Probing the Single-Particle Structure of Exotic Nuclei using Direct Reactions with Radioactive Ion Beams

An area of fundamental interest in nuclear physics is the isospin dependence of the single-particle properties of nuclei. This is expected to reflect modifications to the nuclear mean field, the residual interactions, the long- and short-range correlations and the single-particle occupancies that will arise in isospin-asymmetric nuclei. Experimental studies using direct reactions such as transfer, one-nucleon removal and quasifree scattering are now becoming possible, as a result of the development of beams of exotic nuclei with energies from a few MeV/nucleon to several GeV/nucleon. One-nucleon removal reactions with radioactive beams have been developed over the last decade as a new spectroscopic tool to extract single-particle properties of exotic nuclei such as the orbital angular momentum value of the wavefunction of the removed nucleon and the spectroscopic factors. We have recently undertaken one-neutron removal measurements with the SPEG/EXOGAM+NaI setup at GANIL to study light neutron-rich nuclei between Oxygen and Magnesium around N=16, an area of the nuclear chart which is currently attracting a lot of interest. Preliminary results, including inclusive and exclusive momentum distributions, will be presented. While transfer and one-nucleon removal reactions are sensitive primarily to the asymptotic part of the single-particle wavefunction, quasifree scattering reactions probe the wavefunction at the surface and also in the interior of the nucleus. The use of both hadronic and leptonic probes, e.g. (p,2p) and (e,e'p), have demonstrated conclusively the validity of the single-particle picture and given quantitative evidence of its limitations and the importance of long-and short-range nucleon-nucleon correlations in the nuclear many-body system. In the near future, the hadronic probe is more easily adaptable to the study of exotic nuclei. Preliminary results obtained for (p,2p) and (p,pn) reactions using 12C and 57Ni beams with the ALADIN/LAND setup at GSI will be presented.(author)