Entrance channel effect for complete fusion of O + C isotopes

Abstract

The cross section for total fusion of the reaction ' 0+ ' C was studied over a large range of energies from near the Coulomb barrier B& to -6B~. Good agreement was found between the critical angular momenta deduced from the experimental results and the predictions of different models. The reaction ' 0+ ' C, leading to the same compound nucleus Si, was studied in the second fusion region (above -2B&). By comparing the relative cross sections for fusion-evaporation to each isotope it is shown that for different entrance channels, even at the highest energies studied, the reactions appear to pass by the formation of a compound nucleus. The critical angular momenta were found to be systematically different from ' 0+ ' C. This difference, which may be due partially to the entrance channel spin, is interpreted as arising from the effect of direct reactions diverting flux from the compound nuclear processes. NUCLEAR REACTIONS ' 0, ' 0, and ' 0 beams on ' C, ' C, and ' C targets, respectively; natural and enriched targets; E&,b --32 to 140MeV; time of flight with Z identification technique; fusion evaporation and direct cross section measurements from Z=5 to 14 and 3=10 to 29; statistical model calculations; entrance channel effects discussed; macroscopic model results for total fusion cross sections.

Peripheral elastic and inelastic scattering ofO17,18on light targets at 12 MeV/nucleon

“…Fresnel scattering of 18 O on 28 Si was measured by Mermaz et al [7] at 56 MeV. For the 17 O+ 13 C reaction the data are rather scarce, we identified a single fusion study and poor elastic angular distributions at barrier energies [8]. The main conclusion of these studies was that the interaction of 17,18 O nuclei with light targets is slightly more absorptive compared with that of the closed shell nucleus 16 O and that no significant effects due to the neutron excess were identified.…”

Fusion of neutron-rich oxygen nuclei

“…The measured excitation function is displayed in Fig. 4a together with previously published results [9][10][11]. Vertical error bars on the new data reflect both the statistical uncertainties as well as a 2% systematic error associated with the analysis.…”

Fusion Reactions Between Heavy Nuclei

“…This limitation of the fusion cross section at high energies has been clearly demonstrated to be dependent on the entrance channel in some cases. Such a demonstration can be made if the compound nucleus is formed under the same conditions by different entrance channels (15)(16)(17)(18)(19)(20)(21)(22)(23)(24). However, in other cases, by examination of the angular momentum limits to fusion and by comparison to entrance channel models of fusion, some systems have been interpreted in terms of a compound nucleus (or exit channel) limit to the fusion cross section (23,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37).…”