Astrophysical S_E2 factor of the ¹²C(α, γ)¹⁶O reaction through the ¹²C(¹¹B, ⁷Li)¹⁶O transfer reaction

¹ China Institute of Atomic Energy, P.O. Box 275(10), Beijing, 102413, China
² School of Physics and Nuclear Energy Engineering, Beihang University, Beijing, 100191, China
³ International Research Center for Nuclei and Particles in the Cosmos, Beihang University, Beijing, 100191, China
⁴ College of Physics Science and Technology, Shenzhen University, Shenzhen, 518060, China

^a e-mail: guobing@ciae.ac.cn

Published online: 12 February 2016

Abstract

The ¹²C(α, γ)¹⁶O reaction plays a key role in the evolution of stars with masses of M > 0.55 M_⊙. At the Gamow peak (E_c.m. = 300 ke V, T₉ = 0.2), the cross section of the ¹²C(α, γ)¹⁶O reaction is so small (about 10⁻¹⁷ barn) that the direct measurement in ground laboratory is not feasible with the existing technology. Up to now, the cross sections at lower energies can only be extrapolated from the data at higher energies. However, two subthreshold resonances, locating at E_x = 7.117 MeV and E_x = 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 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 DWBA analysis, we derived the square of ANC of the 6.917 MeV level in ¹⁶O to be (2.45± 0.28) ×10¹⁰ fm⁻¹, with which the reduced-α width can be computed. Finally, we calculated the astrophysical S_E2 factor of the 6.917 MeV resonance to be 67.6 ± 7.7 ke V b.