Resonance neutron-capture cross sections of stable magnesium isotopes and their astrophysical implications

Abstract

We have measured the neutron capture cross sections of the stable magnesium isotopes 24,25,26 Mg in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in 25 Mg and 26 Mg were recorded using the total energy method based on C 6 2 H 6 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for 24 Mg, 25 Mg, and 26 Mg are 3.8±0.2 mb, 4.1±0.6 mb, and 0.14±0.01 mb, respectively.

Decay properties of 22Ne + α resonances and their impact on s-process nucleosynthesis

“…In particular it disagrees by 5.0σ with the Table 2: Resonance parameters determined for the 26 Mg 11.32 MeV state and natural parity states between the neutron threshold and 11.25 MeV identified in Refs. [20,21]. All upper limits are quoted at 90% CL, and uncertainties in parentheses are quoted at 1σ (68% CL).…”

“…Based on these results, the authors established that this state dominates the 22 Ne(α, γ) 26 Mg rate between ∼0.2-0.4 GK and that it could potentially dominate the 22 Ne(α, n) 25 Mg rate below 0.2 GK. More recently, neutron capture studies by Massimi et al have identified four natural-parity resonances in the 26 Mg excitation energy range from 11.1-11.3 MeV [20,21]. Three of these resonances were found to stongly neutron decay, while the fourth, E x = 11.171 MeV, was identified as a 2 + state with a significant γ-ray decay branch (Γ n /Γ γ = 0.2-6).…”

“…Taken in conjunction with the resonance parameters (J, Γ n , Γ γ ) established by Massimi et al, this results in new upper limits on both the (α, n) and (α, γ) strengths for the four natural-parity states in this region identified in Refs. [20,21].…”

Ni62(n,γ) andNiLederer1, Massimi2, Berthoumieux3 et al. 2014Phys. Rev. CSelf Cite332160View full textAdd to dashboardCite

“…Accurate cross sections are particularly important between Fe and Zr and for the light neutron poisons. The uncertainty of a single cross section may be propagated to the abundances of the following isotopes on the s-process path, or over the complete s-process distribution in the case of neutron poisons (see, e.g., [11]). This propagation effect is a peculiar feature of the the weak s process [12,13].…”

Longitudinal and transverse electron-nucleus scattering form factors ofMg25

“…Many papers have recorded the study of the slow-neutron-capture (s) process, an important source of neutrons within the reaction 22 Ne(α,n) 25 Mg. This reaction plays an important role during core helium burning, in carbon-shell burning [1][2][3], and is Mg-Al cycle active in stellar H -shell burning [4]. Recently, the nuclear structure of this isotope has been studied by a number of theoretical methods, all dealing with the hyperon in p orbit [5][6][7].…”