月壤中子辐射环境原位探测任务与载荷设计

Mission and Payload Design for In-situ Detection of Lunar Regolith Neutron Radiation Environment

由于月球没有大气层和全球性的磁场保护,使得高能宇宙线直接与月壤物质的原子核发生散裂反应产生大量中子。月球中子既是载人登月和国际月球科研站辐射防护的主要对象之一,也可用于月球水资源勘查及月球起源、演化历史研究。迄今只有阿波罗17任务测量了月壤2米深度内的中子数密度,文章提出将中子探测载荷部署在月壤钻取后形成的钻井中的任务设想,相比阿波罗任务,月壤钻井中子探测在原位、近实时、多能区等方面具有创新性。基于氦-3正比计数管技术的月壤中子探测载荷重量0.9 kg、功率9 W,对月壤内部水的灵敏度可达500微克每克。月壤钻井中子载荷将极大的丰富月球探测任务的科学与工程产出。文章中的相关方案和技术还可应用于后续其他地外天体的深空探测任务。

Lunar neutron radiation originates from the spallation reactions between high-energy cosmic rays and the atomic nuclei of lunar regolith.Due to the absence of an atmosphere and a global magnetic field on the Moon,lunar neutrons represent a unique environmental element for lunar exploration activities.Compared to electrons and gamma,neutron radiation poses a more severe risk to human health,causing cellular apoptosis and chromosomal aberrations,with radiation weighting factors being 5-20 times higher than those of electrons and gamma.According to the Chang'e-4 mission,neutral particles contribute up to 23.5%of the total dose on the lunar surface.The intensity of epithermal neutron is directly related to the hydrogen content within the lunar regolith.Detecting epithermal neutrons provides a main method for the exploration of lunar water resources and the study of the origins and evolution of lunar water ice.Given the importance of lunar neutrons for manned lunar exploration,we propose a lunar borehole neutron detection payload mission.We intend to use high-detection-efficiency helium-3 proportional counter tubes to measure the vertical distribution of epithermal and thermal neutron fluxes within lunar boreholes.The payload includes three helium-3 proportional counter tubes,one cadmiumcoated tube,and one tin-coated tube connected in series,vertically placed in the borehole formed after lunar regolith drilling,and adjusted in depth by a stepper motor.Another cadmium-coated helium-3 tube is placed on the lunar surface to measure the intensity of epithermal neutron flux.To date,only the Apollo 17 mission has measured the neutron density within 2 meters depth of lunar regolith.The lunar borehole neutron detection payload can be widely deployed in boreholes formed after lunar soil drilling,and is expected to obtain neutron fluxes over a greater depth range.The lunar borehole neutron payload can obtain the vertical distribution of water content within lunar soil in situ,while neutron radiation measurements at different depths can provide important reference data for radiation protection at the International Lunar Research Stations.This paper will provide a detailed introduction to the scientific and engineering objectives,design schemes,and other aspects of the lunar borehole neutron payload.