PARMA: PHITS-based Analytical Radiation Model in the Atmosphere—Verification of Its Accuracy in Estimating Cosmic Radiation Doses

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