Radioactivities in meteorites and cosmic-ray variations

Abstract

The Na 22:Al 26 ratio in six recently fallen meteorites, including Příbram, and the Ar 37: Ar 39 ratio in three recently fallen meteorites were measured. The Na 22:Al 26 and Ar 37: Ar 39 ratios are indicators of variations in the cosmic-ray bombardment of meteorites. The Na 22:Al 26 ratios, which are produced by cosmic rays integrated over the meteoroid orbit, show that the 11-yr cosmic-ray variation is smaller at the average solar distance of most meteoroids than at 1 a.u. The Ar 37: Ar 39 ratios, which compare cosmic rays in the neighborhood of 1 a.u. with those at the average solar distance of the meteoroid, give a high-energy cosmic-ray heliocentric radial gradient of 20 ± 8 per cent/a.u. at solar maximum and at solar minimum.