Georgia High School Physical Science EOC Practice Test

Fission is the splitting of a heavy atomic nucleus into lighter parts, typically producing energy and additional neutrons in the process. This splitting is the defining feature: a large nucleus like uranium or plutonium breaks into two (or sometimes more) smaller nuclei. Emission of gamma rays can occur alongside the reaction, but it isn’t what the process is called. Fusion, by contrast, is the joining of light nuclei to form heavier ones, which is a different kind of nuclear reaction. Absorption of neutrons is a separate step that can even trigger fission in some materials, but it doesn’t describe the act of splitting itself. So the description that matches fission most directly is the splitting of a heavy nucleus into smaller parts.