CN-121978743-A - Neutron nondestructive detection broad spectrum slowing device and detection method for laser neutron source

CN121978743ACN 121978743 ACN121978743 ACN 121978743ACN-121978743-A

Abstract

The invention relates to the technical field of neutron radiation measurement, and discloses a neutron nondestructive testing broad spectrum slowing device and a detection method for a laser neutron source, which adopt a three-in-one design idea of material function compounding, space structure nesting and energy ladder matching; three layers of concentric nested integrated structures of an inner layer, a middle layer and an outer layer which are sequentially arranged from inside to outside are adopted; the inner layer adopts a high Z inelastic slowing body, the middle layer adopts a low absorption elastic slowing agent layer, the outer layer adopts a thermalization and mechanical constraint shell, and the step, the co-assimilation and the stepwise high-efficiency slowing of the laser white light neutron spectrum are realized through the physical combination and the spatial structure optimization of the high atomic number material and the low atomic number material. The integrated slow structure formed by sequentially and concentrically nesting the high atomic number inelastic slow layer, the low absorption elastic slow layer and the thermalization constraint layer from inside to outside is adopted to realize the step, synergistic and stepped efficient slow and regulation of the wide energy spectrum of the laser white light neutron source.

Inventors

ZOU DEBIN
LUO JINLONG
FENG KAIYUAN
WANG YECHEN
FENG JIE
HU LIXIANG
XIE CHEN
ZHANG WENYU
Yu Tongpu

Assignees

中国人民解放军国防科技大学

Dates

Publication Date: 20260505
Application Date: 20260409

Claims (10)

1. A neutron nondestructive testing broad spectrum slowing device for a laser neutron source is characterized by adopting a three-in-one design concept of material function compounding, space structure nesting and energy ladder matching; three layers of inner layers, middle layers and outer layers which are sequentially arranged from inside to outside and from near to far relative to neutron generation points are adopted for concentric nesting of the integrated structure; The inner layer adopts a high-Z inelastic moderator, the middle layer adopts a low-absorption elastic moderator layer, and the outer layer adopts a thermalization and mechanical constraint shell; The steps, the cooperation and the stepwise high-efficiency slowdown of the laser white light neutron spectrum are realized through the physical combination and the spatial structure optimization of the high atomic number material and the low atomic number material.
2. The neutron nondestructive testing broad spectrum slowing down device for a laser neutron source according to claim 1, wherein the inner layer adopts a high atomic number material layer, and the high atomic number material layer is a solid lead block, a solid tungsten block or a solid bismuth block; the shape of the high atomic number material layer is designed to be matched with the shape of the outer layer groove and is fixed in the outer layer groove; The center of the high atomic number material layer is also provided with a groove which is used for fixedly placing a neutron converter; Through strong inelastic scattering between high-Z atomic nuclei and high-energy neutrons, the neutrons lose a large amount of energy in single or few collisions, and rapid energy reduction is realized; the high-energy neutrons refer to kinetic energy of 1MeV.
3. The neutron nondestructive testing broad spectrum slowing down device for a laser neutron source according to claim 2, wherein the middle layer adopts liquid heavy water filled in an outer shell container, and the outer shell container is tightly wrapped outside the high atomic number material layer of the inner layer; the deuteron mass in the liquid heavy water is twice that of neutrons, and the liquid heavy water has strong elastic scattering capability and low absorption cross section of the neutrons; the intermediate energy neutrons pre-moderated by the high atomic number material layer are moderated to an epithermal and thermal energy interval stably, efficiently and with low loss through multiple elastic scattering; the neutron in the middle energy indicates that the kinetic energy is in the range of-keV to MeV; The super heat and heat energy range from eV to meV.
4. The neutron nondestructive testing broad spectrum slowing down device for a laser neutron source according to claim 3, wherein the outer layer is a single-sided concave box body processed by high density polyethylene, the shape of a groove on the inner surface of the box body is matched with the shape of the high atomic number material layer of the inner layer, and the box body is used for fixing the high atomic number material layer and sealing and containing liquid heavy water as a container; Meanwhile, the box body also contains a large number of hydrogen atoms and is used for carrying out final thermalization on neutrons which escape from the liquid heavy water layer and are close to thermalization, so that neutron energy distribution is closer to maxwell distribution, a certain neutron confinement effect is achieved, and leakage to the periphery is reduced.
5. The neutron nondestructive testing broad spectrum slowing down device for a laser neutron source according to claim 4, wherein the wall thickness of the box body is 4mm-6mm.
6. The neutron non-destructive testing broad spectrum moderating apparatus for a laser neutron source according to any one of claims 1 to 5, wherein the optimal dimensions under new conditions, in particular, can be determined by optimization through monte carlo particle transport simulation of the system: The thickness of the high atomic number material layer of the inner layer is the key for balancing the high-energy neutron moderation and the medium-energy neutron yield, in a 1.45PW laser source, the optimized preferable thickness is 9cm-11cm, the high-energy neutron moderation is insufficient when the thickness is too thin, and the medium-energy neutron is unnecessarily attenuated when the thickness is too thick; the effective thickness of the middle layer liquid heavy water layer determines the moderation degree of the medium energy to thermal energy neutrons, the radial thickness is optimally designed to be 18cm-22cm, and the radial thickness of the groove is 9cm-11cm; The overall transverse dimension L is a core design variable and refers to the outer dimension of the outer layer box body in the direction perpendicular to the neutron beam extraction direction; monte Carlo particle transport simulation shows that for a specific neutron source, the moderation efficiency eta is improved monotonically and remarkably along with the increase of L, because the larger size enhances the capturing and moderating capacity of peripheral high-energy neutrons; and through Monte Carlo particle transport simulation, an optimal L value is found in the engineering realization range so as to realize the optimal balance of efficiency, flux and cost.
7. A neutron nondestructive testing broad spectrum moderating detection method for a laser neutron source, characterized in that the neutron nondestructive testing broad spectrum moderating device for a laser neutron source according to any one of claims 1 to 6 is adopted, comprising the following steps: The high-energy ions generated by the action of the laser and the primary target generate nuclear reaction in the neutron converter to generate wide-energy spectrum white neutrons, the wide-energy spectrum white neutrons firstly enter the inner layer and rapidly reduce energy through inelastic scattering, then diffuse to the middle layer, efficiently slow to a thermal energy region or a super thermal energy region through elastic scattering, and finally finish final thermalization by the outer layer.
8. The method for non-destructive testing of neutrons by a laser neutron source according to claim 7, wherein neutrons naturally escape from the side of the slowing device or are led out through a preset duct after being sufficiently slowed down to form neutron beams for testing, and the neutron beam current is irradiated on a sample to be tested which is arranged in front of the slowing device.
9. The method for the non-destructive testing of neutrons from a laser neutron source according to claim 8, wherein a neutron detector is placed behind the sample to be tested for receiving neutrons after penetrating the sample and recording energy spectrum information.
10. The method for the non-destructive inspection of neutrons from a laser neutron source according to claim 9, wherein the transmitted neutron spectrum obtained by the analytical detector, when the sample contains specific elements, is subjected to distinct absorption valleys at the corresponding characteristic resonance energy; By identifying the locations and depths of these absorption valleys, a qualitative or semi-quantitative analysis of the identity and content of the elemental species in the sample can be achieved.

Description

Neutron nondestructive detection broad spectrum slowing device and detection method for laser neutron source Technical Field The invention relates to the technical field of neutron radiation measurement, in particular to a neutron nondestructive testing broad spectrum slowing device and a neutron nondestructive testing broad spectrum slowing method for a laser neutron source. Background The laser-driven neutron source is a novel neutron generation technology which has been rapidly developed in recent years. The technology utilizes the interaction of ultra-short laser pulses with a target material (such as deuterated polymer or metal) to generate high-energy ions (such as protons or deuterons), and the high-energy ions generate neutrons through nuclear reactions (such as (p, n) or (d, n) reactions) with a secondary converter. The laser driven neutron source has the advantages of extremely short pulse width (in the order of picoseconds to nanoseconds), high instantaneous brightness, small source size and the like, and the generated neutron energy spectrum has wide coverage range, and shows typical broad spectrum 'white light' neutron characteristics from a thermal neutron region to tens of MeV. Neutron nondestructive testing, in particular neutron resonance absorption analysis, is one of the important application fields of neutron technology. Such applications typically require the use of thermal or epithermal neutron beams to interact with matter to enable nondestructive detection of material composition, structure, or defects by analyzing changes in neutron energy spectrum. However, the neutron energy directly generated by the laser-driven neutron source is high, most of the neutrons are fast neutrons, and the neutrons cannot be directly used for detection. Therefore, the energetic neutrons must be moderated to the thermal or epithermal neutron energy range by means of a moderator. The performance of the moderator, in particular its moderating efficiency and the quality of the output beam (such as flux, spectral purity and background level), directly determine the sensitivity, resolution and accuracy of the subsequent detection. Currently, the most common technical solution for laser-driven neutron source moderation is to use an integral structure composed of a single moderating material. Most typically, a shell with a central cavity is fabricated using High Density Polyethylene (HDPE) and a neutron producing target is placed within the cavity. This prior art solution is typically a cubic or cylindrical HDPE block with a cylindrical or rectangular cavity in the center to accommodate the neutron conversion target. Polyethylene is rich in hydrogen atoms, and the hydrogen nuclear quality is similar to that of neutrons, and neutrons are slowed down mainly through an elastic scattering mechanism. The scheme has the advantages of simple structure, low cost and easiness in processing and deployment, and is a mainstream design in current experimental research. However, the prior art solutions have significant drawbacks that limit their performance in laser driven neutron source nondestructive testing applications, as follows: 1. The slow-down mechanism is single and is not matched with the wide energy spectrum characteristic, and the single polyethylene slow-down body mainly depends on the elastic scattering of hydrogen nuclei. The elastic scattering cross section decreases significantly with increasing neutron energy, and for high energy neutrons above MeV, its moderating ability decreases dramatically. The method leads a large amount of high-energy neutrons to escape through the moderated body without being sufficiently moderated, thereby not only causing low neutron utilization efficiency, but also introducing indistinguishable high-energy background interference into detection signals and seriously affecting the resolution and detection accuracy of characteristic formants. 2. The slowing-down efficiency is inherently a bottleneck and is difficult to increase by increasing the size, simulation and experimental studies show that the slowing-down efficiency (i.e. the ratio of the number of thermal/epithermal neutrons finally obtained to the number of initial fast neutrons) of a single polyethylene based slowing-down scheme is theoretically limited. Simulation analysis shows that the optimal efficiency is about 37.3%. More importantly, when trying to capture more neutrons by increasing the geometrical size of the moderating body, due to the strong penetrability of high-energy neutrons, increasing the size cannot effectively increase the moderating probability of the high-energy neutrons, but rather increases the probability of adverse processes such as inelastic scattering of neutrons and materials, and aggravates the absorption of neutrons by the materials themselves, and finally leads to the overall moderating efficiency not increasing and decreasing (for example, from 37.3% to 27.0%). This reveals the fundamenta