Radiation Age of a Meteorite from Cosmic-Ray-ProducedHe3andH3

Abstract

The tritium and ${\mathrm{He}}^3$ contents of the Norton County stone meteorite were measured. At the time of fall (1948) the tritium activity of two different specimens were (0.28±0.02) and (0.25±0.02) disintegrations ${\min }^{-1\mathrm{}}$ ${\mathrm{g}}^{-1\mathrm{}}$. The measured ${\mathrm{He}}^3$ contents per gram were (2.27±0.11) and (2.35±0.11)×${10}^{-6\mathrm{}}$ cc STP respectively. Experiments were made which indicate that there has been no appreciable loss of ${\mathrm{He}}^3$. The amount of ${\mathrm{He}}^3$ accumulated and the tritium production rate combined give apparent ${\mathrm{He}}^3$-${\mathrm{He}}^3$ ages for irradiation of 420 and 480 million years respectively. If an assumption is made as to the direct production rate of ${\mathrm{He}}^3$ by spallation, these ages reduce to 240 and 280 million years. The ${\mathrm{A}}^{40}$-${\mathrm{K}}^{40}$ age of this meteorite is ${4400}_{-740\mathrm{}}^{+640\mathrm{}}$ million years. The possible significance of this difference in age is discussed.