Gamma-delayed deuteron emission of the image halo state Original Research Article

M1 transitions from the View the MathML source state at 3.563 MeV to the View the MathML source ground state and to the α+d continuum are studied in a three-body model. The bound states are described as an α+n+p system in hyperspherical coordinates on a Lagrange mesh. The ground-state magnetic moment and the gamma width of the View the MathML source resonance are well reproduced. The halo-like structure of the View the MathML source resonance is confirmed and is probed by the M1 transition probability to the α+d continuum. The spectrum is sensitive to the description of the α+d phase shifts. The corresponding gamma width is around 1.0 meV, with optimal potentials. Charge symmetry is analyzed through a comparison with the β-delayed deuteron spectrum of 6He. In 6He, a nearly perfect cancellation effect between short-range and halo contributions was found. A similar analysis for the View the MathML source decay is performed; it shows that charge-symmetry breaking at large distances, due to the different binding energies and to different charges, reduces this effect. The present branching ratio Γγ(0+→α+d)/Γγ(0+→1+)≈1.3×10−4 should be observable with current experimental facilities.