Theory of relativistic positron and electron bremsstrahlung under channelling conditions

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Abstract
The theory of relativistic electron and positron bremsstrahlung depending on the impact parameter has been developed on the basis of the virtual photon method. This theory is used to calculate bremsstrahlung under channelling conditions. Common bremsstrahlung turned out to be suppressed in the case of relativistic positron channelling. The main mechanism of stopping is, here, the common bremsstrahlung by valence electrons and a specific radiation of channelled positrons considered recently by Kumakhov. Since energy losses connected with the radiation are (two to three) orders smaller than losses of bremsstrahlung in amorphous medium, our theory predicts an anomalous decrease of energy losses of channelled relativistic positrons. Estimates of the bremsstrahlung of electrons under channelling conditions show an increasing yield compared with the random yield that coincides with experimental results. An analysis has been made of physical differences between the Kumakhov radiation and coherent bremsstrahlung. The optimum conditions for observing the Kumakhov radiation have been found.