Variations of the proton energy spectrum with position in the inner Van Allen Belt

Abstract

A cylindrical stack of nuclear emulsions was flown in the payload section of a research rocket into the northern edge of the inner part of the Van Allen radiation region on September 19, 1960. The emulsion stack was shielded inside a tungsten cassette and was then exposed to the ambient radiation by rotation behind a window in the wall of the cassette covered with a 0.04-g/cm2 aluminum shield. In this way it was possible to make a detailed study of the energy spectrum of the trapped particles at various positions in space. The rocket trajectory covered L values ranging from about 1.45 to 1.85RE. Five points along the trajectory were chosen for analysis, and the differential and integral proton energy spectrums were obtained for each point. Above 30 Mev in all cases, and below 30 Mev at the lower L values, the proton energy spectrums were in agreement with previous experiments.; however, there was a sharp change in the slope of the spectrums with a steeper slope (j(E) = KE−4.5 at the higher L (L>1.6R) values than had been expected on the basis of previous experiments and the galactic cosmic ray neutron albedo theory. The data for each of the points are presented, and the results are discussed. No particles of mass greater than the proton were observed in a particle composition study averaged over the trajectory. An upper limit is presented for heavier particles in the trapped radiation.