Backscattering measurement of He6 on Bi209: Critical interaction distance

An elastic backscattering experiment has been performed at energies below the Coulomb barrier to investigate static and dynamic effects in the interaction of He6 with Bi209. The measured cross sections are presented in terms of the dσ/dσRuth ratio, as a function of the distance of closest approach on a Rutherford trajectory. The data are compared with a three-body CDCC calculation and good agreement is observed. In addition, the critical distance of interaction was extracted. A larger value was obtained for the exotic He6 nucleus as compared with the weakly bound Li6 and Be9 nuclei and the tightly bound He4, C12, and O16 nuclei.