Fission-Track Dating Method

Abstract

In 1962, Price and Walker discovered that micas contain natural tracks which can be optically revealed by etching with hydrofluoric acid. This discovery started a search for natural tracks (also called fossil tracks) in different kinds of materials and only two years later, natural tracks had been observed in about 10 different types of minerals and in several glasses (Fleischer and Price, 1964d). The major question that was immediately raised related to the origin of these natural tracks. Due to their low sensitivity for track registration, it could be readily stated that in mineral and glassy substances, tracks could only be created by heavy charged particles (Price and Walker, 1963a). In terrestrial materials, such heavy particles are typically produced by the spontaneous or induced fission of heavy nuclides which are present in the minerals themselves (Section 1.4). Induced fission reactions occur only very rarely in the Earth’s crust. In order to take place, they require a considerable concentration of heavy elements such as uranium residing for a certain time in a flux of energy (e.g.,γ-rays) or particles (e.g., neutrons or α-particles). The Oklo uranium mine in Gabon (West-Central Africa) which was once the site of a natural nuclear reactor, represents one of the very few cases where such induced fissions effectively occurred in significant numbers (Bodu et al., 1972; Petrov, 1977).