Exposure Dose Reconstruction from EPR Spectra of Tooth Enamel Exposed to the Combined Effect of X-rays and Gamma Radiation

Abstract

We have used EPR dosimetry on tooth enamel to show that the combined effect of x-rays with effective energy 34 keV and gamma radiation with average energy 1250 keV leads to a signifi cant increase in the reconstructed absorbed dose compared with the applied dose from a gamma source or from an x-ray source or from both sources of electromagnetic radiation. In simulation experiments, we develop an approach to estimating the contribution of diagnostic x-rays to the exposure dose formed in the tooth enamel by the combined effect of x-rays and gamma radiation.Introduction. Radiation diagnostics in dentistry leads to formation of paramagnetic centers in tooth enamel [1-6]. The energy of medical diagnostic x-rays typically used in dental examination of the dentition is 34 keV. At the same time, the energy of gamma photons from 137 Cs (the radioisotope making the major contribution to the effective external and internal exposure dose for the population in the case of nuclear power plant accidents) is more than an order of magnitude higher (662 keV). Nevertheless, for the same applied dose, the intensity of the EPR signal induced in tooth enamel by x-ray photons is an order of magnitude greater than the intensity of the signal induced by gamma radiation [4,5]. Such an effect leads to unequal overestimation of the dose load formed in tooth enamel by accidental external gamma radiation [5,6].In the case of separate exposure of tooth enamel to x-rays or gamma radiation, reconstruction of the individual absorbed doses from the EPR spectrum is done by additional exposure of the enamel samples to a source of electromagnetic radiation of energy that is identical to that of the source which formed the paramagnetic centers [6]. However, with the combined effect on the tooth from medical diagnostic x-ray photons and accidental gamma radiation, solution of the problem of retrospective dose reconstruction by EPR dosimetry is associated with certain diffi culties. In this case, we can only use the signifi cant decrease in the intensity of the radiation-induced EPR signal in the lingual fraction of the enamel compared with the buccal side to decide if an individual has undergone diagnostic x-ray examination of the dentition or skull [2,3,5].The aim of this study was to use EPR dosimetry to estimate the contribution of x-rays to the cumulative dose formed in tooth enamel in vitro by the combined effect of x-ray photons and gamma radiation, for a known ratio of the applied doses from both sources of electromagnetic radiation.Materials and Methods. We used teeth removed for dental reasons from individuals up to 20 years old, who lived in areas uncontaminated by radionuclides. We selected samples which were not subjected to diagnostic x-ray examination of the teeth, jaw, and skull. In this case, the crown of the tooth was separated from the root and split into the buccal and lingual sides. The halves of the teeth were cleaned to remove residues of organic materials, dental tartar, and pigmented spots, and carious sections were removed. The...