Thermostimulated luminescence characteristics of dolomitic rocks and their use as a gamma ray dosimeter

The thermostimulated luminescence (TSL) glow curve characteristics of ten dolomitic crystals of Salem and Namakkal districts of Tamilnadu are analysed. The natural thermoluminescence (NTL) measurements were carried out for all the samples and show two peaks at 270 °C and 335 °C. The sample irradiated with a gamma dose of 200 Gy shows an additional peak at 180 °C, when recorded with linear heating rate of 10 °Cs⁻¹. At the same time, the NTL peak at 270 °C is shifted to 260 °C while increasing in intensity and there is no change in the peak position of 335 °C. The annealed sample also shows the same trend. The sample was annealed in air at the temperatures ranging from 200 to 950 °C, at an interval of 50 °C, for 1 h duration. Annealing treatment above 250 °C increases the sensitivity of all three TSL peaks. On the other hand, annealing at 800 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 700 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 to 10⁴ Gy. The number of glow peaks was identified through partial heating method. Using peak shape and initial rise method the kinetic parameters (activation energy (E), frequency factor (S) and order of kinetics (b)) were evaluated. The investigations show that the trapping centers are not affected by the annealing procedure. The emission spectra of all the samples show an emission at around 608 nm but with different intensities for each sample. With reference to earlier work, it may be assumed that the recombination site always involves Mn²⁺ ions.