Determination of radium-226 in ores, nuclear wastes and environmental samples by high-resolution alpha spectrometry

Abstract

Management of radioactive wastes requires sensitive, accurate and reliable analytical procedures by which the radionuclides of interest can be determined in a wide variety of sample types. The determination of radium-226 by alpha spectrometry has been investigated critically to determine the exact experimental conditions necessary to achieve these objectives. Refractory solids such as soils, ores, and tailings from uranium mills are dissolved completely by fusion with potassium fluoride in the presence of barium-133 tracer. The fluoride cake is then transposed with sulfuric acid to a pyrosulfate fusion with simultaneous volatilization of all silica and fluoride. Radium is precipitated with barium already present in the sample by addition of lead perchlorate to a dilute hydrochloric acid solution of the pyrosulfate cake. The resulting insoluble sulfates are dissolved in an alkaline solution of diethylenetriaminepentaacetic acid, and the radium and barium sulfates are reprecipitated with acetic acid in the presence of a seeding suspension to produce very small crystals to minimize self-absorption of the alpha particles in getting out of the crystal lattice. The precipitate is mounted on a membrane filter with 0.1-micrometer pores and analyzed by alpha spectrometry. Resolution is about 60 keV full-width-half-maximum which is much better than has been achieved previously from barium sulfate and is as good as is obtained with actinides electrodeposited on polished steel plates. Recovery is over 95% and accuracy is generally as good as the counting statistics obtained will permit. Inaccuracies caused by the differences between radium and the barium tracer and the severe contamination of the detector caused by recoil and volatilization of polonium-210 have been virtually eliminated. Some data on radium-226 in wastes and environmental samples and methods for its removal are presented.