Development of PARMA; PHITS-based Analytical Radiation Model in the Atmosphere

Sato, Tatsuhiko   ; Yasuda, Hiroshi*; Niita, Koji*; Endo, Akira   ; Sihver, L.*

Estimation of cosmic-ray spectra in the atmosphere has been an essential issue for the evaluation of aviation doses. We have therefore calculated these spectra by performing Monte Carlo simulation of cosmic-ray propagation in the atmosphere using the PHITS code. Based on a comprehensive analysis of the simulation results, we proposed an analytical model for estimating the cosmic-ray spectra of neutrons, protons, He nuclei, muons, electrons, positrons and photons applicable to any location in the atmosphere at altitudes below 20 km. Our model, named PARMA, enables us to calculate the cosmic radiation doses instantaneously with precision equivalent to that of the Monte Carlo simulation that requires much computational time. With these properties, PARMA is capable of improving the accuracy and efficiency of the cosmic-ray exposure dose estimations for not only aircrews but also for the public on the ground.