A Direct Study of 20Ne(alpha,p)23Na with the HELIcal Orbit Spectrometer (HELIOS)

Abstract

Type Ia Supernovae are thermonuclear explosions that occur on CO white dwarfs in binary systems, completely disrupting the system. While the exact progenitor of these events is unclear, there have been several studies exploring the nucleosynthesis that drives these stellar explosions. These studies have shown that a handful of reactions have a significant effect on Type Ia Supernova nucleosynthesis, specifically 12C(alpha, gamma), 12C+12C, 20Ne(alpha, p), 20Ne(alpha, gamma), and 30Si(p, gamma). While the 20Ne(alpha,p)23Na reaction has been shown to be one of the five most influential reactions, it has not been directly been measured at astrophysically relevant energies. We performed direct measurements of this reaction with multiple 20Ne beam energies (100 MeV, 80 MeV and 31 MeV) in inverse kinematics. The measurements were performed at Argonne National Laboratory using the HELIOS (HELIcal Orbit Spectrometer) beam line. This measurement is also a proof-of-principle test for a setup designed for reaction studies, using a cryogenic gas target and a fast position-sensitive ionization chamber (IC). This experimental setup especially targets reactions with radioactive ion beams and details of the commissioning runs for the gas target and the IC are discussed. The data obtained was analyzed using a series of timing and particle identification cuts to determine the particle yields from the 4He(20Ne,p)23Na reaction. Efficiencies were determined through a series of simulations using the Geant4 toolkit and the data were normalized using the 2H(20Ne,p)21Ne and 4He(20Ne,4He)20Ne reactions. The yields were corrected for these efficiencies and normalized to determine the reaction cross section. These newly measured cross sections are compared to the ones previously used for nuclear reaction sensitivity studies and the likely effects on Type Ia Supernova nucleosynthesis are discussed. Candidate reactions for future studies are listed and possible improvements are proposed.