$^{24}Mg+\,^{12}C$ fusion reaching the no-coupling limit far below the barrier.

Del Fabbro M., Montagnoli G., Stefanini A.M., Jiang C.L., Hagino K., Niola F., Brugnara D., Colovic P., Colucci G., Corradi L., Depalo R., Fioretto E., Goasduff A., Pasqualato G., Scarlassara F., Szilner S., Zanon I.
  Giovedì 15/09   09:00 - 13:00   Aula B - Maria Goeppert-Mayer   I - Fisica nucleare e subnucleare   Presentazione
The low-energy fusion experiment on $^{24}Mg+\,^{12}C$ showed that the cross-sections far below the Coulomb barrier, actually reach the no-coupling limit. The ratio of experimental cross-sections ($\sigma_{exp}$) to no-coupling calculations ($\sigma_{noc}$) $vs.$ energy distance from the Coulomb barrier has been obtained and compared with $^{30}Si+\,^{12}C$ and two heavier systems $^{48}Ca+\,^{48}Ca$ and $^{58}Ni+\,^{54}Fe$. In all these cases the no-coupling calculations are based on Woods-Saxon potentials. The hindrance effect has been observed in all four systems. As expected, the sub-barrier enhancement is larger for the heavier systems, with respect to the two lighter systems. This prevents observing the behaviour of the ratio $\sigma_{exp}/\sigma_{noc}$ below a certain limit, whereas it is clearly seen that for $^{30}Si+\,^{12}C$ and in particular for $^{24}Mg+\,^{12}C$ the ratio decreases to one (no enhancement) at the lowest energies. The question is then whether the cross-sections follow the no-coupling calculation or if, since the ion-ion potential effectively becomes a one-body potential after the touching point, the excitation function decreases even below that limit.