| With the advancement of science and technology,the plan for human landing on Mars has been put on the agenda of NASA,ESA and the development of space exploration in China.There are two main sources of radiation on the surface of Mars:high energetic solar particles(SEPs)and Galactic Cosmic Rays(GCRs)from the Milky Way.Among them,GCRs have high energy,strong penetrating ability.Its long-term distribution of flux is relatively stable.It’s difficult to protect space craft and astronauts from radiation from GCRs.Therefore,the conventional dose assessment and risk study of GCRs radiation in the space is an important prerequisite for the realization of interplanetary travel and interplanetary migration.Due to the thin atmosphere and weak magnetic field of Mars,the Martian soil with specific ingredients is considered to be the first GCRs radiation barrier after humans land on Mars.This article is based on the Monte Carlo method and uses the soil from the Path Finder landing point as the soil sample.Based on the interplanetary annual average GCRs spectrum(CREME96 model,Cosmic Ray Effects on Micro-Electronics Code)and Mars Climate Database data(MCD),using radiation and material interaction simulation tool GEANT4,consider QGSP BERT HP as physic list,this article simulated the microscopic process of energy deposition and generation of secondary particles in the surface soil of Mars by the main particles(protons,alpha particles,carbon ions,and oxygen ions)of GCRs between 1 × 102MeV and 1 × 106MeV.The total radiation dose of GCRs in the surface soil of Mars during the minimum period of solar activity,and the radiation dose produced by GCRs in different types and different energy ranges,along with the distribution of the surface depth of Mars are showed.The results are:1.Mars atmosphere can almost shield the surface from all protons with energy below 1.86× 10-2MeV and alpha particles with energy below 6.38 × 10-2MeV.The total dose of radiation produced by GCRs on the Martian soil increased rapidly monotonously from the ground surface and gradually decreased.Among them,the surface dose of the uppermost surface layer is 0.061 Gy/year;the peak value is 0.076 Gy/year,which is located 76cm below the surface of Mars;at 1000cm depth,the radiation dose is as low as 1.013 × 10-3Gy;The equivalent dose of GCRs on the surface of Mars is 0.73Sv,the biggest equivalent dose is 0.809Sv at 76 cm.At the depth of 716 cm,the equivalent dose is 0.05Sv,which equals to ICRP biggest regulation dose,and the equivalent dose is 1.04 × 10-2Sv at 1000cm,which is 21%of the biggest regulation.For the polar ice cap,equivalent dose on the surface is 0.95Sv,the biggest equivalent dose is 0.99Sv at 58cm.At the depth of 694cm and 1000cm,equivalent dose is 0.05Sv and 6.51 × 10-3Sv,latter is the 13%of the biggest regulation dose。2.Analysis of the contribution of radiation dose from GCRs in different energy ranges showed that the radiation dose contributed by the GCRs from the 1 × 103 MeV～1× 105 MeV energy segment reached 85.52%of the total dose;the particle doses of GCRs in lower and higher energy segments contributions accounted for 7.20%and 9.19%,respectively.3.The contributions of protons and helium nuclei to the total radiative dose of GCRs were:91.8%and 7.8%,respectively.The respective peaks on the 3D images are located at 1.86 × 102 MeV and 6.38 × 102 MeV positions,which are 1.24× 10-4Gy/year and 5.90 × 10-5Gy/year.In the 1.86 × 102MeV～1.90 ×10-3MeV energy range(0～92cm depth),the combination of the dose caused two particles resulted in that the dose of GCRs remained in the higher range.The above results can provide reference and basis for humans to carry out radiation risk assessment of surface and underground activities on Mars.Based on the work of this paper,we can further analyze the GCRs radiation dose deposition maps of Mars in different geographical locations and geological conditions;and use similar methods to evaluate the impact of SEP events caused by severe solar explosion on the Martian radiation environment. |
PDF Full Text Request