Quasi-free knockout reactions with high-energy radioactive beams


Thomas Aumann

Technical University Darmstadt,  Germany

The measurement of proton-induced reactions in complete kinematics will be an important part of the physics program at the future R3B  (Reactions with Relativistic Radioactive Beams) experiment at FAIR. In particular the quasi-free knockout processes of the type (p,2p), (p,pn), (p,pα) will be used to investigate the single-particle and cluster structure of neutron-proton asymmetric nuclei and the role of nucleon-nucleon correlations in nuclei.

At the present LAND/R3B setup we have performed experiments using a prototype installation for the detection of high-energy protons and neutrons in (p,2p) and (p,pn) reactions, respectively.  Recoil protons have been detected with an array of Si-Strip detectors and the 4π NaI spectrometer “Crystal Ball”. Measurements have been performed with a 12C beam as a benchmark as well as with the proton-dripline nucleus 17Ne.  For comparison, breakup of 17Ne induced by a carbon target has been studied as well in complete kinematics. For 12C, proton knockout from different single-particle states has been identified including knockout from the 0s state by reconstructing the excitation-energy spectrum of 11B utilizing γ spectroscopy and the invariant-mass method.  In case of proton knockout from 17Ne, the excitation energy of the unbound 16F clearly shows contributions from halo and core knockout.  From the analysis of the momentum distributions and cross sections the occupancies for the s and p configurations in the 17Ne ground state have been determined.  Examples for knockout reactions populating unbound states beyond the neutron dripline will be discussed as well.