@article{JRC31029,
	address = {},
	year = {2005},
	author = {Richter S and Alonso Munoz A and De Bolle W and Kuehn H and Verbruggen A and Wellum R and Taylor P},
	abstract = {A set of 3 new synthetic uranium isotope mixtures with 236U/238U isotope ratios in the order of 10-6, 10-7 and 10-8 has been produced and certified for the isotopic composition. For the preparation of these 3 mixtures, a natural uranium starting material (235U/238U = 0.00725) is mixed in 3 different proportions with a non-natural starting material, which is for its part characterized by a 1:1 mixture of IRMM-187 (235U/238U = 0.0475) with a material highly enriched in 235U. The 236U/238U ratios of the 3 mixtures are calculated using the measured 236U/238U ratios of the natural (close to detection limit) and the non-natural starting materials. The 236U isotope intensity of the latter material was measured on a Faraday collector. The minor isotope abundances of the 3 mixtures were calculated from the minor isotope abundances of the starting materials and the measured 235U/238U ratios of the mixtures.
		Direct measurements of the 236U/238U ratios for all 3 mixtures were performed by TIMS using a secondary electron multiplier operated in ion counting mode to detect the 236U ion beam. The results agree well with the ratios obtained from the mixing calculations. This confirmation is considered a proof for the reliability to our TIMS procedure used to measure 236U/238U ratios within a wide dynamic range.
		Based on the confidence provided by the synthetic uranium isotope mixtures, the minor isotope ratios 234U/238U and 236U/238U were re-measured and re-certified by TIMS for the reference materials IRMM-183-187. On the new certificates for IRMM-183-187 the minor ratios 234U/238U and 236U/238U are certified with a ten times lower uncertainty compared to previous values.
		},
	title = {Preparation and Certification of Synthetic Uranium Isotope Mixtures with 236U/238U Ratios of 10-6, 10-7, 10-8},
	type = {},
	url = {},
	volume = {20},
	number = {},
	journal = {JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY},
	pages = {1381-1385},
	issn = {},
	publisher = {ROYAL SOC CHEMISTRY},
	doi = {}
}