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Experimental above-barrier fusion cross-sections for $^{17}$F + $^{12}$C are compared to the fusion excitation functions for $^{16,18}$O, $^{19}$F, and $^{20}$Ne ions on a carbon target. In comparing the different systems both the differing static size of the incident ions and changes in fusion barrier are accounted for by examining the reduced fusion cross-section. Remaining trends of the fusion cross-section above the barrier which reflect the sensitive interplay of the sd protons and neutrons are observed. The experimental data are also compared to both a widely-used analytical model of near-barrier fusion, as well as a time-dependent Hartree-Fock model. Both models fail to describe the trends observed., Comment: 6 pages, 5 figures

Measuring the fusion excitation function for an isotopic chain of projectile nuclei provides a stringent test of a microscopic description of fusion. We report the first measurement of the fusion excitation function at near-barrier energies for the 19 O + 12 C system. The measured excitation function is compared with the fusion excitation function of 18 O + 12 C. A significant enhancement in the fusion probability of 19 O ions with a 12 C target as compared to 18 O ions is observed. The experimental cross-sections observed at near-barrier energies are compared with a state-of-the-art microscopic model.

Measurement of the fusion excitation function for 18 O + 12 C and 19 O + 12 C is described. The fusion cross-section is extracted through the direct measurement of evaporation residues resulting from the fusion process. At near barrier energies, the single additional neutron present in 19 O results in an enhancement in the fusion cross-section by a factor of over three as compared to 18 O.

We demonstrate an approach to measure the total fusion cross-section for beams of low-intensity light nuclei. Fusion residues resulting from the fusion of 20,16 O+ 12 C are directly measured and distinguished from unreacted beam particles on the basis of their energy and time-of-flight. The time-of-flight is measured between a microchannel plate (MCP) detector, which serves as a start, and a segmented silicon detector, which provides a stop. The two main difficulties associated with the initial implementation of this approach are charge trapping in the silicon detector and slit scattering in the MCP detector. Both these obstacles have been characterized and overcome. To reduce atomic slit scattering in the measurement we have eliminated wires from the beam path by developing a gridless MCP detector. The total fusion cross-section for 16 O+ 12 C in the energy range E CM =8.0–12.0 MeV has been measured in agreement with established literature values (down to the 100 mb level).

Background: Measurement of the energy dependence of the fusion cross section at sub-barrier energies provides an important test for theoretical models of fusion.Purpose: The aim of the study is to extend the measurement of fusion cross sections in the sub-barrier domain for the $^{18}\mathrm{O}+^{12}\mathrm{C}$ system, and to use the new experimental data to confront microscopic calculations of fusion.Method: Evaporation residues produced in fusion of $^{18}\mathrm{O}$ ions with $^{12}\mathrm{C}$ target nuclei were detected with good geometric efficiency and identified by measuring their energy and time-of-flight. Theoretical calculations with a density-constrained time-dependent Hartree-Fock (DC-TDHF) theory include for the first time the effect of pairing on the fusion cross section.Results: Comparison of the measured fusion excitation function with the predictions of the DC-TDHF calculations reveal that the experimental data exhibit a smaller decrease in cross section with decreasing energy than is theoretically predicted.Conclusion: The larger cross sections observed at the lowest energies measured indicate a larger tunneling probability for the fusion process. This larger probability can be associated with a smaller, narrower fusion barrier than presently included in the theoretical calculations.

Evaporation residues resulting from fusion of 20O incident ions with 12C target nuclei have been measured for the first time. The cross-section associated with compound nuclei that de-excite via emission of charged particle is extracted. The resulting excitation function is compared with the predictions of a standard fusion model followed by statistical decay code. A significant underprediction of the measured cross-section by the fusion-evaporation model raises the question of whether the fusion cross-section is larger for the neutron-rich projectile or the statistical de-excitation is incorrectly predicted. Improvements in the experimental technique which should allow future measurement of the total fusion cross-section are described.