What element does fission ocurr in?

Fission primarily occurs in heavy elements, most commonly uranium-235 and plutonium-239. When these isotopes are bombarded with neutrons, they can split into smaller nuclei, releasing a significant amount of energy along with additional neutrons. This process is the fundamental principle behind nuclear reactors and atomic bombs. Other heavy elements, such as thorium and uranium-238, can also undergo fission under certain conditions.