Effects of gamma-irradiation on the TL characteristics of pre-annealed natural ZrSiO4

By the use of thermoluminescence (TL) technique we have investigated the effects of gamma irradiation on the TL response of pulverised natural zircon (ZrSiO4) crystals from the Jos Plateau area of Nigeria. Samples of the mineral that have been previously annealed were artificially irradiated to moderate gamma doses ranging from 0.7 to 4.9 Gy using 60Co gamma-source of the CERD. The natural TL glow curve of the sample showed a broad peak around 250 °C, the peak was however, found to be completely erased following heat treatment for 2 h at 400 °C. The TL glow curves of the artificially irradiated samples showed two overlapping glow peaks at about 112 °C (peak I) and at 156 °C (peak II) within the dose range utilised. We note that the natural TL peak appears to be different from the two observed in the artificially irradiated sample. The TL response with dose was investigated for the two glow peaks found in the artificially irradiated sample and in both cases, in the dose range utilised, linear relationship was obtained. The fading pattern of the two peaks was also monitored over a period of 28 days. The change in TL response with storage time was found to be somewhat anomalous especially within the first 24 h after exposure to irradiation. Consequently, we have fitted the fading curves beyond that anomalous region to analytical equations that could then be used in predicting the change in TL intensity with storage time. The implications of these results in terms of the potential of Nigerian zircons for applications in TL dating and radiation dosimetry are briefly discussed.