A compact, platform-agnostic system for underwater radioactivity detection

This work presents the development and evaluation of a compact underwater radioactivity detection system, named Mini KATERINA, designed to be integrated in platform-agnostic mobile robotic vehicles operating in controlled aquatic environments to identify radioactive sources. It employs a 2″ × 2″ NaI(Tl) scintillation crystal coupled to a silicon photomultiplier (SiPM), achieving reduced size, weight, and power consumption. The system was characterized in laboratory conditions using calibrated reference point sources and dedicated simulants (volume sources), enabling training and validation for the identification of suspicious objects. Initial performance assessment was conducted in a water tank to investigate detection capabilities as well as to perform calibrations in terms of energy, energy resolution and full energy peak efficiency. The calculated efficiency of the system for distances between source and detector surface at 4.5, 8.5 and 12.5 cm was 0.0038, 0.0016 and 0.00051, respectively. The limit of detection (LD) of the system at 662 keV for distances between source and detector surface at 4.5, 8.5 and 12.5 cm was 8, 17 and 54 Bq, respectively. Subsequently, field tests were performed in a marine environment to evaluate the limit of detection of a point source using a known radioactive simulant housed in a dedicated enclosure. The Limit of Detection of a point source (LD) of the system in this field configuration in the marine environment resulted a value of 43 Βq when the system is in a distance of 6 cm from the ¹³⁷Cs point source. The results demonstrate the system's effectiveness for underwater radiation monitoring and its potential integration into diverse mobile underwater platforms.