Phototransfer, Sensitization and Re-estimation of Dose in Lithium Fluoride TLD

The normal readout for dose measurement in LiF TLD leaves residual thermoluminescence (RTL). The glow curve can be regenerated by shining UV-light on the sample with RTL. This is phototransferred thermoluminescence (PTTL). PTTL depends upon the RTL and is thus a measure of the latter. LiF is sensitized by giving high dose and annealing at an elevated temperature. The sensitized LiF is exposed to UV light at an elevated temperature in an attempt to bleach the RTL without losing sensitization so that the LiF so obtained can be used for dose measurement and re-estimation. It is shown that peak X (Z3 centres) in LiF constitutes RTL and is the source of PTTL. It is also shown that it is possible to bleach this peak while retaining sensitization but with important limitations. The results are explained in terms of a proposed model.