Background: Type I x-ray bursts are the most frequently observed thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The S30(α,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 Ar34 and determine their quantum properties. In particular, natural-parity states with large α-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of S30+α 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 S30(α,α) near 150 in the center-of-mass frame. The experimental data were analyzed with R-matrix calculations, 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 S30(α,p) based on all available experimental data of Ar34 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 S30(α,p)Cl33 rate significantly affects the predicted nuclear energy generation rate during the burst.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics