Precision Gamma- and X-Ray Energies

Although no longer explicitly directed toward measurement of the Avogadro constant, we continue significant effort on lattice period measurement in monocrystalline silicon. There are currently operating an up-gradad xray/optical interferometer and a recently established lattice comparator. We report the status of measurements with these two instruments. Summarv Almost twenty years ago, several groups at NBS participated in a measurement of the Avogadro constant [l, 2 1. As in the case of efforts which are currently underway elsewhere, the NBS work involved optical interferometry of the spatial period of a Si monocrystal (as registered by x-ray interferometry), density determination using a dimensionally standardized artifact, and estimation of mean molar mass from absolute isotopic abundances. The result obtained was limited by imprecision and inaccuracy in density and molar mass to a claimed accuracy near 1 ppm while suffering from a large systematic error (1.8ppm) in the lattice spacing measurement which came to light through work at the PTB reported in and around 1980 [3, 41. Subsequently, the NBS x-ray/optical interferometry experiment, XROI, was re-established with several technical improvements, including on-line trajectory characterization. This latter capability showed, around 1986, that the original systematic error arose from an interplay of trajectory curvature, inadequate characterization of this curvature (by x-ray fringe contrast) and x-ray intensity distribution [5]. Through this work it became evident that a result of significantly improved accuracy could, in principle, be

show abstract

Precision Gamma- and X-Ray Energies

Cited by 2 publications

References 22 publications

Experimental aspects andZ-dependent systematics in one- and two-electron ions and single vacancy systems

Experimental aspects andZ-dependent systematics in one- and two-electron ions and single vacancy systems

Status of a silicon lattice measurement and dissemination exercise

Contact Info

Product

Resources

About