Angular distribution and energy spectra of protons of energy 5 ≤E≤ 50 MeV at the lower edge of the radiation belt in equatorial latitudes

This is the authors' abstract. We don't add key points for this paper.

The population of protons having energy 5 ≤ Ep ≤ 50 MeV at the inner boundary of the radiation belt was investigated in near-equatorial latitudes by a particle telescope having large gathering power and, consequently, high statistical accuracy. The measurements were performed from March 10 until May 10, 1970, on board the second German research satellite Dial. A nearly complete coverage was obtained for the region 1.15 ≤ L ≤ 1.40 and 1 ≤ B/Bo ≤ 1.7. Particle fluxes are ordered as a function of B/Bo, L being fixed. For B/Bo values corresponding to mirror point heights above 300 ± 50 km the fluxes follow a (B/Bo)−n/2 law which can be converted to equatorial pitch angle distributions J⊥ sinn θ via Liouville's theorem. For 1.15 ≤ L ≤ 1.25 the exponent n increases steeply with decreasing L and the shape of the energy spectrum J⊥ remains essentially constant. At this lower edge of the radiation belt the proton population in the above energy range is determined from an equilibrium between the cosmic ray albedo neutron decay source and atmospheric loss processes. For larger L, radial diffusion sets in and leads to a distortion of the spectrum, with a shift of the intensity maximum toward lower energies with increasing L. The observed spectra are in satisfactory agreement with solutions of the transport equation (Claflin and White, 1974) based on one- and two-term diffusion coefficients.