A nuclide positioning method based on cascade transition and its ray detection system

Abstract

The present invention discloses a nuclide positioning method based on cascade transition and a ray detection system thereof, which relates to the technical field of nuclide positioning. The method solves the current problem of lack of effective positioning of special nuclear materials. Through the cascade transition of nuclear materials, the corresponding energy information and time data are obtained by using detectors, and the samples are quickly detected, which reduces the detection time and effectively assists the staff to act at the first time; by processing the time data, the corresponding single curved surface range is drawn to realize the positioning of the nuclide, the calculation amount is small, and the nuclide positioning rate is further improved; the ray detection system has a simple structure and is easy to operate, and the requirements for the knowledge reserve of the staff are low, so that the staff can quickly master the use method, and can be widely used in multiple fields.

Description

Technical Field

[0001] The invention relates to the technical field of nuclide positioning, and in particular to a nuclide positioning method based on cascade transition and a ray detection system thereof. Background Art

[0002] The smuggling of special nuclear materials (235U and 239Pu) poses a huge threat to human security and world peace. To date, the IAEA's illicit trafficking database has reported thousands of nuclear smuggling incidents, including sensitive materials such as highly enriched uranium and plutonium. At present, traditional X-ray detection devices used at ports or borders cannot effectively detect special nuclear materials. Therefore, it is urgent to develop fast and accurate non-destructive testing technologies for the smuggling of special nuclear materials. Non-destructive testing methods based on nuclear resonance fluorescence (NRF) have been proposed in the context of industrial applications and nuclear safety assurance. Through the NRF non-destructive testing method, contraband can be detected without unpacking, and the missed detection rate is greatly reduced. It is one of the future development directions of nuclear technology. At present, there is a lack of a special nuclear material detection method with a simple structure, easy operation, and independent intellectual property rights, which makes it impossible to effectively and quickly detect special nuclear materials, resulting in the inability of staff to take action in the first time. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a nuclide positioning method based on cascade transition and a ray detection system thereof, which solves the problem that the prior art lacks a special nuclear material detection method with a simple structure, easy operation and independent intellectual property rights, resulting in the inability to effectively and quickly detect special nuclear materials and the inability of staff to take action in the first time.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0005] A method for nuclide positioning based on cascade transition is provided, which comprises the following steps:

[0006] S1. The sample to be tested is activated by irradiation of high-energy particles and cascade transition occurs, thereby obtaining the corresponding cascade transition characteristic rays;

[0007] S2. Continuously capturing cascade transition characteristic rays of different energy levels through at least six detectors, obtaining energy spectrum information of the cascade transition characteristic rays and recording corresponding ray arrival time data; wherein the energy spectrum information includes the energy spectrum and its corresponding energy information;

[0008] S3, judging whether the characteristic peak of the energy spectrum is less than the characteristic threshold value, if so, returning to step S1; otherwise, adding 1 to the effective count of the characteristic peak and entering step S4; wherein the initial value of the effective count of the characteristic peak is 0;

[0009] S4, judging whether the effective count of the characteristic peak reaches the target value, if so, proceeding to step S5; otherwise, returning to step S1;

[0010] S5, judging whether the sample under test contains characteristic peaks of special nuclides according to the energy information of characteristic peaks of the energy spectrum; if so, performing background subtraction on the energy spectrum to obtain a screened energy spectrum and proceeding to step S6; otherwise, the operation is terminated;

[0011] S6, performing cascade transition energy screening on the energy spectrum after the primary screening, identifying the cascade transition characteristic peaks of special nuclides, and obtaining energy information of the cascade characteristic peaks after the secondary screening;

[0012] S7, calculating the ray arrival time data corresponding to the energy information of the cascade characteristic peak after the secondary screening to obtain the corresponding time difference data; and obtaining the corresponding optical path difference data based on the time difference data;

[0013] S8. Draw the corresponding single-curved surface range according to the optical path difference data; and locate the sample to be tested according to each single-curved surface range.

[0014] Further, high-energy particles include X-ray photons, gamma-ray photons, electrons, protons, neutrons and heavy ions.

[0015] Furthermore, the cascade transition rays are gamma rays with time correlation and space correlation.

[0016] Furthermore, the specific process of the screening in step S6 is: judging whether the energy spectrum after one screening meets the screening criteria, if so, retaining the energy spectrum and the corresponding time data; otherwise, discarding the energy spectrum and the corresponding time data.

[0017] Furthermore, step S7 further includes:

[0018] S7-1. The energy information of the cascade characteristic peaks obtained after secondary screening and the arrival time data of the rays corresponding to the detection of each detector are defined as [E i ,t i1 ,t i2 ,…,t i n];

[0019] S7-2, according to the formula:

[0020] Δt ikj =t ij -t kj

[0021] Δt ik =[Δt i,k,2 ,…,Δt i,k,j ,…,Δt i,k,n ]

[0022]

[0023] Get the time difference data matrix Δt between detector i and other detectors i ; where t ij ,t kj Respectively represent the data of detector i and detector k at the jth time, Δt ikj represents the j-th time difference data between detector i and detector k, Δt ik represents the time difference data matrix between detector i and detector k, [Δt i,k,2 ,…,Δt i,k,j ,…,Δt i,k,n ] represent the time difference data of detector i and detector k respectively, and J+1 represents the total number of detectors corresponding to the energy information and time data after secondary screening;

[0024] S7-3. Calculate each time difference data using the optical path difference formula to obtain corresponding optical path difference data.

[0025] Furthermore, step S8 further includes:

[0026] S8-1. Select any two detectors as fixed points, use the line between the two fixed points as the main axis, and draw a single curve and the corresponding single curve range according to each optical path difference data;

[0027] S8-2. Determine whether the ranges of the single curves overlap; if so, use the overlapping range as the spatial position of the sample to be tested, thus completing the positioning of the nuclide.

[0028] A ray detection system is provided, which includes a cascade transition ray acquisition module, a detection module, an energy information processing module, a data screening module, a data analysis module and a nuclide positioning module; wherein:

[0029] A cascade transition ray acquisition module is used to emit high-energy particles to activate the sample under test and emit cascade transition rays;

[0030] A detection module is used to detect the cascade transition rays using a detector, obtain the corresponding energy spectrum information and record the corresponding ray arrival time data;

[0031] The energy information processing module is used to determine whether the energy information is invalid; based on the valid energy information, determine whether the sample under test contains special nuclides, and perform background subtraction on the energy spectrum to obtain a screened energy spectrum;

[0032] The data screening module is used to perform energy screening on the energy spectrum after the primary screening, extract the cascade characteristic peaks of special nuclides on the energy spectrum, and obtain the energy information of the cascade characteristic peaks after the secondary screening;

[0033] A data analysis module is used to calculate the ray arrival time data of the cascade characteristic peak after secondary screening to obtain the corresponding time difference data; and obtain the corresponding optical path difference data based on the time difference data;

[0034] The nuclide positioning module is used to draw the single-curved surface range corresponding to the optical path difference of the cascade characteristic peak after secondary screening, and locate the nuclide according to the single-curved surface range.

[0035] Furthermore, the detection module includes a plurality of lanthanum bromide detectors and high-purity germanium detectors; wherein the number of lanthanum bromide detectors is not less than four.

[0036] The beneficial effects of the present invention are as follows: the present method solves the current problem of lack of effective positioning of special nuclear materials, through the cascade transition of nuclear materials, using the detector to obtain the corresponding energy information and time data, to quickly detect the sample, reduce the detection time and effectively assist the staff to act at the first time; by processing the time data and drawing the corresponding single curved surface range, the positioning of the nuclide is realized, the calculation amount is small, and the nuclide positioning rate is further improved;

[0037] The ray detection system has a simple structure and is easy to operate, and has low requirements on the knowledge reserve of the staff, so that the staff can quickly master the use method, and can be widely used in multiple fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flow chart of the method of the present invention;

[0039] Figure 2 It is a system structure diagram of an embodiment of the present invention;

[0040] Figure 3 It is a schematic diagram of cascade transition;

[0041] Figure 4 This is a schematic diagram of the single curve range. DETAILED DESCRIPTION

[0042] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0043] like Figure 1 As shown, a nuclide positioning method based on cascade transition includes the following steps:

[0044] S1. The sample to be tested is activated by irradiating it with high-energy particles and undergoing cascade transitions, thereby obtaining the corresponding cascade transition characteristic rays. The excited nuclei are obtained by nuclear resonance fluorescence, nuclear reactions, or spontaneous decays. When the excited nuclei return to the ground state through emission cascade transitions, they emit time-correlated rays, namely cascade transition rays.

[0045] High-energy particles include X-ray photons, gamma-ray photons, electrons, protons, neutrons, and heavy ions

[0046] Cascade transition rays are gamma rays with time correlation and space correlation. They are produced by using the cascade rays emitted by spontaneous decay of certain specific radioactive sources, or radioactive nuclides with positron decay, which emit positrons after decay, and positron-electron annihilation occurs, generating two gamma rays with time correlation and space correlation.

[0047] S2. Continuously capture cascade transition characteristic rays of different energy levels through at least six detectors, obtain energy spectrum information of cascade transition characteristic rays and record corresponding ray arrival time data; wherein the energy spectrum information includes the energy spectrum and its corresponding energy information, and the ray arrival time data is the time when each ray signal in the characteristic peak is detected by the detector;

[0048] S3, determine whether the characteristic peak of the energy spectrum is less than the characteristic threshold, if so, return to step S1; otherwise, add 1 to the effective count of the characteristic peak and enter step S4; wherein the initial value of the effective count of the characteristic peak is 0; set the characteristic threshold according to actual needs;

[0049] S4, judging whether the effective count of the characteristic peak has reached the target value, if so, proceeding to step S5; otherwise, returning to step S1, and continuing to accumulate effective counts;

[0050] S5. Determine whether the sample under test contains characteristic peaks of special nuclides based on the energy information of the characteristic peaks of the energy spectrum; if so, it is determined that there are special nuclear materials in the sample under test, which need to be monitored intensively, and the energy spectrum is background-subtracted to obtain the energy spectrum after a screening and enter step S6; otherwise, the operation is terminated; taking 235U as an example, the energy of its nuclear resonance fluorescence characteristic ray is 1734keV, and the characteristic ray energy values ​​of other special nuclear materials such as 239Pu can be queried from the nuclear database.

[0051] S6, performing cascade transition energy screening on the energy spectrum after the primary screening, identifying the cascade transition characteristic peaks of special nuclides, and obtaining energy information of the cascade characteristic peaks after the secondary screening;

[0052] The specific process of screening in step S6 is: determine whether the energy spectrum after one screening meets the screening criteria, if so, retain the energy spectrum and the corresponding time data; otherwise, discard the energy spectrum and the corresponding time data. Among them, the cascade transition characteristic ray information of special nuclides can be queried through the nuclear database, or through experimental testing when the system is built, the cascade transition characteristic peaks of special nuclides with more obvious characteristics can be selected as screening criteria.

[0053] Because in the actual detection process, the detector not only obtains the energy information of the cascade transition rays, but also includes the energy information of the photon scattering background and the noise information of the surrounding environment. Energy screening of the energy information obtained by the detector through energy requirements can further improve the accuracy of judging the type of nuclide and locating the nuclide.

[0054] S7, calculating the ray arrival time data corresponding to the energy information of the cascade characteristic peak after the secondary screening to obtain the corresponding time difference data; and obtaining the corresponding optical path difference data based on the time difference data;

[0055] Step S7 further comprises:

[0056] S7-1. The energy information of the cascade characteristic peaks obtained after secondary screening by each detector and the corresponding ray arrival time data are defined as [E i ,t i1 ,t i2 ,…,t in ];

[0057] S7-2, according to the formula:

[0058] Δt ikj =t ij -t kj

[0059] Δt ik =[Δt i,k,2 ,…,Δt i,k,j ,…,Δt i,k,n ]

[0060]

[0061] Get the time difference data matrix Δt between detector i and other detectors i ; where t ij ,t kj Respectively represent the data of detector i and detector k at the jth time, Δt ikj represents the j-th time difference data between detector i and detector k, Δt ik represents the time difference data matrix between detector i and detector k, [Δt i,k,2 ,…,Δt i,k,j,…,Δt i,k,n ] represent the time difference data of detector i and detector k respectively, and J+1 represents the total number of detectors corresponding to the energy information and time data after secondary screening;

[0062] S7-3. Calculate each time difference data using the optical path difference formula to obtain corresponding optical path difference data.

[0063] S8. Draw the corresponding single-curved surface range according to the optical path difference data; and locate the sample to be tested according to each single-curved surface range.

[0064] Step S8 further comprises:

[0065] S8-1. Select any two detectors as fixed points, take the line between the two fixed points as the main axis, and draw a single curve and the corresponding single curve range according to each optical path difference data; wherein the single curve is half of the hyperbola.

[0066] S8-2. Determine whether the ranges of the single curves overlap; if so, use the overlapping range as the spatial position of the sample to be tested, thus completing the positioning of the nuclide.

[0067] A ray detection system includes a cascade transition ray acquisition module, a detection module, an energy information processing module, a data screening module, a data analysis module and a nuclide positioning module; wherein:

[0068] A cascade transition ray acquisition module is used to emit high-energy particles to activate the sample under test and emit cascade transition rays;

[0069] A detection module is used to detect the cascade transition rays using a detector, obtain the corresponding energy spectrum information and record the corresponding ray arrival time data;

[0070] The energy information processing module is used to determine whether the energy information is invalid; based on the valid energy information, determine whether the sample under test contains special nuclides, and perform background subtraction on the energy spectrum to obtain a screened energy spectrum;

[0071] The data screening module is used to perform energy screening on the energy spectrum after the primary screening, extract the cascade characteristic peaks of special nuclides on the energy spectrum, and obtain the energy information of the cascade characteristic peaks after the secondary screening;

[0072] A data analysis module is used to calculate the ray arrival time data of the cascade characteristic peak after secondary screening to obtain the corresponding time difference data; and obtain the corresponding optical path difference data based on the time difference data;

[0073] The nuclide positioning module is used to draw the single-curved surface range corresponding to the optical path difference of the cascade characteristic peak after secondary screening, and locate the nuclide according to the single-curved surface range.

[0074] The detection module includes multiple lanthanum bromide detectors and high-purity germanium detectors; among them, the number of lanthanum bromide detectors is not less than four, and four or more lanthanum bromide detectors can realize the positioning function. The more lanthanum bromide detectors there are, the more the positioning error can be eliminated, thereby improving the positioning accuracy and making the final positioning information more accurate.

[0075] In one embodiment of the present invention, Figure 2 As shown in the figure, the detectors are 5 lanthanum bromide detectors and 1 high purity germanium detector. The lanthanum bromide detector has high time resolution, which is good for positioning, and the high purity germanium detector has high energy resolution, which is good for nuclide identification. In an ideal state, the lanthanum bromide detector and the high purity germanium detector are evenly placed in the space around the sample to be tested. However, in actual applications, considering the photon scattering background, the detectors are generally placed in the back corners, and the front corners are generally not placed. Figure 3 shown.

[0076] like Figure 3 As shown, taking nuclear resonance fluorescence as an example, by irradiating the sample to be tested with gamma rays of a specific energy, the atomic nuclei of the sample are excited from the ground state to the resonance state, and nuclear resonance fluorescence is generated. The excited atomic nuclei can return to the ground state by directly emitting gamma rays with the same energy as the absorbed energy, or by a series of cascade transitions. The atomic nuclei can return to the excited state by discovering cascade transitions γ1 and γ2. Cascade transitions γ1 and γ2 are the key to the nuclide positioning in this technology; as shown in Figure 4 As shown, the excited nucleus returns to the ground state through the cascade transitions γ1 and γ2. When γ1 is detected by detector 1, the energy value E1 of the ray and the arrival time t1 will be recorded. If the subsequently emitted γ2 happens to be detected by detector 2, the corresponding energy value E2 and the arrival time t2 will also be recorded. If the subsequently emitted γ2 is not detected by detector 2, but is detected by detector 3 at time t3, or by detector 4 at time t4, then the time difference Δt between the time t2, t3, t4 when γ2 is detected by detectors 2, 3, 4 and the time t1 when γ1 is detected by detector 1 is 12 =t2-t2, Δt 13 =t1-t3 and Δt 14 =t1-t4.

[0077] Take detector 1 and detector 2 as fixed points and the line between them as the main axis, such as Figure 4 As shown, the optical path difference can be drawn as c*Δt 12 The single curved surface (half of the hyperbolic surface) of the sample to be tested has a certain spatial distribution, so the time difference Δt is not a fixed value, but satisfies a certain distribution according to the shape of the sample to be tested. The optical path difference c*Δt is also a range, which corresponds to the shape boundary of the sample to be tested. Among them, c represents the speed of light.

[0078] Optical path difference c*Δt between detector 1 and detector 2 12 The single curved surface range in this direction can be drawn; similarly, the optical path difference c*Δt between detectors 1 and 3 13 The single curved surface range in the corresponding direction can also be drawn. If detectors 1, 2, and 3 are on the same plane, the intersection of these single curved surfaces is the projection of the sample to be tested on the plane. It can be seen that three detectors can achieve positioning of a two-dimensional plane.

[0079] If three-dimensional positioning is to be achieved, detector 4 is required, and detector 4 cannot be in the same plane as detectors 1, 2, and 3. Optical path difference c*t 14 The single curved surface range can also be drawn. Optical path difference c*t 12 , c*Δt 13 and c*t 14 The overlapping part in space is the spatial position of the sample to be tested.

[0080] On the basis of 4 detectors, if we continue to increase the number of detectors placed at different positions in the space, such as detector 5 and detector 6, we can calculate the optical path difference c*t 15 and c*Δt 16 , continue to increase the number of single-curved surfaces. The more single-curved surfaces there are, the finer the intersection points of all single-curved surfaces depicted in space will be, which is conducive to increasing the accuracy of positioning. When the number of detectors in space is large enough, it is even possible to roughly depict the outline of the sample to be tested based on the distribution of the common intersection points of all single-curved surfaces. Therefore, increasing the number of detectors can not only increase the probability of cascade transition rays being detected by different detectors, saving the time required for measurement, but also increase positioning accuracy.

[0081] In practical applications, different nuclides emit different characteristic rays after resonance excitation. Therefore, the energy information of the nuclear resonance fluorescence characteristic rays detected by the detector can be used to determine the type of nuclide.

[0082] In summary, the present invention solves the current problem of lack of effective detection of special nuclear materials. By cascading transitions in nuclear materials and using detectors to obtain corresponding energy information and time data, the sample can be quickly detected, the detection time can be reduced, and the staff can be effectively assisted to act at the first time. By processing the time data and drawing the corresponding single curved surface range, the nuclide can be located with a small amount of calculation, which further improves the nuclide location rate. The detection system of the present invention has a simple structure and is easy to operate, and has low requirements on the knowledge reserve of the staff, so that the staff can quickly master the use method, and can be widely used in multiple fields.

Claims

1. A nuclide positioning method based on cascade transition, characterized in that: The following steps are involved: S1. The sample to be tested is activated by irradiation of high-energy particles and cascade transition occurs, thereby obtaining the corresponding cascade transition characteristic rays; S2. Continuously capturing cascade transition characteristic rays of different energy levels through at least six detectors, obtaining energy spectrum information of the cascade transition characteristic rays and recording corresponding ray arrival time data; wherein the energy spectrum information includes the energy spectrum and its corresponding energy information; S3, determine whether the characteristic peak of the energy spectrum is less than the characteristic threshold, if so, return to step S1; otherwise, add 1 to the effective count of the characteristic peak and enter step S4; wherein the initial value of the effective count of the characteristic peak is 0; S4, judging whether the effective count of the characteristic peak reaches the target value, if so, proceeding to step S5; otherwise, returning to step S1; S5, judging whether the sample under test contains characteristic peaks of special nuclides according to the energy information of characteristic peaks of the energy spectrum; if so, performing background subtraction on the energy spectrum to obtain a screened energy spectrum and proceeding to step S6; otherwise, the operation is terminated; S6, performing cascade transition energy screening on the energy spectrum after the primary screening, identifying the cascade transition characteristic peaks of special nuclides, and obtaining energy information of the cascade characteristic peaks after the secondary screening; S7, calculating the ray arrival time data corresponding to the energy information of the cascade characteristic peak after the secondary screening to obtain the corresponding time difference data; and obtaining the corresponding optical path difference data based on the time difference data; S8. Draw the corresponding single-curved surface range according to the optical path difference data; and locate the sample to be tested according to each single-curved surface range.

2. The nuclide localization method based on cascade transition according to claim 1, characterized in that: The high-energy particles include X-ray photons, gamma-ray photons, electrons, protons, neutrons and heavy ions.

3. The nuclide localization method based on cascade transition according to claim 1, characterized in that: The cascade transition rays are gamma rays with time correlation and space correlation.

4. The nuclide localization method based on cascade transition according to claim 1, characterized in that: The specific process of the screening in step S6 is: judging whether the energy spectrum after the screening once meets the screening criteria, if so, retaining the energy spectrum and the corresponding time data; otherwise, discarding the energy spectrum and the corresponding time data.

5. The nuclide localization method based on cascade transition according to claim 1, characterized in that: The step S7 further comprises: S7-1. The energy information of the cascade characteristic peaks obtained by the detection of each detector after secondary screening and the corresponding ray arrival time data are defined as [E i , t i1 , t i2 ,…,t in ]; S7-2, according to the formula: Δt ikj =t ij -t kj Δt ik =[Δt i，k，2 ,…,Δt i，k，j ,…,Δt i，k，n ] Get the time difference data matrix Δt between detector i and other detectors i ; where t ij ,t kj Respectively represent the data of detector i and detector k at the jth time, Δt ikj represents the j-th time difference data between detector i and detector k, Δt ik represents the time difference data matrix between detector i and detector k, [Δt i，k，2 ,…,Δt i，k，j ,…,Δt i，k，n ] represent the time difference data of detector i and detector k respectively, and J+1 represents the total number of detectors corresponding to the energy information and time data after secondary screening; S7-3. Calculate each time difference data using the optical path difference formula to obtain corresponding optical path difference data.

6. The nuclide localization method based on cascade transition according to claim 5, characterized in that: The step S8 further comprises: S8-1. Select any two detectors as fixed points, use the line between the two fixed points as the main axis, and draw a single curve and the corresponding single curve range according to each optical path difference data; S8-2. Determine whether the ranges of the single curves overlap; if so, use the overlapping range as the spatial position of the sample to be tested, thus completing the positioning of the nuclide.

7. A ray detection system based on the nuclide positioning method based on cascade transition according to any one of claims 1 to 6, characterized in that: It includes a cascade transition ray acquisition module, a detection module, an energy information processing module, a data screening module, a data analysis module and a nuclide positioning module; wherein: A cascade transition ray acquisition module is used to emit high-energy particles to activate the sample under test and emit cascade transition rays; A detection module is used to detect the cascade transition rays using a detector, obtain the corresponding energy spectrum information and record the corresponding ray arrival time data; The energy information processing module is used to determine whether the energy information is invalid; based on the valid energy information, determine whether the sample under test contains special nuclides, and perform background subtraction on the energy spectrum to obtain a screened energy spectrum; The data screening module is used to perform energy screening on the energy spectrum after the primary screening, extract the cascade characteristic peaks of special nuclides on the energy spectrum, and obtain the energy information of the cascade characteristic peaks after the secondary screening; A data analysis module is used to calculate the ray arrival time data of the cascade characteristic peak after secondary screening to obtain the corresponding time difference data; and obtain the corresponding optical path difference data based on the time difference data; The nuclide positioning module is used to draw the single-curved surface range corresponding to the optical path difference of the cascade characteristic peak after secondary screening, and locate the nuclide according to the single-curved surface range.

8. The radiation detection system according to claim 7, characterized in that: The detection module includes a plurality of lanthanum bromide detectors and high-purity germanium detectors; wherein the number of the lanthanum bromide detectors is not less than four.

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