Isotopes used for radiological dating
U-235 decays to Pb-207 with a half-life of 704 million years.Due to its long half-life, U-235 is the best isotope for radioactive dating, particularly of older fossils and rocks. The half-life of C-14, however, is only 5,730 years.Corina Fiore is a writer and photographer living in suburban Philadelphia. She worked as a staff writer for science texts and has been published in Praxis review materials for beginning teachers.
A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide.
While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life, usually given in units of years when discussing dating techniques.