Solar particle events with anomalously large relative abundance of 3He

Experimental results on three solar energetic particle events with extremely high abundance of 3He are reported. These events took place during 1969 May 28--29. The measurements, using the Goddard cosmic-ray telescope on board the OGO-5 satellite, cover an energy range of approx.4--80 MeV nucleon-1. In the first of these events GAMMA (3He/4He) =1.52plus-or-minus0.1 (where GAMMA is the ratio of the two species in an energy per nucleon representation). In the two subsequent events GAMMA (3He/4He) had values of 0.71plus-or-minus0.06 and 0.35plus-or-minus0.03, respectively. The abundance of protons relative to He nuclei was significantly low in these events. Not more than four 2H and three 3H were detected during the entire period under study, compared with 11103He nuclei. The lower limits of GAMMA (3He/2H) obtained for these three events were 300, 250, and 63, respectively, and are much higher than the upper limits expected from theoretical considerations. Results from these events are compared with the data available from other experiments. The limitations these observations place on theoretical models to explain 3He-rich flares are discussed