Separation of U, Th, and Ra from silicates for uranium series dating by thermal ionisation mass spectrometry

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SR_1995-004-pdf
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Ditchburn, R.G. 1995 Separation of U, Th, and Ra from silicates for uranium series dating by thermal ionisation mass spectrometry . Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 95/04 12 p.


Abstract: A provisional method of separating U, Th, & Ra from 1 g of silicate has been developed as part of the collaborative program between the Nuclear Sciences Centre, GNS and the Department of Earth Sciences at the University of Queensland. Samples are decomposed in a mixture of hydrofluoric, hydrochloric and nitric acids. A series of evaporations with hydrochloric acid lowers the fluoride ion concentration. Residual fluoride is complexed when the sample is dissolved in equal volumes of saturated boric and hydrochloric acids. Uranium and iron are absorbed on an anion exchange column in the chloride form, the effluent being diluted and passed through a cation exchange column to absorb Ba, Ra, and Th. Most of the matrix elements are flushed through with 3M HCl. Barium and radium are eluted with 6M HCl and thorium with 40% HF. Uranium and thorium are both purified using anion exchange and 7M HNO/sub3. Barium and radium are separated by cation exchange with CDTA as the elutant and Ba/Ra atomic ratios of 10/sup3 - 10/sup4 are attainable, these being easily good enough for TIMS measurements. There is a possibility that protactinium will also be recovered via this method. (auth)