Experimental evidence for a natural parity state inMg26and its impact on the production of neutrons for thesprocess

Abstract

We have studied natural parity states in 26 Mg via the 22 Ne( 6 Li, d) 26 Mg reaction. Our method significantly improves the energy resolution of previous experiments and, as a result, we report the observation of a natural parity state in 26 Mg. Possible spin-parity assignments are suggested on the basis of published γ -ray decay experiments. The stellar rate of the 22 Ne(α, γ ) 26 Mg reaction is reduced and may give rise to an increase in the production of s-process neutrons via the 22 Ne(α, n) 25 Mg reaction.

Probing astrophysically important states in theMg26nucleus to study neutron sources for thesprocess

“…A number of scattering and transfer measurements ( [50], [51], [52], [42], [53], [54] and [55]) have been performed to investigate the level structure of 26 Mg above the α-threshold. 26 Mg by Longland et al [55] and deBoer et al [58] and 26 Mg(γ, n) 25 Mg measurement by deBoer et al [59].…”

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

“…Despite several attempts to measure the reaction cross section [52][53][54][55], these experiments failed to reach the low α energies of astrophysical relevance, mostly because cosmic-ray induced background starts to dominate the experimental signatures below E α = 0.5 MeV. A series of indirect measurements via α-particle transfer reactions have been performed to overcome this limitation [56,57]. Alternatively, the 25 Mg(n, γ ) 26 Mg reaction can be used to populate the same excited states as shown in Fig.…”

The6Li(22Ne,26Mg)d α-transfer experiment for the study of low-energy resonances in22Ne(α,γ)26Mg

“…Energy resolutions of ΔE and E detectors for the upstream detectors are 40 keV and 25 keV respectively, measured using 241 Am α source. Thus a combined energy resolution of < 50 keV, an improvement over the former experiment in the normal kinematics [12], is expected.…”

“…The reaction also acts as a secondary neutron source during the s process in low-mass asymptotic giant branch (AGB) stars during which roughly half the abundances of nuclides in the A=90-209 range are thought to be synthesized [2]. A variety of attempts to experimentally determine the rate for this reaction at the Gamow window corresponding to s process temperatures (T = 0.2-0.3 GK) have been made either through direct 22 Ne(α,n) 25 Mg measurements [e.g., [3][4][5][6] or indirectly via 26 Mg(γ,n) 25 Mg [7], 25 Mg(n,γ) 26 Mg [8], 26 Mg(γ,γ') 26 Mg [9], 26 Mg(p,p'γ) 26 Mg [10], and 22 Ne( 6 Li,d) 26 Mg reactions [11,12]. However, direct measurements have been hindered by the small cross section due to the Coulomb barrier and the resonances at E α < 830 keV have not been identified with this method.…”

“…Of these uncertainties, the ratio of Γ n and Γ γ to determine the branching ratio of n and γ emission channels plays an important role in obtaining the neutron yield for the s process. [11,12]. These studies were hindered however from background due to indirect reactions and the 12 C( 6 Li,d) 16 O reaction from the C backing foil and some unresolved doublets, thus left some resonance energies uncertain.…”