A new study of the $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction deep underground: Feasibility, setup, and first observation of the 186 keV resonance

TL;DR

This study demonstrates the feasibility of measuring the $^{22}$Ne(p,$$)$^{23}$Na reaction underground, reports the first observation of a key resonance at 186 keV, and develops a specialized experimental setup to improve nucleosynthesis data.

Contribution

It presents the first underground direct measurement of the $^{22}$Ne(p,$$)$^{23}$Na resonance at 186 keV and details the development of a dedicated experimental setup.

Findings

First observation of the 186 keV resonance in a direct experiment.

Established an experimental lower limit for the resonance strength.

Developed a specialized setup with characterized temperature and pressure profiles.

Abstract

The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the $^{22}$Ne(p,$\gamma$)$^{23}$Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a $^{22}$Ne(p,$\gamma$)$^{23}$Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400\,kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion beam induced $\gamma$-ray background has been studied. The feasibility study led to the first observation of the $E_{\rm p}$ = 186\,keV resonance in a direct experiment. An experimental lower limit of 0.12\,$\times$\,10$^{-6}$\,eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the $^{22}$Ne(p,$\gamma$)$^{23}$Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.