Discovery of the neutron - wikipedia Discovery of the neutron James Chadwick discovered the neutron in 1932 while working at Cavendish Laboratory. The story of the discovery of the neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century. Early in the century, Ernest Rutherford developed a crude model for the atom, based on the gold foil experiment of Hans Geiger and Ernest Marsden. In this model, atoms had their mass and positive charge concentrated in a very small nucleus. 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. The essential nature of the atomic nucleus was established with the discovery of the neutron by James Chadwick in 1932 and the determination that it was a new elementary particle, distinct from the proton. Both the proton and neutron were presumed to be elementary particles until the 1960s when they were determined to be composite particles built from quarks. Contents 1 Gold foil experiment 2 Discovery of isotopes 3 Rutherford atom 4 Problems of the nuclear electrons hypothesis 5 Discovery of the neutron 6 Proton -- neutron model of the nucleus 7 Neutron physics in the 1930s 8 See also 9 Video 10 References 11 Further reading Gold foil experiment See also : Plum pudding model A schematic of the nucleus of an atom indicating β − radiation, the emission of a fast electron from the nucleus ( the accompanying antineutrino is omitted ). In the Rutherford model for the nucleus, red spheres were protons with positive charge and blue spheres were protons tightly bound to an electron with no net charge. The inset shows beta decay of a free neutron as it is understood today ; an electron and antineutrino are created in this process. At the University of Manchester between 1908 and 1913, Ernest Rutherford directed Hans Geiger and Ernest Marsden in a series of experiments to determine what happens when alpha particles scatter from metal foil. Now called the Rutherford gold foil experiment, or the Geiger -- Marsden experiment, these measurements made the extraordinary discovery that alpha particles would occasionally scatter to high angle when passing through a thin gold foil. The scattering indicated that the alpha particles were reflecting from a small, but dense, component of atoms. Based on these measurements, in 1911 Rutherford developed a model for the atom that consisted of a small massive nucleus with positive charge surrounded by a much larger cloud of negatively charged electrons. The concentrated atomic mass was required to provide the observed reflection of the alpha particles, and Rutherford developed a mathematical model that accounted for the scattering. The Rutherford model was very influential, motivating the Bohr model for electrons orbiting the nucleus in 1913 and eventually leading to quantum mechanics by the mid-1920s. Discovery of isotopes Concurrent with the work of Rutherford, Geiger, and Marsden, the radiochemist Frederick Soddy at the University of Glasgow was studying radioactive decay chains of uranium. Soddy had been a student of Rutherford. Soddy 's study indicated about 40 different radioactive elements, referred to as radioelements, between uranium and lead, although the periodic table only allowed for 11 elements. By 1913 Soddy had determined that several of these elements had identical chemical properties but different atomic weights. He called these chemically similar elements isotopes. For his study of radioactivity and the discovery of isotopes, Soddy was awarded the 1921 Nobel Prize in Chemistry. Building from work by J.J. Thomson on the deflection of positively charged atoms by electric and magnetic fields, Francis Aston built the first mass spectrograph at the Cavendish Laboratory in 1919. His aim was to try to separate the two isotopes of neon, which he was able to easily do. Aston discovered that the masses of all the particles are whole numbers, called the whole number rule, that is, the masses of all the isotopes are whole number multiples of the mass of the hydrogen atom. Aston arbitrarily computed his masses relative to oxygen - 16, which he took to have a mass of exactly 16. ( Today the atomic mass unit ( amu ) is relative to carbon - 12. ) Ironically, the one exception to this rule was hydrogen itself, which had a mass value 1.008. The excess mass was small, but well outside experimental uncertainty. Aston and others quickly realized that the discrepancy was on account of the binding energy of atoms, that is, the mass of a number of hydrogen atoms bound into a single atom must be less than the sum of the masses of the separate hydrogen atoms. Additional work determined the nuclide binding energies. Aston 's work on isotopes garnered him the 1922 Nobel Prize in Chemistry for the discovery of isotopes in a large number of non-radioactive elements, and for his enunciation of the whole - number rule. Noting Aston 's recent discovery of nuclear binding energy, in 1920 Arthur Eddington suggested that stars may obtain their energy by fusing hydrogen ( protons ) into helium and that the heavier elements may form in stars. Rutherford and others noted the disparity between the atomic number of an atom, or number of positive charges, and its mass computed in atomic mass units. The atomic number of an atom is usually about half its atomic mass. Rutherford atom Ernest Rutherford In 1920 Rutherford gave a Bakerian lecture at the Royal Society entitled the `` Nuclear Constitution of Atoms '', a summary of what was then known about the nucleus of the atom. By 1920, the existence of electrons within the atomic nucleus was widely assumed. The atomic number had been not only recognized as the relevant parameter in organizing the chemical elements, but also established as the number of positive charges of the nucleus. This number was about half the value of atomic mass. It was therefore assumed the nucleus consisted of hydrogen nuclei in number equal to the atomic mass. But since each hydrogen had charge + 1, the nucleus required a smaller number of `` internal electrons '' each of charge - 1 to give the nucleus its correct total charge. The mass of protons is about 1800 times greater than that of electrons, so the mass of the electrons is incidental in this computation. Such a model was consistent with the scattering of alpha particles from heavy nuclei, as well as the charge and mass of the many isotopes that had been identified. There were other motivations for the proton -- electron model. As noted by Rutherford at the time, `` We have strong reason for believing that the nuclei of atoms contain electrons as well as positively charged bodies... '', namely, it was known that beta radiation was electrons emitted from the nucleus. In that lecture, Rutherford conjectured the existence of new particles. The alpha particle was known to be very stable, and it was assumed to retain its identity within the nucleus. The alpha particle was presumed to consist of four protons and two closely bound electrons to give it + 2 charge. In a 1919 paper, Rutherford had reported the apparent discovery of a new doubly charged particle of mass 3, denoted the X++, interpreted to consist of three protons and a closely bound electron. This result suggested to Rutherford the likely existence of two new particles, one of two protons with a closely bound electron, and another of one proton and a closely bound electron. The X++ particle was later determined to have mass 4 and to be just a low - energy alpha particle. Nevertheless, a neutral particle of mass 1 and a + 1 charge particle of mass 2 were conjectured. Rutherford had conjectured the existence of the neutron and deuterium ( discovered 1931 by Harold Urey ). The mass of the hypothetical neutral doublet would be little different from that of the proton. Rutherford determined that such a zero - charge particle would be difficult to detect by available techniques. By 1921 Rutherford had named these uncharged particles neutrons, while about that same time the word proton was adopted for the hydrogen nucleus. Neutron was apparently constructed from the Latin root for neutral and the Greek ending - on ( by imitation of electron and proton ). References to the word neutron in connection with the atom can be found in the literature as early as 1899, however. Rutherford 's conjecture was not widely accepted. In his 1931 textbook on the Constitution of Atomic Nuclei and Radioactivity, George Gamow, then at the Institute for Theoretical Physics in Copenhagen, did not mention the neutron. At the time of their 1932 measurements in Paris that would lead to the discovery of the neutron, Irène Joliot - Curie and Frédéric Joliot were unaware of the conjecture. Rutherford and Chadwick immediately began an experimental program to search for the neutron. The experiments continued throughout the 1920s without success. Problems of the nuclear electrons hypothesis Throughout the 1920s, physicists assumed that the atomic nucleus was composed of protons and `` nuclear electrons ''. Under this hypothesis, the nitrogen - 14 ( N ) nucleus would be composed of 14 protons and 7 electrons, so that it would have a net charge of + 7 elementary charge units and a mass of 14 atomic mass units. The nucleus was also orbited by another 7 electrons, termed `` external electrons '' by Rutherford, to complete the N atom. There were obvious problems with the hypothesis, however. By about 1930 it was generally recognized that it was difficult to reconcile the proton -- electron model for nuclei with the Heisenberg uncertainty relation of quantum mechanics. This relation, Δx ⋅ Δp ≥ 1⁄2ħ, implies that an electron confined to a region the size of an atomic nucleus has an expected kinetic energy of 10 -- 100 MeV. This energy is larger than the observed energy of beta particles emitted from the nucleus. The expected electron energy is also larger than the binding energy of nucleons, which Aston and others had shown to be less than 9 MeV per nucleon. The Klein paradox, discovered by Oskar Klein in 1928, presented further quantum mechanical objections to the notion of an electron confined within a nucleus. Derived from the Dirac equation, this clear and precise paradox showed that a high - energy electron approaching a potential barrier has a high probability of passing through the barrier, or escaping, by transforming to a particle of negative mass. Apparently, an electron could not be confined within a nucleus by any potential well. The meaning of this paradox was intensely debated at the time. Observations of the energy levels of atoms and molecules were inconsistent with the nuclear spin expected from proton -- electron hypothesis. Molecular spectroscopy of dinitrogen ( N ) showed that transitions originating from even - numbered rotational levels are more intense than those from odd levels, hence the even levels are more populated. According to quantum mechanics and the Pauli exclusion principle, the spin of the N nucleus is therefore an integer multiple of ħ ( the reduced Planck constant ). Yet both protons and electrons carry an intrinsic spin of 1⁄2 ħ, and there is no way to arrange an odd number ( 14 protons + 7 electrons = 21 ) of spins ± 1⁄2 ħ to give a spin that is an integer multiple of ħ. The observed hyperfine structure of atomic spectra was inconsistent with the proton -- electron hypothesis. This structure is caused by the influence of the nucleus on the dynamics of orbiting electrons. The magnetic moments of supposed `` nuclear electrons '' should produce hyperfine spectral line splittings similar to the Zeeman effect, but no such effects were observed. While all these considerations did not `` prove '' an electron could not exist in the nucleus, they were challenging for physicists to interpret. In his 1931 textbook, Gamow summarized all these contradictions. Adding to the confusion in interpretation, the continuous energy distribution of beta decay electrons seemed to indicate that energy was not conserved by this `` nuclear electrons '' process. Indeed, Bohr, Gamow, Heisenberg and others considered the possibility that the laws of quantum mechanics were not applicable inside the nucleus. Such considerations were apparently reasonable, inasmuch as the laws of quantum mechanics had so recently overturned the laws of classical mechanics. The contradictions were mysterious and troublesome, until it was realized that there are no individual nuclear electrons in the nucleus. Discovery of the neutron In 1931, Walther Bothe and Herbert Becker in Giessen, Germany found that if the very energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium, boron, or lithium, an unusually penetrating radiation was produced. Since this radiation was not influenced by an electric field ( neutrons have no charge ), it was thought to be gamma radiation. The radiation was more penetrating than any gamma rays known, and the details of experimental results were difficult to interpret. The following year Irène Joliot - Curie and Frédéric Joliot in Paris showed that if this unknown radiation fell on paraffin, or any other hydrogen - containing compound, it ejected protons of very high energy. This observation was not in itself inconsistent with the assumed gamma ray nature of the new radiation, but detailed quantitative analysis of the data became increasingly difficult to reconcile with such a hypothesis. In Rome, the young physicist Ettore Majorana suggested that the manner in which the new radiation interacted with protons required a new neutral particle. On hearing of the Paris results in 1932, neither Rutherford nor James Chadwick at the Cavendish Laboratory in Cambridge were convinced by the gamma ray hypothesis. Assisted by Norman Feather, Chadwick quickly performed a series of experiments showing that the gamma ray hypothesis was untenable. He repeated the creation of the radiation using beryllium, used better approaches to detection, and aimed the radiation at paraffin following the Paris experiment. Paraffin is high in hydrogen content, hence offers a target dense with protons ; since neutrons and protons have almost equal mass, protons scatter energetically from neutrons. Chadwick measured the range of these protons, and also measured how the new radiation impacted the atoms of various gases. He found that the new radiation consisted of not gamma rays, but uncharged particles with about the same mass as the proton ; these particles were neutrons. Chadwick won the Nobel Prize in Physics for this discovery in 1935. The year 1932 was later referred to as the `` annus mirabilis '' for nuclear physics in the Cavendish Laboratory, with discoveries of the neutron, artificial nuclear disintegration by the Cockcroft -- Walton particle accelerator, and the positron. Proton -- neutron model of the nucleus Models depicting the nucleus and electron energy levels in hydrogen, helium, lithium, and neon atoms. In reality, the diameter of the nucleus is about 100,000 times smaller than the diameter of the atom. Given the problems of the proton -- electron model, it was quickly accepted that the atomic nucleus is composed of protons and neutrons, although the precise nature of the neutron was initially unclear. Within months after the discovery of the neutron, Werner Heisenberg and Dmitri Ivanenko had proposed proton -- neutron models for the nucleus. Heisenberg 's landmark papers approached the description of protons and neutrons in the nucleus through quantum mechanics. While Heisenberg 's theory for protons and neutrons in the nucleus was a `` major step toward understanding the nucleus as a quantum mechanical system, '' he still assumed the presence of nuclear electrons. In particular, Heisenberg assumed the neutron was a proton -- electron composite, for which there is no quantum mechanical explanation. Heisenberg had no explanation for how lightweight electrons could be bound within the nucleus. Heisenberg introduced the first theory of nuclear exchange forces that bind the nucleons. He considered protons and neutrons to be different quantum states of the same particle, i.e., nucleons distinguished by the value of their nuclear isospin quantum numbers. The proton -- neutron model explained the puzzle of dinitrogen noticed independently by Ralph Kronig and Franco Rasetti. When N was proposed to consist of 3 pairs each of protons and neutrons, with an additional unpaired neutron and proton each contributing a spin of ⁄ ħ in the same direction for a total spin of 1 ħ, the model became viable. Soon, neutrons were used to naturally explain spin differences in many different nuclides in the same way. If the proton -- neutron model for the nucleus resolved many issues, it highlighted the problem of explaining the origins of beta radiation. No existing theory could account for how electrons could emanate from the nucleus. In 1934, Enrico Fermi published his classic paper describing the process of beta decay, in which the neutron decays to a proton by creating an electron and a ( as yet undiscovered ) neutrino. The paper employed the analogy that photons, or electromagnetic radiation, were similarly created and destroyed in atomic processes. Ivanenko had suggested a similar analogy in 1932. Fermi 's theory requires the neutron to be a spin - 1⁄2 particle. The theory preserved the principle of conservation of energy, which had been thrown into question by the continuous energy distribution of beta particles. The basic theory for beta decay proposed by Fermi was the first to show how particles could be created and destroyed. It established a general, basic theory for the interaction of particles by weak or strong forces. While this influential paper has stood the test of time, the ideas within it were so new that when it was first submitted to the journal Nature in 1933 it was rejected as being too speculative. Seventh Solvay Conference, 1933. The question of whether the neutron was a composite particle of a proton and an electron persisted for a few years after its discovery. In 1932 Harrie Massey explored a model for a composite neutron to account for its great penetrating power through matter and its electrical neutrality, for example. The issue was a legacy of the prevailing view from the 1920s that the only elementary particles were the proton and electron. The nature of the neutron was a primary topic of discussion at the 7th Solvay Conference held in October 1933, attended by Heisenberg, Niels Bohr, Lise Meitner, Ernest Lawrence, Fermi, Chadwick, and others. As posed by Chadwick in his Bakerian Lecture in 1933, the primary question was the mass of the neutron relative to the proton. If the neutron 's mass was less than the combined masses of a proton and an electron ( 7000100780000000000 ♠ 1.0078 u ), then the neutron could be a proton - electron composite because of the mass defect from the binding energy. If greater than the combined masses, then the neutron was elementary like the proton. The question was challenging to answer because the electron 's mass is only 0.05 % of the proton 's, hence precise measurements were required. The difficulty of making the measurement is illustrated by the wide - ranging values for the mass of the neutron obtained from 1932 - 1934. The accepted value today is 7000100865999999999 ♠ 1.008 66 u. In Chadwick 's 1932 paper reporting on the discovery, he estimated the mass of the neutron to be between 7000100499999999999 ♠ 1.005 u and 7000100800000000000 ♠ 1.008 u. By bombarding boron with alpha particles, Frédéric and Irène Joliot - Curie obtained a high value of 7000101200000000000 ♠ 1.012 u, while Ernest Lawrence 's team at the University of California measured the small value 7000100060000000000 ♠ 1.0006 u using their new cyclotron. The issue was resolved in 1935 when Chadwick and his doctoral student Maurice Goldhaber, reported the first accurate measurement of the mass of the neutron. They used the 2.6 MeV gamma rays of Thallium - 208 ( Tl ) ( then known as thorium C `` ) to photodisintegrate deuterium : 2 + γ → + n The energies of the resulting proton and neutron could be used to accurately determine the neutron 's mass. Chadwick and Goldhaber found the neutron 's mass to be slightly greater than the mass of the proton ( 7000100840000000000 ♠ 1.0084 u or 7000100899999999999 ♠ 1.0090 u, depending on precise values used for the proton and deuteron masses ), and therefore, in support of Fermi 's theory, predicted that an unbound neutron is unstable and would undergo beta decay. The mass of the neutron was too large to be a proton - electron composite, and the neutron was therefore identified as an elementary particle. Neutron Physics in the 1930s See also : Neutron magnetic moment, Enrico Fermi, Lise Meitner, and Otto Hahn Soon after the discovery of the neutron, indirect evidence suggested the neutron had an unexpected non-zero value for its magnetic moment. Attempts to measure the neutron 's magnetic moment originated with the discovery by Otto Stern in 1933 in Hamburg that the proton had an anomalously large magnetic moment. By 1934 groups led by Stern, now in Pittsburgh, and I.I. Rabi in New York had independently deduced that the magnetic moment of the neutron was negative and unexpectedly large by measuring the magnetic moments of the proton and deuteron. Values for the magnetic moment of the neutron were also determined by Robert Bacher ( 1933 ) at Ann Arbor and I.Y. Tamm and S.A. Altshuler ( 1934 ) in the Soviet Union from studies of the hyperfine structure of atomic spectra. By the late 1930s accurate values for the magnetic moment of the neutron had been deduced by the Rabi group using measurements employing newly developed nuclear magnetic resonance techniques. The large value for the proton 's magnetic moment and the inferred negative value for the neutron 's magnetic moment were unexpected and raised many questions. The discovery of the neutron immediately gave scientists a new tool for probing the properties of atomic nuclei. Alpha particles had been used over the previous decades in scattering experiments, but such particles, which are helium nuclei, have + 2 charge. This charge makes it difficult for alpha particles to overcome the Coulomb repulsive force and interact directly with the nuclei of atoms. Since neutrons have no electric charge, they do not have to overcome this force to interact with nuclei. Almost coincident with its discovery, neutrons were used by Norman Feather, Chadwick 's colleague and protege, in scattering experiments with nitrogen. Feather was able to show that neutrons interacting with nitrogen nuclei scattered to protons or induced nitrogen to disintegrate to form boron with the emission of an alpha particle. Feather was therefore the first to show that neutrons produce nuclear disintegrations. Fermi and his students ( the Via Panisperna boys ) in the courtyard of Rome University 's Physics Institute in Via Panisperna, about 1934. From Left to right : Oscar D'Agostino, Emilio Segrè, Edoardo Amaldi, Franco Rasetti and Fermi In Rome Enrico Fermi bombarded heavier elements with neutrons and found the products to be radioactive. By 1934 Fermi had used neutrons to induce radioactivity in 22 different elements, many of these elements of high atomic number. Noticing that other experiments with neutrons at his laboratory seemed to work better on a wooden table than a marble table, Fermi suspected that the protons of the wood were slowing the neutrons and so increasing the chance for the neutron to interact with nuclei. Fermi therefore passed neutrons through paraffin wax to slow them and found that the radioactivity of bombarded elements increased by a hundredfold. The cross section for interaction with nuclei is much larger for slow neutrons than for fast neutrons. In 1938 Fermi received the Nobel Prize in Physics `` for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons ''. Lise Meitner and Otto Hahn in their laboratory. Jointly with Lise Meitner and his pupil and assistant Fritz Strassmann, Otto Hahn furthered the research begun by Fermi and his team when he bombarded uranium with neutrons at his laboratory in Berlin. Between 1934 and 1938, Hahn, Meitner, and Strassmann found a great number of radioactive transmutation products from these experiments, all of which they regarded as transuranic. The decisive experiment on 16 -- 17 December 1938 ( the celebrated `` radium -- barium -- mesothorium -- fractionation '' ) produced puzzling results : the three isotopes consistently behaved not as radium, but as barium. By January 1939 Hahn had concluded that he was seeing light platinoids, barium, lanthanum, and cerium. Hahn and his collaborators had observed the fractionation of uranium nuclei into light elements by neutron bombardment. Meitner, now in Sweden to escape antisemitic persecution in Nazi Germany, and her nephew Otto Frisch correctly interpreted these observations as nuclear fission, a term coined by Frisch. In their second publication on nuclear fission, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process. Frédéric Joliot and his team proved this phenomenon to be a chain reaction in March 1939. In 1945 Hahn received the 1944 Nobel Prize in Chemistry `` for his discovery of the fission of heavy atomic nuclei. '' The discovery of nuclear fission at the end of 1938 marked a shift in the centers of nuclear research from Europe to the United States. Large numbers of scientists were migrating to the United States to escape the troubles in Europe and the looming war ( See Jewish scientists and the Manhattan Project ). The new centers of nuclear research were the universities in the United States, particularly Columbia University in New York and the University of Chicago where Enrico Fermi had relocated, and a secret research facility at Los Alamos, New Mexico, established in 1942, the new home of the Manhattan project. Nuclear fission caused by absorption of a neutron by uranium - 235. The heavy nuclide fragments into lighter components and additional neutrons. The Trinity test of the Manhattan Project in 1945 was the first atomic bomb. See also Wikimedia Commons has media related to Discovery of the neutron. Ionizing radiation List of particles Neutronium Neutron magnetic moment Neutron radiation and the Sievert radiation scale Nuclear reaction Thermal reactor Nucleosynthesis Video Ernest Rutherford summarizes the state of nuclear physics in 1935. ( 7 min., Nobelprize.org ) References Jump up ^ Campbell, John. `` Rutherford -- A Brief Biography ''. Rutherford.org.nz. Retrieved 4 March 2013. 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Physical Review. 45 : 761 ( A109 ). Bibcode : 1934PhRv... 45... 739S. doi : 10.1103 / PhysRev. 45.739. Jump up ^ Rabi, I.I. ; Kellogg, J.M. ; Zacharias, J.R. ( 1934 ). `` The magnetic moment of the proton ''. Physical Review. 46 ( 3 ) : 157. Bibcode : 1934PhRv... 46... 157R. doi : 10.1103 / PhysRev. 46.157. Jump up ^ Rabi, I.I. ; Kellogg, J.M. ; Zacharias, J.R. ( 1934 ). `` The magnetic moment of the deuton ''. Physical Review. 46 ( 3 ) : 163. Bibcode : 1934PhRv... 46... 163R. doi : 10.1103 / PhysRev. 46.163. ^ Jump up to : John S. Rigden ( 2000 ). Rabi, Scientist and Citizen. Harvard University Press. ISBN 9780674004351. Jump up ^ Bacher, R.F. ( 1933 ). `` Note on the Magnetic Moment of the Nitrogen Nucleus ''. Physical Review. 43 ( 12 ) : 1001. Bibcode : 1933PhRv... 43.1001 B. doi : 10.1103 / PhysRev. 43.1001. Retrieved 2015 - 02 - 10. Jump up ^ Tamm, I.Y. ; Altshuler, S.A. ( 1934 ). `` Magnetic Moment of the Neutron ''. Doklady Akad. Nauk SSSR. 8 : 455. Retrieved 2015 - 01 - 30. Jump up ^ N. Feather ( 1 June 1932 ). `` The Collisions of Neutrons with Nitrogen Nuclei '' ( PDF ). Proceedings of the Royal Society A. 136 ( 830 ) : 709 -- 727. Bibcode : 1932RSPSA. 136... 709F. doi : 10.1098 / rspa. 1932.0113. Jump up ^ Cooper, Dan ( 1999 ). Enrico Fermi : And the Revolutions in Modern physics. New York : Oxford University Press. ISBN 0 - 19 - 511762 - X. OCLC 39508200. Jump up ^ Hahn, O. ( 1958 ). `` The Discovery of Fission ''. Scientific American. 198 ( 2 ) : 76. Bibcode : 1958SciAm. 198b... 76H. doi : 10.1038 / scientificamerican0258 - 76. Jump up ^ Rife, Patricia ( 1999 ). Lise Meitner and the dawn of the nuclear age. Basel, Switzerland : Birkhäuser. ISBN 0 - 8176 - 3732 - X. Jump up ^ Meitner, L. ; Frisch, O.R. ( 1939 ). `` Disintegration of Uranium by Neutrons : A New Type of Nuclear Reaction ''. Nature. 143 ( 3615 ) : 239. Bibcode : 1939Natur. 143... 239M. doi : 10.1038 / 143239a0. Jump up ^ Hahn, O. ; Strassmann, F. ( 10 February 1939 ). `` Proof of the Formation of Active Isotopes of Barium from Uranium and Thorium Irradiated with Neutrons ; Proof of the Existence of More Active Fragments Produced by Uranium Fission ''. Die Naturwissenschaften. 27 ( 6 ) : 89 -- 95. Bibcode : 1939NW... 27... 89H. doi : 10.1007 / BF01488988. Jump up ^ `` The Nobel Prize in Chemistry 1944 ''. Nobel Foundation. Retrieved 2007 - 12 - 17. Jump up ^ Bernstein, Jeremy ( 2001 ). Hitler 's uranium club : the secret recordings at Farm Hall. New York : Copernicus. p. 281. ISBN 0 - 387 - 95089 - 3. Jump up ^ `` The Nobel Prize in Chemistry 1944 : Presentation Speech ''. Nobel Foundation. Retrieved 2008 - 01 - 03. Further reading Annotated bibliography for neutrons from the Alsos Digital Library for Nuclear Issues Abraham Pais, Inward Bound, Oxford : Oxford University Press, 1986. ISBN 0198519974. Herwig Schopper, Weak interactions and nuclear beta decay, Publisher, North - Holland Pub. Co., 1966. Ruth Lewin Sime, Lise Meitner : A Life in Physics, Berkeley, University of California Press, 1996. ISBN 0520208609. Sin - Itiro Tomonaga, The Story of Spin, The University of Chicago Press, 1997 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Discovery_of_the_neutron&oldid=803255736 '' Categories : Neutron Hidden categories : Commons category without a link on Wikidata Talk Contents About Wikipedia Add links This page was last edited on 1 October 2017, at 12 : 33. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: when was the existence of the neutron confirmed
Answer: 1932