For 10 points, name this radioactive element with symbol U.
The only known example of a phi bond has been observed in a diatomic form of this element. A CO2 laser is used in the Silex process to separate isotopes of this element, whose acetate is commonly used as a negative stain in electron microscopy. Lead-206 is the (*) final product in a nuclear decay chain that begins with this element, processing of whose ores involves an intermediate known as yellowcake. Gaseous centrifugation of this element's hexafluoride can separate its 235 and 238 isotopes. For 10 points, name this radioactive element with symbol U.
The only known example of a phi bond has been observed in a diatomic form of this element.
Uranium [or U before mention]