Inadequacy of the Coupled-Channels Born Approximation for Explaining Anomalous Rare-Earth (d,t) Transitions

A CCBA (coupled-channels Born approximation) analysis is used to study the importance of multistep processes involving quadrupole inelastic excitations in producing anomalously shaped angular distributions for rare-earth ($d$,$t$) transitions. The CCBA results are compatible with DWBA (distorted-Wave Born approximation) results in the cases where the DWBA works well and tend to improve agreement for the anomalous transitions —but the overall agreement is still rather poor and additional improvements in the reaction calculations will be needed to understand the anomalous transitions.