Point-counting technique for fission-track dating of tephra glass shards, and its relative standard error

Fission-track dating of glass is potentially an efficient technique for tep hrochronological studies, However, most glasses from Quaternary tephra have very low spontaneous track densities and track counting is laborious. The point-counting technique is a simplified procedure for evaluating fission-t rack areal densities in a glass shard population that allows the analyst to count larger numbers of tracks in significantly shorter times. A field of view is coded as 1 if its center is on glass and is 0 otherwise, and the to tal area of glass is estimated by counting the number of l's, Under simple assumptions, the binomial distribution appears to provide a reasonable eval uation of the additional experimental error in a fission-track density dete rmination by this technique. Glass shard populations have been simulated, a ssuming that glass areas are random samples from distributions analogous to real ones. The effect of variation in glass area on the relative standard error of the estimated track density is found to be small. The point-counti ng technique significantly enhances the potential of fission-track dating, especially for very low track densities typical of most Quaternary tephra, as the additional error associated with its use is largely counterbalanced by the greater number of tracks that can be counted, (C) 1999 University of Washington.