High-energy proton radiation belt

The experiments and theories to explain the high‐energy protons trapped in the earth's radiation belt are reviewed. The theory of cosmic ray albedo neutron decay injection of protons into the radiation belt is discussed. Radial diffusion and change in the earth's dipole moment are considered along with losses of protons by ionization and nuclear collision. It is found that the measured albedo neutron escape current is sufficient to supply trapped protons above 30 Mev. The theoretical calculations of the trapped protons are in agreement with the measurements for L ≤ 1.7 both on and off the equator. Although it appears that diffusion of solar wind protons is responsible for most of the protons less than 30 Mev, additional measurements of the angular distributions and fluxes of low‐energy neutrons are required to determine the contribution of the cosmic ray albedo neutron decay source. For L ≥ 1.7, additional trapped proton differential energy measurements should be made before the theory can be adequately tested. It appears that an additional loss mechanism such as pitch angle scattering may be required.