LENMODEL - A FORWARD MODEL FOR CALCULATING LENGTH DISTRIBUTIONS AND FISSION-TRACK AGES IN APATITE

The program LENMODEL is a forward model for annealing of fission tracks in apatite. It provides estimates of the track-length distribution, fission-track age, and areal track density for any user-supplied thermal history. The program approximates the thermal history, in which temperature is represented as a continuous function of time, by a series of isothermal steps of various durations. Equations describing the production of tracks as a function of time and annealing of tracks as a function of time and temperature are solved for each step. The step calculations are summed to obtain estimates for the entire thermal history. Computational efficiency is maximized by performing the step calculations backwards in model time. The program incorporates an intuitive and easy-to-use graphical interface. Thermal history is input to the program using a mouse. Model options are specified by selecting context-sensitive commands from a bar menu. The program allows for considerable selection of equations and parameters used in the calculations. The program was written for PC-compatible computers running DOS(TM) 3.0 and above (and Windows(TM) 3.0 or above) with VGA or SVGA graphics and a Microsoft(TM)-compatible mouse. Single copies of a runtime version of the program are available from the author by written request as explained in the last section of this paper.