Charged particles in the inner Van Allen radiation belt

Abstract

A nuclear emulsion stack was flown through the lower part of the inner Van Allen radiation belt a few days after the intense solar flares of July 10–16, 1959. The stack ‘looked out’ through a thin window on the mounting plate at the rear of the nose cone. Protons with incident energies down to 42 Mev were recorded. The total proton flux is about ⅓ that reported by Freden and White; the difference may be due to the lower peak altitude of the flight reported here. Above 100 Mev the proton spectrum is consistent with the neutron albedo hypothesis. Below 100 Mev, however, there is evidence of structure, with a peak or plateau in the region of 80 Mev. This structure may be due to solar protons.

Low-altitude trapped protons during Solar Minimum Period, 1962-1966

“…The spectral shape we have measured is in good agreement with those measured in 1959-1960[Freden and White, 1959, 1960Armstrong, Harrison,Heckman, and Rosen, 1961;and Heckman and Armstrong, 1962], irrespective of the fact that these latter experiments were carried out near solar maximum (F::::: 200) at altitudes 460 < h .…”

Solar cycle changes in inner-zone protons

“…Freden and White [1959] identified the penetrating component of the inner zone of the Van Allen belt as due to energetic protons and measured the energy spectrum of the protons of E • 75 Mev. Subsequent experimental work on Atlas rockets [Freden and White, 1960;Freden and White, 1962;Armstrong et al, 1961] has confirmed and extended this finding, and we now have a well-established proton energy spectrum at L •, 1.4, B •, 0.20, which is about apogee for these flights, for near solar maximum (Figure 1). The analysis of this spectrum [Freden and White, 1960] has shown conclusively that the protons are produced by neutron decay.…”

Terrestrial and solar neutrons

“…Neutrons produce radioactive isotopes, such as carbon 14 and tritium, by their capture in the atmosphere. In addition, the earth's neutron albedo is a source of geomagnetically trapped protons and electrons of can adequately explain the anomalously large flux of low-energy trapped protons which is observed at L •> 1.5 [Armstrong et al, 1961;Naugle and Kniy7en, 1961]. [1964] may be due to the Starfish explosion.)…”