Fission fragment tracks in Apatites: recordable track lengths

Abstract

This study is concerned with the measurements of total lengths of fission fragment tracks due to spontaneous fission of ²³⁸U (fossil tracks) and neutron induced fission of ²³⁵U (π -induced tracks) in several terrestrial apatites of geological age exceeding 0.4 billion years. The measurements of total etchable lengths are based on the revelation of confined tracks, TINTs and TINCLEs. The mean etchable length of confined n-induced tracks in fluor- and hydroxyl-apatites is measured to be 15.3 ± 1 μ ; the longest tracks are about 18 μ in length. The length distribution ofconfined natural fossil tracks shows a wider but peaked distribution; the position of peak is shifted to lower lengths as compared to that forn-induced tracks. Thus measurable annealing effects are found in old apatites for the stored fission tracks. The measurements of TINTs and TINCLEs in apatites allow an estimation of the correction needed for annealing effects in fission-tracks ages.