Experimental evidence for a fusion enhancement in $^{19}$O$+^{12}$C at near barrier energies

Fusion of neutron-rich light nuclei in the outer crust of an accreting neutron star has been proposed as responsible for triggering X-ray super-bursts. The underlying hypothesis in this proposition is that the fusion of neutron-rich nuclei is enhanced as compared to stable nuclei. To investigate this hypothesis, an experiment has been performed to measure the fusion excitation function for $^{18}$O and $^{19}$O nuclei incident on a $^{12}$C target. A beam of $^{19}$O was produced by the $^{18}$O(d,p) reaction at Florida State University and separated using the RESOLUT mass spectrometer. The resulting $^{19}$O beam bombarded a 100 $\mu $g/cm$^{2}$ $^{12}$C target at an intensity of 2-4 x 10$^{4\, }$p/s. Evaporation residues resulting from the de-excitation of the fusion product were distinguished by measuring their energy and time-of-flight. Evaporation residues were detected with high efficiency by measuring them in the angular range 4.4\textdegree $\le \theta_{lab}\le $11.7\textdegree . The fusion cross-section has been measured down to 170 mb level. As compared to $^{18}$O$+^{12}$C the fusion cross-section for $^{19}$O$+^{12}$C is enhanced by approximately a factor of 3 times at the lowest energy measured. The measured excitation function will be compared with theoretical calculations.