Modelling He and H Isotopes in the Radiation Belts

Nuclear interactions between inner zone protons and atoms in the upper atmosphere produce energetic H and He nuclei that are an additional radiation belt source. We calculate production rates of these isotopes from models of the inner zone proton intensity, the upper atmosphere drift averaged composition and densities, and cross-sections for the various interaction processes. For comparison with observations of radiation belt H and He isotopes, the production rates are combined with a model of the energy loss rate in the residual atmosphere to calculate particle intensities. Although the calculations are in principle straightforward, they depend on a detailed knowledge of the various model inputs, including models for radiation belt protons, and may also depend on the phase of the solar cycle. On the other hand, the results of the calculations, when compared with the observational data, can provide useful tests of the model inputs. Preliminary results show that the atmosphere is a significant source for inner zone ^4He, ^3He, and d.