Effects of sunlight exposure on the human tooth enamel ESR spectra used for dose reconstruction

The effects of solar radiation on the electron spin resonance (ESR) signals in human tooth enamel were investigated. Enamel samples were exposed to the sunlight in Hiroshima, Japan, on sunny days for a total of about 228 hours over one year. The intensity of the illuminating sunlight was measured with a light meter, which then was converted to the intensity of the solar radiation. Three types of signals caused by the solar radiation were identified. The signal named S1 is identical to the gamma ray radiation-induced axially symmetrical signal and contains two signals S1perpendicular and S1// corresponding to the perpendicular and parallel components of the g-tensor characterized by gperpendicular=2.0018 and g//=1.9975 respectively. In addition, two other peaks named S2 and S3 are induced by the solar radiation. S2 is very near the inherent signal with g=2.0052, possibly created by the same paramagnetic centers as the natural signal, and S3 is a weaker signal with g=2.010. On increasing the amount of solar radiation S1 increases linearly, but S2 and S3 reach saturation. The average effect of the solar radiation on the S1perpendicular signal is estimated by dose equivalent gamma ray irradiation as 7.8±0.5 mGy (MJ m-2)-1, which corresponds to 19.6±1.3 mGy h-1 at the latitude of Hiroshima. Signals S2 and S3 may be used to recognize the effect of solar radiation on the enamel. (author)