Advances in the Direct Study of Carbon Burning in Massive Stars

Abstract

The 12 C þ 12 C fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window-the energy regime relevant to carbon burning in massive stars. The 12 C þ 12 C system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the 12 C þ 12 C fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies.

New Measurement of C12+C12 Fusi

“…1) has a significantly larger contribution from the alpha-particle channels. The recent coincident measurement by the STELLA Collaboration [34] shows similar S Ã ðEÞ factors for both channels above E c:m: ¼ 3 MeV while dramatically higher values in the α 1 channel at energies below 3 MeV. In particular, the STELLA data provide a p 1 upper limit at E c:m: ¼ 2.2 MeV similar to our measurement whereas they claim a much stronger α 1 S Ã ðEÞ factor at the same energy.…”

“…1. The total S Ã ðEÞ factor for this work is shown and compared with previous direct measurement data [22][23][24]26,27,29,[32][33][34]. a layered structure of multiple thin graphene sheets [40].…”

“…An early test experiment using the particle-γ coincidence technique for the 12 C þ 12 C reaction was conducted at Argonne National Laboratory [35]. Similar techniques were then used to measure the cross sections at a few points with energies below E c:m: ≤ 5 MeV (labeled as "Jiang2018" [33] and "STELLA2019" [34,36] in Fig. 1).…”

The Study of Key Reactions Shaping the Post-Main Sequence Evolution of Massive Stars in Underground Facilities

“…The S-factor upper limit at 2.2 MeV for proton (p 1 ) and alpha (α 1 ) channels is lower than THM data. We note that the upper limit for the proton channel disagrees significantly with the recent measurement of Fruet et al (2020). The discrepancy is less evident, but still present, for the alpha channel.…”

“…Another step forward in the knowledge of the 12 C+ 12 C rate has been recently moved by Fruet et al (2020). They performed a direct measurement down to ≈2.2 MeV using the particle-gamma coincidence technique.…”