DETERMINATION OF SR-90 IN ENVIRONMENTAL-SAMPLES CONTAINING THORIUM

A method has been developed for the determination of Sr-90 at low acti vities in environmental samples that also contain thorium. Sr-90 is de termined by separating and measuring its progeny Y-90. Thorium is remo ved by liquid-liquid extraction using 5% tri-n-octylphosphine oxide (T OPO) In toluene. A second liquid-liquid extraction with tributyl phosp hate (TBP) is used to isolate Y-90 from Sr-90. Y-90 is then coprecipit ated with stable yttrium oxalate. The recovery of yttrium, determined by weighing the yttrium oxalate, is 65-85%. The radiochemically separa ted Y-90 is measured with a liquid scintillation analyzer using beta-l iquid 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.