Abstract
Abstract The TL response of CaSO4:Dy to extremely low beta doses delivered by samples of environmental origin was investigated. Taking into account the main factors limiting the precision of measurements below about 5 µGy, a special TL technique was developed. The heating chamber and the PM assembly are placed in a 20 cm thick iron shield. 0.1 g of CaSO4:Dy is spread on the heating plate, constituting a 1.5 cm diam. phosphor layer. The phosphor, heated to 350 oC, can be re-used with no change in sensitivity at low doses. Replacing the PM tube with a container filled with 4 g of sample (soil, pottery clay) or CaSO4:Dy (for background correction), on-plate exposures are made overnight. For calibrations and quick checks, K2CO3 and NBL reference standards with specified U and Th content are used. This technique enables highly reliable measurements to be performed at doses as low as 0.1 µGy. Some of the results relating to isotope dependence, build-up of spurious TL and possible applications in TL dating are also presented.
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