Fusion Cross Sections of Light Heavy-Ion Systems: Resonances and Shell Effects

Abstract

The total fusion cross sections for the systems 12 C + 12 C, 18, 0 + l2 C, and 19 F+ 12 C have been measured as a function of bombarding energy and compared with results for other light heavy-ion systems. The presence or absence of oscillations in the fusion excitation function and the overall magnitude of the cross section at high energies appear to depend on the structure of the colliding nuclei.The energy dependence of the cross section for the complete fusion of two complex nuclei has received considerable recent attention. 1 In most cases the measured excitation functions are smooth, as is consistent with macroscopic models of such processes. In a recent study of the 16 0 + 12 C system, unexpected oscillatory structure was seen in the energy dependence of the fusion cross section. 2 In the present study we have bombarded 12 C targets with several other ions, near in mass to le O, in order to establish the range of nuclei over which structure is seen in the fusion excitation function, and also to delineate the macroscopic features of the fusion process.The fusion cross sections for the systems 12 C + 12 C, 18 0+ 12 C, and 19 F+ 12 C were measured as a function of bombarding energy using beams obtained from the Argonne National Laboratory FN tandem accelerator. The experimental procedure and uncertainties have been described previously. 2 All reaction products with higher Z than the incident ions were assumed to be evaporation residues and were included in defining the fusion cross section.The fusion cross sections [o fus (E)] for the three systems studied are shown in Fig. 1 as a function of cm. energy. The solid lines in Fig. 1 are calculated using the model of Glas and Mosel 3 which is based on the assumption that fusion occurs whenever the nuclei reach a critical separation distance, R c . The parameters used to fit the data are listed in Table I. The experimental results confirm the qualitative prediction of the model that a fus for such a light system should saturate at some critical bombarding energy and then decrease or remain roughly constant at higher energies.There are two qualitative features in our exper-1.2 H -Q 0.61 1.0 0.8 0.6h 0.41

Detailed energy dependence of the elastic and inelastic12C +12C scattering between 5 and 10 MeV/nucleon

“…5, which shows the excitation functions for the inelastic channels It is very instructive to follow the occurrence of the intermediate structures in the studied elastic and inelastic channels and examine the energy dependence of the fusion cross sections. For energies above the barrier and below 5 MeV/nucleon, the most surprising result of the study of the lzC + 12C fusion cross sections was the observation of oscillatory structure in the fusion excitation functions [14]. Similar resonances have been observed in inelastic and transfer reactions in this system at the same energies [9,10].…”

Towards a unified description of light ion fusion cross section excitation functions

“…For severallight systems, especially for the spin-zero cases 12C + 12C [30,31,34], 160 + 160 [32][33][34] and the 12C + 160 [34,35], an oscillation pattern is superimposed on the general trend of OF below Ecm=30 MeV. The structures have been related to entrance channel characteristics [36,37].…”

Fusion of28Si +28Si: oscillations above the barrier and the behavior down to 1μb

“…Oscillatory structures were observed above the Coulomb barrier in the fusion excitation function of light heavy-ion systems like 12 C + 12 C, 12 C + 16 O and 16 O + 16 O, long time ago [1][2][3][4]. Sometimes the oscillations have been associated with resonances, but there are suggestions, supported by coupled-channels (CC) calculations [5], that they may be due to the penetration of successive angular momentum (L) barriers.…”