Publication Abstract

Association of 210Po (210Pb), 239+240Pu and 241Am with different mineral fractions of a beach sand at Seascale, Cumbria, UK

D. McCubbin, K. S. Leonard, B.A. Maher and E.I. Hamilton

A study has been carried out to assess the association of 210Po (in secular equilibrium with 210Pb), 239+240Pu and 241Am with the iron minerals in beach sand. Samples were obtained from Seascale beach (Cumbria), close to the BNF nuclear fuels reprocessing plant at Sellafield (UK), using panning and selective magnetic extraction techniques. Samples were physically and chemically characterised in terms oftheir grain size distribution, radionuclide content and magnetic properties. Low frequency (0.46kHz) susceptibility (c LF) and Saturated Isothermal Remanent Magnetisation (SMM) measurements were used to determine magnetic properties ofthe mineral fractions. It has been possible to estimate the efficiency ofthe magnetic extraction technique, from rock magnetic measurements, before and after the extraction procedure. Iron mineral particles, concentrated into placer deposits by environmental sorting processes, were considerably finer grained and more magnetic than the bulk sand. The mean particle diameter ofthe bulk sand (quartz) was largely (» 75%) greater than 200 [tm whereas the placer material was predominantly fine grained (>88% of particles with mean diameter <200g m). Magnetic property values ofthe 200-100 gm placer material were greater by » 40-50 fold than bulk sand of the equivalent grain size, whilst radionuclide concentrations were greater by » 4-13 fold. The percentage of material extracted from samples ofbulk sand, using a powerful rare earth magnet (» 0.3 T) in terms ofmass was small (» 1-3%). Nevertheless, the magnetic signal was largely associated (>70%) with these extracts. Concentrations of all three radionuclides in the magnetic extracts were significantly enhanced relative to the residue material, following extraction. The proportions of 210Po(210Pb), 239+240Pu and 241Am associated with the magnetic mineral extracts were » 18%, » 13% and » 12%, respectively. Therefore, although the magnetic iron minerals contain measurably enhanced levels ofthese radionuclides, the majority of radioactivity is associated with the weakly magnetic residue.

Reference:

D. McCubbin, K. S. Leonard, B.A. Maher and E.I. Hamilton, 1999. Association of 210Po (210Pb), 239+240Pu and 241Am with different mineral fractions of a beach sand at Seascale, Cumbria, UK. Science of the Total Environment, 254(1): 1-15