Radioactivity Elements may have isotopes that exhibit a spontaneous emission of radiation and are said to be radioactive.
Beta rays consists of negatively and positively charged electrons.
They move at the speed of light and penetrate more deeply than alpha particles. Gamma rays are electromagnetic radiation or high energy photons that have no charge. They are the most penetrating of the three types, making them the most useful in medicine but also the most dangerous. Radioactive elements decay at different rates. Rates are measured as half-lives that is, the time it takes for one half of any given quantity of a radioactive element to disintegrate.