Cross Section for the Astrophysical¹⁴C(<i>n</i>, γ)¹⁵C Reaction via the Inverse Reaction

Abstract

The 14C(n, γ)15C reaction is important in neutron-induced CNO cycles of stellar evolution phases beyond the main sequence. The chain of reactions in primordial nucleosynthesis in the neutron-rich environment of an inhomogeneous big bang also involves the 14C(n, γ)15C reaction. We have used a beam of 15C ions at E/A = 35 MeV to measure cross sections for 15C breakup on targets of C, Al, Zn, Sn, and Pb. The Coulomb part of the breakup cross section was determined as a function of decay energy. By the principle of detailed balance, the neutron capture cross section was then determined as a function of neutron energy. This excitation function rises with energy to 7 μbarns at 300 keV and falls to 2 μbarns at 1.2 MeV. In the stellar-burning region, our cross section exceeds a previous measurement by a factor of 3. Neither the shape nor the magnitude of the excitation function agrees with those of theoretical calculations based on the direct capture model. The reaction rate is calculated reliably up to ~T9 = 5. In the temperature range of inhomogeneous big bang models, our rate exceeds the rate of the 14C(p, γ)15N reaction for T9 < 1.2.