Comment on an improved critical angle equation for channeling

摘要

Recently, Li-Ping Zheng et al., proposed an improved critical angle equation for ion channeling [1,2]. In the comment, we show that the equation leads to a physically unrealistic result. If an ion (atomic number Z, atomic mass M) moving with energy E enters a crystal (atomic number z, atomic mass m) at small enough angle with respect to an atomic row (or string), the ion channeling could happen. Considering the conservation of transverse energy, Lindhard set the critical transverse energy, EΨ_c~2 equal to U_c and derived a formula to determine the critical angle Ψ_c for channeling [3],