jan 1, 1936 - James Chadwick

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British physicist

In 1932, (a student of Ernest Rutherford) discovered the existence of the neutron, completing our picture of the subatomic particles that make up an atom.
They differed from alpha rays because they repelled considerable electrical forces that are in the nucleus of many heavy atoms. A neutron can then penetrate and split the nuclei of most elements.
physicists have since discovered that the protons and neutrons that make up the nucleus are themselves divisible into particles called quarks

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