Measurements of Heavy Elements and Isotopes in Small Solar Energetic Particle Events

Using the Solar Isotope Spectrometer on the Advanced Composition Explorer, we have examined the ~10–20 MeV/nucleon elemental and isotopic composition of heavy (Z≥6) energetic nuclei accelerated in 30 small solar energetic particle (SEP) events which occurred between 31 March 1998 and 2 January 2001. We have measured the average heavy element content, the ^(22)Ne/^(20)Ne ratio, and the ^(26)Mg/^(24)Mg ratio in these events, and find good agreement with past studies. We have categorized the events according to their 3He/4He ratios, and find significant enhancements in the neutron-rich heavy isotopes of Ne and Mg in the combined 3He-rich data set: ^(22)Ne/^(20)Ne = 0.17±0.05 and ^(26)Mg/^(24)Mg = 0.25±0.05. We discuss the implications of these measurements for the acceleration of energetic nuclei in SEP events. ; © 2001 American Institute of Physics. Issue Date: 21 November 2001. This research was supported by NASA at Caltech (under grant NAG5-6912), JPL, and GSFC. We thank the EPAM science team for providing the proton fluxes used to define the time periods of low solar activity in this paper. ; Published - SLOaipcp01.pdf