Competition between β-delayed proton and β-delayed γ decay of the exotic Tz = −2 nucleus 56Zn and fragmentation of the IAS

Expérience GANIL/LISE3International audienceA very exotic decay mode at the proton drip-line, β-delayed γ-proton decay, has been observed in the β decay of the Tz = −2 nucleus $^{56}$Zn. Three γ-proton sequences have been observed following the β 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 γ 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