Non-linearity of TL dose responses in MgSO4:Dy CO-doped with Mn, P and Cu

Thermoluminescence (TL) dose responses to gamma radiation in the dose range from 0.1 Gy to 20 kGy in MgSO4:Dy, MgSO4:Dy,Mn, MgSO4:Dy,P and MgSO4:Dy,P,Cu phosphors were obtained and fitted by the composite action dose response function to obtain non-linear characteristic parameters, one-hit factor R and characteristic dose D0, which indicate that the TL dose responses for individual TL glow peaks in MgSO4:Dy, MgSO4:Dy,Mn and MgSO4:Dy,P phosphors all are supralinear. The non-linearity of dose response for the main dosimetric peak in MgSO4:Dy,P,Cu depends critically on the concentration of doped Cu and sublinearity can be obtained in the dose responses of TL materials doped with a certain amount of Cu. Based on studying the TL glow curves, dose responses and three dimension emission spectra of these phosphors, it is supposed that the TL event is generated via a multi-stage process within a large defect complex in doped magnesium sulphate phosphors. Doping with Cu results in reformation of the defect complex in which there is a strong spatial association between a trapping centre and a recombination centre so that the probability of one-hit TL events increases. The non-linearity of the dose responses is usually a difficulty for measuring higher dose in TL dosemeters. It can be overcome by enlarging the linear range of the dose-response or by calibrating the dose-response curves using non-linear characteristic parameters in a dose response function, such as the composite action dose response function.