Abstract
Measurements made by the Ulysses High Energy Telescope (HET) have made it possible for the first time to resolve the individual isotopes of sulfur 32S,33S, and 34S. The measured ratio of Galactic cosmic-ray 34S/32S in the heliosphere is 24.2% ± 2.7%. Based on this value, the Galactic source composition for 34S/32S has been found to be 6.2% ± 2.6% ± ≤2.9%. The former error reflects the statistical and instrumental uncertainties, while the latter is an estimate of the uncertainty in the derived source abundance arising from the propagation calculation. The 34S/32S source abundance agreement with the solar system abundance of this ratio (4.4%) is in accord with conclusions from other measurements that the overall isotopic cosmic-ray source is solar system-like, with only a couple of notable exceptions. The HET also resolves 33S. The ratio of Galactic cosmic-ray 33S/32S in the heliosphere is 19.0% ± 2.4%, corresponding to a source abundance of 2.6% ± 2.4%, since 33S is mostly secondary. This ratio is higher than, but consistent with, the solar system abundance of 0.8%. Assuming similar systematic errors to those found for 34S/32S, the 33S/32S ratio illustrates the difficulty in finding source abundances for mostly secondary cosmic-ray isotopes. The overall implications of the 33S and 34S measurements and their derived source abundances are included in the report.
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