Bentor, Yinon (2006). "Periodic Table: Date of Discovery" . http://www.chemicalelements.com/show/dateofdiscovery.html . Retrieved on 2008-02-28 .   ^ Partington, J. R. (May 1957). "Discovery of Radon". Nature 179 (4566): 912. doi : 10.1038/179912a0 .   ^ "Timeline of Element Discovery" . The New York Times Company . 2008 . http://chemistry.about.com/library/weekly/aa030303a.htm . Retrieved