During a negative beta decay,
an atomic electron is ejected
an electron which is already present within the nucleus is ejected
a neutron in the nucleus decays emitting an electron
a proton in the nucleus decays emitting an electron
In beta minus decay, a neutron is converted to a proton and the process creates an electron and an electron antineutrino.
During a negative beta decay, a neutron in the nucleus decays emitting an electron.