INTRINSIC SELF-DOSING AND LONG-TERM STABILITY OF LIF TLD-100 AND GR-200 TL DETECTORS

Intrinsic self-dosing effects on LiF TLD-100 and GR-200 have been stud ied experimentally. Samples of these thermoluminescent materials have been stored inside the UDO laboratory (Asse salt mine) where backgroun d air kerma rates as low as 0.7 nGy.h-1 are reported. After six months storage in this ultra-low background environment very small self-dosi ng effects were observed in the two materials. With the highly sensiti ve LiF GR-200 the intrinsic self-dose rate could be directly estimated (approximately 0.8 nGy.h-1) since a clear TL signal in excess of the UDO background was detected. For LiF TLD-100 no appreciable TL signal could be detected after storage and consequently, only a maximum limit for the self-dose contribution could be estimated (approximately 0.9 nGy.h-1) based on the minimum detectable dose of the experimental syst em. The stability of the TL response during the six months at UDO was also studied. Much better stability during storage at room temperature was found in GR-200 than TLD-100.