In-situ remotely controllable ocean radiation monitoring system

Abstract

Prompt in-situ monitoring of sea radiation contamination is crucial to prevent the sea from spreading radioactive materials to other parts of the world and the hazard of internal exposures in marine life and the human through food chain. In this paper, we evaluated the performance of a new ocean radiation monitoring robotic boat prototype system. The system featured real-time and on-site gamma spectroscopy with a portable detector of a CsI(Tl) crystal and a PIN diode carried by an unmanned surface vehicle. The system performed good energy linearity and energy resolution (21% at 662 keV). The efficiency and the minimum detectable activity (24 h acquisition) for underwater 137Cs detection were 1.334 × 10−5 and 2.5 Bq/kg, respectively. We conducted a Monte Carlo simulation to estimate the detection performance with uniform and point source distributions. In the water tank experiments, we measured the count rates with differing depths of a 137Cs point source. The maximum detectable distance was 50 cm according to both experiment and simulation results. Additionally, on-site experiment was conducted to test the operability of the system in a real sea. The overall study showed the feasibility of the system for in-situ ocean radiation monitoring.