Luminescent sensors with differential fading for nuclear safeguards

In pursuing the nuclear safeguards objective of timely detecting the diversion of significant quantities of nuclear material to forbidden purposes, containment and surveillance (C/S) measures and monitoring address the need for maintaining the continuity of knowledge of a safeguarded area or item over the period between two successive inspections. However, unattended and remote-monitoring devices often comprise complex electronic components and circuits that make them potentially vulnerable to tampering and snooping. In this work, we assessed the feasibility of a passive, tamper-indicating device that should be able to record and, most importantly, timestamp a hypothetical undeclared removal of radioactive material from a storage area. The differential time- and temperature-dependent signal loss occurring in peaks II and III of the thermoluminescent curve of LiF:Mg,Cu,P appeared to serve the purpose adequately. We irradiated numerous batches of similarly responding (± 5%) GR-200A crystals using a 2.22 MBq Ra-226 radioactive source. We then staggered their readouts to reconstruct the time evolution of peak area ratios. In pilot testing, estimations of the time elapsed since exposure showed an uncertainty of ± 1 day and ± 1 week over, respectively, the 1st week and the first 2 months.