The probability of photoionization of a heavy hydrogen like ion is calculated
within the relativistic perturbation theory. The Coulomb potential of a heavy
nucleus is taken into account accurately by usage of the corresponding
solutions of the Dirac equation. The obtained probability is compared with both
nonrelativistic limit and with nonperturbative results based on the numerical
solution of the time-dependent Dirac equation. Suppression of ionization is
observed in the secondary ionization channel at photon frequency of about
βΟβmc2.Comment: 15 pages, 5 figure