A quasi-monochromatic neutron target based on a proton accelerator and a method for adjusting a neutron beam

Abstract

The application relates to a quasi-monochromatic neutron target based on a proton accelerator and a neutron beam adjusting method, which comprises a target frame and a water cooling pipe fixed on the back of the target frame and passing through cooling liquid, a plurality of diaphragms are arranged on the target frame, the plurality of diaphragms are respectively used for mounting a fluorescent screen seat, a plurality of lithium target seats and an empty target seat, the fluorescent screen seat is used for mounting a fluorescent screen, the other side of the fluorescent screen is provided with a fluorescent screen cover, the plurality of lithium target seats are respectively used for mounting lithium targets with different thicknesses, the other side of the lithium target is provided with a lithium target cover, the empty target seat is not provided with a target, the other side of the empty target seat is provided with a target cover, and the target frame drives the whole target to move. By adopting the method disclosed in the application, a plurality of quasi-monochromatic neutron beams can be generated by using a plurality of different energy proton beams to hit lithium targets with different thicknesses, the neutron yield can be improved as much as possible on the basis of ensuring the monochromaticity of the quasi-monochromatic neutron beam, the beam adjusting time can be reduced on the basis of ensuring that the quasi-monochromatic neutron is derived from the lithium target, and the test efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of quasi-monoenergetic neutron targets, specifically relating to a quasi-monoenergetic neutron target based on a proton accelerator and a method for adjusting the neutron beam. Background Technology

[0002] Neutrons in the Earth's atmosphere can cause single-event effects in electronic devices used in aircraft, affecting the reliability of avionics systems. With advancements in semiconductor technology, electronic devices are becoming increasingly smaller in feature size and higher in integration, making them more susceptible to radiation damage. This has led to growing attention being paid to the reliability of neutron single-event effects in the field of aerospace microelectronics.

[0003] Conducting flight tests or high-altitude tests directly in the atmospheric radiation environment is extremely time-consuming and costly. Therefore, almost all neutron single-event effect experiments are conducted at ground-based neutron sources, primarily monoenergetic neutron sources using hyperbaric multipliers, as well as quasi-monoenergetic neutron sources and white-light neutron sources based on proton accelerator target firing. Neutron energies in monoenergetic neutron sources are generally below 20 MeV, while neutrons above 20 MeV typically originate from quasi-monoenergetic neutron sources and white-light neutron sources.

[0004] Quasi-monoenergetic neutron sources can achieve a single-energy peak ratio of up to 40%, and by employing certain methods, low-energy tail neutrons can be corrected. This allows for the study of the energy dependence of single-event effect cross-sections, and further, the prediction of single-event error rates of microelectronic devices in various neutron radiation environments. Atmospheric neutrons can reach energies on the order of GeV; therefore, quasi-monoenergetic neutron sources above 20 MeV are of significant value for studying the relationship between radiation damage to electronic devices and neutron energy.

[0005] Internationally, lithium or beryllium targets are mainly used for quasi-monoenergetic neutron targets. Lithium targets generally have higher yields and beryllium targets are highly toxic, so lithium targets are preferred. When a proton passes through a lithium target, it produces a quasi-monoenergetic neutron. The energy of its single-energy peak is typically several MeV lower than that of the incident proton. For example, a 100 MeV proton beam bombarding a 6mm thick lithium target produces a quasi-monoenergetic neutron beam with a single-energy peak at 98.1 MeV. The thinner the lithium target, the higher the proportion of monoenergetic neutrons in the quasi-monoenergetic neutrons, meaning better monochromaticity, but lower neutron yield. Conversely, the thicker the lithium target, the higher the yield of quasi-monoenergetic neutrons, but the worse the monochromaticity. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a quasi-monoenergetic neutron target and neutron beam modulation method based on a proton accelerator. This method enables the generation of multiple quasi-monoenergetic neutron beams by striking lithium targets of different thicknesses with multiple proton beams of different energies. This not only maximizes the neutron yield while ensuring the monochromaticity of the quasi-monoenergetic neutron beams, but also reduces the background neutrons. Furthermore, it reduces beam modulation time and improves experimental efficiency while ensuring that the quasi-monoenergetic neutrons originate from the lithium target.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, a quasi-monoenergetic neutron target based on a proton accelerator is provided. The device includes a target frame and a water-cooling pipe. The water-cooling pipe is fixed to the back of the target frame and is circulated with coolant. A plurality of apertures are provided on the target frame. The plurality of apertures are respectively used to install fluorescent screen holders, a plurality of lithium target holders, and an empty target holder. The fluorescent screen holder is used to install a fluorescent screen. A fluorescent screen cover is provided on the other side of the fluorescent screen. The plurality of lithium target holders are respectively used to install lithium targets of different thicknesses. A lithium target cover is provided on the other side of the lithium targets. The empty target holder does not install a target. A target cover is provided on the other side of the empty target holder. The target frame is movable.

[0009] Furthermore, the target frame is mounted on a motion control device to enable the target frame to move up and down, thereby moving the entire neutron target up and down, so that the proton beam can bombard the center of all targets.

[0010] Furthermore, the diameter of the central hole of the lithium target holder is not greater than the diameter of the target frame aperture, and an inner step is provided on the lithium target holder. The diameter of the inner step is smaller than the diameter of the central hole of the lithium target holder, and the inner step is used to install the lithium target.

[0011] Furthermore, the height of the central hole of the lithium target holder is consistent with the thickness of the corresponding lithium target, and the lithium target holder is provided with external threads for screwing onto the lithium target cover.

[0012] Furthermore, the diameter of the lithium target is the same as the diameter of the central hole of the lithium target holder, and is larger than the diameter of the inner step of the lithium target holder. The lithium target fits into the inner wall of the lithium target holder and the inner step of the lithium target, so that the heat generated after the proton bombards the lithium target is efficiently transferred to the target frame and carried away by the coolant of the water cooling pipe, thereby improving the stability and service life of the lithium target.

[0013] Furthermore, the lithium target cover is used in conjunction with the corresponding lithium target holder. The lithium target cover has internal threads and internal steps to fix the lithium target. The diameter of the center hole of the lithium target cover is the same as the diameter of the corresponding lithium target, and the diameter of the internal step of the lithium target cover is smaller than the diameter of the corresponding lithium target.

[0014] Furthermore, the diameter of the fluorescent screen is the same as the diameter of the central hole of the fluorescent screen holder, and is larger than the diameter of the inner step of the fluorescent screen holder. The height of the central hole of the fluorescent screen holder is the same as the thickness of the corresponding fluorescent target.

[0015] Furthermore, the screen cover is used in conjunction with the screen base. The screen cover has internal threads and internal steps to fix the screen. The diameter of the central hole of the screen cover is the same as the diameter of the screen. The diameter of the internal step of the screen cover is smaller than the diameter of the screen.

[0016] Secondly, a neutron beam modulation method, employing a quasi-monoenergetic neutron target based on a proton accelerator as described in the first aspect of the present invention and any optional embodiment thereof, the method comprising the following steps:

[0017] S1. Move the target frame to focus the fluorescent screen on the beam, and adjust the proton beam current to focus it on the center of the fluorescent screen;

[0018] S2. Move the target frame so that the lithium target is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons;

[0019] S3. Change the energy of the protons incident on the lithium target and move the target frame synchronously so that the lithium target of the corresponding thickness is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons of other energies.

[0020] S4. When the fluorescent screen fails, the proton beam alignment is adjusted by moving the target frame and using an empty target. At this time, a fission ionization chamber is placed behind the quasi-monoenergetic neutron target to measure neutrons.

[0021] S5. Conduct sample irradiation tests.

[0022] Furthermore, adjusting the proton beam in step S4 includes the following sub-steps:

[0023] S4.1. Lift the entire target frame. At this time, the proton beam will not bombard any part of the neutron target. Measure the background neutron count rate S0 and adjust the direction of the proton beam to make S0 as small as possible, effectively reducing the background neutrons generated during the transmission process before the proton hits the target.

[0024] S4.2 Move the target frame so that the aperture at the bottom of the target frame is located in the proton beam stream line. At this time, the target is empty and the beam is in place. Measure the background neutron count rate S1 using the fission ionization chamber and adjust the direction of the proton beam to make S1 as small as possible (S1≈S0) to ensure that the proton beam passes through the empty target and effectively reduce the background neutrons generated by proton bombardment on components such as the target frame, target base, and target cover.

[0025] S4.3. Move the target frame so that the corresponding lithium target is on the proton beam line. Use the fission ionization chamber to measure the neutron count rate S2, and fine-tune the proton beam direction to make the ratio of S1 / S2 as small as possible, with a minimum requirement of S1 / S2≤1 / 3, so as to achieve accurate centering of the proton beam. This ensures that the generated quasi-monoenergetic neutrons mainly come from the neutrons generated by the proton bombardment of the lithium target nucleus, thus guaranteeing the monochromaticity of the neutrons.

[0026] The beneficial technical effects of this invention are as follows: By employing the quasi-monoenergetic neutron target and neutron beam modulation method based on a proton accelerator disclosed in this invention, multiple lithium targets of different thicknesses are designed. For proton beams at multiple energy points, multiple quasi-monoenergetic neutron beams can be generated by striking corresponding lithium targets of different thicknesses. Thicker lithium targets are used for high-energy proton beams, and thinner lithium targets are used for low-energy proton beams, thereby maximizing neutron yield while ensuring the monochromaticity of quasi-monoenergetic neutrons. Furthermore, during beam modulation, to ensure that protons accurately bombard the lithium target, rather than the target frame or other locations, a fluorescent screen and an empty target are set on the quasi-monoenergetic neutron target. Simultaneously, beam modulation methods and steps are designed to ensure that the quasi-monoenergetic neutrons originate from proton bombardment of the lithium target, rather than from proton bombardment of the target frame or other sources, thereby reducing background neutrons, shortening beam modulation time, and improving experimental efficiency. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a quasi-monoenergetic neutron target based on a proton accelerator, as shown in Embodiment 1 of the present invention.

[0028] Among them: ①-proton beam, ②-water cooling tube, ③-target frame, ④-fluorescent screen holder, ⑤-lithium target holder, ⑥-empty target holder, ⑦-fluorescent screen, ⑧-lithium target, ⑨-target cover, ⑩-fastening screw. Detailed Implementation

[0029] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] like Figure 1 As shown, an embodiment of the present invention provides a quasi-monoenergetic neutron target based on a proton accelerator, including a target frame ③ and a water-cooling pipe ②. The target frame ③ is a metal plate, and a plurality of apertures are set on the target frame ③, the number of apertures being ≥4. The water-cooling pipe ② is welded to the back of the target frame ③.

[0032] Several apertures on the target frame ③ are used to install fluorescent screen holders ④, several lithium target holders ⑤, and an empty target holder ⑥. Fluorescent screen holder ④ is used to install fluorescent screens ⑦, and a fluorescent screen cover is set on the other side of fluorescent screen ⑦. Several lithium target holders ⑤ are used to install lithium targets ⑧ of different thicknesses, and a lithium target cover is set on the other side of lithium target ⑧. The empty target holder ⑥ does not install a target, and a target cover ⑨ is set on the other side of the empty target holder ⑥.

[0033] Water-cooled pipe ② carries cooling water and is made of copper or other materials with good thermal conductivity.

[0034] The target frame ③ is mounted on a moving control device, which can move the target frame ③ to multiple positions up and down, thereby moving the entire neutron target up and down. This allows the proton beam to bombard the center of all targets, ensuring that the proton beam ① passes through the centers of multiple apertures on the target frame ③. In addition, the entire target frame ③ can be lifted, allowing the proton beam ① to pass under the target frame ③. The target frame ③ is made of copper, but it can also be made of other materials with good thermal conductivity.

[0035] The lithium target holder ⑤ is fixed on the target frame ③. In this embodiment, the lithium target holder ⑤ is fixed on the target frame ③ by fastening screws ⑩. The diameter of the central hole of the lithium target holder ⑤ is not greater than the diameter of the aperture of the target frame ③, and the lithium target holder ⑤ has an inner step. The diameter of the inner step is smaller than the diameter of the central hole of the lithium target holder ⑤ for mounting the lithium target ⑧. The height of the central hole of the lithium target holder ⑤ is consistent with the thickness of the corresponding lithium target ⑧. The lithium target holder ⑤ is provided with external threads to be screwed into the lithium target cover. The lithium target holder ⑤ is made of copper, or it can be other materials with good thermal conductivity.

[0036] The diameter of the lithium target ⑧ is the same as the diameter of the central hole of the lithium target holder ⑤, and is larger than the diameter of the inner step of the lithium target holder ⑤. The lithium target ⑧ fits into the inner wall of the lithium target holder ⑤ and the inner step of the lithium target to facilitate heat dissipation. This allows the heat generated after the protons bombard the lithium target to be efficiently transferred to the target frame ③ and carried away by the coolant in the water cooling pipe ②, thereby improving the stability and service life of the lithium target ⑧.

[0037] The lithium target cover is used in conjunction with the corresponding lithium target base ⑤. It includes internal threads and internal steps for fixing the lithium target ⑧. The diameter of the center hole of the lithium target cover is the same as the diameter of the corresponding lithium target ⑧. The diameter of the internal step of the lithium target cover is smaller than the diameter of the corresponding lithium target ⑧. The lithium target cover is made of copper, but it can also be made of other materials with good thermal conductivity.

[0038] The diameter of the fluorescent screen ⑦ is the same as the diameter of the central hole of the fluorescent screen base ④, and is larger than the diameter of the inner step of the fluorescent screen base ④. The height of the central hole of the fluorescent screen base ④ is the same as the thickness of the corresponding fluorescent target.

[0039] The fluorescent screen cover is used in conjunction with the fluorescent screen base ④. The fluorescent screen cover includes internal threads and internal steps for fixing the fluorescent screen ⑦. The diameter of the center hole of the fluorescent screen cover is the same as the diameter of the fluorescent screen ⑦. The diameter of the internal step of the fluorescent screen cover is smaller than the diameter of the fluorescent screen. The fluorescent screen cover is made of copper, but it can also be made of other materials with good thermal conductivity.

[0040] The empty target holder ⑥ is used in conjunction with the target cover ⑨, and the diameter of the center hole of the empty target holder ⑥ is the same as the diameter of the center hole of the target cover ⑨.

[0041] The lithium target described in the embodiments of the present invention can also be a beryllium target, and there is no limitation thereto.

[0042] Example 2

[0043] This invention provides a neutron beam modulation method, which is based on a quasi-monoenergetic neutron target based on a proton accelerator provided in Embodiment 1 of this invention. The neutron beam modulation method includes the following steps:

[0044] S1. A quasi-monoenergetic neutron target fluorescent screen is used to focus the proton beam onto the center of the fluorescent screen.

[0045] S2. Move the quasi-monoenergetic neutron target so that the lithium target is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons.

[0046] S3. Change the energy of the protons incident on the lithium target and move the quasi-monoenergetic neutron target synchronously so that the lithium target of the corresponding thickness is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons of the corresponding energy.

[0047] S4. When the fluorescent screen fails, the proton beam alignment can be adjusted by moving the target frame and the empty target. At this time, a fission ionization chamber is placed behind the quasi-monoenergetic neutron target to measure the neutrons.

[0048] S5. Conduct sample irradiation tests.

[0049] Step S4, which involves adjusting the proton beam, includes the following sub-steps:

[0050] S4.1. Lift the entire quasi-monoenergetic neutron target. At this time, the proton beam will not bombard any part of the neutron target. Measure the background neutron count rate S0. The neutrons are generated by the interaction between the protons and the beam lines before the lithium target. Adjust the direction of the proton beam to make S0 as small as possible, effectively reducing the background neutrons generated during the transmission process before the proton hits the target.

[0051] S4.2 Move the target frame so that the aperture at the bottom of the target frame is located in the proton beam line. At this time, the target is empty and the beam is in place. Measure the background neutron count rate S1 using the fission ionization chamber. Neutrons come from the interaction between protons and the beam line in front of the lithium target, as well as from the neutrons generated by the bombardment of particles on the lithium target frame. Adjust the direction of the proton beam to make S1 as small as possible (S1≈S0) to ensure that the proton beam passes through the empty target and effectively reduce the background neutrons generated by the protons bombarding the target frame, target holder, and target cover.

[0052] S4.3. Move the target frame so that the corresponding lithium target is on the proton beam line. Measure the background neutron count rate S2 using the fission ionization chamber and fine-tune the proton beam direction to make the ratio of S1 / S2 as small as possible, with a minimum requirement of S1 / S2 ≤ 1 / 3. This ensures accurate alignment of the proton beam, so that the generated quasi-monoenergetic neutrons mainly originate from the neutrons produced by the proton bombardment of the lithium target nucleus, thus guaranteeing the monochromaticity of the neutrons.

[0053] As can be seen from the above embodiments, the quasi-monoenergetic neutron target and neutron beam modulation method disclosed in this invention based on a proton accelerator can generate multiple quasi-monoenergetic neutron beams by striking lithium targets of different thicknesses with multiple proton beams of different energies. This ensures that the generated neutrons mainly come from the nuclear reaction between protons and lithium targets, thereby maximizing neutron yield while maintaining the monochromaticity of the quasi-monoenergetic neutron beams, and reducing background neutrons. It also reduces beam modulation time and improves experimental efficiency while ensuring that the quasi-monoenergetic neutrons originate from the lithium target, thus laying a reliable foundation for the study of radiation damage to electronic devices and avionics systems.

[0054] The apparatus and method described in this invention are not limited to the embodiments described in the specific implementation. Other implementation methods derived by those skilled in the art based on the technical solution of this invention also fall within the scope of technical innovation of this invention.

Claims

1. A quasi-monoenergetic neutron target based on a proton accelerator, characterized in that: The quasi-monoenergetic neutron target includes a target frame and a water-cooling pipe. The water-cooling pipe is fixed to the back of the target frame and is circulated with coolant. Several apertures are arranged on the target frame, each used to mount a fluorescent screen holder, several lithium target holders, and an empty target holder. The fluorescent screen holder is used to mount a fluorescent screen, and a screen cover is provided on the other side of the screen. The several lithium target holders are used to mount lithium targets of different thicknesses. Multiple proton beams of different energy points strike the lithium targets of different thicknesses to generate multiple quasi-monoenergetic neutron beams, thereby increasing neutron yield while maintaining the monochromaticity of the quasi-monoenergetic neutrons. A lithium target cover is provided on the other side of the lithium targets. The empty target holder does not mount a target, but a target cover is provided on the other side of the empty target holder. The target frame is movable. When the fluorescent screen fails, the proton beam alignment is adjusted by moving the target frame and using an empty target. At this point, a fission ionization chamber is placed behind the quasi-monoenergetic neutron target to measure neutrons. First, the entire target frame is lifted to measure the background neutron count rate S0, and the proton beam direction is adjusted to minimize S0. Then, the target frame is moved so that the lowest aperture is positioned on the proton beam line, resulting in an empty target. The background neutron count rate S1 is measured using the fission ionization chamber, and the proton beam direction is adjusted to make S1≈S0 to ensure the proton beam passes through the empty target. Finally, the target frame is moved so that the corresponding lithium target is positioned on the proton beam line, and the neutron count rate S2 is measured using the fission ionization chamber. The proton beam direction is then fine-tuned to make S1 / S2≤1 / 3, thus achieving accurate proton beam alignment.

2. The quasi-monoenergetic neutron target based on a proton accelerator as described in claim 1, characterized in that: The target frame is mounted on a motion control device to enable the target frame to move up and down, thereby moving the entire quasi-monoenergetic neutron target up and down, so that the proton beam bombards the center of all targets.

3. The quasi-monoenergetic neutron target based on a proton accelerator as described in claim 1, characterized in that: The diameter of the central hole of the lithium target holder is not greater than the diameter of the target frame aperture, and an inner step is provided on the lithium target holder. The diameter of the inner step is smaller than the diameter of the central hole of the lithium target holder, and the inner step is used to install the lithium target.

4. The quasi-monoenergetic neutron target based on a proton accelerator as described in claim 3, characterized in that: The height of the central hole of the lithium target holder is consistent with the thickness of the corresponding lithium target, and the lithium target holder is provided with external threads for screwing onto the lithium target cover.

5. A quasi-monoenergetic neutron target based on a proton accelerator as described in claim 4, characterized in that: The diameter of the lithium target is the same as the diameter of the central hole of the lithium target holder, and is larger than the diameter of the inner step of the lithium target holder. The lithium target is in contact with the inner wall of the lithium target holder and the inner step of the lithium target.

6. A quasi-monoenergetic neutron target based on a proton accelerator as described in claim 1, characterized in that: The lithium target cover is used in conjunction with the corresponding lithium target holder. The lithium target cover has internal threads and internal steps to fix the lithium target. The diameter of the center hole of the lithium target cover is the same as the diameter of the corresponding lithium target. The diameter of the internal step of the lithium target cover is smaller than the diameter of the corresponding lithium target.

7. A quasi-monoenergetic neutron target based on a proton accelerator as described in claim 1, characterized in that: The diameter of the fluorescent screen is the same as the diameter of the central hole of the fluorescent screen base, and is larger than the diameter of the inner step of the fluorescent screen base. The height of the central hole of the fluorescent screen base is the same as the thickness of the corresponding fluorescent target.

8. A quasi-monoenergetic neutron target based on a proton accelerator as described in claim 7, characterized in that: The fluorescent screen cover is used in conjunction with the fluorescent screen base. The fluorescent screen cover is provided with internal threads and internal steps to fix the fluorescent screen. The diameter of the central hole of the fluorescent screen cover is the same as the diameter of the fluorescent screen, and the diameter of the internal step of the fluorescent screen cover is smaller than the diameter of the fluorescent screen.

9. A neutron beam modulation method, employing a quasi-monoenergetic neutron target based on a proton accelerator as described in any one of claims 1-8, the method comprising the following steps: S1. Move the target frame to focus the fluorescent screen on the beam, and adjust the proton beam current to focus it on the center of the fluorescent screen; S2. Move the target frame so that the lithium target is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons; S3. Change the energy of the protons incident on the lithium target and move the target frame synchronously so that the lithium target of the corresponding thickness is in the beam, and the protons bombard the lithium target to produce quasi-monoenergetic neutrons with the corresponding energy. S4. When the fluorescent screen fails, the proton beam alignment is adjusted by moving the target frame and using an empty target. At this time, a fission ionization chamber is placed behind the quasi-monoenergetic neutron target to measure neutrons. S5. Conduct sample irradiation tests; Adjusting the proton beam in step S4 includes the following sub-steps: S4.

1. Lift the entire target frame. At this time, the proton beam will not bombard any part of the neutron target. Measure the background neutron count rate S0 and adjust the direction of the proton beam to make S0 as small as possible. S4.2 Move the target frame so that the aperture at the bottom of the target frame is located in the proton beam stream line. At this time, the target is empty and the beam is in place. Measure the background neutron count rate S1 using the fission ionization chamber and adjust the direction of the proton beam so that S1≈S0 to ensure that the proton beam passes through the empty target. S4.

3. Move the target frame so that the corresponding lithium target is on the proton beam line. Use the fission ionization chamber to measure the neutron count rate S2, and fine-tune the proton beam direction so that the ratio of S1 / S2 is as small as possible, with a minimum requirement of S1 / S2≤1 / 3, thereby achieving accurate proton beam alignment.

Images