Entrance-channel effects in heavy-ion capture: role of octupole phonons

The introduction of the “experimental barrier distribution” d2(Eσfus)/dE2 gave a simple means of highlighting the dynamics of heavy-ion fusion reactions, as well as giving a demanding test of the quality of theoretical calculations. However, in many cases where data have been taken at deep sub-barrier energies, understanding the distribution is not sufficient. Here, the logarithmic derivative d[ln(Eσfus)]/dE provides a very useful additional test. It is suggested that high-lying octupole phonon states, long thought simply to give a global shift of the distribution downward in energy, may play a more complex role in the reaction dynamics, contributing much to the underlying physics of both the above functions.