The Resolving Power of Calcite for X-Rays and the Natural Widths of the MolybdenumKαDoublet

Abstract

The half widths at half maximum of the rocking curves in parallel positions of the double x-ray spectrometer have been observed for the first five orders of reflection of $\mathrm{Mo}K{\ensuremath{\alpha}}_{1}$ from calcite. The calculated half widths for a single crystal have been compared with the theoretical results of Darwin and Ewald. The observed values are of the same order of magnitude as the theoretical, but slightly larger (1.4 times as large in the first order).The rocking curve widths in 8 anti-parallel positions for $\mathrm{Mo}K{\ensuremath{\alpha}}_{1}$ at 50 k.v. have been observed. Geometric corrections arising from the vertical spread of the beam have been applied. The half width at half maximum of $\mathrm{Mo}K{\ensuremath{\alpha}}_{1}$ has been found to be 0.147 X.U. corresponding to an energy width of 3.6 volts. The variation of this width with voltage from 25 to 50 k.v. has been studied, and no significant variation found. The half width at half maximum of $\mathrm{Mo}K{\ensuremath{\alpha}}_{2}$ at 50 k.v. was observed in 2 positions and found to be 0.161 X.U., the corresponding energy width being 3.9 volts. The observed difference between ${\ensuremath{\alpha}}_{1}$ and ${\ensuremath{\alpha}}_{2}$ is close to the experimental error and may not be real. The observed values are 2.5 times as great as the width to be expected from a classical electronic oscillator damped by its electromagnetic radiation.The computed life of the excited $K$ state of molybdenum is 1.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ seconds. No evidence of fine structure of $\mathrm{Mo}K{\ensuremath{\alpha}}_{1}$ or ${\ensuremath{\alpha}}_{2}$ was obtained.