Converter for laser beam target neutron source and optimization design method thereof

Abstract

The invention relates to the technical field of design of conversion bodies for laser beam target neutron sources, and provides a conversion body for a laser beam target neutron source and an optimization design method of the conversion body. The conversion body for the laser beam target neutron source comprises a front plate, a surrounding side plate and a rear plate, the front plate, the surrounding side plate and the rear plate define a sealed inner cavity, and the sealed inner cavity is filled with embedded objects to form a wrapping type cubic structure; at least one of the front plate, the peripheral side plates and the rear plate is made of materials which are stable in chemical property, good in mechanical property and easy to form. And the embedded object is formed by filling a substance with excellent neutron generation capability. The neutron generation capability of beryllium is not affected while the beryllium material is wrapped by designing the wrapping layer, the stability of the neutron yield is ensured while the experiment safety is provided, and the technical problem that an existing conversion body limits popularization of a laser beam target neutron source in high-precision application is solved.

Description

Technical Field

[0001] The invention relates to the technical field of design of a converter for a laser beam target neutron source, in particular to a converter for a laser beam target neutron source and an optimization design method thereof. Background Art

[0002] Neutrons have important application value in neutron photography, neutron activation analysis, neutron cancer treatment, radioisotope production and material research. Neutrons can be divided into cold neutrons, thermal neutrons, resonance neutrons, slow neutrons, medium-energy neutrons, fast neutrons and relativistic neutrons according to their energy. Different application fields have different requirements for neutron energy. There are no free neutrons in nature. The device that releases the "bound state" neutrons in the nucleus from the nucleus through artificial methods is called a neutron source. Neutron sources can be divided into continuous neutron sources and pulsed neutron sources. Compared with continuous neutron sources, pulsed neutron sources have the advantages of short pulse width and high flux (including peak flux and average flux). They have important applications in fast neutron resonance imaging and laboratory astrophysics research. At present, spallation neutron source is the most typical pulsed neutron source, which has the advantages of high yield, short pulse width (nanosecond or microsecond level), easy control and adjustment, wide energy range, low gamma background, etc. It is the neutron source with the most obvious advantages among all traditional neutron sources. However, the spallation neutron source device is relatively large and expensive. In recent years, in order to meet application needs, pulsed neutron sources have mainly developed in the direction of high flux, short pulse width, full energy range, miniaturization and low cost.

[0003] Chirped pulse amplification technology continues to promote the development of ultra-intense ultra-short lasers. Ultra-intense ultra-short lasers can accelerate charged particles to hundreds of mega-electron volts (MeV) on a time scale of picoseconds (ps) or even femtoseconds (fs) and a spatial scale of micrometers (μm). Laser acceleration is an important way to achieve the miniaturization of particle accelerators, and also provides a good opportunity for the development of new neutron sources. Laser neutron sources use the interaction of strong lasers with matter to produce electromagnetic radiation or high-energy particles, which in turn induce different nuclear reactions to produce neutrons. They have the characteristics of micro-focus, short pulse width, and high flux. Laser neutron sources can be divided into cluster neutron sources, fusion neutron sources, photonuclear neutron sources, and target neutron sources based on the way they produce neutrons. In terms of neutron yield, forward momentum, and device compactness, target neutron sources are the best way to drive laser-driven tabletop high-flux pulsed neutron sources. Currently, experiments have shown that more than 10 10 Forward neutrons of n / sr.

[0004] However, existing laser beam target neutron sources still have deficiencies in neutron yield, divergence angle control, and device compactness, which limits their promotion in high-precision applications. In particular, the design of the converter plays a key role in the efficiency and directionality of neutron generation, but there is currently a lack of systematic optimization methods. Summary of the invention

[0005] The present invention provides a converter for a laser beam target neutron source and an optimization design method thereof. Since pure beryllium material with high neutron generation capacity is in powder form and highly toxic, it will contaminate a target chamber during the experiment, which is very unfavorable for conducting laser beam target neutron source experiments. By designing a wrapping layer to wrap the beryllium material without affecting the neutron generation capacity of the beryllium, the experimental safety is provided while ensuring the stability of the neutron yield, so as to solve the technical problem that the existing converter limits the promotion of the laser beam target neutron source in high-precision applications.

[0006] The present invention provides a converter for a laser beam target neutron source, comprising a front plate, surrounding side plates and a rear plate, wherein the front plate, surrounding side plates and the rear plate are enclosed to form a sealed inner cavity, and the sealed inner cavity is filled with embedded objects to form a wrapped cubic structure; at least one of the front plate, the surrounding side plates and the rear plate is made of a material with stable chemical properties, good mechanical properties and easy molding; and the embedded objects are filled with a material with excellent neutron generating ability.

[0007] Further, at least one of the front plate, the surrounding side plates and the rear plate is made of LiH, LiF or LiD.

[0008] Furthermore, the embedded material adopts beryllium powder.

[0009] Furthermore, the thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm.

[0010] Furthermore, the height of the surrounding side panels in the front-rear direction is 1 cm to 8 cm; the thickness of the surrounding side panels is 0.1 cm to 0.5 cm.

[0011] Furthermore, the side length of the front plate and / or the rear plate and / or the surrounding side plates is 3 cm to 10 cm.

[0012] Furthermore, at least one of the front plate, the rear plate and the surrounding side plates is a lithium hydride ceramic plate prepared by warm isostatic pressing.

[0013] Furthermore, the front panel and the surrounding side panels and / or the surrounding side panels and the rear panel are sealed and connected by using high-adhesion glue.

[0014] A method for optimizing the design of a converter for a laser beam target neutron source is also provided, comprising the following steps: S100, selecting two converter structures, the first of which adopts a cubic structure of a single material, and the second adopts a wrapped cubic structure; S200, numerical simulation is carried out by comprehensively adopting the radiation fluid program FLASH, the particle simulation program EPOCH and the Monte Carlo program Geant4; S300, focusing on typical parameter indicators of the output light of a femtosecond laser device of several petawatts, taking into account the laser pre-pulse and the contamination layer behind the target, obtaining the quality characteristics of high-current ion beams driven by lasers of different intensities, and then obtaining the influence of the material, geometric shape and position of the converter structure on the quality of the beam target neutron source, and then improving the converter optimization design scheme for neutron yield and front-to-side neutron yield ratio.

[0015] Furthermore, a cubic structure and a wrapped cubic structure were selected for analysis respectively; the length and width of the converter structure were both 4 cm, the thickness of the converter structure was designed to be 5 cm, and the distance between the converter structure and the throwing target was set to 1 cm; the cubic structure material was LiH, LiF, LiD or Be, and the converter was a single material component; the peripheral material of the wrapped cubic structure was LiH, LiF or LiD, and the embedded material was Be; based on the simulation results of the reaction between the ion beam driven by the interaction between the laser and the solid target with different laser intensities and different converter structures to produce neutrons, the neutron production capacity was obtained.

[0016] The present invention has the following beneficial effects: The converter for the laser beam target neutron source of the present invention seals and wraps an embedded material (such as pure beryllium material, beryllium powder) with strong neutron generating ability but highly toxic by designing a wrapping layer, effectively preventing the highly toxic embedded material from leaking and spreading during the experiment, avoiding the pollution of the target chamber, and thus significantly improving the safety of the experiment; the embedded material is filled with a material with excellent neutron generating ability (such as beryllium), and the wrapping structure ensures the stability and efficiency of the neutron source without affecting its neutron generating ability; the wrapping cubic structure can constrain the divergence angle of neutrons, improve the collimation of the neutron beam, and thus enhance the forward direction of the neutron source. This is of great significance for applications that require highly directional neutron beams (such as neutron photography and material analysis); combined with optimized design, the converter structure of the present invention helps to reduce the neutron pulse width, thereby improving the energy resolution of the neutron source, making it more suitable for high-precision applications such as fast neutron resonance imaging; the design of the converter of the present invention achieves miniaturization and compactness of the converter by optimizing material selection and structural layout, which is conducive to the overall miniaturization and low cost goals of the laser beam target neutron source; by adjusting the composition and structure of the embedded object, the converter can adapt to different neutron energy requirements and meet a variety of applications from fast neutrons to thermal neutrons. The converter for the laser beam target neutron source of the present invention and its optimized design method not only improve the safety of the experiment and the performance of the neutron source, but also provide technical support for the promotion of the laser beam target neutron source in high-precision applications.

[0017] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of a numerical simulation study of an embodiment of the present invention; Figure 2 : is a graph showing the ablation results of a solid target by laser pre-pulses of different intensities according to an embodiment of the present invention (spatial distribution of electron density), wherein Figure 2 (a) Figure 2 (b) Figure 2 (c) Figure 2 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2, 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The ablation result diagram of the laser pre-pulse on the solid target (spatial distribution of electron density); Figure 3 FIG. 1 is a result diagram of the interaction process between the main pulse and the solid target containing pre-plasma according to an embodiment of the present invention, wherein Figure 3 (a) is the proton energy spectrum, Figure 3 (b) is the deuterium ion spectrum. Figure 3 (c) is the proton angular distribution diagram, Figure 3 (d) is the angular distribution diagram of deuterium ions; Figure 4 The cubic converter and the wrapped cubic structure of the embodiment of the present invention are shown in FIG. Figure 4 (a) is the structure diagram of the cubic converter. Figure 4 (b) is the structural diagram of the wrapped cube; Figure 5 The neutron energy spectrum of the ion beam driven by the interaction between the laser of different intensities and the solid target and the cubic converter in the embodiment of the present invention is shown in FIG. Figure 5 (a) Figure 5 (b) Figure 5 (c) Figure 5 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 Neutron energy spectrum of the reaction between ion beam driven by laser and solid target and cubic converter; Figure 6 The neutron angle distribution of the ion beam driven by the interaction between the laser of different intensities and the solid target and the cubic converter in the embodiment of the present invention is shown in FIG. Figure 6 (a) Figure 6 (b) Figure 6 (c) Figure 6 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2The angular distribution of neutrons in the reaction between an ion beam driven by the interaction of a laser with a solid target and a cubic converter; Figure 7 A comparison diagram of neutron yields of ion beams driven by the interaction between lasers of different intensities and solid targets and cubic converters according to an embodiment of the present invention; Figure 8 The neutron energy spectrum of the ion beam driven by the interaction between the laser of different intensities and the solid target and the reaction of the wrapped converter in the embodiment of the present invention is shown in FIG. Figure 8 (a) Figure 8 (b) Figure 8 (c) Figure 8 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 Neutron spectrum of the reaction between ion beam driven by laser and solid target and encapsulated converter; Fig. 9 The neutron angle distribution of the ion beam driven by the interaction between the laser of different intensities and the solid target and the wrapped converter in the embodiment of the present invention is shown in FIG. Fig. 9 (a) Fig. 9 (b) Fig. 9 (c) Fig. 9 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 Comparison of neutron yields of ion beam driven by laser-solid target interaction and wrapped converter reaction; Fig.10 A comparison diagram of neutron yields of ion beams driven by the interaction between lasers of different intensities and solid targets and a wrapped converter according to an embodiment of the present invention; Fig.11 A comparison diagram of neutron yields of four groups of converters in an embodiment of the present invention under ion beam reactions driven by the interaction between lasers of different intensities and solid targets; Fig.12 It is a schematic structural diagram of a converter for a laser beam target neutron source according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Figure 1 A schematic diagram of a numerical simulation study of an embodiment of the present invention; Figure 2 : is a graph showing the ablation results of a solid target by laser pre-pulses of different intensities according to an embodiment of the present invention (spatial distribution of electron density), wherein Figure 2 (a) Figure 2 (b) Figure 2 (c) Figure 2 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The ablation result diagram of the laser pre-pulse on the solid target (spatial distribution of electron density); Figure 3 FIG. 1 is a result diagram of the interaction process between the main pulse and the solid target containing pre-plasma according to an embodiment of the present invention, wherein Figure 3 (a) is the proton energy spectrum, Figure 3 (b) is the deuterium ion spectrum. Figure 3 (c) is the proton angular distribution diagram, Figure 3 (d) is the angular distribution diagram of deuterium ions; Figure 4 The cubic converter and the wrapped cubic structure of the embodiment of the present invention are shown in FIG. Figure 4 (a) is the structure diagram of the cubic converter. Figure 4 (b) is the structure diagram of the wrapped cube; Figure 5 The neutron energy spectrum of the ion beam driven by the interaction between the laser of different intensities and the solid target and the cubic converter in the embodiment of the present invention is shown in FIG. Figure 5 (a) Figure 5 (b) Figure 5 (c) Figure 5 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm2 Neutron energy spectrum of the reaction between ion beam driven by laser and solid target and cubic converter; Figure 6 The neutron angle distribution of the ion beam driven by the interaction between the laser of different intensities and the solid target and the cubic converter in the embodiment of the present invention is shown in FIG. Figure 6 (a) Figure 6 (b) Figure 6 (c) Figure 6 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The angular distribution of neutrons in the reaction between an ion beam driven by the interaction of a laser with a solid target and a cubic converter; Figure 7 A comparison diagram of neutron yields of ion beams driven by the interaction between lasers of different intensities and solid targets and cubic converters according to an embodiment of the present invention; Figure 8 The neutron energy spectrum of the ion beam driven by the interaction between the laser of different intensities and the solid target and the reaction of the wrapped converter in the embodiment of the present invention is shown in FIG. Figure 8 (a) Figure 8 (b) Figure 8 (c) Figure 8 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 Neutron spectrum of the reaction between ion beam driven by laser and solid target and encapsulated converter; Fig. 9 The neutron angle distribution of the ion beam driven by the interaction between the laser of different intensities and the solid target and the wrapped converter in the embodiment of the present invention is shown in FIG. Fig. 9 (a) Fig. 9 (b) Fig. 9 (c) Fig. 9 (d) represents the laser intensity of 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2Comparison of neutron yields of ion beam driven by laser-solid target interaction and wrapped converter reaction; Fig.10 A comparison diagram of neutron yields of ion beams driven by the interaction between lasers of different intensities and solid targets and a wrapped converter according to an embodiment of the present invention; Fig.11 A comparison diagram of neutron yields of four groups of converters in an embodiment of the present invention under ion beam reactions driven by the interaction between lasers of different intensities and solid targets; Fig.12 It is a schematic structural diagram of a converter for a laser beam target neutron source according to an embodiment of the present invention.

[0022] like Fig.12 As shown, the converter for the laser beam target neutron source of this embodiment includes a front plate, a surrounding side plate and a rear plate, which enclose a sealed inner cavity, and the sealed inner cavity is filled with embedded objects to form a wrapped cubic structure; at least one of the front plate, the surrounding side plate and the rear plate is made of a material with stable chemical properties, good mechanical properties and easy to form; and the embedded objects are filled with materials with excellent neutron generation ability. The converter for the laser beam target neutron source of the present invention seals and wraps embedded objects with strong neutron generation ability but highly toxic (for example: pure beryllium material, beryllium powder) by designing a wrapping layer, effectively preventing the highly toxic embedded objects from leaking and spreading during the experiment, avoiding contamination of the target chamber, and thus significantly improving the safety of the experiment; the embedded objects are filled with materials with excellent neutron generation ability (such as beryllium), and the wrapping structure ensures the stability and efficiency of the neutron source without affecting its neutron generation ability; the wrapped cubic structure can constrain the divergence angle of neutrons, improve the collimation of the neutron beam, and thus enhance the forward direction of the neutron source. This is of great significance for applications that require highly directional neutron beams (such as neutron photography and material analysis); combined with optimized design, the converter structure of the present invention helps to reduce the neutron pulse width, thereby improving the energy resolution of the neutron source, making it more suitable for high-precision applications such as fast neutron resonance imaging; the design of the converter of the present invention achieves miniaturization and compactness of the converter by optimizing material selection and structural layout, which is conducive to the overall miniaturization and low cost goals of the laser beam target neutron source; by adjusting the composition and structure of the embedded object, the converter can adapt to different neutron energy requirements and meet a variety of applications from fast neutrons to thermal neutrons. The converter for the laser beam target neutron source of the present invention and its optimized design method not only improve the safety of the experiment and the performance of the neutron source, but also provide technical support for the promotion of the laser beam target neutron source in high-precision applications.

[0023] In this embodiment, at least one of the front plate, the surrounding side plate and the rear plate uses LiH, LiF or LiD. In the design of the converter for the laser beam target neutron source, at least one of the front plate, the surrounding side plate and the rear plate uses LiH, LiF or LiD, and these materials play an important role as target materials. The use of LiD composite component target as a neutron converter can effectively increase the neutron yield of the laser neutron source. Compared with the LiF converter, the LiD converter has two more reaction channels, pD and dD, in addition to the two reaction channels of p-Li and d-Li. Therefore, it can make full use of the advantages of multiple reaction channels of laser-accelerated protons and deuterium ions to increase the probability of neutron production. Experimental results show that compared with the LiF converter, the LiD converter can bring a 2-3 times increase in neutron yield, reaching 5.2×10 8 The experiment also distinguished the contribution of multiple reaction channels, proving that the improvement in neutron yield mainly comes from the pD reaction.

[0024] In this embodiment, the insert uses beryllium powder. Optionally, the material of the insert is not limited to Be, and can also be other materials with good neutron production ability. When the insert uses beryllium powder, beryllium has a strong "braking" effect on neutrons, so it is an excellent neutron moderator in the "atomic boiler". Beryllium also has an important role in the atomic energy industry, that is, it is used as a reflector in atomic reactors. The melting point of beryllium oxide is as high as 2450°C, and its high temperature resistance is very good. It can also reflect neutrons back like a mirror reflects light. Therefore, beryllium oxide is a high-quality material for making neutron reflective layers. In addition, beryllium-9 will react with neutrons with neutron energies higher than 1.9MeV to produce beryllium-8 and two neutrons, and beryllium-8 will immediately split into two alpha particles. So for high-energy neutrons, beryllium is a neutron multiplier because it releases more neutrons than it absorbs. After absorbing low-energy neutrons, beryllium-9 will also generate tritium and helium nuclei and electrons. When beryllium-9 is hit by high-energy alpha particles, it will also release neutrons. Beryllium-9 will undergo a nuclear reaction with the alpha particles to produce carbon-12 and a neutron. Beryllium will also release neutrons when hit by deuterium ions and protons, so radium, polonium and plutonium can be used in the laboratory to irradiate beryllium as a neutron source.

[0025] In this embodiment, the thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm. By adjusting the thickness of the plate, the efficiency of neutron generation can be controlled. A thinner plate (plate thickness less than 0.1 cm) may allow more neutrons to escape, while a thicker plate (plate thickness greater than 0.6 cm) may provide more neutron generation opportunities, but may also absorb or scatter some neutrons; plates of different thicknesses may affect the energy distribution of neutrons; appropriate plate thickness helps to generate neutrons within a specific energy range, which may be necessary for certain applications; while maintaining the overall structural stability of the converter, a plate of appropriate thickness helps to withstand the thermal and mechanical stresses generated during the laser beam-target interaction process; by controlling the thickness of the plate, the leakage of neutrons can be controlled to a certain extent, thereby improving the safety of the experiment.

[0026] In this embodiment, the height of the surrounding side panels in the front-to-back direction is 1 cm to 8 cm; the thickness of the surrounding side panels is 0.1 cm to 0.5 cm. By adjusting the thickness and height of the side panels, the efficiency of neutron generation can be controlled. Thinner panels may allow more neutrons to escape, while thicker panels may provide more opportunities for neutron generation, but may also absorb or scatter some neutrons; side panels of different thicknesses and heights may affect the energy distribution of neutrons, and appropriate design helps to generate neutrons within a specific energy range, which may be necessary for some applications; while maintaining the overall structural stability of the converter, side panels of appropriate thickness and height help to withstand the thermal and mechanical stresses generated during the interaction between the laser beam and the target; by controlling the thickness and height of the side panels, the leakage of neutrons can be controlled to a certain extent, thereby improving the safety of the experiment. If the side panels are too thin (the thickness of the side panels is less than 0.1 cm), the structure may not be effectively supported, resulting in structural instability, and neutrons may not be effectively generated. If the side panels are too thick (the thickness of the side panels is greater than 0.5 cm), too many neutrons may be absorbed, reducing the neutron yield, while increasing the weight and cost of the structure. If the side panels are too low (less than 1 cm), they may not cover enough reaction area, reducing neutron yield; if the side panels are too high (greater than 8 cm), they may increase the complexity and cost of the structure and affect the distribution and directionality of neutrons. The reasonable design of the surrounding side panels is crucial to the performance of the laser beam target neutron source.

[0027] In this embodiment, the side length of the front plate and / or the rear plate and / or the surrounding side plates is 3cm to 10cm. Appropriate side length helps to control the efficiency of neutron generation. Too small side length may limit the space for neutron generation, while too large side length may lead to uneven energy distribution, affecting the efficiency of neutron generation. While maintaining the overall structural stability of the converter, the side length within the range of 3cm to 10cm helps to withstand the heat and mechanical stress generated during the interaction between the laser beam and the target. By controlling the side length of the plate, the leakage of neutrons can be controlled to a certain extent, thereby improving the safety of the experiment. If the side length is less than 3cm, the space for neutron generation may be limited, the neutron yield may be reduced, and the structure may not be effectively supported, resulting in structural instability. If the side length is greater than 10cm, the weight and cost of the structure may be increased, and the distribution and directionality of neutrons may be affected, the collimation ratio of the neutron beam may be reduced, and the resolution of neutron photography may be affected. In addition, too large a side length may lead to uneven energy distribution, affecting the efficiency of neutron generation.

[0028] In this embodiment, at least one of the front plate, the rear plate and the surrounding side plate is a lithium hydride ceramic plate prepared by warm isostatic pressing. The lithium hydride ceramic plate prepared by warm isostatic pressing plays an important role in the converter for the neutron source of the laser beam target. Warm isostatic pressing (WIP) is a versatile technology that is used in various industries such as ceramics, metals, composite materials and electronic components. The process usually applies pressure and heat to the material at a temperature below 100°C to obtain high-density, near-net components with excellent mechanical and electrical properties. In the ceramic industry, WIP is widely used to produce high-quality monolithic multilayer ceramic electronic components, such as multilayer ceramic capacitors (MLCC), multilayer ceramic inductors (MLCI) and low-temperature co-fired ceramics (LTCC). Warm isostatic pressing can eliminate internal defects such as pores, cracks, shrinkage, segregation and stress in the product and improve the performance of the product. The warm isostatic pressing method can effectively solve the problem of low density of existing lithium hydride products. The density of the prepared product exceeds 99.2%, reaching 99.2%~99.7%, and the crushing strength can reach 145MPa~210MPa. This shows that the lithium hydride ceramic plate prepared by the warm isostatic pressing method has high density and good mechanical properties, which is conducive to improving the neutron generation efficiency and the overall performance of the converter.

[0029] In this embodiment, high-adhesion glue is used to seal the front plate and the surrounding side plates and / or the surrounding side plates and the rear plate. High-adhesion glue can ensure the sealed connection between the plates, prevent the leakage of neutrons generated during the experiment, and thus improve the safety and reliability of the experiment; by using high-adhesion glue, the overall structural stability of the converter can be enhanced, so that it can withstand the thermal and mechanical stresses generated during the interaction between the laser beam and the target; the use of high-adhesion glue helps to maintain the integrity of the inside of the converter, thereby improving the efficiency of neutron generation. It can ensure that embedded materials such as beryllium powder are effectively wrapped without affecting the ability to generate neutrons. High-adhesion glue should have the following characteristics and will not affect the function of the converter for the laser beam target neutron source: remain stable in the high temperature and radiation environment generated by the interaction between the laser beam and the target, and will not decompose or release substances that affect the efficiency of neutron generation; can firmly bond plates of different materials to ensure the durability and reliability of the connection; will not chemically react with other materials in the converter during the experiment to avoid the production of harmful substances or affect the performance of the neutron source. For example, a quick-drying and fine-grinding adhesive for laser ablation sample target preparation, such as CN110763544A, has no effect on laser in-situ analysis, has strong adhesion and quick drying, and is suitable for use in laser ablation sample target preparation.

[0030] The optimization design method of the converter for the laser beam target neutron source of this embodiment includes the following steps: S100, selecting two converter structures, the first of which adopts a cubic structure of a single material, and the second adopts a wrapped cubic structure; S200, numerical simulation is carried out by comprehensively adopting the radiation fluid program FLASH, the particle simulation program EPOCH and the Monte Carlo program Geant4; S300, focusing on the typical parameter indicators of the output light of a femtosecond laser device of several petawatts, taking into account the laser pre-pulse and the contamination layer behind the target, obtaining the quality characteristics of high-current ion beams driven by lasers of different intensities, and then obtaining the influence of the material, geometric shape and position of the converter structure on the quality of the beam target neutron source, and then improving the converter optimization design scheme for neutron yield and front-to-side neutron yield ratio. By selecting two converter structures, namely a cubic structure of a single material and a wrapped cubic structure, the radiation fluid program FLASH, the particle simulation program EPOCH and the Monte Carlo program Geant4 are used to carry out numerical simulation. This method focuses on the typical parameter indicators of the output light of a femtosecond laser device of several petawatts, and obtains the quality characteristics of high-current ion beams driven by lasers of different intensities while considering the laser pre-pulse and the contamination layer behind the target. Through this process, the influence of the material, geometry and position of the converter structure on the quality of the beam target neutron source can be obtained, thereby improving the conversion of neutron yield and front-to-side neutron yield ratio. The optimized design of the converter can improve the efficiency of neutron generation and thus increase the total neutron yield. Improving the neutron yield and the front-to-side neutron yield ratio can help improve the directivity of the neutron beam, which is crucial for applications such as neutron photography and neutron activation analysis. Through numerical simulation and optimized design, the structural stability of the converter during the laser beam-target interaction can be ensured, thereby improving the reliability of the experiment. The optimized design helps to control the leakage of neutrons, thereby improving the safety of the experiment. Through optimized design, the material and manufacturing costs can be reduced while ensuring the performance, thereby improving the economy of the laser beam target neutron source. The quality characteristics of high-current ion beams driven by lasers of different intensities can be obtained, and then the influence of the material, geometry and position of the converter structure on the quality of the beam target neutron source can be obtained, thereby improving the optimized design of the converter with neutron yield and the front-to-side neutron yield ratio. This method helps to improve neutron yield, optimize neutron directivity, enhance structural stability and improve experimental safety, while also helping to reduce costs and improve economy.

[0031] In this embodiment, a cubic structure and a wrapped cubic structure are selected for analysis respectively; the length and width of the converter structure are both 4 cm, the thickness of the converter structure is designed to be 5 cm, and the distance between the converter structure and the throwing target is set to 1 cm; the cubic structure material is LiH, LiF, LiD or Be, and the converter is a single material component; the peripheral material of the wrapped cubic structure is LiH, LiF or LiD, and the embedded material is Be; based on the simulation results of the ion beam driven by the interaction between the laser with different laser intensities and the solid target and the reaction of different converter structures to produce neutrons, the neutron production capacity is obtained. This optimization design method helps to increase the neutron yield, optimize the neutron directionality, enhance the structural stability and improve the experimental safety, and also helps to reduce costs and improve economy. In addition, through numerical simulation and optimization design, the structural stability of the converter during the laser beam target interaction process can be ensured, thereby improving the reliability of the experiment.

[0032] During implementation, the present invention uses the radiation fluid program FLASH, the particle simulation program EPOCH and the Monte Carlo program Geant4 to conduct numerical simulation research. Specific research methods: (1) Radiation fluid method: Laser ASE and pre-pulse ablation of solid targets involve many physical processes such as laser energy deposition, electron ion heat exchange, heat conduction, radiation diffusion, etc. The radiation fluid method is the most suitable simulation method. The present invention uses the FLASH program (Fast, Low-mass Astrophysical Simulations with High-accuracy) to numerically simulate the process. The FLASH program is a radiation magnetofluid program developed by the FLASH Research Center of the University of Chicago. The program is based on an Euler framework with a fixed grid and uses the finite volume method to solve the control equation. The latest version 4.7 of the program was released in January 2023. Its biggest advantage is the complete diffusion magnetofluid model. The latest transport coefficients are added to the material module, which significantly improves the simulation capability of the program in the field of high energy density physics. It is very suitable for the simulation of the interaction between laser ASE or pre-pulse and solid target in the present invention.

[0033] (2) Particle simulation (PIC) method: The PIC method obtains the macroscopic characteristics and motion laws of plasma by tracking the motion behavior of a large number of charged particles in an external and self-consistent electromagnetic field. It is a very effective computer simulation method for studying the kinetic behavior of plasma. The interaction between ultra-strong laser and solid target is a highly nonlinear physical process, which contains both rich collective interactions and various instabilities. As a "numerical experiment", plasma particle simulation has the advantages of good repeatability, intuitive and rich physical images, and easy parameter research. It is particularly suitable for studying such highly nonlinear physical processes. The present invention uses the PIC program EPOCH to carry out the study of laser-plasma interaction. The program is an open source parallel particle simulation program developed by the CFSA team of the University of Warwick in the UK. The program has complete functions and rich modules. According to user feedback and needs, the development team will continue to optimize the program algorithm and expand the program function. In addition, the program has a variety of data processing and visualization options, and provides corresponding data loading scripts for various software such as MatLab, Visit, IDL and Python, which can easily visualize the simulation results and obtain rich physical images. The calculation results based on the EPOCH program have been confirmed by a large number of experiments, and the program has become the international mainstream program for studying the interaction between lasers and matter.

[0034] (3) Monte Carlo method: Monte Carlo method is a statistical method based on random sampling, which estimates the results through a large number of repeated random experiments. Because the neutron's trajectory, flight direction and reaction type all follow the principle of randomness, it is very suitable for simulating the movement and reaction of neutrons. Geant4 is an open source simulation software developed based on C++ (developed by CERN). It is designed to expose the physical models used, handle complex geometry, and make it optimally used in different fields (particle physics and nuclear physics, etc.). Geant4 is a toolkit for simulating the interaction between particles and matter and has a complete set of functions for these processes. The physical processes cover electromagnetic, hadronic and optical processes, as well as a series of particles, materials and elements. In some cases, the energy of these particles can be as low as 250 eV and as high as TeV. When defining and implementing software components, all aspects of the simulation process include: the geometric model of the entire system, all events in the process, and the capture process of the detector, etc. In the present invention, the accelerated ion information obtained in PIC is first imported into Geant4 in the form of data stream for the relevant simulation of neutron generation.

[0035] The research diagram is as follows Figure 1 . Figure 1A schematic diagram of a numerical simulation study is shown, which combines three different programs: the radiation fluid program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4. These programs are used to simulate complex physical processes such as nuclear reactions, particle transport, and radiation fluid transport. Figure 1 middle: The figure on the left shows a high-energy laser beam. High-energy laser consists of a pre-pulse and a main pulse.

[0036] The "throwing target" structure in the middle represents the material of the laser-matter interaction. The process uses the FLASH program to simulate the interaction between high-energy laser pre-pulses and matter. FLASH is a program used to simulate fluid dynamics and radiation transmission. It can simulate physical processes under high temperature and high pressure environments, such as plasma behavior in nuclear fusion reactions. Using the radiation fluid program FLASH, the ablation effect of amplified spontaneous radiation (ASE) of different intensities and laser rising edges on solid targets is studied, and the influence of pre-pulse intensity, incident angle, etc. on the pre-plasma density and temperature distribution state is obtained. The interaction process between the main pulse and the thrown target ablated by the pre-pulse is simulated using the particle simulation program EPOCH. EPOCH is a particle simulation program specifically used to simulate the movement and interaction of charged particles in electromagnetic fields. Using the particle simulation program EPOCH, the laser ion acceleration process considering the existence of actual pre-plasma and target back contamination layer is studied, and the quality characteristic parameters of proton beam and ion beam under different laser intensities are obtained.

[0037] The "Converter" structure on the right represents the converter. The material that is bombarded by high-energy ions produced by the laser irradiated target and produces neutrons through the beam-target nuclear reaction is called the converter. The process is simulated using the Monte Carlo program Geant4. Geant4 is a widely used Monte Carlo program for simulating the transport and interaction of particles in matter, including neutrons, photons, electrons, etc. Using the Monte Carlo program Geant4, the transport and nuclear reaction processes of high-current proton / ion beams with different parameters in the converter are studied, and the influence of the quality parameters of the incident ion beam and the converter temperature on the neutron yield, energy and angular distribution are explored.

[0038] Figure 1The colored circles (yellow, blue, and brown) in the figure represent different types of particles, such as protons (p⁺), neutrons (n), and deuterium ions (D⁺), which are tracked and analyzed in different simulation programs. The entire schematic diagram shows the simulation process from FLASH to EPOCH and then to Geant4, indicating that the full-process numerical simulation study of the optimization of the converter in the laser beam target neutron source carried out by the radiation fluid program FLASH, the particle simulation program EPOCH, and the Monte Carlo program Geant4 adopted in the present invention is completely feasible. Among them, the FLASH program is used to simulate the physical process of ASE and pre-pulse ablation of solid targets to obtain state parameters such as pre-plasma density and temperature; the EPOCH program is used to simulate the nonlinear interaction dynamics of laser plasma considering the presence of pre-plasma and target back contamination layer, and obtain quality characteristic parameters such as ion beam energy spectrum and angular distribution; the Geant4 program is used to simulate the transport of high-current ion beams with different quality characteristics in the converter and the detailed process of neutron production by nuclear reactions, and obtain information such as neutron energy spectrum, divergence angle, and yield.

[0039] This comprehensive simulation approach can help researchers more fully understand and predict experimental outcomes, optimize designs, and guide experimental operations.

[0040] Figure 2 The laser intensity (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 The ablation results (spatial distribution of electron density) of a solid target (5µm carbon deuterium target plus 20nm carbon hydrogen contamination layer) by a pre-pulse of a laser (with the laser pulse width set to 30fs and the focal spot radius set to 4.8µm). The horizontal axis (x-axis) and vertical axis (y-axis) of each sub-graph represent the spatial coordinates in micrometers (μm), and the color bar represents the distribution of electron density, with colors ranging from blue (low electron density) to red (high electron density).

[0041] 5×10 20 W / cm 2 : At this laser intensity, the distribution of electron density is relatively concentrated, mainly near the surface of the target, forming a narrow high-density area.

[0042] 1×10 21 W / cm 2 : As the laser intensity increases, the high electron density area becomes wider, indicating that the ablation area expands. The distribution of electron density begins to extend toward the interior of the target.

[0043] 2×10 21 W / cm 2 : At this intensity, the ablation area is further expanded and the distribution of electron density is more uniform, indicating that both the surface and the interior of the target have been significantly ablated.

[0044] 4×10 21 W / cm 2 : At the highest laser intensity, the ablation area reaches the maximum, and the distribution of electron density is very wide, almost covering the entire surface and interior of the target. This shows that at high laser intensity, the ablation of the target material is very intense.

[0045] In summary, as the laser intensity increases, the ablation area of ​​the solid target gradually expands, and the distribution of electron density changes from concentrated to extensive. High laser intensity leads to more intense ablation of the target material, and the electron density increases significantly on the surface and inside of the entire target. These results are of great significance for understanding the physical process of the interaction between lasers and solid targets, as well as for optimizing the laser ablation process.

[0046] Figure 3 It is the result of the interaction between the main pulse and the solid target containing the pre-plasma, including the particle energy distribution and the distribution of particles in the phase space. The figure is divided into four sub-figures, showing the hydrogen ion ( ) and deuterium ions ( ) distribution under different laser intensities. Details are as follows: Figure 3 (a) and Figure 3 (b) Subfigure: Particle energy distribution.

[0047] Figure 3 (a) Energy distribution: shows different laser intensities (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 ) under the condition of . The horizontal axis represents the particle energy (ε / MeV) and the vertical axis represents the particle number (dN / dε). As the laser intensity increases, the energy distribution of hydrogen ions moves toward high energy, indicating that the higher the laser intensity, the more high-energy hydrogen ions are produced.

[0048] Figure 3 (b) Energy distribution: shows the energy distribution of deuterium ions under different laser intensities. Similar to hydrogen ions, as the laser intensity increases, the energy distribution of deuterium ions also moves toward higher energy.

[0049] Figure 3 (c) and Figure 3 (d) Subfigure: distribution of particles in phase space.

[0050] Figure 3 (c) Phase space distribution: shows the distribution of hydrogen ions in phase space. The horizontal and vertical axes represent the two dimensions of phase space respectively. Curves of different colors represent different laser intensities. As the laser intensity increases, the distribution of hydrogen ions in phase space becomes more concentrated, indicating that the higher the laser intensity, the stronger the emission directionality of hydrogen ions.

[0051] Figure 3 (d) Phase space distribution: shows the distribution of deuterium ions in phase space. Similar to hydrogen ions, as the laser intensity increases, the distribution of deuterium ions in phase space becomes more concentrated.

[0052] In summary, as the laser intensity increases, the energy distribution of hydrogen and deuterium ions moves toward high energy, indicating that the higher the laser intensity, the more high-energy ions are produced. In phase space, as the laser intensity increases, the distribution of hydrogen and deuterium ions becomes more concentrated, indicating that the higher the laser intensity, the stronger the ion emission directionality. These results are of great significance for understanding the physical process of the interaction between lasers and solid targets and for optimizing the design of laser plasma sources.

[0053] The present invention uses the Monte Carlo program Geant4 to simulate the ion beam transport and neutron generation process in the converter. The present invention sets two converter structures, one is a cubic structure commonly used in the laser beam target neutron source for comparison, and the other is a wrapped cubic structure designed by the present invention, such as Figure 4 shown.

[0054] First, the cube structure commonly used in laser beam target neutron sources is selected for analysis. The simulation results of the neutron generation by the ion beam driven by the interaction between the laser and the solid target with different laser intensities and the cube configuration converter are shown in Figure 2. Figure 5 , Figure 6 , Figure 7 The length and width of the converter are both 4 cm, the thickness of the converter is designed to be 5 cm, the distance between the converter and the throwing target is set to 1 cm, the materials selected are LiH, LiF, LiD, and Be, and the converter is a single material component.

[0055] Figure 5 The neutron energy spectrum produced by the reaction between the ion beam driven by the interaction between the laser and the solid target with different intensities and the cubic converter is shown. The figure contains four sub-graphs, each corresponding to a different laser intensity: 5×10 20 W / cm2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 In each sub-figure, the neutron energy spectra of lithium hydride (LiH), lithium fluoride (LiF), lithium deuteride (LiD) and beryllium (Be) as target materials are shown. The details are as follows: Horizontal axis (ε / MeV): represents the energy of neutrons in mega-electron volts (MeV).

[0056] Vertical axis (dN / dε): represents the number of neutrons, that is, the number of neutrons in a unit energy interval, reflecting the yield of neutrons of different energies.

[0057] Curves of different colors represent different target materials (LiH, LiF, LiD, Be).

[0058] Specific analysis: 5×10 20 W / cm 2 : At the lowest laser intensity, the neutron energy spectrum produced by all target materials is relatively low and the energy distribution is narrow.

[0059] 1×10 21 W / cm 2 :With the increase of laser intensity, the neutron yield increases significantly and the energy distribution becomes wider, indicating that the neutron production efficiency is higher at higher laser intensities.

[0060] 2×10 21 W / cm 2 :The neutron yield further increased, and the neutron energy spectra of different target materials began to show more obvious differences. The neutron energy spectrum produced when beryllium (Be) was used as the target material was the highest.

[0061] 4×10 21 W / cm 2 :At the highest laser intensity, the neutron yield reaches the maximum, and the neutron energy spectrum produced when beryllium (Be) is used as the target material is significantly higher than that of other materials, indicating that beryllium is the most effective neutron production target material under high laser intensity.

[0062] In summary, as the laser intensity increases, the neutron yield increases significantly, and the energy distribution becomes wider. There are differences in the neutron energy spectra produced by different target materials at the same laser intensity, among which beryllium (Be) shows the highest neutron yield at high laser intensity. These results are of great significance for selecting suitable target materials to optimize the performance of neutron sources, especially when high-efficiency neutron production is required.

[0063] Figure 6 The angular distribution of neutrons produced by the reaction between an ion beam driven by the interaction between lasers of different intensities and a solid target and a cubic converter is shown. The figure contains four sub-graphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 In each sub-figure, the neutron angular distribution when lithium hydride (LiH), lithium fluoride (LiF), lithium deuteride (LiD) and beryllium (Be) are used as target materials is shown. The details are as follows: Polar Plot: Each subplot uses a polar plot to show the angular distribution of neutrons, where the radius represents the number of neutrons and the angle represents the direction of neutron emission.

[0064] Curves of different colors represent different target materials (LiH, LiF, LiD, Be).

[0065] Effect of laser intensity: As the laser intensity increases, the total number of neutrons (radius size) increases significantly, indicating that higher laser intensity produces more neutrons. 20 W / cm 2 ) the distribution of neutrons is relatively narrow and mainly concentrated in a specific direction. 21 W / cm 2 ) the distribution of neutrons becomes wider, indicating that the directionality of neutron emission is wider.

[0066] Influence of target materials: Different target materials have different angular distributions of neutrons produced at the same laser intensity. When beryllium (Be) is used as the target material, the distribution of neutrons is relatively wide, indicating that beryllium has good directionality when producing neutrons. The neutron distributions of lithium hydride (LiH), lithium fluoride (LiF), and lithium deuteride (LiD) are relatively narrow, indicating that these materials have poor directionality when producing neutrons.

[0067] In summary, as the laser intensity increases, the total number of neutrons increases significantly, and the neutron emission has a wider directionality. Different target materials produce different angular distributions of neutrons at the same laser intensity, among which beryllium (Be) shows better directionality. These results are of great significance for selecting appropriate target materials to optimize the performance of neutron sources, especially in applications that require neutron beams in a specific direction.

[0068] Figure 7The neutron yield produced by the reaction between the ion beam and the cubic converter under the interaction of different laser intensities and solid targets is shown. The figure uses a bar graph to show the neutron yield of different target materials (LiH, LiF, LiD, Be) under different laser intensities (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 ) N The details are as follows: Horizontal axis: represents different laser intensity levels, from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 .

[0069] Vertical axis: Neutron yield N , using a logarithmic scale ranging from 10 6 to 10 11 .

[0070] Columns of different colors represent different target materials. Blue represents lithium hydride (LiH), orange represents lithium fluoride (LiF), yellow represents lithium deuteride (LiD), and purple represents beryllium (Be). Specific analysis: Neutron yield increases with laser intensity: for all target materials, as the laser intensity increases from 5×10 20 W / cm 2 Increased to 4×10 21 W / cm 2 , the neutron yield increased significantly. This shows that laser intensity is an important factor affecting neutron yield.

[0071] Comparison of neutron yields of different target materials: Under all laser intensities, beryllium (Be) has the highest neutron yield when used as a target material, followed by lithium deuteride (LiD) and lithium fluoride (LiF). Lithium hydride (LiH) has the lowest neutron yield.

[0072] This is related to the nuclear reaction cross-section and neutron production mechanism of different materials.

[0073] Logarithmic growth of neutron yield: Since the vertical axis is a logarithmic scale, it can be seen that the neutron yield shows a nonlinear growth trend with the increase of laser intensity, especially from 2×10 21 W / cm 2 to 4×10 21 W / cm 2 The increase in neutron yield is more significant in the intensity range of .

[0074] In summary, Figure 7 The neutron yields of different target materials at different laser intensities are clearly shown, providing an important reference for selecting appropriate target materials and optimizing laser parameters. Beryllium (Be) as a target material performs best in producing neutrons, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments.

[0075] The neutron generation capabilities of the four materials are as follows: Be, LiD, LiH, LiF. However, after investigation, it was found that pure beryllium material is in powder form and highly toxic, which will contaminate the target chamber during the experiment, so it is very unfavorable to carry out laser beam target neutron source experiments. Based on this, the present invention designs a wrapped cubic structure, such as Figure 4 (b) The wrapped cube consists of a front plate, a back plate, a surrounding side plate (hollow shell) and an embedded object. The advantage of this configuration is that the beryllium with the highest neutron production capacity is isolated from the target chamber through a physical barrier, which effectively solves the problem of the target chamber being contaminated by the toxicity of the beryllium material. Figure 8 , Fig. 9 , Fig.10 These are the simulation results of different wrapping layers containing Be.

[0076] Figure 8 The neutron energy spectrum produced by the reaction between the driven ion beam and the encapsulated converter under the interaction of laser with different intensities and solid targets is described. The figure contains four sub-graphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 In each sub-figure, the neutron energy spectra of different target material combinations (LiH(Be), LiF(Be), LiD(Be)) are shown. The details are as follows: Horizontal axis (ε / MeV): represents the energy of neutrons in mega-electron volts (MeV).

[0077] Vertical axis (dN / dε): represents the number of neutrons, that is, the number of neutrons in a unit energy interval. It is a logarithmic scale that reflects the yield of neutrons of different energies.

[0078] Curves of different colors represent different target material combinations, where red represents LiH(Be), blue represents LiF(Be), and black represents LiD(Be).

[0079] Specific analysis: Effect of laser intensity on neutron energy spectrum: As the laser intensity increases, the neutron energy spectrum shifts to the right as a whole, indicating that the average energy of neutrons increases. 21 W / cm 2 ), the neutron energy spectrum extends to a higher energy range, showing a stronger ability to produce high-energy neutrons. Comparison of different target material combinations: At all laser intensities, the LiD(Be) combination produces the highest neutron energy spectrum, indicating that it is superior to LiH(Be) and LiF(Be) in neutron production efficiency. The neutron energy spectrum of the LiH(Be) and LiF(Be) combination is relatively low, and the difference between the two is small.

[0080] Energy distribution changes: At lower laser intensity (5×10 20 W / cm 2 ) the neutron spectrum is more concentrated and the energy distribution is narrow. At higher laser intensities, the neutron spectrum becomes broader, showing a wider distribution of neutron energies.

[0081] In summary, Figure 8 The effects of different laser intensities and target material combinations on the neutron energy spectrum are demonstrated, providing important data for optimizing the design of neutron sources. The LiD(Be) combination shows the highest neutron production efficiency at all tested laser intensities and is the optimal target material choice. As the laser intensity increases, the average energy of the neutrons increases and the energy distribution becomes wider, which helps to achieve more efficient neutron applications.

[0082] Fig. 9 The angular distribution of neutrons generated by the reaction between the ion beam and the encapsulated converter under the interaction of lasers with different intensities and solid targets is shown. The figure contains four sub-graphs, each corresponding to a different laser intensity: 5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 In each sub-figure, the neutron angular distribution of different target material combinations (LiH(Be), LiF(Be), LiD(Be)) is shown. The details are as follows: Polar Plot: Each subplot uses a polar plot to show the angular distribution of neutrons, where the radius represents the number of neutrons and the angle represents the direction of neutron emission.

[0083] Curves of different colors represent different target material combinations, red represents LiH(Be), blue represents LiF(Be), and black represents LiD(Be).

[0084] Effect of laser intensity: As the laser intensity increases, the total number of neutrons (radius size) increases significantly, indicating that higher laser intensity produces more neutrons. 20 W / cm 2 ) the distribution of neutrons is relatively narrow and mainly concentrated in a specific direction. 21 W / cm 2 ) the distribution of neutrons becomes wider, indicating that the directionality of neutron emission is wider.

[0085] Effect of target material combination: Different target material combinations have different angular distributions of neutrons produced at the same laser intensity. The LiD(Be) combination produces the most neutrons at all laser intensities, indicating that it has a high efficiency in producing neutrons. The LiH(Be) and LiF(Be) combinations produce relatively few neutrons, and the difference between the two is small.

[0086] In summary, Fig. 9 The angular distribution of neutrons for different target material combinations at different laser intensities is clearly demonstrated, providing an important reference for selecting appropriate target materials and optimizing laser parameters. The LiD(Be) combination performs best in producing neutrons, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments, especially in applications that require neutron beams in a specific direction.

[0087] Fig.10 The figure shows the neutron yield produced by the reaction between the driven ion beam and the wrapped converter under the interaction of laser and solid target at different intensities. The figure uses a bar graph to show the neutron yield of different target material combinations (LiH(Be), LiF(Be), LiD(Be)) at different laser intensities (5×10 20 W / cm 2 , 1×10 21 W / cm 2 , 2×10 21 W / cm 2 , 4×10 21 W / cm 2 ) N The details are as follows: Horizontal axis: represents different laser intensity levels, from 5×10 20 W / cm 2 to 4×10 21 W / cm 2 .

[0088] Vertical axis: Neutron yield N , using a logarithmic scale ranging from 10 6 to 10 11 .

[0089] Columns of different colors represent different target material combinations. Blue represents LiH (Be), orange represents LiF (Be), and yellow represents LiD (Be).

[0090] Specific analysis: Neutron yield increases with laser intensity: for all target material combinations, as the laser intensity increases from 5×10 20 W / cm 2 Increased to 4×10 21 W / cm 2 , the neutron yield increased significantly. This shows that laser intensity is an important factor affecting neutron yield.

[0091] Comparison of neutron yields of different target material combinations: Under all laser intensities, the LiD(Be) combination produces the highest neutron yield, followed by LiH(Be), and LiF(Be) has the lowest neutron yield. This may be related to the nuclear reaction cross-sections and neutron production mechanisms of different materials. Logarithmic growth of neutron yield: Since the vertical axis is a logarithmic scale, it can be seen that the neutron yield shows a nonlinear growth trend with the increase of laser intensity, especially from I 3 arrive I 4 The increase in neutron yield is more significant in the intensity range of .

[0092] In summary, Fig.10 The neutron yields of different target material combinations at different laser intensities are clearly demonstrated, providing an important reference for selecting appropriate target materials and optimizing laser parameters. The LiD(Be) combination performs best in producing neutrons, especially at high laser intensities. These results are of great significance for designing efficient neutron sources and optimizing related experiments, and will help achieve more efficient neutron generation and application.

[0093] like Figure 8 , Fig. 9 and Fig.10As shown, it is not difficult to find from the above simulation results that the neutron production ability is from large to small, LiD-wrapped Be, LiH-wrapped Be and LiF-wrapped Be. First, LiD-wrapped Be is considered. Since LiD is easily deliquesced when exposed to air and its properties are unstable, it is not considered as the material of the encapsulation layer; the second is LiH-wrapped Be. Ordinary LiH is stable at room temperature, in dry air or oxygen. In humid air, it can be slowly decomposed by atmospheric moisture. However, after investigation, it was found that this material can be prepared by warm isostatic pressing to form a LiH ceramic material with a density of more than 99.2%. It has stable properties, excellent mechanical properties and can effectively alleviate the deliquesce and oxidation of lithium hydride; the last is LiF-wrapped Be. Although LiF has stable chemical properties, its mechanical properties are poor and cannot be used as an encapsulation layer. After comprehensive consideration, LiH is used as the encapsulation layer material and Be is used as the filler. Finally, the neutron yields of the four groups of converters, LiF, LiD, Be and LiH-wrapped Be, under ion beam reactions driven by the interaction of lasers of different intensities and solid targets were compared. The results are as follows Fig.11 .

[0094] like Fig.11 As shown, the neutron yields of four groups of converters under ion beam reactions driven by the interaction of lasers of different intensities and solid targets are shown. By comparing the data, it can be found that the neutron yield of the encapsulated converter designed by the present invention, i.e., the LiH-encapsulated Be-type encapsulated converter, is generally similar to that of the pure Be converter of the same size (neutron yield comparison data is shown in the figure), and is significantly better than the LiF and LiD converters of the same size, proving that the encapsulated converter is feasible.

[0095] Matters not covered by the present invention are known technologies.

[0096] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0097] The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A converter for a laser beam target neutron source, characterized in that: It includes a front plate, surrounding side plates and a rear plate, which are enclosed to form a sealed inner cavity, and the sealed inner cavity is filled with embedded objects to form a wrapped cubic structure; At least one of the front plate, the surrounding side plates and the rear plate is made of a material that is chemically stable, mechanically good and easy to shape; The embedded material is filled with a material having excellent neutron generating ability.

2. The laser beam target neutron source converter according to claim 1, characterized in that: At least one of the front plate, the surrounding side plates and the rear plate uses LiH, LiF or LiD.

3. The conversion body for laser beam target neutron source according to claim 1, characterized in that: The inlay is made of beryllium powder.

4. The converter for laser beam target neutron source according to any one of claims 1 to 3, characterized in that: The thickness of the front plate and / or the rear plate is 0.1 cm to 0.6 cm.

5. The converter for laser beam target neutron source according to any one of claims 1 to 3, characterized in that: The height of the surrounding side panels in the front-to-back direction is 1 cm to 8 cm; the thickness of the surrounding side panels is 0.1 cm to 0.5 cm.

6. The converter for laser beam target neutron source according to any one of claims 1 to 3, characterized in that: The side length of the front panel and / or the back panel and / or the surrounding side panels is 3 cm to 10 cm.

7. The converter for laser beam target neutron source according to any one of claims 1 to 3, characterized in that: At least one of the front plate, the rear plate and the surrounding side plates is a lithium hydride ceramic plate prepared by a warm isostatic pressing method.

8. The conversion body for laser beam target neutron source according to any one of claims 1 to 3, characterized in that: The front panel and the surrounding side panels and / or the surrounding side panels and the rear panel are sealed and connected by high-adhesion glue.

9. A method for optimizing the design of a converter for a laser beam target neutron source, characterized in that: The following steps are involved: S100, selecting two transformant structures, the first one adopts a cubic structure of a single material, and the second one adopts a wrapped cubic structure; S200, numerical simulation is carried out by comprehensively using the radiation fluid program FLASH, the particle simulation program EPOCH and the Monte Carlo program Geant4; S300, focusing on the typical parameter indicators of the output light of a femtosecond laser device of several petawatts, taking into account the laser pre-pulse and the contamination layer behind the target, obtains the quality characteristics of high-current ion beams driven by lasers of different intensities, and then obtains the influence of the material, geometry and position of the converter structure on the quality of the beam target neutron source, and then improves the converter optimization design scheme for neutron yield and front-to-side neutron yield ratio.

10. The optimization design method for a converter for a laser beam target neutron source according to claim 9, characterized in that: The cubic structure and the wrapped cubic structure are selected for analysis respectively; The length and width of the converter structure are both 4 cm, the thickness of the converter structure is designed to be 5 cm, and the distance between the converter structure and the throwing target is set to 1 cm; The cubic structural material is selected from LiH, LiF, LiD or Be, and the converter is a single material component; The outer material of the wrapped cubic structure is LiH, LiF or LiD, and the embedded material is Be; Based on the simulation results of neutron production generated by the interaction between lasers of different laser intensities and solid targets and the reaction between ion beams and different converter structures, the neutron production capacity is obtained.

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