In-Situ Radionuclide Quantitative Characterization in Aquatic Ecosystems Using the KATERINA Detector

A new detection system, named 'KATERINA', based on NaI(Tl) crystal has been developed and applied for in-situ measurements of radioactivity in aquatic ecosystems. The detection system is designed for qualitative and quantitative radionuclide detection (gamma-ray emitters) in any aquatic environment (sea, groundwater, lakes, etc) with a maximum depth of deployment up to 400 m. It offers volumetric activities in absolute units (Bq/m³ or Bq/L) for all gamma-ray emitters in the energy range from the threshold energy of 50 keV up to 3,000 keV. The efficiency calibration in aquatic environment was first realized by dilution of three reference sources (^99mTc, ¹³⁷Cs and ⁴⁰K) inside a special tank filled with water and then it was simulated using the GEANT4 code. The system could be deployed immersed in two ways. Powered by batteries, it incorporates special memory and microcontroller operating autonomously in-situ as stand-alone unit acquiring and buffering data for periods up to three months without any maintenance. Alternatively, it can be installed into supporting floating stations (buoys) for longer period performing continuous in-situ measurements at sites where contamination by artificial and/or natural occurring radioactive materials could be observed (i.e. in regions with enhanced industrial fertilizer activities or other 'hot-spot' areas). Unlike laboratory methods, its continued operation into supporting floating stations makes it ideal to monitor radioactivity in real-time, enabling early warning in the case of a contamination event. Till nowadays, the detector has been deployed in autonomous mode, acquiring radon's daughters (²¹⁴Pb and ²¹⁴Bi) concentrations in several coastal regions around the Mediterranean Sea where submarine groundwater is discharged and also, over submarine magmatic regions of the Adriatic Sea, monitoring natural radioactivity. During these studies inter-comparison exercises were performed with standard laboratory methods (i.e. germanium detector techniques) obtaining satisfactory results. (author)