IRMM-3100a: A new certified isotopic reference material with equal abundances of 233U, 235U, 236U and 238U

Abstract

The new so-called Quad-IRM (“Quadruple Isotope Reference Material”) was prepared from highly enriched 233U, 235U, 236U and 238U isotopic materials using an optimized combination of gravimetrical mixing and mass spectrometry. Within the mixing process the isotope ratios were adjusted to about n( 233U)/ n( 235U)/ n( 236U)/ n( 238U) = 1/1/1/1 and certified with expanded relative uncertainties of 0.0054% per mass unit (coverage factor k = 2). This new isotope reference material is ideal for verifying the inter-calibration of multi-detector systems in isotope mass spectrometry. The certified n( 233U)/ n( 236U) ratio of IRMM-3100a was derived from the mass metrology data of the gravimetrical mixing of highly enriched 233U and 236U materials. It was verified by thermal ionization mass spectrometry (TIMS) measurements using the classical total evaporation (TE) and modified total evaporation (MTE) methods. The n( 234U)/ n( 236U), n( 235U)/ n( 236U) and n( 238U)/ n( 236U) ratios were then determined by TIMS using the n( 233U)/ n( 236U) ratio for internal normalization and using a multi-dynamic measurement procedure in order to circumvent any possible influence and uncertainties from Faraday cup efficiencies and amplifier gain factors. The certified n( 235U)/ n( 236U) and n( 238U)/ n( 236U) ratios were additionally verified using the classical and modified total evaporation methods using two TIMS instruments at IRMM and one TIMS instrument at IAEA-SGAS. The verification data can be regarded as results obtained at three independent instruments at two different nuclear safeguards laboratories.