Determination of the isotope composition and content of U and Pu in environmental samples on the ultrasmall level by isotope dilution mass spectrometry

A procedure was developed for isolation and determination of the isotope composition and content of U and Pu on the ultrasmall level in environmental samples of technogenic origin, characterized by a small mass (up to 0.l g) and complex macrocomposition. The procedure is based on isotope dilution and mass-spectrometric measurement of the isotope ratios (IDMS). Subnanogram quantities of U and Pu were isolated using a modification of resin bead technique, involving sorption on a limited number of anion exchanger beads and allowing, after desorption, analysis of the solutions containing the selectively isolated nanogram quantities of U or 10 −12 −10 −15 g of Pu. The measurements were carried out on thermal ionization mass spectrometers manufactured in Ukraine and Russia with a modernized ion registration system utilizing a position-sensitive detector based on microchannel plates. Uranium was analyzed by the laser luminescence method suitable for measuring fractions of nanograms of U accurately to within 10%. This procedure, combining highly sensitive methods of isolation of ultrasmall quantities of U and Pu with the mass-spectrometric method of analysis, is applied at the Radium Institute (acting as a national laboratory of IAEA) and at the Institute of Analytical Instrument Designing, Russian Academy of Sciences, in analysis of inspection samples submitted by IAEA for monitoring the activity of nuclear facilities under the Treaty on Nonproliferation of Nuclear Weapons.