Detection of radioactive particles offshore by γ-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 γ-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 105 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 (∼10 cm) and small detector–particle distances (<30 cm). Higher strength particles would be detectable at greater distance; the simulations indicate 50 cm for a 106 Bq source and 80 cm for 108 Bq at the same burial depth.