Gamma spectrum stabilization and energy linearity correction method

Abstract

The gamma spectrum stabilizes and energy linear correction method, including: using a variety of radionuclides to carry out energy curve calibration for the detector, the characteristic peak energy of the selected radionuclide combination should cover the low, medium and high energy regions;Through real-time measurement of the energy spectrum, the characteristic peak channel of the natural radionuclide K-40 and Th-232 in the background is obtained;Adjust the linear digital gain;Correct the energy curve;Use the corrected energy curve to analyze the energy spectrum, in the implementation process, through uninterrupted energy spectrum measurement, long-term continuous dynamic stable spectrum is displayed.The application does not use radioactive sources or LED reference sources, and is simple to integrate;The natural radioactivity existing in the background is used for stable spectrum, and the stable spectrum reference is stable and reliable;The natural K-40 and Th-232 two reference peaks are used for detector energy linear correction, the problem of change of detector energy linearity in long-term use is solved, and the long-term accuracy of energy spectrum analysis is maintained.

Description

Technical Field

[0001] This invention relates to a correction method, specifically a method for stabilizing the measured gamma spectrum based on natural background and correcting for linear variations in the detector system. It relates to the field of nuclear radiation monitoring. Background Technology

[0002] Currently, in order to ensure the accuracy and stability of measurement results, general gamma-ray spectral analysis instruments must continuously stabilize the measured energy spectrum during operation. Otherwise, spectral drift caused by factors such as temperature drift of the detector system and long-term operation will lead to errors in energy spectrum resolution and affect the analysis results.

[0003] Existing spectral stabilization methods mainly include hardware stabilization, "reference source" stabilization, and "natural nuclide characteristic peak stabilization". The main method of hardware stabilization is to adjust the amplifier, high voltage power supply and other hardware to achieve the effect of stabilizing the system gain. This method has two major problems: (1) It has very high requirements for the stability of electronic devices, especially the high voltage power supply. Even a small disturbance can affect the gain change of the energy spectrum, which is difficult to achieve accurately in actual processing; (2) Since this processing method is often not linear, it is generally necessary to predict the drift of the system under different temperatures and operating conditions. Moreover, this prediction is often not accurate enough because it is difficult to control all external conditions to be completely consistent in actual use. This also makes it difficult to guarantee the accuracy of this stabilization method. For example, the prior art: CN112684491B, discloses a digital automatic spectral stabilization method for gamma spectrometer based on temperature change. The invention discloses a digital automatic spectral stabilization method for gamma spectrometer based on temperature change. The steps are as follows: establish the curve relationship between the spectral drift of the gamma spectrometer based on temperature change and temperature change, and perform digital automatic spectral stabilization based on temperature change during the measurement process of the gamma spectrometer. The advantages of this invention are: utilizing a temperature-based digital automatic spectrum stabilization method for gamma spectrometers, passive spectrum stabilization can be achieved without adjusting the detector's operating high voltage and amplifier gain. Digital automatic spectrum stabilization is achieved solely by correcting the pulse amplitude through temperature changes, making it particularly suitable for gamma spectrum measurements under conditions of significant environmental temperature variations. However, the biggest problem with this approach in practice is that while the effect of temperature changes on the spectrum is consistent with a certain pattern, the linearity and gain of the spectrometer system are affected not only by temperature but also by factors such as device characteristics and long-term stability. Therefore, this method is only applicable to stabilizing the gamma spectrum under conditions of significant temperature variations, and the stabilization accuracy is relatively low. In real-world environments, temperature changes are often small, making hardware-level stabilization extremely difficult to implement in practice.

[0004] The "reference source" spectral stabilization is achieved by embedding a stable radioactive source or a collection of radioactive sources within the spectrometer system. This source continuously releases radioactivity, forming fixed characteristic peaks in the energy spectrum. During spectral stabilization, the change in the peak position of this defined characteristic peak is used to adjust the linear gain, ultimately stabilizing the energy spectrum. The advantages of this method are the use of a defined reference peak, high adjustment accuracy, and a simple algorithm. For example, existing technologies such as CN110515116B disclose an unmanned aerial vehicle (UAV) airborne gamma-ray spectrum detection and data processing system and its processing method, which uses a built-in Am-241 radioactive source for spectral stabilization. CN204575860U discloses a portable gamma-ray spectrometer, which uses a built-in pure potassium nitrate (containing K-40) system for spectral stabilization. CN106405612A discloses an in-situ marine water gamma-ray radiation detector and its data processing method, which uses an LED light source built into the detector to correct spectral drift. However, the aforementioned existing technologies have significant drawbacks: (1) Radioactive sources are controlled substances, and carrying radioactive sources in equipment incurs considerable manufacturing costs, management costs, and management risks for environmental pollution treatment and future waste disposal; (2) Due to the built-in radioactive source, this internal influence must be removed during nuclide identification and analysis, which significantly affects the overall analytical accuracy. To avoid the defects of radioactive source usage, some spectrometer systems use stable LED light sources for spectral stabilization, replacing scintillator crystals with LEDs to generate light signals, which are then used in the electronic system to form a spectrum, and the peak positions of characteristic peaks are used for spectral stabilization. The major drawback of this method is that it can only stabilize the electronic system, mainly the photoelectric conversion device, and cannot solve the drift of the detector itself. Since the main drift factor in the spectrometer system is often the detector, it lacks sufficient practicality.

[0005] “Spectrum stabilization using natural nuclide characteristic peaks” is a relatively mainstream implementation method in recent years. The biggest difference between it and “reference source” spectrum stabilization is that it uses characteristic peaks generated by natural nuclides for spectrum stabilization. This natural nuclide is often K-40. K-40 characteristic peaks are obtained through long-term accumulation. By accurately measuring the K-40 peak position, the linear gain of the system is adjusted accordingly to stabilize the measured energy spectrum of the system. This method is currently the mainstream technology on the market and has strong practicality. For example, the existing technology CN111679312A discloses a spectrum stabilization method for an N-16 radiation monitor and proposes a method for stabilizing the spectrum using the 1460.8keV characteristic peak of natural K-40. However, it has the following disadvantages: (1) In actual use, it is generally necessary to use characteristic rays of different energies to prefit the scale energy curve. The subsequent spectrum stabilization is adjusted based on this standard. Using a single energy characteristic peak for correction has a relatively high risk and can easily cause spectrum stabilization deviation or even error. (2) The conventional method of using natural nuclide characteristic peaks for spectrum stabilization does not consider the linear change of detector energy after long-term operation. If the detector linearity changes, the pre-calibrated energy curve cannot accurately represent the current detector energy linearity, and the energy spectrum analysis results of the system after stabilization will also be deviated accordingly. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention discloses a method for stabilizing the gamma spectrum and linearly correcting its energy, the technical solution of which is as follows:

[0007] A method for stabilizing the gamma spectrum and linearly correcting its energy, characterized by:

[0008] Step 1: Calibrate the detector's energy profile using multiple radionuclides. The characteristic peak energies of the selected radionuclide combination should cover the low, medium, and high energy regions. After calibration, obtain the detector's energy profile, expressed as E = S0 + S1*A + S2*A. 2 Where A is the tunnel address, S0, S1, and S2 are curve polynomial parameters, and the K-40 reference peak tunnel address is A0.

[0009] Step 2: Obtain the characteristic peak addresses of natural nuclides K-40 and Th-232 in the background spectrum by measuring the background spectrum; record the characteristic peak address of K-40 as A1 and the characteristic peak address of Th-232 as A2;

[0010] Step 3: Adjust the linear digital gain p = A0 / A1 to adjust the peak position of K-40 to the initial reference peak address. At this time, the characteristic peak address of K-40 is A0, and the characteristic peak address of Th-232 is A2' = A2*p.

[0011] Step 4: Correct the energy curve;

[0012] Step 5: Perform energy spectrum analysis using the corrected energy curve.

[0013] During implementation, steps two through five are repeated through continuous energy spectrum measurements to achieve long-term, continuous, and dynamically stable energy spectrum.

[0014] Beneficial effects

[0015] (1) No radioactive source or LED reference source is used, making integration simple. (2) Natural radioactivity present in the background is used for spectrum stabilization, ensuring a stable and reliable spectrum reference. (3) Two reference peaks, natural K-40 and Th232, are used for detector energy linear correction, solving the problem of detector energy linearity changes during long-term use and maintaining the long-term accuracy of energy spectrum analysis. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the process for the γ-ray spectrum stabilization and energy linear correction method of the present invention;

[0017] Figure 2 This is a schematic diagram of the mixed spectrum of Am-241, Cs-137, and Co-60 obtained in this invention;

[0018] Figure 3 This is a schematic diagram illustrating the peak positions of characteristic peaks of Am-241, Cs-137, and Co-60 obtained by peak finding in this invention.

[0019] Figure 4 This is a schematic diagram of the energy curve calibration process of the present invention;

[0020] Figure 5 A schematic diagram showing the reference peak position of the characteristic peak of the natural nuclide K-40 for this invention;

[0021] Figure 6 This is a schematic diagram showing the peak positions of the natural K-40 and Th-232 characteristic peaks obtained in the actual measurement of this invention. Detailed Implementation

[0022] The method for stabilizing the gamma spectrum and linearly correcting its energy includes the following steps:

[0023] Step 1: Calibrate the detector's energy profile using multiple radionuclides. The characteristic peak energies of the selected radionuclide combination should cover the low, medium, and high energy regions. As an example, Am-241, Cs-137, and Co-60 can be used as calibration nuclides. After calibration, obtain the detector's energy profile, which can be expressed as E = S0 + S1*A + S2*A. 2 Where A is the channel address, and S0, S1, and S2 are the curve polynomial parameters. The channel address of the natural K-40 reference peak is obtained by measuring the natural background energy spectrum, which is A0.

[0024] 1-1 Using radioactive sources Am-241, Cs-137, and Co-60 placed near the detector, energy spectrum measurements were performed to obtain the mixed spectrum of Am-241, Cs-137, and Co-60, such as... Figure 2 As shown.

[0025] 1-2 Gaussian fitting was performed on the characteristic peaks of Am-241, Cs-137, and Co-60 respectively to obtain the peak positions of the fitted Gaussian peaks. In the above embodiment, the characteristic peak energy of Am-241 is 59.5 keV, and the peak position is channel 105.622; the characteristic peak energy of Cs-137 is 661.7 keV, and the peak position is channel 1035.82; the characteristic peak energies of Co-60 are 1173 keV and 1332 keV, and the peak positions are channels 1797.23 and 2034.2 respectively. Figure 3 As shown.

[0026] Steps 1-3 involve fitting the energy and peak position information of all characteristic peaks to obtain an energy scale curve. In this embodiment, the scale points [105.622, 59.5], [1035.82, 661.7], [1797.23, 1173], and [2034.2, 1332] are subjected to polynomial fitting to obtain the energy scale curve E = S0 + S1*A + S2*A. 2 The scale results are S0 = -7.5415, S1 = 0.6333, and S2 = 1.265e-5. For example... Figure 4 As shown.

[0027] 1-4 The background energy spectrum was measured, and the K-40 reference peak address A0 = 2220 was obtained. Figure 5 As shown.

[0028] Step 2: In actual measurement, the characteristic peak addresses of natural nuclides K-40 and Th-232 in the background spectrum are obtained by measuring the background spectrum in real time. The characteristic peak address of K-40 (E1 = 1460.8 keV) is recorded as A1, and the characteristic peak address of Th-232 (E2 = 2614.5 keV) is recorded as A2.

[0029] In this embodiment, the software automatically stabilizes the energy spectrum by measuring it over a period of time. Automatic stabilization requires acquiring stable characteristic peaks, but generally, no known artificial nuclides are available to provide reference characteristic peaks during the measurement process. In the software implementation, the characteristic peak energies of K-40 and Th-232 are higher than those of most artificial nuclides, are largely undisturbed, and are naturally occurring, with stable peak count rates. Because the K-40 characteristic peak count rate is higher than that of Th-232, this method uses the naturally occurring K-40 characteristic peak as the reference peak. This acquisition process uses a peak-finding algorithm, the basic principle of which is to search for peaks from high-energy regions to low-energy regions, finding all characteristic peaks in the energy spectrum. The K-40 characteristic peak is then confirmed by comparing it with the characteristics of the natural K-40 characteristic peak. The comparison features include peak area and peak half-width at half-maximum (FWHM), etc. (The content of K-40 in nature is a small range; the FWHM of the detector for the K-40 characteristic peak is a confirmatory value when the statistical count is sufficiently large).

[0030] Taking the absence of artificial nuclides in the surrounding environment as an example, the measured energy spectrum during software operation is shown in the figure. Peak locations corresponding to the characteristic peak energies of K-40 and Th-232 are recorded separately, as shown below. Figure 6 As shown, the records are A1 = 2025.78 questions and A2 = 3553.49 questions.

[0031] Step 3: Adjust the linear digital gain p = A0 / A1 to adjust the peak position of the K-40 characteristic peak to the initial reference peak address. After adjustment, the peak position address of the K-40 characteristic peak is A0, and the peak position address of the Th-232 characteristic peak is A2'.

[0032] Adjusting the gain is to move the reference peak position to the same fixed channel address, because energy spectrum analysis relies on knowing the energies of all characteristic peaks. Spectral drift caused by various reasons alters the correspondence between channel addresses and energies, leading to deviations in the energy of the characteristic peaks obtained through peak finding, and consequently, inaccurate energy spectrum analysis results. Therefore, by adjusting the gain, the reference peak is first adjusted to a fixed channel address, and then the energy curve is corrected. In this embodiment, the gain adjustment value is P = 2220 / 2025.78 = 1.096. After adjustment, the channel address of the K-40 characteristic peak is A0 = channel 2220, and the channel address of the Th-232 characteristic peak is A2' = 3553.49 * 1.096 = channel 3894.62.

[0033] Step 4: Correct the energy curve. The specific implementation method is as follows: S1' = S1; Substitute the two points [A0, E1] and [A2', E2] into E = S0' + S1'*A + S2'*A 2 , thus obtaining new S0' and S2'.

[0034] In this embodiment, S1' = S1 = 0.6333. Substituting [2220, 1460.8] and [3894.62, 2614.5] into E = S0' + S1' * A + S2' * A 2 Calculations show that S0' = 10.01 and S2' = 9.103e-6.

[0035] Step 5: Perform energy spectrum analysis using the corrected energy curve.

[0036] During software implementation, steps two through five are repeated through continuous energy spectrum measurements to achieve long-term, continuous, and dynamically stable energy spectrum.

[0037] Energy spectrum analysis is used to identify radionuclides and subsequently perform quantitative activity calculations. Accurate energy calibration is a prerequisite for correct energy spectrum analysis. During long-term measurements, it's generally not possible to continuously calibrate using a radioactive source. Furthermore, with prolonged use or other factors causing detector aging, the detector's energy linearity changes. Simply adjusting the linear gain to stabilize the reference peak at a fixed address without correcting the energy curve leads to deviations in the characteristic peak positions, ultimately affecting identification accuracy. In software implementation, the K-40 and Th-232 characteristic peak energies are higher than those of most artificial nuclides, are largely undisturbed, and naturally exist, with stable peak count rates and other values. Long-term spectral stabilization and energy linearity correction using the K-40 and Th-232 characteristic peak energies ensure that the equipment's energy linearity remains relatively accurate, allowing for long-term high-precision measurements.

[0038] This invention uses the characteristic information of two or more background natural radionuclides to correct the linearity of detector energy; uses different types of radioactive sources for pre-energy calibration; and uses the energy spectrum characteristic information of natural nuclides for spectrum stabilization during actual use, adjusting the K-40 peak position to the initial reference peak address through linear digital gain.

[0039] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A method for stabilizing the gamma spectrum and linearly correcting its energy, characterized by: Step 1: Calibrate the detector's energy curve using multiple radionuclides. After calibration, obtain the detector's energy curve, which is expressed as E = S0 + S1*A + S2*A. 2 Where A is the channel address, S0, S1, and S2 are curve polynomial parameters. The characteristic peak channel address of K-40 is obtained by measuring the natural background spectrum and used as the initial reference peak, with the channel address being A0. Step 2: Obtain the characteristic peak addresses of natural nuclides K-40 and Th-232 in the background by measuring the energy spectrum in real time; record the characteristic peak address of K-40 as A1 and the characteristic peak address of Th-232 as A2; Step 3: Adjust the linear digital gain p=A0 / A1 to adjust the peak position of K-40 to the initial reference peak address. At this time, the characteristic peak address of K-40 is A0, and the characteristic peak address of Th-232 is A2'=A2*p. Step 4: Correct the energy curve; Step 5: Perform energy spectrum analysis using the corrected energy curve; use Am-241, Cs-137, and Co-60 as nuclides for energy curve calibration; record the characteristic peak E1=1460.8keV of K-40 as channel A1, and record the characteristic peak E2=2614.5keV of Th-232 as channel A2; the method for correcting the energy curve is as follows: S1'=S1; substitute the two points [A0,E1] and [A2',E2] into E=S0'+S1'*A+S2'*A 2 To obtain new S0' and S2'; the characteristic peak energies of the selected radionuclide combination should cover the low, medium and high energy regions.

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