Presentation Contribution of proton- and helium-induced secondary target fragments to space radiation dose

小平, 聡

Exposure from high energy protons and helium nuclei, the main components of the space radiation environment, dominate the radiation risk for astronauts in space. While the linear energy transfer (LET) of these light particles is lower than that of heavy ions such as carbon and iron nuclei, their flux is extremely high in space radiation in low Earth orbit, mixing of galactic cosmic rays (GCRs) and trapped particles (TPs). Space radiation data obtained with CR-39 plastic nuclear track detectors (PNTD) indicates the relatively large contribution of proton and helium induced secondary target fragments to total dose. One of the few methods available to measure these particles is by means of CR-39 PNTD analyzed with an atomic force microscope (AFM). CR-39 (BARYOTRAK) PNTDs were irradiated with energetic 160 MeV proton and 150 MeV/n helium beams at HIMAC in order to determine their dose contribution. Following chemical processing of about 1µm bulk etch and analyzing sub-microscopic tracks with AFM, the LET spectra and dosimetric data due to secondary target fragments were measured for primary protons and helium beam irradiations, respectively. Based on this ground based data, we have estimated the dose contribution in space radiation by using experimental data measured with CR-39 PNTD irradiated to space radiation on the ISS. We found that the LET spectra measured with CR-39 PNTD, which include secondary target fragments in addition to primary heavy GCRs, contribute up to 12% of the absorbed dose and 16% of the dose equivalent, respectively, for LET particles of 10 keV/um.
5th International Symposium on Space Radiation and Particle Therapy

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