@book{JRC41803,
	editor = {},
	address = {Northbrook, Illinois (United States of America)},
	year = {2007},
	author = {Wellum R and Verbruggen A and Eykens R and Richter S},
	isbn = {},
	abstract = {Over the last 5 years, IRMM has been developing new sets of isotope reference materials based on proven methods of purifying and mixing highly enriched oxides. In the first stage, oxides of 233U, 235U and 238U were purified and from these a set of 10 mixtures were made in which the 235U:238U ratios was 1:1 and the 233U abundance varied from 0.3 to 10-6 (IRMM-074). From the solutions of 235U and 238U a number of mixes (20%, 35%, 75%, 90% 235U enrichment) were also made to act as primary isotopic mixes for later calibration and certification of uranium isotopic standards jointly with DOE/NBL.
		Two further uranium materials were purified: a natural uranium and an enriched 236U oxide. From these materials a set of isotopic standards of 236U in natural uranium, with 236U abundances from 10-5 to 10-9 were made and certified. These were then verified against the new series IRMM-074. 
		From the 233U and 236U solutions a 1:1 spike has been made and certified. The advantage of this material was shown in the certification of the mixtures of 235U and 238U to measure the mass-fractionation on each filament measured by TIMS.
		The purification, mixing and certification of the new materials will be discussed and the application of these new reference materials in measurements of uranium by mass-spectrometry will be illustrated.
		},
	title = {The Uranium Isotope Mixing Program at the European Commission Institute for Reference Materials and Measurements, IRMM},
	url = {},
	volume = {},
	number = {},
	journal = {},
	pages = {1-5},
	issn = {},
	publisher = {Institute of Nuclear Materials Management},
	doi = {}
}