Probability of hippocampus cell hits by high-LET space radiation in a low-Earth-orbit mission (STS-91)

High-LET particles (HLP) of space radiation in the brain were measured with plastic nuclear track detectors (PNTD) using a life-size human phantom in the 9th Shuttle-Mir Mission (STS-91). Relationship between PNTD track-formation sensitivity (S) and LET infinity H2O was examined using heavy-ion beams at NIRS-HIMAC. Average fluence of the HLP (HLP10) with LET infinity H2O greater than 10 keV micrometers-1 was evaluated as 1.3 x 10(4) n cm-2 for the 9.8-day low-Earth-orbit mission (400 km x 51.65 degrees). Based on a simple extrapolation of these data, probability of HLP10 hits to hippocampus cells and cell-nuclei were estimated to be 45% and 7.0%, respectively, in a 90-day ISS mission. For 1 year, 91% of cells and 25% of cell-nuclei will be hit by HLP10.