We have now analyzed 17 yr of Voyager 1 and Voyager 2 data and derived isotopic composition ratios for C, N, and 0 elements in cosmic rays with a statistical accuracy exceeding that of the sum of all previously published spacecraft measurements. We have also used newly measured cross sections in the propagation calculations to derive the source composition of these elements. We find (1) the source ¹³C/¹²C ratio is 2.5 σ lower than the solar ratio of 1.1%. (2) For N we find the source ¹⁴N/¹⁶O ratio to be 5.0% and the source ¹⁵N/¹⁶O ratio to be 0.97% about 1 σ larger than the ratio of 0.37% expected for a solar composition. (3) The source ¹⁸O/¹⁶O ratio is determined to be 0.24±0.17% including both measurement and propagation errors, almost exactly the solar ratio of 0.23%. The implications of these results for cosmic-ray origin theories are discussed.
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Webber et al. (1996) studied this question.