Enhancement of sub-barrier fusion of two-neutron halo nuclei

TL;DR

This paper investigates how the extended matter density of two-neutron halo nuclei enhances sub-barrier fusion, contrasting with the general breakup hindrance, and highlights implications for stellar processes.

Contribution

It provides experimental evidence that halo nuclei like $^{6}$He exhibit enhanced fusion at sub-barrier energies, challenging previous claims and emphasizing the role of extended density distributions.

Findings

Fusion cross section of $^{6}$He + $^{238}$U is significantly enhanced at sub-barrier energies.

Enhanced fusion observed in $^{6}$He + $^{209}$Bi system.

Halo effects can overcome breakup hindrance at low energies.

Abstract

The tunneling of composite systems, where breakup may occur during the barrier penetration process is considered in connection with the fusion of halo-like radioactive, neutron- and proton-rich nuclei on heavy targets. The large amount of recent and new data clearly indicates that breakup hinders the fusion at near and below the Coulomb barrier energies. However, clear evidence for the halo enhancements, seems to over ride the breakup hindrance at lower energies, owing, to a large extent, to the extended matter density distribution. In particular we report here that at sub-barrier energies the fusion cross section of the Borromean two-neutron halo nucleus $^{6}$He with the actinide nucleus $^{238}$U is significantly enhanced compared to the fusion of a no-halo $^{6}$He. This conclusion differs from that of the original work, where it was claimed that no such enhancement ensues. This sub-barrier fusion enhancement was also observed in the $^{6}$He + $^{209}$% Bi system. The role of the corresponding easily excitable low lying dipole pygmy resonance in these systems is therefore significant. The consequence of this overall enhanced fusion of halo nuclei at sub-barrier energies, on stellar evolution and nucleosynthesis is evident.