Airy minima in the scattering of weakly bound light heavy ions

Abstract

We reanalyze the existing $^{6}\mathrm{Li}$ + $^{12}\mathrm{C}$ elastic scattering angular distributions for incident energies ranging from a few MeV to 318 MeV within the frame of the optical model. Despite the important breakup effects expected in the scattering of such a fragile projectile, the system is found to display a surprising transparency. Indeed the barrier-wave/internal-wave decomposition of the elastic scattering amplitude reveals that a substantial part of the incident flux that penetrates the nuclear interior reemerges in the elastic channel, and typical refractive effects, like Airy minima, are clearly identified in the angular distributions. Coupled channel calculations performed on $^{12}\mathrm{C}$($^{6}\mathrm{Li}$,$^{6}\mathrm{Li}'$)$^{12}\mathrm{C}$${}^{*}$(${J}^{\ensuremath{\pi}}={2}^{+},{E}_{x}=4.44$ MeV) angular distributions extending through the whole angular range confirm the existence of an important internal-wave contribution in the backward hemisphere. A similar transparency is observed in other systems of this mass region, such as $^{7}\mathrm{Li}$ + $^{12}\mathrm{C}$ or $^{6}\mathrm{Li}$ + $^{16}\mathrm{O}$. Finally, we examine recent $^{6}\mathrm{He}$ + $^{12}\mathrm{C}$ elastic scattering data obtained at 18 MeV by Milin et al. [Nucl. Phys. A730, 285 (2004)] and extending up to ${\ensuremath{\theta}}_{\mathrm{c.m.}}\ensuremath{\simeq}{85}^{\ifmmode^\circ\else\textdegree\fi{}}$, and we suggest additional measurements that could ascertain whether some transparency persists in the scattering of this radioactive projectile.