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Published 1975 | Published
Book Section - Chapter Open

The Isotopic Composition of Hydrogen and Helium in Low Energy Cosmic Rays


The Caltech Electron/Isotope Spectrometer on IMP-7 has been used to identify the isotopes ^2H and ^3He in low energy cosmic rays during solar quiet periods from October 1972 to October 1974. These observations cover the energy intervals 5 - 29 MeV/nuc for ^2H and 7 - 50 MeV/nuc for ^3He. The energy spectra of ^1H, ^2H and ^3He all fall rapidly with decreasing energy, giving ^2H/ ^1H and ^3He/ ^1H ratios essentially independent of energy as expected from adiabatic acceleration. The measured ^4He spectrum, however, was essentially flat over this energy interval, and therefore the ^2H/^4He ratio observed at 1 AU is not simply related to the interstellar abundances of these nuclei. However, comparisons of the ^2H/^1H and ^3He/^1H ratios with calculated spectra are possible.

Additional Information

This work was supported in part by NASA under contract NAS5-11066 and Grant NGR 05-002-160. G. J. Hurford made important contributions to a number of aspects of this work.

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August 19, 2023
October 26, 2023