Neutron limit. As stated in Chapter 4, the Exclusion Principle places a limit on the number of electrons in an atomic nucleus. Just as electrons added to an atom must go into higher energy states if the lower ones are occupied, so neutrons added to a nucleus must go into higher energy states if the lower ones are occupied. Then, because of their higher energy, these neutrons may be able to escape the strong binding force and leave. This is why the number of neutrons in a given nucleus cannot increase indefinitely.
( Rodney A. Brooks )
[ Fields of Color: The theory ]
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