Estimation of the time of exposure from the differential fading of luminescent detectors

¹ School of Engineering, University of Pisa, Italy
² National Institute of Geophysics and Volcanology, Italy
³ S.C. Fisica Sanitaria Azienda Toscana Nord Ovest - Lucca, Italy
⁴ School of Public Health, Yale University, and Yale Center for Emergency Preparedness and Disaster Response, USA

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Published online: 6 November 2025

Abstract

Containment and surveillance measures for unattended or remotely monitored items and areas serve to detect, timestamp, and thereby deter the illicit movement and trafficking of radioactive material in the interval between two successive inspections. This study explores the feasibility of a passive solution that does not rely on complex electronic components, thus mitigating common vulnerabilities of active instruments, including risks of tampering and unauthorised data access. The signal loss in luminescent materials – dependent on both time and temperature and previously investigated as a means of estimating the time of exposure – proved applicable in this safeguards-relevant context as well. The differential fading of peaks II and III of the glow curve of LiF:Mg,Cu,P (GR-200A), compared to the stable dosimetric peak IV, provided a means to timestamp the moment of irradiation with reasonable accuracy in the shortand medium-term after exposure. While the analysis primarily focused on the behaviour of individual crystals, the averaging of multiple responses was also explored for comparison, to assess its potential for reducing estimation error.