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The neutron is a subatomic particle. As its name indicates it, the neutron is neutral and thus has electric Charge (neither positive, nor negative). The neutrons, with the protons, are the components of the core of the Atome. For an atom, one notes Z the number of protons (which one calls Atomic number or atomic number ), has the number of protons + neutrons. The number of neutrons is thus NR or A-Z.

Mass neutron: m_n = 939.56533 ± 0.00004 MeV /c ²

A neutron belongs to the Baryon S (Hadron formed of 3 quarks) and is composed of a Quark of valence up (load 2/3e) and of two quarks of valence down (2 loads of -1/3e). Because of this structure, the neutron presents a magnetic Moment.

The neutron was discovered by the English physicist James Chadwick in 1932.

History

The discovery of the neutron resulted from three series of experiments, made in three different countries, one involving the other. In this direction it is exemplary research of knowledge.

In 1930, in Germany, W. Bothe and H. Becker, specialists in the cosmic Rayonnement observes that light elements, bombarded by Particules alpha, emit penetrating “ultra” rays which they suppose being of the Gamma rays much more energetic than those emitted by radioactive cores or accompanying the nuclear Transmutation S.

In 1931, in France, Irene and Frederic Joliot-Curie intrigued by these results seeks to include/understand the nature of this radiation and discovers that it with the property to put moving atomic nuclei and in particular of the protons… They suppose that it is a Effect Compton between gamma of which they estimate energy at approximately 50 MeV (a very high energy for the time) and of hydrogen.

In 1932, in England, at once these published results, James Chadwick makes a test confirming the results and goes further and measuring with precision the energy of the cores projected by using the reaction alpha + Be → C + N, it can affirm that the penetrating “ultra” radiation cannot be an gamma ray, of very high energy, but must be made up of particles of mass 1 and electric charge 0: it is the neutron.

Each of the three teams had worked with the apparatuses it had, but also with its knowledge and had bathed in the tradition of its laboratory. It is not astonishing that it is at the laboratory of Cambridge, directed by Ernest Rutherford that the neutron was discovered. Since 1920, Rutherford, indeed, had put forth the assumption of the existence of the neutron.

James Chadwick, was the assistant of Rutherford and one of his more brilliant disciples. It was on June 3rd, 1920 that he heard Rutherford, in the circle of accustomed Bakerian Lectures of the Royal Society , to formulate the idea of a kind of atom of mass 1 and load 0 which was not hydrogen: this object, not being prone to the electric repulsions that the protons and the particles alpha underwent, was to be able to approach the cores and to penetrate there easily. Chadwick remembered 12 years later this communication, when it had to interpret the results of its experiments.

Later, learning that the Nobel Prize had been decreed in Chadwick for the discovery of the neutron, Rutherford will say, according to Emilio Segré: “ For the neutron, it is all alone Chadwick. The Joliot-Curie are so brilliant that they will quickly deserve it for something of other! ”.

Radioactivity

The Radioactivité produces free neutrons. These neutrons can be absorptive by the cores of other atoms which can then become unstable. They can also cause a Nuclear fission by collision with the core.

The neutron being overall neutral, it directly does not produce ionizations while crossing the matter. On the other hand, it can have many reactions with the cores of the atoms (radiative Capture, inelastic Scattering, reactions producing of the particles alpha or other neutrons, fission of the core,…), producing each ionizing ray. For this reason, the neutrons are regarded as a Ionizing ray, that is to say a radiation which produces ionizations in the matter that it crosses.

Application

• the rays of neutrons are used for the neutron diffusion, process making it possible to study matter in a condensed state. This penetrating radiation makes it possible to see the interiors of the bodies, like metals, ores, fluids and makes it possible to examine their structures on an atomic scale by Diffraction. The neutron Spectroscopie makes it possible to study in a single way the excitations of the bodies, like the Phonon S and the vibrations atomic. Another advantage of the neutrons lies in their magnetic sensitivity. In these uses, the neutron Rayonnement is complementary to X-rays.

Sources

The neutron sources with high flow are either of the nuclear reactors dedicated to the production of this radiation, or of the sources of Spallation, large accelerating S of protons which send an evaporating beam of protons accelerated on a target of the neutrons. Typically, the neutron sources gather a forming park of instrumentation of great centers of national or international users.

Centers

• Australia:
• Australian Nuclear Science and Technology Organization () operates the historical engine and brings into service one of the most modern neutron centers.
• Europe:
• the Institut Laue-Langevin is the greatest center of the world around a neutron engine.

See too

Internal bonds

• Antineutron
• Physical Nuclear physics
• of the particles
• Proton
• Neutronthérapie

External bonds

• Characteristic of the neutron ( Particle Dated Group )

Beats-smg: Neutruons Simple: Neutron Zh-min-nan: Tiong-chú Zh-yue: 中子

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