Fission Track Dating of Archaeological Glass Materials from Japan

Abstract

THE method of dating by fission tracks¹ which has been applied to glass² depends on the spontaneous fission of ²³⁸U atoms contained in glass taking place at a constant rate, and leaving fission tracks (that is, detectable damage trails of nuclear fragments). Once formed, the fission tracks in a glass disappear if the glass is heated above a critical temperature. It may be assumed that the density, ρs, of spontaneous fission tracks of ²³⁸U atoms in a glass is proportional to the lapse of time T after the glass was either produced or last heated above the critical temperature, and to the density of ²³⁸U atoms contained in the glass. The latter can be determined from the density of ²³⁵U atoms, ρi, which are induced by bombarding the glass with a known dose of thermal neutrons φ. Then the lapse of time T is given approximately by the simplified formula³