X-Ray Wavelengths

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 K₁ 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 W K₁= (0. 20901005 ppm). This may be used to define a new unit, denoted by *, such that the W K₁ wavelength is exactly 0. 2090100 *; hence 1*=15 ppm. The wavelengths of the Ag K₁, Mo K₁, Cu K₁, and the Cr K₂ 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 * 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.