Determination of radium isotopes in soil samples by alpha-spectrometry

A sensitive and accurate method for determination of radium isotopes in soil samples by α-spectrometry has been developed 225Ra, which is in equilibrium with its mother 229Th, was used as a yield tracer. Radium in soil samples was fused together with Na2CO3 and Na2O2 at 600 °C, leached with HNO3, HCl and HF, preconcentrated by coprecipitation with BaSO4, separated from uranium, thorium and iron using a Microthene-TOPO chromatographic column, isolated from barium in a cation-exchange resin column using 0.05M 1,2-cyclohexylene-dinitrilo-tetraacetic acid monohydrate as an eluant, electrodeposited on a stainless steel disc, and counted by α-spectrometry. The detection limit of the method is 0.43 Bq·kg−1 for 226Ra, 228Ra and 224Ra if 0.50 g of soil sample are analyzed. The method was checked with two certified reference materials supplied by the IAEA, and reliable results were obtained Fourteen soil samples collected from the refractory industry in Italy were also analyzed. The mean radiochemical yields for radium were 85.7±4.3%, and the obtained radium concentrations in the soil samples were in the range of 8.08–3878 Bq·kg−1 for 226Ra, of 1.60–678 Bq·kg−1 for 228Ra and 1.25–550 Bq·kg−1 for 224Ra, with 228Ra/226Ra and 224Ra/226Ra ratios ranged from 0.159–0.821 and from 0.142 to 0.525, respectively.