ABCs of Radioactivity

Atoms are made of protons, neutrons, and electrons. The number of protons determines what element it is. Atoms have the same number of protons. Atoms with different numbers of neutrons are called isotopes. Radioactive elements, called radioisotopes or radionuclides, are unstable. They spontaneously “decay,” releasing particles and/or energy. Radioisotopes can emit three kinds of ionizing radiation from their nuclei.