Fission is a nuclear
process in which a heavy nucleus splits into two smaller nuclei. An
example of a fission reaction that was used in the first atomic bomb
and is still used in nuclear reactors is:
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The
products shown in the above equation are only one set of many possible
product nuclei. Fission reactions can produce any combination of
lighter nuclei so long as the number of protons and neutrons in the
products sum up to those in the initial fissioning nucleus. As with
fusion, a great amount of energy can be released in fission because for
heavy nuclei, the summed masses of the lighter product nuclei is less
than the mass of the fissioning nucleus.
Fission occurs
because of the electrostatic repulsion created by the large number of
positively charged protons contained in a heavy nucleus. Two smaller
nuclei have less internal electrostatic repulsion than one larger
nucleus. So, once the larger nucleus can overcome the strong nuclear
force which holds it together, it can fission. Fission can be seen as a
"tug-of-war" between the strong attractive nuclear force and the
repulsive electrostatic force. In fission reactions, electrostatic
repulsion wins.
Fission is a process that has been occurring in the universe for
billions of years. As mentioned above, we have not only used fission to
produce energy for nuclear bombs, but we also use fission peacefully
everyday to produce energy in nuclear power plants. Interestingly,
although the first man-made nuclear reactor was produced only about
fifty years ago, the Earth operated a natural fission reactor in a
uranium deposit in West Africa about two billion years ago!
Source:
http://www.lbl.gov/abc/Basic.html
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