High Quality Content by WIKIPEDIA articles! Ununtrium is the temporary name of a chemical element with the temporary symbol Uut and atomic number 113. It is an extremely radioactive synthetic element (an element that can be created in a laboratory but is not found in nature); the most stable known isotope, ununtrium-286, has a half-life of 20 seconds. Ununtrium was first created in 2003 by the Joint Institute for Nuclear Research in Dubna, Russia.