| Popis: |
An empirical study of luminescence around 360 nm from limestone is presented. Thermoluminescence glow curves from natural limestone show broad peaks at 440°C, 350°C, 530°C and 286°C in order of decreasing amplitude in contrast to the usual observation, for luminescence around 535 nm , of a sharp peak at 286°C with a broader less intense peak at 350°C. Recuperation occurs around 350°C and 525°C, which has a time dependence consistent with quantum tunnelling. Dependent on the history of heating and light exposure of the sample, sharp peaks at about 325°C and 425°C can be observed. Laboratory irradiated limestone shows a peak at 140°C. The stimulation of luminescence by light of 470 nm with preheating at 145°C for 300 s , shows an increasing signal for successive cycles of measurement associated with the heating, light exposure having little influence. Beta irradiation of a sample, with the same measurement conditions, gives a signal which increases in proportion to radiation dose but which does not survive storage for 17 h . Time resolved luminescence spectra, with no preheating, show a luminescence lifetime between stimulation and emission of less than a few μs for natural limestone, and an exponential increase in signal with increase in temperature (over the range 20–167°C) during stimulation. A signal proportional to laboratory applied beta dose is measurable at room temperature, with lifetime between stimulation and emission of this signal of 35 μs , but it does not survive heating to 100°C. |
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