We present a method for smoothing discrete breakup S-matrix elements
calculated by the method of continuum-discretized coupled-channels (CDCC). This
smoothing method makes it possible to apply CDCC to four-body breakup
reactions. The reliability of the smoothing method is confirmed for two cases,
58Ni(d, pn) at 80 MeV and the E1 transition of 6He. We apply
CDCC with the smoothing method to 6He breakup reaction at 22.5 MeV.
Multi-step breakup processes are found to be important.Comment: 19 pages, 7 figures, published in Progress of Theoretical Physic