Fossil Alpha-Particle Recoil Tracks: A New Method of Age Determination

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Abstract
The discovery of a new type of fossil nuclear track in mica is reported. This track is produced by the recoil nucleus accompanying the α-particle decay of uranium and thorium impurities. The tracks are very short and can be seen with phase contrast microscopy. Measurement of fossil α-recoil track densities, coupled with determinations of the thorium and uranium contents, provides a new dating technique analogous to the previously discovered "fission-track method." The primary advantage of the α-recoil method is a several-thousand-fold increase in sensitivity over the fission-track technique. The α-recoil method should also prove useful in studying the problem of extinct isotopes in meteorites.