Determination of strontium-90 in environmental samples containing thorium

A method has been developed for the determination of Sr-90 at low activities in environmental samples that also contain thorium. Sr-90 is determined by separating and measuring its progeny Y-90. Thorium is removed by liquid-liquid extraction using 5% tri-n-octylphosphine oxide (TOPO) In toluene. A second liquid-liquid extraction with tributyl phosphate (TBP) is used to isolate Y-90 from Sr-90. Y-90 is then coprecipitated with stable yttrium oxalate. The recovery of yttrium, determined by weighing the yttrium oxalate, is 65-85%. The radiochemically separated Y-90 is measured with a liquid scintillation analyzer using beta-liquid scintillation counting or Cerenkov counting, For quality control Sr-90 was determined in IAEA reference materials. To demonstrate the applicability of the method, concentrations of Cs-137 and Sr-90 and Cs:Sr ratios are presented for contaminated surface soils from Maralinga. South Australia, and for coastal marine sediments from Port Phillip Bay, Victoria.