Systematics of low-lying state transition probabilities and excitation energies in the region30≤Z≤38and30≤N≤50

Abstract

Background: Single-particle and collective modes of nuclear excitation compete in the isotopes of the elements ${}_{30}$Zn, ${}_{32}$Ge, ${}_{34}$Se, ${}_{36}$Kr, and ${}_{38}$Sr.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 $P={N}_{p}{N}_{n}/({N}_{p}+{N}_{n})$ related to the number of valence protons and neutrons, ${N}_{p}$ and ${N}_{n}$, in the $28\ensuremath{\le}Z,N\ensuremath{\le}50$ 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 $30\ensuremath{\le}Z,N\ensuremath{\le}50$. Backbends appear in the data showing that particles and holes in the major shell behave differently. The ${2}_{2}^{+}$ states exhibit single particle behavior. The transition probabilities of the ${2}_{2}^{+}$ states in the Kr isotopes differ significantly from the systematics.