Deep underground laboratory measurement of $^{13}$C($\alpha$,$n$)$^{16}$O in the Gamow windows of the $s$- and $i$-processes

TL;DR

This study presents the first direct measurement of the $^{13}$C($ ext{α}$,$n$)$^{16}$O reaction at astrophysical energies using underground laboratories, significantly reducing uncertainties in reaction rates relevant to stellar nucleosynthesis.

Contribution

It provides the first consistent direct measurement of the reaction in the relevant energy range, reducing previous uncertainties and improving reaction rate estimates for s- and i-process nucleosynthesis.

Findings

Reduced the uncertainty of the reaction rate from 60% to 15%.

Eliminated systematic uncertainties from previous inconsistent data.

First direct determination of alpha strength for the near-threshold state.

Abstract

The $^{13}$C($\alpha$,$n$)$^{16}$O reaction is the main neutron source for the slow-neutron-capture (s-) process in Asymptotic Giant Branch stars and for the intermediate (i-) process. Direct measurements at astrophysical energies in above-ground laboratories are hindered by the extremely small cross sections and vast cosmic-ray induced background. We performed the first consistent direct measurement in the range of $E_{\rm c.m.}=$0.24 MeV to 1.9 MeV using the accelerators at the China Jinping Underground Laboratory (CJPL) and Sichuan University. Our measurement covers almost the entire i-process Gamow window in which the large uncertainty of the previous experiments has been reduced from 60\% down to 15\%, eliminates the large systematic uncertainty in the extrapolation arising from the inconsistency of existing data sets, and provides a more reliable reaction rate for the studies of the s- and i-processes along with the first direct determination of the alpha strength for the near-threshold state.