Extinct radionuclides

"Extinct radionuclides' are radioactive isotopes with lifetimes of the order of 10⁶ to 10⁸ yr, long enough to survive the interval between nucleosynthesis and the formation of solids in the solar system but short enough so that they are essentially fully decayed and now extinct in the solar system. There is good evidence for the presence of several such radionuclides in the early solar system: ²⁶Al, ⁵³Mn, ¹⁰⁷Pd, ¹²⁹I, ²⁴⁴Pu, ¹⁴⁶Sm. Together with longer-lived radionuclides the abundances of these short-lived species provide significant constraints on nucleosynthetic time scales and the history of solar system materials before they became the solar system. -from Authors