Can’t the etch pit diameter be used instead?

A recent laboratory study of fission track annealing by Barbarand et al. (Chemical Geology, 198, 2003, 107-137) claimed that “etch pit size is a valuable estimator of annealing rate of an individual apatite grain”, which could be used instead of chlorine content to assess differential annealing between different apatite grains. This echoes earlier suggestions that etch pit size provides a practical alternative or even a better approach than using Chlorine (e.g. Burtner et al., AAPG Bulletin, 78, 1994, 1613-1636). As explained in detail in the accompanying article (pdf), we believe that chlorine provides a much better indicator of annealing properties, and that the data provided by Barbarand et al. demonstrate this point clearly.