, and low-energy gamma-ray spectrum is obtained.

Description

Technical Field

[0001] This invention relates to a method for measuring gamma-ray energy spectrum, specifically a method for measuring low-energy gamma-ray energy spectrum based on the gamma-ray attenuation law. Background Technology

[0002] Gamma spectroscopy is a commonly used method for analyzing radioactive samples, frequently applied in scenarios related to nuclear test ban verification, nuclear environmental monitoring, and the treatment and disposal of spent nuclear waste. Radioactive samples have complex compositions, typically containing multiple radionuclides. During non-destructive gamma spectroscopy analysis, the characteristic gamma rays emitted by these radionuclides can interfere with each other, especially low-energy gamma rays. Their characteristic peaks superimpose on the Compton plateau generated by high-energy gamma rays. When the relative abundance of the corresponding nuclide is low or the measurement statistics are insufficient, the low-energy gamma ray peaks are easily "submerged" on the Compton plateau, affecting the accurate identification and quantitative analysis of nuclides in the sample. Therefore, reducing the interference of high-energy gamma rays on the low-energy region is crucial for low-energy gamma spectroscopy analysis.

[0003] Currently, the main methods for measuring low-energy characteristic peaks of radionuclides using gamma spectroscopy are:

[0004] Method 1) Increase the measurement time to improve the count of characteristic peaks, or use multiple measurements to reduce the statistical error of the measurement;

[0005] Method 2) Use an anti-Compton spectrometer to measure the sample to reduce the Compton plateau generated by high-energy gamma rays;

[0006] Method 3) First, the target nuclide is purified using radiochemical separation, and then gamma spectroscopy is performed to measure and analyze the sample containing only the target nuclide.

[0007] in:

[0008] Method 1) requires long-term measurements to improve the statistical properties of the energy spectrum, and has limited effect on improving the relative count of characteristic peaks in the low-energy region of the γ-ray spectrum, resulting in low efficiency.

[0009] Method 2) requires a relatively complex anti-Compton spectrometer device, and the anti-Compton spectrometer has limited effectiveness in measuring the anti-coincidence of high-energy scattered photons and relatively poor suppression effect on the low-energy region of the energy spectrum.

[0010] Method 3) requires complex radiochemical separation of radioactive samples, which is detrimental to the timeliness of analysis and the safety of analysts. Summary of the Invention

[0011] The purpose of this invention is to solve the problems of low efficiency, complex equipment, poor timeliness and safety in existing gamma-ray energy spectroscopy methods for measuring low-energy characteristic peaks, and to provide a low-energy gamma-ray energy spectroscopy measurement method based on the gamma-ray attenuation law.

[0012] To achieve the above objectives, the technical solution provided by this invention is:

[0013] A method for measuring low-energy gamma-ray energy spectra based on the attenuation law of gamma rays, characterized by the following steps:

[0014] Step 1: Use a three-dimensional position-sensitive zinc-cadmium telluride detector to detect gamma rays in the radioactive sample;

[0015] Step 2: Based on the anode signal intensity and electron carrier drift time in the three-dimensional position-sensitive cadmium zinc telluride detector, obtain the three-dimensional coordinates (x, y, z) of the location where the γ-ray interacts with the three-dimensional position-sensitive cadmium zinc telluride detector. Here, x and y are the coordinates of the interaction location between the γ-ray and the three-dimensional position-sensitive cadmium zinc telluride detector in the direction parallel to the electrode plate, and z is the coordinate of the interaction location between the γ-ray and the three-dimensional position-sensitive cadmium zinc telluride detector in the direction perpendicular to the electrode.

[0016] Step 3: Calculate the attenuation curves ΔR of γ-rays at different depths of the detector by utilizing the attenuation law of γ-rays passing through a three-dimensional position-sensitive cadmium zinc telluride detector.

[0017] Step 4: Based on the attenuation ΔR curves of γ-rays at different depths of the three-dimensional position-sensitive cadmium zinc telluride detector, perform energy statistics on all γ-rays deposited at depths where the attenuation ΔR is less than a set threshold to obtain the low-energy γ-ray energy spectrum.

[0018] Furthermore, in step 1, the cathode plate of the three-dimensional position-sensitive cadmium zinc telluride detector is of the common cathode type, and the anode plate is of the array type.

[0019] Furthermore, in step 2, the formula for calculating the coordinate z of the interaction position between the γ-ray and the three-dimensional position-sensitive cadmium zinc telluride detector in the direction perpendicular to the electrode is:

[0020]

[0021] Among them, t a t represents the time of data acquisition at the anode readout terminal. c The time of acquisition at the cathode readout terminal, (t) a -t c ) represents the drift time of electron carriers; d0 represents the thickness of the three-dimensional position-sensitive cadmium zinc telluride detector; μ e V represents the electron carrier mobility in the three-dimensional position-sensitive cadmium zinc telluride detector; V is the bias voltage of the three-dimensional position-sensitive cadmium zinc telluride detector.

[0022] Furthermore, in step 3, the formula for calculating the attenuation ΔR curve of γ-rays at different depths of the three-dimensional position-sensitive cadmium zinc telluride detector is as follows:

[0023] ΔR=1-e -μd

[0024] Where μ is the linear attenuation coefficient of γ-rays in the three-dimensional position-sensitive cadmium zinc telluride detector, representing the probability of γ-rays interacting with the three-dimensional position-sensitive cadmium zinc telluride detector per unit distance; d is the depth of the three-dimensional position-sensitive cadmium zinc telluride detector; and e is the base of the natural logarithm.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. The present invention provides a low-energy gamma-ray energy spectrum measurement method based on the attenuation law of radiation, which can detect low-energy gamma rays of radioactive samples in a short time. The measuring device has a simple structure, is easy to assemble, and saves measurement time.

[0027] 2. The low-energy gamma-ray energy spectrum measurement method based on the attenuation law of gamma rays in this invention can solve the problem of severe interference of high-energy gamma rays with low-energy gamma rays during gamma-ray energy spectrum analysis, and realize the distinction between high-energy gamma rays and low-energy gamma rays. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a three-dimensional position-sensitive cadmium zinc telluride detector in an embodiment of the low-energy gamma-ray energy spectrum measurement method based on the attenuation law of the present invention.

[0029] Figure 2 for 241 Am and 137 Figure showing the variation of characteristic gamma-ray intensity attenuation of Cs with detection depth;

[0030] Figure labels: 1-Three-dimensional position-sensitive cadmium zinc telluride detector, 11-Cathode plate, 12-Anode plate; 21-Low-energy gamma rays, 22-High-energy gamma rays; 3-Electron carriers. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] A method for measuring low-energy gamma-ray energy spectrum based on the attenuation law of gamma rays includes the following steps:

[0033] Step 1: Prepare the radioactive sample and the three-dimensional position-sensitive cadmium zinc telluride detector 1. Place the three-dimensional position-sensitive cadmium zinc telluride detector 1 within the measurement range of the radioactive sample and begin the measurement. See [link to relevant documentation]. Figure 1 The three-dimensional position sensitive zinc cadmium telluride detector 1 has a common cathode cathode plate 11 and an array of anode plates 12, wherein the anode plate 12 has an anode readout terminal and the cathode plate 11 has a cathode readout terminal;

[0034] Step 2: The γ-rays emitted by the radioactive sample are incident on the three-dimensional position sensitive cadmium zinc telluride detector 1. The two-dimensional projection coordinates of the interaction position between the γ-rays and the three-dimensional position sensitive cadmium zinc telluride detector 1 on the anode plate 12 are obtained based on the signal intensity collected by the anode readout end of the three-dimensional position sensitive cadmium zinc telluride detector 1. The plane in which the cathode plate 11 is located is the xoy plane, and the z direction is perpendicular to the xoy plane.

[0035] Step 3: Using the signal acquisition times at the anode and cathode readout terminals of the three-dimensional position-sensitive cadmium zinc telluride detector 1, the drift time of electron carrier 3 is obtained, thereby calculating the coordinate z of the interaction position between the γ-ray and the three-dimensional position-sensitive cadmium zinc telluride detector 1 in the direction perpendicular to the electrode.

[0036]

[0037] in:

[0038] t a This is the time when the signal is acquired at the anode readout terminal;

[0039] t c The time of signal acquisition at the cathode readout end;

[0040] (t a -t c () represents the drift time of electron carrier 3;

[0041] d0 is the thickness of the three-dimensional position-sensitive cadmium zinc telluride detector 1;

[0042] μ e The mobility of electron carrier 3 in the three-dimensional position-sensitive cadmium zinc telluride detector 1;

[0043] V is the bias voltage of the three-dimensional position-sensitive cadmium zinc telluride detector 1;

[0044] Then, based on the two-dimensional projection coordinates obtained in step 2, the three-dimensional coordinates of the interaction positions are obtained;

[0045] Step 4: Using the attenuation law of γ-rays passing through the three-dimensional position-sensitive cadmium zinc telluride detector 1, the γ-ray intensity I at different depths of the three-dimensional position-sensitive cadmium zinc telluride detector 1 is calculated.

[0046] I = I0·e -μd ;

[0047] in:

[0048] I0 is the initial intensity of the incident γ-rays;

[0049] μ is the linear attenuation coefficient of γ-rays in the three-dimensional position-sensitive cadmium zinc telluride detector 1, which represents the probability of γ-rays interacting with the three-dimensional position-sensitive cadmium zinc telluride detector 1 per unit distance.

[0050] d represents the depth of the three-dimensional position-sensitive cadmium zinc telluride detector 1;

[0051] Step 5: Based on the ray intensity I obtained in Step 4, calculate the deposition intensity ΔI of the γ-rays within depth d of the three-dimensional position-sensitive cadmium zinc telluride detector.

[0052] ΔI=I0-I=I0-I0·e -μd =I0·(1-e -μd );

[0053] Step 6: Based on the deposition intensity ΔI obtained in Step 5, calculate the attenuation ΔR of γ-rays within depth d of the three-dimensional position-sensitive cadmium zinc telluride detector.

[0054]

[0055] Step 7: Based on the coordinate z of the interaction position between the γ-ray and the three-dimensional position-sensitive cadmium zinc telluride detector 1 in the direction perpendicular to the electrode obtained in Step 3, and the relationship between the γ-ray attenuation amount ΔR and the depth d of the three-dimensional position-sensitive cadmium zinc telluride detector 1 obtained in Step 6, the depth corresponding to the attenuation threshold is set as the statistical depth. Energy statistics are performed on the γ-rays deposited within the statistical depth to distinguish between low-energy γ-rays 21 and high-energy γ-rays 22, thereby completing the measurement of the low-energy γ-ray energy spectrum of the radioactive sample.

[0056] like Figure 2 As shown, 241 Am and 137 The characteristic gamma-ray intensity attenuation of Cs varies with detection depth. Two commonly used gamma-ray standard sources are used. 241 Am and 137 Cs are standard sources for low-energy and high-energy gamma rays, respectively. 241 Am and 137 The characteristic gamma-ray energies of Cs are 59.5 keV and 661.6 keV, respectively. 241 The characteristic gamma rays of Am attenuate by ΔR at a depth of 1 mm (i.e., z = 1 mm) in the three-dimensional position-sensitive cadmium zinc telluride detector 1, while 137 The characteristic gamma rays of Cs attenuate by only 3.5% at the same detection depth. It can be seen that the three-dimensional position-sensitive cadmium zinc telluride detector 1 is insensitive to the detection of high-energy gamma rays in the shallow layer, but has a high detection efficiency for low-energy gamma rays.

[0057] During data acquisition and analysis, only gamma rays deposited in the shallow layer of the detector (i.e., when z is small) are selected for energy statistics. At this time, most of the gamma spectrum count is contributed by low-energy gamma rays, and the portion of high-energy gamma rays deposited outside the shallow layer is not counted, nor is the background signal generated outside the shallow layer. This reduces the interference of high-energy gamma rays and background signals on low-energy gamma rays during the measurement process, resulting in a purer low-energy gamma ray spectrum. This can effectively solve the problem of high-energy gamma rays severely interfering with low-energy gamma ray measurements during gamma spectrum analysis.

Claims

1. A method for measuring low-energy gamma-ray energy spectra based on the attenuation law of gamma rays, characterized in that, Includes the following steps: Step 1: Use a three-dimensional position-sensitive zinc-cadmium telluride detector to detect radioactive samples with gamma rays; the cathode plate of the three-dimensional position-sensitive zinc-cadmium telluride detector is a common cathode type, and the anode plate is an array type; Step 2: Based on the anode signal intensity and electron carrier drift time in the three-dimensional position-sensitive cadmium zinc telluride detector, obtain the three-dimensional coordinates (x, y, z) of the location where the gamma ray interacts with the detector. Here, x and y are the coordinates of the interaction point between the gamma ray and the detector in the direction parallel to the electrode plate, and z is the coordinate of the interaction point in the direction perpendicular to the electrode. The formula for calculating the coordinate z of the interaction point in the direction perpendicular to the electrode is as follows: Among them, t a t represents the time when the signal is acquired at the anode readout terminal. c The time of signal acquisition at the cathode readout terminal, (t) a -t c ) represents the drift time of electron carriers; d0 represents the thickness of the three-dimensional position-sensitive cadmium zinc telluride detector; μ e V represents the electron carrier mobility in the three-dimensional position-sensitive zinc-cadmium telluride detector; V is the bias voltage of the three-dimensional position-sensitive zinc-cadmium telluride detector. Step 3: Utilizing the attenuation law of γ-rays passing through a three-dimensional position-sensitive cadmium zinc telluride detector, calculate the attenuation ΔR curves of γ-rays at different depths within the three-dimensional position-sensitive cadmium zinc telluride detector; the formula for calculating the attenuation ΔR curves of γ-rays at different depths within the three-dimensional position-sensitive cadmium zinc telluride detector is as follows: ΔR=1-e -μd Where μ is the linear attenuation coefficient of γ-rays in the three-dimensional position-sensitive cadmium zinc telluride detector, representing the probability of γ-rays interacting with the three-dimensional position-sensitive cadmium zinc telluride detector per unit distance; d is the depth of the three-dimensional position-sensitive cadmium zinc telluride detector; and e is the base of the natural logarithm. Step 4: Based on the attenuation ΔR curves of γ-rays at different depths of the three-dimensional position-sensitive cadmium zinc telluride detector, perform energy statistics on all γ-rays deposited at depths where the attenuation ΔR is less than a set threshold to obtain the low-energy γ-ray energy spectrum.

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