Organ Dose Equivalents of Albedo Protons and Neutrons Under Exposure to Large Solar Particle Events during Lunar Human Landing Missions

TL;DR

This study evaluates organ dose equivalents from albedo protons and neutrons during large solar particle events on the Moon, revealing significant contributions depending on shielding and particle energy.

Contribution

It provides the first detailed assessment of organ dose equivalents from albedo particles during large SPEs using realistic human phantoms and advanced Monte Carlo simulations.

Findings

Albedo contribution to organ dose is less than 3% with 1 g/cm2 shielding.

Contributions exceed 20% in some organs with 20 g/cm2 shielding.

Results depend on shielding thickness and particle energy spectra.

Abstract

Astronauts participating in lunar landing missions will encounter exposure to albedo particles emitted from the lunar surface as well as primary high-energy particles in the spectra of galactic cosmic rays (GCRs) and solar particle events (SPEs). While existing studies have examined particle energy spectra and absorbed doses in limited radiation exposure scenarios on and near the Moon, comprehensive research encompassing various shielding amounts and large SPEs on the lunar surface remains lacking. Additionally, detailed organ dose equivalents of albedo particles in a human model on the lunar surface have yet to be investigated. This work assesses the organ dose equivalents of albedo neutrons and protons during historically large SPEs in August 1972 and September 1989 utilizing realistic computational anthropomorphic human phantom for the first time. Dosimetric quantities within human organs have been evaluated based on the PHITS Monte Carlo simulation results and quality factors of the state-of-the-art NASA Space Cancer Risk (NSCR) model, as well as ICRP publications. The results with the NSCR model indicate that the albedo contribution to organ dose equivalent is less than 3% for 1 g/cm2 aluminum shielding, while it increases to more than 20% in some organs for 20 g/cm2 aluminum shielding during exposure to low-energy-proton-rich SPEs.