Nuclear forces violating parity and time reversal invariance ($\mathcal{P},\mathcal{T}$-odd) produce $\mathcal{P},\mathcal{T}$-odd nuclear moments, for example, the nuclear Schiff moment. In turn, this moment can induce the electric dipole moment in the atom. The nuclear Schiff moment is predicted to be enhanced in nuclei with static quadru pole and octupole deformation. The analogous suggestion of the enhanced contribution to the Schiff moment from the soft collective quadrupole and octupole vibrations in spherical nuclei is tested in this article in the framework of the quasiparticle random phase approximation with separable quadrupole and octupole forces applied to the odd ${}^{217-221}\mathrm{Ra}$ and ${}^{217-221}\mathrm{Rn}$ isotopes. In this framework, we confirm the existence of the enhancement effect due to the soft modes, but only in the limit when the frequencies of quadrupole and octupole vibrations are close to zero. According to the QRPA, in realistic cases the enhancement in spherical nuclei is strongly reduced by a small weight of the corresponding “particle + phonon” component in a complicated wave function of a soft nucleus. The perspectives of a better description of the structure of heavy soft nuclei are discussed.

• Received 20 February 2006

DOI:https://doi.org/10.1103/PhysRevC.74.025502