Channeling of MeVHe+Ions in Tungsten and Other Crystals: An Intercomparison of Rutherford Scattering and of CharacteristicLandMX-Ray Yields

Measurements of wide-angle (150°) scattering and of $L$ and $M$ x-ray yields in tungsten single crystals are reported as a function of crystallographic orientation with respect to an incident beam of 1.4-MeV helium ions. Comparison of these yields establishes both lower and upper limits for the minimum impact parameter ($r_{min}$) between a channeled ion and the tungsten-lattice atoms; these limits are consistent with Lindhard's estimate that $r_{min}\sim \mathrm{a}$, the Thomas-Fermi screening distance (i.e.,∼0.11 Å for He in W). A similar comparison between wide-angle scattering and x-ray yield curves is reported for several other lattices—Al, Si, GaP, GaSb, and U${\mathrm{O}}_2$; again the results are consistent with the predicted relationship: $r_{min}\sim \mathrm{a}$. Anomalies in published orientation studies of $K$, $L$, and $M$ x-ray yields are shown to be due to depth effects.