Neutrons, Protons, and Quarks
Name: Kevin L.
Date: Thursday, June 06, 2002
How do I explain to a student how a neutron is made up
of three quarks (UDD), but can decay into a proton (UUD) upon beta decay?
I am not sure how to explain that quarks are fundamental, and so are
electrons, but the neutron will emit an electron in its decay, yet still
be made up of three quarks?
I do not know of an "easy" or "simple" explanation to your question.
This is how nature behaves, so there is no "explanation" it is experimental
results. Why is a neutron inside an atomic nucleus indefinitely stable (not
counting radioactive fission etc.), but a free neutron has a half life of
only 12 min!!!
The "explanation", to the extent that one exists, lies in the domain of
quantum electrodynamics (QED), which is the theory of the interaction of
photons and electrons. A small book, just over 100 pages, by Richard Feynman
entitled, "Q.E.D." is the best treatment of the topic I have seen. It is the
transcript of a series of four lectures given by Feynman. It is readable,
even for high schoolers, and I do not think it has a single equation in it.
Highly recommended reading.
When a neutron undergoes beta decay, it becomes a set of three particles:
proton, electron, anti-neutrino. The number of quarks is still the same:
three. The number of leptons is the same: zero. An electron has a lepton
number of +1. An anti-neutrino has a lepton number of -1. It is an
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012