A vacuum double-crystal spectrometer for reference-free highly charged ions X-ray spectroscopy

We have built a vacuum double crystal spectrometer, which coupled to an electron-cyclotron resonance ion source, allows to measure low-energy x-ray transitions in highly-charged ions with accuracies of the order of a few parts per million. We describe in detail the instrument and its performances. Furthermore, we present a few spectra of transitions in Ar$^{14+}$, Ar$^{15+}$ and Ar$^{16+}$. We have developed an ab initio simulation code that allows us to obtain accurate line profiles. It can reproduce experimental spectra with unprecedented accuracy. The quality of the profiles allows the direct determination of line width.Comment: 21 pages; Version

Counting the Atoms in a 28Si Crystal for a New Kilogram Definition

This paper concerns an international research project aimed at determining the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The counting procedure was based on the measurement of the molar volume and the volume of an atom in two 1 kg crystal spheres. The novelty was the use of isotope dilution mass spectrometry as a new and very accurate method for the determination of the molar mass of enriched silicon. Because of an unexpected metallic contamination of the sphere surfaces, the relative measurement uncertainty, 3 × 10-8 NA, is larger by a factor 1.5 than that targeted. The measured value of the Avogadro constant, NA = 6.022 140 82(18) × 1023 mol-1, is the most accurate input datum for the kilogram redefinition and differs by 16 × 10-8 NA from the CODATA 2006 adjusted value. This value is midway between the NIST and NPL watt-balance values.JRC.DG.D.4-Isotope measurement