Evaluation of theoretical critical angle including mass effects for channeling by computer simulation

The calculated critical angles using the theory included mass effects of Zheng et al. for the axial channeling of ion have been investigated by the computer simulations, making comparisons with the theory of Lindhard and the precise formula of Barrett's numerical simulations. The computer simulations employing the ACOCT program code, which treats the atomic collisions three-dimensionally and is based on the binary collision approximation (BCA), were carried out for the channeling of He, Ne, Ar, Kr, Xe and Rn ions incident along the <1 0 0> axis in Al, Cu, Ag and Pt crystals. A slight dependence of the channeling critical angle on the atomic number of incident ion in the ACOCT results is in agreement with that in the calculated ones using the theory of mass effects. The average critical angles in the ACOCT results for the channeling of six rare gas ions are approximately 5.0/Z2 times the magnitude of the theoretical critical angles with mass effects, where Z2 is the atomic number of crystal atom. Besides, the results show that the calculated critical angles using the theory with mass effects are substantially larger than those using the theory of Lindhard, the Barrett's formula and the formula by the ACOCT simulations for He ions impinging on Al, Cu, Ag and Pt crystals, and that the channeling critical angles in the ACOCT results agree well with those in the calculated ones using Barrett's formula for 0.6-50 MeV He ions incident on Cu and Ag crystals and 5-50 MeV He ions impinging on Al and Pt crystals.