How can carbon 14 be converted to carbon 12?
C-14 would have to lose 2 neutrons to become C-12, and this doesn't happen (except for very heavy elements).
In stead it emits a beta-particle (=electron) and changes into N-14.
C-14 nucleus = 6 protons + 8 neutrons
One of those neutrons decays into 1 proton+1 electron
N-14 nucleus = 7 protons + 7 neutrons.