Nuclear matter distributions of neutron-rich halo nuclei from intermediate energy elastic proton scattering in inverse kinematics

Abstract

Neutron-rich light nuclei near or at the neutron drip line have attracted much attention in recent years since there is clear evidence that they reveal a qualitatively new type of nuclear structure, namely an extended distribution of valence neutrons surrounding a compact nuclear core. A brief overview is given on this phenomenon, and on the various methods which gave first evidence for, and qualitative confirmation of our present picture on halo nuclei. For gaining more quantitative information on the radial shape of halo nuclei, elastic proton scattering on neutron-rich light nuclei at intermediate energies was investigated for the first time. This method is demonstrated to be an effective means for obtaining accurate and detailed information on nuclear matter distributions and nuclear matter radii of halo nuclei. Data in the energy range around 700 MeV/u have been taken at GSI Darmstadt for the neutron-rich helium isotopes 6He and 8He and more recently for the lithium isotopes 6Li, 9Li and 11Li. The experimental method is based on the high-pressure hydrogen-filled ionization chamber IKAR which serves simultaneously as gas target and recoil proton detector. Projectile scattering angles were measured precisely with multiwire tracking detectors. For obtaining the nuclear matter distributions, the measured differential cross sections have been compared with cross sections calculated with the aid of the Glauber multiple-scattering theory, using various parametrizations for the nucleon density distributions as input. The results on the nuclear matter radii, the matter distributions, and the significance of the data for a halo structure are discussed. For 6He, 8He and for 11Li, in particular, the deduced nuclear matter distributions exhibit a fairly pronounced halo structure. The present data allow also a sensitive test for theoretical model calculations on the structure of neutron-rich helium and lithium isotopes. A few examples are presented.