Studies of the radiation environment on the Mars surface using the Geant4 toolkit
Junliang Chen, Sujun Yun, Tiekuang Dong, Zhongzhou Ren, Xiaoping Zhang
Abstract
Abstract The radiation environment on the surface of Mars is a potential threat for future manned exploration missions to this planet. In this study, a simple geometrical model was built for simulating the radiation environment on the Mars surface caused by galactic cosmic rays; the model was built and studied using the Geant4 toolkit. The simulation results were compared with the data reported by a radiation assessment detector (RAD). The simulated spectra of neutrons, photons, protons, $$\alpha$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> particles, and particle groups $$Z=3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Z</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:math> –5, $$Z=6$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Z</mml:mi> <mml:mo>=</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:math> –8, $$Z=9$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Z</mml:mi> <mml:mo>=</mml:mo> <mml:mn>9</mml:mn> </mml:mrow> </mml:math> –13, and $$Z=14$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Z</mml:mi> <mml:mo>=</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:math> –24 were in a reasonable agreement with the RAD data. However, for deuterons, tritons, and $$\,^{3}{\mathrm{He}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mspace/> <mml:mn>3</mml:mn> </mml:msup> <mml:mi>He</mml:mi> </mml:mrow> </mml:math> , the simulations yielded much smaller values than for the corresponding RAD data. In addition, the particles’ spectra within the $$90^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>90</mml:mn> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> zenith angle were also obtained. Based on these spectra, we calculated the radiation dose that would have been received by an average human body on Mars. The distribution of the dose throughout the human body was not uniform. The absorbed and equivalent doses for the brain were the highest among all of the organs, reaching 62.0 ± 1.7 mGy/y and 234.1 ± 8.0 mSv/y, respectively. The average absorbed and equivalent doses for the entire body were approximately 44 mGy/y and 153 mSv/y, respectively. Further analysis revealed that most of the radiation dose was owing to $$\alpha$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> particles, protons, and heavy ions. We then studied the shielding effect of the Mars soil with respect to the radiation. The body dose decreased significantly with increasing soil depth. At the depth of 1.5 m, the effective dose for the entire body was 17.9 ± 2.4 mSv/y, lower than the dose limit for occupational exposure. At the depth of 3 m, the effective dose to the body was 2.7 ± 1.0 mSv/y, still higher than the accepted dose limit.