Strong Neutron-γ Competition above the Neutron Threshold in the Decay of 70Co

The beta-decay intensity of Co-70 was measured for the first time using the technique of total absorption spectroscopy. The large beta-decay Q value [12.3( 3) MeV] offers a rare opportunity to study beta-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the beta intensity at high energies, as well as the strong competition between. rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed gamma-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global beta-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the beta-decay intensity is crucial for our understanding of nuclear structure as well as of gamma-process nucleosynthesis.