Correlation between the thermoluminescence property and thermal activation energies of the carrier-capture process during irradiation of thermoluminescence phosphors

Abstract

It is theoretically and experimentally established that changes in the ’’proper’’ thermoluminescence sensitivity of a phosphor can be approximated by a quadratic equation in terms of the reciprocal of the irradiation temperature, when the phosphor is irradiated in the region of high temperatures, with low linear energy transfer (LET) radiation to a low dose; moreover, the curve of the ’’proper’’ sensitivity shifts toward the lower side of the irradiation temperature with a decreasing rate of energy absorption. A method is presented for evaluating the activation energy describing the carrier-capture reaction during irradiation. Experimentally determined values of the activation energies are given for Mg2SiO4(Tb), CaSO4(Tm), and LiF(Mg,Cu,P) phosphors. The carrier-capture reaction of these phosphors during irradiation is shown to be exothermic, and it is demonstrated that thermoluminescent dosimeter (TLD) phosphors, intended for high sensitivity measurements, should present the relationship expressed by Ed ≳E2≳E1 = 0, where E1, E2, and Ed are the thermal activation energies for carrier trapping, for carrier escape, and for carrier disappearance, respectively. The relationship holding between these three activation energies further serves to explain the batch-to-batch variation observed in the LET dependence of TLD sensitivity and other phenomena that have been noted in respect to TLD sensitivity.