Estimation of cosmic-ray neutron spectra in the atmosphere has been an essential issue in the evaluation of the aircrew doses and the soft-error rates of semiconductor devices. We therefore performed Monte Carlo simulations for estimating neutron spectra, using the PHITS code coupled with the nuclear data library JENDL-High-Energy (JENDL/HE) file or the intra-nuclear cascade (INC) model for simulating high-energy neutron and proton induced nuclear reactions. The calculated spectra based on JENDL/HE agree with measured data very much for a wide altitude range even at ground level. On the other hand, the calculation adopting INC generally overestimates the measured data, especially at lower altitudes. These tendencies indicate that JENDL/HE can play an important role not only in the cosmic-ray transport simulation, but also in the deep-penetration simulation for the shielding design of high-energy accelerator facilities, since the two simulations have a lot of similarities with respect to the source terms, shielding properties and so on. The incorporation of the pion-production channels into JENDL/HE will be very helpful in the future study of radiation protection dosimetry.
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