Gaseous target for generating monoenergetic neutrons

Abstract

The invention provides a gaseous target for generating monoenergetic neutrons. The gaseous target comprises a sealing flange, an inlet window front window, an inlet window rear window, a blocking window and a vacuum system. Two inlet windows are arranged in the front and back, a front gas target chamber and a rear gas target chamber are constructed in a gaseous target, helium is filled into the target chamber composed of the front window and the rear window, deuterium or tritium gas is filled into the target chamber composed of the rear window and the stopping window, and the situation that radioactive gas escapes to pollute an accelerator pipeline due to damage of the inlet windows of the target chambers is effectively prevented through redundancy design. An inlet window of the gaseous target is made of Mo foil with the thickness smaller than 10 micrometers, a blocking window is made of Au foil with the thickness smaller than 150 micrometers, the energy width of the generated neutrons is smaller than 2%, and when the beam intensity is stable, the variation of the neutron fluence within 8 hours is smaller than 5%. The monoenergetic neutrons generated by the gaseous target are low in energy loss and excellent in monochromaticity, the design precision requirement of the fourth-generation nuclear reactor is met, and a guarantee is provided for commercialized popularization of the fourth-generation nuclear reactor.

Description

Technical Field

[0001] This invention belongs to the field of neutron source technology, and specifically relates to a gaseous target for generating monoenergetic neutrons. Background Technology

[0002] The design of fourth-generation nuclear reactors places higher demands on the accuracy of neutron cross-section measurements, requiring a relative standard uncertainty of less than 1% for neutron-induced standard nuclear reactions. ISO 8529 recommends that neutron radiation field assessments consider factors such as chamber scattering, external air scattering, internal air scattering, support scattering, target scattering, spectral effects, and photon radiation effects. Currently, water cooling is the primary cooling method for solid targets used to generate monoenergetic neutrons, leading to an increased proportion of scattered neutrons and a decrease in neutron monochromaticity. Furthermore, the high target surface temperature poses a risk of tritium escaping from the target material for tritium targets. Additionally, under the same beam conditions, the neutron flux of solid targets is lower than that of gas targets. Therefore, existing technologies generally employ gas targets to generate neutron sources. Gas targets not only offer higher yields than solid targets but also effectively reduce energy loss from the target substrate and walls, minimizing energy broadening and resulting in better monoenergetic neutron monochromaticity. Therefore, there is an urgent need to design a gaseous target capable of generating monoenergetic neutrons with excellent monochromaticity. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a gaseous target for generating monoenergetic neutrons. Through the material selection and design of the inlet window and the blocking window, the two-stage redundant design of the gas target chamber, and the linkage design of the accelerator pipeline, not only is the neutron energy width reduced and the monochromaticity of the center improved, but the airtightness of the target chamber and the safety of the pipeline are also ensured.

[0004] This invention discloses a gaseous target for generating monoenergetic neutrons, comprising a sealing flange, an inlet window, a blocking window, and a vacuum system; the inlet window is made of Mo foil with a thickness of less than 10 μm, and the blocking window is made of Au foil with a thickness of less than 150 μm; the inlet window includes a front window and a rear window, which are sequentially arranged on the target wall along the beam direction, dividing the gaseous target into two gas target chambers; helium is filled into the gas target chamber composed of the front window, the rear window, and the target wall, and the gas pressure is maintained at 10. 2 The pressure is maintained at 1 to 1 standard atmosphere. The gas target chamber, consisting of a rear window, a stop window, and a target wall, is filled with deuterium or tritium gas, and the pressure is maintained at 1 to 1.3 standard atmospheres.

[0005] Furthermore, a linkage gate valve is installed at the connection between the gaseous target and the accelerator pipeline. When the inlet window is damaged or gas escapes from the target chamber, the linkage gate valve is closed to disconnect the gaseous target from the accelerator pipeline.

[0006] Furthermore, the outer threaded seal of the blocking window is connected to a sleeve, and circulating cooling gas is passed through the sleeve to cool the target chamber.

[0007] Furthermore, each of the target chambers is connected to a vacuum gauge for monitoring the air pressure inside the target chamber.

[0008] Furthermore, each of the target chambers is connected to a vacuum system, which includes an oil-free dry pump forepump and a molecular pump.

[0009] Furthermore, the interface between the gas target and the beam pipeline is a sealing flange, with the front window tightly fitted to the flange plate of the sealing flange, achieving a target chamber leakage rate of 10%. -7 Pa·m 3 / s.

[0010] Compared with the prior art, the technical solution adopted in this invention can achieve the following beneficial effects: (1) The gaseous target of the present invention has two entrance windows set at the front and back to construct a two-stage target chamber. This redundant design can effectively prevent radioactive tritium or deuterium from escaping into the accelerator pipeline due to damage to the entrance window of the target chamber, thereby causing contamination of the accelerator pipeline. This not only enhances the airtightness of the secondary target chamber, but also improves the overall pipeline safety.

[0011] (2) By setting a linkage gate valve at the connection between the gaseous target and the accelerator pipeline, the present invention can ensure that when the inlet window is damaged or the gas in the target chamber escapes, the linkage gate valve will automatically close and disconnect the connection between the gaseous target and the accelerator pipeline at the first time, thereby further improving the overall pipeline safety.

[0012] (3) The neutron energy width generated by the gaseous target of the present invention is less than 2%, and the change in neutron flux within 8 hours is less than 5% when the beam intensity is stable. The monoenergetic neutrons generated by the gaseous target of the present invention not only have less energy loss, but also have good monochromaticity, which fully meets the design accuracy requirements of the fourth generation nuclear reactor, and provides performance and safety assurance for the commercial promotion and application of the fourth generation nuclear reactor. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a schematic diagram of the structure of the gaseous target of the present invention.

[0014] Figure label: Sealing flange 1, front window 2-1, rear window 2-2, stop window 3, vacuum system 4, target wall 5, linkage slide valve 6, sleeve 7, vacuum gauge 8, accelerator pipeline 9, beam pipeline 10, aperture 11, focusing magnet 12. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0016] This invention proposes a gaseous target for generating monoenergetic neutrons, comprising a sealing flange 1, an inlet window, a blocking window 3, and a vacuum system 4. The inlet window is made of Mo foil with a thickness of less than 10 μm. The small interaction cross-section between the Mo foil and the incident beam effectively reduces beam loss. The blocking window is made of Au foil with a thickness of less than 150 μm. Au foil has a low neutron reaction cross-section and a high beam reaction cross-section, thereby ensuring that the beam is effectively blocked and the number of scattered neutrons is minimized. The inlet window includes a front window 2-1 and a rear window 2-2. The front window 2-1, the rear window 2-2, and the blocking window 3 are sequentially arranged on the gaseous target wall 5 along the beam direction, dividing the gaseous target into two gas target chambers. The target wall material can be 304 stainless steel with a thickness of 2 mm. Helium gas is filled into the gas target chamber composed of the front window 2-1, the rear window 2-2, and the target wall 5, and the gas pressure is maintained at 10. 2 A slight negative pressure level of 1 atmosphere is maintained; deuterium or tritium gas is filled into the gas target chamber, which consists of the rear window 2-2, the stop window 3, and the target wall 5, and the gas pressure is maintained at 1~1.3 atmospheres. The gas target chamber is preferably cylindrical, with an outer diameter of Φ35mm, and the vacuum level of the target chamber should be <2.0×10⁻⁶. - 5 Pa. The inlet and stop windows are preferably circular foils with a diameter of 25-30 mm. For tritium, the gas source input within the target chamber should be carried out in a sealed glove box to prevent tritium escape. For non-radioactive deuterium, the target chamber vacuum can reach a limit of 10 Pa. -5 Performed after Pa.

[0017] Preferably, a linkage gate valve 6 is provided at the connection between the gaseous target and the accelerator pipeline 9. When the inlet window is damaged or gas escapes from the target chamber, the linkage gate valve 6 is closed to disconnect the gaseous target from the accelerator pipeline 9, preventing deuterium or tritium gas from contaminating the accelerator pipeline. The linkage time of the linkage gate valve 6 is controlled on the order of milliseconds.

[0018] Preferably, the outer side of the blocking window 3 is threadedly sealed with a sleeve 7, and the sleeve 7 is filled with uninterrupted circulating cooling gas for cooling the target chamber.

[0019] Preferably, both gas target chambers are connected to a vacuum gauge 8 for monitoring the gas pressure inside the chamber. The ultimate vacuum of the vacuum gauge 8 is 10⁻⁶. -9 Pa can monitor the gas pressure inside the target chamber after maintaining a vacuum in the target chamber and after the target chamber is filled with gas.

[0020] Preferably, both gas target chambers are connected to a vacuum system 4, which includes an oil-free dry pump foreboard pump and a molecular pump to achieve target chamber vacuum. The overall target chamber vacuum should reach and maintain its ultimate vacuum within 5-10 minutes. The molecular pump should be selected with a pumping rate for N2 > 85 L / s and an ultimate pressure < 8 × 10⁻⁶ L / s. -6 Pa, compression ratio 10 8 Under water cooling, the maximum inlet flow rate is 140 sccm; under air cooling, the maximum inlet flow rate is 100 sccm. At a speed of 1250 Hz, the maximum inlet pressure is 5 Pa for water cooling and 2 Pa for air cooling. The preferred oil-free dry pump backing pump has a flow rate of 0.5~2 L / s and an ultimate vacuum of 10. - 1 Pa.

[0021] Preferably, the interface between the gas target and the beam line 10 is a sealing flange 1, which is preferably a CF35 flange and an O-ring seal. The inlet window 2-1 is tightly fitted to the flange of the sealing flange 1. The connection between the gas source valve and the vacuum gauge 8 and the target chamber meets the relevant requirements for the target chamber leakage rate, and the remaining gaps are seamlessly welded.

[0022] Preferably, to ensure collimated output of the accelerator beam, an annular focusing magnet 12 can be installed around the accelerator tube 9 at the accelerator outlet. To further improve the accuracy of beam bombardment, an aperture 11 can also be installed inside the beam tube 10 to achieve beam focusing and collimation.

[0023] Target chamber performance testing After the gas target is assembled, the airtightness of the target chamber is tested, and the monoenergetic neutrons produced by the gas target chamber are characterized. The airtightness of the target chamber is tested using a helium mass spectrometer leak detector. Monoenergetic neutron characterization is the final step in evaluating whether the gas target chamber meets the design requirements. This is mainly done by bombarding the gas target chamber with a deuterium beam or proton beam of a certain intensity (with constant current, energy, and energy broadening). The energy broadening of the produced neutrons is then measured using a neutron detection instrument at the back end, employing the Time-of-Flight (TOF) method or the accompanying particle method. If the energy broadening is less than 2%, the requirements are met.

[0024] Tested using a helium mass spectrometer leak detector, the gas chamber airtightness of the gas target of this invention reaches 10. -7 Pa·m 3 / s, meeting the target chamber leak rate requirements. The neutron energy broadening produced by the gas target of this invention was determined using the TOF method; the neutron energy E n With a beam intensity greater than 250 keV and an energy broadening of less than 2%, the gaseous target of this invention can produce monoenergetic neutrons with excellent monochromaticity. Furthermore, by measuring the neutron fluence over time using an absolute measurement device and a relative measurement method, the neutron fluence of the gaseous target of this invention changes by less than 5% over 8 hours when the beam intensity is stable. This indicates that the gaseous target of this invention can reduce the proportion of scattered neutrons and effectively increase the neutron yield.

[0025] All the equipment and testing instruments used in the specific embodiments of this invention can be purchased through commercial channels.

[0026] The specific embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A gaseous target for generating monoenergetic neutrons, characterized in that, The gaseous target includes a sealing flange, an inlet window, a stop window, and a vacuum system. The inlet window is made of Mo foil with a thickness of less than 10 μm, and the stop window is made of Au foil with a thickness of less than 150 μm. The inlet window includes a front window and a rear window, which are sequentially arranged on the target wall along the beam direction, dividing the gaseous target into two gas target chambers. Helium is filled into the gas target chamber formed by the front window, rear window, and target wall, and the gas pressure is maintained at 10. 2 The pressure is maintained at 1 to 1 standard atmosphere; the gas target chamber, consisting of the rear window, the stop window, and the target wall, is filled with deuterium or tritium gas, and the pressure is maintained at 1 to 1.3 standard atmospheres.

2. The gaseous target according to claim 1, characterized in that, A linkage gate valve is installed at the connection between the gaseous target and the accelerator pipeline. When the inlet window is damaged or gas escapes from the target chamber, the linkage gate valve closes to disconnect the gaseous target from the accelerator pipeline.

3. The gaseous target according to claim 1, characterized in that, The outer threaded seal of the blocking window is connected to a sleeve, and circulating cooling gas is passed through the sleeve to cool the target chamber.

4. The gaseous target according to claim 1, characterized in that, Each target chamber is connected to a vacuum gauge for monitoring the air pressure inside the target chamber.

5. The gaseous target according to claim 1, characterized in that, Each target chamber is connected to a vacuum system, which includes an oil-free dry pump foreboard pump and a molecular pump.

6. The gaseous target according to claim 1, characterized in that, The interface between the gas target and the beam pipeline is a sealing flange, with the front window tightly fitted to the flange plate of the sealing flange, resulting in a target chamber leakage rate of 10%. -7 Pa·m 3 / s.

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