Systematics of low-lying state transition probabilities and excitation energies in the region $30\ensuremath{\le}Z\ensuremath{\le}38$ and $30\ensuremath{\le}N\ensuremath{\le}50$

Systematics of low-lying state transition probabilities and excitation energies in the region $30 \leq Z \leq 38$ and $30 \leq N \leq 50$

S. L. Rice, Y. Y. Sharon, N. Benczer-Koller, G. J. Kumbartzki, and L. Zamick

Phys. Rev. C 88, 044334 – Published 31 October 2013

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 $B (E 2)$ 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 $28 \leq Z, N \leq 50$ 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 $30 \leq Z, N \leq 50$ . 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.