delayed neutronn. a neutron emitted as a result of the radioactive decay of any of the nuclei produced in a fission reaction, rather than during the reaction itself; contrasted with prompt neutron (see promptadj. 5).
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1939 Sci. News Let. 11 Mar. 149/1 Only rarely would one of the delayed neutrons happen to hit another uranium atom and break it, too.
2017 S. MarguetPhysics Nucl. Reactors ii. 145Delayed neutrons are emitted at a lower energy level.