Observation of space radiation environment with EXOS-D

Space radiation environmental data, mainly in the radiation belt, were obtained during the quiet condition of the magnetosphere from March 1989 to December 1991. The measured electron and proton energy spectra for the EXOS-D satellite were harder than predicted spectra from the NASA radiation belt models. The spatial distribution of alpha particle flux was obtained. Alpha particles in the radiation belt were very limited, but they are important for dose calculations. The new data will be very useful for estimating the dose for spacecraft and astronauts in the inner radiation belt. The observation period included some big geomagnetic storms, and the data are helpful for making clear the detailed behavior of charged particles in the radiation belt