Line-shape analysis of Doppler-broadened [gamma] lines following the [beta] decay of [superscript 11]Li

Abstract

The [beta] decay of [superscript 11]Li is studied at the TRIUMF Isotope Separation and Acceleration (ISAC) facility using the 8[pi] [gamma]-ray spectrometer coupled with an inner array of 20 plastic scintillators for [beta] detection. Doppler-broadened line shapes resulting from the decay of the excited states in [superscript 10]Be populated by [beta]-delayed one-neutron emission are analyzed using Monte Carlo simulations. New [beta]-delayed neutron decay branches are shown to contribute to the complex decay of [superscript 11]Li. The half-lives of all but one bound excited state in [superscript 10]Be are also deduced from this work. Among them, the half-life of the 2[superscript −] state in [superscript 10]Be is shown to be much shorter than previously thought, yielding a new experimental B(E1) now well within the range of theoretical predictions and providing further evidence that the 2[superscript −] state in [superscript 10]Be is an excited halo state. The nature of the 8.82-MeV state in [superscript 11]Be and its decay paths to excited states in [superscript 10]Be are found to be consistent with the [beta] decay of the core proceeding through this particular state.