The minimum yield of axial channeling and its half angular width in <100>, <110> and <111> cut Si wafers were investigated by the simultaneous observation of ion induced X-rays and backscattered ions. Helium ions at 0.25, 0.5, 1 and 2 MeV were used to cover a range of velocities and impact parameters in order to study the K and L shell X-ray production. Both minimum yield and half angle for Si K X-ray production are very similar to those for backscattering. The minimum yield for the Si L X-ray is considerably higher and the half angle is considerably narrower than those of backscattered ions. © 1978.