Heavy-ion reactions near the Coulomb barrier

Fusion reactions between different Kr and Ni isotopes were measured recently at ATLAS. We performed coupled-channels calculations and made comparisons to the measurements. Such calculations become increasingly difficult for heavy, soft nuclei due to strong couplings and the importance of higher-order, multi-step processes. The calculations were made possible by adopting the so-called rotating frame approximation, and they included one- and two-phonon excitations of the low-lying 2+ and 3- states in both the projectile and the target. These calculations reproduced quite accurately the measured fusion cross sections for a beam of 86Kr. Some discrepancies remain for the much softer 78Kr nucleus; the calculations were clearly much more sensitive to higher-order processes in this case. In particular, it was important to implement the correct coupling strength and excitation energy for the soft, one- to two-phonon quadrupole transition in 78Kr, which differs significantly from the vibrational limit. This work was performed in collaboration with the experimentalists and was submitted for publication