GDR EXCITATION BY ISOSCALAR PROBES - A MEANS TO DETERMINE THE NEUTRON-SKIN THICKNESS

Inelastic scattering of a-particles can excite the isovector giant dip ole resonance (GDR) via the Coulomb interaction. In spite of their iso scalar nature alpha-particles carl also excite the GDR via the nuclear interaction due to the difference in the radii of the neutron and pro ton density distributions. The absolute cross section to excite the GD R in inelastic alpha-scattering is therefore a measure of this radial difference, the so-called neutron-skin thickness. Furthermore, since t he GDR strength distribution has a centroid energy which depends on th e nuclear radius, these studies, when performed in deformed nuclei, ca n measure the neutron-skin thickness along both the short and the long axes independently. Results of an experiment performed at KVI at E-al pha = 120 MeV and small scattering angles, including 0 degrees, to det ermine the neutron-skin thickness in Pb-208, Sn-116, Sn-124, and the d eformed Nd-150 are discussed and compared to earlier measurements and theoretical predictions. Future improvements in the experimental set-u p are also discussed.