A method for neutron spectrum measurement based on a single long scintillator detector
By employing a neutron energy spectrum measurement method based on a single long scintillator detector, and utilizing a neutron gamma discrimination algorithm and response matrix spectral decomposition, the problems of high cost, large space requirements, and low accuracy of existing neutron spectrometers are solved, achieving flexible and efficient neutron energy spectrum measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SICHUAN UNIV
- Filing Date
- 2023-08-23
- Publication Date
- 2026-07-21
AI Technical Summary
Existing multi-sphere and single-sphere neutron spectrometers require multiple detectors and moderation spheres, resulting in high costs, cumbersome operation, and large space requirements. Furthermore, the response functions of each detector interfere with each other, reducing measurement accuracy and making it difficult to adapt to radiation fields with large gradient changes.
A neutron energy spectrum measurement method based on a single long scintillator detector is adopted. By using the neutron gamma discrimination algorithm and the relationship between the two-end response signal of the long scintillator and the neutron reaction position, a neutron response matrix is established. The neutron energy spectrum is then measured by combining Gravel, MLEM, Bayesian or machine learning algorithms for spectrum decomposition.
It enables flexible measurement of neutron energy spectrum, reduces cost and space occupation, avoids interference between detectors, is suitable for occasions with small space and drastic changes in neutron field gradient, and can measure neutron energy spectrum, gamma fluence and dose under gamma interference.
Smart Images
Figure CN117111137B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of radiation detection technology, and in particular to a method for measuring neutron energy spectrum based on a single long scintillator detector. Background Technology
[0002] Accurate measurement of neutron energy spectrum is extremely important for fields such as neutron physics, nuclear data, and radiation protection. Nuclide identification technology based on neutron energy spectrum has a strong advantage in accurately and efficiently identifying nuclear materials and plays an important role in preventing nuclear proliferation.
[0003] In the field of radiation detection technology, the most commonly used method for measuring neutron energy spectrum is the multi-sphere neutron spectrometer. This method utilizes multiple slowing spheres with different slowing thicknesses to slow down fast neutrons in different energy ranges to the slow neutron energy region, which are then measured by internal slow neutron detectors. Each slowing sphere has a different neutron response function, and the combination of multiple slowing spheres forms a unique neutron response matrix. By obtaining the neutron response matrix of the multi-sphere spectrometer through experiments or simulations, the neutron energy spectrum of the radiation source under test can be obtained by using iterative algorithms based on the neutron response matrix of the multi-sphere spectrometer and its output vector in an unknown radiation source. A single-sphere neutron spectrometer is a special type of multi-sphere spectrometer that uses multiple slow neutron detectors placed at different depths inside a large slowing sphere, and its principle is similar to that of the multi-sphere neutron spectrometer. In addition, there are other similar neutron spectrometers, such as those that use multiple slow neutron detectors, each with a different thickness of slowing material in front of it, similar to the multi-sphere spectrometer, and are suitable for measuring directional or collimated neutron fields.
[0004] The existing multi-sphere neutron spectrometers require multiple detectors and moderator spheres, each with a different neutron energy spectrum response. Neutron energy spectrum measurements are performed by combining these detectors, which is costly and cumbersome. In addition, a large number of moderator spheres occupy a lot of space and are not suitable for measuring radiation fields with large gradient changes. Mutual interference between the moderator spheres also reduces the measurement accuracy. Although single-sphere neutron spectrometers use only one sphere, they also suffer from the problems of a large number of detectors, high cost, and mutual interference between the response functions of the detectors. Therefore, this invention proposes a neutron energy spectrum measurement method based on a single long scintillator detector to solve the problems existing in the prior art. Summary of the Invention
[0005] To address the aforementioned problems, the present invention aims to propose a neutron energy spectrum measurement method based on a single long scintillator detector. This method, through a neutron gamma discrimination algorithm, can not only measure the neutron energy spectrum of the neutron gamma radiation field, but also measure gamma fluence, energy spectrum, etc., exhibiting greater flexibility and advantages in practical applications.
[0006] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a neutron energy spectrum measurement method based on a single long scintillator detector, comprising the following steps:
[0007] Step 1: By coupling optoelectronic devices at both ends of a single long scintillator, the scintillating light signals at both ends of the long scintillator are extracted. The dual-end response signals are then sampled by the signal acquisition card after passing through a preamplifier circuit and a signal processing circuit.
[0008] Step 2: Extract neutron signals using the neutron-gamma signal discrimination method, and establish the relationship between the double-ended response signal of the long scintillator and the neutron reaction position using the double-ended response signal and the reaction position of the neutron in the long scintillator.
[0009] Step 3: By establishing the relationship, obtain a large number of neutron reaction positions in the long scintillator, and statistically obtain the depth probability density distribution N of neutrons in the detector;
[0010] Step 4: Obtain the depth probability density distribution of monoenergetic neutrons in the detector through simulation or experiment, and then construct the neutron response matrix R over a wide energy range.
[0011] Step 5: Based on the neutron response matrix R and the measured depth probability density distribution N of the unknown source, the neutron energy spectrum of the unknown source is obtained by inverse solving using a spectrum decomposition algorithm.
[0012] A further improvement is that: in step one, the long scintillator is a plastic long scintillator, scintillating glass, or inorganic scintillator (such as B-loaded plastic scintillator, lithium glass, CLYC, etc.) containing B or Li nuclides. The scintillator contains B or Li material inside and serves as both a neutron sensitive detection material and a neutron moderator. It is long and strip-shaped, with a reflective layer wrapped around it. Except for the side facing the neutron source, the reflective layer is wrapped with a neutron shielding layer.
[0013] A further improvement is that in step two, the neutron gamma signal discrimination is performed using online or offline processing, and the neutron signal is extracted from the neutron gamma radiation field by combining the charge comparison method or pulse amplitude discrimination method with the measurement data.
[0014] A further improvement lies in the following: In step two, the relationship is established by first setting a narrow beam of neutrons or gamma rays to be incident perpendicularly at different axial positions of the long scintillator, thus obtaining the two-end response of the long scintillator. Since the transmission of scintillating photons in the long scintillator follows an exponential decay law, an exponential function is used to fit the relationship between the two-end response signal of the long scintillator and the neutron reaction position. The corresponding exponential functions at both ends are shown below.
[0015] S1(x)=C0e -x / λ S2(x)=C1e -(L-x) / λ
[0016] By combining S1 and S2, we can obtain the following relationship:
[0017]
[0018] Where S1 and S2 are the output signals at both ends of the detector at the neutron incident position x, x represents the distance between the measurement position and the end face of S1, C0 and C1 are constant coefficients, L represents the length of the long scintillator, λ represents the effective attenuation length of the scintillator photons, and a is a constant related to C0, C1, L and λ.
[0019] The further improvement lies in the following: In step three, a large number of neutron reaction positions in the long scintillator are obtained according to the relationship in step two, and the number of neutron reactions at different positions is obtained, thereby obtaining the depth probability density distribution N of neutrons in the long scintillator detector.
[0020] A further improvement is that the simulation or experiment method in step four is to first set up different monoenergetic narrow beam neutron sources, and then incident them parallel to the axis from one end of the long scintillator. Then, according to the relationship in step two, the number of reactions of a large number of monoenergetic neutrons at different positions is obtained, and the depth probability density distribution of monoenergetic neutrons is obtained. The depth probability density distributions of a series of monoenergetic neutrons are combined to form the neutron response matrix R of the detector.
[0021] A further improvement is that, in step five, the optimal neutron energy spectrum of the unknown source is obtained by inverse solving using one of the following algorithms: Gravel algorithm, MLEM algorithm, Bayesian algorithm, and machine learning algorithm, based on the neutron response matrix R and the measured depth probability density distribution N of the unknown source.
[0022] The beneficial effects of this invention are as follows: This invention establishes the relationship between the two-end response signal of a long scintillator and the neutron reaction position, thereby obtaining the depth probability density distribution and the response matrix. It aims to obtain a large number of energy points through simulation and correct only some key energy points through experiments, which can save a lot of manpower and material resources in actual experiments and facilitate adjustment and optimization.
[0023] Meanwhile, neutron spectrum measurement based on a detector with a single long scintillator is simpler and less costly; this method occupies little space and can effectively avoid mutual interference between multiple slowing spheres, making it suitable for applications with limited space and drastic changes in the neutron field gradient; furthermore, this method can measure neutron spectrum under gamma interference conditions, and can also measure gamma fluence and dose; for the inverse solution of the neutron spectrum, various algorithms can be used to obtain the optimal neutron spectrum of the unknown source. Attached Figure Description
[0024] Figure 1 This is a flowchart of the method of the present invention.
[0025] Figure 2 This is a schematic diagram of the system of the present invention.
[0026] Figure 3 This is a schematic diagram of the long scintillator structure of the present invention.
[0027] Figure 4 This is a schematic diagram of the experimental measurement or Monte Carlo simulation of the narrow beam neutron or gamma of the present invention.
[0028] Figure 5 This is a schematic diagram of experimental measurements or Monte Carlo simulations of the monoenergetic neutron source of this invention.
[0029] Among them: 1. Long scintillator; 2. Reflector layer; 3. Neutron shielding layer. Detailed Implementation
[0030] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.
[0031] according to Figures 1-5 As shown, this embodiment provides a neutron energy spectrum measurement method based on a single long scintillator detector. A schematic diagram of the system used for actual neutron energy spectrum measurement of an unknown source is attached to the specification. Figure 2 As shown, the specific implementation steps are as follows:
[0032] Step 1: By coupling optoelectronic devices at both ends of a single long scintillator, the scintillating light signals at both ends of the long scintillator are extracted. The dual-end response signals are then processed by a preamplifier circuit and a signal processing circuit before being sampled by a signal acquisition card.
[0033] The structure of the long scintillator is as shown in the instruction manual. Figure 3 As shown, the long scintillator 3 is elongated in shape (including cuboids, cylinders, and other regular or irregular elongated shapes). The long scintillator is a plastic scintillator, scintillating glass, or inorganic scintillator (such as B-loaded plastic scintillator, lithium glass, CLYC scintillator, etc.) containing Li-6 or B nuclides. It is doped with Li or B elements, so that a single long scintillator can simultaneously serve as a neutron sensitive material and a neutron moderator. This long scintillator can be equivalent to a combination of countless moderators with continuously adjustable moderation thickness and countless sensitive detectors to achieve the measurement of neutron energy spectrum.
[0034] The long scintillator is encased in a reflective layer 2, which improves the collection efficiency of scintillating photons inside the scintillator, enhances the uniformity of photon distribution, and effectively reduces the transmission of scintillating photons from the sides of the scintillator. The specific material composition of the reflective layer is not limited here; it can be aluminum, silver, ESR film, etc. The reflective layer is then encased in a neutron shielding layer 1, which prevents external radiation from interfering with neutron energy spectrum measurements. The specific material composition of the neutron shielding layer is not limited here; it can be made of materials such as polyethylene.
[0035] The preamplifier circuit converts the current signal into a voltage pulse signal and amplifies it. Then, it enters the signal processing circuit, which filters and reduces noise on the voltage pulse signal. Depending on the situation, modules such as the comparator circuit and the control circuit can be added. The signal acquisition card collects information such as signal amplitude and time. The ADQ12DC high-speed digital converter with a sampling rate of 1GHz and a vertical resolution of 12 bits is used to collect the voltage pulse signal.
[0036] Step 2: Extract neutron signals using the neutron-gamma signal discrimination method, and establish the relationship between the two-end response signal of the long scintillator and the neutron reaction position using the two-end response signal and the reaction position of the neutron in the long scintillator.
[0037] Neutron gamma signal discrimination can be achieved by using online or offline processing and employing various discrimination methods to achieve better discrimination results, thereby enabling the measurement of the neutron energy spectrum in the neutron gamma radiation field.
[0038] The charge comparison method is used to identify neutron-gamma signals. When pulse accumulation exists, a machine learning algorithm combined with the charge comparison method is used to identify neutron-gamma signals and extract neutron signals. The pulse amplitude discrimination method is used to identify neutron-gamma signals, taking advantage of the characteristic that the amplitude of the neutron signal is greater than that of the gamma signal.
[0039] The relationship between the two-terminal response signal of the long scintillator and the neutron reaction position is determined in one embodiment, as shown in the appendix to the specification. Figure 4 As shown, a narrow beam of neutrons or gamma rays is incident perpendicularly at different axial positions of a long scintillator, yielding the two-end response of the long scintillator. Since the propagation of scintillating photons within the long scintillator follows an exponential decay law, an exponential function is used to fit the relationship between the two-end response signal of the long scintillator and the neutron reaction position. The corresponding exponential functions at both ends are shown below.
[0040] S1(x)=C0e -x / λ S2(x)=C1e -(L-x) / λ
[0041] By combining S1 and S2, we can obtain the following relationship:
[0042]
[0043] Where S1 and S2 are the output signals at both ends of the detector at the neutron incident position x, x represents the distance between the measurement position and the end face of S1, C0 and C1 are constant coefficients, L represents the length of the long scintillator, λ represents the effective attenuation length of the scintillator photons, and a is a constant related to C0, C1, L and λ.
[0044] Step 3: By using the relationship between the two-end response signal of the long scintillator and the neutron reaction position, a large number of neutron reaction positions in the scintillator are obtained, and the depth probability density distribution N of neutrons in the detector is statistically obtained.
[0045] Step 4: Obtain the depth probability density distribution of monoenergetic neutrons in the detector through simulation or experimental methods, and then construct the neutron response matrix R in a wide energy range.
[0046] Multiple monoenergetic narrow-beam neutron sources are configured, with energies ranging from eV to MeV, as shown in the attached manual. Figure 5 As shown, a monoenergetic neutron source is incident parallel to the axis from one end of a long scintillator. Based on the relationship between the response signals at both ends of the long scintillator and the neutron reaction positions, the neutron response at different positions of the long scintillator is obtained. Then, the position responses of all monoenergetic neutron sources are obtained through simulation or experimental methods, forming a response matrix R.
[0047] Step 5: Based on the neutron response matrix R and the measured depth probability density distribution N of the unknown source, the neutron energy spectrum of the unknown source is obtained by inverse solving using a spectrum decomposition algorithm.
[0048] Neutron energy spectrum interpretation involves the following relationships:
[0049]
[0050] Where N is the measured depth probability density distribution of the unknown source, and R is the simulated response matrix. Let n be the neutron energy spectrum of the unknown source, n be the number of neutron response locations, and m be the number of partitions of the neutron energy spectrum to be solved.
[0051] The response matrix R typically has n << m, therefore the above equation has no analytical solution. A few-channel spectral analysis algorithm is used to iteratively solve the equation for the neutron energy spectrum. The spectral analysis algorithm uses either the Gravel algorithm or the MLEM algorithm. Both algorithms are relatively simple and can be combined with hardware circuits to realize on-site neutron energy spectrum analysis.
[0052] In addition, the inverse solution of the neutron energy spectrum can also be achieved using Bayesian algorithms or machine learning algorithms.
[0053] 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 illustrative of the 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 present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for measuring neutron energy spectrum based on a single long scintillator detector, characterized in that, Includes the following steps: Step 1: By coupling optoelectronic devices at both ends of a single long scintillator, the scintillating light signals at both ends of the long scintillator are extracted. The dual-end response signals are then sampled by the signal acquisition card after passing through a preamplifier circuit and a signal processing circuit. Step 2: Extract neutron signals using the neutron-gamma signal discrimination method, and establish the relationship between the double-ended response signal of the long scintillator and the neutron reaction position using the double-ended response signal and the reaction position of the neutron in the long scintillator. Step 3: By establishing the relationship, obtain a large number of neutron reaction positions in the long scintillator, and statistically obtain the depth probability density distribution N of neutrons in the detector; Step 4: Obtain the depth probability density distribution of monoenergetic neutrons in the detector through simulation or experiment, and then construct the neutron response matrix R over a wide energy range. Step 5: Based on the neutron response matrix R and the measured depth probability density distribution N of the unknown source, the neutron energy spectrum of the unknown source is obtained by inverse solving using a spectrum decomposition algorithm.
2. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: In step one, the long scintillator is a plastic long scintillator, scintillating glass, or inorganic scintillator containing B-10 or Li-7 nuclides. It is wrapped with a reflective layer, and the reflective layer is wrapped with a neutron shielding layer except for the side facing the neutron source.
3. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: In step two, the neutron gamma signal discrimination is carried out through online or offline processing, and the neutron signal is extracted from the neutron gamma radiation field by combining the charge comparison method or pulse amplitude discrimination method with the measurement data.
4. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: In step two, establishing the relationship involves first setting a narrow beam of neutrons or gamma rays to be incident perpendicularly at different axial positions of the long scintillator, obtaining the two-end response of the long scintillator. Since the transmission of scintillating photons in the long scintillator follows an exponential decay law, an exponential function is then used to fit the relationship between the two-end response signal of the long scintillator and the neutron reaction position. The exponential functions corresponding to the two ends are shown below. S1(x)=C0e -x / λ ,S2(x)=C1e -(L-x) / λ By combining S1 and S2, we can obtain the following relationship: Where S1 and S2 are the output signals at both ends of the detector at the neutron incident position x, x represents the distance between the measurement position and the end face of S1, C0 and C1 are constant coefficients, L represents the length of the long scintillator, λ represents the effective attenuation length of the scintillator photons, and a is a constant related to C0, C1, L and λ.
5. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: Specifically, in step three, a large number of neutron reaction positions in the long scintillator are obtained according to the relationship in step two, and the number of neutron reactions at different positions is obtained, thereby obtaining the depth probability density distribution N of neutrons in the long scintillator detector.
6. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: The specific method of simulation or experimentation in step four is to first set up different monoenergetic narrow beam neutron sources, and incident them parallel to the axis from one end of the long scintillator. Then, according to the relationship in step two, the number of reactions of a large number of monoenergetic neutrons at different positions is obtained, and the depth probability density distribution of monoenergetic neutrons is obtained. The depth probability density distributions of a series of monoenergetic neutrons are combined to form the neutron response matrix R of the detector.
7. The neutron energy spectrum measurement method based on a single long scintillator detector according to claim 1, characterized in that: In step five, the optimal neutron energy spectrum of the unknown source is obtained by inverse solving using one of the following algorithms: Gravel algorithm, MLEM algorithm, Bayesian algorithm, and machine learning algorithm, based on the neutron response matrix R and the measured depth probability density distribution N of the unknown source.