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

• Published in: Physical review letters 2016
• Main Authors: Spyrou, Artemis, Liddick, Sean N, Naqvi, Farheen, Crider, Benjamin P, Dombos, Alexander C, Bleuel, Darren L, Brown, B.Alex, Couture, Aaron J, Crespo Campo, Lucia, Guttormsen, Magne Sveen, Larsen, Ann-Cecilie, Lewis, Rebecca, Möller, P, Mosby, Shea, Mumpower, Matthew R, Perdikakis, Georgios, Prokop, C. J, Renstrøm, Therese, Siem, Sunniva, Quinn, S. J, Valenta, S
• Format: Article
• Language: Norwegian
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.117.142701

The β-decay intensity of 70Co was measured for the first time using the technique of total absorption spectroscopy. The large β-decay Q value [12.3(3) MeV] offers a rare opportunity to study β-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the β intensity at high energies, as well as the strong competition between γ 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 γ-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global β-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 β-decay intensity is crucial for our understanding of nuclear structure as well as of r-process nucleosynthesis.