Line-shape analysis of Doppler-broadened γ lines following the β decay of Li11

Abstract

The β decay of Li11 is studied at the TRIUMF Isotope Separation and Acceleration (ISAC) facility using the 8π γ-ray spectrometer coupled with an inner array of 20 plastic scintillators for β detection. Doppler-broadened line shapes resulting from the decay of the excited states in Be10 populated by β-delayed one-neutron emission are analyzed using Monte Carlo simulations. New β-delayed neutron decay branches are shown to contribute to the complex decay of Li11. The half-lives of all but one bound excited state in Be10 are also deduced from this work. Among them, the half-life of the 2- state in Be10 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- state in Be10 is an excited halo state. The nature of the 8.82-MeV state in Be11 and its decay paths to excited states in Be10 are found to be consistent with the β decay of the core proceeding through this particular state. © 2009 The American Physical Society.