Ultra-Heavy Elements Above 10 MeV/nucleon in Solar Energetic Particle Events

Abstract

Recent measurements from Wind/LEMT and ACE/ULEIS show that elements heavier than Zn (Z=30) can be enhanced by factors of ~100 to 10,000 in impulsive solar energetic particle (SEP) events at energies below several MeV/nuc. Using data from the Solar Isotope Spectrometer (SIS) on ACE at energies from ~10 to >100 MeV/nuc, we find that even large gradual events at these energies often are very iron rich and may appear similar in composition to impulsive events. Since August 1997, SIS has recorded ~1000 nuclei with Z of 29 or greater, including measurable quantities of Zn, Ge and Se (Z=30, 32, and 34). Although quantitative analysis to obtain ultra-heavy abundances remains to be done, we present sample observations that establish the potential of extending ultra-heavy SEP measurements up to higher energies in order to test models of acceleration and abundance enhancements in both gradual and impulsive events.

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