Injection of protons into the radiation belt by solar neutron decay

The coefficient χ for injecting protons into the earth’s radiation belt by solar neutron decay (SND) is calculated as a function of the magnetic shell number L and the pitch angle α. The χ is found by a Monte Carlo-like method for a variety of tilt angles from 0° to 35°. The tilt angle is the angle between the earth's magnetic field and the earth-sun line. A weighting factor proportional to the fraction of the time that the neutrons are incident at each tilt angle is used to compute a time-averaged injection coefficient. A solar neutron spectrum and a mean atmospheric density, both averaged over the solar cycle, are used to find the contribution of solar neutrons to the equilibrium high-energy proton flux. This equilibrium SND injection proton flux is compared with that from cosmic-ray albedo neutron decay (CRAND) injection and with experiment. In addition, the relative proton injection rates for SND and CRAND are compared on the magnetic equator as a function of both L and energy. We find that SND dominates over CRAND injection at higher L values and higher energies.