Thermonuclear S30(p,γ)Cl31 reaction in type i x-ray bursts

C. Wrede, Yale University
J. A. Caggiano, TRIUMF
J. A. Clark, Yale University
C. M. Deibel, Yale University
A. Parikh, Yale University
P. D. Parker, Yale University


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.