Measurement of the $^{18}$Ne($\alpha,p$)$^{21}$Na reaction with ANASEN at $E_{c.m.} = $ 2.5-4 MeV

TL;DR

This study measures the $^{18}$Ne($ extalpha$,p)$^{21}$Na reaction cross section at energies relevant to astrophysical processes, providing new data that refines understanding of nucleosynthesis in X-ray bursts.

Contribution

It presents the first experimental cross section measurements of the $^{18}$Ne($ extalpha$,p)$^{21}$Na reaction in the 2.5-4 MeV range using the ANASEN detector, improving upon previous data.

Findings

Measured cross sections align with inverse reaction results.

Cross sections are lower than previous direct measurements.

Data highlights excited states' role in the reaction.

Abstract

The $^{18}$Ne($\alpha,p$)$^{21}$Na reaction plays a significant role in Type-I X-ray bursts. It is a major path in the breakout from the hot-CNO cycles to the synthesis of heavier elements in the $\alpha p$-- and $rp$-processes. An experiment to determine the cross section of this reaction was performed with the ANASEN active-target detector system, determining the cross section at energies between 2.5 and 4 MeV in the center-of-mass frame. The measured cross sections for reactions populating the ground state in $^{21}$Na are consistent with results obtained from the time-inverse reaction, but significantly lower than the previously published experimental data of direct measurements. The total cross sections are also compared with those derived from indirect methods and statistical-model calculations. This experiment establishes a new experimental data set on the excitation function of the $^{18}$Ne($\alpha,p$)$^{21}$Na reaction, revealing the significance of the excited states' contributions to the total reaction cross section and allowing to separate the contribution of the $(\alpha,2p)$ reaction. The impact of the measured cross section on thermal reaction rates is discussed.