Charge Composition and Energy Spectrum of Primary Cosmic-Ray Electrons

The flux, energy spectrum, and charge composition of the electron component of primary cosmic rays was measured in 1965 and 1966 in the range from 170 MeV to 14.3 BeV, and a finite flux of positrons was observed up to 4 BeV. The positron fraction N+/(N+ + Nj is shown to decrease as a function of energy. For the first time, it has been possible to determine the energy spectrum of primary positrons above 220 MeV. To approximate this observed spectrum above 860 MeV by a power law requires an exponent of 2.6 ± 0.5, consistent with negligible modification of the source spectrum below 10 BeV by energy4oss processes. Comparison of the differential energy spectrum of positrons with calculations based on a collision origin leads to a reasonable agreement for a disk model with passage of cosmic rays through 3-4 g cm2 of interstellar material and modulation parameters ~ = 0.6 BY and R0 = 0.3 BV