Onset of nuclear structure effects in near-barrier elastic scattering of weakly bound nuclei: ${}^6\mathrm{He}$ and ${}^6\mathrm{Li}$ compared

The elastic scattering of the halo nucleus ${}^6\mathrm{He}$ from heavy targets at incident energies near the Coulomb barrier displays a marked deviation from the standard Fresnel-type diffraction behavior. This deviation is due to the strong Coulomb dipole breakup coupling produced by the Coulomb field of the heavy target, a specific feature of the nuclear structure of ${}^6\mathrm{He}$. We have performed Continuum Discretized Coupled Channels calculations for the elastic scattering of ${}^6\mathrm{He}$ and ${}^6\mathrm{Li}$ from ${}^{58}\mathrm{Ni}$, ${}^{120}\mathrm{Sn}$, ${}^{144}\mathrm{Sm}$, ${}^{181}\mathrm{Ta}$ and ${}^{208}\mathrm{Pb}$ targets in order to determine the range of $Z_{\mathrm{T}}$ where this nuclear-structure specific coupling effect becomes manifest. We find that the strong Coulomb dipole breakup coupling effect is only clearly experimentally distinguishable for targets of $Z_{\mathrm{T}}\approx 80$.

Figure 1

Angular distributions of differential cross section (ratio to Rutherford cross section) for ${}^6\mathrm{He}$ (dashed curves) and ${}^6\mathrm{Li}$ (solid curves) $+{}^{58}\mathrm{Ni}$, ${}^{120}\mathrm{Sn}$, and ${}^{144}\mathrm{Sm}$ elastic scattering. The left-hand panels are for $E_{\mathrm{c}.\mathrm{m}.}-V_{\mathrm{B}}=1.005$ MeV and the right-hand panels for $E_{\mathrm{c}.\mathrm{m}.}-V_{\mathrm{B}}=5.534$ MeV.

Figure 2

Angular distributions of differential cross section (ratio to Rutherford cross section) for ${}^6\mathrm{He}$ (dashed curves) and ${}^6\mathrm{Li}$ (solid curves) $+{}^{181}\mathrm{Ta}$ and ${}^{208}\mathrm{Pb}$ elastic scattering. The left-hand panels are for $E_{\mathrm{c}.\mathrm{m}.}-V_{\mathrm{B}}=1.005$ MeV and the right-hand panels for $E_{\mathrm{c}.\mathrm{m}.}-V_{\mathrm{B}}=5.534$ MeV.

Figure 3

Experimental angular distributions of the differential cross section (ratio to Rutherford cross section) for ${}^6\mathrm{He}$ (unfilled circles) and ${}^6\mathrm{Li}$ (filled circles) elastic scattering from ${}^{208}\mathrm{Pb}$ at incident energies of 22.0 MeV [20] and 33.0 MeV [4], respectively. Solid and dashed curves denote CDCC calculations for ${}^6\mathrm{Li}$ and ${}^6\mathrm{He}$ projectiles, respectively.