Compact high-resolution epithermal neutron resonance absorption spectrum method and device

Abstract

The invention discloses a compact high-resolution epithermal neutron resonance absorption spectrum method and a compact high-resolution epithermal neutron resonance absorption spectrum device in the technical field of nuclear physics application, and aims to solve the problems of large size, high cost and limited application of a traditional epithermal neutron source. The method comprises the following steps: generating an epithermal neutron source with high repetition frequency and microsecond-level pulse by using a kilohertz femtosecond laser, accelerating an electron beam through a laser plasma wake field, bombarding a metal target to generate fast neutrons, and processing the fast neutrons through a polyethylene body to obtain an epithermal neutron energy spectrum with ultrahigh energy resolution; the device comprises a femtosecond laser, a vacuum target chamber, a supersonic nozzle, a high-atomic-number metal target, polyethylene, a collimator, an EJ-420 detector and other key components, and is compact in design, convenient to move and convenient for multi-scene application. The technology can realize accurate diagnosis of the type and abundance of nuclides in nuclear fuel and nuclear waste and non-contact temperature measurement in a special environment, and has important nuclear safety and nuclear guarantee application values.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear physics applications, and particularly to a compact high-resolution epithermal neutron resonance absorption spectroscopy method and device. Background Art

[0002] Neutrons are one of the nucleons that make up the atomic nucleus. Due to their uncharged nature, when interacting with matter, they have completely different properties from charged particles or electromagnetic radiation, thus enabling complementary information to be obtained. In the past few decades, the research on neutrons and their applications has expanded from nuclear physics to fields such as biology, archaeology, medicine, materials science, and high energy density physics. Neutrons can be classified according to their energy levels as follows: fast neutrons (E > 100 keV); intermediate energy neutrons (100 keV > E > 100 eV); slow neutrons (100 eV > E > 25 meV); thermal neutrons (E < 25 meV). Since there are a large number of nuclear reaction resonance peaks between neutrons and most nuclei in the range of 1 - 100 eV, the existence of these characteristic peaks enables the use of the absorption spectrum in this energy range (i.e., epithermal neutrons) to diagnose the types and abundances of nuclides, and the diagnostic accuracy of the abundance can reach the order of 0.0001.

[0003] However, the realization of high-resolution epithermal neutron resonance absorption spectroscopy requires a short-pulse epithermal neutron source. For example, spallation inverse-angle white light neutron sources and photonuclear neutron sources based on electron accelerators all have extremely large volumes and high costs, which greatly limit the application of resonance absorption spectroscopy in nuclide diagnosis under different scenarios. Of course, there are also small continuous neutron sources used to diagnose the types and abundances of nuclides in samples through neutron activation analysis, but the diagnostic accuracy of the abundance only reaches the order of 0.1. Therefore, the development of a miniaturized short-pulse neutron source is of great significance for the flexible application of high-precision nuclide analysis.

[0004] Although there have been studies on laser wakefield electron accelerators for photonuclear neutron sources, their application in epithermal neutron resonance absorption has not been reported. Recently, researchers in this field have successfully used high-repetition-rate lasers to drive electron beams, achieved high-resolution epithermal neutron resonance absorption spectroscopy, and built the world's first compact prototype.

[0005] The method and device of the present invention are intended to be used for diagnosing the types and abundances of nuclides in nuclear fuels and nuclear wastes, non-contact temperature measurement in special environments, and meeting the requirements of being mobile, miniaturized, and vehicle-mounted, and are suitable for use in a variety of special scenarios. Summary of the Invention

[0006] The purpose of the present invention is to provide a compact high-resolution epithermal neutron resonance absorption spectroscopy method and device to solve the problems raised in the above background art.

[0007] To achieve the above object, the present invention specifically adopts the following technical solutions: A compact high-resolution epithermal neutron resonance absorption spectroscopy method, comprising the following steps: S1. Insert the flap valve, open the vacuum target chamber, install the lead and polyethylene targets on the neutron generation target, and then close the vacuum target chamber; S2. Turn on the kilohertz femtosecond laser, optimize the optical path by adjusting the multilayer dielectric mirror 1 and the multilayer dielectric mirror 3, then optimize the laser focusing state through the off-axis parabolic mirror and the focal spot and the post-target monitoring system, and finally adjust the relative position of the micro supersonic nozzle and the laser focus; S3. Turn on the femtosecond laser to conduct single-shot bombardment on the gas ejected from the micro supersonic nozzle to accelerate electrons by laser wakefield. Measure the electron angular distribution using the phosphor screen monitored by the electron beam spot. Record the fluorescence generated by the electron bombardment of the phosphor screen through the metal film mirror and the visible light CCD 1, and then obtain the electron angular distribution information; Then, deflect the electrons using the magnet spectrometer, collect the deflected electrons using the phosphor screen monitored by the electron energy distribution, and record the electron energy distribution information with the visible light CCD 2; Finally, optimize the outgoing electron angular distribution, charge quantity, and energy distribution by moving the micro supersonic nozzle to finely scan the distance between the laser focus and the nozzle; S4. Move the neutron generation target to place the converter in the laser emission direction. Generate ultrashort pulse fast neutrons through the electron beam bombardment of lead to induce a photofission reaction, and then obtain a short pulse epithermal neutron beam through polyethylene. Measure the time-of-flight spectrum of the epithermal neutrons using the EJ-420 detector; S5. Turn on the kilohertz target shooting mode, continuously shoot the target and accumulate the neutron time-of-flight spectrum for several minutes to obtain a high-energy resolution epithermal neutron energy spectrum; S6. Insert the sample for neutron absorption, place the sample at the neutron transmission pipe orifice, turn on the kilohertz target shooting, and continuously accumulate for several minutes to obtain a high-resolution epithermal neutron resonance absorption energy spectrum.

[0008] A compact high-resolution epithermal neutron resonance absorption spectroscopy device, comprising: A kilohertz femtosecond laser; The multilayer dielectric mirror 1, the multilayer dielectric mirror 2, and the multilayer dielectric mirror 3 that are successively installed behind the kilohertz femtosecond laser and used for transmitting the laser; A vacuum compression chamber located behind the multilayer dielectric mirror 3 and used for compressing the laser pulse; A vacuum target chamber; A flap valve that isolates the vacuum compression chamber from the vacuum target chamber; The mirror, the off-axis parabolic mirror for focusing the laser, the micro supersonic nozzle, and the neutron generation target located in the vacuum target chamber; Plasma channel monitoring system for monitoring the vacuum target chamber; Spot and post-target monitoring system for monitoring the vacuum target chamber; Electron diagnostic chamber connected to the vacuum target chamber; Laser blocking aluminum film and electron beam spot monitoring phosphor screen located between the vacuum target chamber and the electron diagnostic chamber; Visible light CCD-1 and visible light CCD-2 located on one side of the electron diagnostic chamber; Lead shield-1 covering the visible light CCD-1 and the visible light CCD-2; Magnetic spectrometer located inside the electron diagnostic chamber; Lead shield-2 covering the magnetic spectrometer; Electron energy distribution monitoring phosphor screen installed on the lead shield-2 and corresponding to the visible light CCD-1 and the visible light CCD-2 Metal film mirror located inside the electron diagnostic chamber and corresponding to the electron beam spot monitoring phosphor screen; Boron-containing polyethylene collimating hole-1, lead collimating hole, Kapton film window, boron-containing polyethylene collimating hole-2, sample and EJ-420 detector located at the outlet end of the vacuum target chamber; Among them, the laser pulse output by the kilohertz femtosecond laser is transmitted and focused in a vacuum environment, the micro supersonic nozzle can generate a gas density distribution with a half-width reaching the order of hundreds of micrometers, the neutron generation target is used for photo-fission reaction to generate a fast neutron beam, the polyethylene body is used to generate a super-thermal neutron beam, the boron-containing polyethylene collimator and the lead shield are used to improve the signal-to-noise ratio, and the EJ-detector can generate a super-thermal neutron recording signal with fast rising and slow falling edge pulses, which can be distinguished from the gamma pulses of the background.

[0009] Furthermore, the kilohertz femtosecond laser tightly focuses through the off-axis parabolic mirror to bombard the micro supersonic nozzle that rapidly ejects a supersonic gas flow to drive a collimated, repetitive frequency electron beam.

[0010] Furthermore, the electron beam bombards the neutron generation target with a high atomic number to generate a repetitive frequency fast neutron source with pulses in the range of hundreds of picoseconds to nanoseconds, and then a repetitive frequency super-thermal neutron source with microsecond-level pulses is obtained through a high-density polyethylene plate.

[0011] Furthermore, the EJ-420 detector records non-overlapping neutron pulse signals, and then through multiple-shot accumulation, a multiple-shot averaged, ultra-high energy resolution super-thermal neutron energy spectrum is obtained.

[0012] Furthermore, based on the ultra-high energy resolution super-thermal neutron energy spectrum, by placing the sample on the detection path, ultra-high energy resolution super-thermal neutron resonance absorption spectrum measurement is carried out.

[0013] Furthermore, by adjusting the position of the laser focus relative to the gas nozzle, the charge and energy of the emitted electron beam are optimized.

[0014] Furthermore, it also includes a tip and a post-target imaging system for adjusting the position of the laser focus relative to the gas nozzle.

[0015] Furthermore, by placing a specific sample on the collimation path, the measurement of the ultra-high energy resolution epithermal neutron resonance absorption spectrum is carried out.

[0016] Furthermore, it also includes a polyethylene body for generating an epithermal neutron beam.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The method in this solution uses a kHz femtosecond laser to generate an epithermal neutron source with a high repetition rate and microsecond-level pulses, realizing ultra-high energy resolution epithermal neutron resonance absorption spectroscopy. The EJ-420 detector accurately records the flight time of epithermal neutrons and discriminates the background gamma rays, and a high signal-to-noise ratio and high-resolution epithermal neutron energy spectrum are cumulatively obtained.

[0018] The method in the present invention meets the requirements of being mobile, miniaturized, and vehicle-mounted, and is suitable for use in a variety of special scenarios. This method can be used to diagnose the types and abundances of nuclides in nuclear fuels and nuclear wastes, and the diagnostic accuracy of the abundance can reach the order of 0.0001, far higher than the 0.1 order of magnitude of traditional methods. Compared with traditional large accelerators, it has a broader application prospect. This method can also be applied to non-contact temperature measurement in special environments and burnup measurement of nuclear fuels, increasing the diversity of applications.

[0019] The device in the present invention has a compact design and includes key components such as a kHz femtosecond laser, a vacuum target chamber, and an electron diagnostic chamber, all integrated in one system, which is convenient for transportation and use.

[0020] The device in the present invention drives a photofission reaction in a metal target by accelerating an electron beam through a laser wakefield to efficiently generate an ultrashort pulse of photonuclear fast neutron beam. A boron-containing polyethylene collimator and a lead shielding body are used to improve the signal-to-noise ratio, ensuring the clarity and accuracy of the neutron signal. The device can not only be used for nuclear physics research but also be extended to fields such as biology, archaeology, and medicine, and has a broad application prospect. Description of the Drawings

[0021] Figure 1 It is a step flow chart of a compact high-resolution epithermal neutron resonance absorption spectrum method in the present invention; Figure 2 It is a structural schematic diagram of a compact high-resolution epithermal neutron resonance absorption spectrum device in the present invention.

[0022] In the figure: 1. kHz femtosecond laser; 2. Multilayer dielectric mirror I; 3. Multilayer dielectric mirror II; 4. Multilayer dielectric mirror III; 5. Vacuum compression chamber; 6. Gate valve; 7. Vacuum target chamber; 8. Mirror; 9. Off-axis paraboloid mirror; 10. Micro supersonic nozzle; 11. Plasma channel monitoring system; 12. Focal spot and post-target monitoring system; 13. Neutron generation target; 14. Laser shielding aluminum film; 15. Electron beam spot monitoring phosphor screen; 16. Electron diagnostic chamber; 17. Lead shielding I; 18. Visible light CCD I; 19. Visible light CCD II; 20. Electron energy distribution monitoring phosphor screen; 21. Magnet spectrometer; 22. Lead shielding II; 23. Metal film mirror; 24. Boron-containing polyethylene collimating hole I; 25. Lead collimating hole; 26. Kapton film window; 27. Boron-containing polyethylene collimating hole II; 28. Sample; 29. EJ-420 detector. Specific implementation manner

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0024] A compact high-resolution epithermal neutron resonance absorption spectrum method and device provided in this embodiment are mainly used to solve the problem that the realization of the existing high-resolution epithermal neutron resonance absorption spectrum requires a short-pulse epithermal neutron source. For example, a spallation inverse-angle white neutron source and a photonuclear neutron source based on an electron accelerator. These accelerators have extremely large volumes and high costs, which greatly limit the application of resonance absorption spectra in nuclide diagnosis in different scenarios. There are also small continuous neutron sources used to diagnose the nuclide types and abundances in sample 28 through neutron activation analysis, but the diagnostic accuracy of abundances only reaches the order of 0.1. To overcome the above situations, the following technical solutions are provided. The following will be combined with Figure 1 - Figure 2 make a detailed description: Embodiment

[0025] A compact high-resolution epithermal neutron resonance absorption spectrum method in this solution is described in detail as follows: S1. First, in the preparation stage, open the vacuum target chamber 7 by inserting the gate valve 6 to ensure the environmental stability and safety during the subsequent experiment. Then, carefully install the lead and polyethylene targets on the neutron generation target 13, which is a key step in generating the epithermal neutron source. Then, close the vacuum target chamber 7 again to create a closed environment for the experiment; S2. Subsequently, turn on the kilohertz femtosecond laser 1. Optimize the optical path by precisely adjusting the multilayer dielectric mirror 1 2 and the multilayer dielectric mirror 3 4 to ensure the effective transmission and concentration of laser energy. Further optimize the focusing state of the laser through the off-axis parabolic mirror 9 and the focal spot and post-target monitoring system 12. This is the key to achieving high energy resolution. Finally, by adjusting the relative position between the micro-supersonic nozzle 10 and the laser focus, precisely control the interaction between the laser and the gas to create conditions for generating high-energy electron beams; S3. In the step of accelerating electrons by laser wakefield, turn on the kilohertz femtosecond laser 1 to bombard the gas ejected from the micro-supersonic nozzle 10 in single-shot mode. Use the electron beam spot monitoring phosphor screen 15 to measure the electron angular distribution. Record the fluorescence generated by the electron bombardment of the phosphor screen through the metal film mirror 23 and the visible light CCD 1 18, and then obtain the electron angular distribution information. Next, deflect the electrons using the magnet spectrometer 21, collect the deflected electrons using the electron energy distribution monitoring phosphor screen 20, and record the electron energy distribution information using the visible light CCD 2 19. By moving the micro-supersonic nozzle 10 to finely scan the distance between the laser focus and the nozzle, optimize the angular distribution, charge quantity, and energy distribution of the outgoing electrons to provide high-quality electron beams for generating a super-thermal neutron source; S4. In the neutron generation stage, move the neutron generation target 13 to place the converter in the laser output direction. Generate ultra-short pulse fast neutrons through the electron beam bombarding lead to induce a photofission reaction. These fast neutrons are then passed through polyethylene to obtain a short-pulse super-thermal neutron beam. Use the EJ-420 detector 29 to measure the time-of-flight spectrum of the super-thermal neutrons. This step is the key to achieving a high-energy resolution super-thermal neutron energy spectrum; S5. In the energy spectrum acquisition stage, turn on the kilohertz shooting mode, continuously shoot and accumulate the neutron time-of-flight spectrum for several minutes to obtain a high-energy resolution super-thermal neutron energy spectrum. This process improves the accuracy and reliability of the energy spectrum through multiple accumulations; S6. Finally, in the sample 28 analysis stage, insert the neutron-absorbing sample 28, place the sample 28 at the neutron transmission pipeline opening, turn on the kilohertz shooting, and continuously accumulate for several minutes to obtain a high-resolution super-thermal neutron resonance absorption energy spectrum. This step enables the method to not only generate a super-thermal neutron source but also perform precise nuclide diagnosis on the sample 28.

[0026] Through this series of carefully designed steps, the implementation method of this solution not only improves the energy resolution of the epithermal neutron resonance absorption spectrum, but also realizes the miniaturization and mobility of the device, enabling it to adapt to the use in a variety of special scenarios. The beneficial effect of this method is that it can provide an epithermal neutron energy spectrum with ultra-high energy resolution, which has important value for applications such as the diagnosis of nuclide types and abundances in nuclear fuels and nuclear waste, and non-contact temperature measurement in special environments. In addition, the operation method of this method is simple and flexible, can quickly respond to different experimental requirements, and has high practical value.

[0027] In this solution, by finely adjusting the position of the laser focus relative to the gas nozzle, the charge and energy of the outgoing electron beam can be effectively optimized, which is one of the key technologies for realizing an epithermal neutron resonance absorption spectrum with ultra-high energy resolution. Specifically, the precise positioning of the laser focus is crucial for the generation and characteristics of the electron beam. By fine-tuning the laser focus, the charge of the electron beam can be controlled, thereby generating a more stable and uniform electron beam. This step is crucial for the subsequent photofission reaction and neutron generation process because it directly affects the neutron yield and stability.

[0028] Furthermore, by placing a specific sample 28 on the collimation path, it is possible to carry out the measurement of the epithermal neutron resonance absorption spectrum with ultra-high energy resolution. This step allows for the precise diagnosis of the nuclides in sample 28, including the identification of nuclide types and the determination of abundances. The placement position and method of sample 28 are carefully designed to ensure that the neutron beam can pass through sample 28 evenly, thereby obtaining representative resonance absorption data. This measurement method can not only provide detailed information about the composition of sample 28, but also realize non-destructive analysis of the structure and state of sample 28.

[0029] Through this fine adjustment and precise measurement, this solution can achieve the measurement of the epithermal neutron resonance absorption spectrum of sample 28 with ultra-high energy resolution. The beneficial effect of this method is that it can provide precise information about the nuclide composition of sample 28, which has important application value in the fields of nuclear fuel and nuclear waste management, nuclear safety monitoring, and materials science. In addition, this method is simple and flexible to operate, can adapt to different experimental conditions and requirements, has high practical value and broad application prospects. In this way, this solution can not only improve the efficiency and accuracy of the experiment, but also expand the application scope of the epithermal neutron resonance absorption spectrum technology, providing strong technical support for the research and application in related fields. Embodiment

[0030] In the second embodiment of this solution, we introduce a compact high-resolution epithermal neutron resonance absorption spectrum device, which integrates multiple key components to achieve efficient and precise generation and detection of an epithermal neutron source. Please refer toFigure 1 and Figure 2 This device takes the kHz femtosecond laser 1 as the core and is equipped with a multi-layer dielectric film mirror 1 2, a multi-layer dielectric film mirror 2 3, and a multi-layer dielectric film mirror 3 4, which are successively installed behind the kHz femtosecond laser 1 and are used to transmit and adjust the laser beam to ensure the effective transmission and precise focusing of laser energy; Immediately afterwards, the vacuum compression chamber 5 located behind the multi-layer dielectric film mirror 3 4 is responsible for compressing the laser pulse to meet the needs of subsequent experiments. Through the gate valve 6, the vacuum compression chamber 5 can be isolated from the vacuum target chamber 7 to ensure the environmental stability during the experiment. Inside the vacuum target chamber 7, key components such as a mirror 8, an off-axis parabolic mirror 9, a micro supersonic nozzle 10, and a neutron generation target 13 are equipped. These components work together to generate and control the hot neutron source; The plasma channel monitoring system 11 and the focal spot and post-target monitoring system 12 are used to monitor the environment inside the vacuum target chamber 7 and the interaction between the laser and the target material in real time to ensure the safety and effectiveness of the experiment. The electron diagnostic chamber 16 connected to the vacuum target chamber 7 is equipped with a laser blocking aluminum film 14, an electron beam spot monitoring phosphor screen 15, a visible light CCD 1 18, a visible light CCD 2 19, a lead shield 1 17, a magnet spectrometer 21, a lead shield 2 22, and an electron energy distribution monitoring phosphor screen 20 and other equipment. These equipment work together to monitor and analyze the characteristics of the electron beam, including its angular distribution and energy distribution; The metal film mirror 23 is located inside the electron diagnostic chamber 16 and corresponds to the electron beam spot monitoring phosphor screen 15 and is used to monitor the electron beam. At the outlet end of the vacuum target chamber 7, a boron-containing polyethylene collimation hole 1 24, a lead collimation hole 25, a Kapton film window 26, a boron-containing polyethylene collimation hole 2 27, a sample 28, and an EJ-420 detector 29 are provided. These components together constitute the neutron beam transmission and detection system; The laser pulse output by the kHz femtosecond laser 1 is transmitted and focused in a vacuum environment. The gas density distribution half-width generated by the micro supersonic nozzle 10 reaches the order of hundreds of micrometers, providing ideal conditions for generating high-energy electron beams. The neutron generation target 13 generates a fast neutron beam in the photofission reaction, while the polyethylene body is used to generate a hot neutron beam. The boron-containing polyethylene collimator and the lead shield are used to improve the signal-to-noise ratio and ensure the sensitivity and accuracy of the detection system. The EJ-420 detector 29 can generate a hot neutron recording signal with a fast rising and slow falling edge pulse to effectively distinguish the hot neutrons from the background gamma pulses.

[0031] Overall, this compact high-resolution epithermal neutron resonance absorption spectroscopy device realizes the efficient generation and precise detection of epithermal neutron sources through fine component design and layout, providing an advanced technical means for nuclear physics research, nuclear material analysis, and other related fields. Its beneficial effects are reflected in improving the flexibility and portability of experiments while maintaining high energy resolution and high signal-to-noise ratio detection capabilities, which are of great significance for achieving precise nuclide diagnosis and material analysis.

[0032] In this solution, the kilohertz femtosecond laser 1 plays a core role in generating high-frequency pulsed lasers. These laser pulses are the key energy sources driving subsequent processes. When these laser pulses pass through the off-axis parabolic mirror 9, they are precisely focused to ensure the concentration and efficient transmission of laser energy. The special design of the off-axis parabolic mirror 9 enables the laser beam to be tightly focused, forming a high-energy density beam, which is crucial for the subsequent electron acceleration process. Immediately afterwards, the focused laser pulses bombard the micro supersonic nozzle 10, which is designed to quickly eject supersonic airflow. This supersonic airflow interacts with the focused laser pulses to create a high-density plasma environment in which the laser wakefield acceleration mechanism is realized, thereby driving collimated, high-repetition-rate electron beams. These electron beams have high energy and high density and are the key to realizing the epithermal neutron source. Through this configuration, the coordinated operation of the kilohertz femtosecond laser 1 and the micro supersonic nozzle 10 enables the device to generate electron beams with specific energy and directionality. These electron beams are then used to bombard the neutron production target 13, inducing photonuclear fission reactions to generate fast neutrons. This process not only improves the efficiency of neutron production but also helps control the directional production of neutrons, providing a basis for achieving ultra-high energy resolution epithermal neutron resonance absorption spectroscopy.

[0033] In the description of this solution, the interaction between the electron beam and the high atomic number neutron production target 13 is a key step, which involves the physical process of generating fast neutrons. When the high-repetition-rate electron beam generated by the kilohertz femtosecond laser 1 is precisely guided to the neutron production target 13, these high-energy electrons interact with the atomic nuclei in the target material, generating fast neutrons through photonuclear fission reactions. This process can generate a series of pulses on a time scale from hundreds of picoseconds to nanoseconds, forming a high-repetition-rate fast neutron source. These fast neutrons have relatively high energy and are suitable for subsequent epithermal neutron production. Subsequently, these fast neutrons pass through a high-density polyethylene plate, which is a crucial step in converting fast neutrons into epithermal neutrons. As an effective neutron moderator, the polyethylene plate can gradually slow down the fast neutrons, thereby reducing their energy to the energy range of epithermal neutrons. This process not only changes the energy distribution of neutrons but also extends the pulse width of neutrons, thus obtaining a repetition-rate epithermal neutron source with microsecond-level pulses. Such an epithermal neutron source is crucial for performing high-resolution resonance absorption spectroscopy measurements because they can undergo resonance absorption with nuclides in sample 28 within a specific energy range.

[0034] In this way, the device can generate epithermal neutrons with specific time characteristics and energy distributions, which is very useful for accurately measuring and analyzing the nuclear properties of sample 28. The generation and control technology of this epithermal neutron source enable the device to achieve high-efficiency and high-energy-resolution epithermal neutron resonance absorption spectroscopy while maintaining a compact form. This is an innovative technological breakthrough for nuclear physics research, nuclear material analysis, and other application fields that require precise neutron sources.

[0035] In this solution, the EJ-420 detector 29 plays a key role in accurately recording non-overlapping neutron pulse signals. This process begins with the neutron beam after the generation of the epithermal neutron source. After passing through sample 28, they are captured by the EJ-420 detector 29. The design of the EJ-420 detector 29 enables it to distinguish and record each individual neutron pulse, and these pulses are non-overlapping in time, ensuring the clarity and resolvability of the signals. By accurately recording these non-overlapping neutron pulse signals, the EJ-420 detector 29 can collect detailed information about the neutron energy distribution. However, to improve the statistical accuracy and reliability of the energy spectrum, this solution adopts a strategy of multiple-shot accumulation, which means that by repeating the above process multiple times, collecting a large amount of neutron pulse data, and then averaging these data. This method of accumulation and averaging enables the detector to obtain an ultra-high energy-resolution epithermal neutron energy spectrum. This energy spectrum not only has high resolution but also, due to being the result of multiple averaging, is more reliable statistically and can more accurately reflect the nuclide composition and properties of sample 28. Such an ultra-high energy-resolution epithermal neutron energy spectrum is an extremely valuable information source for nuclear physics research, nuclear material analysis, and other related fields. In this way, this solution not only improves the accuracy of neutron energy spectrum measurement, but also enhances the adaptability and flexibility of the device to different samples 28. This high-precision measurement ability enables the device to provide important technical support and data guarantee in various application scenarios, such as nuclear fuel and nuclear waste analysis, materials science, medical research and other fields. Therefore, the EJ-420 detector 29 plays an indispensable role in this solution. Its high-performance recording and data processing capabilities are the key to achieving ultra-high energy resolution epithermal neutron resonance absorption spectroscopy.

[0036] In this solution, based on the obtained ultra-high energy resolution epithermal neutron energy spectrum, the solution further carefully places the sample 28 on the detection path to carry out ultra-high energy resolution epithermal neutron resonance absorption spectrum measurement. This step is the key link to achieve the accurate diagnosis of the nuclide type and its abundance of the sample 28; By placing the sample 28 at the mouth of the neutron transport pipe, it is ensured that the epithermal neutron beam can pass through the sample 28 evenly and directly. During this process, the nuclides in the sample 28 undergo resonance absorption with the epithermal neutrons, generating specific absorption peaks. The shape and position of these absorption peaks directly reflect the characteristics of the nuclides in the sample 28, providing detailed information about the composition of the sample 28 for the experiment; Using the EJ-420 detector 29, these resonance absorption events are recorded to obtain an ultra-high energy resolution epithermal neutron resonance absorption spectrum. This spectrum can not only reveal the types of nuclides in the sample 28, but also accurately measure their abundances, and even detect tiny changes and differences; The beneficial effect of this method lies in its ultra-high energy resolution ability, which enables the experiment to conduct more accurate and detailed analysis. Compared with traditional methods, this solution can provide clearer nuclide identification and more accurate abundance measurement, which has important application value in the fields of nuclear safety, nuclear safeguards, materials science and medical research.

[0037] In this solution, in order to further improve the generation efficiency and accuracy of the epithermal neutron source, the device also introduces a set of precise tip and post-target imaging system to adjust the position of the laser focus relative to the gas nozzle. The addition of this system enables the device to precisely control the accuracy of the interaction between the laser and the gas nozzle, thereby optimizing the generation and characteristics of the electron beam in the laser wakefield. By finely adjusting the laser focus, the device can ensure that the laser energy reaches the best distribution in the supersonic airflow generated by the micro-supersonic nozzle 10, which is crucial for generating high-quality electron beams; In addition, this solution also includes a polyethylene body, which is a key component for generating a beam of epithermal neutrons. When a fast neutron beam passes through this high-density polyethylene body, the neutrons interact with the polyethylene nuclei, causing the neutrons to slow down, thereby converting the fast neutrons into epithermal neutrons with lower energy. This process not only changes the energy distribution of the neutrons but also helps to generate a more stable neutron beam, which is crucial for subsequent measurements of the epithermal neutron resonance absorption spectrum; The design and material selection of the polyethylene body are both aimed at maximizing the neutron efficiency and reducing neutron losses. In this way, the device can generate a beam of epithermal neutrons with specific energy and wide pulse width, and these neutron beams are very useful for detecting the nuclide composition and structural characteristics of the sample 28.

[0038] The operation process of this device is as follows: First, start the device, insert the plug valve 6 to open the vacuum target chamber 7, and ensure that the internal environment is stable and not interfered by external air. In this environment, install the lead and polyethylene target materials on the neutron generation target 13. These target materials are the key to generating the epithermal neutron source. After installation, close the vacuum target chamber 7 again to prepare for the subsequent laser operation; Next, turn on the kHz femtosecond laser 1, optimize the optical path by adjusting the multilayer dielectric mirror 1, multilayer dielectric mirror 2, and multilayer dielectric mirror 3 to ensure that the laser energy can be effectively transmitted to the target point. Subsequently, further optimize the focusing state of the laser using the off-axis parabolic mirror 9 and the focal spot and post-target monitoring system 12 to ensure that the laser beam is accurately focused on the supersonic airflow ejected from the micro supersonic nozzle 10, thereby driving a collimated, high-repetition-rate electron beam; After the electron beam is generated, measure the electron angular distribution using the electron beam spot monitoring phosphor screen 15, record the fluorescence generated by the electron bombardment of the phosphor screen using the metal film mirror 23 and the visible light CCD 1, and then obtain the electron angular distribution information. Next, deflect the electrons using the magnet spectrometer 21, collect the deflected electrons using the electron energy distribution monitoring phosphor screen 20, and record the electron energy distribution information using the visible light CCD 2. By moving the micro supersonic nozzle 10 to finely scan the distance between the laser focus and the nozzle, optimize the angular distribution, charge quantity, and energy distribution of the outgoing electrons to provide a high-quality electron beam for generating the epithermal neutron source; Subsequently, move the neutron generation target 13 to the laser output direction. The electron beam bombards the lead target to induce a photofission reaction, generating ultrashort pulse fast neutrons. These fast neutrons pass through the high-density polyethylene body and are converted into a short pulse epithermal neutron beam. At this time, the EJ-420 detector 29 starts to work, measures the time-of-flight spectrum of the epithermal neutrons, and records the non-overlapping neutron pulse signals; After accumulating sufficient neutron time-of-flight spectrum data, the kHz target shooting mode is activated, and the target is continuously shot and the neutron time-of-flight spectrum is accumulated for several minutes, so as to obtain a super-thermal neutron energy spectrum with high energy resolution. Finally, the sample 28 for neutron absorption is placed at the mouth of the neutron transmission pipeline, and the kHz target shooting is continued to continuously accumulate for several minutes to obtain a high-resolution super-thermal neutron resonance absorption energy spectrum, thereby completing the precise analysis of the sample 28.

[0039] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A compact high-resolution epithermal neutron resonance absorption spectroscopy method, characterized in that: The following steps are involved: S1, plug in the gate valve (6), open the vacuum target chamber (7), install the lead and polyethylene targets on the neutron generation target (13), and then close the vacuum target chamber (7); S2, turning on the kilohertz femtosecond laser (1), optimizing the optical path by adjusting the multilayer dielectric film reflector 1 (2) and the multilayer dielectric film reflector 3 (4), optimizing the laser focusing state by using the off-axis parabolic mirror (9) and the focal spot and post-target monitoring system (12), and finally adjusting the relative position between the micro supersonic nozzle (10) and the laser focus; S3, turning on the femtosecond laser (1) to bombard the gas ejected from the micro-supersonic nozzle (10) with a single shot to accelerate the electrons with the laser wake, using the electron beam spot monitoring phosphor screen (15) to measure the electron angular distribution, and recording the fluorescence generated by the electron bombardment of the phosphor screen through the metal film reflector (23) and the visible light CCD one (18), thereby obtaining the electron angular distribution information; then, using the magnet spectrometer (21) to deflect the electrons, using the electron energy distribution monitoring phosphor screen (20) to collect the deflected electrons, and using the visible light CCD two (19) to record the electron energy distribution information; finally, by moving the micro-supersonic nozzle (10) to finely scan the distance between the laser focus and the nozzle, the emitted electron angular distribution, charge amount and energy distribution are optimized; S4, moving the neutron generating target (13) to place the converter in the direction of laser emission, bombarding lead with an electron beam to induce a photofission reaction to generate ultrashort pulse fast neutrons, and then obtaining a short pulse epithermal neutron beam through polyethylene, and using an EJ-420 detector (29) to measure the flight time spectrum of the epithermal neutrons; S5. Turn on the kilohertz target shooting mode, shoot continuously and accumulate the neutron flight time spectrum for several minutes to obtain the epithermal neutron energy spectrum with high energy resolution; S6. Insert the neutron absorbing sample (28), place the sample (28) at the mouth of the neutron transmission pipeline, start kilohertz targeting, accumulate continuously for several minutes, and obtain a high-resolution epithermal neutron resonance absorption energy spectrum.

2. A compact high-resolution epithermal neutron resonance absorption spectroscopy device, characterized in that: include: Kilohertz femtosecond lasers (1); A multilayer dielectric film reflector 1 (2), a multilayer dielectric film reflector 2 (3) and a multilayer dielectric film reflector 3 (4) which are sequentially installed behind the kilohertz femtosecond laser (1) and used for transmitting laser light; A vacuum compression chamber (5) located behind the multilayer dielectric film reflector three (4) and used for compressing laser pulses; Vacuum target chamber (7); A gate valve (6) isolating the vacuum compression chamber (5) from the vacuum target chamber (7); A reflector (8), an off-axis parabolic mirror (9) for focusing laser light, a micro-supersonic nozzle (10), and a neutron generating target (13) located in the vacuum target chamber (7); A plasma channel monitoring system (11) for monitoring the vacuum target chamber (7); A focus spot and post-target monitoring system (12) for monitoring the vacuum target chamber (7); An electronic diagnostic chamber (16) connected to the vacuum target chamber (7); A laser barrier aluminum film (14) and an electron beam spot monitoring phosphor screen (15) located between the vacuum target chamber (7) and the electronic diagnostic chamber (16); A visible light CCD 1 (18) and a visible light CCD 2 (19) located on one side of the electronic diagnosis room (16); A lead shield (17) covering the visible light CCD (18) and the visible light CCD (19); A magnetic spectrometer (21) located inside the electronic diagnostic room (16); A second lead shield (22) disposed on the magnet spectrometer (21); An electron energy distribution monitoring phosphor screen (20) mounted on the lead shield 2 (22) and corresponding to the visible light CCD 1 (18) and the visible light CCD 2 (19) A metal film reflector (23) located inside the electronic diagnosis room (16) and corresponding to the electron beam spot monitoring phosphor screen (15); A boron-containing polyethylene collimation hole 1 (24), a lead collimation hole (25), a Kapton film window (26), a boron-containing polyethylene collimation hole 2 (27), a sample (28) and an EJ-420 detector (29) located at the outlet of the vacuum target chamber (7); The laser pulse output by the kilohertz femtosecond laser (1) is transmitted and focused in a vacuum environment, the micro-supersonic nozzle (10) can generate a gas density distribution with a half-width of up to 100 micrometers, the neutron generation target (13) is used for photo-fission reaction to generate a fast neutron beam, the polyethylene body is used for generating an epithermal neutron beam, the boron-containing polyethylene collimator and the lead shielding body are used to improve the signal-to-noise ratio of the signal, and the EJ-420 detector (29) can generate an epithermal neutron recording signal with a fast rise and slow fall edge pulse, which can be distinguished from a background gamma pulse.

3. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 2, characterized in that: The kilohertz femtosecond laser (1) is tightly focused by the off-axis parabolic mirror (9) to bombard the micro-supersonic nozzle (10) that rapidly ejects a supersonic airflow, driving a collimated, high-frequency electron beam.

4. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 3, characterized in that: The electron beam bombards the neutron generating target (13) with a high atomic number to generate a repetition rate fast neutron source with pulses of hundreds of picoseconds to nanoseconds, and then obtains a repetition rate epithermal neutron source with pulses of microseconds through a high-density polyethylene plate.

5. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 2, characterized in that: The EJ-420 detector (29) records non-overlapping neutron pulse signals, and then obtains a multi-shot averaged, ultra-high energy-resolved epithermal neutron energy spectrum through multiple shot accumulation.

6. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 5, characterized in that: Based on the ultra-high energy resolution epithermal neutron energy spectrum, the ultra-high energy resolution epithermal neutron resonance absorption spectrum measurement is carried out by placing the sample (28) on the detection path.

7. A compact high-resolution epithermal neutron resonance absorption spectroscopy method according to claim 1, characterized in that: By adjusting the position of the laser focus relative to the gas nozzle, the charge and energy of the outgoing electron beam can be optimized.

8. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 2, characterized in that: Also included is a needle tip and a post-target imaging system for adjusting the position of the laser focus relative to the gas nozzle.

9. A compact high-resolution epithermal neutron resonance absorption spectroscopy method according to claim 1, characterized in that: By placing the specific sample (28) on the collimated path, ultra-high energy resolution epithermal neutron resonance absorption spectrum measurement is carried out.

10. A compact high-resolution epithermal neutron resonance absorption spectroscopy device according to claim 2, characterized in that: Also included is a polyethylene body for producing an epithermal neutron beam.

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