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Pré-Publication, Document De Travail (Preprint/Prepublication) Année : 2022

Understanding the cosmic abundance of $^{22}$Na: lifetime measurements in $^{23}$Mg

Résumé

Simulations of explosive nucleosynthesis in novae predict the production of 22 Na, a key astronomical observable to constrain nova models. Its gamma-ray line at 1.275 MeV has not yet been observed by the gamma-ray space telescopes. The 20 Ne/ 22 Ne ratio in presolar grains, a possible tool to identify nova grains, also depends on 22 Na produced. Uncertainties on its yield in classical novae currently originate from the rate of the 22 Na(p, γ) 23 Mg reaction. At peak novae temperatures, this reaction is dominated by a resonance at E R =0.204 MeV, corresponding to the E x =7.785 MeV excited state in 23 Mg. The resonance strengths measured so far disagree by one order of magnitude. An experiment has been performed at GANIL to measure the lifetime and the proton branching ratio of this key state, with a femtosecond resolution for the former. The reactions populating states in 23 Mg have been studied with a high resolution detection setup , i.e. the particle VAMOS, SPIDER and gamma tracking AGATA spectrometers, allowing the measurements of lifetimes and proton branchings. We present here a comparison between experimental results and shell-model calculations, that allowed us to assign the spin and parity of the key state. Rather small values obtained for reduced M1 matrix elements, |M(M1)| 0.5 µ N , and proton spectroscopic factors, C 2 S p <10 −2 , seem to be beyond the accuracy of the shell model. With the reevaluated 22 Na(p, γ) 23 Mg rate, the 22 Na detectability limit and its observation frequency from novae are found promising for the future space telescopes.
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Dates et versions

hal-03832433 , version 1 (27-10-2022)

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Chloé Fougères, Francois de Oliveira Santos, Nadezda A. Smirnova, Caterina Michelagnoli. Understanding the cosmic abundance of $^{22}$Na: lifetime measurements in $^{23}$Mg. 2022. ⟨hal-03832433⟩
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