Compact laser neutron imaging device

Abstract

The invention discloses a compact laser neutron imaging device, which comprises a laser system, a neutron generation system and a terminal thermal neutron imaging system, and is characterized in that the laser system is used for generating laser and transmitting the laser to the neutron generation system; the neutron generation system is in a sealed vacuum state, and a first target and a second target are arranged in the neutron generation system; the laser is emitted to the first target to excite the back surface of the first target to generate a high-current particle beam, and the high-current particle beam is emitted to the second target to generate a neutron beam; and the terminal thermal neutron imaging system is used for detecting scattered neutron information, calculating composition and density of substances on a path through the neutron information and forming an image. By using the invention, the internal structural characteristics of the sample can be revealed on the premise of not damaging the sample. The method can be widely applied to the field of neutron imaging.

Description

Technical Field

[0001] The invention relates to the field of neutron imaging, and in particular to a compact laser neutron imaging device. Background Art

[0002] As the demand for cultural heritage development and research increases, the main archaeological imaging devices currently used are ground radar, laser scanners, magnetometers, optical cameras, and aerial photography. However, many of the archaeological imaging devices currently have the following disadvantages: 1. Limited resolution and depth: The resolution and depth of many traditional devices are limited and cannot provide sufficiently detailed underground structure information, especially for complex geological environments or deeply buried cultural relics. 2. Dependence on environmental conditions: Some devices such as ground radar and optical cameras are sensitive to environmental conditions, such as soil type, vegetation cover or weather, which may affect the imaging effect and data quality. 3. Expensive: Some advanced equipment such as LiDAR and high-resolution ground radar are expensive, and the cost of use and maintenance is also high, which limits their application in large-scale archaeological surveys. 4. Complex data processing: The raw data obtained from these devices usually requires complex processing and analysis, requiring professional skills and a lot of time to extract useful geological or cultural information from them. 5. Limited to surface features: Some devices such as optical cameras and aerial photography mainly rely on visible features on the surface, and may not provide enough information for deeply buried cultural relics or structures that require deeper detection. 6. Limited non-destructive performance: Although most of these technologies are non-destructive, in some cases, operation or incorrect use may still cause damage to cultural relics or the environment. In summary, although traditional archaeological imaging devices are helpful for archaeological research and discovery, they have some limitations and challenges in depth, resolution, cost and data processing, which also prompts researchers to continuously explore new technologies and methods to improve the capabilities and effects of archaeological imaging.

[0003] However, with the advancement of technology and the expansion of application fields, neutron imaging has generated potential valuable applications in the fields of archaeology and cultural heritage protection. At present, the main neutron sources and methods of generating neutrons are: radioisotope neutron sources; reactor neutron sources; spallation neutron sources driven by proton accelerators. The above methods of generating neutrons can basically be summarized as using particle beams to target and generate neutron fluxes. The problem is that they cannot meet the requirements of miniaturization, compactness, and economy at the same time. Summary of the invention

[0004] In view of this, in order to solve the technical problem that the existing neutron source device cannot simultaneously meet the requirements of miniaturization, compactness and economy in the field of archaeology, the present invention proposes a compact laser neutron imaging device, including a laser system, a neutron generation system and a terminal thermal neutron imaging system, wherein:

[0005] The laser system is used to generate laser light and emit it to the neutron generation system;

[0006] The laser system includes a laser generator and a cooling unit. During the laser generation process, a large amount of heat will be generated, and a water cooling system is required for cooling to prevent the equipment from being severely thermally deformed or even damaged due to excessive power.

[0007] The neutron generation system is in a sealed vacuum state, and a first target and a second target are provided in the neutron generation system;

[0008] The laser is emitted to the first target to excite the back side of the first target to generate a high-current particle beam, and the high-current particle beam is emitted to the second target to generate a neutron beam;

[0009] The terminal thermal neutron imaging system is used to detect scattered neutron information, calculate the composition and density of the material on the path through the neutron information, and form an image.

[0010] Among them, the sample is placed between the seed production system and the terminal thermal neutron imaging system, and the composition and density of the sample can be inferred from the neutron information.

[0011] In some embodiments, the neutron generation system further includes a flange, a magnet, an outer box, an inner cavity, a post-target beam detection unit, and a pre-target beam detection unit, wherein:

[0012] The flange and the outer box body are combined to form a sealed state;

[0013] At least one of the flanges must be placed parallel to the beam, allowing the beam to travel in that direction. In addition, flanges can be placed at other locations for beam observation or other beam detection work.

[0014] The inner cavity, the post-target beam detection unit and the pre-target beam detection unit are all placed inside the outer box;

[0015] Flanges need to be installed between the pre-target beam detection unit, the post-target beam detection unit and the outer wall, mainly to facilitate the connection of the detection device and form a closed space.

[0016] The flange mainly provides sealing and supports operation in a vacuum environment, allowing the laser to penetrate the flange and hit the first target. If laser focusing is involved, multiple groups of focusing lenses can be added in front of the first target for laser focusing. The specific details shall be subject to actual data measurement.

[0017] Multiple groups of magnets are mainly placed outside the cavity wall, and their main function is to focus the beam and reduce the divergence and loss of primary particles.

[0018] The high-current particle beam is transmitted in the inner cavity, which reduces the loss of beam to the cavity and pollutes the entire device, and protects other auxiliary devices.

[0019] The post-target beam detection unit and the pre-target beam detection unit are both used to measure the dose distribution of the particle beam.

[0020] In some embodiments, the terminal thermal neutron imaging system comprises a camera and a scintillator device, wherein:

[0021] Real-time acquisition of thermal neutron imaging is achieved by converting neutrons into optical photons through a scintillator and detecting these photons with a camera.

[0022] In some embodiments, a moderator and a collimator are also included, wherein:

[0023] The moderator is mainly located behind the second target, and its main function is to slow down fast neutrons into thermal neutrons to facilitate subsequent imaging by the imaging system.

[0024] The collimation device is added after the moderator, mainly to shape the neutron beam into a parallel beam and scrape off the divergent neutron beam, making thermal neutron imaging clearer.

[0025] Based on the above scheme, the present invention provides a compact laser neutron imaging device, which can provide an effective means for non-destructive detection of the internal structure, composition and state of cultural relics for cultural heritage protection with its non-destructive characteristics. Compared with the existing technology that may cause permanent damage to cultural relics, the present invention uses neutron imaging to non-destructively reveal the internal structural characteristics of cultural relics under complex production processes, including material distribution, connection methods, and potential corrosion and damage, thereby providing guidance for material analysis, authenticity authentication, preservation and restoration of cultural relics, and providing high-resolution internal information of cultural relics for academic research and exhibitions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural block diagram of a compact laser neutron imaging device of the present invention;

[0027] Figure numerals: 1. laser generator; 2. cooling unit; 3. vacuum unit; 4. flange; 5. first target; 6. post-target beam detection unit; 7. magnet; 8. inner cavity; 9. pre-target beam detection unit; 10. second target; 11. moderator; 12. sample. DETAILED DESCRIPTION

[0028] In the face of challenges in cultural heritage research, it is necessary to comprehensively utilize science and technology, policies, talents and other resources, formulate strict protection measures and research processes, and ensure that the cultural relics themselves are respected and the most in-depth understanding and effective protection are achieved. This comprehensive work requires not only the participation and support of the whole society, but also professional technical support to achieve the development and protection of cultural heritage.

[0029] Based on the current imaging technology, neutron imaging technology has become possible. Here, a compact laser neutron imaging device is designed to meet the needs of archaeological and cultural heritage research. Of course, the device can also be used to study mineral exploration, materials science and engineering, geology and environmental science, safety and security, nuclear physics and astrophysics, etc.

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] It should be noted that, for the convenience of description, only the parts related to the relevant invention are shown in the drawings. In the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0032] It should be understood that the "system", "device", "unit" and / or "module" used in this application is a method for distinguishing different components, elements, parts, portions or assemblies at different levels. However, if other words can achieve the same purpose, the word can be replaced by other expressions.

[0033] As shown in this application and claims, unless the context clearly indicates an exception, the words "a", "an", "a kind" and / or "the" do not refer to the singular, but also include the plural. Generally speaking, the terms "include" and "comprise" only indicate the inclusion of clearly identified steps and elements, and these steps and elements do not constitute an exclusive list. The method or device may also include other steps or elements. The elements defined by the sentence "includes a..." do not exclude the existence of other identical elements in the process, method, commodity or device that includes the elements.

[0034] In the description of the embodiments of the present application, "plurality" means two or more than two. The following terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features.

[0035] In addition, flow charts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, the various steps may be processed in reverse order or simultaneously. At the same time, other operations may also be added to these processes, or a certain step or several steps of operations may be removed from these processes.

[0036] Reference Figure 1 , which is a flow chart of an optional example of a compact laser neutron imaging device proposed in the present invention, comprising a laser system, a neutron generation system and a terminal thermal neutron imaging system, wherein:

[0037] The laser system includes a laser generator and a cooling unit;

[0038] Specifically, the cooling unit mainly uses water cooling, which is mainly used to control and stabilize the working temperature of the laser generator to ensure that the laser generator maintains stable performance and output power during long-term operation. The specific functions of the water cooling device include: (1) Heat dissipation: The laser will generate a large amount of heat during operation. If it is not dissipated in time, it may cause the internal temperature of the laser to rise, affecting the working efficiency and life of the laser. The water cooling device effectively removes the heat inside the laser by circulating cooling water or other cooling media to keep the laser within a suitable operating temperature range. (2) Stable output power: The output power of the laser usually fluctuates with changes in temperature. Controlling the temperature of the laser through a water cooling device can reduce the power fluctuation caused by temperature, thereby maintaining the stability and consistency of the laser output. (3) Protecting equipment: In high-power lasers, if they cannot be effectively cooled, the laser medium may be damaged. The water cooling device can provide the necessary cooling capacity to protect the equipment from heat overload.

[0039] Based on the horizontal moving direction of the beam, the neutron generation system includes a flange, a first target, a post-target beam detection unit, an inner cavity, a pre-target beam detection unit and a second target in sequence;

[0040] In addition, the magnet is arranged between the outer box body and the inner cavity body;

[0041] Specifically, the flange and the outer box are combined to form a sealed structure, and evacuated by additional equipment to form a vacuum state.

[0042] The pre-target beam detection system and the post-target beam detection system refer to a device used to detect and measure radiation dose. The basic principle is to use special materials or devices to record or display changes in radiation dose. The characteristic of this type of detector is that it can respond to the presence and intensity of radiation through a specific reaction or mechanism. These detection systems mainly use various detection devices and are widely used in the fields of radioactive monitoring, radiation dose measurement, nuclear radiation protection, etc. Their advantages include fast response speed, high sensitivity, simple structure and easy use. However, it should be noted that different types of radiation (such as α rays, β rays, γ rays, etc.) may require different types of radiochromic materials or detectors for effective detection and measurement. (5) The first target is mainly used to generate primary particles (such as electrons, protons, heavy ions, etc.). The target material is located at the front end of the neutron generation device. Different target materials generate different particle beams. The appropriate target material is selected according to the simulation optimization data (including the type of target material, thickness, surface flatness and the size of the laser beam focus on the target material). (6) The second target is mainly used to generate fast neutrons. After the primary particles are excited by the strong electric field on the back of the first target, a primary particle beam is formed. The primary beam is transmitted in the cavity wall, and will pass through the post-target beam detection system, which detects the relevant information of the beam (including beam intensity, emittance, number of particles, etc.), and the primary particle beam is also constrained by the external magnetic field, which is mainly used to focus the beam. It is worth mentioning that the first target and the second target can be controlled and moved by a CNC device. After laser target shooting, the target needs to be moved and a new target surface is used to generate particles.

[0043] The terminal thermal neutron imaging system includes a camera and a scintillator device.

[0044] The camera may be a CCD or EMCCD camera.

[0045] Based on the above scheme, the working process of the device is as follows:

[0046] Its main principle involves the use of a high-intensity laser (ARCTURUS laser system), in which the laser energy is about 3J, the laser power density is 1×10^20W / (cm^2), and the laser pulse is 30fs. The entire laser device includes a laser generator and a cooling system. During the laser generation process, a large amount of heat will be generated. A water cooling system is required for cooling to prevent the equipment from being severely thermally deformed due to excessive power, or even causing damage to the instrument. When the laser system ① bombards the first target in the neutron generator ②, the water cooling system is first controlled by the PC to perform a water cooling cycle. At the same time, the vacuum system in the neutron generator ② also needs to start running, and the device ② is evacuated. The whole purpose is to prevent the impurity gas in the cavity from affecting the beam: 1. Reduce gas scattering and absorption; 2 Maintain the stability of the particle beam; 3. Reduce beam loss. In short, the main purpose of evacuating the cavity in the accelerator is to create a high vacuum environment, reduce the interference of gas on the movement of the particle beam and the experimental results, and ensure the efficient operation of the accelerator and the accuracy of the experiment.

[0047] After the laser is generated, it bombards the first target (metal solid target) of the neutron generating device ②. This target can mainly generate proton beams or other ion beams or electron streams. The laser hitting the first target will generate an electric field gradient of the order of TV / m. This electric field gradient will stimulate the back of the target to generate a high-current particle beam. The types of particles generated for different target materials are different, and the particle flux rate is also different. This is directly related to the target material, surface contamination level, laser intensity, energy, and target material thickness. According to the relevant results of the previous experiments, The most important factor related to the number of particles produced is the intensity of the laser. However, there is no further research on the target material. If you need to refine the data, you need to further consider the target material. The first target material here is mainly thin metal foil (the specific material needs to be determined according to the number of protons produced. The more protons produced at the same energy, the better, which is conducive to increasing the flux rate of neutron removal). The second solid target is mainly lithium fluoride (LIF) or beryllium (Be). The second solid target is mainly used to produce neutron beams. The main reaction used is 7 Li+p→ 7Be+n-1.644MeV, for the same reaction, the yield may be different, which may be due to the instability of the beam or the loss of the target after being bombarded by protons. According to previous studies, the neutron yield produced by LIF is higher than that of Be target, but the yield of surface hydrogenated Be target may be higher, which needs to be considered in detail. Here we only consider the LiF solid target. The efficiency of converting a 0.2cm solid lithium fluoride target into fast neutrons when bombarded by a 5MeV proton is 1.55×10^(-4) (unit: neutron / proton n / p).

[0048] The beam is accelerated on the back of the first target to bombard the second target, and neutrons are generated on the second target. This is the main principle of the entire neutron generator ②, which also involves some auxiliary device descriptions. The entire neutron generator is in a sealed state so that the vacuum system can perform vacuum processing. The flange mainly provides sealing and supports the operation of the vacuum environment. The post-target beam detection system and the post-target beam detection system mainly use a stacked radiochromic film detector (Radiochromic film (RCF) detectors) composed of multiple layers of RCF film, fixed on the support structure, for measuring and recording the dose distribution of the particle beam. Accurate dose distribution data can be obtained through optical reading or digital image processing, which is mainly used to detect the beam data between the two targets. Of course, there are many devices that can be used for beam detection, such as: Faraday cup, semiconductor detector, scintillator detector, BPM (beam position monitor), etc. If there are other more suitable ones, they can be used as substitutes. A cavity is placed outside the beam of the device, and its main function is to reduce the contamination of the entire device caused by the loss of the beam to the cavity. A series of magnets are placed outside the cavity, and the function of the magnets is mainly to focus the beam, increase the beam intensity, and reduce the beam emittance to reduce beam loss. In this process, the design process of beam dynamics is involved to simulate the optimal state of the beam to hit the second target. The ultimate goal is of course to increase the neutron yield.

[0049] After completing the neutron source generating device, it is necessary to design the moderation of fast neutrons. A moderator needs to be designed to slow down the fast neutrons into thermal neutrons. A HOTNES-like moderator can be used. The efficiency of slowing down fast neutrons into thermal neutrons is about 2.3×10^(-4)cm^-2. According to past experimental studies, when the laser energy is greater than 3J, the power density is greater than 1×10^18W / (cm^2), and the generated proton beam energy is greater than 5MeV, the number of protons can be roughly 10^11 / MeV. According to the laser frequency conversion, the frequency f=1 / T, and the proton injection rate can be calculated through basic calculations. At this order of magnitude, there will be a conversion efficiency when the proton beam produces neutrons by hitting the second target. At this time, according to the primary particles (or protons, the primary particles produced by different target materials are different) bombarding the second target, the neutron flux rate of conversion, and then according to the neutron slowing down efficiency, the final flux rate of thermal neutrons is greater than 2×10^(4) (unit: neutron n / s / (cm)^2). The current flux rate requirement for neutron imaging is 10^4-10^6 (unit: neutron n / s / (cm)^2), which fully meets the needs and can be driven (which can be understood as not being controlled or movable).

[0050] The terminal thermal neutron imaging system is placed behind the cultural relic to detect the scattering of thermal neutrons with matter. The detector can detect the number and energy of scattered neutrons and other information. Finally, the composition and density of the material on the path can be inferred from the data collected by the neutrons, and finally an image is formed. The distance to the cultural relic can be considered according to the actual situation and the location of the detector.

[0051] In the whole process, this embodiment uses the computer terminal to control the automation equipment to realize the coordinated operation of related equipment, reducing the incoordination of operation caused by the complexity of the equipment. At the same time, the PC terminal can be used to view the detection situation in real time, improve the efficiency of cultural heritage and mineral resource exploration, and realize efficient utilization and stable operation of equipment.

[0052] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A compact laser neutron imaging device, characterized in that: It includes laser system, neutron generation system and terminal thermal neutron imaging system, among which: The laser system is used to generate laser light and emit it to the neutron generation system; The neutron generation system is in a sealed vacuum state, and a first target and a second target are provided in the neutron generation system; The laser is emitted to the first target to excite the back side of the first target to generate a high-current particle beam, and the high-current particle beam is emitted to the second target to generate a neutron beam; The terminal thermal neutron imaging system is used to detect scattered neutron information, calculate the composition and density of the material on the path through the neutron information, and form an image.

2. A compact laser neutron imaging device according to claim 1, characterized in that: Also included is a sample, which is placed between the neutron generation system and the terminal thermal neutron imaging system.

3. A compact laser neutron imaging device according to claim 1, characterized in that: The laser system includes a laser generator and a cooling unit.

4. A compact laser neutron imaging device according to claim 1, characterized in that: The neutron generation system further comprises a flange, an outer box, an inner cavity, a post-target beam detection unit and a pre-target beam detection unit, wherein: The flange and the outer box are combined to form a sealed state; The inner cavity, the post-target beam detection unit and the pre-target beam detection unit are all placed inside the outer box; The high-current particle beam is transmitted in the inner cavity; The post-target beam detection unit and the pre-target beam detection unit are both used to measure the dose distribution of the particle beam.

5. A compact laser neutron imaging device according to claim 4, characterized in that: It also includes a magnet, which is placed inside the outer box and is used to focus the beam.

6. A compact laser neutron imaging device according to claim 4, characterized in that: The post-target beam detection unit and the pre-target beam detection unit both use radiochromic film detectors.

7. A compact laser neutron imaging device according to claim 4, characterized in that: The system also includes a moderator, which is located behind the second target and is used to moderate the fast neutrons generated by the second target into thermal neutrons.

8. A compact laser neutron imaging device according to claim 7, characterized in that: It also includes a collimating device, which is located behind the moderator.

9. A compact laser neutron imaging device according to claim 4, characterized in that: The terminal thermal neutron imaging system comprises a camera and a scintillator device, wherein: The scintillator device is used to convert neutrons into optical photons; The camera is used to detect the optical photons.

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