II.

Beta Decay

Atoms emit beta particles through a process known as beta decay. Beta decay occurs when an atom has either too many protons (positively charged particles) or too many neutrons (electrically neutral particles) in its nucleus. When this occurs, a force called the weak nuclear force causes the unstable atom to change an extra proton into a neutron, or neutron into a proton, and become stable.

Beta decay can produce positive or negative particles. In positive beta decay, a proton in an unstable nucleus turns into a neutron by emitting a positively charged beta particle (positron) and an electron neutrino. Neutrinos are high-energy elementary particles with little or no mass. In negative beta decay, a neutron in an unstable nucleus turns into a proton by emitting a negatively charged beta particle (negatron, or electron) and an electron antineutrino, the antimatter counterpart of the electron neutrino. Negative beta decay, which occurs in atoms having too many neutrons, is far more common than positive beta decay.