Determination of radium isotopes in mineral and environmental water samples by alpha-spectrometry

Summary  A method for the determination of low-level radium isotopes in mineral and environmental water samples by alpha-spectrometry has been developed. Radium-225, which is in equilibrium with its mother ²²⁹Th, was used as a yield tracer. Radium were preconcentrated from water samples by coprecipitation with BaSO₄and iron (III) hydroxide at pH 8-9 using ammonia solution, then isolated from uranium, thorium and iron using a Microthene-TOPO chromatography column at 8M HCl, separated from barium in a cation-exchange resin column using 0.05M 1,2-cyclohexylenedinitrilotetraacetic acid monohydrate at pH 8.5 as an eluant, and finally electrodeposited on a stainless steel disc in a medium of 0.17M (NH₄)₂C₂O₄at pH 2.6 and current density of 400 mA^. cm^-2, and counted bya-spectrometry. Optimum experimental conditions for radium separation, purification and electrodeposition have been studied and discussed in the paper. The lower limits of detection of the method are 0.11 mBq^. l^-1for ²²⁶Ra, ²²⁸Ra and ²²⁴Ra, respectively, if 2 l of water are analyzed. The method has been checked with a certified reference material IAEA-Soil-6 supplied by the International Atomic Energy Agency and reliable results were obtained. Eighteen water samples collected in Italy have been analyzed with the method, the mean radiochemical yields for radium were 86.2±6.5%. The obtained radium concentrations were in the range of 0.50-60.8 mBq^. l^-1for ²²⁶Ra, of 0.10-25.7 mBq^. l^-1for ²²⁸Ra, and of￡LLD-7.97 mBq^. l^-1for ²²⁴Ra. The ²²⁸Ra/²²⁶Ra and ²²⁴Ra/²²⁶Ra ratios were in the range of 0.189-4.45 and￡LLD-0.941, respectively.