Calcium fluoride, CaF2:Tm (TLD-300) as a thermoluminescence one hit detector

The Microdosimetric One-Hit Detector Model was applied to analyse the thermoluminescence response of peak 3 in Harshaw-produced TLD-300 CaF2:Tm ribbons (0.9x3.2x3.2 mm) after doses of X-rays, gamma-rays, alpha-particles and protons. The model was able to fit the relative TL efficiency for X-rays, alpha-particles and protons and dose response curves for gamma-rays. The model uses two parameters: the diameter of the spherical, sensitive volume (target) d and the saturation coefficient α which determines the probability of TL effects occurring following the energy deposition event. A fit to the set of experimental values of relative TL efficiency of CaF2:Tm, published by , , , , and yielded d=14 nm in 3.54 g cm-3 CaF2 and α=3.47x10-3 Gy. The estimated target dimensions are of the same order of magnitude as the 24 nm target site, found for LiF:Mg,Cu,P TL detectors. The hypothetical target could perhaps be related to large defect complexes in CaF2:Tm, comprising recombination centres and charge traps. The fairly good agreement of the model prediction with experimental data supports the hypothesis that for peak 3 in TLD-300 the initial spatial distribution of energy deposited in the detector is stored in the detector and serves as the pattern for further TL phenomena during the heating stage