Near-barrier fission of the system ¹²C+ ²³²Th

Abstract

The fission fragment angular distributions for the system ¹²C +²³²Th have been measured in the energy range 0.97<E_c.m./V_B<1.22. The measured anisotropies have been compared with the predictions of the standard saddle point statistical model, using the second moment of the compound nucleus spin distribution <l²> deduced from a Wong model fit to the fission excitation function. While the measured anisotropies agree with the standard saddle point statistical model for E_c.m./V_B>1.05, they are abnormally large at lower energies. This is also true for the existing measurements of ¹⁶O and ¹⁹F +²³²Th systems. Since for this system pre-equilibrium fission contributions are not expected, this anomaly indicates strong channel coupling effects leading to an increase in <l²> at sub-barrier energies.