What occurs during nuclear fission?

During nuclear fission, a heavy nucleus, such as that of uranium or plutonium, undergoes a process where it splits into lighter nuclei. This splitting releases a substantial amount of energy, primarily due to the conversion of mass into energy as described by Einstein’s equation (E=mc^2). The fission process typically also releases neutrons, which can further induce fission in nearby heavy nuclei, leading to a chain reaction. This characteristic of fission is exploited in nuclear power plants and atomic bombs.

The other options describe different nuclear processes. The second option refers to nuclear fusion, where light nuclei combine to form heavier nuclei, a process that generally requires and absorbs a large amount of energy. The third option mentions proton decay, which is a rare process where protons can decay into neutrons, but this is not a typical feature of fission. The fourth option also pertains to fusion and the formation of heavier elements, which is distinct from the splitting action that characterizes nuclear fission. Thus, the correct answer accurately captures the essence of what occurs during the fission process.