Terrestrial helium

Abstract

The problem of terrestrial helium is considered in the light of the measured isotopic abundance ratio of helium in the atmosphere. It appears from new evidence now available that the rate of release of He 4 to the atmosphere from the earth's crust is about sixty times greater than previous estimates. Thus, in order to maintain the atmospheric helium isotopic abundance ratio, the production of He 3 in the atmosphere must be considerably greater than that already calculated on the basis of cosmic-ray induced ( n,H 3) reactions on nitrogen (even in the limiting case of equal escape probabilities for the two helium isotopes). The extraterrestrial dust, which is continuously accreted by the earth, is considered as a source of He 2, and an estimate is made of the amount which is required to be collected per day, on the basis of recent work on meteoritic material. An infall of about 5000 tons per day for the whole earth is indicated; this figure depends on the history of the dust particles. The origin of the dust is considered; and the desirability of making a collection of this cosmic dust is discussed.