This project will construct a comprehensive theoretical model of the Earth's inner radiation belt protons and light ions. The model will be based on an existing simplified proton model. It will describe the inner zone's full spatial dependence, energy dependence, and solar cycle time dependence. Components of the model will include: Monte Carlo simulation of the albedo neutron decay source; injection of solar protons and helium; secondary sources of light ions from nuclear reactions of trapped protons with the neutral atmosphere; energy loss to ionization of the neutral atmosphere, and to free electrons in the ionosphere and plasmasphere, with solar cycle dependence from the historical solar activity record; particle acceleration by adiabatic compression based on multipole geomagnetic field models from the archeomagnetic record and the International Geomagnetic Reference Field; numerical trapped particle trajectory tracing to calculate drift averages of the neutron decay source and the atmospheric densities, and the rigidity trapping limits; nuclear scattering of the trapped particles from the neutral atmosphere, including elastic and inelastic processes; radial diffusion with empirically determined diffusion coefficients; and decay of radioactive trapped secondaries. The resulting model will be compared to existing radiation belt data and empirical models for validation.
The model will provide a framework for understanding the physical processes occurring in the inner zone of the radiation belt. The proposed quantitative study of the relative importance of each model component will lead to a new understanding of the dominant physical mechanisms. In particular, the lifetimes and significant loss mechanisms of the trapped particles will be determined, the relative significance of the external (radial diffusion) and internal (neutron decay and nuclear reaction) sources will be evaluated, and the nuclear reactions that are significant for populating the inner radiation belt will be identified. An accurate model the inner radiation belt will be of practical value for specifying the hazardous radiation environment in low Earth orbit. Current empirical models are used extensively in spacecraft design but are lacking in the detailed energy, spatial, and temporal variations that will be addressed in this work.
