Three-body continuum structure and response functions of halo nuclei (I).: 6He

Three-body scattering states of the Borromean two-neutron halo nuclei are explored in a core + n + n model using the method of hyperspherical harmonics. We analyse the continuum structure (the properties of the continuum wave functions) separately from the continuum response (the magnitudes of one-step transitions from the ground state to the continuum). Predictions are made for the positions and strengths of the isoscalar monopole, electric dipole and quadrupole excitations, as well as for nuclear inelastic and charge-exchange response functions, for the He-6 nucleus. The known 2(+) resonance in He-6 is reproduced. We find 1(-) strength concentrations at lower energies in the proximity of the three-body threshold and predict new 2(+), 1(+) (and possibly 0(+)) resonances at slightly higher energies in He-6. (C) 1998 Elsevier Science B.V.