EPR study on biominerals as materials for retrospective dosimetry

In numerous biominerals exposed to ionizing radiation some stable paramagnetic species are induced. Their nature can differ depending on chemical composition of biominerals. The method of choice to study paramagnetic centers in biominerals is electron paramagnetic resonance (EPR) spectroscopy. When the relationship between EPR signal intensity of stable paramagnetic center and the dose has a linear or almost linear character, the material can be used as dosimeter of absorbed radiation. Depending on sensitivity and range of linearity of intensity-dose dependence, the dosimeters can be used for different purposes as geological and archeological dating, standard and accidental dosimetry, detection of irradiated food [4]. The most important are low-dose dosimeters, with a detection limit of about 1 Gy or less. In the most frequently used biomineral dosimeters, the stable EPR signal is generated by ionizing radiation in hydroxyapatite Ca10(PO4)6(OH)2, the main mineral component of bones and teeth. The natural hydroxyapatite, as well as synthetic apatites, exposed to ionizing radiation, have been investigated by EPR for more than 35 years [10]. The EPR spectrum detected in γ-irradiated apatites in the g = 2 region is complex. It consist of several signals due to paramagnetic species derived mainly from carbonate impurities, substituting hydroxy groups (so-called A site) or phosphate groups (B site) or those located on the surface of microcrystallites. The species differ in molecular structure and charge, for EPR study on biominerals as materials for retrospective dosimetry Jarosław Sadło, Jacek Michalik, Wacław Stachowicz, Grażyna Strzelczak, Anna Dziedzic-Gocławska, Kazimierz Ostrowski