title: Evidence of a systematic deviation of the isotopic composition of neon from commercial sources compared with its isotopic composition in air.
abstract: Results are reported of a study concerning the variation in isotopic composition of a limited number of neon samples of commercial origin and the resulting influence on the temperature of the triple point of this element. All seven neon samples investigated were found to contain more 22Ne than neon in air, and the amount fraction of 22Ne varied by as much as 0.2% from sample to sample. This variation corresponds to a range of triple-point temperatures (Ttp) of more than 200 microK, much larger than the state-of-the-art uncertainty in the realization of this phase transition for metrological purposes. Deviations in the amount fractions of 21Ne were irrelevant, as far as their effect on T(tp) is concerned, though they may have relevance to other isotope studies. Ratios of amounts of neon isotopes at IRMM-Geel were obtained using the same measurement procedures, and instrumentation developed in the framework of the redetermination of the Avogadro constant and all significant sources of uncertainty were taken into account. The repeatability of the ion current ratio measurements on individual samples was 5 x 10(-5) relative. All uncertainty statements are made following the ISO/BIPM Guide to the Expression of Uncertainty in Measurements. Whereas these results proved unexpected, a more comprehensive study will follow incorporating a much wider range of samples of commercial origin.
authors.forename: Franco
authors.initials: F
authors.lastname: Pavese
authors.forename: Bernd
authors.initials: B
authors.lastname: Fellmuth
authors.forename: David I
authors.initials: DI
authors.lastname: Head
authors.forename: Yves
authors.initials: Y
authors.lastname: Hermier
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Hill
authors.forename: Staf
authors.initials: S
authors.lastname: Valkiers