  The elastic scattering of the halo nucleus $^6$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 $^6$He. We have
performed Continuum Discretized Coupled Channels calculations for the elastic
scattering of $^{6}$He and $^6$Li from $^{58}$Ni, $^{120}$Sn, $^{144}$Sm,
$^{181}$Ta and $^{208}$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 $Z_{\mathrm T}
\approx 80$.
