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Fission | Fusion | Links to Additional Information
The word fission means "a splitting or breaking up into parts", and specifically nuclear fission means the "splitting of atomic nuclei resulting in the release of large amounts of energy" (Merriam-Webster Online, http://www.m-w.com). Nuclear fission takes place when a large, somewhat unstable isotope, is bombarded by high-speed particles (usually neutrons). These neutrons are accelerated and then slammed into the unstable isotope, causing it to fission, or break into smaller particles.
A neutron is accelerated and strikes the target nucleus (in the majority of nuclear power reactors today, that target is Uranium-235). This splits the target nucleus and breaks it down into two smaller isotopes (the fission products), three high-speed neutrons, and a large amount of energy. This energy is what is used to heat water in the reactor and later produce electricity. The high-speed electrons that are ejected become projectiles that will initiate other fission reactions, just as the first neutron did. Just think...if every fission reaction produces three neutrons, and each of those neutrons liberates 3 more in the next fission reaction, the number of reactions increases exponentially! This is what is called a chain reaction.
The word fusion means "a merging of separate elements into a unified whole". Nuclear fusion refers to the "union of atomic nuclei to form heavier nuclei resulting in the release of enormous amounts of energy" (Merriam-Webster Online, http://www.m-w.com). Fusion takes place when two low-mass isotopes (typically isotopes of hydrogen) unite under conditions of extreme pressure and temperature.
Fusion is what powers our sun. Atoms of Tritium and Deuterium (isotopes of hydrogen, Hydrogen-3 and Hydrogen-2, respectively) unite under extreme pressure and temperature to produce a neutron and a helium isotope. Along with this, an enormous amount of energy is liberated (several times the amount produced from fission).
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