Mechanisms of Supralinearity in Lithium Fluoride Thermoluminescence Dosemeters

The factors that affect the dose response function of LiF thermoluminescence dosemeters are examined. Experimental data are described concerning how the dose response is affected by varying the linear energy transfer of the incident radiation, varying the impurity contents of the samples, and varying the heating rate during TL readout. From the data obtained, along with optical absorption data, it is shown that the mechanisms which govern the thermoluminescence dose response are operative in the heating stage of the thermoluminescence process and not during the radiation absorption stage. A model is described which is based on charge transfer interactions between the defects during the heating phase, and its mathematical formulation is successful in qualitatively describing the observed experimental behaviour. The model invokes competition between defects and, for the case of gamma-irradiated samples, is conceptually the same as the 'competition during heating' model as advanced by other workers. For the case of irradiation with heavy charged particles the present model naturally encompasses the 'track interaction' model suggested by others. Spatial association of the traps and luminescence centres is seen to be a necessary component of the model in order to explain some aspects of the behaviour of gamma-irradiated LiF dosemeters.