Containment and surveillance (C/S) and monitoring are important measures to complement nuclear material accountancy and control (NMAC) in pursuing IAEA’s Nuclear Safeguards objective of timely detecting the diversion of significant quantities of nuclear material to proscribed purposes. They address the need for maintaining the continuity of knowledge of a safeguarded area or item over the period between two successive inspections, when an inspector is not physically present on site. However, devices for such unattended and remote monitoring are often made of complex electronic components and circuits which make them potentially vulnerable to tampering and snooping. In this work, we assessed the feasibility of a passive, tamper-indicating device which should be able to record and, most importantly, timestamp an undeclared removal of radioactive material that could possibly occur from a storage area. The differential time- and temperature-dependent loss of signal occurring in peaks II and III of the thermoluminescent curve of LiF:Mg,Cu,P appeared to adequately serve the purpose. We irradiated numerous batches of similarly responding (± 5%) GR-200A crystals using a 60 μCi Ra-226 radioactive source and staggered their readouts to reconstruct the time evolution of peak areas. The uncertainty affecting estimations of the time elapsed since irradiation in preliminary trials was found to be of ± 1 day and ± 1 week over, respectively, the first week and the first two months. In parallel, the decomposition of the obtained glow curves also allowed to calculate the kinetics parameters associated to the charge transfer process. Their statistical evaluation made it possible to reconstruct the distribution of the electrons trapped in the localized levels of the crystal lattice, unveiling what appears to be a shift towards deeper energy levels with increasing storage time. This suggests that radiation-less, centre-to-centre transitions occur within the fine structure of its trapping centres. At present, knowledge of the phenomenon is largely based on limited data and further investigation is currently ongoing. If confirmed, however, it will provide an additional method to establish the time elapsed after irradiation, which will back up what determined by calculations of peak area ratios and potentially reduce the uncertainty on the obtained results.
Luminescent sensors with differential fading for Nuclear Safeguards
Roina G.;Ciolini R.;d’Errico F.
2023-01-01
Abstract
Containment and surveillance (C/S) and monitoring are important measures to complement nuclear material accountancy and control (NMAC) in pursuing IAEA’s Nuclear Safeguards objective of timely detecting the diversion of significant quantities of nuclear material to proscribed purposes. They address the need for maintaining the continuity of knowledge of a safeguarded area or item over the period between two successive inspections, when an inspector is not physically present on site. However, devices for such unattended and remote monitoring are often made of complex electronic components and circuits which make them potentially vulnerable to tampering and snooping. In this work, we assessed the feasibility of a passive, tamper-indicating device which should be able to record and, most importantly, timestamp an undeclared removal of radioactive material that could possibly occur from a storage area. The differential time- and temperature-dependent loss of signal occurring in peaks II and III of the thermoluminescent curve of LiF:Mg,Cu,P appeared to adequately serve the purpose. We irradiated numerous batches of similarly responding (± 5%) GR-200A crystals using a 60 μCi Ra-226 radioactive source and staggered their readouts to reconstruct the time evolution of peak areas. The uncertainty affecting estimations of the time elapsed since irradiation in preliminary trials was found to be of ± 1 day and ± 1 week over, respectively, the first week and the first two months. In parallel, the decomposition of the obtained glow curves also allowed to calculate the kinetics parameters associated to the charge transfer process. Their statistical evaluation made it possible to reconstruct the distribution of the electrons trapped in the localized levels of the crystal lattice, unveiling what appears to be a shift towards deeper energy levels with increasing storage time. This suggests that radiation-less, centre-to-centre transitions occur within the fine structure of its trapping centres. At present, knowledge of the phenomenon is largely based on limited data and further investigation is currently ongoing. If confirmed, however, it will provide an additional method to establish the time elapsed after irradiation, which will back up what determined by calculations of peak area ratios and potentially reduce the uncertainty on the obtained results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
