Experimental investigation of the ³⁰S(α, p) thermonuclear reaction in x-ray bursts

¹ Center for Nuclear Study, Graduate School of Science, the University of Tokyo, Japan
² Department of Physics & Astronomy, McMaster University, Canada
³ RIKEN Nishina Center, RIKEN (The Institute of Physical and Chemical Research), Japan
⁴ Institute of Modern Physics, Chinese Academy of Sciences, China
⁵ Institute of Physics, Vietnam
⁶ Department of Physics, University of Catania & INFN, Italy
⁷ Department of Physics, Tohoku University, Japan
⁸ Department of Physics, Chung-Ang University, Korea
⁹ Department of Physics, Yamagata University, Japan
¹⁰ Department of Physics, Kyushu University, Japan

^a e-mail: daid@cns.s.u-tokyo.ac.jp

Published online: 12 February 2016

Abstract

We performed the first measurement of ³⁰S_+α resonant elastic scattering to experimentally examine the ³⁰S(α, p) stellar reaction rate in type I x-ray bursts. These bursts are the most frequent thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of accreting neutron star binaries. The ³⁰S(α, p) reaction plays a critical role in burst models, yet very little is known about the compound nucleus ³⁴Ar at these energies nor the reaction rate itself. We performed a measurement of alpha elastic scattering with a radioactive beam of ³⁰S to experimentally probe the entrance channel. Utilizing a gaseous active target system and silicon detector array, we extracted the excitation function from 1.8 to 5.5 MeV near 160° in the center-of-mass frame. The experimental data were analyzed with an R-Matrix calculation, and we discovered several new resonances and extracted their quantum properties (resonance energy, width, spin, and parity). Finally, we calculated the narrow resonant thermonuclear reaction rate of ³⁰S(α, p) for these new resonances.