Geomagnetically Trapped Alpha Particles. Low-Altitude Outer-Zone Alpha-Proton Comparisons.

The outer-zone population of trapped alpha particles and protons was measured off the equator BBo 1.3-2.3 in the L interval 2 or L or 4 during 1969. The alpha-particle spectra are best represented by a power law with spectral indices between 2.4 and 4.0 over the energy range 0.85 or E sub alpha or 9.0 MeV. The alpha-particle and proton spectra have the same slope at the same total energy. The distribution functions for alpha particles and protons have similar shapes and they suggest that the location of the source of these particles is at L 4. The proton pitch-angle distribution at small pitch angles is flatter than near the equator. It is suggested that pitch-angle scattering may be the primary source of the low-altitude ions. The measurements are compared with recent theoretical predictions. Modified author abstract