This report describes the development and certification of IRMM-1000a and IRMM-1000b, a uranium reference material certified for the production date based on the 230Th/234U radiochronometer. The certified value was assigned following ISO Guide 34:2009 [ ].
The starting material was low-enriched uranium with a relative mass fraction, m(235U)/m(U) of 3.6%. The chemical separation of the 230Th decay product from its parent nuclide 234U to the maximum extent of completeness was achieved. The certified production date was confirmed using the 230Th/234U radiochronometer, and corresponds to the last chemical separation, i.e. the removal of 230Th from the material to the maximum extent achievable.
The between unit-homogeneity and the stability of the certified value were assessed in accordance with ISO Guide 35:2006 [ ].
The material was characterised by taking into account the date and time elapsed of the last chemical and complete separation of 230Th from 234U.
The completeness of the separation was confirmed firstly by determining the U/Th separation factors and uranium recoveries using -ray spectrometry, and then by means of ICP-MS measurements using a 232Th tracer. After sufficient ingrowth of thorium into the characterised uranium reference material, measurements of the 234U and the 230Th amount contents were carried out by isotope dilution mass spectrometry (IDMS) in compliance with ISO/IEC 17025:2005 [ ]). Subsequently, the determined n(230Th)/n(234U) was used in the calculation to confirm the certified production date.
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 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. There is no minimum sample intake to be taken into account.JRC.D.2-Standards for Innovation and sustainable Developmen
