neutron

One of the three main subatomic particles, the others being the proton and the electron. Neutrons have about the same mass as protons but no electric charge, and occur in the nuclei of all atoms except hydrogen. They contribute to the mass of atoms but hardly affect their chemistry.

The isotopes of a single element differ only in the number of neutrons in their nuclei but have almost identical chemical properties. Neutrons and protons have masses approximately 2,000 times those of electrons.

The neutron is a composite particle, being made up of three quarks, and therefore belongs to the baryon group of the hadrons. Outside a nucleus, a free neutron is unstable, decaying with a half-life of 11.6 minutes into a proton, an electron, and an antineutrino. The process by which a neutron changes into a proton is called beta decay.

The neutron was discovered by the British chemist James Chadwick in 1932.