Influence of concentration of magnesium on the dose response and LET-dependence of TL efficiency in LiF:Mg,Cu,P (MCP-N) detectors

The highly-sensitive LiF:Mg,Cu,P phosphor, unlike the supralinear LiF:Mg,Ti, exhibits a linear-sublinear dose response after high doses of photon radiation. Also, LiF:Mg,Cu,P shows a much stronger decrease of relative efficiency with increasing ionisation density, especially for heavy charged particle irradiation. The magnesium dopant most likely governs the trap structure in both phosphors. Dose-response and LET-dependence were therefore studied in LiF:Mg,Cu,P with different concentrations of Mg. Samples of LiF:Mg,Cu,P detectors with eight different values of magnesium concentration C-Mg ranging from 0.05 to 0.8 mol%, were produced in which the Concentration of P and Cu was fixed at 1.25 and 0.05 mol%, respectively. Detectors were irradiated with 5.3 MeV alpha-particles and Cs-137 gamma-rays and relative efficiency evaluated for all groups of samples. Relative efficiency eta(alpha gamma) appears to decrease with increasing magnesium content: from eta(alpha gamma) approximate to 0.13 at C-Mg = 0.05 mol% to eta(alpha gamma) approximate to 0.06 at C-Mg = 0.20 mol%, and is less dependent on C-Mg at higher concentration of Mg. In the study of LiF:Mg,Cu,P response after Cs-137 photon doses (1-1000 Gy) in samples with C-Mg = 0.1 and 0.2 mol%, typical sublinear response was observed, the sublinearity of 0.1 mol% detectors commencing at higher doses. In contrast, in the least Mg-doped sample (0.05 mol%) strong supralinearity in the dose response was found, resulting from the growth of a new peak at about 200 degrees C which at 1000 Gy and at 500 Gy dominates the TL glow-curve over the usual main peak at 240 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.