Valence<i>p</i>-<i>n</i>interactions and the development of collectivity in heavy nuclei

Abstract

A universal, physically intuitive description of collectivity in heavy nuclei is obtained in terms of the parameter P=${N}_{p}$${N}_{n}$/(${N}_{p}$+${N}_{n}$) which gives the average number of interactions of each valence nucleon with those of the other type. Regardless of mass region, deformation sets in when P=${P}_{\mathrm{crit}\mathrm{\ensuremath{\approxeq}}4--}$5. This, in turn, gives a rule that medium-mass and heavy nuclei with effective ${N}_{p}$ or ${N}_{n}$\ensuremath{\le}4 cannot be deformed. An interpretation in terms of the monopole and quadrupole p-n interactions is discussed.