格子定数の絶対測定

概要

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There is no secondary standard of length established in the region of 10-10m. In the field of X-ray spectroscopy, x-unit, introduced by Siegbahn, was used as a relative scale of length. The x-unit was determined by the grating constant of calcite crystal. Since variation was observed among the lattice spacings of calcite crystals, wavelengths of certain X-ray lines, mainly CuKα1and MoKα1, were employed as empirical working standard. Discrepancy was found in the commonly used wavelength values of CuKα1 and MoKα1. Bearden introduced a new secondary standard A based on the peak wavelength of WKα1 line ( (WKα1) =0. 209 010 0A) . The absolute value of A, however, has no greater accuracy than the order of ppm. With X-ray/optical interferometer, Deslattes and co-workers have measured the grating constant of silicon α0in terms of optical wavelength (a0 (25°C) =0.543106 61 nm (±0.25 ppm) ) . They measured the densities and isotopic abundances for highly perfect silicon crystals. Finally they have determined the Avogadro constant NA=6. 022 0943×1023mol-1. This new NAreduced the uncertainty of previous direct measurements to one-thirtieth.
日本結晶学会の論文