On the anomalous component of low-energy geomagnetically trapped protons

Abstract

The energy spectrum of trapped protons shows a pronounced variation with latitude at energies <30 Mev. An anomalous, low-energy component is found on relatively high magnetic shells in the inner zone. The interpretation in terms of the decay of albedo neutrons generated in the polar caps by solar cosmic rays is examined. This interpretation requires that the inner shells, where a normal spectrum is seen, should be shielded from the polar source. The intensity of albedo neutrons as a function of energy, latitude, and zenith angle is computed. The injection rate into specific trapped orbits is then evaluated, and it is shown that those orbits where no anomalous component exists cannot be populated by the solar cosmic-ray mechanism, whereas the orbits where the anomalous component is seen can be populated. Assuming adiabatic trapping in this low-energy region, lifetimes are long compared with the average intervals between large injection events. Therefore, the anomalous component may represent an equilibrium phenomenon rather than a transient. This component should extend into the outer belt.