2000 年 35 巻 2 号 p. 177-185
The fluence of high-LET particles in space radiation was measured with plastic nuclear track detectors (PNTDs) in the brain of a life-size human phantom in the 9th Shuttle-Mir Mission (STS-91). The relationship between PNTD track-formation sensitivity (S) and LET∞·H2O was examined using heavy-ion beams at the NIRS-HIMAC and the incident-angle dependence of S was corrected using an empirical function. The particle fluence of space radiation with LET∞·H2O greater than 10keVμm-1 in the brain was evaluated as 1.3×104ncm-2 in a 9.8-day low-Earth-orbit mission at 400km×51.6°. Based on these data, the ratio (the number) of hits to hippocampus cells and cell-nuclei were calculated for long missions. As a result, it was estimated that 45% (2.2×107) cells and 7.0% (3.4×106) cell-nuclei will be hit by high-LET particles (LET∞·H2O>10keVμm-1) in a 90-day mission, and 91% (4.4×107) and 25% (1.2×107) of cell-nuclei will be hit in a 1-year mission.