Detection, Estimation and Radiological Significance of Silver-110m in Oysters in the Irish Sea and the Blackwater Estuary

Abstract

THE Fisheries Radiobiological Laboratory of the Ministry of Agriculture, Fisheries and Food conducts extensive monitoring and research programmes in United Kingdom coastal waters¹ to measure the extent and significance of contamination of the marine environment resulting from radioactive waste discharges and from fallout from nuclear weapon tests. Oysters (Ostrea edulis) are occasionally sampled in the vicinity of the UKAEA spent-fuel reprocessing factory at Windscale as part of this programme; these are freeze-dried after removal of the shell, and their radioactivity is measured by gamma spectrometry. The gamma spectrum of oysters collected in June 1967 is shown in Fig. 1, in which the gamma photons associated with radioisotopes in the Windscale discharge can easily be identified: 0.14, 0.51, 0.62, 0.66 and 0.75. MeV from cerium-144 (and 141), ruthenium-106 (and 103), caesium-137 and zirconium-95/niobium-95. Two further gamma photons can, however, be seen at 0.89 and 1.12. MeV. The 1.12 MeV photon was ascribed to the presence of zinc-65, which is a neutron activation product from zinc impurity in the magnox cladding of spent fuel elements, and which is known both to be present in the liquid discharge from nuclear power station cooling ponds and to be reconcentrated to a high degree in oysters.