Beta-delayed deuteron emission from (11)Li: decay of the halo.

The deuteron-emission channel in the {beta} decay of the halo nucleus {sup 11}Li was measured at the Isotope Separator and Accelerator facility at TRIUMF by implanting postaccelerated {sup 11}Li ions into a segmented silicon detector. The events of interest were identified by correlating the decays of {sup 11}Li 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{sub d}=1.30(13)x10{sup -4} to be deduced for E{sub c.m.}>200 keV. The results provide the first unambiguous experimental evidence that the decay takes place essentially in the halo of {sup 11}Li and that it proceeds mainly to the {sup 9}Li+d continuum, opening up a new means to study the halo wave function of {sup 11}Li.