Science glossary film: Radioactivity

The emission of particles as a result of the spontaneous decay of atomic nuclei. Many isotopes of elements have unstable nuclei which will eventually decay into a different isotope plus one of three kinds of decay products. Alpha particles are helium nuclei, and tend to have low energy. Beta particles are electrons, often with quite high velocity and more penetrating power than alpha particles. Gamma rays, high energy photons, tend to have the highest energy.

Many isotopes of elements have unstable nuclei which will eventually decay into a different isotope plus one of three kinds of decay products. Alpha particles are helium nuclei, and tend to have low energy. Beta particles are electrons, often with quite high velocity and more penetrating power than alpha particles. Gamma rays, high energy photons, tend to have the highest energy.