First inverse kinematics study of the Ne22(p,γ)Na23 reaction and its role in AGB star and classical nova nucleosynthesis

Abstract

Background: Globular clusters are known to exhibit anomalous abundance trends such as the sodium-oxygen anticorrelation. This trend is thought to arise via pollution of the cluster interstellar medium from a previous generation of stars. Intermediate-mass asymptotic giant branch stars undergoing hot bottom burning (HBB) are a prime candidate for producing sodium-rich oxygen-poor material, and then expelling this material via strong stellar winds. The amount of 23 Na produced in this environment has been shown to be sensitive to uncertainties in the 22 Ne(p, γ ) 23 Na reaction rate. The 22 Ne(p, γ ) 23 Na reaction is also activated in classical nova nucleosynthesis, strongly influencing predicted isotopic abundance ratios in the Na-Al region. Therefore, improved nuclear physics uncertainties for this reaction rate are of critical importance for the identification and classification of pre-solar grains produced by classical novae. Purpose: At temperatures relevant for both HBB in AGB stars and classical nova nucleosynthesis, the 22 Ne(p, γ ) 23 Na reaction rate is dominated by narrow resonances, with additional contribution from direct capture. This study presents new strength values for seven resonances, as well as a study of direct capture. Method: The experiment was performed in inverse kinematics by impinging an intense isotopically pure beam of 22 Ne onto a windowless H 2 gas target. The 23 Na recoils and prompt γ rays were detected in coincidence using a recoil mass separator coupled to a 4π bismuth-germanate scintillator array surrounding the target. Results: For the low-energy resonances, located at center of mass energies of 149, 181, and 248 keV, we recover stength values of ωγ 149 = 0.17 +0.05 −0.04 , ωγ 181 = 2.2 ± 0.4, and ωγ 248 = 8.2 ± 0.7 μeV, respectively. These results are in broad agreement with recent studies performed by the LUNA and TUNL groups. However, for the important reference resonance at 458 keV we obtain a strength value of ωγ 458 = 0.44 ± 0.02 eV, which is significantly lower than recently reported values. This is the first time that this resonance has been studied completely independently from other resonance strengths. For the 632-keV resonance we recover a strength value of ωγ 632 = 0.48 ± 0.02 eV, which is an order of magnitude higher than a recent study. For reference resonances at 610-and 1222-keV, our strength values are in agreement with the literature. In the case of direct capture, we recover an S factor of 60 keV b, consistent with prior forward kinematics experiments. Conclusions: In summary, we have performed the first direct measurement of 22 Ne(p, γ ) 23 Na in inverse kinematics. Our results are in broad agreement with the literature, with the notable exception of the 458-keV

New measurement of the $E_{\mathrm{c.m.}}=323$ keV resonance in the $^{19}$F$($p,γ$)$^{20}$Ne reaction

“…The data analysis follows similarly to recently published work using the DRAGON facility aimed at determining absolute resonance strengths for narrow, isolated resonances [10]. The only difference in the analysis procedure in this work is the absence of any result obtained from heavy-ion only detection ('singles' events), due to a large quantity of scattered beam, from which genuine recoils could not be distinguished without a coincident γray ('coincidence' events).…”

“…The only difference between the present set-up and that of Ref. [10] is that the second MCP (MCP1) was not part of the local time-of-flight system due to difficulties with excessive noise, which significantly lowered the detection efficiency. However, as described in Section III F, recoils could nonethe-less be readily identified using signals from the first MCP (MCP0) and the DSSD.…”

“…A detailed description of the DRAGON facility, including its detectors and key components, is given in Refs. [7,10] and so will not be repeated here. The only difference between the present set-up and that of Ref.…”

The Status and Future of Direct Nuclear Reaction Measurements for Stellar Burning

“…The data taken for resonances in the 22 Ne(α,γ) 26 Mg reaction in 2019 are expected to be published in 2021. Further, the results from stable beam measurements to investigate reactions such as 22 Ne(p,γ) 23 Na [193,194], 76 Se(α,γ) [195], 34 S(p,γ) [196] and 19 F(p,γ) [197] have recently been published.…”

Polarization Effects in the Reaction d+eˉ → d+eˉ

“…Ne p Na  reaction has, for the first time, been investigated directly in inverse kinematics [10]. A total of 7 resonances were measured.…”