Low-energy proton radiation belts

B-L flux plots and differential energy distributions for low-energy protons in nine energy intervals from. 0.17 to 3.4 Mev are presented. The data were obtained from a directional low-energy proton spectrometer on the satellite 1964-45A. The satellite was launched on August 14, 1964, into a near-polar orbit with a 3765-km apogee and 270-km perigee. The data presented here were taken during August 15–22, 1964. The results show that protons of different energies are concentrated on concentric L shells about the earth. The lowest energy protons of 0.19 Mev peak at L = 4.4, while the highest measured ones of 2.8 Mev peak at L = 2.40. For energies ≤ 0.75 Mev the quantity L3E for the proton maxima is constant to within 20%, indicating that the first adiabatic invariant is conserved. At higher energies, however, L3E increases. The fluxes at the maxima and at constant B are approximately constant up to 0.5 Mev (in to L = 3.0) but fall rapidly at higher energies and lower L values. The flux, j⊥, at B = 0.10 gauss has a maximum peak value of 4×106 protons/cm2-sec-ster-Mev for 0.48-Mev protons at L = 3.0. The differential energy distributions are soft at high L values. Quite narrow peaks in the energy distributions first appear at 0.26 Mev for L = 4.0. At L = 3.0 the peak moves to 0.42 Mev and remains at this energy until it is no longer measurable at L = 2.1. Here the fluxes are lower, but the spectra are harder. Beyond the peak the flux decreases as a power of the energy with the exponent varying from −4.1 at L = 4.0 to −2.0 at L = 2.1. The data give support to the theory that the protons' source is inward diffusion while conserving the magnetic moment but not the third adiabatic invariant. However, there are disagreements in detailed comparisons of the theory with the results, particularly for L < 3.0.