RECENT OBSERVATIONS OF SPACE RADIATION ENVIRONMENT IN A HUMAN PHANTOM ONBOARD ISS BY LIULIN-5 PARTICLE TELESCOPE

摘要

The radiation field onboard the International Space Station (ISS) is complex, composed of galactic cosmic rays, trapped radiation of the Earth radiation belts, solar energetic particles, albedo particles from Earth's atmosphere and the secondary radiation produced in the shielding materials of the spacecraft and in human body. An essential parameter for assessment of radiation hazards to human in space is the organ dose determination. Human phantoms equipped with active and passive radiation detectors are used to obtain a better knowledge of the dose distribution inside the human body. The Liulin-5 charged particle telescope has directly observed the radiation environment in the tissue-equivalent phantom of MATROSHKA-R international project on ISS during the period June 2007-June 2010. The objectives of Liulin-5 experiment are studying the dynamics of depth-dose distribution of the different components of the orbital radiation field inside the phantom and mapping the radiation environment and its variations with time and orbital parameters (such as solar cycle, solar flare events, inclination and altitude). The particle telescope Liulin-5 measures time-resolved linear energy transfer spectrum, flux and absorbed dose rates for electrons, protons and the biologically relevant heavy ion components of the cosmic radiation. In this report we present new results of Liulin-5 experiment for radiation quantities obtained from different components of the complex radiation field in low-Earth orbit. Measurements show that due to the self-shielding of the phantom from trapped protons the absorbed doses close to the centre of the phantom decrease by a factor of 1.6- 1.8 compared to the doses at depths corresponding to the depth of blood forming organs in human body. It is shown that the shielding provided from Shuttle and connected with Shuttle docking change of ISS attitude leads to a decrease of daily absorbed doses from trapped protons. During the minimum of the solar activity in cycle 23 the average dose equivalent at 40 mm depth is 590+32 μSV/day and the galactic cosmic rays (GCR) contribute at least 70% of total dose equivalent at that depth. The comparison with results obtained from TLD detectors in the spherical phantom during 2007-2008 show good agreement.