Neutron
An electrically neutral subatomic particle found in the nucleus, with a mass slightly greater than that of a proton.
Formula / equation
m_n = 1.6749 × 10⁻²⁷ kg
Unit
u
In depth
At 1.00866 u, the neutron dilutes the mutual repulsion between protons and supplies additional strong-force binding, which is why heavy nuclei need progressively more neutrons than protons to stay stable. A free neutron is unstable, decaying to a proton, electron and antineutrino with a half-life of about 10 minutes.
Examples in the real world
Deuterium's single neutron doubles hydrogen's mass; slow neutrons trigger the fission of uranium-235 in a reactor.