BEXCO - Room F(201/202/203/204)
[SH064] Updated model CRAC:HEPII of atmospheric ionization due to high energy protons
An extension of the previous version of the CRAC model - CRAC:HEPII (Cosmic Ray Atmospheric Cascade: High Energy Proton Induced Ionization) is presented. The model allows one to compute the ion production by high energy protons entering the Earth's atmosphere. The model is an extension of the CRAC:CRII model and it is focused on the mesosphere and the upper part of the stratosphere, but is applicable also for the low thermosphere. The CRAC:HEPPI model is based on pre-computed ionization yield functions, computed with high precision using a full Monte Carlo simulation of primary proton propagation and interaction with the atmosphere by explicitly considering various physical processes involved in ion production. All simulations were performed using the GEANT 4 simulation tool PLANETOCOSMICS with NRLMSISE 00 atmospheric model. The ionization yield function allows one to compute the ion production rates due to various populations of primary protons in a wide energy range from 100 keV/nucleon to 20 GeV/nucleon for a given altitude, from about 6.5x10E-9 g/cm2 (about 200 km a.s.l.) to the sea level, and location, considering a given spectrum of primary protons. The spatial and height resolution of the model has been significantly improved compared to the previous version of the CRAC model. An application of the model for computation of the ion production rate during ground level enhancement (GLE) events is demonstrated. A quasi-analytical approach, which allows one to compute the ionization yields for oblique events and/or isotropic protons from ionization yields of protons with vertical incidence is also presented. It is compared with Monte Carlo simulations and good agreement between Monte Carlo simulations and quasi-analytical approach is achieved. With this extension the CRAC model is applicable to the entire atmosphere.