Mapping of the distribution of Cs-137 in Irish Sea sediments

The Sellafield nuclear fuel reprocessing plant released a total of 41 PBq o f Cs-137 into the Irish Sea in the period 1952-1998. The present work integ rates a series of surveys of the Cs-137 distribution in sediment offshore S ellafield which was aimed at obtaining a detailed picture of the patterns o f sediment contamination and their time evolution, and an estimate of the C s-137 inventory in sediment The authors applied NaI(Tl)based underwater gam ma -ray spectrometry to record a series of 1800 one-minute spectra along 14 transects totaling 160 Nm. The dominant feature of the contamination patte rn obtained from this survey remains a stripe extending northwestwards alon g the coast from the discharge point, as reported for previous surveys. Ste ep gradients are observed perpendicular to the coast, with Cs-137 countrate s decreasing to half the recorded maximum over a distance of less than 2000 m.