The authors measure the energy spectra of high energy trapped protons utilizing nuclear emulsions exposed on low altitude polar orbiting satellites. The spectra are compared with those obtained by Heckman and Nakano (1969) at solar minimum and the effects of solar cycle atmospheric density changes are evaluated. (Author).

The authors measure the energy spectra of high energy trapped protons utilizing nuclear emulsions exposed on low altitude polar orbiting satellites. The spectra are compared with those obtained by Heckman and Nakano (1969) at solar minimum and the effects of solar cycle atmospheric density changes are evaluated. (Author)

The time dependence of the low energy proton space distributions and differential energy distributions at 8 energies from 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/tau 1/(DAY) = ( -.0007 + or - 0007) + (.0033 + or - 0009) 1n sub e 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. PHE 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. (Author).