Direct Measurements ofNa22(p,γ)Mg23Resonances and Consequences for

A. L. Sallaska

¹

,

C. Wrede

²

,

A. Garcı́a

³

et al.

Abstract

The radionuclide 22Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22Na(p,γ)23Mg reaction. We have measured the strengths of low-energy 22Na(p,γ)23Mg resonances directly and absolutely using a radioactive 22Na target. We find the strengths of resonances at Ep=213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4-3.2, and we exclude important contributions to the rate from proposed resonances at Ep=198, 209, and 232 keV. The 22Na abundances expected in the ejecta of classical novae are reduced by a factor of ≈2.

Measurement of lifetimes inMg23

“…We note that our result is consistent with the mean lifetime of τ = 10 ± 3 fs reported in Ref. [11], but also the mean lifetime of τ = 2.4 −0.9 meV [8,9], assuming B p = 0.037 ± 0.07 [13].…”

“…At the peak temperatures occurring in classical novae, the reaction rate is dominated by a single resonance due to an excited state in the compound nucleus, 23 Mg, at an excitation energy of 7787 keV. The two direct measurements of the resonance strength reported in the literature differ by a factor of 3 [7,8]. The resonance strength deduced indirectly from the properties of the 7787 keV state is consistent with the lower of the two reported direct measurements, but hinges on a single lifetime measurement with a 30% error bar [11].…”

“…The first measurement was performed at RuhrUniversität Bochum, Germany, in two attempts with results published in 1990 [6] and 1996 [7]. The second measurement was performed at the University of Washington in Seattle with results published in 2010 [8] and 2011 [9]. Both studies conclude that at peak nova temperatures the reaction is dominated by a resonance at a proton energy of E p = 213 keV, corresponding to an excitation energy of E x = 7787 keV in the compound nucleus 23 Mg. (At the very highest nova temperatures a resonance at 288 keV also makes a significant contribution.)…”

Precise and accurate determination of theB8decay spectrum

“…The two least energetic β-delayed proton peaks of 23 energetic proton peak is particularly well determined through measurements of the 22 Na(p, γ ) 23 Mg reaction [36,37]. The remaining proton peaks have not previously been observed but can, in most cases, be identified with known states in 23 Mg.…”

Strengths of the resonances at 436, 479, 639, 661, and 1279 keV in theNe22(p,γ)Na23Depalo1, Cavanna2, Ferraro3 et al. 2015Phys. Rev. C425585View full textAdd to dashboardCite

“…Whithin the cycle, 22 Ne can only be produced by the decay of radioactive 22 Na (T 1/2 = 2.6027 y [2]). However, this decay competes with proton capture on 22 Na [3]. At temperatures T > 70 MK, proton capture surpasses the decay, and 22 Ne is effectively bypassed in the NeNa cycle.…”