An accurate determination of the Avogadro constant by counting the atoms in a 28Si crystal

The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant. We describe a new approach for its determination by "counting" the atoms in 1 kg single-crystal spheres, which are highly enriched with the 28Si isotope. It enabled isotope dilution mass spectroscopy to determine the molar mass of the silicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18) x 10^23 mol^-1, is the most accurate input datum for a new definition of the kilogram.Comment: 4 pages, 5 figures, 3 table

Characterisation of Conventional 87Sr/86Sr Isotope Ratios in Cement, Limestone and Slate Reference Materials Based on an Interlaboratory Comparison Study

An interlaboratory comparison (ILC) was organised to characterise 87Sr/86Sr isotope ratios in geological and industrial reference materials by applying the so-called conventional method for determining 87Sr/86Sr isotope ratios. Four cements (VDZ 100a, VDZ 200a, VDZ 300a, IAG OPC-1), one limestone (IAG CGL ML-3) and one slate (IAG OU-6) reference materials were selected, covering a wide range of naturally occurring Sr isotopic signatures. Thirteen laboratories received aliquots of these six reference materials together with a detailed technical protocol. The consensus values for the six reference materials and their associated measurement uncertainties were obtained by applying a Gaussian, linear mixed effects model fitted to all the measurement results. By combining the consensus values and their uncertainties with an uncertainty contribution for potential heterogeneity, reference values ranging from 0.708134 mol mol-1 to 0.729778 mol mol-1 were obtained with relative expanded uncertainties of ≤ 0.007 %. This study represents an ILC on conventional 87Sr/86Sr isotope ratios, within which metrological principles were considered and the compatibility of measurement results obtained by MC-ICP-MS and by MC-TIMS is demonstrated. The materials characterised in this study can be used as reference materials for validation and quality control purposes and to estimate measurement uncertainties in conventional 87Sr/86Sr isotope ratio measurement

Improved measurement results for the Avogadro constant using a 28Si-enriched crystal

New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New measurements were then made on these two reconditioned spheres using improved methods and apparatuses. When combined with other recently refined parameter measurements, the Avogadro constant derived from these new results has a value of $N_A = 6.022 140 76(12) \times 10^{23}$ mol$^{-1}$. The X-ray crystal density method has thus achieved the target relative standard uncertainty of $2.0 \times 10^{-8}$ necessary for the realization of the definition of the new kilogram.Comment: postprint, 22 page, 3 figures, 14 table

A new 28Si single crystal: counting the atoms for the new kilogram definition

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Entwicklung chemisch-analytischer Primaermethoden zur Bestimmung physiologisch relevanter anorganischer Bestandteile in Humanserum

SIGLEAvailable from TIB Hannover: RR 9173(19) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Novel Concept for the Mass Spectrometric Determination of Absolute Isotopic Abundances with Improved Measurement Uncertainty: Part 3 - Molar Mass of Silicon Highly Enriched in 28Si

A novel method of isotope amount ratio measurements using state-of-the-art techniques of a double focusing sector field mass spectrometer combined with isotope dilution mass spectrometry (IDMS) has been applied connecting analytical chemistry with metrology in chemistry aiming at the determination of the Avogadro constant (NA). The molar mass M(“Si28”) and the corresponding isotopic composition of an artificial silicon crystal material highly enriched in the 28Si isotope has been measured for the first time using a combination of a modified IDMS- and a multicollector-ICP-mass spectrometer (MC-ICPMS) technique. A value M(“Si28”) = 27.97697027(23) g/mol has been determined. This corresponds to a relative uncertainty urel = 8.2×10−9 (k = 1). From this silicon crystal material two 1 kg spheres were manufactured which are used by the International Avogadro Coordination (IAC) in order to reassess (NA) with an associated relative measurement uncertainty urel(NA) ≤1×10−8. The experiment presented here is the advancement and completion of parts 1 and 2 of this series of papers, describing the theoretical and general experimental applicability of the novel method. The current work summarizes the experimental findings aiming at the determination of the molar mass of the “Si28” material with the lowest uncertainty possible so far. The experimental prerequisites and bottlenecks for examining this highly enriched silicon material as well as experimental proofs for the verification of the presented results are described in detail. The experimental results are supplemented by an uncertainty budget according to the Guide to the Expression of Uncertainty in Measurement (GUM).JRC.D.4-Isotope measurement