Search

Differential cross sections for p-Ni56 and p-Ni58 elastic scattering, measured at low momentum transfer and at projectile energies of about 400 MeV/u with beams stored in the Experimental Storage Ring (ESR) at GSI, Darmstadt, have been analyzed up to |t|=0.06 (GeV/c)2 applying the model-independent Sum-of-Gaussians (SOG) method based on the Glauber multiple-scattering theory. The rms point matter radius of the self-conjugate doubly magic radioactive Ni56 nucleus was deduced to be 3.62(6) fm, to be compared to the known radius of the stable Ni58 nucleus, 3.67(7) fm. Although the radii of both nuclei differ only slightly, and there is close agreement of the matter radii of Ni58 from former analyses using phenomenological parametrizations of the matter distribution, the SOG method was capable of elucidating pronounced differences in the shapes of the radial matter distributions between both nuclei. Consequences for the understanding of nuclear structure in the vicinity of the N=Z=28 magic shell are briefly discussed.

A new technique developed for measuring nuclear reactions at low momentum transfer with stored beams in inverse kinematics was successfully used to study isoscalar giant resonances. The experiment was carried out at the experimental heavy-ion storage ring (ESR) at the GSI facility using a stored 58Ni beam at 100 MeV/u and an internal helium gas-jet target. In these measurements, inelastically scattered α-recoils at very forward center-of-mass angles (θcm≤1.5°) were detected with a dedicated setup, including ultra-high vacuum compatible detectors. Experimental results indicate a dominant contribution of the isoscalar giant monopole resonance at this very forward angular range. It was found that the monopole contribution exhausts 79−11+12% of the energy-weighted sum rule (EWSR), which agrees with measurements performed in normal kinematics. This opens up the opportunity to investigate the giant resonances in a large domain of unstable and exotic nuclei in the near future. It is a fundamental milestone towards new nuclear reaction studies with stored ion beams. Keywords: Storage ring, Inverse kinematics, Isoscalar giant resonances