Comparison of the INRIM and PTB lattice-spacing standards

To base the kilogram definition on the atomic mass of the silicon 28 atom, the present relative uncertainty of the silicon 28 lattice parameter must lowered to 3E-9. To achieve this goal, a new experimental apparatus capable of a centimetre measurement-baseline has been made at the INRIM. The comparison between the determinations of the lattice parameter of crystals MO*4 of INRIM and WASO4.2a of PTB is intended to verify the measurement capabilities and to assess the limits of this experiment.Comment: 10 pages, 8 figures, submitted to Metrologi

measurement of the lattice parameter of a silicon crystal

The silicon crystal WASO04 is a reference in the adjustment of fundamental physical constants, but its lattice parameter has never been measured in absolute terms. In the framework of an international project meant to base the kilogram definition on the molar volume and the lattice parameter of 28Si, the WASO04 crystal has been used to manufacture an interferometer prototype for the performance testing and the fine-tuning of a new experimental apparatus for lattice parameter measurements by combined x-ray and optical interferometry. The present paper discusses the test results and gives an accurate lattice parameter determination. With respect to previous determinations, the value obtained, d220(WASO04)=192.015 570 2(10) pm, displays a four-fold improvement in accurracy

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

ELECTRONIC-STRUCTURE OF THIOMETALATES [MS4](N-) (M=MO, W, RE) - XANES SPECTRA AND SCF-X-ALPHA-SW CALCULATIONS

Müller A, Wittneben V, Diemann E, Hormes J, Kuetgens U. ELECTRONIC-STRUCTURE OF THIOMETALATES [MS4](N-) (M=MO, W, RE) - XANES SPECTRA AND SCF-X-ALPHA-SW CALCULATIONS. CHEMICAL PHYSICS LETTERS. 1994;225(4-6):359-363.Sulfur K-edge XANES spectra of PPh4+ salts of the title species are reported. Assignments for the characteristic positions in the spectra are given and discussed. The energies of the pre-edge peaks and the main absorption edges are used to determine the ''crystal-field' splitting energies DELTA, i.e. the energy difference between the 2e and 4t2 levels (1.4 eV for [ReS4]-, 1.1 eV for [WS4]2-and [MoS4]2-) and the energies of some frontier orbitals (HOMO-LUMO region). These data are compared with results from Xalpha calculations, electronic absorption and ESCA spectra

High resolution x‐ray absorption spectroscopy with absolute energy calibration for the determination of absorption edge energies

The general characteristics and spectrometric features of a high resolution four‐crystal reflection x‐ray monochromator with wavelength analysis installed at the HASYLAB beam line L at DESY are presented. The monochromator is part of a spectrometer developed to calibrate x‐ray absorption edge spectra in the energy range of 6–36 keV with a relative uncertainty ΔE/E from 10−5 to 10−6. This requires an extremely effective suppression of harmonics and also a negligible instrumental influence in order to obtain almost intrinsic spectra. As the results show, the monochromator fulfills the requirements, including very high stability. An example of the calibration procedure for the copper K edge is given as well as a comparison of the remeasured absorption edge energies with the previously tabulated data