Solar energetic particle event with ³He/⁴He>1

Abstract

OBSERVATIONS of γ rays and the short lived isotope ³H provide evidence for the occurrence of nuclear reactions by high energy particles accelerated in solar flares^1,2. Stable isotopes such as ²H and ³He should also be produced in these reactions. Solar ³He particles were first detected by Hsieh and Simpson³. In the energy range 10 to 100 MeV per nucleon they obtained ³He/⁴He = (2.1±0.4) × 10⁻² by summing over seven solar particle events. Garrard et al.⁴ and Anglin et al.⁵ have reported that ³He/⁴He was highly variable from event to event. (Table 1). In the ‘³He-rich events’, ²H and ³H were not detected and the resulting upper limits were much less than expected from the theory of nuclear reactions⁶. These events were small, and the number of ³He particles observed was low (∼ 70). This anomalous production of ³He should provide new insight into the acceleration and confinement process of energetic particles in solar flares.