Determination of Strontium-90 in Environmental Samples Containing Thorium
Abstract
A method has been developed for the determination of 90Sr at low activities in environmental samples that also contain thorium. 90Sr is determined by separating and measuring its progeny 90Y. 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 90Y from 90Sr. 90Y is then coprecipitated with stable yttrium oxalate. The recovery of yttrium, determined by weighing the yttrium oxalate, is 65–85%. The radiochemically separated 90Y is measured with a liquid scintillation analyzer using beta-liquid scintillation counting or Cerenkov counting. For quality control 90Sr was determined in IAEA reference materials. To demonstrate the applicability of the method, concentrations of 137Cs and 90Sr and Cs:Sr ratios are presented for contaminated surface soils from Maralinga, South Australia, and for coastal marine sediments from Port Phillip Bay, Victoria.