Results are reported for cosmic-ray positrons obtained in a balloon flight of the University of Chicago electron telescope in Hawaii in April 1984. Making use of the east-west asymmetry in the geomagnetic cutoff rigidity, cosmic-ray positrons and negatrons were separated over the range 10-20 GeV. The resulting positron to electron ratio is 12-22 percent, significantly higher than the ratio measured in the 1-10 Gev range by other experiments. This increase appears to suggest that either a primary component of positrons becomes significant above 10 GeV or that the spectrum of primary negatrons decreases above 10 GeV more sharply than that of secondary positrons.
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Mueller et al. (1987) studied this question.