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 229 Th, was used as a yield tracer. Radium were preconcentrated from water samples by coprecipitation with BaSO 4 and 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 (NH 4 ) 2 C 2 O 4 at 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 -1 for 226 Ra, 228 Ra and 224 Ra, 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 -1 for 226 Ra, of 0.10-25.7 mBq . l -1 for 228 Ra, and of£LLD-7.97 mBq . l -1 for 224 Ra. The 228 Ra/ 226 Ra and 224 Ra/ 226 Ra ratios were in the range of 0.189-4.45 and£LLD-0.941, respectively.