PhD Dissertation Defense

Study of the fusion reaction ¹²C + ¹²C towards the Gamow energy

The fusion reactions ¹²C(¹²C,α)²⁰Ne and ¹²C(¹²C,p)²³Na are critically important in nuclear astrophysics.  Previous experimental cross section measurements of these reactions have been carried out, however the existing data does not extend into the energy range relevant to astrophysical processes. Additionally, there is a great deal of uncertainty and disagreement in the existing data.  In the present work targets of ultralow hydrogen contamination have been produced, allowing measurement of the cross sections of the ¹²C+¹²C reactions into the astrophysical energy region for the first time. The deduced astrophysical S(E) factor exhibits previously unknown resonances at energies less than 3.0 MeV, in particular the data suggest a strong resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak.  In spite of the resonant structure the energy averaged S(E) factor is a factor of two smaller than previous extrapolations have suggested.  These two findings cast serious doubt on the current use of extrapolation of the reaction cross section into the Gamow window to model the astrophysical reaction rate of these reactions, suggesting instead that direct measurement through the Gamow window is necessary.