See table. - actinium: a radioactive isotope of thorium produced in actinium decay, namely 227Th (half life = 19 d). [Soddy & ] - elements: For occurrences before 1913 ( i.e., before the concept of isotopy), radioisotopes is often a more appropriate modern term. [Soddy , , ] - lead: a radioactive isotope of lead produced in uranium decay, namely 210Pb (half life = 21 y). Also radium D. - tellurium: An isotope of polonium produced in uranium decay, namely 210Po (half life = 140 d). [Markwald] Also called radium F. - thorium: an isotope of thorium produced in thorium decay, namely 228Th (half-life = 1.9 y). [Hahn & Ramsay, Soddy & ].