Thermal Annealing of Ion Tracks

At ambient temperatures, ion tracks in minerals are known to be stable and fairly constant in size. Even over geological timescales, in the range of hundreds of million years, only small reductions in length occur [1]. This changes dramatically when the tracks are exposed to elevated temperatures, leading to a recrystallisation of the damaged structure and a shrinkage in track size (i.e. length and radius). This process is extremely temperature-dependent, with a full recovery and disappearance of all tracks at 170–200 \(^{\circ }\)C over geological timescales of 10\(^{6}\) years [2]. When annealed at 350–400 \(^{\circ }\)C, however, a duration of less than 1 hr is sufficient to fully erase all tracks [3]. This is a result of the rate of recrystallization being typically associated with an exponential dependence of the diffusion rate of the displaced atoms incorporated in the ion tracks on temperature.