the radioactive series that starts with uranium 238 and ends with a stable isotope of lead of mass number 206.
Also u·ra·ni·um-ra·di·um se·ries [yoo-rey-nee-uh m-rey-dee-uh m] /yʊˈreɪ ni əmˈreɪ di əm/.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
physics a radioactive series that starts with uranium-238 and proceeds by radioactive decay to lead-206
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012