Simultaneous Determination of ²³⁴Th and ²²⁸Th in Environmental Samples using Cerenkov Counting

Abstract

A simple Cerenkov based method has been developed for the simultaneous determination of 228 Th and 234 Th via their betaemitting daughters, 212 Bi, 2,2 Pb, 208 T1, and 234m Pa. The thorium isotopes are concentrated along with other actinides by coprecipitation on ferric hydroxide which is then dissolved in 8 Μ HCl and passed through an änion exchange column (Dowex 1 X 4). The eluate, containing thorium isotopes, is evaporated and dissolved in 15 ml of 0.1 Μ HCl. For 234 Th determination, the sample is counted in a 22 ml plastic vial immediately after preparation using the tritium channel of a liquid scintillation counter while for 228 Th, the sample is recounted after one month when 228 Th has reached secular equilibrium with its daughters. Cerenkov counting efficiencies of 61.65% and 52.63% were observed for 234m Pa and the daughters of 228 Th respectively. Chemical recovery as high as 98% was obtained and a lower limit of detection of 1.41 mBql 1 (based on 3σ of the background with 500 min counting time) was achieved.