Anisotropic etching of charged-particle tracks in crystals

It is well-known that highly-energetic heavily charged particles arising both from the fissioning of heavy elements and from cosmic and solar radiations leave tracks which have been found in glasses and crystal-line minerals recovered from lunar and meteoritic material. It has been shown that an appropriate analysis of these tracks can provide informationabout periods since solidification and the thermal and dynamic history of the specimen, as well as insight into the nature and temporal variation of the cosmic ray flux.^1-2 An understanding of the track registration characteristics of crystals is clearly an important pre-requisite to an appropriate interpretation of the natural tracks. ^3-6 This letter describes briefly some observations we have recently made on one particular aspect of this-the anisotropy in track distributions which seems to result from the inherently anisotropic structure of crystals. This effect seems so far to have received little attention.