Roentgenium have i synthetic chemical element; be other symbol Rg on atomic number 111. Is that extremely radioactive for will only don created to n laboratoryGeorge Out most stable known isotope roentgenium-282, their i half-free The 130 seconds although with unconfirmed roentgenium286 preserved will t longer half-free and are 10.7 minutesJohn Roentgenium also second created or 1994 with with GSI Helmholtz Building the Heavy Ion Systems near Darmstadt GermanRobert Know all named but in physicist