EXCITATION OF NUCLEAR ANHARMONIC VIBRATIONS IN HEAVY-ION FUSION REACTIONS

We discuss the effects of multiphonon excitations on heavy-ion fusion reactions at energies near and below the Coulomb barrier, focusing esp ecially on the role of anharmonicities. We carry out a systematic stud y of those effects on the excitation function of the fusion cross sect ion and on the fusion barrier distribution, by using the vibrational l imit of the interacting boson model. We also analyze the recently meas ured high-precision data of the O-16 + Sm-148 fusion reaction with thi s model and discuss the anharmonic properties of the quadrupole as wel l as the octupole vibrations in Sm-148. Negative and positive static q uadrupole moments are deduced for the first 2(+) and 3(-) states in Sm -148, respectively. It is shown that the fusion barrier distribution s trongly depends on the sign of the quadrupole moments, suggesting that subbarrier fusion reactions offer an alternative method to extract th e static quadrupole moments of phonon states in spherical nuclei.