In 1932 English physicist James Chadwick (1891–1974) discovered another matter particle, the neutron. The neutron is very similar to the proton except that it is electrically neutral (i.e., has no charge). Chadwick found the neutron by hitting a chemical called beryllium with alpha particles. When this occurred, highly penetrating radiation was emitted. This "radiation" turned out to be a stream of neutrons. After Chadwick's experiment, Werner Heisenberg proposed that the nucleus is made up of protons and neutrons, which was later found to be true.
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