Simulations of the MTR-R and MTR experiments at ISS, and shielding properties using PHITS

Concerns about the biological effects of space radiation are increasing rapidly due to the perspective of long-duration manned missions, both in relation to the International Space Station (ISS) and to manned interplanetary missions to the Moon and Mars in the future. As a preparation for these long duration space missions it is important to ensure an excellent capability to evaluate the impact of space radiation on human health in order to secure the safety of the astronauts/cosmonauts and minimize their risks. It is therefore necessary to measure the radiation load on the personnel both inside and outside the space vehicles and certify that organ and tissue equivalent doses can be simulated as accurate as possible. In this paper we will present preliminary results from simulations, using the three-dimensional Monte Carlo Particle and Heavy Ions Transport code System (PHITS), of long term dose distribution measurements performed with the joint ESA-FSA experiment MATROSHKA-R (MTR-R) led by the Russian Federation Institute of Biomedical Problems (IMBP). MTR-R is a spherical phantom located inside the crew cabin of ISS. We also show some results from PHITS simulations of the ESA supported experiment MATROSHKA (MTR), which consists of an anthropomorphic phantom containing over 6000 radiation detectors, mimicking a human head and torso. The MTR experiment, led by the German Aerospace Center (DLR), was launched in January 2004 and has measured the absorbed dose from space radiation both inside and outside the ISS. In this paper preliminary comparisons of measurements outside the ISS will be presented. For the purpose of examining the applicability of PHITS to the shielding design, the absorbed doses and dose equivalents in a cylindrical phantom with tissue equivalent material inside an imaginary space vessel on a geostationary orbit at solar minimum has also been estimated for different shielding materials of different thicknesses. All the results indicate that PHITS is a suitable tool when estimating radiation risks for humans on manned space missions and when performing shielding design studies of spacecraft.