HEAVY-ION ISOTOPIC ANOMALIES IN HE-3-RICH SOLAR PARTICLE EVENTS

We have measured the similar to 1 MeV nucleon(-1) heavy-ion mass compo sition during a series of He-3-rich solar particle events during 1992 July using the University of Maryland instrument on the SAMPEX spacecr aft. In addition to enhancements of He-3/He-4 of similar to 10(3)-10(4 ) larger than coronal values, these events also showed typical enhance ments of heavy nuclei of up to a factor of similar to 10 compared with large solar particle events. Over the energy range of similar to 0.4- 4.0 MeV nucleon(-1) the spectra of both He isotopes as well as heavier ions C, N, O, Ne, Mg, Si, S, Ca+Ar, and Fe were found to be power law s in energy per nucleon with nearly identical spectral indices, indica ting that both the He and heavier ions were accelerated by the same me chanism. We obtain upper limits of similar to 15 for possible enrichme nts of neutron-rich isotopes of C, N, O, and Fe compared to large sola r particle events; however, we find Ne-22/Ne-20 = 0.29 +/- 0.10, an en hancement of a factor of 3-4 compared with large solar particle event abundances. We also find evidence of enrichments of similar to 2-3 for Mg-25/ Mg-24 and Mg-26/Mg-24, although the uncertainties are large. T hus, while at least one of the heavy elements shows isotopic enhanceme nts of neutron-rich isotopes, the mechanisms that produce the extremel y large He-3 enrichments apparently do not produce similarly dramatic isotopic anomalies in the heavy nuclei. These observations constrain p ossible acceleration models and may indicate that the particles are en ergized in solar coronal locations enhanced in heavy ions.