Cosmic-ray production rates of neon isotopes in meteorite

Abstract

The rates of production of ²¹Ne and ²²Ne in spallation reactions, both due to solar as well as galactic cosmic rays, in some major meteoritic minerals, e.g. olivines, feldspars and pyroxenes, are calculated using their energy spectra and excitation functions. The production profiles of ²¹Ne and ²²Ne due to galactic cosmic rays, and the ²²Ne/²¹Ne ratio depend upon the size of the meteoroid. The ²²Ne/²¹Ne ratio is very sensitive to the abundance of sodium and consequently its depth profile is distinctly different in feldspars, the ratio increasing with depth rather than decreasing as in pyroxenes and olivines. In the near-surface regions, up to a depth of 2cm, production due to solar flare protons dominates, giving rise to a steep gradient in isotopic production as well as in the ²²Ne/²¹Ne ratio. Composite production profiles are given and compared with measurements in some meteorites.