Agradecimentos: This work has been supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Brazil) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil). We thank Dr Adolfo Marra Neto, IPEN, Brazil, for the irradiations. We are grateful to an anonymous reviewer Ver menos

Abstract: In fission track thermochronology (FIT) latent fission tracks can be observed under the optical microscope only after chemical etching. The understanding of the etching process in the origin of this track is important for fission track annealing models. This may allow the determination of parameters related to etching kinetics independently of the models fit to the annealing data. In this work, a chemical etching kinetic model based on chemical principles and geometric track features is presented. The relation between track mean length, L (mu m), and etching time, t (s), is given by L = L-0[1-(Kt+1)(M)](n) where L-0 (mu m), K (s(-1)), M and n are parameters. M and n are dimensionless. The L-0 can be associated with the initial mean length of the tracks. The model fits well experimental data for apatite and muscovite mica. In addition, it corroborates the assumption of one of the fission-track annealing models proposed for FFT that strength and efficiency of etching depend on the amount of defects (or displaced atoms) compounding the track Ver menos