11. Elements heavier than lead, and the elements technetium and promethium , exist only as radionuclides. 12. Now only promethium and fermium don't have images; any help is obviously appreciated! 13. Promethium belongs to the cerium group of lanthanides and is chemically very similar to the neighboring elements.14. Marinsky and Glendenin produced promethium both by extraction from fission products and by bombarding neodymium with neutrons. 15. Following Shocker leads him to Alistair Smythe and the Promethium X, which Spider-Man steals. 16. Finally, promethium can be formed in nature as a product of spontaneous fission of uranium-238. 17. It is constructed of promethium and uses highly advanced Martian, Thanagarian, Kryptonian, and Earth technologies. 18. It was the first to create the element promethium , used in nuclear-powered batteries in guided missiles. 19. Quite a few years later, this element 61 was created artificially in nuclear reactors and was named promethium . 20. Many properties of promethium rely on its position among lanthanides and are intermediate between those of neodymium and samarium.
