First measurement of ${}^{30}$S+$\alpha$ resonant elastic scattering for the ${}^{30}$S($\alpha$,p) reaction rate

Abstract

Background: Type I x-ray bursts are the most frequent thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The ${}^{30}$S($\alpha$,p) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in ${}^{34}$Ar and determine their quantum properties. In particular, natural-parity states with large $\alpha$-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of ${}^{30}$S+$\alpha$ resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for ${}^{30}$S($\alpha$,$\alpha$) near $150^{\circ }$ in the center-of-mass frame. The experimental data were analyzed with an $R$-Matrix calculation, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of ${}^{30}$S($\alpha$,p) based on all available experimental data of ${}^{34}$Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the ${}^{30}$S($\alpha$,p)${}^{33}$Cl rate significantly affects the predicted nuclear energy generation rate during the burst.

arXiv comment16 pages, 12 figures

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• Progress in Nuclear Astrophysics of East and Southeast Asia
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