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Discovery of the neutron

James Chadwick at the 1933 Solvay Conference. Chadwick had discovered the neutron the year before while working at Cavendish Laboratory.

The discovery of the neutron and its properties was central to the extraordinary developments in atomic physics in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model of the atom,[1]: 188 [2] based on the gold foil experiment of Hans Geiger and Ernest Marsden. In this model, atoms had their mass and positive electric charge concentrated in a very small nucleus.[3] By 1920, isotopes of chemical elements had been discovered, the atomic masses had been determined to be (approximately) integer multiples of the mass of the hydrogen atom,[4] and the atomic number had been identified as the charge on the nucleus.[5]: §1.1.2  Throughout the 1920s, the nucleus was viewed as composed of combinations of protons and electrons, the two elementary particles known at the time, but that model presented several experimental and theoretical contradictions.[1]: 298 

The essential nature of the atomic nucleus was established with the discovery of the neutron by James Chadwick in 1932[6] and the determination that it was a new elementary particle, distinct from the proton.[7][8]: 55 

The uncharged neutron was immediately exploited as a new means to probe nuclear structure, leading to such discoveries as the creation of new radioactive elements by neutron irradiation (1934) and the fission of uranium atoms by neutrons (1938).[9] The discovery of fission led to the creation of both nuclear power and nuclear weapons by the end of World War II. Both the proton and the neutron were presumed to be elementary particles until the 1960s, when they were determined to be composite particles built from quarks.[10]

  1. ^ a b Pais, Abraham (1986). Inward Bound. Oxford: Oxford University Press. ISBN 978-0198519973.
  2. ^ Rutherford, E. (1911). "The Scattering of α and β Particles by Matter and the Structure of the Atom". Philosophical Magazine. Series 6 (21): 669–688. doi:10.1080/14786440508637080. Retrieved 15 November 2017.
  3. ^ Longair, M.S. (2003). Theoretical concepts in physics: an alternative view of theoretical reasoning in physics. Cambridge University Press. pp. 377–378. ISBN 978-0-521-52878-8.
  4. ^ Squires, Gordon (1998). "Francis Aston and the mass spectrograph". Dalton Transactions (23): 3893–3900. doi:10.1039/a804629h.
  5. ^ Byrne, J. Neutrons, Nuclei, and Matter, Dover Publications, Mineola, New York, 2011, ISBN 0486482383
  6. ^ Chadwick, James (1932). "Existence of a Neutron". Proceedings of the Royal Society A. 136 (830): 692–708. Bibcode:1932RSPSA.136..692C. doi:10.1098/rspa.1932.0112.
  7. ^ Chadwick, J.; Goldhaber, M. (1935). "A nuclear photoelectric effect". Proceedings of the Royal Society A. 151 (873): 479–493. Bibcode:1935RSPSA.151..479C. doi:10.1098/rspa.1935.0162.
  8. ^ Stuewer, Roger H. (1983). "The Nuclear Electron Hypothesis". In Shea, William R. (ed.). Otto Hahn and the Rise of Nuclear Physics. Dordrecht, Holland: D. Riedel Publishing Company. pp. 19–67. ISBN 978-90-277-1584-5.
  9. ^ Rife, Patricia (1999). Lise Meitner and the dawn of the nuclear age. Basel, Switzerland: Birkhäuser. ISBN 978-0-8176-3732-3.
  10. ^ Perkins, Donald H. (1982), Introduction to High Energy Physics, Addison Wesley, Reading, Massachusetts, pp. 201–202, ISBN 978-0-201-05757-7

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