Very heavy ion track etching in olivine

Abstract

Track etch rate has been measured as a function of residual range R for 12–16 MeV/amu Kr, Pb and U ions in olivine, and has been found not to vary with R for Pb and U ions. For this reason, 16 MeV/amu U ions have been used to specifically study the influence of the etching process on track etch rate in this mineral. The track etch rate is found to decrease with time, i.e. with etched track length, even for constant radiation damage. Small changes in composition of the WN etchant can considerably modify the olivine bulk etch rate and, to a much lesser extent, the tract etch rate. Evidence is presented for the existence of an etch induction time, with characteristics strikingly similar to those known for plastic track detectors, and of the etch blocking features, some of which have been identified with tubular inclusions. An attempt is made to explain and link together these experimental results. The track etch rate is expressed in terms of a competition between two components, one depending on radiation damage, the other on etching chemistry. Implications for the interpretation of track etch rate measurements and for proper revelation of tracks, in particular very long tracks, are pointed out.