A theory of the transition radiation and the transition pair creation is de
veloped in the frame of QED. The spectral-angular distributions of probabil
ity of the transition radiation and of the transition pair creation are fou
nd. The total energy losses of an electron and the total probability of pai
r creation by a photon are calculated and analyzed. Features of radiation a
nd pair creation processes in a superdense medium (typical for white dwarfs
) are discussed. (C) 1999 Published by Elsevier Science B.V.