Light Isotope Abundances in Solar Energetic Particles Measured by the Space Instrument NINA

This article reports nine solar energetic particle (SEP) events detected by the New Instrument for Nuclear Analysis (NINA) between 1998 October and 1999 April. NINA is a silicon-based particle detector mounted on board the Russian satellite Resurs-01-4, which has flown at an altitude of about 800 km in polar inclination since 1998 July. For every solar event, the power-law 4He spectrum across the energy interval 10-50 MeV nucleon-1 was reconstructed and spectral indexes, γ, from 1.8 to 6.8 extracted. Data of 3He and 4He were used to determine the 3He/4He ratio, which for some SEP events indicated an enrichment in 3He. For the 1998 November 7 event, the ratio reached a maximum value of 0.33 ± 0.06, with spectral indexes of γ = 2.5 ± 0.6 and γ = 3.7 ± 0.3 for 3He and 4He, respectively. The 3He/4He ratio averaged over the remaining events was 0.011 ± 0.004. For all events, a deuterium-to-proton ratio was estimated. An upper limit on the average value over all events was 2H/1H < 4 × 10-5 across the energy interval 9-12 MeV nucleon-1. Upper limits on the 3H/1H counting ratio for all events were determined. For the 1998 November 14 SEP event, the high flux of heavy particles detected made it possible to reconstruct the carbon, nitrogen, and oxygen flux.