Plutonium hexafluoride
Plutonium hexafluoride is the highest fluoride of plutonium, and is of interest for laser enrichment of plutonium, in particular for the production of pure plutonium-239 from irradiated uranium. This pure plutonium is needed to avoid premature ignition of low-mass nuclear weapon designs by neutrons produced by spontaneous fission of plutonium-240.
It is a red-brown volatile crystalline solid; the heat of sublimation is 12.1 kcal/mol and the heat of vaporization 7.4 kcal/mol. It is relatively hard to handle, being very corrosive and prone to auto-radiolysis.
It is prepared by fluorination of plutonium tetrafluoride by powerful fluorinating agents such as elemental fluorine.
It can also be obtained by fluorination of plutonium fluoride or plutonium oxide.
In 1984, the synthesis of plutonium hexafluoride was achieved at unprecedented low temperatures through the use of dioxygen difluoride. Previous techniques needed temperatures so high that the plutonium hexafluoride produced would decompose rapidly. Hydrogen fluoride is not sufficient; even though it is a powerful fluorinating agent.
Under laser irradiation at a wavelength of less than 520 nm, it decomposes to plutonium pentafluoride and fluorine; after more irradiation it decomposes further to plutonium tetrafluoride.
