Mononeutron: An isolated neutron undergoes beta decay with a mean lifetime of approximately 15 minutes (half-life of approximately 10 minutes), becoming a proton (the nucleus of hydrogen), an electron and an antineutrino. Its existence has been proven to be relevant for nuclear structure of exotic nuclei.

1 amu
It weighs 1 amu. neutron: A subatomic particle forming part of the nucleus of an atom. It has no charge. It is equal in mass to a proton or it weighs 1 amu.

a proton has a mass of approximately 1 dalton. a neutron has a mass of approx 1 dalton. an electron has a mass of 1/1840th daltons.

hydrogen
Deuterium is a hydrogen isotope consisting of one proton, one neutron and one electron.

Neutrons

Electrons have a negative charge but are extremely small and have a mass only 1/1850 that of a proton or neutron. They are so small that for practical purposes they do not contribute to the mass of the atom. The nitrogen nucleus contains 7 protons (orange) and 7 neutrons (green).

Protons and neutrons have almost the same mass and are both located in the nucleus of the atom. Protons are charged particles. Neutrons are neutral particles.

There is only one stable atom that does not have neutrons. It is an isotope of the element hydrogen called protium. Protium, which contains a single proton and a single electron, is the simplest atom. All other stable atoms contain some number of neutrons.

Assuming that the neutron mass was close to that of the proton, Chadwick bombarded hydrogen atoms with his produced neutrons to learn the speed of the protons after the collisions. Then setting the neutron speed equal to those proton speeds, he used the above energy expression to get a neutron mass of 938 +/- 1.8 MeV.

Now, the element having no neutron in the nucleus of its atom is hydrogen. Its atomic number is one and it consists of a single proton and exists in diatomic form.

A typical neutron star has a mass between 1.35 to about 2.1 solar masses, with a corresponding radius between 20 and 10 km (they shrink as their mass increases) — 30,000 to 70,000 times smaller than the Sun.

A neutron. A proton has the same mass as a neutron. An electron has the same mass as a beta particle. An alpha particle has a mass of 4: two protons plus two neutrons. See Table O for further information.

The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of − 1, which is equal but opposite to the charge of a proton, which is + 1.

Neutrons are one of the three types of subatomic particles, the other two being protons and electrons. A neutron has slightly more mass than a proton and unlike the electrons and protons has no charge.