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We discuss a parity nonconserving asymmetry in the cross section of KLL dielectronic recombination of polarized electrons on the hydrogen-like ions with Z < ∼ 60. This effect is strongly enhanced because of the near-degeneracy of doubly-excited 2l2l ′ states of opposite parity in He-like ions. For ions with Z ∼ 30 the asymmetry is of the order of 10 −9. For Z ≈ 48 a level crossing takes place, leading to the PNC asymmetry of −1.3 × 10 −8 , which is 10 8 times greater than the basic strength of the weak interaction in atoms.

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The cross section for single K-shell ionization by a high-energy photon is evaluated in the next-to-leading order of the nonrelativistic perturbation theory with respect to the electron-electron interaction. The screening corrections are of particular importance for light helium-like ions. Even in the case of neutral He atom, our analytical predictions turn out to be in good agreement with the numerical calculations performed with the use of the sophisticated wave functions. The universal high-energy behavior is studied for the ratio of double-to-single photoionization cross sections. We also discuss the fast convergence of the perturbation theory over the reversed nuclear charge number 1/Z.