DEVELOPMENT OF A SEQUENTIAL METHOD FOR THE DETERMINATION OF U-238, U-234, TH-232, TH-228, RA-228, RA-226, AND PB-210 IN ENVIRONMENTAL-SAMPLES

A sequential analytical method for the determination of U-238, U-234, Th-232, Th-230, Th-228, Ra-228, Ra-226 and Pb-210 in environmental sam ples was developed. Uranium and thorium isotopes are first chromatogra phically separated using tri-n-octyl phosphine oxide (TOPO) supported on silica gel. The uranium isotopes are determined by alpha-spectromet ry following extraction with TOPO onto a polymeric membrane. Thorium i sotopes are co-precipitated with lanthanum fluoride before counting in an alpha spectrometer. Radium isotopes and Pb-210 are separated by co -precipitation/precipitation with mixed barium/lead sulphate. Radium-2 26 is determined by gross alpha counting of the final BaSO4 precipitat e and Ra-228 by gross beta counting of the same source. Lead-210 is de termined through beta counting of its daughter product Bi-210.