G. Zosi

A determination of the Avogadro constant

We have determined Avogadros constantNA using a direct method. The result ofNA=6.0221363×1023 mol−1 differs from the most recent CODATA value of 6.0221367×1023 mol−1 by only 0.07 ppm, the relative uncertainties being 1.1. ppm and 0.6 ppm, respectively. The value was derived from the determination of the lattice parameter, the density and the molar mass of a silicon single crystal. It will be possible in the future to further reduce the uncertainties of measurement by the procedure described here.

Combined optical and X–ray interferometry for high–precision dimensional metrology

The requirement for calibrating transducers having subnanometre displacement sensitivities stimulated the development of an instrument in which the displacement is measured by a combination of optical and X–ray interferometry. The need to combine both types of interferometry arises from the fact that optical interferometry enables displacements corresponding to whole numbers of optical fringes to be measured very precisely, but subdivision of an optical fringe may give rise to errors that are significant at the subnanometre level. The X–ray interferometer is used to subdivide the optical fringes. Traceability to the meter is achieved via traceable calibrations of the lattice parameter of silicon and of the laser frequency. Polarization encoding and phase modulation allow the optical interferometer to be precisely set on a specific position of the interference fringe—the null point setting. The null point settings in the interference fringe field correspond to dark or bright fringes. Null measurement ensures maximum possible noise rejection. However, polarization encoding makes the interferometer nonlinear, but all nonlinearity effects are effectively zero at the fringe set point. The X–ray interferometer provides the means for linear subdivision of optical fringes. Each X–ray fringe corresponds to a displacement that is equal to the lattice parameter of silicon, which is ca .0.19 nm for the (220) lattice planes. For displacements up to 1 m the measurement uncertainties at 95% confidence level are ± 30 pm, and for displacements up to 100 m and 1 mm the uncertainties are ± 35 and ± 170 pm, respectively. Important features of the instrument, which is located at the National Physical Laboratory, are the silicon monolith interferometer that both diffracts X–rays and forms part of the optical interferometer, a totally reflecting parabolic collimator for enhancing the usable X–ray flux and the servo–control for the interferometers.

phi and omega meson production in p p reactions at p(lab) = 3.67-GeV/c

The exclusive production cross sections for

A new determination of N/sub A/

\omega

Meson spectroscopy with antineutrons

and

Interferometric measurements of the diameters of a single‐crystal silicon sphere

\phi

Lattice parameter and thermal expansion of monocrystalline silicon

mesons have been measured in proton-proton reactions at

φ and ω meson production in n¯p annihilation and the OZI rule

p_{lab}=3.67

K- meson production in the proton proton reaction at 3.67-GeV/c

GeV/c. The observed

The Avogadro constant

\phi/\omega