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This is the simplest - "first order" -
Feynman diagram
of the sub-atomic reaction used
by Drs. Cowan and Reines in the detection of the neutrino at the Savannah River Site.
For this reaction, picture time as flowing from bottom to the top.
The neutrino labeled "ν" is produced by the P-reactor and interacts with a
proton "p" (contained in the liquid of the detector) by an exchange of a W
- particle.
As a result of this interaction, the proton is turned into a neutron "n" and the
neutrino is turned into a positive electron - a positron "e
+."
Later research determined that there are six types of neutrinos and the one detected
originally was an electron anti-neutrino.
Feynman diagrams - they can be quite complex - are used to aid in the computation
of the rate of such reactions - how probable are they to happen? - and this reaction
is very improbable, thus the difficulty of doing the experiment.
Feynman diagrams were invented by
Dr. Richard Feynman , also a Nobel Prize winner.
If you are further interested, a web search will reveal many excellent sources of information at different levels. Be advised, however, that physicists who work with Feynman diagrams typically spend several years of graduate work to become knowledgeable.
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