The time dependence of the low-energy proton belts

Abstract

The time dependences of the low-energy proton space distributions and differential energy distributions at 8 energies 0.17–3.4 Mev are presented for the period of August 15, 1964, to February 8, 1965. The data were obtained from the directional proton spectrometer on the satellite 1964-45A, which was launched on August 14, 1964, into a near polar orbit with a 3765-km apogee and a 270-km perigee. The proton flux decay constant can be expressed as (1/τ) (day)−1 = (−0.0007 ± 0.0007) + (0.0033 ± 0.0009) Ine E (Mev). Protons of 0.2 Mev decreased with an apparent lifetime of 150 days, those of 1 Mev were constant, and protons of 2.5 Mev increased with an apparent lifetime of 500 days. The maximum peak heights of the energy distributions decreased by less than a factor of 2, and the energy spectra hardened slightly with time. The positions of the maxima remained almost constant. Therefore, the low-energy proton radiation belts were rather stable from August 15, 1964, to February 8, 1965.