A free neutron is a neutron that exists outside of a nucleus. It is unstable and must undergo decay in order to reach a state of stability. A free neutron has a half-life of about ten minutes. The decay products of the free neutron are an electron, a proton, and an antineutrino. A free neutron is considered a subatomic particle.
A free neutron has an atomic number of zero and a mass number of one. Even though it does not have a proton, a free neutron is often listed as an isotope in data tables.
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