GCR Neon Isotopic Abundances: Comparison with Wolf-Rayet Star Models and Meteoritic Abundances

Abstract

Measurements of the neon isotopic abundances from the ACE-CRIS experiment are presented. These abundances have been obtained in seven energy intervals over the energy range of ~80≤E≤280 MeV/nucleon. The ^(22)Ne/^(20)Ne source ratio is derived using the measured ^(21)Ne/^(20)Ne abundance as a "tracer" of secondary production of the neon isotopes. We find that the ^(22)Ne/^(20)Ne abundance ratio at the cosmic-ray source is a factor of 5.0±0.2 greater than in the solar wind. The GCR ^(22)Ne/^(20)Ne ratio is also shown to be considerably larger than that found in anomalous cosmic rays, solar energetic particles, most meteoritic samples of matter, and interplanetary dust particles. Recent two-component Wolf-Rayet models provide predictions for the ^(22)Ne/^(20)Ne ratio and other isotope ratios. Comparison of the CRIS neon, iron, and nickel isotopic source abundance ratios with predictions indicate possible enhanced abundances of some neutron-rich nuclides that are expected to accompany the ^(22)Ne excess.

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