Thermonuclear S30(p,γ)Cl31 reaction in type i x-ray bursts
In the explosive astrophysical environment of a type I x-ray burst, the low Q value of 293(50) keV for proton capture on S30 induces a (p,γ)(γ, p) equilibrium that may lead to a waiting point in the rapid proton capture (rp) process at S30. The excitation energies of the first and candidate second T=3/2 levels in S31 were recently determined to an uncertainty of 2 keV by measuring triton spectra and t-p angular correlations from the P31(He3,t)S31*(p)P30 reaction. By using this new information together with existing experimental information on the first T=3/2, A=31 isobaric multiplet and the isobaric multiplet mass equation, the S30(p,γ)Cl31Q value is predicted to be 284(7) keV. Similarly, by using the second T=3/2 multiplet, the energy of the dominant resonance in the thermonuclear S30(p,γ)Cl31 reaction is tentatively predicted to be Ec.m.=453(8) keV and this supports a Ar31 β+-delayed proton-decay observation of this resonance at Ec.m.=461(15) keV. These substantial reductions in the uncertainties in the thermonuclear S30(p,γ)Cl31 reaction rate and Q value constrain the region of temperature-density-composition parameter space where the S30(p,γ) (γ,p) equilibrium and the S30 waiting point may be active. © 2009 The American Physical Society.