Experiment for radiation dose measurements in a human phantom onboard the ISS for estimation of the radiation risk in long duration space flights

Radiation exposure of crewmembers on manned space flight has been recognised as an important factor in the planning and design of such missions. Indeed, the effects of ionising radiation on crew health, performance and life expectancy are a limitation to the duration of man's sojourn in space. Predicting the effects of radiation on humans during a long-term space mission requires: i) accurate knowledge and modeling of the space radiation environment; ii) calculation of primary and secondary particle transport through shielding materials and though the human body; and iii) assessment of the biological effect of cosmic particles, especially highly energetic particles in the heavy ion component (HZE particles). The International Space Station (ISS) internal radiation environment is complex, with incident external space radiation field modulated by widely varying amounts of shielding and internal material, including the astronaut's bodies. For the estimation of the organ doses, and thus the radiation risk, measurements in human phantoms are essential. In the present paper the dosimetric telescope Liulin-5 developed for investigation of the radiation environment dynamics within the Russian spherical tissue-equivalent phantom on ISS is presented. Described are the measurement method, the functional requirements to the instrumentation and the technical specifications. Liulin-5 experiment is an adherent part of the international project MATROSHKA-R on ISS. The MATROSHKA-R project, launched in 2004, is aimed to study the radiation doses distribution at the sites of critical organs of the human body, using models of human body anthropomorphic and spherical tissue-equivalent phantoms. The aim of Liulin-5 experiment is long term investigation of the depth-dose distribution inside the spherical tissue-equivalent phantom, mounted in different places of the Russian Segment of ISS. Energy deposition spectra, linear energy transfer (LET) spectra, flux and absorbed dose rates for protons and the biologically-relevant heavy ion components of the cosmic radiation will be measured simultaneously with near real time resolution at different depths of the phantom's radial channel. Dose equivalent rates at these depths will be calculated from the absorbed dose rates multiplied by quality factor Q(LET). The doses in intermediate points will be determined by interpolation. Data obtained together with data from other active and passive dosimeters will be used to estimate the radiation risk to the crewmembers, verify the models of radiation environment, validate body transport model and correlate organ level dose to skin dose. Liulin-5 is planned to be flown on the ISS in 2006 year. Modifications of the Liulin-5 instrument for radiation monitoring outside the phantom are under development. Discussed are the possibilities analogues of these techniques to be used for investigation of the radiation hazards during future exploratory unmanned interplanetary missions, as well as a part of the radiation safety system for manned deep space missions.