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

## TL;DR

This study provides the first experimental measurement of $^{30}$S+$\alpha$ resonant elastic scattering, identifying new resonant states in $^{34}$Ar that significantly influence the $^{30}$S($\alpha$,p) reaction rate critical for modeling type I x-ray bursts.

## Contribution

First measurement of $^{30}$S+$\alpha$ resonant elastic scattering, discovering new resonant states and refining the $^{30}$S($\alpha$,p) reaction rate for astrophysical models.

## Key findings

- Identified three new resonant states in $^{34}$Ar between 11.1 and 12.1 MeV.
- Calculated an upper limit for the $^{30}$S($\alpha$,p) reaction rate that exceeds statistical model estimates.
- Showed that the new reaction rate significantly impacts x-ray burst energy predictions.

## 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.