Parity-violation effect in heliumlike gadolinium and europium

Parity nonconservation that originates from the weak interaction of atomic electrons with the nuclei in heliumlike gadolinium and europium is considered. An experiment with a polarized ion beam is discussed. The mixed hyperfine- and weak-quenching effect in ${\mathrm{Gd}}^{62+}$ and ${\mathrm{Eu}}^{61+}$ isotopes is shown to lead to an asymmetry of the photon emission relative to the ion beam polarization. With complete beam polarization, the magnitude of the asymmetry in photon counting rates reaches about $0.39\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in gadolinium and is about $0.11\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in europium.