Accepted Wednesday Oct 28, 2009
The deuteron-emission branch of the b-decay of the halo-nucleus has been measured using the technique of implantation in a highly-segmented silicon detector. The method, used here for the first time with a beam of ions, ensured a precise normalization; the value obtained for the branching ratio is [`B] = (1.65 0.10)×10-6 (6% error). The summed energy spectrum of the emitted a and d particles has also been measured. The results allow a comparison between calculations from various models, potentially setting strong constraints on the precision required for the description of the ground-state wave function.