TL dating technique based on a trap model and its application as a geochronometer for granitic quartz

Abstract

A trap model is introduced to describe the behaviours of both thermally sensitive and radiation sensitive TL traps. The former are relatively shallow traps. The latter are deep traps, in which population increases with exposure to alpha dose. Thermal decay of both types of traps at ambient temperature is dependent on the trap lifetimes. A trap's population can be measured as TL sensitivity to a laboratory test dose. The trap model has been supported by observations of age dependent TL signals from granitic quartz samples with different crystallisation ages. The trap lifetimes are from 1.98 x 109 to 5.36 X 1015 years estimated using the isothermal decay experiment with the assumption of first order kinetics. Dating techniques are proposed based on the trap model. For old granites (> 400 Ma), ages can be obtained by measuring the total exposed alpha dose using the additive alpha dose method, whereas for young granites (< 400 Ma), ages can also be obtained by interpolating the TL sensitivity to a curve of TL sensitivities for known ages.