Low-energy neutron capture reactions via the surrogate method

Indirect methods, such as the surrogate approach, play a crucial role in determining cross sections for reactions on unstable nuclei. In a surrogate experiment, the compound nucleus of interest is produced using a light-ion direct reaction on a target that is easier to produce. The decay of the compound nucleus is measured in coincidence with the outgoing direct-reaction particle and the coincidence probabilities are used to infer the desired cross sections. The method is expected to play an important role in cross-section measurements with radioactive ion beams (RIBs), since inverse-kinematics experiments cannot be performed on a neutron target. For example, if one measures (d,p$\gamma$) instead of (n,$\gamma$), one carries out a surrogate measurement. To make full use of radioactive-beam capabilities, the inverse-kinematics surrogate method needs to be developed further. This presentation summarizes recent applications of the surrogate approach to (n,$\gamma$) reactions. The limitations of frequently-employed approximation schemes will be discussed, as well as progress made in moving beyond these limitations. Results will be shown for the gadolinium region.