Event-to-event variations in the isotopic composition of neon in solar energetic particle events

Using the Solar Isotope Spectrometer on the Advanced Composition Explorer, we have measured the isotopic composition of neon at 24-72 MeV/nucleon in n ine solar energetic particle events between 4 November 1997 and 16 November 1998. The Ne-22/Ne-20 ratio varies from similar to 0.7 to similar to 2 tim es the solar wind value from event to event, indicating significant mass fr actionation in the acceleration and/or transport of these particles. The ma ss fractionation is strongly correlated with the Fe/O and Na/Mg element abu ndance ratios, suggesting that elemental and isotopic fractionation are bot h governed by the ionic charge to mass ratio.