Preparation and certification of IRMM- 1000a (20 mg) and IRMM-1000b (50 mg) : certified uranium reference material for the production date

This report describes the production and certification of IRMM-1000a and IRMM-1000b, uranium reference materials certified for the production date based on the 230Th/234U radiochronometer, which corresponds to the last chemical separation, i.e. the removal of any 230Th from the material to the maximum extent achievable. The starting material was low-enriched uranium with a relative mass fraction, m(235U)/m(U) of 3.6 %. The targeted completeness for the last chemical separation of the 230Th decay product from its parent nuclide 234U was achieved. The certified production date was assigned following ISO Guide 34:2009. The between unit-homogeneity and the stability of the certified value were assessed in accordance with ISO Guide 35:2006. The uncertainty of the certified value was estimated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM) and includes uncertainties related to characterisation, possible inhomogeneity and instability. The material is mainly intended for calibration of methods, quality control, and assessment of method performance with isotope mass spectrometry and radiometry techniques. As any reference material, it can also be used for control charts or validation studies. The certified reference material is available in two sizes: 20 mg (IRMM-1000a) and 50 mg uranium (IRMM-1000b) as dried uranyl nitrate in screw-cap Teflon (PFA) vials.