~8there may be 26 to 34 neutrons, of iron. thereby forming 9 isotopes Certain ratios of neutrons to protons create an unstable condition in the nucleus. When in this condition the nucleus attempts to reach the stable state by the release of energy. Such an isotope is known as a radio- isotope. The energy is released from the nucleus as an alpha particle, a beta particle, a gamma photon or a neutron and each energy release is known as a disintegration. one or sometimes more disintegrations, After the nucleus reaches the stable state and is no longer radioactive. The rate at which a group of radioactive nuclei disintegrates varies from one radioisotope to another but occurs at an accurately predicted rate for any specific radioisotope. The time re- quired for one-half of the nuclei in a group of atoms to disintegrate is known as the half life of the isotope. The half lives of radioisotopes range from a fraction or a second to trillions of years. Almost all of the radioisotopes created by the fission process are shortlived. For the mixture of all fission products, radioac- tivity decreases tenfold for each sevenfold increase in time following the detonation in which the isotopes were