Final answer:
Nuclear fission is the splitting of an atom into smaller atoms, releasing energy, and is used in nuclear reactors and weapons. Nuclear fusion is the merging of two light atoms into a heavier atom, releasing even more energy and occurs naturally in stars. Fusion has the potential for greater energy but is harder to control.
Step-by-step explanation:
The key distinction between nuclear fission and nuclear fusion lies in their opposite mechanisms. Nuclear fission is the process in which an atomic nucleus splits into two or more smaller nuclei, along with other particles and energy release. This process is utilized in nuclear reactors and was employed in the two types of nuclear weapons detonated at the end of World War II. On the other hand, nuclear fusion involves the merging of two light atomic nuclei to form a heavier nucleus with the subsequent release of energy. The energy from fusion is primarily due to the transformation of mass into energy as per Einstein's equation E=mc^2, and it is a reaction that sustains the burning of stars, including our sun. Fission reactions take place when a neutron strikes an unstable nucleus, causing it to split. This can lead to a chain reaction as neutrons produced can induce further fissions. The fuels for nuclear fission are heavy elements like uranium-235 or plutonium-239. Conversely, nuclear fusion reactions occur when two lighter atomic nuclei combine under high temperature and pressure conditions, akin to those found at the core of stars, resulting in the production of a heavier nucleus and the release of energy. While nuclear fission has been harnessed for both power generation and weaponry, nuclear fusion holds the promise of providing a more potent and cleaner energy source. However, despite significant research, sustained and controlled nuclear fusion remains a challenge to achieve on Earth.