Nuclear Power Plant Isar, Germany

What Is a Neutron?

A neutron is a subatomic particle that is part of the atom (along with the proton and the electron). Neutrons and protons form the atomic nucleus. Neutrons have no net electric charge, unlike the proton that has a positive electric charge.

What is a neutron?

The difference in the number of neutrons in the nucleus of an atom does not imply the variation of the nature of the atom itself, but it does determine the isotope to which it is a part.

In nuclear energy the concept " uranium enrichment" refers to the alteration of the number of neutrons in the atomic nucleus in order to obtain another more unstable uranium atom. This modification implies, therefore, an isotope change.

Since protons and neutrons behave similarly within the nucleus, and each has a mass of about one unit of atomic mass, both are called nucleons. Its properties and interactions are described by nuclear physics.

Neutrons and Nuclear Fission

Nuclear fission reactors are reactors that are powered by nuclear energy generated through nuclear fission reactions.

To generate a nuclear fission reaction, the nucleus of a nuclear fuel atom (normally uranium or plutonium: specifically the isotopesuranium-235 and plutonium-239) is bombarded with a neutron. The shock of the neutron with the atomic nucleus is sufficient for it to break and decompose into two particles and two or three free neutrons. These free neutrons, in turn, may collide with other atomic nuclei thus generating a succession of nuclear chain reactions.

The speed with which the neutrons move and the amount of free neutrons in the core of the nuclear reactor determine the reactor power of the nuclear power plant. In order to control the number of fission reactions per unit of time, nuclear power plants have mechanisms to control the number of free electrons. Some of these control mechanisms are the neutron moderator, the reflector, the control rods, etc.

Characteristics of Neutrons

The neutron is formed by three quarks, one quark above and two quarks below.

The neutron does not exist outside the atomic nucleus. The average life of a neutron outside the nucleus is only about 885 seconds (15 minutes).

The mass of a neutron can not be determined directly by mass spectrometry due to the lack of electrical charge. However, it can be deduced since the masses of a proton and a deuteron can be measured with a mass spectrometer. With all this we know that the mass of a neutron is 1.67492729 × 10 -27  kg. The mass of the neutron is slightly larger than that of the proton.

The total electric charge of the neutron is 0. This zero value has been tested experimentally. The experimental limit obtained in the neutron charge is so close to zero that, given the experimental uncertainties, it is considered zero in comparison with the proton charge. Therefore, the neutron is considered to have zero charge or zero charge.

The neutron is a 1/2 spin particle, that is, it is a fermion. For many years after the discovery of the neutron, its exact turn was ambiguous. Although it was assumed to be a Dirac particle of spin 1/2, the possibility that the neutron was a 3/2 spin particle persisted.

As a fermion, the neutron is subject to the Pauli exclusion principle. According to Pauli's exclusion principle, two neutrons can not have the same quantum numbers.

The antineutron is the antiparticle of the neutron. The antineutron was discovered by Bruce Cork in 1956, a year after the antiproton was discovered.

Neutron Discovery

The first indication of the existence of the neutron occurred in 1930, when Walther Bothe and Becker, H. found that when the alpha radiation fell on elements such as lithium and boron a new form of radiation was emitted.

Initially, this radiation was thought to be a type of gamma radiation, but it was more penetrating than any known gamma radiation. The work done by Irene Joliot-Curie and Joliot Frederic in 1932, although it does not refute the hypothesis of gamma radiation, does not support it all well.

In 1932, James Chadwick showed that these results could not be explained by gamma rays and proposed an alternative explanation of no-charge particles about the same size as a proton. Chadwick was able to experimentally verify this conjecture and thus demonstrate the existence of the neutron.


Published: March 19, 2019
Last review: March 19, 2019