Excitation of the GDR and the compressional isoscalar dipole state by alpha scattering

The excitation of the isovector giant dipole resonance (GDR) by alpha scatt ering is investigated as a method of probing the neutron excess in exotic n uclei. DWBA calculations are presented for O-28 and Ca-70 and the interplay of Coulomb and nuclear excitation is discussed. Since the magnitude of the Coulomb excitation amplitude is strongly influenced by the Q-value, the ne utron excess plays an important role, as it tends to lower the energy of th e GDR. The excitation of the compressional isoscalar dipole state in Ca-70 by alpha scattering is also investigated. It is shown that the population o f this latter state may be an even more sensitive probe of the neutron skin than the isovector GDR.