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

Le résumé fourni par la source

The $\ensuremath{\beta}$ decay of $^{11}\mathrm{Li}$ is studied at the TRIUMF Isotope Separation and Acceleration (ISAC) facility using the $8\ensuremath{\pi} \ensuremath{\gamma}$-ray spectrometer coupled with an inner array of $20$ plastic scintillators for $\ensuremath{\beta}$ detection. Doppler-broadened line shapes resulting from the decay of the excited states in $^{10}\mathrm{Be}$ populated by $\ensuremath{\beta}$-delayed one-neutron emission are analyzed using Monte Carlo simulations. New $\ensuremath{\beta}$-delayed neutron decay branches are shown to contribute to the complex decay of $^{11}\mathrm{Li}$. The half-lives of all but one bound excited state in $^{10}\mathrm{Be}$ are also deduced from this work. Among them, the half-life of the ${2}^{\ensuremath{-}}$ state in $^{10}\mathrm{Be}$ 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 ${2}^{\ensuremath{-}}$ state in $^{10}\mathrm{Be}$ is an excited halo state. The nature of the $8.82$-MeV state in $^{11}\mathrm{Be}$ and its decay paths to excited states in $^{10}\mathrm{Be}$ are found to be consistent with the $\ensuremath{\beta}$ decay of the core proceeding through this particular state.

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