Proton capture on ³⁴S in the astrophysical energy regime

Abstract

Novae are unique environments for nucleosynthesis, fueled by the thermonuclear runaway of material accreted onto the surface of the white dwarf component of a close binary system. In order to properly model these systems, precise knowledge of the nuclear reactions in the complex reaction networks is required. Many of the reaction rates, often preceding via narrow resonances, are theoretically calculated, leading to large uncertainties that have been shown to be able to drastically alter the expected production of novae material. The uncertainties in theoretical calculations of the radiative proton capture strengths of 34S in novae conditions with peak temperatures, T = 0.145-0.418 GK have been shown to cause deviations in the production of 35Cl and 36Ar by factors up to 20 and 7 respectively. Previous measurements of the 34S(p,γ)35Cl reaction only went down to Ep= 400 keV and saw no notable features below 510.6 keV. In order to properly model the nova phenomenon, the strength of various resonances of the 34S(p,γ)35Cl reaction needed to be measured directly and the uncertainties needed to be better constrained. Simulations show evidence of the production of 35Cl through proton capture in Gamma-Ray Burst (GRB) x-ray afterglows and Type 1a supernova. Cl and S isotopic ratios are also an important tool in determining the potential nova or supernova source of pre-solar meteoritic grains, so a precise knowledge of the potential novae source of these isotopes is needed. The resonance strength of proton capture on 34S was measured directly at DRAGON using the electromagnetic mass separator at the center of mass energies from 272 to 495.5 keV in inverse kinematics. In addition, a 21Ne + p calibration reaction was evaluated and the analysis of several years of accumulated energy loss and charge state distribution data was done to provide a realistic means of access for this information and to update a semi-empirical formula for predicting the charge state distributions of ions passing through gas.