EFFECTIVE PROTON-NEUTRON INTERACTION IN THE SINGLY CLOSED-SHELL REGION

The empirical effective proton-neutron interaction was investigated in the singly closed shell region. It was found that the quadrupole comp onent of the effective interaction is about twice as strong in this re gion as in the doubly magic one. The presence of the additional quadru pole-quadrupole interaction was explained as the first experimental ev idence for the existence of the polarization interaction predicted by Bohr and Mottelson as a second order consequence of the particle-vibra tion coupling. It was shown that the renormalization of higher order m ultipole coefficients is also necessary to take into account all effec ts of the particle-vibration coupling. We pointed out that this renorm alization can be approximated by lengthening the range of the effectiv e interaction.