Multipole Expansion for Relativistic Coulomb Excitation

We derive a general expression for the multipole expansion of the electro-magnetic interaction in relativistic heavy-ion collisions, which can be employed in higher-order dynamical calculations of Coulomb excitation. The interaction has diagonal as well as off-diagonal multipole components, associated with the intrinsic and relative coordinates of projectile and target. A simple truncation in the off-diagonal components gives excellent results in first-order perturbation theory for distant collisions and for beam energies up to 200 MeV/nucleon.Comment: 3 figures, Accepted for publication in Phys. Rev.

Hindrance of heavy-ion fusion due to nuclear incompressibility

We propose a new mechanism to explain the unexpected steep falloff of fusion cross sections at energies far below the Coulomb barrier. The saturation properties of nuclear matter are causing a hindrance to large overlap of the reacting nuclei and consequently a sensitive change of the nuclear potential inside the barrier. We report in this letter a good agreement with the data of coupled-channels calculation for the {64}Ni+{64}Ni combination using the double-folding potential with M3Y-Reid effective N-N forces supplemented with a repulsive core that reproduces the nuclear incompressibility for total overlap.Comment: 4 pages, 3 figure

Sensitivity to multi-phonon excitations in heavy-ion fusion reactions

Measured cross sections for the fusion of {64}Ni with {64}Ni, {74}Ge, and {100}Mo targets are analyzed in a coupled-channels approach. The data for the {64}Ni target above 0.1 mb are reproduced by including couplings to the low-lying 2^+ and 3^- states and the mutual and two-phonon excitations of these states. The calculations become more challenging as the fusing nuclei become softer and heavier, and excitations to multi-phonon states start to play an increasingly important role. Thus it is necessary to include up to four-phonon excitations in order to reproduce the data for the {64}Ni+{74}Ge system. Similar calculations for {64}Ni+{100}Mo, and also for the symmetric {74}Ge+{74}Ge system, show large discrepancies with the data. Possible ways to improve the calculations are discussed.Comment: 24 pages, 7 figures, 4 table

A non-perturbative approach to halo breakup

The theory of weakly bound cluster breakup, like halo nucleus breakup, needs an accurate treatment of the transitions from bound to continuum states induced by the nuclear and Coulomb potentials. When the transition probability is not very small, a non-perturbative framework might be necessary. Nuclear excitation dominates at small impact parameters whereas the Coulomb potential being long range acts over a larger impact parameter interval. In this article, we propose an effective breakup amplitude which meets a number of requirements necessary for an accurate quantitative description of the breakup reaction mechanism. Furthermore our treatment gives some insight on the interplay between time dependent perturbation theory and sudden approximation and it allows to include the nuclear and Coulomb potentials to all orders within an eikonal-like framework.Comment: 22 Latex pages, 1 table, 8 eps figures. Accepted for publication on Nucl. Phys.