This article reports a fission track method for determining the concentration of uranium in a mica specimen. Tracks produced by the radiation damage due to individual fragments of uranium can be widened to optical dimensions by etching in hydrofluoric acid. To determine the concentration of uranium, a sample is first etched to determine the number of background tracks. The sample is then exposed to a source of thermal neutrons, re-etched, and the tracks are recounted. The authors point out that measuring the background track density combined with determining the concentration of uranium can provide a basis for determining the geologic age of a specimen. They allude to upcoming publication of this dating technique, which has subsequently been referred to as fission track dating.