THE COSMIC - RAY 3 He / 4 He RATIO FROM 200 MeV PER NUCLEON ~ 1 TO 3 . 7 GeV PER NUCLEON
نویسنده
چکیده
The abundances of cosmic-ray helium isotopes between 0.2 and 3.7 GeV nucleon~1 were measured by the Isotope Matter Antimatter Experiment (IMAX) during a Ñight from Lynn Lake, Manitoba, Canada on 1992 July 16È17. The IMAX balloon-borne magnetic spectrometer realized a direct measurement of the charge, the velocity, and the rigidity of cosmic rays using plastic scintillators, a high-resolution timeof-Ñight system, and two silica-aerogel Cerenkov counters in conjunction with a drift chamber/multiwire proportional chamber tracking system. About 75,000 helium isotopes are identiÐed by their mass using the velocity versus magnetic rigidity technique. The measured 3He/4He ratios are corrected to the top of the atmosphere, and a comparison with previous data is given. The observed isotopic composition is found to be generally consistent with the predictions of a standard leaky box model of cosmic-ray transport in the Galaxy. Subject headings : acceleration of particles È balloons È cosmic rays È nuclear reactions, nucleosynthesis, abundances
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