Even though there are 103 known elements there are thousands of isotopes. In nature atoms are mostly stable with a small portion that are unstable. An unstable atom has too much energy or is excited and wants to become a stable atom. Radioactivity is a collection of unstable atoms that emit ionizing radiation to become stable atoms. Or, the radiation may be so strong that it alters another atom s nucleus.
Fission occurs when a neutron is absorbed into the nucleus of an atom and causes it to split.
Half-Life One aspect of radioactivity is that atoms produce radiation to become stable over time. In other word, atoms of the same radioactive isotope do not emit radiation instantly. Half-life is the time in which half the atoms of a particular radioactive isotope decay into another atomic form. Radioactive half-lives may range from fractions of seconds for some radioactive isotopes to thousands of years for others. Even half-lives of radioactive isotopes of the same elements differ.