X-Ray Wavelengths

Abstract

Inconsistencies in accepted values (in x units) of x-ray reference lines have recently been demonstrated, although all are supposedly based on "good" calcite crystals. Factors supporting the selection of the W $K{\ensuremath{\alpha}}_{1}$ line as the X-Ray Wavelength Standard are critically discussed. A review is given of the experimental measurements which are used to establish the wavelength of this line on an absolute angstrom basis. Its value is $\ensuremath{\lambda}$ W $K{\ensuremath{\alpha}}_{1}=(0.2090100\ifmmode\pm\else\textpm\fi{}5 \mathrm{ppm})$ \AA{}. This may be used to define a new unit, denoted by \AA{}*, such that the W $K{\ensuremath{\alpha}}_{1}$ wavelength is exactly 0.2090100 \AA{}*; hence 1\AA{}*=1\AA{}\ifmmode\pm\else\textpm\fi{}5 ppm. The wavelengths of the Ag $K{\ensuremath{\alpha}}_{1}$, Mo $K{\ensuremath{\alpha}}_{1}$, Cu $K{\ensuremath{\alpha}}_{1}$, and the Cr $K{\ensuremath{\alpha}}_{2}$ have been established as secondary standards with probable error of approximately one part per million. Sixty-one additional x-ray lines have been used as reference values in a comprehensive review and reevaluation of more than 2700 emission and absorption wavelengths. The recommended wavelength values are listed in \AA{}* units together with probable errors; corresponding energies are given in keV. A second table lists the wavelengths in numerical order, and likewise includes their energies in keV.