CaF2:Mn extreme dosimeter: Effects of Mn concentration on thermoluminescence mechanisms and properties

Concentration of manganese in CaF2:Mn (TLD-400) is shown to exert the most essential influence on thermoluminescent (TL) properties. The TL curve demonstrates a single high-temperature peak only when CaF2 is doped with a high manganese concentration, being close but still below the decomposition threshold of a solid solution. In case of lower manganese concentrations, the TL curve shows several peaks overlapping with each other. The optimum manganese concentration in thermoluminophor is found to be about 2.1-2.5mol%. The influence of different factors on the actual Mn concentration in CaF2:Mn is reported for the case where the material is prepared by the co-precipitation method. The CaF2 crystal lattice stress due to the Mn incorporation is studied by means of the X-ray diffraction technique. The solid solution decomposition threshold is estimated. The EPR studies of both γ-irradiated and non-irradiated samples have demonstrated that the amount of Mn2+ does not change as a result of the irradiation. The model of energy storage is suggested. It is based on a pair of VK and F centres, induced by radiation near Mn2+, which immediately turns into an exciton-like state with a partial relaxation of the lattice stress caused by the Mn impurity. Partial relaxation of the lattice stress increases the thermal stability of the stored excitation