The spacing of the {2 2 0} lattice planes of a 28Si crystal, used to determine the Avogadro constant by counting silicon atoms, was measured by combined x-ray and optical interferometry to a relative accuracy of 3.5 × 10-9. The result is d2 2 0 = (192 014 712.67 ± 0.67) am, at 20.0 °C and 0 Pa. This value is greater by (1.9464 ± 0.0067) × 10-6d2 2 0 than the spacing in natural Si, a difference which confirms quantum-mechanics calculations. This result is a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constant. © 2011 BIPM & IOP Publishing Ltd.
Measurement of the {2 2 0} lattice-plane spacing of a 28Si x-ray interferometer / Massa, Enrico; Mana, Giovanni; U., Kuetgens; L., Ferroglio. - In: METROLOGIA. - ISSN 0026-1394. - 48:(2011), pp. s37-s43. [10.1088/0026-1394/48/2/S06]
Measurement of the {2 2 0} lattice-plane spacing of a 28Si x-ray interferometer
MASSA, ENRICO;MANA, GIOVANNI;
2011
Abstract
The spacing of the {2 2 0} lattice planes of a 28Si crystal, used to determine the Avogadro constant by counting silicon atoms, was measured by combined x-ray and optical interferometry to a relative accuracy of 3.5 × 10-9. The result is d2 2 0 = (192 014 712.67 ± 0.67) am, at 20.0 °C and 0 Pa. This value is greater by (1.9464 ± 0.0067) × 10-6d2 2 0 than the spacing in natural Si, a difference which confirms quantum-mechanics calculations. This result is a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constant. © 2011 BIPM & IOP Publishing Ltd.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
