X-Ray Wave-Lengths from Crystals and Ruled Gratings

Energies of photoelectrons ejected by x-rays from thin foils have been measured by Kretschmar and by Robinson and his colleagues, using the magnetic spectrograph. Their values are compared with those computed from wave-lengths of the incident rays and x-ray terms of the atoms in the foils, using (a) wave-lengths measured with crystals, based on the actual calcite spacing rather than the conventional one; (b) ruled grating wave-lengths, which are higher by 0.25 percent. Using Birge's value of $e$, 4.7668×${10}^{-10\mathrm{}}$ e.s.u., Bearden's value for the calcite spacing becomes (3027.91±1.0)${10}^{-11\mathrm{}}$ cm. To get photoelectron energies from crystal wave-lengths, accurate x-ray terms are worked out by a new plan, which avoids uncertainties involved in using absorption-edge wave-lengths. Term differences are obtained from x-ray line spectra, and are added to the value of some low term obtained from optical spectra. Birge's values of universal constants are employed in getting photoelectron energies. These energy values average 0.36 percent higher than those computed from crystal wave-lengths, or 0.61 percent higher than those from ruled-grating wave-lengths. This fact supports, but does not conclusively prove, the correctness of crystal wave-lengths based on the actual calcite grating space.