Observations on a high temperature peak in the thermoluminescence of fluorites

A new peak at about 650deg C has been observed in the thermoluminescence (TL) emission of gamma irradiated natural fluorites containing significant quantities of lanthanide rare-earth (RE) elements as impurities. Thermal activation energy of the corresponding trap has been evaluated to be 2.99 eV with a frequency factor of 1016 sec-1. The optical activation energy, as deduced from photo-transfer-induced-TL from this trap, is 5.36 eV. Many types of natural fluorites as well as synthetically grown CaF2 crystals doped with single and pairs of rare earth elements have been studied and the results indicate that the high temperature peak is associated with Sm impurity coexisting with Y, La or Ce in CaF2. There are indications that this newly observed TL peak can be gainfully employed in ultraviolet dosimetry and geological dating of fluorite deposits. (auth.)