Heavy-ion fusion reaction as a quantum tunneling microscope

Heavy-ion fusion reactions take place via quantum tunneling when the incident energy is below the Coulomb barrier. Since the tunneling probability depends on the barrier height exponentially, the fusion cross section is sensitive to the nuclear intrinsic degrees of freedom such as deformation, rotation and vibrational modes of excitation of the target and/or projectile nuclei. It has been recognised that the effects of coupling of the relative motion between the colliding nuclei to nuclear intrinsic degrees of freedom can be well expressed in terms of a distribution of potential barriers. This has opened up the possibility of using the heavy-ion fusion reaction as a quantum tunneling microscope' in order to investigate the static as well as dynamical properties of atomic nuclei. We review the activities of this exciting current research field, focusing particularly on the deformation parameters describing nuclear shapes. (author)