Neutrons They are electrically neutral particles, with a mass 1,838.4 times that of the electron and 1,00014 times that of the proton ; Along with protons, neutrons are the fundamental constituents of the atomic nucleus and are considered as two forms of the same particle: the nucleon.

The neutron is a particle with no net charge, present in the atomic nucleus of practically all atoms except the protium. Although the neutron is said to be uncharged, it is actually made up of three fundamental charged particles called quarks, whose summed charges are zero. Therefore, the neutron is a neutral baryon made up of two type quarks below, and one type quark above. Outside the atomic nucleus, neutrons are unstable, having a half-life of 15 minutes (885.7 ± 0.8 s), each neutron breaks down into an electron, an antineutrino, and a proton. Its mass is very similar to that of the proton, although slightly greater.

The neutron is necessary for the stability of almost all atomic nuclei, except for the hydrogen-1 isotope. Strong nuclear interaction is responsible for keeping them stable in atomic nuclei.


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  • 1 History
  • 2 Some of its properties
  • 3 Nuclear fission
  • 4 See also
  • 5 Source


The existence of neutrons was discovered in 1932 by Chadwick; studying the radiation emitted by beryllium bombarded with particles, it showed that it was made up of neutral particles of great penetrating power, which had a mass somewhat higher than that of the proton .

Ernest Rutherford first proposed the existence of the neutron in 1920 , to try to explain that nuclei do not decay by electromagnetic repulsion of protons. In 1909 , in Germany , Walther Bothe and H. Becker discovered that if the high energy alpha particles of polonium fell on light materials, specifically beryllium, boron or lithium , particularly penetrating radiation was produced. At first they were thought to be gamma raysAlthough these were more penetrating than all previously known gamma rays, and the details of the experimental results were difficult to interpret on this basis.

In 1932 , in Paris , Irène Joliot-Curie and Frédéric Joliot showed that this unknown radiation, by striking paraffin or other hydrogen-containing compounds, produced protons at high energy. That was not inconsistent with the assumption that they were gamma rays of radiation, but a detailed quantitative analysis of the data made it difficult to reconcile the aforementioned hypothesis. Finally (in late 1932 ) the English physicist James Chadwick , in England, carried out a series of experiments from which he obtained results that did not agree with those predicted by the physical formulas: the energy produced by the radiation was much higher and in shocks the moment was not conserved. To explain these results, it was necessary to choose one of the following hypotheses: either the non-conservation of the moment in the collisions was accepted or the corpuscular nature of the radiation was affirmed. Since the first hypothesis contradicted the laws of physics, the second was preferred. With this, the results obtained were explained, but it was necessary to accept that the particles that formed the radiation had no electric charge. Such particles had a mass very similar to that of the proton, but without electric charge, so it was thought that they were the result of the union of a proton and aElectron forming a kind of electric dipole. Later experiments discarded the idea of ​​the dipole and the nature of the neutrons was known.

Some of its properties

Mass: mn = 1,675×10-27 Kg = 1.008587833 amu

  • Average life: tn = 886.7 ± 1.9 s
  • Magnetic moment: mn = -1.9130427 ± 0.0000005 mN
  • Electric charge: qn = (-0.4 ± 1.1) x 10-21 e

Nuclear fision

The fundamental process leading to the production of nuclear energy is the fission of a uranium nucleus originated by a neutron: in fission the nucleus splits into two parts and around three neutrons on average (fast neutrons); the fragments resulting from the cleavage also emit other neutrons. Neutrons are essential in nuclear reactions: a chain reaction occurs when a neutron causes fission of a fissile Atom , producing a greater number of neutrons that in turn cause other fissions. Depending on whether this reaction occurs in a controlled or uncontrolled manner, you have the following:

  • Uncontrolled reaction: it only occurs when you have a sufficient quantity of nuclear fuel -critical mass-; foundation of the nuclear bomb.
  • Controlled reaction: by using a moderator in the nuclear reactor; basis of the use of nuclear energy.


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