Reference Radiation for Cosmic Rays in RBE Research
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When astronauts travel in space, they are exposed to high energy cosmic radiations. The cosmic ray spectrum contains very high energy particles, generally up to several GeV per nucleon. Currently NASA is funding research on the effects, such as acute radiation sickness, of cosmic radiation. Animal models are used to conduct the studies of radiation effects of particles in the range of several MeV/nucleon to about 1000 MeV/nucleon. In order to compare different radiations, the biological effectiveness relative to a specific radiation is usually used. For low energy heavy ions and neutrons 250 keV photons are usually used for the reference radiation but their depth dose distribution is very different from that for cosmic rays. In this research, the advantages of using high energy electrons as the reference radiation for research on cosmic radiation were demonstrated. The conclusion is based on the evaluation of the dose distributions and microdosimetric spectra of the electrons and high energy protons as a function of depth in a tissue equivalent absorber as determined by Geant4 simulation.