Theoretical studies of 8He β-decay

Abstract

Abstract According to selection rules the β-decay of 8He 0g.s.+ to the first excited 1+, 0.98 MeV state of 8Li is an allowed Gamow-Teller transition, but it is strongly suppressed by the different SU(4) spin-isospin structure of the 8He and 8Li states. We find that a three-body α + t + n model of 8Li strongly underestimates the probability for β-decay (to the 8Li (0.98) state, 7 Li + n continuum and α + t + n continuum). A qualitative explanation of total BGT values, extracted from experiment, to different 1+ states can be given supposing an admixture of a “democratic” α + 4N configuration in the 8Li wave functions. We show that the experimental β-delayed neutron spectrum provides some evidence for the existence of 1− and/or 2− states in the vicinity of the two-body 7 Li + n and 7 Li ∗ (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 8Li spectrum. One of the possibilities to excite this state could be the 6Li(6He,α)8He∗ reaction.