Lasers uranium isotopes separated using

Uranium isotope separation using a molecular approach is based on selective multi-photon dissocation of UPg. The relevant vibrational isotope shift is 0.6 cm in the primary vibrational transition at 628 cm (16 pm). In the development of the technique, experiments on SFg have been very important. The conditions are inucli more favourable for SFe than for UFg- The isotope shift is 17cm between and in the IR active vibrational mode that involves asymmetric stretdiing of two S-F bonds. The spectrum has a typical P, Q and R branch structure and the whole region of absorption for the rotational level popnlation distribution that is obtained at room temperature is 15 cm . Thus, the isotopic molecules are spectroscopically totally separated. Furthermore, the vibrational transition in SFg well matches the emission of a free-ruiniing pulsed CO2 laser. 

Experiments on the sky. Two experiments have been carried out at the sky, using two laser installations built for the American and French programmes for Uranium isotope separation, respectively AVLIS at the Lawrence Livermore Nat l Lab (California) in 1996 and SILVA at CEA/Pierrelatte (Southern France) in 1999. The average power was high pa 2 x 175 W, with a pulse repetition rate of 12.9 and 4.3 kHz, a pulse width of 40 ns and a spectral width of 1 and 3 GHz. Polarization was linear. The return flux was < 5 10 photons/m /s (Foy et al., 2000). Thus incoherent two-photon resonant absorption works, with a behavior consistent with models. But we do need lower powers at observatories ... 

Bradley reported that homoleptic uranium hexakis(alkoxide) complexes coordinated by secondary and tertiary alkoxides (U(OR)6 R = Pr , Bu , Bu ) were produced from thermal disproportionation of U0(0R)4 vide suprd) U(OMe)6 was initially prepared from oxidation of U (OMe)5 in the presence of benzoyl peroxide. Interest in a more convenient synthetic route to U(OMe)6 was stimulated by its potential use in uranium isotope separation, which can be achieved with a CO2 laser. Facile syntheses of U(OMe)6 were reported by different groups (see Equations (48) to (51)) ... 

The impetus for laser isotope separation studies is given by UFg. As mentioned in the previous section the presently known infrared lasers emit in the vicinity of 2.7 [xm (HF), 5 [xm (CO), and 10 [xm (CO2). Thus to employ the laser approach in uranium isotope separation requires the development of a new high-power, low-frequency, laser source since the V3 excitation mode used in the SFg experiments appears at 16.0 [xm in... 

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. 

Several years ago, there was a lot of excitement concerning a method of using lasers to separate isotopes. A laser was adjusted to a very narrow wavelength that would excite only one of the uranium isotopes. With only one isotope excited it was projected that a near single stage separation method was possible. Little has been said about this method in recent years. The lack of the need for uranium separation has placed a damper on the developments. 

Accurate results of this type are needed for determining laser utilization in laser isotope separation of uranium. The application of this technique to obtain results for other elements would be useful in astronomy and plasma physics. 

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. 

When the first tunable dye lasers made their appearance late in the 1960s (see Stuke 1992), suggestions were put forward as to the use of resonance stepwise ionization for separating isotopes on the basis of isotope shifts in atomic spectra (Letokhov 1969). Following the first successful experiments on the selective ionization of Rb atoms and their isotopes (Ambartzumian et al. 1971), programs were initiated in a number of countries on laser separation of uranium isotopes ( U/ U) by a method that came to be known as the atomic-vapor-laser-isotope-separation (AVLIS) technique (Paisner... 

SIMS techniques have occupied somewhat of a narrower niche in uranium-series analysis, but have significantly improved Th isotope analysis relative to TIMS for chemically separated samples. The major improvement relative to TIMS is an improvement by about an order of magnitude in efficiency or sample size requirements for silicates. For uranium and/or thorium rich minerals such as carbonates and zircons, both SIMS and laser-ablation MC-ICPMS have been used for the direct in situ analysis of U and Th isotopes (Reid et al. 1997 Stirling et al. 2000) on very small (pg to ng levels of total U and Th) samples, at 10-100 pm scale resolution. 

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