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Published September 15, 2000 | Published
Book Section - Chapter Open

The Isotopic Composition of Solar Energetic Particles


Since the launch of ACE in August 1997, the Solar Isotope Spectrometer (SIS) has observed 11 large solar particle events in which elemental and isotopic composition was determined over a large energy range. The composition of these events has raised many issues and challenged generally accepted characterizations of solar energetic particle (SEP) events. In particular, ^3He/^4He enhancements have been observed in several large events as well as enhancements of heavy ions typically associated with smaller impulsive events. The isotopic composition varies substantially from event to event (a factor of 3 for ^(22)Ne/^(20)Ne) with enhancements and depletions that are generally correlated with elemental composition. This correlation suggests that the isotopic enhancements may be related to the Q/M fractionation typically evident in the elemental composition of SEP events. However, there are also significant deviations from this pattern, which may imply that wave-particle resonances or other mass fractionation processes may be involved. We review the recent isotopic observations made with ACE and discuss their implications for particle acceleration and transport.

Additional Information

© 2000 American Institute of Physics. Issue Date: 15 September 2000. This work was supported by NASA at the California Institute of Technology (under grant NAS5- 6912), the Jet Propulsion Laboratory, and the Goddard Space Flight Center. Climax neutron monitor data were obtained from the University of Chicago, National Science Foundation grant ATM-9613963.

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