PhD Dissertation Defense
Department of Physics, University of Connecticut
Knowledge of carbon fusion reaction rates at stellar temperatures is necessary for a complete picture of stellar evolution. The minimum stellar mass necessary for quiescent carbon burning as well as the conditions necessary for type Ia supernovae depend on them. The astrophysically relevant region of reaction rates is contained within a narrow energy band (the Gamow window), which lies on the far low energy end of the cross section curve. Due to the difficulty in measurement, current rates in this regime rely heavily on extrapolated values from higher energies and ignore the effects of possible resonances in or near the Gamow window. The challenge in obtaining data at low energy primarily stems from observing very low counting rates, due to the exponentially falling cross section, in the presence of background that is insignificant at higher energies. Historically the measurement of the total fusion cross section has been halted at the high energy edge of the Gamow window by background radiation from hydrogen isotopes. Recent advances in target preparation have extended the data near the region of stellar interest, but the emergence of a highly improbable “two-step” reaction has again limited the lowest attained energy. However, improvements in target quality and vacuum composition have yielded promising results. The identification and reduction of this background will be discussed along with carbon fusion data, implications, and future techniques.