A New Approach in ESR Tooth Enamel for Retrospective Dosimetry-Measurements of Spin-Spin Relaxation Time

Conducting a large-scale triage after major radiological events, such as nuclear reactor accidents or radiological terrorist attacks, requires fast, accurate, and non-invasive methods of dose estimation. The main challenge for retrospective biodosimetry (RBD) is to quantify exposures to ionizing radiation with doses in the range of 0.5–6 Gy, based only on monitoring their effects on the human body.

This study examines radiation-induced paramagnetic defects in the enamel layer of the human tooth using advanced pulse Electron Spin Resonance (ESR) methods, with the ultimate goal of applying these methods in RBD. ESR is a well-known method which can be used to detect and measure radiation-induced radicals in the enamel layer of the teeth. The concentration of these radicals in teeth is known to be linearly correlated with the dose in the applicable range. Despite its great potential and its proven results when applied to extracted teeth, ESR is still struggling to provide accurate in-vivo readings.

We use advance pulse ESR techniques in order to measure the relaxation time, T₂, related to the spin-spin interactions. The relationship between the radiation dose and T₂ was investigated. Our hypothesis is that this type of ESR data can be well correlated with the concentration of radicals, and can thus enable the development of new markers for an in-vivo estimation of the dose without the need for quantitative measurements of both the ESR signal and the enamel volume. In this study, we used teeth irradiated with relatively high doses of 10-100 Gy to develop the approach, which will be subsequently applied to measure relaxation times in samples irradiated with lower doses. Our measurements show dose dependence relaxation times in the range of hundreds of nanoseconds.