Three-Body Spectrum of ~(18)C and its Relevance to r -Process Nucleosynthesis

摘要

The ~(18)C spectrum has been studied in a three body n + n +~(16)C model that includes deformation and the 2~+ excitation of the ~(16)C core as well as Pauli projection of forbidden states. The ~(16) - n interaction employed in this study has been fitted to reproduce the experimental spectrum of ~(17)C. The calculations show that two neutron separation energy in ~(18)C in consistent with three-body structure of this nucleus and predict more states bound with respect to three-body decay. The comparison of their position to known excited states in ~(18)C is discussed. These calculations suggest also that a few states may exist in astrophysically relevant region between the ~(17)C + n and ~(16)C + 2n decay thresholds. The most important of them is 1~- as it can give a large E1 resonant contribution to ~(17)C+(n, γ)~(18)C neutron capture. The calculations also suggest that a virtual s-wave state may exist above the ~(17)C+n threshold that can give rise to non-negligible M1 contributions to the ~(17)C (n, γ)~(18)C reaction rate. The presence of these states in the ~(18)C spectrum can lead to an increased ~(17)C(n, γ)~(18) reaction rate, which can significantly influence the abundances of uranium and thorium synthesized in the r-process in the supernovae explosions.