Multi-step processes in the (d, t) and (d, 3He) reactions on 116Sn and 208Pb targets at Ed = 200 MeV

The role of multi-step processes in the reactions 116Sn(d,t), 208Pb(d,t) and 116Sn(d,3He), previously studied at Ed = 200 MeV at forward angles and for relatively low energy transfers, has been investigated. We have performed for the first time multi-step calculations taking into account systematically collective excitations in the second and higher order step inelastic transitions. A calculation code based on the Feshbach, Kerman and Koonin model has been modified to handle explicitly these collective excitations, most important in the forward angle domain. One step double differential pick-up cross sections were built from finite range distorted wave results spread in energy using known or estimated hole state characteristics. It is shown that two-step cross sections calculated using the above method compare rather well with those deduced via coupled channel calculations for the same collective excitations. The multi-step calculations performed up to 6 steps reproduce reasonably well the 115Sn, 207Pb and 115In experimental spectra measured up to Ex∼- 40 MeV and 15 deg. The relative contributions of steps of increasing order to pick-up cross sections at Ed = 200 MeV and 150 MeV are discussed. (authors)