Fission Track Annealing and Fission Track Age-Temperature Relationship in Sphene

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Abstract
Annealing characteristics of spontaneous (fossil) and induced (recent) fission tracks in sphene were measured in a temperature range of 873 to 768 K. Results include the reduction of number density, maximum track length (horizontal projection), and average track length (horizontal projection) as a function of annealing time [up to 1.5-107 s (175 days)]. Using the track dimension method, a corrected fission track age for sphene tlmin was derived. The annealing characteristics are interpreted by means of a new annealing model, yielding information about the elementary processes governing the annealing mechanism for the etchable zone of fission tracks. Monomolecular recombination and the annealing of dislocation loops are proposed as the likely dominant annealing processes. Annealing coefficients α(T) obtained from the number density annealing characteristics under the assumption of a single exponential function approximation are used to derive an age-temperature relationship giving for a measured corrected fission track age tlmin in sphene the corresponding temperature Tlmin. This age-temperature relationship of sphene is compared with the age-temperature relationship of apatite.