Chadwick

Chadwick discovered neutron particles in the nucleus of atoms, so this particle was added to atomic theory. http://www.nuclear-power.net/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/neutron/#8e74e7178ec1f94c8

More on neutrons: http://www.fnal.gov/pub/today/archive/archive_2013/today13-04-12.html Neutrons are important to the nucleus. Most importantly, neutrons hold the nucleus together. All protons have an electric charge. All have the same charge. All protons repel each other with the electric force. But when they are close together, this does not matter much. Protons AND neutrons have a very short range force called the strong force. When right next to each other, this strong force is much more powerful than the electric force. If the protons would sit still in a nucleus, this would be enough. However, this only happens at VERY cold temperatures, near what is called "absolute zero": 273 degrees below zero on the Celsius scale. At common temperatures, protons are jumping all over they place. They need extra holding force to stay in the nucleus. This is where neutrons come in.

Neutrons, like protons, have this strong force that attracts neighboring nucleons. Unlike protons, neutrons do not have electric charge. They are only attracted to each other and to protons. Their strong force helps hold the nucleus together more tightly than the protons alone can accomplish. All protons work together to push on each other. As a nucleus gets larger, it gets more electric force pushing out the protons. A larger nucleus needs more neutrons. Look at the elements. The lighter elements are about half proton and half neutron. The heaviest elements have many more neutrons than protons.

Neutrons are Invisible http://www.fnal.gov/pub/today/archive/archive_2014/today14-08-29.html

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