Measurement of the {220} lattice-plane spacing of a ²⁸Si crystal

الأصل · EN

The spacing of the {220} lattice planes of a ²⁸Si crystal was measured by combined x-ray and optical interferometry to a 3.5× 10⁻⁹ relative accuracy. The result is d₂₂₀=(192014712.67 ± 0.67) am, at 20.0 and 0 Pa. This value is greater by (1.9464 ± 0.0067)× 10⁻⁹ d₂₂₀ than the spacing in natural Si, a difference which confirms quantum mechanics calculations. Subsequently, this crystal has been used to determine the Avogadro constant by counting the Si atoms, a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constants.