Spectroscopic and reaction mechanism implications fromDy164(d,t)Dy163andEr166(d,t)Er165measurements

Angular distributions have been measured for transitions populating residual states of ${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$ and ${}_{}{}^{165}{}_{}{}^{}\mathrm{Er}$ through the ($d,t$) reaction at $E_d=17\mathrm{}$ MeV. Many of these angular distributions have shapes which are well reproduced by distorted wave Born approximation calculations which assume orbital angular momentum transfers $l$ which are compatible with the previously assigned spin-parities of the states. But a significant number of angular distributions are anomalous; i.e., either they cannot be fitted by 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 of the state. While the summed spectroscopic factors are in good agreement with Nilsson model expectations, there is considerable evidence of fragmentation of single-quasihole strength (most dramatically for ${}_{}{}^{164}{}_{}{}^{}\mathrm{Dy}$→${}_{}{}^{163}{}_{}{}^{}\mathrm{Dy}$ $l=0\mathrm{}$ transitions, 12 of which are observed) and the spectroscopic factors for several levels deviate significantly from Nilsson model predictions, even though Coriolis coupling has been included in the model calculation. This observation of several strongly anomalous angular distributions, along with large discrepancies between observed and model-predicted spectroscopic factors, almost certainly indicates that the assumption of a simple one-step direct reaction mechanism breaks down for some of these transitions. No evidence is found to indicate the position of the (expected strongly populated) ${7/2}^{+}$[404] state. Several other possible changes in previous Nilsson model assignments are indicated.