The term "fission" is used to describe the splitting of a heavy nucleus into two roughly equal-sized lighter nuclei. The revelation that such an unusual nuclear reaction could occur marked the conclusion of a really spectacular event in the history of science, and it ushered in an era of intense and fruitful research.
The history of nuclear fusion began at the turn of the 20th century with research into how stars generate their own energy. As potential applications increased to include warfare, energy generation, and rocket propulsion, the field's emphasis broadened to include a comprehensive examination into the nature of matter and energy. In the 1930s, scientists, led by Hans Bethe, determined that nuclear fusion was the sun's energy source and that it was both theoretically and practically practicable.
Fission refers to the fragmentation of anything into smaller pieces. In this sense, nuclear fission refers to the splitting or fragmentation of a large atom into two or more smaller atoms. These little atoms are technically light in weight. Breakdown of the nuclear fission process releases large amounts of energy, proving that it is an exothermic process. The uranium fission process is described below.