Techniques for the study of fossil tracks in extraterrestrial and terrestrial samples. I: Methods of high contrast and high resolution study

Abstract

Techniques developed for high contrast optical examination and high resolution study of fossil tracks are described. We find that depositing a thin layer of silver (or gold) on the surfaces of trackholes greatly enhances optical contrast allowing accurate measurement of track lengths. This technique has been successfully employed to measure lengths of “complete” tracks using the TINT and TINCLE method. Such measurements are useful in a study of the chemical composition of cosmic radiation and fossil records of transuranic elements in lunar and meteoritic samples. Another application for silver (or gold) coating of track hole surfaces lies in the study of long tracks due to cosmic ray nuclei of Z>30; epoxy resin adheres firmly to the coated surface and the tracks can be sealed against further chemical attack. The plastic replication and Pd shadowing technique was developed and used to examine fossil tracks occurring with high track densities, >107cm-2, in gas rich meteorites and in lunar regolith samples. The method seems to be accurate up to densities of about 3 × 109 cm-2.