Nuclear Excitation by Electron Capture in Stellar Environments

Abstract

In the resonant process of nuclear excitation by electron capture (NEEC), a free electron recombines into the atomic shell of an ion with the simultaneous excitation of the nucleus. This process is expected to be efficient in populating excited nuclear states in stellar plasmas of high electron density. In this work, we study the possible interplay of NEEC with nuclear excitation by neutron capture as well as associated gamma-decay and neutron emission in the context of nucleosynthesis. Neutron capture followed by beta-decay of the thus formed neutron-rich daughter isotopes constitutes the basic reaction leading to the synthesis of heavy isotopes. For the first time the impact of NEEC taking place prior to the decay of the high-energy state formed by neutron capture is investigated. We show that an additional nuclear excitation of the order of magnitude of 10 keV can cause substantial changes to the net decay rates of the excited nucleus making neutron re-emission predominant. As a consequence, the production of the daughter isotopes would be signi_cantly damped. This first estimate motivates further studies on the impact of NEEC on neutron capture nucleosynthesis