How does beta decay occur?
Beta decay occurs when a neutron emits an electron.
This decay produces a proton, an electron, and an electron antineutrino.
The electron (beta particle) is ejected from the nucleus.
An example is the beta decay of carbon-14:
#""_6^14"C" → _7^14"N" + _0^0bar(ν) + _(-1)^0"e" #
The result: the atomic number increases by one and the mass remains unchanged.