DIRECT DETERMINATION OF 39AR RECOIL DISTANCE

Abstract

The recoil distance of 39Ar is a vital discriminant among geochronological models. Direct measurement of recoil is possible by studying 39Ar implantation in SiO2 glass from a KCl crystal, and comparing one such glass immediately juxtaposed to KCl with one shielded by a ~0.1 μm Si coating. This simple technique offers ample potential for future refinements. The recoil distance in pure Si was determined as 78 +/- 20 nm, confirming the predictions of nuclear physics. Thus, tectonic interpretations based on nanometer-sized ''domains'' in K-feldspars should be re-examined.