Fusion in neutron-rich environments is presently a topic of considerable interest. For example, the optical emission spectrum from the neutron star merger GRB170817A clearly establishes this neutron-rich environment as an important nucleosynthetic site. Fusion of neutron-rich light nuclei in the outer crust of an accreting neutron star has also 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. A good approach to understand how fusion proceeds in neutron-rich nuclei is to measure the fusion excitation function for an isotopic chain of nuclei. Modern radioactive beam facilities provide the opportunity to systematically address this question. An experimental program has been established to measure the fusion excitation function for light and mid-mass neutron-rich nuclei using low-intensity radioactive beams. The technique was initially demonstrated by measuring the fusion excitation functions for 18O and 19O nuclei incident on a 12C target. The beam of 19O ions was produced by the 18O(d,p) reaction with an intensity of 2-4 x 104 p/s at Florida State University. Evaporation residues resulting from the de-excitation of the fusion product were distinguished by measuring their energy and time-of-flight. To explore mid-mass neutron-rich nuclei much further from stability, the fusion excitation functions for 39,47K + 28Si were measured using the ReA3 reaccelerator facility at the National Superconducting Cyclotron Laboratory at Michigan State University. Incident ions were identified on a particle-by-particle basis by ΔE-TOF just upstream of the target. Fusion products were directly measured and identified by the E-TOF technique with an efficiency of ~70%. The measured fusion excitation functions for both the light and mid-mass systems have been compared to various theoretical models to elucidate how structure and dynamics impact the fusion of neutron-rich nuclei.
|Advisor:||Souza, Romualdo T. de|
|Commitee:||Horowitz, Charles J., Jarrold, Caroline C., Ortoleva, Peter J.|
|School Location:||United States -- Indiana|
|Source:||DAI-B 80/05(E), Dissertation Abstracts International|
|Subjects:||Physics, Nuclear chemistry, Nuclear physics|
|Keywords:||Barrier, Beam, Cross-section, Fusion, Neutron-rich, Radioactive|
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