Nuclear Physics Seminar: August Gula & Shahina, University of Notre Dame


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Progress in low energy nuclear reaction measurements

August Gula 
Physics Graduate Students
University of Notre Dame

Ever since the discovery of nuclear fusion in stars, the need for high fidelity low energy nuclear reaction data has been apparent. At the Institute for Structure and Nuclear Astrophysics, an intensive effort to study these reactions is ongoing despite lockdowns. Using the 5U Pelletron, studies of the nuclear reactions 10B(a,pg), 10B(a,d), and 11B(a,p) have been furthered and near completion. Narrow resonant structures in the energy range of 0.6-2 MeV were characterized by investigations into the 11B(a,p) reaction. Additionally, current results for 10B+a show a strong resonant contribution at E_Lab=273 keV corresponding to the 11.807MeV state in the compound system of 14N. Both datasets were put through R-matrix analysis and preliminary fits will be presented at this talk.


Measurement of the 25Mg(α, n) 28Si reaction cross-section at low energy

Physics Graduate Student
University of Notre Dame

There is uncertainty regarding the available neutron flux for the weak s-process in massive stars. In order to correctly model the s-process nucleosynthesis, one key ingredient is the rate of neutron producing reactions. The 22Ne(α, n) 25Mg is the main neutron source, but other reactions also contribute. In the present work we study one such reaction, namely 25Mg(α, n) 28Si, which acts as a potential neutron source for weak s-process and destroys the strongest neutron poison 25Mg. Previous measurements for this reaction suffered from two shortcomings: they were not performed at low enough energies relevant for weak s-process in massive stars and measurements using neutron counters were hindered by the contamination of targets with lower Z material. In this work, we used two different setups consisting of deuterated liquid scintillator detectors for neutrons and LaBr3 for γ-rays in order to measure the 25Mg(α, n) 28Si cross- section in the Gamow range 1.4-2.6 MeV. The neutron spectroscopy was performed via neutron spectrum unfolding technique which allows for a clear separation of the signal and the background. Preliminary results, including cross-sections determined from gamma-ray and neutron spectroscopy will be presented.

Hosted by Prof. Wiescher


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