Beta-decays of  79,80,81Cu to the neutron-unbound states in 79,80,81Zn

Decays of Cu isotopes provide a laboratory to study the properties for nearly doubly-magic nuclei with a significant neutron excess which are also relevant for the r-process models. It can be shown that the beta-decay properties of doubly-magic 78Ni (N=50) are imprinted in the neighboring Cu decay, nuclei with a single proton outside the Z=28 core. The investigated isotopes 79,80,81Cu are strong beta-delayed neutron precursors, suggesting that their decay strength distribution lies above neutron separation energies in 79,80,81Zn daughters.

An experiment aiming to measure the beta-decay strength distribution in the 78Ni region (27≤Z≤33) was performed at the RIBF facility at RIKEN Nishina Center, JAPAN using a YSO-based implantation detector and VANDLE array for Time-of-Flight-based spectroscopy of the delayed neutrons.  I will present the first results of the β-decay strength distribution measurement from the decays of 79,80,81Cu to neutron-unbound states in respective daughter nuclei. Reconstruction of the feeding intensities requires analysis of neutron-gamma cascades, as is suggested by the statistical model. The results from the experiment are compared to shell-model calculations, with various sets of single-particle energies and residual interactions. Finally, predictions for 78Ni decay are made based on the model best-describing 79Cu.