Source and loss processes of protons of the inner radiation belt

Abstract

The adequacy of the known source and loss processes to populate the inner radiation belt with protons is examined by calculating the equilibrium trapped-proton distribution, which would result from decay of albedo neutrons, energy-loss collisions, and radial diffusion by changes in the third adiabatic invariant. The strength of the neutron source and the rates of atmospheric energy loss are obtained from available theoretical and experimental data, and the radial-diffusion coefficient is adjusted to give agreement between theory and experiment for equatorially trapped protons with first invariants between 200 and 3000 Mev gauss−1. Since there is strong evidence for additional loss mechanisms above L=1.8, this comparison is limited to L<1.7, and in the calculation all processes above that boundary are simulated by setting the fluxes at 1.7 equal to the experimental values. The flux intensities, energy spectrums, and radial distributions obtained by this theory are in good agreement with observations, and the radial-diffusion coefficient required is consistent with diffusion coefficients derived by a variety of other methods. It is concluded that these processes are adequate to explain the gross characteristics of protons of the inner radiation belt, although off-equatorial protons have not been considered and the solar-cycle variations have not been computed.