Interplay of static and dynamic effects in ${}^6\mathrm{He}+{}^{238}\mathrm{U}$ fusion

We investigate the influence of the neutron halo and the breakup channel on the total ${}^6\mathrm{He}+{}^{238}\mathrm{U}$ fusion cross section at near-barrier energies. To include static effects of the $2n$-halo in ${}^6\mathrm{He}$ nuclei, we use a single-folding potential obtained from an appropriate nucleon-${}^{238}\mathrm{U}$ interaction and a realistic ${}^6\mathrm{He}$ density. Dynamical effects arising from the breakup process are then included through coupled-channel calculations. These calculations suggest that static effects dominate the cross section at energies above the Coulomb barrier, while the coupling to the breakup channel is more important at sub-barrier energies. The comparison of our calculations with recent data suggests that the coupling to other channels may be influencing the cross section at very low energies.

Figure 1

${}^4\mathrm{He}+{}^{238}\mathrm{U}$ fusion cross sections. The data of Refs. 7 (solid squares) and [14] (open squares) are compared with the calculations of the present work. The barrier energy is indicated by an arrow. For further details see the text.

Figure 2

Coulomb coupling to the breakup channel for the ${}^6\mathrm{He}+{}^{238}\mathrm{U}$ fusion cross section. Experimental results [7] are compared with a static calculation similar to that of Fig. 1, with just a scaling of the potential ${}^4\mathrm{He}$ (dashed line), and taking into account the fact that ${}^6\mathrm{He}$ is a halo nucleus (full line).

Figure 3

Coulomb and nuclear dipole form factors (a) and their ratio (b). See text for details.

Figure 4

Total fusion data of ${}^6\mathrm{He}$ incident on ${}^{238}\mathrm{U}$ in comparison to the static calculation, including the ${}^6\mathrm{He}$ halo, of Fig. 2 (dashed line), a coupled-channel calculation including only the Coulomb interaction (thin full line), and also including nuclear effects (thick full line). See text for details on these two last calculations.