Proton intensities and energy spectrums in the inner Van Allen belt

Abstract

Proton intensities and energy spectrums in the inner Van Allen belt have been measured with shielded plastic scintillators on three satellites and an Atlas pod. Omnidirectional fluxes of protons above 59, 95, and 148 Mev are given at the equator for L values of 1.25 and 1.48-1.60, and isofiux contours are given in B, L space for protons above 59 Mev. The counting rates of three scintillation counters having threshold energies of 46, 76, and 128 Mev have been analyzed in terms of assumed energy spectrums of the form d•/dE --AE -'• and d•/dE --Ae -•/•o. The second form produces a dependence on the geomagnetic parameter L given by E0 --460L -4-8 Mev. For the theoretical spectral shapes of Lenchek and Singer, cutoff energies have been derived from the ratios of counting rates in the three detectors. The results are in moderately good agreement with the calculations of Singer (in which, because of nonadiabatic effects, the cutoff momentum was found to be of the form Pmax •-PoL-•), with a best fit value P0 --2000 Mev/c. Introduction. Since the experimental verification by Freden and White [1959] of the existence of protons in the inner Van Allen belt, considerable theoretical and experimental effort has been devoted to understanding the spacial and energy variations of the proton flux. Theoretical calculations have been devoted to both injection mechanisms [Singer, 1958, 1960; Hess, 1959; Kellogg, 1959; Vernov et al., 1959; Ray, 1960] and various loss mechanisms, involving both quiescent nonadiabatic effects [Singer, 1959] and the possible existence of hydromagnetic waves [Dragt, 1961; Wentzel, 1961]. Proton energy spectrums have been measured with emulsions by Freden and White [1959], Armstrong et al. [1961], Heckman and Armstrong [1962], and Naugle and Kniffen [1961]. These experiments provide excellent measurements of energy spectrums, but with one exception [Naugle and Kniffen, 1961] they do not provide information on variations of the spectrum with position in space. Spacial variations of the proton flux have been obtained with counters placed on various satellites, but most of these measurements have not been accompanied by the detailed spectral measurements necessary for a complete understanding of the phenomena involved. With two Geiger counters aboard the satellite Explorer 4, Mcoe1wain and Pizzella [1963] have studied variations of the energy spectrum with position in space for protons in the range of 30 to 40 Mev. A wide range of energy spectrums have

The behavior of trapped electrons and protons at the lower edge of the inner radiation belt

“…The agreement leads us to attribute the measured distributions below L ----1.14 to protons, and to consider the overload channel as an essentially omnidirectional high-energy proton counter with an effective threshold of about 70 Mev and a geometric factor of 13.5 cm •. The resulting proton fluxes above 70 Mev, deduced from thee overload measurements below L = 1.17, are consistent with an extrapolation of the proton fluxes in the interval 40-110 Mev reported by Valerio [1964] from Injun 3, when corrected for the energy difference using avail- Smith, 1964]. Based on the above agreement of both the pulse-height distribution and the absolute rate in the overload channel with that expected for protons, we have subtracted a proton contribution from the electron data presented here, assuming an intensity given by the overload rate and the distribution given in Figure 1.…”