Isotope composition of secondary hydrogen and helium above the atmosphere measured by the instruments NINA and NINA‐2

Abstract

In this paper we report on the energy spectra and abundance ratios of hydrogen and helium isotopes of albedo origin, measured by the instruments NINA and NINA‐2 in near‐equatorial regions. The instrument NINA flew on board the satellite Resurs‐01‐N4 between 1998 and 1999, at a 830 km average altitude. The NINA‐2 apparatus, on board the satellite MITA, was put into orbit in July 2000 at an altitude of about 450 km. NINA and NINA‐2 measurements revealed that 2H, 3H, 3He, and 4He are a significant portion of the secondary flux above the atmosphere. The energy spectra of hydrogen isotopes are practically flat across the energy range of 10–40 MeV/n, while the spectra of helium isotopes can be fitted by a power law of spectral indexes γ = 0.8 and γ = 1.5 for 3He and 4He, respectively.