Characteristics of fission tracks in zircon: applications to Geochronology and Cosmology

Abstract

We describe a simple method for nearly isotropic revelation of fission tracks in zircon. The etchant is an equivolume mixture of 48% HF and 98% H₂SO₄; etching is carried out under pressure at 150° - 180°C. For fossil track densities above ~ 5 × 10⁶, the etching time is strongly anticorrelated with track density. The total etchable fission fragment track length (2 fragments) is 11 ± 0.5 µm. The length distribution is sharply peaked; the standard deviation in different samples is ± (0.7 - 0.8) µm. Thermal annealing studies indicate a lower activation energy for track fading than was previously repoted using a phosphoric acid etchant. A practical chemical dissolution method is described for quantitatively recovering zircon crystals from rock samples; this method should find application in fission track dating of even zircon poor rocks.