Fading of LiF-teflon dosimeters used in identification badges

The results of a study carried out to determine the long term (up to 5 yr) loss of sensitivity before exposure and the loss of stored TL signal after exposure of LiF-Teflon dosimeters at 220C are presented. Both 7LiF(TLD-700) and 6LiF(TLD-600) were investigated but no difference in loss of sensitivity was observed between the two types within experimental error. From graphs presented of the loss of sensitivty, expressed as the ratio of dosimeters dosed after storage to those dosed and read promptly after annealing, vs storage time and loss of stored TL signal, expressed as the ratio of dosimeters dosed before storage to those dosed and read promptly after annealing, vs storage time it is seen that there is a rather rapid loss of sensitivity for the first year, followed by a relatively stable period for approximately 2 yr and a further more rapid loss for the next 2 yr. It was also found that the loss of sensitivity before exposure is approximately equal to the loss of stored TL signal after exposure. (U.K.)