Effective nucleon mass in deformed nuclei

The coupling of vibrations to nucleons moving in levels lying close to the Fermi energy of deformed rotating nuclei is found to lead to a number of effects: (i) shifts of the single-particle levels of the order of 0.5 MeV towards the Fermi energy and thus to an increase of the level density, (ii) single-particle state depopulation of the order of 30 %, and thus spectroscopic factors ∼ 0.7, etc. These effects, which we have calculated for ¹⁶⁸Yb, can be expressed in terms of an effective mass, the so-called ? mass (m_ω), which is ≈40% larger than the bare nucleon mass in the ground state. It is found that m_ω displays a strong dependence with rotational frequency, eventually approaching the bare mass for hω_rot≈ 0.5-0.6 MeV .