Neutrons are subatomic particles located within the nucleus of an atom. However, the hydrogen isotope – called protium – is the only atom not housing a neutron in its nucleus. A neutron carries no electrical charge, or is neutral; therefore, the name. An atom may have different variants – called isotopes – and the number of neutrons changes across diverse versions. In other words, the varying number of neutrons gives isotopes their identities. The total number of neutrons in an atom can be determined by subtracting the atom’s atomic number from its mass number (no. of neutrons = mass number – atomic number).

Formation and Discovery

Image credit: Flickr
Image credit: Flickr

Similar to protons, neutrons first came into being post the Big Bang, during the initial period of the universe. However, its discovery happened in 1932. James Chadwick discovered the particle when he was employed at England’s Cambridge University. In 1930, Dmitri Ivanenko and Viktor Ambartsumian, who contradicted the mainstream scientific notion back then, stated an atom’s nucleus doesn’t comprise protons and electrons but there are some neutral particles present in atoms’ nuclei instead of electrons.


Neutrons are not the smallest subatomic particles; they can be further divided into quarks, just like protons. A neutron usually has three quarks – two down and one up, and which are attached to each other courtesy a strong nuclear force. In fact, this nuclear force contributes to the total weight of a neutron, rather than the quarks themselves. The two down and one up quark composition makes a neutron neutral or not carrying any electrical charge.

Size and Mass

A neutron is larger than a proton or electron. It has a mass of 1.67493×10−27 kg, which makes it slightly heavier than proton, but having much more mass than an electron. In fact, the weight of an atom is mostly based on its neutron mass. Though some neutrons may hover outside an atom’s nucleus, the journey doesn’t last too long. On an average, a wandering neutron gets back into the nucleus within 15 minutes. Unlike electrons, a neutron does not hop across different atoms. When moving, with its density combined, the extremely powerful neutron can cause deadly radiation, which can kill people and animals that come in contact.

Neutron Star

Neutrons play an important role in the formation of neutron stars (one of the densest stars in the universe) as well. As a neutron doesn’t carry any electrical charge, neutrons in the neutron star do not push each other away, resulting in a closely packed, extremely dense star.