Apsidium: Roentgenium
   Basic information and atomic structure.
   http://www.apsidium.com/elements/111.htm

IUPAC: Roentgenium
   A note about confirmation of synthesis of the element 111.
   http://www.iupac.org/news/archives/2004/naming111.html

Wikipedia: Roentgenium
   Basic physical and historical information.
   http://en.wikipedia.org/wiki/Roentgenium