Study of the ¹⁸Ne(α, p)²¹Na Reaction with ANASEN and Its Significance in the Breakout from the Hot-CNO Cycle

18Ne(α,p)21Na reaction is one of the reactions providing a pathway for breakout from the hot CNO cycles to the rp-process in Type I X-ray bursts. The actual conditions under which the breakout occurs depend critically on the thermonuclear reaction rate. This rate has not been sufficiently determined yet over the temperatures present under X-ray burst conditions. We study the direct 18Ne(α,p)21Na reaction with the Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN), using a helium gas target and an 18Ne radioactive beam. ANASEN is an active gas target detection system that uses tracking of the light reaction products in conjunction with energy measurements in Silicon detectors. The position information required for the tracking is provided by a Multi-Anode Proportional Counter in combination with the Silicon detectors. From the tracking the location of the interaction is obtained, which is directly correlated to the energy of the beam particle. While the beam is losing energy while traveling in the gas target, a wide range of reaction energies can be measured simultaneously and without changing the accelerator parameters. The difficulty of this particular experiment lies on the fact that we are trying to detect one single proton from the 18Ne(α,p)21Na reaction per event. Proton background is caused by fusion evaporation reactions of the 18Ne with the CO2 quenching gas added on the 4He target gas. For the first time in the ANASEN setup, we have implemented a cylindrical Ion Chamber for coincident heavy-recoil detection, which was successfully used to suppress such background events. The 18Ne(α,p)21Na cross section was measured in the context of this dissertation. The experiment allows for a determination of the cross section down to reaction energies ∼2 MeV in the center-of- mass system. The results are compared to the previous (α,p) reaction measurement, as well as to the time-inverse (p,α) reaction measurement and theoretically calculated cross sections. Our work resolves significant inconsistencies between the experimental information on the 18Ne(α,p) reaction and the indirect information available, giving larger credence to the use of such indirect methods. At the same time, more sensitive measurements of the 18Ne(α,p) reaction are needed to provide experimental information on the reaction energies below 2 MeV, most important for the break-out phase of X-ray bursts. The experimental techniques developed in this work would have to be applied to a beam of 18Ne with significantly higher quality and intensity.