A simplified calculation of parity non conserving E1 transitions in the oscillator shell model

Contributions of excitations of the neutron core to the circular polarization of γ emitted in the transition $\text{5}\text{2}{}^{\mathrm{+}}\text{→}\text{7}\text{2}{}^{\mathrm{+}}\text{in}{}^{181}\text{Ta}$ are calculated. We show in a very simple model that these contributions are coherent and multiply by a factor 2 the polarizations calculated previously with proton-neutron parity-violating potentials.