First measurement of β-decay strength to neutron-unbound states in the decay of Cu isotopes with N≥50*

Cu isotopes with N ≥ 50  lying on the r-process pathway offer a laboratory to study the nature of nuclear forces in nuclei with a large neutron-to-proton (N/Z) ratio and also engage in β-delayed neutron emission. Most of the β-decay strength from the decay of these nuclei is expected due to Gamow-Teller transitions above the neutron separation energy of the daughter nucleus. An experiment for measuring the 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 [1] and VANDLE [2] array for Time-of-Flight-based spectroscopy of the β-delayed neutrons. For γ-ray detection, two HPGe clovers and 10 LaBr₃  detectors were used. This contribution presents the first results on the β-decay feeding to neutron-unbound states in the decay of  ^79,80,81Cu. For ⁷⁹Cu decay, we identified neutrons in the energy range ~ 0.3-2.3 MeV, emitted from neutron-unbound states in ⁷⁹Zn. We also identified neutrons in coincidence with the 2⁺→0⁺ transition of 730 keV to the ground state in ⁷⁸Zn, needed to ascertain the excitation energy for strength distribution. For ^80,81Cu (N = 51,52), we report on the first measurement of the β-delayed neutron spectra. These measurements will highlight the impact of the N=50 shell-closure on β-decay.