The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons. Their properties and interactions are described by nuclear physics. The chemical properties of an atom are mostly determined by the configuration of electrons that orbit the atom's heavy nucleus. The electron configuration is determined by the charge of the nucleus, set by the number of protons, or atomic number.
Introduction
Neutron
Neutron | Introduction
It is a subatomic particle, symbol or which has a neutral (not positive or negative) charge and a mass slightly greater than that of a proton. The neutron is a subatomic particle, which has a neutral charge and a mass slightly greater than that of a proton. The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge and a mass slightly greater than that of a proton. It is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge.
who headed up the manhattan project in britain
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James Chadwick
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who is he?
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He was a British physicist.
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what was he known for?
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His discovery of the neutron.
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can you describe this thing he discovered?
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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 (), then the neutron could be a proton-electron composite because of the mass defect from the nuclear 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 exceptionally 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.
Discovery of the neutron | The nature of the neutron
The accepted value today is . In Chadwick's 1932 paper reporting on the discovery, he estimated the mass of the neutron to be between and . By bombarding boron with alpha particles, Frédéric and Irène Joliot-Curie obtained a high value of , while Ernest Lawrence's team at the University of California measured the small value using their new cyclotron.
Discovery of the neutron | The nature of the neutron
These particles were neutrons. Chadwick won the Nobel Prize in Physics in 1935 for this discovery.
Discovery of the neutron | Discovery of the neutron
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"".
Discovery of the neutron | Neutron physics in the 1930s
In 1932 Chadwick realized that radiation that had been observed by Walther Bothe, Herbert Becker, Irène and Frédéric Joliot-Curie was actually due to a neutral particle of about the same mass as the proton, that he called the neutron (following a suggestion from Rutherford about the need for such a particle). In the same year Dmitri Ivanenko suggested that there were no electrons in the nucleus — only protons and neutrons — and that neutrons were spin particles, which explained the mass not due to protons. The neutron spin immediately solved the problem of the spin of nitrogen-14, as the one unpaired proton and one unpaired neutron in this model each contributed a spin of in the same direction, giving a final total spin of 1.
Nuclear physics | James Chadwick discovers the neutron
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. In April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. Enrico Fermi and his team in Rome conducted experiments involving the bombardment of elements by slow neutrons, which produced heavier elements and isotopes. Then, in December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slowed neutrons, and discovered that barium had been produced, and therefore that the uranium atomic nucleus had been split. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Robert Frisch, developed a theoretical justification which they published in "Nature" in 1939.
Tube Alloys | Discovery of fission
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. 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).
Discovery of the neutron | Introduction
With the discovery of the neutron, scientists could at last calculate what fraction of binding energy each nucleus had, by comparing the nuclear mass with that of the protons and neutrons which composed it. Differences between nuclear masses were calculated in this way. When nuclear reactions were measured, these were found to agree with Einstein's calculation of the equivalence of mass and energy to within 1% as of 1934.
Nuclear physics | James Chadwick discovers the neutron
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. In April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. Enrico Fermi and his team in Rome conducted experiments involving the bombardment of elements by slow neutrons, which produced heavier elements and isotopes. Then, in December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slowed neutrons, and discovered that barium had been produced, and therefore that the uranium nucleus had been split. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, developed a theoretical justification for the process, which they published in "Nature" in 1939.
High Explosive Research | Tube Alloys
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, 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. By 1920 chemical isotopes had been discovered, the atomic masses had been determined to be (approximately) integer multiples of the mass of the hydrogen atom, and the atomic number had been identified as the charge on the nucleus.
Discovery of the neutron | Introduction
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932, and in April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. In December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slow neutrons, and discovered that barium had been produced. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, determined that the uranium nucleus had been split, a conclusion they published in "Nature" in 1939. By analogy with the division of biological cells, they named the process "fission".
Nuclear weapons of the United Kingdom | Tube Alloys
This wartime project was focussed on the construction of nuclear weapons, exploiting the enormous energy released by the fission of uranium or plutonium through neutron-based chain reactions. The discoveries of the neutron and positron in 1932 were the start of the discoveries of many new particles. Muons were discovered in 1936. Pions and kaons were discovered in 1947, while lambda particles were discovered in 1950. Throughout the 1950s and 1960s, a large number of particles called hadrons were discovered. A classification scheme for organizing all these particles, proposed independently by Murray Gell-Mann and George Zweig in 1964, became known as the quark model.
Discovery of the neutron | After 1939
During the 1920s, it was thought that the atomic nucleus was made of protons and electrons, which would account for the disparity between the atomic number of an atom and its atomic mass. In 1932, James Chadwick discovered an uncharged particle of approximately the mass as the proton, which he called the neutron. The fact that the atomic nucleus is composed of protons and neutrons was rapidly accepted and Chadwick was awarded the Nobel Prize in Physics in 1935 for his discovery. The modern form of the whole number rule is that the atomic mass of a given elemental isotope is approximately the mass number (number of protons plus neutrons) times an atomic mass unit (approximate mass of a proton, neutron, or hydrogen-1 atom).
Whole number rule | Discovery of the neutron
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.
Discovery of the neutron | Neutron physics in the 1930s
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.
Discovery of the neutron | Neutron physics in the 1930s
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. 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.
Discovery of the neutron | Proton–neutron model of the nucleus
The discovery of fission led to the creation of both nuclear power and 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.
Discovery of the neutron | Introduction
References to the word "neutron" in connection with the atom can be found in the literature as early as 1899, however.
Discovery of the neutron | Rutherford atom
Nevertheless, Rutherford had conjectured the existence of the deuteron, a +1 charge particle of mass 2, and the neutron, a neutral particle of mass 1. The former is the nucleus of deuterium, discovered in 1931 by Harold Urey. The mass of the hypothetical neutral particle 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 and William Harkins had independently named the uncharged particle the "neutron", 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").
Discovery of the neutron | Rutherford atom
In 1934, working at the Cavendish Laboratory in Cambridge, England he and James Chadwick, through what they called the nuclear photo-electric effect, established that the neutron has a great enough mass over the proton to decay. He moved to the University of Illinois in 1938. In the 1940s with his wife Gertrude Scharff-Goldhaber he established that beta particles are identical to electrons. He joined Brookhaven National Laboratory in 1950. With Edward Teller he proposed that the so-called "giant-dipole nuclear resonance" was due to the neutrons in a nucleus vibrating as a group against the protons as a group (Goldhaber-Teller model).
Maurice Goldhaber | Career
The discovery came after forty years of investigation into the nature and properties of radioactivity and radioactive substances. The discovery of the neutron by James Chadwick in 1932 created a new means of nuclear transmutation. Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons, and Fermi concluded that his experiments had created new elements with 93 and 94 protons, which his group dubbed ausonium and hesperium. Fermi won the 1938 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".
Discovery of nuclear fission | Introduction
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, leading ultimately to the atomic bomb in 1945. In the 1911 Rutherford model, the atom consisted of a small positively charged massive nucleus surrounded by a much larger cloud of negatively charged electrons. In 1920, Rutherford suggested that the nucleus consisted of positive protons and neutrally-charged particles, suggested to be a proton and an electron bound in some way. Electrons were assumed to reside within the nucleus because it was known that beta radiation consisted of electrons emitted from the nucleus.
Neutron | Discovery
Chadwick repeated the creation of the radiation using beryllium to absorb the alpha particles: Be + He (α) → C + n. Following the Paris experiment, he aimed the radiation at paraffin wax, a hydrocarbon high in hydrogen content, hence offering a target dense with protons. As in the Paris experiment, the radiation energetically scattered some of the protons. 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.
Discovery of the neutron | Discovery of the neutron
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932, and in April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. In December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slow neutrons, and discovered that barium had been produced, and therefore that the uranium nucleus had been split. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Robert Frisch, developed a theoretical explanation of the process. By analogy with the division of biological cells, they named the process "fission".
British hydrogen bomb programme | Tube Alloys
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. Two months later, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. In December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slow neutrons, and discovered that barium had been produced. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, proved that the uranium nucleus had been split. They published their finding in "Nature" in 1939. This phenomenon was a new type of nuclear disintegration, and was more powerful than any seen before.
MAUD Committee | The discovery of fission
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.
Discovery of the neutron | The nature of the neutron
This experiment was conducted a year later by the English physicist James Chadwick, leading to the discovery a new type of particle, the neutron, for which Chadwick won the 1935 Nobel Prize in Physics.
Wang Ganchang | Introduction
The neutron was discovered by James Chadwick at the Cavendish Laboratory at the University of Cambridge in February 1932. In April 1932, his Cavendish colleagues John Cockcroft and Ernest Walton split lithium atoms with accelerated protons. Then, in December 1938, Otto Hahn and Fritz Strassmann at Hahn's laboratory in Berlin-Dahlem bombarded uranium with slowed neutrons, and discovered that barium had been produced. Hahn wrote to his colleague Lise Meitner, who, with her nephew Otto Frisch, explained that the uranium nucleus had been split. By analogy with the division of biological cells, they named the process "fission". The discovery of fission raised the possibility that an extremely powerful atomic bomb could be created.
Quebec Agreement | Tube Alloys
Franz Newell Devereux Kurie (February 6, 1907 in Victor, Colorado – June 12, 1972) was an American physicist who, while working at Yale in 1933, showed that the neutron was neither a dumbbell-shaped combination of proton and electron, nor an onion-shaped combination of an electron embracing the proton. Consequently, and until the discovery of the quark structure of hadrons, the neutron was assumed to be an elementary particle. His Kurie plot is used in the study of beta decay. Kurie earned his B.Sc. at McGill University in Montreal, Quebec, Canada, in 1927 and his Ph.D. at Yale in 1932. He then worked with Ernest Lawrence at the new Radiation Laboratory in Berkeley, California before taking up an assistant professorship at Indiana University Bloomington.
Franz N. D. Kurie | Introduction
The neutron was discovered in 1932 by British physicist James Chadwick. The concept of a nuclear chain reaction brought about by nuclear reactions mediated by neutrons was first realized shortly thereafter, by Hungarian scientist Leó Szilárd, in 1933. He filed a patent for his idea of a simple reactor the following year while working at the Admiralty in London. However, Szilárd's idea did not incorporate the idea of nuclear fission as a neutron source, since that process was not yet discovered. Szilárd's ideas for nuclear reactors using neutron-mediated nuclear chain reactions in light elements proved unworkable. Inspiration for a new type of reactor using uranium came from the discovery by Lise Meitner, Fritz Strassmann and Otto Hahn in 1938 that bombardment of uranium with neutrons (provided by an alpha-on-beryllium fusion reaction, a "neutron howitzer") produced a barium residue, which they reasoned was created by the fissioning of the uranium nuclei.
Nuclear reactor | Early reactors
By this model, particles such as the proton and neutron were not elementary, but composed of various configurations of a small number of other truly elementary particles called partons or quarks. The quark model received experimental verification beginning in the late 1960s and finally provided an explanation for the neutron's anomalous magnetic moment.
Discovery of the neutron | After 1939
Shull (Nobel Laureate), focusing specifically on dynamical diffraction effects of neutrons in perfect crystals which are due to multi-wave coherent superposition. After his return to Europe, he built up an interferometer for very cold neutrons which preceded later similar experiments with atoms. The fundamental experiments there included a most precise test of the linearity of quantum mechanics and a beautiful double-slit diffraction experiment with only one neutron at a time in the apparatus. Actually, in that experiment, while one neutron was registered, the next neutron still resided in its Uranium nucleus waiting for fission to happen. Then, as a professor at the University of Innsbruck, Zeilinger started experiments on entangled photons, as the low phase space density of neutrons produced by reactors precluded their use in such experiments.
Anton Zeilinger | Neutron interferometry
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.
Discovery of the neutron | Proton–neutron model of the nucleus
He was Rutherford's assistant director of research at the Cavendish Laboratory for over a decade at a time when it was one of the world's foremost centres for the study of physics, attracting students like John Cockcroft, Norman Feather, and Mark Oliphant. Chadwick followed his discovery of the neutron by measuring its mass. He anticipated that neutrons would become a major weapon in the fight against cancer. Chadwick left the Cavendish Laboratory in 1935 to become a professor of physics at the University of Liverpool, where he overhauled an antiquated laboratory and, by installing a cyclotron, made it an important centre for the study of nuclear physics.
James Chadwick | Introduction
In these measurements, 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 of 1.008. The excess mass was small, but well outside the limits of experimental uncertainty. Aston and others quickly realized that the discrepancy is due to 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.
Discovery of the neutron | Discovery of isotopes
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. It seemed that the magnetic moment of the electron vanished when it was within the nucleus. While on a visit to Utrecht University in 1928, Kronig learned of a surprising aspect of the rotational spectrum of N. The precision measurement made by Leonard Ornstein, the director of Utrecht's Physical Laboratory, showed that the spin of nitrogen nucleus must be equal to one.
Discovery of the neutron | Problems of the nuclear electrons hypothesis
Hahn was a Boy Scout fascinated by chemistry, and spent years conducting amateur chemistry experiments, which sometimes caused small explosions and other mishaps. He was inspired in part by reading "The Golden Book of Chemistry Experiments", and tried to collect samples of every element in the periodic table, including the radioactive ones. He later received a merit badge in Atomic Energy and became fascinated with the idea of creating a breeder reactor in his home. Hahn diligently amassed radioactive material by collecting small amounts from household products, such as americium from smoke detectors, thorium from camping lantern mantles, radium from clocks, and tritium from gunsights.
David Hahn | Creation of the neutron source
Aston's work on isotopes won 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.
Discovery of the neutron | Discovery of isotopes
Feather assisted Chadwick with his investigations leading to the discovery of the neutron. He then conducted some of the earliest investigations with the neutron. Feather obtained the first evidence that neutrons can produce nuclear disintegrations. The year 1932 would later be referred to as the "annus mirabilis" for nuclear physics in the Cavendish Laboratory.
Norman Feather | Discovery of the Neutron
The neutron was discovered by James Chadwick in 1932. The first demonstration of neutron radiography was made by Hartmut Kallmann and E. Kuhn in the late nineteen thirties; they discovered that upon bombardment with neutrons, some materials emitted radiation that could expose film. The discovery remained a curiosity until 1946 when low quality radiographs were made by Peters. The first neutron radiographs of reasonable quality were made by J. Thewlis (UK) in 1955. Around 1960, Harold Berger (US) and John P. Barton (UK) began evaluating neutrons for investigating irradiated reactor fuel. Subsequently, a number of research facilities were developed. The first commercial facilities came on-line in the late sixties, mostly in the United States and France, and eventually in many other countries including Canada, Japan, South Africa, Germany, and Switzerland.
Neutron imaging | History
In Rome, the young physicist Ettore Majorana declared that the manner in which the new radiation interacted with protons required a new neutral particle. On hearing of the Paris results, neither Rutherford nor James Chadwick at the Cavendish Laboratory believed the gamma ray hypothesis. Assisted by Norman Feather, Chadwick quickly performed a series of experiments showing that the gamma ray hypothesis was untenable. The previous year, Chadwick, J.E.R. Constable, and E.C. Pollard had already conducted experiments on disintegrating light elements using alpha radiation from polonium. They had also developed more accurate and efficient methods for detecting, counting, and recording the ejected protons.
Discovery of the neutron | Discovery of the neutron
The next important contribution was reported in 1932 by Irène Joliot-Curie and Frédéric Joliot in Paris, who showed that if this unknown radiation fell on paraffin wax or any other hydrogen-containing compound it ejected protons of very high energy. Finally, in 1932 the physicist James Chadwick in England performed a series of experiments showing that the gamma ray hypothesis was untenable, and suggested that the new radiation consisted of uncharged particles of approximately the mass of the proton. He performed a series of experiments to verify this, these uncharged particles were eventually called "neutrons", and Chadwick is credited with this discovery.
Neutron howitzer | Introduction
Rutherford called these uncharged particles "neutrons", by the Latin root for "neutralis" (neuter) and the Greek suffix "-on" (a suffix used in the names of subatomic particles, i.e. "electron" and "proton"). References to the word "neutron" in connection with the atom can be found in the literature as early as 1899, however. Throughout the 1920s, physicists assumed that the atomic nucleus was composed of protons and "nuclear electrons" but there were obvious problems. It was difficult to reconcile the proton–electron model for nuclei with the Heisenberg uncertainty relation of quantum mechanics. The Klein paradox, discovered by Oskar Klein in 1928, presented further quantum mechanical objections to the notion of an electron confined within a nucleus.
Neutron | Discovery
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.
Discovery of the neutron | Neutron physics in the 1930s
In 1920 Rutherford gave a Bakerian lecture at the Royal Society entitled the "Nuclear Constitution of Atoms", a summary of recent experiments on atomic nuclei and conclusions as to the structure of atomic nuclei. By 1920, the existence of electrons within the atomic nucleus was widely assumed. It was assumed the nucleus consisted of hydrogen nuclei in number equal to the atomic mass. But since each hydrogen nucleus 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.
Discovery of the neutron | Rutherford atom
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.
Discovery of the neutron | Neutron physics in the 1930s
After James Chadwick discovered the neutron in 1932, Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, they found that this results in a short-lived radioactive isotope of phosphorus. They noted that positron emission continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before. Radiochemistry was now no longer confined to certain heavy elements, but extended to the entire periodic table. Chadwick noted that being electrically neutral, neutrons could penetrate the atomic nucleus more easily than protons or alpha particles.
Otto Hahn | Discovery of nuclear fission
In 1929, Feather took a year-long visit to Johns Hopkins University in Baltimore, USA. During his visit, he learned that Kelly Hospital used radon tubes in the treatment of cancers, and that the expired tubes were discarded after use. The expired radon tubes were a source of polonium, a source of energetic alpha particles. Since polonium was difficult to obtain and expensive at the time, Feather acquired a large number of the discarded radon tubes. The expired radon was to be used as a source of alpha particles for experiments in Cambridge. Indeed, the radioactive polonium source used by James Chadwick to discover the neutron in 1932 was derived from these radon tubes.
Norman Feather | Discovery of the Neutron
He was awarded his Ph.D. from Purdue in 1941, writing a thesis on an "Investigation of Nuclear Reactions and Scattering Produced by Neutrons". For his thesis, he constructed a neutron generator, and originally intended to discuss the possibilities of studying neutron diffraction in crystals, but this really only became possible with the development of nuclear reactors that produced large quantities of high energy neutrons. After the discovery of nuclear fission in 1939, he became interested in the phenomenon, and re-oriented his thesis to the study of neutrons emitted by fission.
Raemer Schreiber | Early life
Pegram was investigating the phenomena associated with the newly discovered neutron. In 1938, Enrico Fermi escaped fascist Italy after winning the Nobel prize for his work on induced radioactivity. In fact, he took his wife and children with him to Stockholm and immediately emigrated to New York. Shortly after arriving he began working at Columbia. His work on nuclear fission, together with Rabi's work on atomic and molecular physics, ushered in a golden era of fundamental research at the university. One of the country's first cyclotrons was built in the basement of Pupin Hall, where parts of it still remain.
Columbia University Physics Department | History
The neutron is a spin 1/2 particle, that is, it is a fermion with intrinsic angular momentum equal to 1/2 , where is the reduced Planck constant. For many years after the discovery of the neutron, its exact spin was ambiguous. Although it was assumed to be a spin 1/2 Dirac particle, the possibility that the neutron was a spin 3/2 particle lingered. The interactions of the neutron's magnetic moment with an external magnetic field were exploited to finally determine the spin of the neutron. In 1949, Hughes and Burgy measured neutrons reflected from a ferromagnetic mirror and found that the angular distribution of the reflections was consistent with spin 1/2.
Neutron | Spin
The radiation was not influenced by an electric field, so Bothe and Becker assumed it was gamma radiation. The following year Irène Joliot-Curie and Frédéric Joliot-Curie in Paris showed that if this "gamma" radiation fell on paraffin, or any other hydrogen-containing compound, it ejected protons of very high energy. Neither Rutherford nor James Chadwick at the Cavendish Laboratory in Cambridge were convinced by the gamma ray interpretation. Chadwick quickly performed a series of experiments that showed that the new radiation consisted of uncharged particles with about the same mass as the proton. These particles were neutrons. Chadwick won the 1935 Nobel Prize in Physics for this discovery.
Neutron | Discovery
Frances Pleasonton (1912–1990) was a Particle Physicist at the Oak Ridge National Laboratory. She was an active teacher and researcher, and a member of the team who first demonstrated neutron decay in 1951.
Frances Pleasonton | Introduction
Just a few weeks before Cockcroft and Walton's feat, another scientist at the Cavendish Laboratory, James Chadwick, discovered the neutron, using an ingenious device made with sealing wax, through the reaction of beryllium with alpha particles: Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, they found that this results in a short-lived radioactive isotope of phosphorus with a half-life of around three minutes: which then decays to a stable isotope of silicon They noted that radioactivity continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay in the form of positron emission, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before.
Discovery of nuclear fission | Transmutation
Isotopes were then explained as elements with the same number of protons, but different numbers of neutrons within the nucleus.
Atom | Discovery of the neutron
Neutron stars were thought to be too faint to be detectable and little work was done on them until November 1967, when Franco Pacini pointed out that if the neutron stars were spinning and had large magnetic fields, then electromagnetic waves would be emitted. Unbeknown to him, radio astronomer Antony Hewish and his research assistant Jocelyn Bell at Cambridge were shortly to detect radio pulses from stars that are now believed to be highly magnetized, rapidly spinning neutron stars, known as pulsars. In 1965, Antony Hewish and Samuel Okoye discovered "an unusual source of high radio brightness temperature in the Crab Nebula".
Neutron star | History of discoveries
Two years later, Paul Villard discovered gamma rays, which possessed even more penetrating power. These radiations were soon identified with known particles: beta rays were shown to be electrons by Walter Kaufmann in 1902; alpha rays were shown to be helium ions by Rutherford and Thomas Royds in 1907; and gamma rays were shown to be electromagnetic radiation, that is, a form of light, by Rutherford and Edward Andrade in 1914. These radiations had also been identified as emanating from atoms, hence they provided clues to processes occurring within atoms. Conversely, the radiations were also recognized as tools that could be exploited in scattering experiments to probe the interior of atoms.
Discovery of the neutron | Discovery of radioactivity
Dunning. Fellow graduate students in physics at the time included James Rainwater, Herbert L. Anderson and George Weil. He worked with Rainwater on the construction of a neutron spectrometer. His thesis, on "Slow neutron cross sections of indium, gold, silver, antimony, lithium and mercury as measured with a neutron beam spectrometer", was classified.
William W. Havens Jr. | Early life
After it was discovered that the Thin Man design would not work, he was transferred to Robert Bacher's Gadget Division as the leader of the Initiator group, which was responsible for the design and testing of the "Urchin" neutron initiator that provided the burst of neutrons that kick-started the nuclear detonation of the Fat Man weapon. After the war he became a professor at the University of Minnesota, and then vice president for research at the Convair division of General Dynamics, where he worked on the Atlas family of rockets. In 1961, J. Carson Mark and Norris Bradbury offered him a position at Los Alamos, which he held until he retired in 1977.
Charles Critchfield | Introduction
The table is also notable for including the solo Neutron as an entry on its own, "above" Hydrogen, and given the symbol lower-case 'n'.
Henry D. Hubbard | Introduction
Also, those radioelements that reside in the same places in the periodic system are chemically identical. Soddy called these chemically identical 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, which he easily achieved, was to separate the two isotopes of neon, and . Aston discovered that the masses of all the particles are whole numbers (the whole number rule): that is, the masses of all the isotopes are whole number multiples of the mass of the hydrogen atom.
Discovery of the neutron | Discovery of isotopes
Pauli originally named his proposed light particle a "neutron". When James Chadwick discovered a much more massive nuclear particle in 1932 and also named it a neutron, this left the two particles with the same name. Enrico Fermi, who developed the theory of beta decay, introduced the term "neutrino" in 1934 (it was jokingly coined by Edoardo Amaldi during a conversation with Fermi at the Institute of physics of via Panisperna in Rome, in order to distinguish this light neutral particle from Chadwick's neutron) to resolve the confusion. It was a pun on neutrone, the Italian equivalent of "neutron": the "-one" ending can be an augmentative in Italian, so "neutrone" could be read as the "large neutral thing"; "-ino" replaces the augmentative suffix with a diminutive one.
Electron neutrino | Name
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, or positrons, 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.
Discovery of the neutron | Proton–neutron model of the nucleus
The radiation was more penetrating than any gamma rays known, and the details of experimental results were difficult to interpret. Two years later Irène Joliot-Curie and Frédéric Joliot in Paris showed that if this unknown radiation fell on paraffin wax, or any other hydrogen-containing compound, it ejected protons of very high energy (5 MeV). This observation was not in itself inconsistent with the assumed gamma ray nature of the new radiation, but that interpretation (Compton scattering) had a logical problem. From energy and momentum considerations, a gamma ray would have to have impossibly high energy (50 MeV) to scatter a massive proton.
Discovery of the neutron | Discovery of the neutron
By 1931, the building which later became Pupin Hall was a leading research center. During this time Harold Urey (Nobel laureate in Chemistry) discovered deuterium and George B. Pegram was investigating the phenomena associated with the newly discovered neutron. In 1938, Enrico Fermi escaped fascist Italy after winning the Nobel prize for his work on induced radioactivity. In fact, he took his wife and children with him to Stockholm and immediately emigrated to New York. Shortly after arriving he began working at Columbia University with Dr. John Dunning. His work on nuclear fission, together with I. I. Rabi's work on atomic and molecular physics, ushered in a golden era of fundamental research at the university.
Pupin Hall | History
The development of the mass spectrometer allowed the mass of atoms to be measured with increased accuracy. The device uses a magnet to bend the trajectory of a beam of ions, and the amount of deflection is determined by the ratio of an atom's mass to its charge. The chemist Francis William Aston used this instrument to show that isotopes had different masses. The atomic mass of these isotopes varied by integer amounts, called the whole number rule. The explanation for these different isotopes awaited the discovery of the neutron, an uncharged particle with a mass similar to the proton, by the physicist James Chadwick in 1932.
Atom | Discovery of the neutron
These facts were realized first-hand at the "Operation Crossroads" atomic test series in 1946.
Neutron activation | Introduction
The concentrated atomic mass was required to provide the observed deflection 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 the neutron | The gold foil experiment and the discovery of the atomic nucleus
Neutron generators have applications in medicine, security, and materials analysis. The basic concept was first developed by Ernest Rutherford's team in the Cavendish Laboratory in the early 1930s. Using a linear accelerator driven by a Cockcroft–Walton generator, Mark Oliphant led an experiment that fired deuterium ions into a deuterium-infused metal foil and noticed that a small number of these particles gave off alpha particles. This was the first demonstration of nuclear fusion, as well as the first discovery of Helium-3 and tritium, created in these reactions. The introduction of new power sources has continually shrunk the size of these machines, from Oliphant's that filled the corner of the lab, to modern machines that are highly portable.
Neutron generator | Introduction
Kanner the first demonstration of fission by fast neutrons and thorium and uranium. His thesis was on the interaction of fast neutrons with helium. In a paper with John A. Wheeler he reported the discovery of spin-orbit coupling in neutron scattering. He worked at the University of Kansas, and then at the Manhattan Project in Los Alamos, New Mexico continuing his work with fast neutrons. In 1946 he joined the University of Wisconsin–Madison, where he remained for most of his career following a program on determining fast neutron cross-sections, directing the doctoral dissertation research of over forty students. In 1970, his laboratory was destroyed by a terrorist attack on a military research facility there, which seriously injured one of his graduate students and killed a member of another research group.
Henry H. Barschall | Biography
Harkins was born in Titusville, Pennsylvania, and graduated with a PhD from Stanford University in 1907. He subsequently taught chemistry at the University of Montana from 1900 to 1912, and then spent the rest of his career at the University of Chicago. Harkins correctly predicted the existence of the neutron in 1920 (as a proton–electron complex) and was the first to use the word "neutron" in connection with the atomic nucleus. The neutron was detected experimentally by James Chadwick in 1932. In the beginning of the 1930s, Harkins built a cyclotron. From experiments with this, he concluded that the sun might be powered by nuclear fusion.
William Draper Harkins | Introduction
There is a theory that strange particles such as hyperons and dibaryons could form in the interior of a neutron star, changing its mass–radius ratio in ways that might be detectable. Accordingly, measurements of neutron stars could set constraints on possible dibaryon properties. A large fraction of the neutrons in a neutron star could turn into hyperons and merge into dibaryons during the early part of its collapse into a black hole . These dibaryons would very quickly dissolve into quark–gluon plasma during the collapse, or go into some currently unknown state of matter.
Hexaquark | Introduction
Working at the Oak Ridge National Laboratory (ORNL) after World War II, he continued study into neutron scattering, using the neutrons emitted from the X-10 Graphite Reactor and a modified X-ray diffractometer.
Ernest O. Wollan | Biography
In 1930, Walther Bothe and Herbert Becker in Giessen, Germany found that if the energetic alpha particles emitted from polonium fell on certain light elements, specifically beryllium (), boron (), or lithium (), an unusually penetrating radiation was produced. Beryllium produced the most intense radiation. Polonium is highly radioactive, producing energetic alpha radiation, and it was commonly used for scattering experiments at the time. Alpha radiation can be influenced by an electric field, because it is composed of charged particles. The observed penetrating radiation was not influenced by an electric field, however, so it was thought to be gamma radiation.
Discovery of the neutron | Discovery of the neutron
Soon after the neutron was discovered in 1932, 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. The proton's magnetic moment had been determined by measuring the deflection of a beam of molecular hydrogen by a magnetic field. Stern won the Nobel Prize in 1943 for this discovery. By 1934 groups led by Stern, now in Pittsburgh, and I. I. Rabi in New York had independently measured the magnetic moments of the proton and deuteron.
Neutron magnetic moment | Measurement
Neutron is an Italian comic book series and the name of the eponymous main character created in 1965 by Guido Crepax. The series eventually became "Valentina".
Neutron (Linus) | Introduction
A neutron howitzer is a neutron source that emits neutrons in a single direction. It was discovered in the 1930s that alpha radiation that strikes the beryllium nucleus would release neutrons. The high speed of the alpha is sufficient to overcome the relatively low Coulomb barrier of the beryllium nucleus, the repulsive force due to the positive charge of the nucleus, which contains only four protons, allowing for fusion of the two particles, releasing energetic neutrons. In 1930 Walther Bothe and Herbert Becker in Germany found that alpha particles striking light elements such as beryllium, boron, or lithium would release a highly penetrating radiation, at first believed to be gamma radiation, although it was more penetrating than any gamma rays known.
Neutron howitzer | Introduction
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.
Discovery of the neutron | Rutherford atom
Bacon built the first neutron diffractometer in the UK at the Atomic Energy Research Establishment, Harwell, and then made the first experiments outside the United States in neutron diffraction, a means of studying the basic structures and dynamics of materials. He wrote scientific papers, textbooks and review articles on the use of neutron scattering. His work included a study of the neutron intensities diffracted by crystals, which led to studies of the basic structure of molecules and of magnetism. His book "Neutron Diffraction" was a standard text, beginning with the first edition in 1955.
George Bacon (physicist) | Career
Several important early physics discoveries were made here, including the discovery of the electron by J.J. Thomson (1897) the Townsend discharge by John Sealy Townsend, and the development of the cloud chamber by C.T.R. Wilson. Ernest Rutherford became Director of the Cavendish Laboratory in 1919. Under his leadership the neutron was discovered by James Chadwick in 1932, and in the same year the first experiment to split the nucleus in a fully controlled manner was performed by students working under his direction; John Cockcroft and Ernest Walton.
Cavendish Laboratory | Physics
Hahn refused medical evaluation for radiation exposure. EPA scientists believe that Hahn's life expectancy may have been greatly shortened by his exposure to radioactivity, particularly since he spent long periods in the small, enclosed shed with large amounts of radioactive material and only minimal safety precautions, but he refused their recommendation that he be examined at the Enrico Fermi Nuclear Generating Station.
David Hahn | Creation of the neutron source
Ivanenko had suggested a similar analogy in 1932. Fermi's theory requires the neutron to be a spin- 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.
Discovery of the neutron | Proton–neutron model of the nucleus
He received a Chemical Engineering degree from the University of Lyon and an Sc.B. and Ph.D. from the University of Paris where he carried out research on neutron counting.
Lew Kowarski | Education
Rutherford and others had noted the disparity between the mass of an atom, computed in atomic mass units, and the approximate charge required on the nucleus for the Rutherford model to work. The required charge of the atomic nucleus was usually about half its atomic mass. Antonius van den Broek boldly hypothesized that the required charge, denoted by "Z", was not half of the atomic weight for elements, but instead was exactly equal to the element's ordinal position in the periodic table. At that time, the positions of the elements in the periodic table were not known to have any physical significance.
Discovery of the neutron | Atomic number and Moseley's law
The feat was popularly known as "splitting the atom", and would win them the 1951 Nobel Prize in Physics for ""Transmutation of atomic nuclei by artificially accelerated atomic particles"", although it was not the nuclear fission reaction later discovered in heavy elements. After English physicist James Chadwick discovered the neutron in 1932, Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons in 1934. Fermi concluded that his experiments had created new elements with 93 and 94 protons, which the group dubbed ausonium and hesperium. However, not all were convinced by Fermi's analysis of his results, though he would win the 1938 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".
Nuclear fission | Discovery of nuclear fission
If the elements were ordered based on increasing atomic mass, however, periodicity in chemical properties was exhibited. Exceptions to this periodicity were apparent, however, such as cobalt and nickel. At the University of Manchester in 1913 Henry Moseley discussed the new Bohr model of the atom with the visiting Bohr. The model accounted for the electromagnetic emission spectrum from the hydrogen atom, and Moseley and Bohr wondered if the electromagnetic emission spectra of heavier elements such as cobalt and nickel would follow their ordering by weight, or by their position in the periodic table. In 1913-1914 Moseley tested the question experimentally by using X-ray diffraction techniques.
Discovery of the neutron | Atomic number and Moseley's law
The alpha particle was presumed to consist of four protons and two closely bound electrons to give it +2 charge and mass 4. 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.
Discovery of the neutron | Rutherford atom
Jimmy Neutron, a fictional character, may also refer to:
Jimmy Neutron (disambiguation) | Introduction
Concurrent with the work of Rutherford, Geiger, and Marsden, the radiochemist Frederick Soddy at the University of Glasgow was studying chemistry related problems on radioactive materials. Soddy had worked with Rutherford on radioactivity at McGill University. By 1910, about 40 different radioactive elements, referred to as "radioelements", had been identified between uranium and lead, although the periodic table only allowed for 11 elements. Soddy and Kazimierz Fajans independently found in 1913 that an element undergoing alpha decay will produce an element two places to the left in the periodic system and an element undergoing beta decay will produce an element one place to the right in the periodic system.
Discovery of the neutron | Discovery of isotopes
Initially nothing registered on the oscilloscope, but then Zinn realized that it was not plugged in. On doing so, they discovered significant neutron multiplication in natural uranium, proving that a chain reaction might be possible. Szilard later described the event: "We turned the switch and saw the flashes. We watched them for a little while and then we switched everything off and went home." He understood the implications and consequences of this discovery, though. "That night, there was very little doubt in my mind that the world was headed for grief".
Leo Szilard | Columbia University
All consideration of nuclear electrons ended with James Chadwick's discovery of the neutron in 1932. An atom of gold now was seen as containing 118 neutrons rather than 118 nuclear electrons, and its positive charge now was realized to come entirely from a content of 79 protons. After 1932, therefore, an element's atomic number "Z" was also realized to be identical to the proton number of its nuclei.
Atomic number | The discovery of the neutron makes "Z" the proton number
His "reactor" was a bored-out block of lead, and he used lithium from $1,000 worth of purchased batteries to purify the thorium ash using a Bunsen burner. Hahn posed as an adult scientist or high school teacher to gain the trust of many professionals in letters—and succeeded, despite misspellings and obvious errors. Hahn ultimately hoped to create a breeder reactor, using low-level isotopes to transform samples of thorium and uranium into fissionable isotopes. His homemade neutron source was often incorrectly referred to as a reactor, but it did end up emitting dangerous levels of radiation, likely well over 1,000 times normal background radiation.
David Hahn | Creation of the neutron source
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. This nucleus would also be orbited by another 7 electrons, termed "external electrons" by Rutherford, to complete the N atom. However problems with the hypothesis soon became apparent. Ralph Kronig pointed out in 1926 that the observed hyperfine structure of atomic spectra was inconsistent with the proton–electron hypothesis.
Discovery of the neutron | Problems of the nuclear electrons hypothesis
In the US, Leó Szilárd, a former chemical engineer, discovered the problem.
Neutron moderator | Moderator impurities
He Xiantu (; born September 28, 1937), also romanized as Xian-Tu He, is a Chinese nuclear and theoretical physicist. He is the chief scientist of many Chinese national nuclear research and development programs. He designed the first neutron bomb in China.
He Xiantu | Introduction
In 1932, Chadwick exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles which could not be massless like the gamma ray, but instead were required to have a mass similar to that of a proton. Chadwick now claimed these particles as Rutherford's neutrons. For his discovery of the neutron, Chadwick received the Nobel Prize in 1935.
Atomic theory | Discovery of nuclear particles
He found that the most intense short-wavelength line in the X-ray spectrum of a particular element, known as the K-alpha line, was related to the element's position in the periodic table, that is, its atomic number, "Z". Indeed, Moseley introduced this nomenclature. Moseley found that the frequencies of the radiation were related in a simple way to the atomic number of the elements for a large number of elements. Within a year it was noted that the equation for the relation, now called Moseley's law, could be explained in terms of the 1913 Bohr model, with reasonable extra assumptions about atomic structure in other elements.
Discovery of the neutron | Atomic number and Moseley's law
Neutron is a two-player abstract strategy game invented by Robert A. Kraus. The game was first published in the Playroom section of Games & Puzzles 71 in July/August 1978. It is a game where each player moves two different pieces in a single turn without the use of dice. There are 15 variants to this game. Neutron and some of its variants are some of the main games featured in "Zillions of Games". The game has been solved to some degree. Analysis has shown that the first player wins. It is unknown whether the other variants have been solved or not, and to what degree.
Neutron (game) | Introduction
Anderson, Eugene T. Booth, G. Norris Glasoe, and Francis G. Slack conducted the first nuclear fission experiment in the United States on 25 January 1939. Subsequent work confirmed that fast neutrons were indeed produced by fission. Szilard obtained permission from the head of the Physics Department at Columbia, George B. Pegram, to use a laboratory for three months, and persuaded Walter Zinn to become his collaborator. They conducted a simple experiment on the seventh floor of Pupin Hall at Columbia, using a radium-beryllium source to bombard uranium with neutrons. They discovered significant neutron multiplication in natural uranium, proving that a chain reaction might be possible.
Chicago Pile-1 | Origins
At the age of 18 he was admitted to the third year of Physics. Fermi described Pontecorvo as "scientifically one of the brightest men with whom I have come in contact in my scientific career". As their youngest member, the group nicknamed him "Cucciolo", which means "puppy". In 1934, Pontecorvo contributed to Fermi's famous experiment showing the properties of slow neutrons that led the way to the discovery of nuclear fission. Pontecorvo's name was included on the Via Panisperna boys' patent "To increase the production of artificial radioactivity with neutron bombardment". He was made a temporary assistant at the Royal Institute of Physics on 1 November 1934 and the University of Rome, and on 7 November, he was listed as co-author, along with Fermi and Rasetti, of a landmark paper on slow neutrons that reported that hydrogen slowed neutrons more than heavy elements, and that slow neutrons were more easily absorbed.
Bruno Pontecorvo | Early life and education