[Bubble] Astrophysical SE2 factor of the 12C(α,γ)16O reaction through the 12C(11B,7Li)16O transfer reaction

[Jay Benesch]

https://arxiv.org/abs/1811.06220

Astrophysical SE2 factor of the 12C(α,γ)16O reaction through the 
12C(11B,7Li)16O transfer reaction
Y. P. Shen, B. Guo, Z. H. Li, Y. J. Li, D. Y. Pang, S. Adhikari, Z. D. 
An, J. Su, S. Q. Yan, X. C. Du, Q. W. Fan, L. Gan, Z. Y. Han, D. H. Li, 
E. T. Li, G. Lian, J. C. Liu, T. L. Ma, C. J. Pei, Y. Su, Y. B. Wang, Y. 
Zhou, W. P. Liu
(Submitted on 15 Nov 2018)

     The 12C(α,γ)16O reaction plays a key role in the evolution of stars 
with masses of M> 0.55 M⊙. The cross-section of the 12C(α,γ)16O reaction 
within the Gamow window (Ec.m. = 300 keV, T9 = 0.2) is extremely small 
(about 10−17 barn), which makes the direct measurement in a ground-based 
laboratory with existing techniques unfeasible. Up until now, the 
cross-sections at lower energies can only be extrapolated from the data 
at higher energies. However, two subthreshold resonances, located at Ex 
= 7.117 MeV and Ex = 6.917 MeV, make this extrapolation more 
complicated. In this work, the 6.917 MeV subthreshold resonance in the 
12C(α,γ)16O reaction was investigated via the 12C(11B,7Li)16O reaction. 
The experiment was performed using the Q3D magnetic spectrograph at the 
HI-13 tandem accelerator. We measured the angular distribution of the 
12C(11B,7Li)16O transfer reaction leading to the 6.917 MeV state. Based 
on the FRDWBA analysis, we derived the asymptotic normalization 
coefficient (ANC) of the 6.917 MeV level in 16O to be (1.10 ± 0.29) 
×1010 fm−1, with which the reduced α width was computed to be 18.0±4.7 
keV at the channel radius of 6.5 fm. Finally, we calculated the 
astrophysical SE2(300) factor of the ground-state transitions to be 46.2 
± 7.7 keV b. The result for the astrophysical SE2(300) factor confirms 
the values obtained in various direct and indirect measurements and 
presents an independent examination of the most important data in 
nuclear astrophysics.