Enhanced GEANT4 Monte Carlo simulations of the space radiation effects on the international space Station and Apollo missions using high performance computing environment

A significant challenge to current and any future manned and/or unmanned space missions comes from the space radiation environment. An improvement in achieving more realistic (more accurate) models in predicting the effects of radiation transport through spacecraft is required. Especially, to better predict dose to the astronauts, energy deposition within sensitive electronics, and analyse radiation shielding for long-term space missions. The International Space Station provides an invaluable resource for long-term measurements of the radiation environment in Low Earth Orbit (LEO); however, the only manned missions with dosimetry data available beyond LEO are the Apollo Missions. Thus the physiological effects and dosimetry for deep space missions are not well understood in planning extended missions. GEANT4, a Monte Carlo method, represents a powerful physics simulation tool to assess the effects of radiation transport through spacecraft. The newest version of GEANT4 supports multithreading and MPI allowing for much faster distributive processing of simulations using high performance computing environment. In this paper we introduce a new application of GEANT4 that greatly reduces its computational time using high performance computing to hours instead of weeks without any post simulation processing. We also introduce a new set of GEANT4 computational detectors besides the historically used International Commission of Radiation Units (ICRU) simulation spheres for calculating dose distribution including a thermoluminescent detector (TLD), tissue equivalent proportional counter (TEPC), and human phantom along with a series of new scorers to calculate dose equivalence based on the International Commission of Radiation Protection (ICRP) standards. This study presents Monte Carlo simulation of the dose deposition. The models based on GEANT4 are developed for the International Space Station and the Apollo missions showing to replicate well the experimental measurements. The greatest contributor to radiation dose for the Apollo missions was found to come from galactic cosmic rays. The Apollo 14 dose measurements were an order of magnitude higher compared to other Apollo missions. The GEANT4 model of the Apollo command module shows consistent doses from galactic cosmic rays and radiation belts for all missions with a small variation in dose distribution across the Apollo capsule. The GEANT4 model also provides the values of the dose deposition and equivalent dose for various organs within a human phantom in the International Space Station or Apollo command module. These models are developed for the first time using GEANT4 code.