Gamma detector activation analysis method and pgnaa detection system

Abstract

The application relates to the technical field of gamma spectrum analysis, and particularly provides a gamma detector activation analysis method and a PGNAA detection system, which aims to solve the technical problem that the gamma rays obtained by detecting the existing gamma detector include rays generated by the activation and decay of crystals in a neutron field, thereby causing the component detection result of a to-be-detected sample to be inaccurate. For this purpose, the gamma detector activation analysis method comprises the following steps: irradiating a to-be-detected sample by using a neutron source; repeatedly collecting multiple groups of gamma spectra of the to-be-detected sample by using a gamma detector; constructing a spectrum signal matrix based on the gamma spectra of the to-be-detected sample, wherein the spectrum signal matrix is a mixed signal composed of prompt gamma rays generated by the neutron activation of the to-be-detected sample, environmental background gamma rays and interference signals generated by the activation of crystals in the gamma detector; and obtaining effective prompt gamma rays based on the spectrum signal matrix. The self-interference influence of the detector is effectively reduced, and the evaluation precision of the target element content of the to-be-detected sample is improved.

Description

Technical Field

[0001] This invention relates to the field of gamma energy spectrum analysis technology, specifically providing a gamma detector activation analysis method and a PGNAA detection system. Background Technology

[0002] In the mining, beneficiation, smelting, and refining processes of rare metals, non-ferrous metals, and other strategic materials, there is an urgent need for accurate, real-time online measurement of the composition of raw materials to provide crucial data for the technological processes. Promptly emitted gamma-ray neutron activation analysis (PGNAA) technology, with its features of simultaneous multi-element analysis, short analysis time, and volumetric measurement, can fully meet the real-time online material analysis needs of traditional industrial and mining enterprises such as cement, coal, and metallurgy.

[0003] Gamma detectors are the most commonly used detectors in neutron activation analysis systems. During the detection process, the crystal in the detector mainly responds to gamma rays. However, when the neutron source in the activation analysis system is strong, the crystal in the detector will be activated and produce corresponding activation products. During the decay of the activation products, continuous beta and gamma rays will be generated, which will cause great interference and influence on the detection results and directly affect the accuracy of component detection. Summary of the Invention

[0004] To overcome the aforementioned deficiencies, this application is proposed to provide a solution, or at least a partial solution, to the technical problem that existing gamma detectors detect gamma rays, including those generated by the decay of crystals activated under a neutron field, leading to inaccurate compositional results of the sample. This application provides a gamma detector activation analysis method and a PGNAA detection system.

[0005] In a first aspect, this application provides a method for analyzing the activation of a gamma detector, the method comprising:

[0006] The sample to be tested is irradiated using a neutron source;

[0007] Multiple sets of gamma energy spectra of the sample under test were repeatedly acquired using a gamma detector.

[0008] An energy spectrum signal matrix is ​​constructed based on multiple sets of gamma energy spectra of the sample to be tested. The energy spectrum signal matrix is ​​a mixed signal composed of transient gamma rays generated by neutron activation of the sample to be tested, background gamma rays in the environment, and interference signals generated by crystal activation in the gamma detector.

[0009] Effective transient gamma rays are obtained based on the energy spectrum signal matrix.

[0010] In one specific embodiment of this application, the step of repeatedly acquiring multiple sets of gamma energy spectra of the sample to be tested using a gamma detector includes: acquiring multiple sets of gamma energy spectra of the sample to be tested using a gamma detector at equal time intervals.

[0011] In one specific embodiment of this application, the step of constructing an energy spectrum signal matrix based on the gamma energy spectrum of the sample to be tested includes: constructing the energy spectrum signal matrix by constructing the gamma energy spectrum of each group of samples to be tested according to a preset channel address.

[0012] In one specific embodiment of this application, the gamma detector is a scintillator detector.

[0013] In one specific embodiment of this application, when the scintillator detector is a NaI detector, the interference signal generated by crystal activation in the gamma detector includes... and Gamma rays produced by decay;

[0014] The energy spectrum signal matrix satisfies the following relationship:

[0015] Where S is the energy spectrum signal matrix, A is the background count of the sample and the environment, and B and C are respectively... and The interference counting weights, M1 and M2 are respectively related to the interference count weights. and Nuclide activity-related coefficient matrix.

[0016] In one specific embodiment of this application, the step of obtaining effective transient gamma rays based on the energy spectrum signal matrix includes:

[0017] The energy spectrum signal matrix is ​​vectorized;

[0018] The vectorized energy spectrum signal matrix is ​​then solved.

[0019] The effective transient gamma rays are extracted from the energy spectrum signal matrix based on the solution results.

[0020] In one specific embodiment of this application, the vectorization of the energy spectrum signal matrix includes: vectorizing the energy spectrum signal matrix using the Kronecker product, wherein the vectorized energy spectrum signal matrix is ​​represented as:

[0021] Where vec represents vectorization, I 306 It is a 306×306 identity matrix. Indicates the Kronecker product; and / or

[0022] Solving the vectorized energy spectrum signal matrix includes: solving the vectorized energy spectrum signal matrix using the least squares method.

[0023] In one specific embodiment of this application, the neutron source is an isotopic neutron source or an accelerator neutron source.

[0024] In one specific embodiment of this application, the method further includes: evaluating the content of the target element in the sample to be tested based on the effective transient gamma rays.

[0025] In a second aspect, a PGNAA detection system is provided, which is used to perform the aforementioned gamma detector activation analysis method.

[0026] The above-described technical solutions of this application have at least one or more of the following features. Beneficial effects:

[0027] The gamma detector activation analysis method in this application includes: irradiating the sample to be tested with a neutron source; repeatedly acquiring multiple sets of gamma energy spectra of the sample to be tested using a gamma detector; constructing an energy spectrum signal matrix based on the multiple sets of gamma energy spectra of the sample to be tested. The energy spectrum signal matrix is ​​a mixed signal composed of transient gamma rays generated by neutron activation of the sample to be tested, background gamma rays in the environment, and interference signals generated by crystal activation in the gamma detector; and obtaining effective transient gamma rays based on the energy spectrum signal matrix. The neutron source provides a neutron beam to irradiate the sample to be tested, thereby inducing neutron activation reactions in specific elements of the sample to generate transient gamma rays. The gamma detector acquires multiple sets of gamma energy spectrum data of the sample to be tested. This data includes the mixture of transient gamma rays generated in the sample, background gamma rays in the environment, and interference signals generated by the crystal inside the gamma detector after irradiation by the neutron source. By constructing the energy spectrum signal matrix, these complex data can be integrated, thereby effectively distinguishing and extracting the main transient gamma ray signals. This provides a reliable means for non-destructive analysis of sample components. By accurately identifying and quantifying the transient gamma-ray signal, the influence of detector interference is effectively reduced, improving the accuracy and reliability of activation analysis. It also helps to improve the detection accuracy of the presence and content of specific elements in the sample. Attached Figure Description

[0028] The disclosure of this application will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application. Furthermore, similar numbers in the drawings are used to denote similar components, wherein:

[0029] Figure 1 This is a schematic diagram of the counting of the same group of NaCl solution samples using a NaI gamma detector;

[0030] Figure 2 This is a schematic diagram of the main process of the gamma detector activation analysis method in one embodiment of this application. Detailed Implementation

[0031] Some embodiments of this application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this application and are not intended to limit the scope of protection of this application.

[0032] In the description of this application, "module" and "processor" can include hardware, software, or a combination of both. A module can include hardware circuitry, various suitable sensors, communication ports, memory, and can also include software components, such as program code, or a combination of software and hardware. A processor can be a central processing unit, microprocessor, image processor, digital signal processor, or any other suitable processor. The processor has data and / or signal processing capabilities. The processor can be implemented in software, in hardware, or a combination of both. Non-transitory computer-readable storage media includes any suitable medium capable of storing program code, such as magnetic disks, hard disks, optical disks, flash memory, read-only memory, random access memory, etc. The term "A and / or B" means all possible combinations of A and B, such as only A, only B, or A and B. The terms "at least one A or B" or "at least one of A and B" have a similar meaning to "A and / or B" and can include only A, only B, or A and B. The singular terms "a" or "this" can also include plural forms.

[0033] Currently, traditional gamma detectors detect gamma rays generated by the decay of crystals activated under a neutron field, leading to inaccurate component detection results for the tested samples. For example, sodium iodide (NaI) gamma detectors are the most commonly used detectors in neutron activation analysis systems. During detection, the NaI crystal primarily responds to gamma rays. However, when the neutron source strength in the activation analysis system is high, reaching 1e10 n / s or higher, the Na and I elements in the NaI detector crystal are activated by the system's thermal neutrons to generate Na24 and I128 activation products. The decay of Na24 and I128 produces continuous β and γ rays, which significantly interfere with the detection results and directly affect the accuracy of component detection.

[0034] In PGNAA detection based on a NaI gamma detector, the crystal of the NaI detector will undergo an activation reaction under a thermal neutron field, as follows:

[0035] Na23+n→Na24; I 127+n→I 128

[0036] The attenuation equations for Na24 and I 128 are as follows:

[0037] Among them, the β and γ rays in the decay process directly trigger signal counting in the gamma detector, interfering with the actual effective signal. Its half-life is approximately 15 hours (14.956 hours). Its half-life is approximately 25 minutes (24.99 minutes). The decay of [certain substances] contributes the majority of this, therefore in the continuously measured (20-minute) group, The content of [something] is constantly increasing (and the rate of increase is getting lower and lower).

[0038] During the detection process, the contribution ratio of NaI activation to the total signal varied due to different time intervals. Figure 1 This can serve as a schematic diagram for counting the same group of (sodium chloride) solution samples using a NaI gamma detector. Figure 1 It can be seen that with the increase of irradiation time, there are obvious differences in the number of counts for the same sample in the range of 600keV to 2MeV.

[0039] Therefore, this application proposes a gamma detector activation analysis method and a PGNAA detection system.

[0040] Before explaining the execution process of this application, let me first explain the principle of this application.

[0041] Generally, the contribution of NaI crystal activation to the gamma detector signal is considered to be directly proportional to the content of the products after the activation of Na and I nuclides. The change of NaI crystal activity over time is as follows: A Na-I =N Na-I *σ Na-I *Φ*[1-exp(-λ Na-I *t)]

[0042] Among them, A Na-I The activity of Na24 or I128, N Na-I The nucleon density is Na24 or I128, σ Na-I The thermal neutron microstructure of Na24 or I128 is given by Φ, where Φ is the thermal neutron flux density of the NaI crystal, and λ is the thermal neutron cross section. Na-I t is the decay constant of Na24 or I128, and t is the irradiation time.

[0043] In the time interval [t1, t2], the signal b acquired by the NaI detector i It can consist of the following three parts:

[0044] Among them, a g(t) is the count rate of the instantaneous gamma rays, a 24Na (t) is decay count rate, a 128I (t) is The decay count rate.

[0045] and The decay count rate is directly proportional to their activity at the corresponding moment. Generally speaking, the decay law of radioactive nuclide activity follows an exponential function characteristic, that is...

[0046] The final expression for the change in the NaI activation interference signal count over time exhibits an exponential relationship. Assuming two consecutive measurement segments are [t1, t2] and [t2, t3], then we have:

[0047] When the subsource in the segment [t1,t2] is enabled

[0048] When the neutron source in the range [t1,t2] is turned off

[0049] Where k1 and k2 are coefficients to be determined, λ 24Na yes The decay constant is approximately 7.7243 × 10⁻⁶. -4 min -1 , λ 128I yes The decay constant is approximately 0.02774 min. -1 .

[0050] because The content of [the signal] is directly proportional to the count of the interference signal it contributes. In order to separate the interference signal component from each set of count results, the difference between the two sets of count results is calculated:

[0051] in, This represents all signals detected by the NaI detector within the measurement time interval t2 and t1, a g (t) represents the signal from the sample and surrounding environment that enters the detector due to gamma rays induced by PGNAA.

[0052] During PGNAA detection, the neutron source remains in a stable state. When the sample and other environmental background counts are performed at the same measurement time, the two counts of their contributions should be identical. The experimental intervals for each group of detections should be consistent, i.e., t3 - t2 = t2 - t1.

[0053] So there are

[0054] Therefore,

[0055] C1 and C2 are data associated with the decay constants of the relevant nuclides.

[0056] Based on the above analysis, it can be seen that by collecting multiple sets of data within the same time period, interference signals can be separated from mixed signals.

[0057] The specific implementation of this application will be explained in detail below.

[0058] See appendix Figure 2 , Figure 2 This is a schematic flowchart of the main steps of a gamma detector activation analysis method according to an embodiment of this application.

[0059] like Figure 2 As shown, the gamma detector activation analysis method in this application embodiment mainly includes the following steps S10-S40.

[0060] Step S10: Irradiate the sample to be tested using a neutron source.

[0061] A neutron source is a device or substance capable of producing neutrons to trigger nuclear reactions (such as neutron capture and fission). Neutron sources can be isotopic neutron sources or accelerator neutron sources. Cf-252 (californium-252) is an example of an isotopic neutron source, primarily releasing neutrons through spontaneous fission. Accelerator neutron sources mainly utilize particle accelerators to bombard a target material (such as a Be target) to produce neutrons.

[0062] Specifically, the sample to be tested is irradiated with a neutron source, causing the atomic nuclei in the sample to absorb neutrons and generate radioactive isotopes, which then release transient gamma rays.

[0063] Step S20: Repeatedly acquire multiple sets of gamma energy spectra of the sample to be tested using a gamma detector.

[0064] A gamma detector is a device used to detect gamma rays by converting gamma ray energy into an electrical signal for measurement. Exemplary examples include scintillator detectors, semiconductor detectors, and gas detectors.

[0065] In one specific embodiment of this application, the step of repeatedly acquiring multiple sets of gamma energy spectra of the sample to be tested using a gamma detector includes: acquiring multiple sets of gamma energy spectra of the sample to be tested using a gamma detector at equal time intervals.

[0066] The gamma detector in this embodiment can be a scintillator detector, such as a NaI detector.

[0067] Specifically, a gamma detector can be used to acquire multiple sets of gamma spectra of the sample at equal time intervals. For example, by performing the acquisition at a fixed period, such as every 10 seconds, 1 minute, or longer, multiple sets of gamma spectra of the sample can be obtained.

[0068] Step S30: Construct an energy spectrum signal matrix based on the gamma energy spectrum of the sample to be tested. The energy spectrum signal matrix is ​​a mixed signal composed of the transient gamma rays generated by neutron activation in the sample to be tested, the background gamma rays in the environment, and the interference signal generated by crystal activation in the gamma detector.

[0069] In one specific embodiment of this application, the step of constructing an energy spectrum signal matrix based on the gamma energy spectrum of the sample to be tested includes: constructing the energy spectrum signal matrix by constructing the gamma energy spectrum of each group of samples to be tested according to a preset channel address.

[0070] The channel address refers to the channel address of the multichannel analyzer, which is a component of the detector. The preset channel address range is 110 to 415 channels.

[0071] An energy spectrum signal matrix is ​​a two-dimensional matrix composed of multiple sets of gamma energy spectra arranged according to time series and energy channels. It is used for mathematical modeling and signal separation. The rows of the two-dimensional matrix represent the channel addresses of the acquired signals, and the columns represent the time periods of the measured signals.

[0072] In one specific embodiment of this application, when the scintillator detector is a NaI detector, the interference signal generated by crystal activation in the gamma detector includes... and Gamma rays produced by decay;

[0073] The energy spectrum signal matrix satisfies the following relationship:

[0074] Where S is the energy spectrum signal matrix, A is the background count of the sample and the environment, and B and C are respectively... and The interference counting weights, M1 and M2 are respectively related to the interference count weights. and Nuclide activity-related coefficient matrix.

[0075] Regarding the relation satisfied by the energy spectrum signal matrix, A1 T These could be transient gamma rays generated by neutron activation in the sample under test or background gamma rays from the environment. and This is an interference signal generated by crystal activation in the gamma detector, specifically in the NaI detector. It could be in a gamma detector Interference signals generated by activation It could be in a gamma detector Interference signals generated by activation.

[0076] Specifically, Na I activation interferes with PGNAA detection mainly in the range of 600 keV to 2 MeV, and for the detector multichannel analyzer, the channel address ranges from 110 to 415.

[0077] For example, taking the measurement of multiple sets of gamma spectra of 7 groups of samples as an example, the count of the measurement result of the i-th group (i = 1, 2, 3, ..., 7) in the j-th channel (j = 110, 111, ..., 415) is: S(j,i) = A(j) + B(j)N 24Na (t i )+C(j)N 128I (t i ).

[0078] Where S(j,i) is the total count, A(j) is the count of the sample being tested and the contribution of the background environment, and B(j)N 24Na (t i )yes The decay-induced interference count, C(j)N 128I (t i )yes The count of interference caused by decay is directly proportional to the content of the corresponding element.

[0079] For (j,i)=A(j)+B(j)N 24Na (t i )+C(j)N 128I (t i Transforming the matrix yields the following matrix form:

[0080] Where S is a known 306×7 matrix (corresponding to channels 110–415 of the existing 7 sets of measured energy spectra); A is a 306*1 matrix representing the counts of the sample and background contributions in these channels; 1 T B is a 1×7 vector of all ones; B is a 306*1 matrix. A constant 1×7 matrix, represent The count of interference caused by decay; C is a 306*1 matrix. A constant 1×7 matrix, represent Interference count caused by decay.

[0081] By constructing an energy spectrum signal matrix, it is beneficial to effectively correct the signal collected by the NaI detector, solve the problem of NaI activation interfering with PGNAA detection, and avoid the time and material costs incurred by adding shielding or changing physical methods in existing methods.

[0082] Step S40: Obtain effective transient gamma rays based on the energy spectrum signal matrix.

[0083] Specifically, step S40 can be implemented by the following steps S401 to S403.

[0084] Step S401: Vectorize the energy spectrum signal matrix.

[0085] In one specific embodiment of this application, vectorizing the energy spectrum signal matrix includes: using the properties of the Kronecker product to vectorize the energy spectrum signal matrix, and the vectorized energy spectrum signal matrix is ​​represented as:

[0086] Where vec represents vectorization, I 306 It is a 306×306 identity matrix. It represents the Kronecker product.

[0087] Step S402: Solve for the vectorized energy spectrum signal matrix.

[0088] Specifically, the vectorized energy spectrum signal matrix consists of a series of overdetermined equations. These overdetermined equations can be solved using the least squares method. The basic idea is that for an overdetermined equation ax = b, consider the residual term r = ax - b, and find the x value that minimizes the Euclidean norm of r. Therefore, solving the vectorized energy spectrum signal matrix can be expressed as a least squares problem:

[0089] Solving the above equations yields the coefficients A, B, and C in the energy spectrum signal matrix.

[0090] Step S403: Extract effective transient gamma rays from the energy spectrum signal matrix based on the solution results.

[0091] Specifically, after solving for the coefficients A in the energy spectrum signal matrix, the effective transient gamma rays can be obtained. The effective transient gamma rays refer to the transient gamma rays generated by the activation of neutrons in the sample and the background gamma rays in the environment (that is, A1 in the energy spectrum signal matrix). T ).

[0092] By acquiring effective transient gamma rays based on the energy spectrum signal matrix, correction processing was performed on all signals received by the Na I detector, eliminating interference signals caused by the activation of Na24 and I128, and retaining the transient gamma characteristic signals induced by the sample during the detection process, thereby improving the accuracy and reliability of neutron component detection.

[0093] Based on steps S10-S40 above, the sample to be tested is first irradiated using a neutron source; multiple sets of gamma energy spectra of the sample are repeatedly acquired using a gamma detector; an energy spectrum signal matrix is ​​constructed based on these multiple sets of gamma energy spectra of the sample. This energy spectrum signal matrix is ​​a mixed signal composed of transient gamma rays generated by neutron activation in the sample, background gamma rays in the environment, and interference signals generated by crystal activation in the gamma detector; effective transient gamma rays are obtained based on the energy spectrum signal matrix. The neutron source provides the neutron beam to irradiate the sample, thereby inducing neutron activation reactions in specific elements within the sample, generating transient gamma rays. The gamma detector acquires multiple sets of gamma energy spectrum data from the sample, which includes the transient gamma rays generated in the sample, background gamma rays in the environment, and interference signals generated by neutron irradiation of the crystal inside the gamma detector. By constructing the energy spectrum signal matrix, these complex data can be integrated, thereby effectively distinguishing and extracting the main transient gamma ray signals. This provides a reliable means for non-destructive analysis of sample components. By accurately identifying and quantifying the transient gamma-ray signal, the influence of detector interference is effectively reduced, improving the accuracy and reliability of activation analysis. It also helps to improve the detection accuracy of the presence and content of specific elements in the sample.

[0094] In another embodiment of this application, the method further includes: assessing the content of the target element in the sample to be tested based on the effective transient gamma rays.

[0095] Specifically, the content of the target element in the sample can be further assessed based on the effective transient gamma rays. Assessing the content of the target element in the sample based on the effective transient gamma rays is a quantitative analysis method of the PGNAA system, which will not be elaborated here.

[0096] The method for NaI detector activation analysis applied to PGNAA detection in this application effectively corrects the NaI detector acquisition signal, solves the problem of NaI activation interfering with PGNAA detection, avoids the time and material costs incurred by adding shielding or changing physical methods in existing methods, and improves the accuracy of evaluating the content of target elements in the sample.

[0097] It should be noted that although the steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effect of this application, different steps do not necessarily have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the scope of protection of this application.

[0098] Furthermore, this application also provides a PGNAA detection system for performing the aforementioned gamma detector activation analysis method.

[0099] The technical solution of this application has been described in conjunction with the specific embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A method for analyzing the activation of a gamma detector, characterized in that, The method includes: The sample to be tested is irradiated using a neutron source; Multiple sets of gamma energy spectra of the sample under test were repeatedly acquired using a gamma detector. An energy spectrum signal matrix is ​​constructed based on multiple sets of gamma energy spectra of the sample under test. This energy spectrum signal matrix is ​​a mixed signal composed of transient gamma rays generated by neutron activation in the sample under test, background gamma rays from the environment, and interference signals generated by crystal activation in the gamma detector. When the gamma detector is a NaI detector, the interference signals generated by crystal activation in the gamma detector include… and Gamma rays generated by decay; the energy spectrum signal matrix satisfies the following relationship: in, It is an energy spectrum signal matrix. It is a count of the background levels of the sample and the environment. and They are and Interference count weight, and They are respectively with and Nuclide activity-related coefficient matrix; Obtaining effective transient gamma rays based on the energy spectrum signal matrix includes: Vectorizing the energy spectrum signal matrix includes: vectorizing the energy spectrum signal matrix using the Kronecker product, and the vectorized energy spectrum signal matrix is ​​represented as follows: in, Vectorization is represented. It is a 306×306 identity matrix. Indicates the Kronecker product; Solving the vectorized energy spectrum signal matrix includes: solving the vectorized energy spectrum signal matrix using the least squares method; The effective transient gamma rays are extracted from the energy spectrum signal matrix based on the solution results.

2. The gamma detector activation analysis method according to claim 1, characterized in that, The method of repeatedly acquiring multiple sets of gamma energy spectra of the sample under test using a gamma detector includes: acquiring multiple sets of gamma energy spectra of the sample under test using a gamma detector at equal time intervals.

3. The gamma detector activation analysis method according to claim 1, characterized in that, The construction of the energy spectrum signal matrix based on the gamma energy spectrum of the sample to be tested includes: constructing the energy spectrum signal matrix by dividing the gamma energy spectrum of each group of samples to be tested according to a preset channel address.

4. The gamma detector activation analysis method according to claim 1, characterized in that, The neutron source is an isotopic neutron source or an accelerator neutron source.

5. The gamma detector activation analysis method according to claim 1, characterized in that, The method further includes: assessing the content of the target element in the sample to be tested based on the effective transient gamma rays.

6. A PGNAA detection system, characterized in that, The PGNAA detection system is used to perform the gamma detector activation analysis method according to any one of claims 1 to 5.

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