Study of various approximations for the continuum planar potentials at channeling. 1

A detailed analysis of different approximations for the continuum planar potentials under the channeling conditions is given. The continuum potentials for positrons (electrons) channeled in (110) and (100) planes in crystals of diamond, silicon, and tungsten are calculated in different approximations to the screening function. The model of an atom with a piecewise exponentially decaying electron density is discussed. The influence of the thermal vibrations and the atomic shell structure on the potentials is investigated. Some estimates of the photon energy radiated at channeling of 56 MeV electrons in (110) planes of C are given. (author)