EFFECT OF MECHANICALLY INDUCED BACKGROUND SIGNAL ON EPR DOSIMETRY OF TOOTH ENAMEL

The effect of the mechanically induced background ESR signal whose Lan de factor is g = 2.0038, width = 0.798 mT, on absorbed dose estimation using the additive method was studied. The intensity and width of thi s signal increases with decreasing grain size. It was found to be ther mally stable and sensitive to Sr-90 radiation. The latter phenomenon s hould lead to its increasing contribution to the radiation-induced hyd roxyapatite signal at g(perpendicular to) = 2.0018 at irradiation with higher doses. However, it was found that the interference between mec hanically induced and the hydroxyapatite signals may be interpreted as either 'negative' for larger grain size or 'positive' for finer grain size. This feature in turn leads to under and overestimation of the h ydroxyapatite signal, respectively, and is apparently caused by the in verse relationship between the signal width and grain size. Enamel sam ples were irradiated with 44, 88, 220, 440, 660 and 880 mGy from a Cs- 137 gamma ray source. It was determined that 220 mGy was the lowest ab sorbed dose that could be reliably detected, while doses as low as 44 mGy could tentatively be identified.