A radionuclide decay pair is a link in a radionuclide decay chain. The pair specifies a parent radionuclide and a daughter radionuclide as well as a branching ratio. The branching ratio is necessary because a parent may have several daughter radionuclides. The branching ratio is a number between 0 and 1 which determines how much of ratio of the parent radionuclide is transformed into the daughter due to radioactive decay.