Low dose measurements with thermoluminescent phosphor/PTFE discs

Sources of background variations in thermoluminescent phosphor/PTFE discs have been investigated, enabling the design of the dosemeters and operational techniques for precise measurements with them at low dose levels to be optimized. The background signal contains several components whose magnitude and variability increase rapidly with temperature, and therefore it is very dependent on the heating cycle profiles, and heat transfer to the dosemeter. Plateaux type heating profiles were employed, to minimize temperature gradients across the dosemeter, and to allow lower read zone temperatures to be used while still achieving adequate heating efficiencies. The limiting factor in low dose measurements with phosphor/PTFE discs is a background signal believed to be due to oxygen adsorbed too deeply in the PTFE surface to be removed by nitrogen. The signal is largely diminished by the readout process, and only recovers to its initial value after the dosemeter has been exposed to air for some time. The extent of the operational problem of sensitivity to light has been gauged by experiments in daylight, exposure to a UV lamp, and exposure to typical laboratory fluorescent lighting