A quantitative assessment of geometry factors for use in fission track studies

Various reasons are analysed for finding values of the geometry factor G in fission track dating (i.e. the ratio of track density in an “external” to that in an “internal” surface) to be greater than the “ideal” value of 0.5. It is shown that revelation of “new” tracks by prolonged etching is a minor effect, and that the effects of the minimum observable track length and differing distributions of etched track length in different surfaces are the major causes of values of G ≫ 0.5. It is also shown experimentally that with modern equipment, which allows tracks of ∼0.5 μm length to be resolved, it is possible to obtain values of G ∼ 0.5, and the use of this “ideal” value introduces little error in the final analysis. The behaviour of some other geometry ratios is also discussed.