Role of the Surface Energy in Heavy-Ion Collisions

TL;DR

This paper investigates how variations in nuclear surface energy influence fusion reactions near the Coulomb barrier, using Hartree-Fock calculations on calcium isotopes to reveal unexpected effects on fusion barriers.

Contribution

It systematically studies the impact of surface energy variations on nuclear fusion dynamics using advanced computational models.

Findings

Higher surface energy leads to greater dynamical lowering of fusion barriers.

Unexpectedly, the largest surface energy results in the greatest barrier reduction.

Variation in nuclear matter properties may explain the observed effects.

Abstract

The surface energy is one of the fundamental properties nuclei, appearing in the simplest form of the semi-empirical mass formula. The surface enery has an influence on e.g. the shape of a nucleus and its ability to deform. This in turn could be expected to have an effect in fusion reactions around the Coulomb barrier where dynamical effects such as the formation of a neck is part of the fusion process. Frozen Hartree-Fock and Time-Dependent Hartree-Fock calculations are made for a series of effective interactions in which the surface energy is systematically varied, using $^{40}$Ca + $^{48}$Ca as a test case. The dynamical lowering of the barrier is greatest for the largest surface energy, contrary to naive expectations, and we speculate that this may be due to the variation in other nuclear matter properties for these effective interactions