Fission Vs. Fusion
How does a chain reaction happen?
A nucleus splits when hit by neutrons. This makes smaller nuclei that need less neutrons to be held together. The extra neutrons are released and hit other large nuclei and those release neutrons that hit other nuclei that split and release neutrons and so on.
What is nuclear fission?
The process by which a nucleus splits into two or more smaller fragments, releasing neutrons and energy. Requires a neutron to start it. Large nucleus divides into smaller nuclei. Results in smaller total mass. Missing mass is changed into lots of energy. Occurs uncontrolled in a nuclear bomb or controlled in a nuclear power plant (reactor).
what is nuclear fission?
a nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy. When a nucleus fissions, it splits into several smaller fragments. These fragments, or fission products, are about equal to half the original mass. Two or three neutrons are also emitted. The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation. Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.
What is nuclear fusion?
a nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy. In physics, nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy depending on the masses of the nuclei involved. Iron and nickel nuclei have the largest binding energies per nucleon of all nuclei and therefore are the most stable. The fusion of two nuclei lighter than iron or nickel generally releases energy while the fusion of nuclei heavier than iron or nickel absorbs energy; vice-versa for the reverse process, nuclear fission. Nuclear fusion of light elements releases the energy that causes stars to shine and hydrogen bombs to explode. Nuclear fusion of heavy elements (absorbing energy) occurs in the extremely high-energy conditions of supernova explosions. Nuclear fusion in stars and supernovae is the primary process by which new natural elements are created. It is this reaction that is harnessed in fusion power. It takes considerable energy to force nuclei to fuse, even those of the lightest element, hydrogen.
what makes the nucleus unstable?
neutrons help stability but too many or too few will make the nucleus unstable. Stable atoms have equal numbers or protons and neutrons. >83 (the atomic number) are always unstable. Nuclear force can't act over something so big.
what is the strong nuclear force?
the force that holds protons and neutrons together. The strong nuclear force is stronger than the repelling force of proton to proton. Works over a short distance.
What is fusion?
when lighter nuclei combine to make heavier nuclei. very hard to do. happens in stars (because of the heat and hydrogen available) releases tons of energy as gamma rays.
Are chain reactions controllable?
yes, by using materials that absorb neutrons. (control rods in a reactor block the neutrons)