Analysis of theEr168(d,t)Er167reaction at 17 MeV

Angular distributions have been measured for transitions populating residual states of ${}_{}{}^{167}{}_{}{}^{}\mathrm{Er}$ through the ${}_{}{}^{168}{}_{}{}^{}\mathrm{Er}\mathrm{}(d,t)\mathrm{}$ reaction at $E_d=17\mathrm{}$ MeV. Many of these angular distributions have shapes which are well reproduced by distorted-wave Born-approximation calculations. A small but significant number of angular distributions are anomalous; i.e., either they do not resemble any reasonable distorted-wave Born-approximation calculation or they can only be fitted with a calculation which assumes an $l$ value incompatible with the previous Nilsson model assignment for the residual state. While the summed spectroscopic factors are in good agreement with Nilsson model expectations, there is considerable evidence of fragmentation of the single-quasihole strength and the spectroscopic factors for several levels deviate significantly from Nilsson model predictions, even though Coriolis coupling has been included in the model calculation. The observation of several strongly anomalous angular distributions almost certainly indicates that the assumption of a simple one-step direct reaction mechanism breaks down for some of these transitions. The discrepancies between the model prediction and the experimental spectroscopic factors could arise either from a multistep mechanism or from mixing of the simple quasihole states with more complicated states of the same spin-parity. The observed fragmentation of strength is strong evidence for such mixing.