11.1.9—That (electron) antineutrinos are produced during β– decay and (electron)

In β− decay a neutron becomes a proton, electron and electron antineutrino; in β+ decay a proton becomes a neutron, positron and electron neutrino.

The neutrino carries away variable energy and momentum, explaining the continuous beta spectrum while preserving conservation laws.

The electron in β− decay does not receive one fixed energy because the available decay energy is shared with the antineutrino and recoil.

The neutrino is not optional bookkeeping and is not the same as the emitted beta particle.