Neutrons are found in the nucleus of an atom and make up half the weight of the atom.
A neutron is a small subatomic particle that can be found in virtually all forms of conventional matter, with the only stable exception being the hydrogen atom. The particle’s home is in the atomic nucleus, where it is tightly bound to protons through the strong nuclear force, the strongest force in nature. Neutrons make up about half the weight of conventional matter by volume.
Neutrons are found in almost all forms of conventional matter.
This particle got its name because it is electrically neutral. It can be seen as a squashed proton and electron. Since these two particles have opposite charges of the same magnitude, their fusion results in an uncharged particle. This lack of charge can make neutrons difficult to detect, but techniques have been developed to observe them that take advantage of the way they interact with the nuclei of various atoms. Particles can sometimes behave in limited ways because their constituents, the quarks, have small charges.
Neutron microscopes can use neutrons to create images.
Normal atoms have a balanced number of protons and neutrons in their nuclei. For example, helium has two protons and two neutrons, and iron has 26 protons and 26 neutrons. When this equilibrium is broken, the atom is called an isotope, although technically normal atoms are just stable isotopes, and the word “isotope” is used colloquially to describe non-stable atomic variants.
The neutron was originally discovered in 1930. Its antiparticle, the antineutron, was discovered in 1956. Although it is a subatomic particle, the neutron is not fundamental. It is made up of two down quarks and one up quark, making it a baryon. The fact that it was made up of smaller parts was not theorized until 1961.
This particle is similar in mass to its nuclear partner, the proton, but is slightly larger. It can survive outside the nucleus of an atom, but only for a period of about 15 minutes. At the end of this period, it undergoes a process called beta decay, whereby it decays into a proton, an electron, and an antineutrino.
Understanding neutrons has been central to the development of nuclear power and nuclear weapons. Unstable isotopes give off these particles when they decay, which can start nuclear chain reactions. The large rods inserted into nuclear reactors exist to limit the number of bouncing neutrons.