Neutron capture is a nuclear process where an atomic nucleus absorbs a neutron. This can occur in various elements, particularly in heavy nuclei like those of uranium or plutonium. When a nucleus captures a neutron, it may become unstable and can either emit radiation or undergo fission, splitting into smaller nuclei. This process is significant in nuclear reactions, such as those occurring in nuclear reactors and stellar nucleosynthesis. In stars, neutron capture contributes to the formation of heavier elements, playing a crucial role in the evolution of the universe and the creation of elements beyond iron in the periodic table.