First direct lifetime measurement of the 2+1 state in 72,74Zn: new evidence for shape transition between N = 40 and N = 42 close to Z = 28

TL;DR

This study presents the first direct lifetime measurements of the 2+1 states in 72,74Zn, providing evidence for a shape transition and maximum collectivity at N=42 near Z=28, using advanced in-beam spectroscopy techniques.

Contribution

It offers the first direct lifetime data for 72,74Zn's 2+1 states, revealing shape evolution and collectivity maximum near N=42 in zinc isotopes.

Findings

Lifetimes of 17.9(18) and 27.0(24) ps for 72,74Zn 2+1 states.

Corresponding B(E2) values of 385(39) and 370(33) e2fm4.

Evidence for shape transition from spherical to gamma-softness at N=42.

Abstract

We report here the first direct lifetime measurement of the 2+1 state in 72,74Zn. The neutron-rich beam was produced by in-flight fragmentation of 76Ge at the Grand Acc\'el\'erateur National d'Ions Lourds and separated with the LISE spectrometer. The 2+1 state was excited by inelastic scattering and knock-out reaction on a CD2 target and its lifetime was measured by the recoil-distance Dopplershift method with the K\"oln plunger device combined with the EXOGAM detectors. The lifetimes of the 2+1 states in 72,74Zn were determined to be 17.9(18) and 27.0(24) ps, which correspond to reduced transition probabilities B(E2; 2+1 \rightarrow 0+) = 385(39) and 370(33) e2fm4, respectively. These values support the idea of a systematic maximum of collectivity at N = 42 for Zn, Ge and Se nuclei. In addition, the available systematics in the neighboring nuclei point towards a transition from a spherical oscillator at N = 40 to complete {\gamma}-softness at N = 42.