TL and PTTL in natural fluorite previously irradiated with gamma rays and heavy ions

The effect of annealing temperature on the phototransfer thermoluminescence (PTTL) signal was studied to determine the appropriate annealing temperature for treating the natural powder before irradiation. The temperatures used to anneal virgin natural fluorite samples (only natural dose without giving the samples any artificial doses) were 150, 250, 350, 450, 550, 650 and 750oC for a duration of 1 h in each case. The results show that the PTTL response did not change for anneal temperatures up to 450oC, but at higher temperatures the signal decreased rapidly. The height of the 90oC peak decreased by two orders of magnitude as the anneal temperature increased from 450 to 750oC, whilst the height of the 180oC peak decreased by three orders of magnitude between the same two annealing temperatures. In order to investigate the effect of previous gamma rays and heavy ion irradiation on thermoluminescence (TL) and PTTL signals, powdered samples of natural fluorite from Cornwall, England, were annealed at 500oC and then irradiated (at GSI, Darmstadt, Germany) with 161Dy ions of energy 13 Mev/n; the range of fluences used was from 104to 1012 ion cm-2. Identical samples were given gamma doses in the range 1 Gy to 2.6 x 104 Gy in order to compare the effects of gamma rays and heavy ions. The sensitivities of TL and PTTL were studied by giving the samples a gamma test dose of 1 Gy after annealing the samples at 500oC for 30 min in order to eliminate the TL resulting from previous gamma or heavy ion irradiation. (Author)