Electron Paramagnetic Resonance of Human Tooth Enamel at High Gamma Ray Doses.

Powdered human tooth enamel was exposed to Co-60 gamma rays up to a dose of 100 kGy. The electron paramagnetic resonance (EPR) signal intensity (1) of the radiation-generated carbon dioxide radicals was measured for dependence on absorbed dose (D). The EPR dose response can be fitted with an exponential saturation function I I-M[1 - exp(-D/D-37)] with the saturated signal intensity (I-M) and the dose saturation value (D-37). The obtained value D-37 = 9.64 (+/- 0.96) kGy (measured at least one month after irradiation) exceeds those given in the literature. The saturated concentration of orthorhombic CO2- radicals was estimated at 6.5 X 10(17) per gram of enamel by comparing the integrated EPR spectra of enamel and a standard MgO:Cr probe. For enamel samples, which were heated before irradiation for one hour at +405degreesC, the value of D-37T = 3.89 (+/- 0.44) kGy and the saturated value of CO2- radicals 3.4 X 10(17) per gram of enamel were lower than for unheated samples. The initial rise of the signal with the dose was slightly higher (8.8 X 10(13) radicals/g X Gy) for heated compared with unheated samples (6.8 X 10(13) radicals/g X Gy)