Excitation of the isovector GDR by inelastic α-scattering as a measure of the neutron skin of nuclei

The cross section of the isovector giant dipole resonance (GDR) has been measured in the Sn-116, Sn-124(alpha, alpha'gamma0), 150Nd(alpha, alpha'gamma0) and Pb-208(alpha, alpha'gamma0) reactions at E(alpha) = 120 MeV and 0-degrees less-than-or-equal-to THETA(alpha') less-than-or-equal-to 3-degrees. The results are compared with DWBA calculations performed with nuclear GDR form factors that depend on the relative difference between the radii of proton and neutron distributions (DELTAR(PN)/R0). Taking a linear combination of form factors provided by the Gold-haber-Teller and Steinwedel-Jensen models in a ratio that fits the GDR systematics, the DELTAR(PN) Values for Sn-116, 124Sn and Pb-208 were deduced by comparing measured and calculated cross sections to be 0.02 +/- 0.12 fm, 0.21 +/- 0. 11 fm, and 0. 19 +/- 0.09 fm, respectively. For the deformed 150Nd, the neutron-skin thickness along and perpendicular to the symmetry axis was found to be 0.22 +/- 0.16 and 0.50 +/- 0.15 fm, respectively, yielding beta2n/beta2p = 0.92 +/- 0.08