A procedure for the radiochemical determination of 228Th, 230Th, 232Th, 234U, 235U, and 238U in soil and sediment samples is described. The analytical method is based on the decomposition of the sample by fluoride-pyrosulphate fusion technique to allow total dissolution and chemical exchange between natural isotopes and added yield tracer nuclides. Uranium and thorium are coprecipitated as hydrolyzable metals with natural Fe and Al acting as carriers. Separation of thorium and uranium is carried out by reversed-phase chromatography using a column filled with Microthene impregnated with tri-n-octylphosphine oxide (TOPO) as stationary phase followed by final purification by anion exchange chromatography. Each fraction is electrodeposited and final measurements are made by alpha spectrometry with surface barrier detector. Overall chemical yields generally are better than 60%. For individual isotopes, the lower limit of detection at the 95% confidence level is 10 -3 Bq/g for a counting time of 1000'. One of the most important applications of the present procedure is its use in environmental monitoring, particularly in the vicinity of nuclear facilities and uranium mills, and for the study on the distributions and geochemical behaviors of natural actinides.

cited By 2