Detection of radioactive particles offshore by gamma-ray spectrometry - Part II: Monte Carlo assessment of acquisition times

This paper represents a supplementary study to Part I: Monte Carlo assessment of detection depth limits, aimed at estimating the acquisition times, required to detect radioactive particles offshore by towed gamma-ray spectrometry. Using Monte Carlo simulations, sets of measuring conditions were covered, addressing different types and sizes of scintillation detectors as well as variations in source strength, source-detector geometry and intensity of the natural gamma background. The performance of a large-volume BGO detector (12.7 cm diameter, 15 cm length) was assessed, to further enhance the sensitivity of simulated towed measurements. The simulations indicate that this detector represent a major step forward in detecting the radioactive particles offshore by gamma-ray spectrometry, particularly in a variable naturally radioactive background. With this detector, particles with an activity as low as 10(5) Bq should be detectable, at a towing speed of 2 knots (1 m/s), with an acquisition time of 2 s. However, detection of such particles is limited to relatively shallow burial depths (similar to10 cm) and small detector-particle distances