Strong Two-Step Contributions in Direct Allowed Two-Nucleon Transfers

The $h_{\frac{9}{2}}{g}_{\frac{9}{2}}$ multiplet in ${}_{}{}^{210}{}_{}{}^{}\mathrm{Bi}$ was populated by ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\alpha , d)$ in experiments at 33 and 48 MeV. The strong favoring of the five unnatural-parity states of the multiplet disagrees with one-step transfer distorted-wave Born-approximation predictions. Coupled-reaction-channels calculations explain this effect as interference of direct $\mathrm{np}$ transfer and successive stripping amplitudes of comparable magnitude. This holds for weak (low-spin) and strong (high-spin) members of the multiplet.