Theoretical studies of He-8 beta-decay

According to selection rules the beta-decay of He-8 O-g.s.(+) to the first excited 1(+), 0.98 MeV state of Li-8 is an allowed Gamow-Teller transition, but it is strongly suppressed by the different SU(4) spin-isospin structure of the He-8 and Li-8 stares. We find that a three-body alpha + t + n model of Li-8 strongly underestimates the probability for beta-decay (to the Li-8 (0.98) state, Li-7 + n continuum and alpha + t + n continuum). A qualitative explanation of total B-GT values, extracted from experiment, to different 1(+) states can be given supposing an admixture of a ''democratic'' alpha + 4N configuration in the Li-8 wave functions. We show that the experimental beta-delayed neutron spectrum provides some evidence for the existence of 1(-) and/or 2(-) states in the vicinity of the two-body Li-7 + n and Li-7* (0.47) + n thresholds. Using the phase volume approximation to the analysis of the triton spectrum, the position of the Gamow-Teller resonance (Halo Analogue state) is estimated between 8.5 and 8.8 MeV excitation energy in the Li-8 spectrum. One of the possibilities to excite this state could be the Li-6(He-6,alpha)He-8* reaction.