U.V. induced thermoluminescence on natural calcium fluoride.

Abstract

Abstract Samples of a green variety of fluorite found at Circuit, Brazil, annealed at 580°C for 10 min and then at 400°C for 2 hr were exposed to 365 nm u.v. light. The transferred TL from deep trap to lower temperature trap gives rise to a glow curve containing peaks I, II, III', III and IV in a readout up to 400°C. This TL response was measured as a function of u.v. exposure time t and the result is not a saturation curve, but, TL tends to zero for large t indicating a simultaneous bleaching effect. The curve of TL vs number n of cycles in an exposure-readout cycle was obtained for different durations of exposure in each cycle. For large n the rate of decrease of log (TL) is independent of the time interval of exposure to u.v. light in each cycle. The effect of duration and temperature of pre-annealing on TL transfer under u.v. exposure as well as the dependence of transferred TL on previous gamma radiation were investigated. Finally a mathematical model is proposed.