β-Delayed Deuteron Emission from 11Li: Decay of the Halo

The deuteron-emission channel in the beta decay of the halo nucleus Li-11 was measured at the Isotope Separator and Accelerator facility at TRIUMF by implanting postaccelerated Li-11 ions into a segmented silicon detector. The events of interest were identified by correlating the decays of Li-11 with those of the daughter nuclei. This method allowed the energy spectrum of the emitted deuterons to be extracted, free from contributions from other channels, and a precise value for the branching ratio B-d=1.30(13)x10(-4) to be deduced for E-c.m.> 200 keV. The results provide the first unambiguous experimental evidence that the decay takes place essentially in the halo of Li-11 and that it proceeds mainly to the Li-9+d continuum, opening up a new means to study the halo wave function of Li-11.