Factors affecting the precision of TLD dose measurements using an automatic TLD reader

An increase in the variability of TLD dose measurements prompted a study of the precision of dose measurements with a Rialto automatic TLD reader. It was found that readings with the same chip measured using two different trays could differ by as much as 7%. In order to overcome this problem it was necessary to ensure that individual chips were correctly identified. Marking the chips with a hard graphite pencil was found 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 typical value of 1%. A system of quality assurance based on these findings is described.