| Rapid and accurate retrospective radiation dosimetry is of critical importance and strategic value in the emergency medical response to a large-scale radiological/nuclear event. There is a growing interest in the technique of Electron Paramagnetic Resonance (EPR) dosimetry using human nail clippings. This ex vivo nail dosimetry has a number of attractive features such as ubiquitous availability, easy and non-invasive sampling, and the potential for immediate and rapid dose assessment. However, accurate estimation of the dose-dependent amplitude of the Radiation Induced Signals (RIS) is complicated by the generation of a set of mechanically induced signals (MIS), which arise during the nail clipping process. This research was undertaken to address several key factors leading to improvements in the spectral analysis and dose assessment of nail dosimetry. First, a thorough understanding of the chemical nature, the decay behavior, and the microwave power dependence of the EPR signals, as well as the effect of variation in temperature, humidity, water content, and O2 level, has helped to elucidate the complexity of the EPR spectra. Second, finding ways to control the variability among individual samples has helped to achieve consistent shape and kinetics of the EPR spectra. Third, careful observation of the EPR spectra has helped to explore possible correlations between the multiple MIS components. Finally, good modeling and fitting of the EPR spectra has been shown to further improve the accuracy and precision of nail dosimetry.;In the final test, a large data set, simulating the field situation, has been studied. Good consistency has been obtained between the actual RIS and the estimated RIS determined from spectral analysis. In addition to the success in RIS estimation, we have also achieved linear dose response from 0 Gy to 6 Gy for each individual in this study.;These results have demonstrated the potential for EPR nail dosimetry, which can be readily implemented for direct measurement in the field or on nail samples transported to off-site laboratory in response to a medical emergency. |
