PARMA: PHITS-based Analytical RadiationModel in the Atmosphere – Verification of ItsAccuracy in Estimating Cosmic Radiation Doses

摘要

Estimation of cosmic-ray spectra in the atmosphere has been an essential issue in theevaluation of the aircrew doses. We therefore developed an analytical model that can predict theterrestrial neutron, proton, He nucleus, muon, electron, positron and photon spectra at altitudesbelow 20 km, based on the Monte Carlo simulation results of cosmic-ray propagation in theatmosphere performed by the PHITS code. The model was designated PARMA. In order toexamine the accuracy of PARMA in terms of the neutron dose estimation, we measured theneutron dose rates at the altitudes between 20 to 10400 m, using our developed dose monitorDARWIN mounted on an aircraft. Excellent agreement was observed between the measured doserates and the corresponding data calculated by PARMA coupled with the fluence-to-doseconversion coefficients, indicating the applicability of the model to be utilized in the route-dosecalculation.