Speaker
Description
Type-I X-rays bursts are thermonuclear flashes ignited on the surface of a neutron star which is accreting hydrogen and helium-rich material from its companion star. With an hours-long stellar half-life and a low proton capture Q value (~690 keV), doubly magic 56Ni has long been defined as one of the waiting points in the rapid proton capture (rp) process that powers the type-I X-ray bursts. However, a strong bypass circumventing 56Ni and diverting the rp-process flow through the path 55Ni(p,γ)56Cu(p, γ)57Zn(β+)57Cu(p,γ) 58Zn has been proposed [1]. The astrophysical 55Ni(p,γ) and 56Cu(p, γ) forward and reverse reaction rates calculated with the recently measured mass of 56Cu [2] show that the rp-process flow redirects around the 56Ni waiting point through the 55Ni(p,γ) route. The dominant source of uncertainty regarding the strength of this bypass is the β delayed proton emission decay branch of 57Zn, having a present estimate of 78±17% [3]. We measured the
β-delayed proton (βp) and γ emission at the National Superconducting Cyclotron Laboratory. We substantially improved the precision for the beta-delayed proton emission branching ratio for 57Zn, definitively determining that there is a 56Ni bypass, with 14-17% of the rp-process flow taking this route. We also identified four new γ-ray transitions forming the exotic β-γ-p decay branch.
References:
1. W.-J.Ong et. al, Phy. Rev C 95 055806 (2017).
2. A.A. Valverde et. al, Phy. Rev. Lett. 120, 032701 (2018)
3. B. Blank et. al, Eur. Phys J. A, 31 (3) 267-272 (2007
