Osmium [SEP] time of discovery
isotopes, but it has been observed only for , presumably due to very long half-lives. It is predicted that and can undergo double beta decay but this radioactivity has not been observed yet.
History.
Osmium was discovered in 1803 by Smithson Tennant and William Hyde Wollaston in London, England. The discovery of osmium is intertwined with that of platinum and the other metals of the platinum group. Platinum reached Europe as "platina" ("small silver"), first encountered in the late 17th century in
Cecilius Calvert, 2nd Baron Baltimore).
His own name derives from his grandmother Rebecca Smithson, widow of Joshua Hitchling. He attended Beverley Grammar School and there is a plaque over one of the entrances to the present school commemorating his discovery of the two elements, osmium and iridium. 
He began to study medicine at Edinburgh in 1781, but after a few months moved to Cambridge, where he devoted himself to botany and chemistry. 
He graduated M.D. at Cambridge in 1796, and about the same time purchased an