Directionality of the Martian Surface Radiation and Derivation of the Upward Albedo Radiation

Abstract

Health risks induced by exposure to space radiation have been classified as one of the potential "show stoppers" for future human missions to Mars (e.g.,

Radiation environment for future human exploration on the surface of Mars: the current understanding based on MSL/RAD dose measurements

“…The resulting $ 5% of reduction in dose rate is not significant enough to efficiently protect the future astronauts from cosmic radiation on Mars, but it is suggestive of an operational approach that would exploit features of the local terrain to shield habitats and other frequently occupied structures. This is the first direct illustration that an existing geological structure such as a simple butte may serve as a potential radiation shelter for future habitats on Mars (Ehresmann et al 2021;Guo et al 2021).…”

“…It is also important to note that the reduction of the dose seen by RAD at the butte is the difference between the shielded radiation from the sky direction and the secondary albedo radiation coming from the butte itself (Guo et al 2021). The resulting $ 5% of reduction in dose rate is not significant enough to efficiently protect the future astronauts from cosmic radiation on Mars, but it is suggestive of an operational approach that would exploit features of the local terrain to shield habitats and other frequently occupied structures.…”

“…The average normalized values during this window of the superposed time are shown in different horizontal lines for previous 4 solar rotational cycles and their average value is about 1.0. Adapted fromGuo et al (2021)…”

The Zenith‐Angle Dependence of the Downward Radiation Dose Rate on the Martian Surface: Modeling Versus MSL/RAD Measurement

“…For helium ions, this angle is smaller, about 45°. As described by Guo, Khaksarighiri, et al (2021), two factors play a role here: (a) the atmospheric column depth increases from about 21 g/cm 2 at θ = 0° to more than 400 g/cm 2 at the horizon; a thicker traverse path would result in primaries losing more energy and becoming more ionizing or more easily stopped before reaching the surface; moreover, more secondaries are generated along a thicker path and can contribute to the total dose; (b) the area of the source particles incident at each degree of zenith angle is different (distributed as rings on the spherical shell), and it increases with θ. These two concurrent reasons result in the directionality of the dose rate on the surface of Mars as shown in (a) and (b).…”

“…Second, secondary particles created in the Martian soil (so-called albedo particles which move upward, away from Mars) also in principle contribute to the measured LET-cone dose rate. Guo, Khaksarighiri, et al (2021) used the absorbed dose in the plastic detector "E" and estimated that the albedo radiation, measured as an absorbed dose by RAD, on flat terrain is about 19% of the total surface dose. Although these albedo particles need energy higher than about 110 MeV/nuc to reach the B detector, and the low-energy albedo particles traveling upward from the surface are likely to deposit energy in E and stop in the detector stack before reaching B.…”