Measurement of fusion cross sections in 12C + 12C at Low beam energies using a particle-gamma coincidence technique, C. L. Jiang1, M. Alcorta1, B. B. Back1, B. Bucher2, P. Collon2, C. M. Deibel1;3, B. DiGiovine1, J. P. Greene1, D. J. Henderson1, R. V. F. Janssens1, X. Fang2, T. Lauritsen1, C. J. Lister1, S. T. Marley1;4, R. C. Pardo1, K. E. Rehm1, D. Seweryniak1, X. D. Tang2, C. Ugalde1, and S. Zhu1, [1] Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA, [2] University of Notre Dame, Notre Dame, IN 46556, USA, [3] Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824, USA and, [4] Western Michigan University, Kalamazoo, MI 49008, USA − Carbon burning, the fusion of two 12C nuclei, plays an important role in stellar evolution, especially in the interior of highly developed stars, such as type Ia supernovae and X-ray superbursts, where this reaction is an important route for the production of heavier elements.  Because of its importance in nuclear astrophysics, many measurements of the 12C + 12C reaction have been performed in the past.  Although in explosive scenarios this reaction occurs at higher temperatures, the corresponding Gamow energies are still very low, resulting in extremely small cross sections, which so far are inaccessible experimentally.  As a result, one has to rely on phenomenological extrapolations and/or model calculations in order to obtain the appropriate astrophysical reaction rates. 

 

From a comparison of various experimental excitation functions of the fusion reaction 12C + 12C one observes that the measurements are consistent only at higher energies.   At lower energies, large deviations among the various experiments or extrapolations are observed.  There has recently been some controversy about the existence of a possible new resonance at Ecm = 2.14 MeV. This resonance, with cross sections reaching 1.5 nb, was first observed by studying the γ-rays from the 23Na evaporation residues [1].  However, a subsequent measurement using the charged-particle technique by the same collaboration gave a preliminary cross section of only about 25 pb [2].  Similarly, due to heavy ion fusion hindrance, the behaviors of the extrapolated excitation function at very low energy differ by many orders of magnitude [3].  Since the extrapolations and theoretical calculations are based on the data in the experimentally accessible region, it is important to measure the fusion cross sections in 12C + 12C down to the lowest energies in a reliable fashion.