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diffraction pattern, alpha particles, particle accelerator, gravitational attraction, Nuclear reactions

Following his discovery of the proton in 1919, British physicist Ernest Rutherford suggested that a third particle, in addition to the proton and the electron, existed inside the atom. In 1930 the German physicists Walther Bothe and Herbert Becker bombarded beryllium with alpha particles and produced a radiation that passed through ten centimeters of lead. In 1932 French physicists Irene and Frederic Joliot-Curie found that this radiation could knock protons out of hydrogen atoms. In the same year, British physicist James Chadwick measured the energy of the protons emerging from the hydrogen atoms and showed that they had been knocked out by a particle of about the same mass, but electrically neutral. This new particle was therefore named the neutron.

By studying the physics of the neutron, scientists can better understand what happens inside neutron stars, stars that are made up entirely of neutrons. Neutron stars form when a star contains so much matter that the gravitational attraction between all of its atoms is powerful enough to crush them. The outer electrons are forced into the nucleus and combine with protons, thus creating a neutron star. One cubic centimeter of a neutron star weighs 100 million tons.

Knowledge of neutron physics also aids in the design of nuclear reactors and nuclear weapons, and it furthers the study of molecular structure. Nuclear reactions release a tremendous amount of energy. This energy can be used in nuclear weapons or, when the reactions are carefully controlled in nuclear reactors, as a source of electricity (See also Nuclear Energy: Nuclear Power Reactors). Physics researchers use beams of neutrons to study the inner structure of materials. They create the neutron beams from reactors, or by accelerating protons with magnetic fields in a particle accelerator, then slamming these protons into large nuclei such as uranium. These neutron beams can be directed at a sample material. When the neutrons pass through the sample, they behave like waves traveling around barriers and their paths bend to form a pattern called a diffraction pattern. This pattern reveals information about the internal structure of the sample.



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