FACTORS AFFECTING THE PRECISION OF TLD DOSE MEASUREMENTS USING AN AUTOMATIC TLD READER

An increase in the variability of TLD dose measurements prompted a stu dy of the precision of dose measurements with a Rialto automatic TLD r eader. It was found that readings with the same chip measured using tw o different trays could differ by as much as 7%. In order to overcome this problem it was necessary to ensure that individual chips were cor rectly identified. Marking the chips with a hard graphite pencil was f ound to be a satisfactory method of identifying them, which, although it reduced the light output by approximately 3%, had no effect on the reproducibility of readings. Using marked chips and an individual tray for each chip, the reproducibility of a reading was reduced to a typi cal value of 1%. A system of quality assurance based on these findings is described.