Production by Cosmic Rays of Helium-3 in Meteorites

Abstract

THE helium content of iron meteorites varies from less than 10⁻⁹ c.c. to 4 × 10⁻⁵ c.c. per gm.¹. Since their uranium and thorium content is fairly constant, this variation was considered as an indication of their very different ages. During the past decade, however, it has been discovered that by the impact of cosmic rays on matter helium is formed, and Bauer² and Huntley³ have pointed out that a considerable part of the meteoritie helium might have this origin. Although attempts to calculate this amount on the basis of our published figures and of certain assumptions about the masses of meteorites⁴ were open to criticism⁵, it was predicted^6,7 from cosmic ray observations that in meteoritie helium the proportion of helium-3 to helium-4 may amount to about 30 per cent, and in five iron meteorites helium-3/helium-4 ratios varying from 17.8 to 31.5 per cent were found⁸.