X-Ray Wavelength Conversion FactorΛ(λgλs)

A new experimental value of the x-ray conversion factor $\Lambda$ (mÅ/xu) has been obtained through a precision experiment on calcite crystals, and a recommended value of $\Lambda$ adopted based on this and other data. Nine selected crystals were used and the principal impurities determined by spectrochemical analysis. Grating constants were measured with the Cu $K{\alpha }_1$ and Ag $K{\alpha }_1$ emission lines, and the density of each crystal obtained by hydrostatic weighing in ethylene bromide. The product $\rho d^{\prime 3}$ for an ideal impurity-free crystal was then computed by a linear extrapolation, with a least-squares adjustment to determine coefficients. The geometrical volume factor $\Phi$ was found by experimental measurement of dihedral angles on five of the crystals. Combining these data with the best available values for atomic weight and Avogadro's number yields $N{\Lambda }^3=(6.05972\mathrm{}\pm 0.00015)\times {10}^{23}$ ${\mathrm{}\left(\mathrm{g}\mathrm{mole}\right)\mathrm{}}^{-1\mathrm{}}$ ${(\mathrm{m}\mathrm{\AA }/\mathrm{x}\mathrm{u})}^3$ and $\Lambda =1.002055\mathrm{}$ mÅ/xu, where the x unit is based on ${\lambda }_{\mathrm{Cu}K{\alpha }_1}=1537.400\mathrm{}$ xu. Taking a weighted average of this result and other high-precision data on $\Lambda$ has led to the adoption of $\Lambda =(1.002056\mathrm{}\pm 0.000005)$ mÅ/xu expressed on the same basis. The result becomes $\Lambda =(1.002076\mathrm{}\pm 0.000005)$ mÅ/xu when referred to an x-unit scale on which ${\lambda }_{\mathrm{W}K{\alpha }_1}=208.5770\mathrm{}$ xu. This last wavelength then becomes ${\lambda }_{\mathrm{W}K{\alpha }_1}=0.2090100\mathrm{}$ Å, which value has been adopted by the author as a wavelength standard.