Channeling dips for outer-shell X-ray yields

Abstract

The sensitivity of channeling dips to small ‘displacements’ of atoms from lattice sites has been investigated by measuring axial and planar dips in tungsten M X-ray yield and comparing with dips in Rutherford-backscattering yield. In comparison with an earlier investigation, the sensitivity was improved by cooling the crystal to 40 K. Since the width of the ionization probability as a function of impact parameter depends on projectile velocity, the effective ‘displacement’ could be changed by varying the projectile energy and mass. Except for the lowest velocity, differences in minimum yield as well as in width are clearly observed for the axial dips. The results imply that for very small displacements, the effect is most easily observed in the width. Furthermore, planar dips are less sensitive than axial dips. The results are compared in detail with predictions based on the calculated dependence of the ionization probability on impact parameter, and possible implications are discussed for the analysis of crystal-blocking measurements of short nuclear lifetimes.