Identification of significant $E0$ strength in the $2^+_2 \rightarrow 2^+_1$ transitions of $^{58, 60, 62}$Ni

TL;DR

This study measures the $E0$ transition strengths in $^{58,60,62}$Ni, revealing unexpectedly large values in nuclei with spherical ground states, using advanced gamma-ray detection and scattering techniques.

Contribution

First measurement of $E0$ transition strengths in $2^+_2 ightarrow 2^+_1$ transitions of nickel isotopes with spherical ground states, showing significant $E0$ strength.

Findings

$E0$ strengths are among the largest reported in medium-heavy nuclei.

$E0$ transition strengths are unexpectedly large in spherical nuclei.

New spectroscopic data obtained from inelastic scattering experiments.

Abstract

The $E0$ transition strength in the $2^+_2 \rightarrow 2^+_1$ transitions of $^{58,60,62}$Ni have been determined for the first time following a series of measurements at the Australian National University (ANU) and the University of Kentucky (UK). The CAESAR Compton-suppressed HPGe array and the Super-e solenoid at ANU were used to measure the $\delta(E2/M1)$ mixing ratio and internal conversion coefficient of each transition following inelastic proton scattering. Level half-lives, $\delta(E2/M1)$ mixing ratios and $\gamma$-ray branching ratios were measured at UK following inelastic neutron scattering. The new spectroscopic information was used to determine the $E0$ strengths. These are the first $2^+ \rightarrow 2^+$ $E0$ transition strengths measured in nuclei with spherical ground states and the $E0$ component is found to be unexpectedly large; in fact, these are amongst the largest $E0$ transition strengths in medium and heavy nuclei reported to date.