Chronology of accidental exposures based on differential thermoluminescence fading

A variety of Nuclear Safeguards measures, including periodic on-site inspections, are applied at the international level to verify that nuclear materials are not used for forbidden purposes by the States that are signatories to the Non-Proliferation Treaty. The need for maintaining the continuity of knowledge of safeguarded areas/items between two successive inspections has led to the development and implementation of containment and surveillance measures for unattended or remote monitoring. In this work, we assessed the feasibility of a passive, tamper-indicating device that, besides being able to record an undeclared removal of radioactive materials from a storage area, could provide information about the moment when such an illicit movement took place. The time- and temperature-dependent loss of signal occurring in luminescent materials with storage time adequately served the purpose. This concept was further explored for applications in accidental exposure scenarios, where precise timestamping is crucial for accurate dose reconstruction to support incident investigation and optimize medical intervention strategies. Differing from previous approaches that relied on comparing differently doped materials, we utilized a single material, LiF:Mg,Cu,P (GR-200A), employing two distinct methodologies: one based on series of equally responding crystals (±5%) and the other on the characterization of individual crystal fading behavior. The differential fading of peaks II and III of their glow curves, as compared to the stable dosimetric peak IV, provided a means to timestamp the moment of irradiation with reasonable uncertainty over, respectively, the first week and the first two months.