4 Electron Paramagnetic Resonance Dosimetry

Electron paramagnetic resonance (EPR), also termed electron spin resonance, is a spectroscopic technique known since the 1950s and used to detect and/or identify the sites of unpaired electrons in materials. These can be present in atoms, molecules, or molecular ions with incompletely filled atomic or molecular orbitals, and can be either endogenous such as in metals, or induced by processes such as oxidation (e.g., reactive oxidative species). Relevant to the current Report are those radicals induced by ionizing radiation. Electron paramagnetic resonance dosimetry for retrospective dose measurements performed a long time after a radiological incident has been described in ICRU Report 68 (ICRU, 2002). However, that report was limited to dosimetry using tooth enamel because this is the only material with radiation-induced EPR signals that are stable enough to maintain the information on radiation exposures for decades. Ionizing radiation generates radicals in several other materials, including glass, plastics, and keratinous tissues. Although these materials do not have EPR signals as sensitive and stable as those of tooth enamel, their ubiquity and the ease of sample acquisition make them very appealing for early-phase dose assessment in the aftermath of an acute radiation event. Ideally, a material for EPR dosimetry should have a minimum number of properties: