= Beta decay
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<Beta decay> is a <weak interaction> process changing the proton-to-neutron composition of an <atomic nucleus> while preserving its <mass number>. In <beta-minus decay>, a <neutron> converts to a <proton> with an emitted <electron> and <electron antineutrino>; in <beta-plus decay>, a <proton> converts to a <neutron> with an emitted <Positron> and <electron neutrino>, when the complete <energy> balance permits it.<DOE Explains Beta Decay by United States Department of Energy>[Beta-minus and beta-plus transformations and emitted particles]{ref}
The emitted <beta particle> is created in the transition rather than being an ordinary orbital <electron> expelled from the atom. Its <kinetic energy> varies because the available <Q value> is shared with the <neutrino> and daughter recoil. A magnetic <electron spectrometer> can separate different emitted momenta; a detector then records a continuous distribution rather than one universal <electron> <energy>.
<Conservation of electric charge>, <energy> and <angular momentum> constrains the final state. Nuclear binding matters: a free <proton> cannot undergo ordinary beta-plus decay, although an energetically allowed proton-to-neutron transition can occur within an appropriate <atomic nucleus>.
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