Free neutron decay

Free neutron decay is the radioactive transformation of an unbound neutron, usually into a proton, an electron, and an electron antineutrino through the weak interaction.

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Beta decay: A radioactive process in which a nucleus or free neutron changes through the weak interaction, emitting an electron or positron and a neutrino. Free neutron decay is beta-minus decay without a nucleus.
Neutron: A neutral baryon composed primarily of one up quark and two down quarks. The free neutron is the unstable initial particle in this decay.
James Chadwick: The physicist who discovered the neutron in 1932. The discovery made the free neutron available as a distinct object of study.
Neutron lifetime puzzle: The persistent discrepancy between neutron lifetimes measured by beam and bottle methods. Different decay and disappearance measurements have produced values that do not fully agree.
Bound neutron: A neutron incorporated into an atomic nucleus and subject to nuclear binding and surrounding nucleons. Some bound neutrons are stable because nuclear energy differences forbid beta decay.
Weak interaction: A fundamental interaction responsible for processes that change quark flavor and produce beta decay. It converts a down quark inside the neutron into an up quark.
Proton: A positively charged baryon composed primarily of two up quarks and one down quark. The proton is the baryon left after a neutron's down quark changes flavor.
Enrico Fermi: The physicist who formulated a successful theory of beta decay in 1933–1934. His theory provided an early framework for explaining neutron decay.
Beam neutron lifetime measurement: A method that infers neutron lifetime from the number of beta-decay products produced by a neutron beam. Beam experiments count protons created by free neutron decay.
Proton decay: A hypothetical transformation of a proton into lighter particles that would violate baryon number. Unlike neutron beta decay, proton decay has not been observed.