Interference effects in transition radiation near the threshold of Vavilov-Cherenkov radiation. V

The properties of transition radiation (TR) originating when a charged particle crosses the vacuum-transparent dielectric boundary has been analysed in detail. This made it possible to observe the interference effects between transition and Cherenkov radiations in a pure form. An unusual kind of angular distribution of TR photons (a distribution with a minimum) arising near the threshold of Vavilov-Cherenkov radiation and directed to a transparent medium has been observed. The shape of the total TR intensity due to the minima in the angular distributions of TR photons has also a peculiarity in the pre-threshold region (the total intensity is decreased with increasing γ). It is shown that this effect can be explained only after studying the radiation from a charge-image. The summed up TR emitted in a medium by a particle with β>1/n is a result of the interference of three radiations: TR from a particle, hybrid radiation (HR) from a particle and TR (or hybrid radiation) from a particle-image. It is shown that HR can be emitted from a charge-image. (Auth.)