First Accurate Normalization of the β -delayed α Decay of N16

Abstract

The 12 C(α, γ) 16 O reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ11, of the bound 1 − level in 16 O is particularly important to determine the cross section. The magnitude of γ11 is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of 16 N, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1 − level [b β,11 = (5.02 ± 0.10) × 10 −2 ] and for β-delayed α emission [b βα = (1.59 ± 0.06) × 10 −5 ]. Our value for b βα is 33% larger than previously held, leading to a substantial increase in γ11. Our revised value for γ11 is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ11, which provides significantly improved constraints on the 12 C(α, γ) cross section in the energy range relevant to hydrostatic He burning.

Impact ofO16(γ,α)C12measurements on theFilippone1, Pieper2 2019Phys. Rev. C

“…We then calculated the E L ground-state radiative cross section [15] for the 12 C(α, γ ) 16 O reaction from the collision TABLE I. Parameters used in the present simultaneous fits to original data for E 1 and E 2 and a channel radius of 5.43 fm. These parameters were used to generate the curves in Fig.…”

“…The 12 C(α, γ ) 16 O reaction is believed to be one of the most important reactions in nuclear astrophysics [1,2]. A recent review [3] highlights the key role played by this reaction in both the evolution of and nucleosynthetic yields from massive stars.…”

“…A recent review [3] highlights the key role played by this reaction in both the evolution of and nucleosynthetic yields from massive stars. The purpose of this study is to explore the role that forthcoming measurements of the inverse reaction- 16 O(γ , α) 12 C (OSGA)-could have on reducing the overall uncertainty in the cross section for the 12 C(α, γ ) 16 O reaction at helium burning temperatures. To do this, we perform fits to the existing data using the R-matrix approach [4] and study the impact of including new data on the inverse reaction.…”

“…To do this, we perform fits to the existing data using the R-matrix approach [4] and study the impact of including new data on the inverse reaction. This is achieved by starting with a reasonable R-matrix fit that can be used as a basis for comparison to fits with and without projected 16 O(γ , α) 12 C data. For the inverse capture data, we start with a proposed Jefferson Laboratory (JLab) experiment [5] in order to assess the possible role of new measurements in reducing the overall uncertainty in the cross section [6].…”

“…Measurements of the S factor as a function of energy are often reported in the literature. For the 12 C(α, γ ) 16 O reaction, the value of S at E = 300 keV is typically quoted as the most probable energy for stellar helium burning. Of course, the cross section is so small at 300 keV that it cannot be directly measured.…”