Human EPR Dosimetry at Low Accumulated Dose of Ionizing Radiation Human EPR Dosimetry at Low Accumulated Dose of Ionizing Radiation

A new method for tooth (enamel and dentine) and bone EPR dosimetry is proposed that enhances substantially the dosimetric sensitivity. The method is based on the nonstandard spectra registration mode (the second harmonic phase quadrature detection of absorption under rapid passage conditions). This method provides an apparent enhancement of the component ratio of radiation to a nonradiative background (approximately fivefold) and allows to increase the radiation signal to noise ratio (approx. twofold) in comparison to the standard method used in EPR dosimetry. The data handling procedure is more simple and reliable than the standard mode procedure. Introduction A wide exploitation of ionizing radiation sources in medicine and industry, and the possibility of occuring accidents at nuclear power stations led to the development of dosimetric methods. Tooth Electron Paramagnetic Resonance (EPR) dosimetry became one of the most attractive methods either for human and animal retrospective or for accident dosimetry [1, 6, 10]. Tooth EPR dosimetry is of a significant practical interest due to the possibility of using human and animal teeth as individual dosimeters. The retrospective dosimetry is of highest importance for the dose evaluations of inhabitants of regions with radioactively contaminated soils. In such cases any available data concerning the extent of the radiation effect on inhabitants are necessary to be determined if urgent medical treatment and any activity aimed at elimination of the pathogenic irradiation effect is needed. The EPR method was applied for a long time as a tool to study radiation effects. Under ionizing irradiation unpaired electrons in materials are produced, whose concentration is dependent on the absorbed dose. Therefore the latter can be determined from the EPR spectrum of the sample. Radiation induced center' lifetime in solid specimens (minerals, teeth, bones, mollusk shells, ets.) is long enough (ca. 109 years for tooth enamel, for example [14]) to be detected. This procedure allows to determine, with a high accuracy, the total dose absorbed by the sample by using the signal intensity of radiation induced unpaired electrons. The following advantages are pertinent to EPR in comparison to other dosimetry methods (e.g. thermoluminescence, or spectrophotometry): 1) -the possibility of nondestructive analysis; 2) quantitative dose evaluation; 3) high sensitivity and large dynamic range of dose evaluation. The tooth EPR dosimetry procedure is as follows: The samples are extracted human tooth pieces from which any dentine-and caries-damaged parts are carefully removed. For these prepared samples, the EPR signal is measured either before or after a series of artificial irradiation (in steps of 40-200 cGy 4-5 irradiations in all). The dependence of the EPR signal on the artificial irradiation dose is extrapolated to the zero value of the EPR signal and an appropriate dose value is ascribed to the dose accumulated by the sample (initial dose Do at the investigation momentum).