Total Absorption Spectroscopy of ⁷⁹Cu

⁷⁸Ni is a doubly magic nucleus far from stability, which was identified as an early “waiting point” for r-process nucleosynthesis. Recent measurements indicate that decays of nuclei beyond N=50 can be understood as the decay of the ⁷⁸Ni core, with the valence neutrons outside N=50 playing only a spectator role [1]. In this experiment, the focus was extended to also study the decay of nearby ⁷⁹Cu. The N=50 isotones near ⁷⁸Ni were studied for the first time using total-absorption spectroscopy, with the beta-decay strength distribution measured at the FRIB Decay Station initiator (FDSi). The experiment employed the Modular Total Absorption Spectrometer (MTAS) to measure complete γ-ray cascades following decays to neutron-bound states in ⁷⁹Cu. The isotopes were implanted at the second focal plane of the FDSi into a Yttrium Ortho-silicate(YSO) segmented scintillator detector system inside the MTAS. An ion-beta correlation was performed on the collected isotopes, and the optimal correlation radius was found to acquire the best signal-to-background ratio. Further analysis will be performed using the Geant4 simulations to obtain the MTAS response functions. A complete deconvolution of MTAS spectra allows for the extraction of β-decay strength distribution for ⁷⁹Cu. The experimental findings will be compared with the nuclear shell models to study the evolution of the N=50 shell closure in the region.

[1] M. Madurga et al., Phys. Rev. Lett. 117, 092502 (2016).