Laser isotope separation enrichment

Uranium enrichment using LIS has been exhaustively studied and the conceptual outlines of two different methods can be found in the open literature. These methods are multi-photon dissociation of UF6 (SILEX, or Separation of Isotopes by Laser Excitation) and laser excitation of monatomic uranium vapor (Atomic Vapor Laser Isotope Separation, or AVLIS). Following an enormous investment, AVLIS was used by the United States DOE in the 1980s and early 1990s, but due to the present oversupply of separated uranium, the plant has been shut down. 

Laser isotope separation is one area where multistep excitation and ionization has great commercial potential. The research and development efforts in atomic vapor laser enrichment of 235y are a major factor contributing to the current research activities in laser excitation and ionization processes. The first paper on selective multistep photoionization of atoms was published in 1971. (.62) Since then numerous review articles( 15, 16 >L7,63 >54, (i5) ave been written on laser isotope separation and, in each review, there is a section on atomic vapor photoionization processes. The subjects of economics and critical parameters have been well covered in previous reviews and will not be discussed in detail here. We... 

Davis, J. I. and Davis, R. W., "Some Aspects of the Laser Isotope Separation Program at Lawrence Livermore Laboratory," in "Developments in Uranium Enrichment, AIChE Symposium Series, V.73, No. 169" Benedict, M., Ed.,... 

There also have been gaseous diffusion plants built in other coimtries, some still in operation, but the gaseous diffusion process is gradually being replaced by the gas centrifuge process. Another method of enrichment, laser isotopic separation, has generated interest in recent years. 

Laser isotope separation techniques Laser-based isotope enrichment techniques deploy selective photo-excitation principles to excite a particular isotope as an atom or molecule (Rao 2003). Each device consists of three parts the laser system, the optical system, and the separation module. These methods include the atomic vapor laser isotope separation (AVLIS) that uses a fine-tuned laser beam to selectively ionize vapors of atomic the molecular laser isotope separation (MLIS), and separation of isotopes by laser excitation (SD EX) that use a laser to selectively dissociate or excite molecules. 

Finally, it should be noted that all the methods that rely on mass differaice, mass ratio, or kinetics to separate U-235 from U-238 will also lead to enrichment of U-234 (even to greater relative extent than U-235). Elevated levels of U-234 may complicate the utilization of the enrichment product. Similarly, use of reprocessed uranium that contains U-236 (and perhaps some U-232) may also affect the product quality. On the other hand, laser isotope separation methods will selectively enrich U-235 with only very slight changes in the U-234 and U-236 content. 

A similar technique has been used by Zare et al. (261, 643) for chlorine isotope separation. Isotopic mixtures of iodine monochloride (l35CI, lJ7CI) are irradiated in the presence of dibromoethylene by a laser line at 6053 A which selectively excites I37C1. An adjacent vibrational band of I35C1 is about 15 A away. The excited I37C1 reacts with added 1,2-dibromoethylene lo form the product f/wi.v-ClHC=CHCI enriched in 37C1. At this wavelength no photodissociation of ICI takes place. See p. 191. 

A method for Li isotope separation has been described by Arisawa et which makes use of the increased reactivity of a laser-excited beam of Li atoms with a beam of CHClFj. Isotope enrichment in the product LiF was observed, but no selectivity in LiCl was obtained. Balia and Heicklen have studied the photo-oxidation of CHjSH and CH3S2CH3 in the presence of NO. Chemiluminescent emission in Mg-N20-C0 flames has been studied by Michels and Meinzer. Inoue ef measured electron-impact lumines-... 

Laser separation of isotopes for enrichment of is in development and is not yet ripe for industrial exploitation... 

Elements.—The use of a tunable narrow-frequency laser to produce an isotopically selected chemical reaction has been described by Leone and Moore 1 this approach should permit efficient isotope separations to be performed. In the example reported, natural Br2 (79Br/81Br = 1) is photo-predissociated by selective excitation into the 3n0+ state. Bromine atoms, enriched in one isotope, react with HI before scrambling occurs, to produce 80—85% enriched H81Br. 

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