Nuclear processes involve changes within the nucleus of an atom, releasing immense energy. These reactions contrast with chemical reactions that involve only the atom’s electrons. Nuclear fission and nuclear fusion are two fundamental methods through which this energy can be released. Both processes convert a small amount of mass into a substantial amount of energy, as described by Einstein’s famous equation, E=mc².
Understanding Nuclear Fission
Nuclear fission is a process where the nucleus of a heavy atom splits into two or more smaller nuclei. This reaction is typically initiated when a neutron strikes a large, unstable atomic nucleus, such as uranium-235 or plutonium-239. The impact causes the nucleus to become unstable and break apart, releasing considerable energy and additional neutrons.
These newly released neutrons can then strike other heavy nuclei, causing them to fission, leading to a self-sustaining nuclear chain reaction. For instance, when a neutron is absorbed by a uranium-235 nucleus, it forms an excited uranium-236 nucleus, which then splits into lighter elements and releases more neutrons and energy. This controlled chain reaction forms the basis for nuclear power generation.
Understanding Nuclear Fusion
Nuclear fusion involves the combination of two light atomic nuclei to form a single, heavier nucleus, releasing a large amount of energy. This process powers the sun and other stars, where extreme conditions allow hydrogen nuclei to fuse into helium. Achieving fusion on Earth requires overcoming the natural electrostatic repulsion between positively charged nuclei, which demands extremely high temperatures and pressures. For terrestrial applications, the most promising fusion reactions involve isotopes of hydrogen, specifically deuterium and tritium, which combine to form helium and a neutron. Scientists aim to replicate the stellar conditions by heating hydrogen isotopes to temperatures exceeding 100 million degrees Celsius, creating a plasma where fusion can occur.
Comparing Fission and Fusion
Fission and fusion represent opposing nuclear processes, differing in their fundamental mechanisms. Fission involves splitting heavy, unstable nuclei, such as uranium-235 or plutonium-239. Conversely, fusion combines light nuclei, like hydrogen isotopes deuterium and tritium.
Both processes release immense energy, but fusion generally yields significantly more energy per unit mass than fission. Fission reactions are initiated by neutron bombardment, which is relatively easier to achieve and control. Conversely, fusion requires extreme conditions of heat and pressure, akin to those found in stellar cores, to overcome electrostatic repulsion and initiate the reaction.
Regarding byproducts, fission produces radioactive waste that can remain hazardous for thousands of years. Fusion, however, produces significantly less or no long-lived radioactive waste, with helium being a primary byproduct, which is an inert gas.
Where Fission and Fusion Occur
Nuclear fission is currently harnessed in nuclear power plants worldwide to generate electricity. In these facilities, controlled chain reactions of uranium-235 or plutonium-239 heat water to produce steam, which then drives turbines. Fission is also the principle behind atomic bombs, where an uncontrolled chain reaction leads to an explosive release of energy.
Beyond energy production, fission has applications in medical research for producing radioisotopes, industrial uses, and even in studying geological processes.
Nuclear fusion is the natural energy source of stars, including our Sun, where hydrogen atoms continuously fuse to form helium under immense gravitational pressure and heat. On Earth, scientists are actively researching and developing controlled fusion power as a potential clean energy source. Large international projects, such as the International Thermonuclear Experimental Reactor (ITER) in France, are building experimental devices called tokamaks to demonstrate the feasibility of fusion. These efforts aim to replicate the conditions of the Sun to provide a nearly limitless, carbon-free energy supply, with deuterium extracted from seawater and tritium produced from lithium.