Competition between $\beta$-delayed proton and $\beta$-delayed $\gamma$ decay of the exotic $T_z$ = -2 nucleus $^{56}$Zn and fragmentation of the IAS

TL;DR

This paper reports the observation of a rare decay mode in the proton drip-line nucleus $^{56}$Zn, analyzing the competition between proton and gamma decays and exploring nuclear structure effects near $^{56}$Ni.

Contribution

It provides the first observation of $eta$-delayed $ ext{γ}$-proton decay and fragmentation of the IAS in $^{56}$Cu, offering insights into nuclear structure near doubly magic nuclei.

Findings

Observation of $eta$-delayed $ ext{γ}$-proton decay in $^{56}$Zn

First detection of IAS fragmentation in $^{56}$Cu

Determination of charge-dependent Hamiltonian matrix element

Abstract

A very exotic decay mode at the proton drip-line, $\beta$-delayed $\gamma$-proton decay, has been observed in the $\beta$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $\gamma$-proton sequences have been observed following the $\beta$ decay. The fragmentation of the IAS in $^{56}$Cu has also been observed for the first time. The results were reported in a recent publication. At the time of publication the authors were puzzled by the competition between proton and $\gamma$ decays from the main component of the IAS. Here we outline a possible explanation based on the nuclear structure properties of the three nuclei involved, namely $^{56}$Zn, $^{56}$Cu and $^{55}$Ni, close to the doubly magic nucleus $^{56}$Ni. From the fragmentation of the Fermi strength and the excitation energy of the two populated 0$^{+}$ states we could deduce the off-diagonal matrix element of the charge-dependent part of the Hamiltonian responsible for the mixing. These results are compared with the decay of $^{55}$Cu with one proton less than $^{56}$Zn. For completeness we summarise the results already published.