Neutron (Encyclopedia of Science)
A neutron is one of two particles found inside the nucleus (central part) of an atom. The other particle is called a proton. Electrons are particles that move around an atom outside the nucleus.
Discovery of the atom
British physicist Ernest Rutherford discovered the atom in 1911. He constructed a model showing an atom with a nucleus containing protons and electrons. Scientists studying the model knew that something must be missing from it. Rutherford suggested that some sort of neutral particle might exist in the nucleus. He and a graduate student working with him, James Chadwick, could not prove his theory, mainly because neutrons cannot be detected by any standard tools such as cloud chambers or Geiger counters.
(The entire section is 391 words.)
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