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 ef fects: (i) shifts of the single-particle levels of the order of 0.5 MeV tow ards the Fermi energy and thus to an increase of the level density, (ii) si ngle-particle state depopulation of the order of 30%, and thus spectroscopi c factors similar to 0.7, etc. These effects, which we have calculated for Yb-168, can be expressed in terms of an effective mass, the so-called omega mass (m(omega)), which is approximate to 40% larger than the bare nucleon mass in the ground state. It is found that m(omega) displays a strong depen dence with rotational frequency, eventually approaching the bare mass for ( h) over bar omega(rot) approximate to 0.5-0.6 MeV.