FUSION BARRIER DISTRIBUTIONS IN HEAVY-ION REACTIONS: A PEDAGOGICAL INTRODUCTION WITH THE 16O+144SM BENCHMARK

Abstract

The barrier distribution extracted from precise excitation-function data offers one of the clearest experimental views of the multidimensional quantum tunnelling that controls heavy-ion fusion near and below the Coulomb barrier. This study revisits the barrier-distribution representation, , and applies it to the benchmark system  together with a comparative survey of related systems. Within a coupled-channels framework recast in the eigenbarrier (multi-barrier) picture, the single, sharply peaked barrier of the uncoupled one-dimensional model is shown to give way to a broad, structured distribution once couplings to the low-lying collective excitations of the colliding nuclei are switched on. The resulting enhancement of the sub-barrier fusion cross section reaches two orders of magnitude relative to the no-coupling prediction, in close quantitative agreement with the measured excitation function. The shape, centroid, and width of  are sensitive fingerprints of the dominant inelastic and transfer channels, and a systematic comparison across six systems is presented. The barrier distribution is found to remain an indispensable diagnostic tool for disentangling the reaction dynamics of heavy-ion fusion.