• differential fading
• non-proliferation treaties
• nuclear safeguards
• tamper-proof Chain of Custody verification
• thermoluminescence

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 inspections has led to the development and implementation of containment and surveillance measures for unattended or remote monitoring. These form the framework for the present work, in which the feasibility was assessed of a passive, tamper-indicating device that, besides being able to record an undeclared removal of radioactive materials from a storage area, can provide the information about when such an illicit movement took place. The time- and temperature-dependent loss of signal occurring in luminescent materials with storage time was found to serve the purpose: the differential fading of the 2nd and 3rd peaks of the glow curve of LiF:Mg,Cu,P allow to timestamp an illicit movement of radioactive material with an uncertainty of ± 1 day and ± 1 week over, respectively, the first week and the first two months after irradiation. In addition, an analysis of the time evolution of the distribution of electrons trapped in the localized energy levels of the crystal lattice has unveiled what appears to be a shift towards deeper levels with increasing storage time due to radiation-less centre-to-centre transitions.