Gamma-ray suppression neutron imaging system based on boron nitride scintillation screen
By fabricating a boron nitride scintillator and combining it with a specific optical path system, the problem of gamma ray interference with neutron imaging was solved, achieving high signal-to-noise ratio neutron imaging, improving imaging quality and detection accuracy, and making it suitable for high-energy physics experiments and nuclear industry detection.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- SUN YAT SEN UNIV
- Filing Date
- 2025-10-30
- Publication Date
- 2026-07-30
AI Technical Summary
In existing neutron imaging technologies, background noise and artifacts introduced by gamma rays interfere with the accuracy of neutron imaging, especially in nuclear reactors, where existing neutron scintillation screens have a strong response to gamma rays, affecting imaging quality and detection accuracy.
A boron nitride scintillator screen is prepared by high-temperature chemical vapor deposition. The light element composition of boron nitride suppresses gamma-ray interference and generates scintillating light under neutron excitation. Combined with a specific optical path system and camera, the neutron signal can be effectively captured and imaged.
It improves the signal-to-noise ratio of neutron imaging, reduces artifacts and noise, and enhances imaging quality and detection accuracy, especially showing significant application potential in high-energy physics experiments and nuclear industry detection.
Smart Images
Figure CN2025131091_30072026_PF_FP_ABST
Abstract
Description
Gamma-ray suppressed neutron imaging system based on boron nitride scintillation screen Technical Field
[0001] This invention relates to the field of neutron imaging technology, and more particularly to a gamma-ray suppressed neutron imaging system based on a boron nitride scintillator screen. Background Technology
[0002] In the field of nuclear reactions, neutrons are the core particles that determine the process of nuclear reactions and the state of reactors. Neutron imaging diagnostics of nuclear reactors is a method that uses neutron imaging technology to observe and analyze the internal structure, fuel distribution, and neutron flow field of a nuclear reactor. However, the radiation field produced by nuclear reactions is usually a complex mixture of neutrons and gamma rays. Gamma rays introduce background noise and artifacts, reducing the accuracy of neutron imaging, which poses a challenge. Furthermore, detecting irradiated nuclear fuel assemblies in the nuclear industry is crucial for ensuring the safety of nuclear power plants, assessing fuel performance, preventing nuclear accidents, and optimizing fuel efficiency. Neutron imaging technology utilizes the strong penetrating power of thermal neutrons to effectively detect irradiated nuclear fuel assemblies, clearly revealing internal macroscopic cracks and volume changes. However, these assemblies are usually highly radioactive, especially with the accompanying gamma rays, which can interfere with the results of neutron imaging.
[0003] Against this backdrop, there is an urgent need to develop a neutron imaging system that effectively suppresses gamma rays, capable of accurately capturing neutron images in a mixed neutron / gamma radiation field and effectively detecting irradiated radioactive nuclear fuel assemblies. The neutron scintillation screen, as the core component of the system, functions to convert neutron signals into visible light signals. In practice, to effectively suppress gamma ray interference, an ideal neutron scintillation screen should have low sensitivity to gamma rays. However, currently used neutron scintillation screens, such as GOS, still have a strong response to gamma rays. To improve imaging quality and detection accuracy, and reduce background noise and artifacts, it is necessary to develop a scintillation screen with high gamma ray suppression capabilities. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention provides a gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen and a method for preparing the boron nitride scintillation screen 1, which solves the problems of insufficient imaging quality and detection accuracy of neutron scintillation screens under gamma-ray background.
[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions.
[0006] A first aspect of the present invention provides a gamma-ray suppressed neutron imaging system based on a boron nitride scintillator, comprising a boron nitride scintillator, an optical path system, and a camera, wherein the boron nitride scintillator is located in front of the optical path system and installed at the position of the neutron incident window, and the optical path system is connected to the camera, wherein:
[0007] The boron nitride scintillation screen is used to absorb neutron beams, suppress gamma-ray interference using its light element composition, and generate scintillation light under neutron excitation; wherein,
[0008] The boron nitride material of the boron nitride scintillator screen is epitaxially grown using a high-temperature chemical vapor deposition method with silicon carbide single crystal as substrate and NH3 and BCl3 or NH3 and BF3 as raw material gases.
[0009] The optical path system is used to transmit the scintillation light generated by the boron nitride scintillation screen under neutron excitation and project it onto the camera. The optical path system is equipped with different optical path units according to high-throughput neutron beam sources, low-throughput neutron beam sources and long-distance neutron imaging.
[0010] The camera is used to receive the flashing light processed by the optical path system and record photon information.
[0011] Furthermore, for a high-flux neutron beam source, the optical path system is provided with a reflector and an imaging lens; wherein, the plane of the reflector forms a 45° angle with the plane of the boron nitride scintillation screen, for reflecting the scintillation light generated by the boron nitride scintillation screen; the imaging lens is located between the reflector and the camera, for receiving the scintillation light reflected by the reflector and transmitting it to the camera.
[0012] Furthermore, for a low-flux neutron beam source, the optical path system includes a reflector, an imaging lens, and an image intensifier; wherein, the plane of the reflector forms a 45° angle with the plane of the boron nitride scintillation screen, for reflecting the scintillation light generated by the boron nitride scintillation screen; the imaging lens is located between the reflector and the camera, for receiving the scintillation light reflected by the reflector;
[0013] Furthermore, the neutron imaging system for both high-throughput and low-throughput neutron beam sources is shielded using boron-aluminum alloy plates.
[0014] Furthermore, for long-distance neutron imaging, the optical path system (2) includes an objective lens (24), a coupling lens (26), and a radiation-resistant imaging fiber (25); wherein, the radiation-resistant imaging fiber (25) connects the boron nitride scintillation screen (1) and the camera (3) for long-distance transmission of scintillation light; the objective lens (24) is located at the front end of the radiation-resistant imaging fiber (25) for capturing the scintillation light emitted by the boron nitride scintillation screen (1) and focusing the image to the front end of the fiber; the coupling lens (26) is connected to the end of the radiation-resistant imaging fiber (25) for coupling the image at the end of the fiber to the camera.
[0015] Furthermore, the boron nitride scintillator screen is prepared by the following method, which includes the following steps:
[0016] S1. After fixing the silicon carbide single crystal substrate with a graphite clamp, place it into a chemical vapor deposition furnace, and evacuate the furnace to 10°C. -3 Pa;
[0017] S2. After heating the furnace body to the reaction temperature, keep it at the temperature. At the same time, introduce two raw material gases, NH3 and BCl3 or NH3 and BF3, into the furnace body. Use N2 as the carrier gas. The reaction equation is: BCl3+NH3→BN+3HCl, or BF3+NH3→BN+3HF.
[0018] S3. After ventilation, the temperature is maintained at the reaction temperature, and the growth is continuously kept warm.
[0019] S4. After growth is complete, power is turned off and the film is cooled to obtain a boron nitride film with a thickness of micrometers.
[0020] S5. Finally, the boron nitride film is peeled off from the silicon carbide substrate by immersion in alcohol. Then, the boron nitride film is cut to the required size and fixed on the mirror aluminum plate to make a boron nitride flickering screen.
[0021] Furthermore, in step S2 of the method for preparing the boron nitride scintillator screen, the furnace body is heated to a reaction temperature of 1500-1800°C and then kept at that temperature. At the same time, two raw material gases, NH3 and BCl3 or NH3 and BF3, are introduced into the furnace body at a volume ratio of 1.2:1.
[0022] Furthermore, in step S3 of the method for preparing the boron nitride scintillator screen, the temperature is maintained at 1500–1800°C for 120–180 minutes.
[0023] A second aspect of the present invention provides the application of the above-described gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen in a direct neutron computed tomography imaging apparatus for detecting irradiated nuclear fuel assemblies.
[0024] Compared with the prior art, the present invention has the following beneficial effects:
[0025] 1. In this invention, a boron nitride scintillation screen obtained by epitaxial growth using high-temperature chemical vapor deposition is applied to a gamma-ray suppressed neutron imaging system. Since boron nitride is composed of two light elements, boron and nitrogen, it has high sensitivity to neutrons. At the same time, the light element composition of boron nitride (boron and nitrogen) has a weak interaction with gamma rays, which can reduce the background signal caused by gamma rays, thereby improving the signal-to-noise ratio, resulting in a clearer image, reducing noise and artifacts, and improving the imaging quality and detection accuracy.
[0026] 2. The boron nitride scintillation screen of the present invention has significant advantages in gamma ray suppression, and the neutron imaging system based on the boron nitride scintillation screen of the present invention has important application potential in high-energy physics experiments and industrial detection. Attached Figure Description
[0027] Figure 1 is a schematic diagram of the gamma-ray suppressed neutron imaging system based on a boron nitride scintillator screen according to Embodiment 1 of the present invention;
[0028] Figure 2 is a schematic diagram of the gamma-ray suppression system for the detection and imaging of samples under a low-flux neutron beam source according to Embodiment 2 of the present invention.
[0029] Figure 3 is a schematic diagram of the gamma-ray suppression system for long-distance neutron imaging according to Embodiment 2 of the present invention;
[0030] Figure 4 shows a physical image of the boron nitride film sample and the boron nitride neutron scintillation screen prepared using the preparation method of Example 3 of the present invention, and a schematic diagram of the results of neutron imaging and gamma imaging of the mechanical pocket watch.
[0031] Figure 5 is a comparative schematic diagram of traditional and novel NCT imaging techniques for detecting irradiated nuclear fuel assemblies in Embodiment 4 of the present invention.
[0032] In the picture:
[0033] 1-Boron nitride scintillator; 2-Optical path system; 21-Reflector; 22-Imaging lens; 23-Image intensifier; 24-Objective lens; 25-Radiation-resistant imaging fiber; 26-Coupled lens; 3-Camera. Detailed Implementation
[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0035] Example 1: Gamma-ray suppressed neutron imaging system based on boron nitride scintillation screen
[0036] This embodiment provides a gamma-ray suppressed neutron imaging system based on a boron nitride scintillator screen according to the present invention. As shown in Figure 1, a gamma-ray suppressed neutron imaging system based on a boron nitride scintillator screen includes a boron nitride scintillator screen 1, an optical path system 2, and a camera 3. The boron nitride scintillator screen 1 is located in front of the optical path system 2 and at the position of the neutron incident window. It is used to absorb the neutron beam and use its boron and nitrogen elements to suppress gamma-ray interference, as well as to generate scintillator light under neutron excitation. The optical path system 2 is connected to the camera 3 and is used to transmit the scintillator light generated by the boron nitride scintillator screen 1 under neutron excitation and project it onto the camera 3. The optical path system 2 is equipped with different optical path units according to high-flux neutron beam sources, low-flux neutron beam sources, and long-distance neutron imaging. The camera 3 is used to receive the scintillator light processed by the optical path system 2 and record photon information.
[0037] The boron nitride scintillation screen of this invention utilizes its light element composition to suppress gamma-ray interference and generates scintillation light under neutron excitation to absorb neutron beams, thereby reducing the impact of sample radioactivity on neutron imaging. Specifically, boron nitride, composed of boron and nitrogen, has a small gamma-ray absorption cross-section, resulting in extremely low gamma-ray sensitivity. This small absorption cross-section effectively suppresses gamma-ray interference during operation. Furthermore, boron has a large neutron capture cross-section, giving boron nitride high neutron sensitivity. When neutrons are absorbed by boron-10, alpha particles and lithium-7 nuclei are generated. These secondary particles can excite the scintillation screen to emit light signals. Simultaneously, the light element composition of boron nitride (boron and nitrogen) has a weak interaction with gamma rays, thus reducing background signals caused by gamma rays and improving the signal-to-noise ratio.
[0038] The optical path system 2 of this invention is used to transmit the scintillation light generated by the boron nitride scintillation screen 1 under neutron excitation, amplify it, and project it onto the camera 3. The neutron source is divided into two types: a high-flux neutron beam source and a low-flux neutron beam source. Figure 1 shows the optical path system 2 for a high-flux neutron beam source, including a reflector 21 and an imaging lens 22. Figure 2 shows the optical path system 2 for a low-flux neutron beam source, including a reflector 21 and an imaging lens 22. An image intensifier 23 is introduced between the imaging lens 22 and the camera 3 to amplify the scintillation light, thereby enhancing the brightness and contrast of the image, enabling a clear image to be obtained even under low-light conditions.
[0039] In the optical path system 2 for high-throughput and low-throughput neutron beam sources, the plane of the reflector 21 forms a 45° angle with the plane of the boron nitride scintillator 1 to reflect the scintillator light generated by the boron nitride scintillator 1; the imaging lens 22 is located between the reflector 21 and the camera 3 to receive the scintillator light reflected by the reflector 21 and transmit it to the camera.
[0040] To protect the back-end camera 3 from damage by unabsorbed neutrons or gamma rays, in one specific embodiment, the reflector 21 deflects the scintillation light by 90°. The imaging lens 22 receives the reflected scintillation light, which is ultimately captured and recorded by the camera 3. To further reduce the stray neutron background, the entire imaging system is shielded using a boron-aluminum alloy plate. This design not only improves image quality but also enhances the system's safety and stability.
[0041] Example 2: Optical path system for long distances in a gamma-ray suppressed neutron imaging system
[0042] This embodiment provides an optical path system different from that described in Embodiment 1 for long-distance neutron imaging systems. Its overall structure is shown in Figure 3. Based on the neutron imaging system described in Embodiment 1, the optical path system 2 includes an objective lens 24, a radiation-resistant imaging fiber 25, and a coupling lens 26. The radiation-resistant imaging fiber 25 connects the boron nitride scintillation screen 1 and the camera 3, used for long-distance transmission of the scintillation light. The objective lens 24 is located at the front end of the radiation-resistant imaging fiber 25, used to capture the scintillation light emitted by the boron nitride scintillation screen 1 and focus the image to the fiber front end. The coupling lens 26 is connected to the end of the radiation-resistant imaging fiber 25, used to couple the image at the fiber end to the camera. This optical path system 2 has significant applications in some special ultra-strong radiation fields, such as nuclear reactors. Placing the neutron scintillation screen 1 near a nuclear reactor and transmitting the neutron scintillation light long-distance through the radiation-resistant imaging fiber 25 for imaging can greatly reduce the damage and interference of the radiation field to the downstream camera 3. This design not only enhances the safety of the imaging system but also allows for precise imaging without direct exposure to high-radiation environments, which is crucial for fields such as the nuclear industry and nuclear safety inspection. In this manner, operators can monitor and analyze data in a safe area while ensuring the quality and integrity of the imaging data. Furthermore, the application of radiation-hardened imaging fiber 25 helps reduce signal attenuation and distortion caused by radiation, thereby improving the overall performance and reliability of the imaging system.
[0043] Example 3: Preparation method of boron nitride scintillation screen in neutron imaging system
[0044] This embodiment provides a method for fabricating a boron nitride scintillation screen in the neutron imaging system described in Embodiments 1 and 2. In this embodiment, the boron nitride material of the boron nitride scintillation screen is epitaxially grown using a 6-inch silicon carbide single crystal as a substrate and NH3 and BCl3 (or NH3 and BF3) as raw material gases via high-temperature chemical vapor deposition. The fabrication method of the boron nitride scintillation screen 1 includes the following steps:
[0045] S1. After fixing the silicon carbide single crystal substrate with a graphite clamp, place it into a chemical vapor deposition furnace, and evacuate the furnace to 10°C.-3 Pa;
[0046] S2. The furnace body is heated to 1750℃ and held at that temperature. At the same time, two raw material gases, NH3 and BCl3 (or NH3 and BF3), are introduced into the furnace body at a volume ratio of 1.2:1. N2 is used as the carrier gas. The reaction equation is: BCl3(g) + NH3(g) → BN(s) + 3HCl(g). When the raw material gases introduced are NH3 and BF3, the reaction equation is: BF3(g) + NH3(g) → BN(s) + 3HF(g).
[0047] S3. After ventilation, maintain the furnace pressure at 50Pa and the temperature at 1750℃, and keep it at this temperature for 130 minutes to carry out deposition growth.
[0048] S4. After growth is complete, power is turned off and the film is cooled to obtain a boron nitride film with a thickness of micrometers.
[0049] S5. Finally, the boron nitride film is peeled off from the silicon carbide substrate by immersion in alcohol. Then, the boron nitride film is cut into 9×9cm pieces and fixed on a mirror aluminum plate to make the boron nitride flickering screen of the present invention.
[0050] Figures 4a and 4b show the boron nitride film sample and the boron nitride neutron scintillation screen prepared by the above preparation method. Figure 4a is a physical image of the 6-inch boron nitride film grown by the above high-temperature chemical vapor deposition method, and Figure 4b is a physical image of the boron nitride neutron scintillation screen prepared by the present invention.
[0051] By installing a boron nitride neutron scintillation screen into a neutron imaging system, gamma-ray suppressed neutron imaging can be performed. This can be achieved using a spallation neutron source and... 60 The mechanical pocket watch was imaged using a Co gamma-ray source. In both cases, a boron nitride scintillation screen was used to convert the high-energy radiation signal into a visible light signal. This signal was then collected by a camera after passing through a mirror and an imaging lens. The imaging systems for neutrons and gamma rays have similar structures; for specific configurations, please refer to the neutron imaging system in Embodiment 1 of this invention. The results of neutron and gamma-ray imaging of the mechanical pocket watch using a boron nitride neutron scintillation screen are shown in Figures 4c and 4d, where Figure 4c shows the neutron imaging result and Figure 4d shows the gamma-ray imaging result.
[0052] The experimental results shown in Figures 4c and 4d demonstrate that the neutron imaging system based on a boron nitride scintillation screen of this invention can effectively and clearly image a mechanical pocket watch, revealing the internal rubber rings and gear structure. In contrast, the system does not respond to gamma rays. These results indicate that the boron nitride scintillation screen of this invention has significant advantages in gamma ray suppression, and the neutron imaging system based on a boron nitride scintillation screen of this invention has important application potential in high-energy physics experiments and industrial detection.
[0053] Example 4: Application of Gamma-ray Suppressed Neutron Imaging System in Neutron Computed Tomography
[0054] This embodiment is used to provide the application of the gamma-ray suppressed neutron imaging system of the present invention in neutron computed tomography (NCT) technology. Figure 5 is a comparative schematic diagram of traditional and novel NCT imaging technologies for the detection of irradiated nuclear fuel assemblies. Figure 5a is a schematic diagram of traditional indirect NCT imaging technology, and Figure 5b is a structural schematic diagram of a direct NCT imaging device based on the neutron imaging system of the present invention.
[0055] Neutron computed tomography (NCT) technology images an object with neutrons from multiple angles, collects data, and then uses computer reconstruction algorithms to integrate these two-dimensional slice data to generate a three-dimensional image of the object's internal structure. In the detection of irradiated nuclear fuel assemblies, due to the strong gamma radioactivity of these components, traditional CT methods are difficult to apply directly. Therefore, indirect NCT imaging technology is usually used, as shown in Figure 5a. Traditional indirect NCT imaging technology involves placing a metal activation screen, which is insensitive to gamma rays, behind the sample, so that neutrons are absorbed by the activation screen after passing through the sample, forming a radioactive latent image. Subsequently, the activation screen needs to be moved to a darkroom, and an IP plate / film is exposed to form an image. Rotating the sample and changing the activation screen yields a series of neutron images. However, this process is cumbersome and time-consuming, hindering rapid imaging. In contrast, direct NCT imaging technology uses a neutron imaging system including a neutron scintillation screen to directly detect neutrons, providing a faster and more flexible imaging solution. For highly radioactive samples, the neutron scintillation screen in direct NCT imaging must possess strong gamma-ray suppression capabilities to ensure that gamma-ray interference is effectively eliminated during imaging. Since the boron nitride scintillation screen of this invention possesses strong gamma-ray suppression capabilities, in practical applications, the gamma-ray suppressed neutron imaging system of this invention can be applied to neutron computed tomography (CT) technology, enabling the detection of irradiated nuclear fuel assemblies using direct NCT imaging.
[0056] As shown in Figure 5b, the direct NCT imaging device includes a neutron source, a rotatable sample stage, and the gamma-ray suppressed neutron imaging system of the present invention. The neutron source, rotatable sample stage, and gamma-ray suppressed neutron detection system are arranged sequentially along the same line to ensure that the neutron beam can irradiate the sample and be detected by the neutron imaging system. Using the gamma-ray suppressed neutron imaging system of the present invention in the direct NCT imaging device allows for three-dimensional detection and imaging of radioactive nuclear fuel assembly samples. The operation steps are as follows:
[0057] a) Place and fix a radioactive nuclear fuel assembly sample on a rotatable sample platform, and fine-tune the height of the sample stage to obtain the desired imaging area;
[0058] b) Turn on the neutron source to extract the neutron beam. After the neutron beam passes through the nuclear fuel assembly sample, it is detected by the neutron imaging system to obtain a two-dimensional detection image. Then turn off the neutron source.
[0059] c) Rotate the sample stage to precisely rotate the nuclear fuel assembly sample by 1 degree;
[0060] d) Repeat steps ② and ③ continuously until 180 two-dimensional detection images are obtained;
[0061] e) The 180 two-dimensional detection images mentioned above were reconstructed into three dimensions using CT reconstruction technology to obtain three-dimensional detection images of the nuclear fuel assembly sample.
[0062] Indirect NCT imaging requires replacing the metal activation screen with a new one each time the sample is rotated to form a latent image. Furthermore, the exposed IP plate / film needs to be scanned to become a two-dimensional digital image before subsequent CT reconstruction can acquire a three-dimensional image. Direct NCT imaging, on the other hand, only requires rotating the sample to acquire a single two-dimensional digital image, which can then be directly reconstructed into a three-dimensional image using CT. This significantly simplifies the procedure, reduces operation time, and improves imaging accuracy.
[0063] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen, characterized in that, The system includes a boron nitride scintillator (1), an optical path system (2), and a camera (3). The boron nitride scintillator (1) is located in front of the optical path system (2) and installed at the position of the neutron entrance window. The optical path system (2) is connected to the camera (3). The boron nitride scintillator (1) is used to absorb neutron beams, suppress gamma-ray interference using its light element composition, and generate scintillation light under neutron excitation; wherein, The boron nitride scintillator (1) is made of boron nitride material grown by epitaxial growth using silicon carbide single crystal as substrate and NH3 and BCl3 or NH3 and BF3 as raw material gas by high temperature chemical vapor deposition. The optical path system (2) is used to transmit the scintillation light generated by the boron nitride scintillation screen (1) under neutron excitation and project it onto the camera (3). The optical path system (2) is equipped with different optical path units according to high-throughput neutron beam sources, low-throughput neutron beam sources and long-distance neutron imaging. The camera (3) is used to receive the flashing light processed by the optical path system (2) and record photon information.
2. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 1, characterized in that, For a high-throughput neutron beam source, the optical path system (2) is provided with a reflector (21) and an imaging lens (22); wherein, The plane of the reflector (21) forms a 45° angle with the plane of the boron nitride scintillator (1) to reflect the scintillator light generated by the boron nitride scintillator (1); The imaging lens (22) is located between the reflector (21) and the camera (3) and is used to receive the flash light reflected by the reflector (21) and transmit it to the camera.
3. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 1, characterized in that, For a low-flux neutron beam source, the optical path system (2) includes a mirror (21), an imaging lens (22), and an image intensifier (23); wherein, The plane of the reflector (21) forms a 45° angle with the plane of the boron nitride scintillator (1) to reflect the scintillator light generated by the boron nitride scintillator (1); The imaging lens (22) is located between the reflector (21) and the camera (3) and is used to receive the flash light reflected by the reflector (21); The image intensifier (23) is located between the imaging lens (22) and the camera (3) and is used to amplify the scintillation light received by the imaging lens (22).
4. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 2 or 3, characterized in that, The neutron imaging system is shielded entirely using boron-aluminum alloy plates.
5. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 1, characterized in that, For long-distance neutron imaging, the optical path system (2) includes an objective lens (24), a coupling lens (26), and a radiation-resistant imaging fiber (25); wherein, The radiation-resistant imaging fiber (25) connects the boron nitride scintillator (1) and the camera (3) for transmitting scintillator light over long distances; The objective lens (24) is located at the front end of the radiation-resistant imaging fiber (25) and is used to capture the scintillation light emitted by the boron nitride scintillation screen (1) and to focus the image and transmit it to the front end of the fiber. The coupling lens (26) is connected to the end of the radiation-resistant imaging fiber (25) to couple the image at the end of the fiber to the camera.
6. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to any one of claims 1-5, characterized in that, The boron nitride scintillator screen is prepared by the following method, which includes the following steps: S1. After fixing the silicon carbide single crystal substrate with a graphite clamp, place it into a chemical vapor deposition furnace, and evacuate the furnace to 10°C. -3 Pa; S2. After heating the furnace body to the reaction temperature, keep it at the temperature. At the same time, introduce two raw material gases, NH3 and BCl3 or NH3 and BF3, into the furnace body. Use N2 as the carrier gas. The reaction equation is: BCl3+NH3→BN+3HCl, or BF3+NH3→BN+3HF. S3. After ventilation, the temperature is maintained at the reaction temperature, and the growth is continuously kept warm. S4. After growth is complete, power is turned off and the film is cooled to obtain a boron nitride film with a thickness of micrometers. S5. Finally, the boron nitride film is peeled off from the silicon carbide substrate by immersion in alcohol. Then, the boron nitride film is cut to the required size and fixed on the mirror aluminum plate to make a boron nitride flickering screen.
7. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 6, characterized in that, In step S2 of the method for preparing the boron nitride scintillator screen, the furnace body is heated to a reaction temperature of 1500-1800℃ and then kept at that temperature. At the same time, two raw material gases, NH3 and BCl3 or NH3 and BF3, are introduced into the furnace body at a volume ratio of 1.2:
1.
8. The gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen according to claim 6, characterized in that, In step S3 of the method for preparing the boron nitride scintillator screen, the temperature is maintained at 1500-1800℃ for 120-180 minutes.
9. The application of the gamma-ray suppressed neutron imaging system based on a boron nitride scintillation screen as described in any one of claims 1 to 8 in a direct neutron computed tomography imaging apparatus for detecting irradiated nuclear fuel assemblies.