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 p hoton radiation. Also, LiF:Mg,Cu,P shows a much stronger decrease of r elative efficiency with increasing ionisation density, especially for heavy charged particle irradiation. The magnesium dopant most likely g overns the trap structure in both phosphors. Dose-response and LET-dep endence were therefore studied in LiF:Mg,Cu,P with different concentra tions of Mg. Samples of LiF:Mg,Cu,P detectors with eight different val ues of magnesium concentration C-Mg ranging from 0.05 to 0.8 mol%, wer e produced in which the Concentration of P and Cu was fixed at 1.25 an d 0.05 mol%, respectively. Detectors were irradiated with 5.3 MeV alph a-particles and Cs-137 gamma-rays and relative efficiency evaluated fo r all groups of samples. Relative efficiency eta(alpha gamma) appears to decrease with increasing magnesium content: from eta(alpha gamma) a pproximate 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%, typ ical sublinear response was observed, the sublinearity of 0.1 mol% det ectors commencing at higher doses. In contrast, in the least Mg-doped sample (0.05 mol%) strong supralinearity in the dose response was foun d, resulting from the growth of a new peak at about 200 degrees C whic h 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.