Ambiguities in the rate of oxygen formation during stellar helium burning in the C-12(alpha,gamma) reaction

作者：Gai Moshe^*

来源：Physical Review C, 2013, 88(6): 062801.

DOI：10.1103/PhysRevC.88.062801

The rate of oxygen formation determines the C/O ratio during stellar helium burning. It is the single most important nuclear input in stellar evolution theory, including the evolution of type II and type Ia supernova. However, the low-energy cross section of the fusion of He-4 + C-12, denoted as the C-12(alpha, gamma)O-16 reaction, still remains uncertain. I analyze and critically review the most recent measurements of complete angular distributions of the outgoing gamma rays at very low energies (E-c.m. %26gt;= 1.0 MeV). My analysis of the angular distributions measured with the EUROGAM/GANDI arrays leads to considerably larger error bars than have been published, which excludes them from the current sample of %26quot;world data.%26quot; I show that the current sample of %26quot;world data%26quot; of the measured E2 cross-section factors below 1.7 MeV cluster into two distinct groups that lead to two distinct extrapolations: S-E2(300) approximate to 60 or S-E2(300) approximate to 154 keVb. There is a discrepancy between the measured E1-E2 phase difference (phi(12)) and unitarity as required by the Watson theorem, which suggests systematic problem(s) in some of the measured gamma-ray angular distributions. The ambiguity of the extrapolated S-E2(300) together with the previously observed ambiguity of S-E1(300) (approximately 80 or 10 keVb) must be resolved by future measurements of complete and detailed angular distributions of the C-12(alpha, gamma) reaction at very low energies (E-c.m. %26lt;= 1.0 MeV).

• 出版日期2013-12-4