New $\alpha$ ANC measurement of the 1/2$^+$ state in $^{17}$O at 6.356 MeV, that dominates the $^{13}$C($\alpha$,n)$^{16}$O reaction rate at temperatures relevant for the s-process

TL;DR

This study provides a new measurement of the alpha Asymptotic Normalization Coefficient (ANC) for the 1/2+ state in $^{17}$O at 6.356 MeV, clarifying previous experimental discrepancies and refining the reaction rate relevant for the s-process in stars.

Contribution

The paper introduces a novel alpha transfer measurement technique to accurately determine the ANC of the 1/2+ state in $^{17}$O, resolving prior experimental inconsistencies.

Findings

Discrepancies between previous alpha transfer experiments are resolved.

The measured ANC value is $( ilde C^{^{17} ext{O}(1/2+)}_{ ext{α-}^{13} ext{C}})^2=3.6 extpm0.7$ fm$^{-1}$.

Some disagreement remains with the Trojan Horse method measurement.

Abstract

Background: Accurate knowledge of the $^{13}$C($\alpha$,$n$)$^{16}$O reaction cross section is important for the understanding of the s-process in AGB stars, since it is considered to be the main source of neutrons. The sub-threshold 1/2$^+$ state at excitation energy of 6.356 MeV in $^{17}$O has a strong influence on the reaction cross section at energies relevant for astrophysics. Several experiments have been performed to determine the contribution of this state to the $^{13}$C($\alpha,n)^{16}$O reaction rate. Nevertheless, significant discrepancies between different measurements remain. Purpose: The aim of this work is to investigate these discrepancies. Method: An 8 MeV $^{13}$C beam (below the Coulomb barrier) was used to study the $\alpha$-transfer reaction $^6$Li($^{13}$C,$d$)$^{17}$O. Results: The squared Coulomb modified ANC of the 1/2$^+$ state in $^{17}$O measured in this work is $(\tilde C^{^{17}\text{O}(1/2+)}_{\alpha-^{13}\text{C}})^2=3.6\pm0.7\hspace{0.2cm}\text{fm}^{-1}$. Conclusions: Discrepancy between the results of $\alpha$-transfer experiments have been resolved. However, some discrepancy with the most recent measurement using the Trojan Horse method remains.