Indirect study of the 12C(α,γ)16O reaction via the 12C(7Li, t)16O transfer reaction

N. Oulebsir, F. Hammache, P. Roussel, M. G. Pellegriti, L. Audouin, D. Beaumel, A. Bouda, P. Descouvemont, S. Fortier, L. Gaudefroy, J. Kiener, A. Lefebvre-Schuhl, and V. Tatischeff
Phys. Rev. C 85, 035804 – Published 16 March 2012

Abstract

The 12C(α,γ)16O reaction plays a crucial role in stellar evolution. The rate of this reaction determines directly the 12C-to-16O abundance ratio at the end of the helium burning phase of stars and consequently has a big effect on the subsequent nucleosynthesis and even on the evolution of massive stars. However, despite many experimental studies, the low-energy cross section of 12C(α,γ)16O remains uncertain. The extrapolation of the measured cross sections to stellar energies (E300 keV) is made particularly difficult by the presence of the 2+ (Ex=6.92 MeV) and 1 (Ex=7.12 MeV) subthreshold states of 16O. To further investigate the contribution of these two subthreshold resonances to the 12C(α,γ)16O cross section, we determine their α-reduced widths via a measurement of the transfer reaction 12C(7Li, t)16O at two incident energies, 28 and 34 MeV. The uncertainties on the determined α-spectroscopic factors and the α-reduced widths were reduced thanks to a detailed distorted-wave Born approximation analysis of the transfer angular distributions measured at the two incident energies. The R-matrix calculations of 12C(α,γ)16O cross section using our obtained α-reduced widths for the 2+ and 1 subthreshold resonances lead to an E1 S factor at 300 keV of 100±28 keV b, which is consistent with values obtained in most of the direct and indirect measurements as well as the NACRE collaboration compilation while the result for the E2 component SE2(300keV)=50±19 keV b disagrees with the NACRE adopted value .

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  • Received 21 July 2011

DOI:https://doi.org/10.1103/PhysRevC.85.035804

©2012 American Physical Society

Authors & Affiliations

N. Oulebsir1,2, F. Hammache1,*, P. Roussel1, M. G. Pellegriti1,†, L. Audouin1, D. Beaumel1, A. Bouda2, P. Descouvemont3, S. Fortier1, L. Gaudefroy4,‡, J. Kiener5, A. Lefebvre-Schuhl5, and V. Tatischeff5

  • 1Institut de Physique Nucléaire d’Orsay, UMR8608, IN2P3-CNRS, Université Paris sud 11, 91406 Orsay, France
  • 2Laboratoire de Physique Théorique, Université Abderahmane Mira, 06000 Béjaia, Algeria
  • 3Physique théorique et Mathématique, ULB CP229, B-1050 Brussels, Belgium
  • 4Grand Accélérateur National d'Ions Lourds, BP55076, 14076 Caen Cedex 5, France
  • 5CSNSM, IN2P3-CNRS, Université Paris sud 11, 91405 Orsay, France

  • *Corresponding author: hammache@ipno.in2p3.fr
  • Present address: Dipartimento di Fisica e Astronomia, Universitá di Catania and Laboratori Nazionali del Sud-INFN, Catania, Italy.
  • Present address: CEA, DAM, DIF, F-91297 Arpajon, France.

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Issue

Vol. 85, Iss. 3 — March 2012

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