Nuclear Structure Studies by Direct Reaction Experiments with Stored Radioactive Beams

The experimental conditions at the next generation facilities for stored radioactive ion beams presently proposed or under construction will provide unique opportunities for nuclear structure studies on nuclei far off stability and will enable to explore completely new and unknown regions in the chart of nuclides. In particular, the predicted luminosities will allow for the investigation of direct reactions with stored and cooled radioactive beams in inverse kinematics using internal H, He, etc. targets. Such light-ion induced direct reactions, as for example elastic and inelastic scattering, transfer, charge exchange, or knock-out reactions, have been proved in the past, for the case of stable nuclei, to be powerful tools for obtaining nuclear structure information, and were also applied within the last decade for the investigation of light exotic nuclei with radioactive beams bombarding external targets. A brief overview on the physics program planned at the future NESR storage ring at GSI, the physics questions to be addressed, the dedicated reactions to be used, and the regions of interest in the chart of nuclides is given. The advantage of using stored beams and internal targets for such investigations will depend on the specific exotic nuclei and reactions chosen. This is discussed by a comparison of the conditions for the application of internal and external targets for reaction experiments with exotic beams. For the special case of elastic proton scattering at intermediate energies a feasibility study is presented, including a discussion of the experimental scenario. This method was applied recently for the investigation of nuclear matter distributions of the light neutron-rich halo nuclei 6,8He and 11Li using external targets. A few examples of the results are briefly discussed. The use of internal targets and stored beams will allow in future to extend such investigations to a wide range of medium heavy and heavy nuclei far off stability, and will therefore be one of the key reactions of the experimental program at the future NESR facility.