Abstract
Sudden two nucleon removal reactions on light, nuclear targets offer an excellent probe of the properties of exotic nuclei and are ideally suited to studying the evolution of nuclear structure far from stability. Here we extend the theoretical formalism for two-nucleon knockout to calculate heavy residue longitudinal momentum distributions, which are shown to be a sensitive probe of the total angular momentum of the nucleon pair. In tandem with γ-ray spectroscopy, residue momentum distribution measurements provide a powerful tool for the identification of final state spins in very exotic systems. The sensitivity of the residue momentum distributions with respect to the nucleon binding energy and other factors is investigated. Two-nucleon angular correlations are discussed, indicating that the total orbital angular momentum is key to determining the residue momentum distribution shape. In addition, this provides a further insight regarding subtle differences in the residue momentum distribution associated with the particular quantum numbers of the individual nucleons. Experimental sd-shell examples (22Mg(—2n), 38Si(—2p) and 28Mg(—2p)) are confronted and excellent agreement is obtained with experimentally measured residue momentum distributions. The application of knockout reactions to heavy systems is considered, using two-proton removal from 208Pb as an example. Experimental isomeric ratios for this reaction are reasonably reproduced and the complications in their calculation, due to the high density of residue states and absence of prompt γ-decay measurements, are highlighted. We also emphasise the importance of complete transmission of the full longitudinal momentum distribution of the residues in experiments measuring the isomeric ratios of high-spin states.