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.