The effect of a neutron skin on the collective states of medium and heavy-mass nuclei is discussed. We consider two well-known collective modes which correspond to the motion of neutrons with respect to protons, namely, the M1 (scissors) and the isovector E1 (giant dipole) resonance. For nuclei with a sufficient excess of neutrons the behavior of the ‘‘pygmy resonance’’ is also discussed.

• Received 26 July 1991

DOI:https://doi.org/10.1103/PhysRevC.45.R13