Atomic vapor laser isotope separation

Atomic vapor laser isotope separation (AVLIS)... 

Atomic- Vapor Laser Isotope-Separation. Although the technology has been around since the 1970s, laser isotope separation has only recently matured to the point of industrialization. In particular, laser isotope separation for the production of fuel and moderators for nuclear power generation is on the threshold of pilot-plant demonstrations in several countries. In the atomic vapor laser isotope-separation (AVLIS) process, vibrationaHy cooled U metal atoms are selectively ionized by means of a high power (1—2 kW) tunable copper vapor or dye laser operated at high (kHz) repetition rates (51,59,60). 

LLNL AVLIS Laser. The first WFS measurements using a Na LGS were performed at LLNL (Max et al., 1994 Avicola et al., 1994). These experiments utilized an 1100 W dye laser, developed for atomic vapor laser isotope separation (AVLIS). The wavefront was better than 0.03 wave rms. The dye laser was pumped by 1500 W copper vapor lasers. They are not well suited as a pump for LGSs because of their 26 kHz pulse rate and 32 ns pulse length. The peak intensity at the Na layer, with an atmospheric transmission of 0.6 and a spot diameter of 2.0 m, is 25 W/cm, 4x the saturation. The laser linewidth and shape were tailored to match the D2 line. The power was varied from 7 to 1100 W on Na layer to study saturation. The spot size was measured to be 7 arcsec FWHM at 1100 W. It reduced to 4.6 arcsec after accounting for satura-... 

Atomic systems, in lasers, 74 666-669 Atomic Vapor Laser Isotope Separation (AVLIS) process, 25 416 Atomic weight, 75 748 Atomization, 77 774-775 in spray coating, 7 69-74 technology of, 23 175 Atomizer operation, concerns related to, 23 195... 

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. 

These results indicate that long lived autoionization states with excitation cross-sections comparable to those for excitation of bound high-lying states exist in heavy atoms with complex spectra. Transitions to these autoionization states can radically increase the efficiency of photoionization of atoms, a factor very important in atomic vapor laser isotope separation. 

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... 

The Energy Research and Development Agency (ERDA), the forerunner to the DOE, through the late 1970s to 1981 supported the study of three new experimental processes for uranium enrichment. Two were based upon laser separation, and one on plasma separation. Jersey Nuclear-Avco Isotopes Incorporated (subsidiary of Exxon) and the LLNL worked on atomic uranium vapor. LLNL referred to it as AVUS. The LANL and a group at Exxon Research Laboratories (not connected with Jersey-Avco) worked on molecular UFg. TRW Incorporated pursued research work on a plasma separation process. Union Carbide Nuclear Division (UCC-ND) supported each in their efforts. In 1981, the AVLIS process at LLNL was selected as the process to be developed further and the other processes were subsequently phased out. 

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. 

A fundamentally different technique is laser isotope separation (LIS) or atomic vapor laser isotope separation (AVLIS). A laser beam is tuned to a wavelength that excites only one isotope of the material and ionizes those atoms preferentially. After the atom is ionized, it can be removed from the sample by applying an electric field. 

J.A. Paisner Atomic vapor laser isotope separation, in [Ref.l0.2,p.253]... 

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... 

Paisner, J. A. (1988). Atomic vapor laser isotope separation. Applied Physics B, 46, 253-260. 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

The spectrum of uranium metal vapor is complex with over 3x10 lines in the visible region. Still, many of these are very sharp and show sufficient isotope separation to permit selective excitation. The basic idea of AVLIS is to irradiate uranium metal vapor at a concentration around 10 atoms cm (higher concentrations destroy the separation due to collisional broadening). Uranium is a refractory metal, and vaporization is difficult. Electron bombardment under high vacuum yields an atomic beam that passes through the laser radiation field where U is selectively excited. 

Laser ablation ICP-MS is used for direct analysis of the elemental and isotopic composition of solid samples. Photons from the laser system are focused into a high peak power energy pulse that interacts with the sample. As a result of this interaction, small particles, atoms and ions are removed from the topmost atomic layers forming a laser-induced aerosol above the sample surface. The aerosol is then transported by an inert gas stream to the ICP-MS. After vaporization, atomization and ionization of the particles in the ICP, quadrupole, magnetic sector field or time-of-flight mass filters are used for mass separation. Because of the properties of the laser systems available today, bulk analysis with low spatial resolution (>100 p-m) as well as local analysis with high spatial resolution (<20 p.m) are possible. Since only small sample amounts are ablated per laser shot, a high sensitivity analytical detection system is a prerequisite for trace and ultratrace analysis. 

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