Background: Single-particle and collective modes of nuclear excitation compete in the isotopes of the elements 30Zn, 32Ge, 34Se, 36Kr, and 38Sr. Purpose: To study the factors which determine the onset of collectivity in this region. Methods: Data obtained from National Nuclear Data Center compilations supplemented by recent measurements of excitation energies and B(E2) reduced transition probabilities between the low-lying states in these elements were examined. The data were analyzed as a function of the neutron number N as well as the parameter P=N pNn/(Np+Nn) related to the number of valence protons and neutrons, Np and Nn, in the 28≤Z,N≤50 shell. Results: The systematics of the data show variations ranging from mostly single-particle to collective excitations. Conclusions: Collectivity sets in when the number of both protons and neutrons lie near the middle of the shell 30≤Z,N≤50. Backbends appear in the data showing that particles and holes in the major shell behave differently. The 22+ states exhibit single particle behavior. The transition probabilities of the 22+ states in the Kr isotopes differ significantly from the systematics.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics