Radioactive decay is the emision of energy in the form of ionizing radiation. The ionizing radiation that is emitted can unclude alpha particles, beta particles and gamma rays. Alpha particles are positively charged and made up of two protons and two neutrons from the atoms nucleus. Alpha particles also come from the decay of the heaviest radioactive elemnts, Uranium, Radium and Polonium. Beta particles are high energy, high speed electrons or positrons that are ejected from the nucleus by radioactive decay called beta-decay. Gamma rays have the smallest wavelenghts and most energy of any wave in the "electromagnetic spectrum". "They are produced by the hottest and most energetic objects in the universe", such as neutrons and starts. On Earth gamma rays are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.