Precipitation of actinides as fluorides or hydroxides for 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. Procedures are given for precipitating and mounting all actinides from thorium through californium for high-resolution alpha spectrometry by two mutually complimentary systems. One system involves precipitation of fluorides from dilute acid in which most actinides can be separated from each other and from many common interferences by proper use of oxidizing and reducing agents. Elements forming strong fluoride complexes such as iron, titanium, zirconium, etc., do not interfere, but calcium interferes seriously. The other system involves precipitation of hydroxides from strongly alkaline solutions of ethylenediaminetetraacetic acid in which large quantities of calcium can be tolerated. More importantly, the latter system can be used to recover actinides coprecipitated with barium sulfate, which in turn permits use of potassium fluoride fusion to guarantee complete dissolution of the most refractory types of samples. Either system can be used to precipitate all actinides simultaneously to give a true gross alpha procedure. The resolution of the subsequent alpha spectra is typically 50 to 60 keV full-width-half-maximum with a 450 mm 2 detector at 25% counting efficiency which is almost as good as that obtained from sources prepared by electrodeposition onto polished steel plates. However, the procedures are much faster and generally give chemical yields greater than 98% much more reliably than are obtained with electrodeposition. Some results are given on the content of several actinides in ores, soils, mill tailings and other radioactive wastes. Also, some data and general conclusions are given on the leachability of transuranium elements from candidate wasteforms for long-term retention of radioactive wastes.