
Total absorption spectroscopy is used to investigate the betadecay intensity to states above the neutron separation energy followed by gammaray emission in Br87,Br88 and Rb94. Accurate results are obtained thanks to a careful control of systematic errors. An unexpectedly large. intensity is observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The gamma branching as a function of excitation energy is compared to HauserFeshbach model calculations. For Br87 and Br88 the gamma branching reaches 57% and 20%, respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutronrich Rb94 the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled by introducing an enhancement of 1 order of magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutronrich nuclei, if it proves to be correct, leads to a similar increase in the (n, gamma) cross section that would have an impact on r process abundance calculations


Taín Enríquez, José Luis Valencia, Ebhelixes Algora, Alejandro Agramunt Ros, Jorge Rubio Barroso, Berta Estévez Aguado, María Esther Jordán Martín, María Dolores 2015 Enhanced gammaRay Emission from Neutron Unbound States Populated in beta Decay Physical Review Letters 115 6 062502 