Single-nucleon knockout reactions at fragmentation beam energies

Abstract

Single-nucleon knockout reactions show considerable promise as a spectroscopic tool for mapping the migration of the dominant single-particle strength in rare isotopes, produced as fragmentation beams with energies > 40 MeV/nucleon. In this paper the theoretical assumptions which underpin the eikonal theory treatment of these reactions are reviewed. Certain sensitivities to input parameters are discussed, as are the possible importance of classes of higher order corrections. The eikonal model prediction for the elastic breakup component of the nucleon removal cross sections is also compared with that from fully-quantum mechanical calculations using the discretised continuum coupled channels method. An asymmetry, manifest in the experimental longitudinal momentum distributions of the ground state residues in weakly-bound-nucleon removal, is well reproduced. 1. INTRODUCTION An ability to map the evolution of the positions and order of nuclear single particle states in rare nuclei of high isospin will be an important component in developing our understanding and the reliability of structure models in these regions. The low intensities of secondary beams of these species, combined with the small number of excited states available in lighter systems, mean that conventional (but in inverse kinematics) lightion single-nucleon transfer reaction and gamma spectroscopic methods are non-trivial. Nucleon-knockout reactions appear to offer an alternative and complementary technique which is particularly well adapted for rare isotope beams produced using fragmentation. From a reaction theory point of view, it has been extremely fortuitous that many of the first generation facilities for the production of rare unstable nuclei have been based on nuclear fragmentation. The high secondary beam energies, and fast collisions with a secondary target, have allowed a rapid development and application of reaction methods, based on the sudden/adiabatic and/or eikonal-like approximations [1–8]. These lead to considerable simplifications and also practical and accurate calculation schemes which have relatively simple and physically transparent input parameters. This has allowed new experimental results to gain feedback rapidly from theory, and vice versa. Having said this, very little of the extensive literature to date has discussed possible schemes to obtain detailed spectroscopic information from data. To a large extent,