Neutron = 2 down quarks + 1 up quark.
Proton = 2 up quarks + 1 down quark.
When a Neutron changes into a Proton, basically a down quark is changing into an up quark.
The result is that the new Neucleon (Proton) takes on a positive charge; an anti-Neutrino & a beta-Electron are emitted. This is beta-decay.
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