The effective neutron-proton interaction in rare-earth nuclei

The available experimental information concerning the low-lying rotational-band energies in rare-earth nuclei with odd neutron and proton numbers is analysed within the framework of the unified model. 69 empirical values are extracted for 51 two-particle matrix elements of the effective neutron-proton interaction in 16 nuclei. This information deals with 43 two-quasi-particle configurations. Strength and range parameters for various types of effective interaction are determined from least-squares fits of calculated matrix elements to the empirical values. A significant improvement in the fit is found when spin-polarized and long-range components are included in the effective force, indicating the importance of core-polarization effects. The sensitivity of the calculation to the choice of experimental information, to the single-particle model, and to the radial shape of the force is investigated. Some predictions are made concerning as yet unconfirmed or unobserved configurations. (Auth.)