Reply on RC1

Abstract

The tools for interpreting fission-track data are evolving apace but, even so, the outcomes cannot be better than the data. Recent studies that have again taken up the issues of etching and observation have shown that both have an effect on confined-track length measurements. We report experiments concerning the effects of grain orientation, polishing, etching and observation on fission-track counts in apatite. The results cannot be generalized to circumstances other than those of the experiments, and thus do not solve the problems of track counting. Our findings nevertheless throw light on the factors affecting the track counts, and thence the sample ages, whilst raising the question: what counts as an etched surface track? This is pertinent to manual and automatic track counts and to designing training strategies for neural networks. We cannot be confident that counting prism faces and using the ζ-calibration for age calculation are adequate for dealing with all etching- and counting-related factors across all samples. Prism faces are not unproblematic for counting and other surface orientations are not per se useless. Our results suggest that a reinvestigation of the etching properties of different apatite faces could increase the range useful for dating, and so lift a severe restriction for provenance studies.