Fusion of 12C+28Si at deep sub-barrier energies

The sub-barrier fusion hindrance phenomenon is systematically observed in heavy-ion systems, but its evidence for light-mass cases of astrophysical interest, like C+C, C+O and O+O, is controversial. Their low-energy behaviour may be clarified by studying slightly heavier systems, so to extrapolate their trend to the lighter cases. In this work, fusion of 12C + 28Si has been measured down to deep sub-barrier energies, using 28Si beams from the XTU Tandem accelerator of LNL on thin 12C targets. Two different set-ups were employed: 1) the fusion-evaporation residues were identified by a detector telescope following an electrostatic beam separator, and 2) coincidences between the γ -ray array AGATA and segmented silicon detectors DSSD were performed, where the evaporated light charged particles were identified by pulse shape analysis. Fusion cross sections have been obtained in the wide range σ ≈ 150 mb – 42 nb. Coupled-channel (CC) calculations using a Woods-Saxon potential reproduce the data above ≃ 0.1 mb. Below that, hindrance shows up and the CC results overestimate the cross sections which get close to the one-dimensional potential tunnelling limit. This suggests that the coupling strengths gradually vanish, as predicted by the adiabatic model. The hindrance threshold follows a recently updated phenomenological systematics.