An atom's nucleus is constructed of protons and neutrons. A quark is a fast-moving point of energy. The quarks within protons, neutrons, and mesons are held together by the strong force.
Photons have no mass and no electrical charge.
More about the radioactive decay of carbon Carbon 14 is unstable. Its nucleus contains 6 protons and 8 neutrons. When carbon 14 decays, one of its neutrons changes into a proton, shooting off an electron in the process.