Atomic vapor

Atomic vapor laser isotope separation (AVLIS)... 

The predorninant method for the analysis of alurninum-base alloys is spark source emission spectroscopy. SoHd metal samples are sparked direcdy, simultaneously eroding the metal surface, vaporizing the metal, and exciting the atomic vapor to emit light ia proportion to the amount of material present. Standard spark emission analytical techniques are described in ASTM ElOl, E607, E1251 and E716 (36). A wide variety of weU-characterized soHd reference materials are available from major aluminum producers for instmment caUbration. 

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). 

FIGURE 1.11 When white light shines through an atomic vapor, radiation is absorbed at frequencies that correspond to excitation energies of the atoms. Here is a small section of the spectrum of the Sun. in which atoms in its outer layers absorb the radiation from the incandescence below. Many of the lines have been ascribed to hydrogen, showing that hydrogen is present in the cooler outer layers of the Sun. 

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-... 

Heating of Electrically Heated Nonflame Atomic Vapor Cells". Anal. Chem. (1975), 38-45. 

Thinking Critically The K-Ar data for this experiment were obtained using a mass spectrometer. In this process, a small sample is heated with a laser until its constituent atoms vaporize and become ionized. A voltage is then applied that accelerates the charged ions towards a detector. The lightest ions reach the detector first, and the numbers of ions of each mass are identified and counted. There are a number of practical concerns that researchers must address in order to be confident that the measurements truly yield an accurate age for the object. List and explain a few possible concerns. 

In marked contrast to the majority of activated metals prepared by the reduction process, cobalt showed limited reactivity toward oxidative addition with carbon halogen bonds. Iodopentafluorobenzene reacted with 2 to give the solvated oxidative addition products CoL and Co(C,F5)2 or Co(C F )L The compound CoiOJF 2PEt, was isolated in 54% yield by addition of triethylphosphine to tne solvated materials. This compound was also prepared in comparable yield from 1 by a similar procedure. This compound had previously been prepared by the reaction of cobalt atom vapor with C6F5I(81). 

The experimental apparatus used consisted of a stationary metal atom-vapor reactor which has been detailed in the literature earlier. (39) Metal was evaporated (-0.1 to 0.5 g) and codeposited at -196°C with excess organic solvent vapor (- MO-150 mL). The frozen matrix was allowed to warm under controlled conditions, and upon melting stirring was commenced. After warming to room temperature stable colloidal solutions were obtained and syphoned out under N. ... 

Walsh, in 1955, described the theoretical principles of atomic absorption spectroscopy10). Briefly, it can be defined as the absorption of radiant energy by ground state atomic vapor. There are several ways of obtaining atomic vapor, but aspiration of a solution into a flame is the most conventient and most widely used method. 

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... 

AFS quantifies the discrete radiation emitted by excited state atoms that have been excited by radiation from a spectral source. There are a number of mechanisms that are responsible for the atomic fluorescence signal resonance fluorescence, step-wise fluorescence, direct-line fluorescence, and sensitized fluorescence. Generally, the lowest resonance transition (l->0) is used for AFS. If a line source is used for excitation and if the atomic vapor is dilute, then the radiant power of the atomic... 

Describe exactly how the atomic vapor is produced in a graphite furnace. 

The analyte solution is placed (injected) into the furnace with a micropipet or auto-sampler. Following this, a temperature program is initiated in which the furnace heats rapidly to 1) evaporate the solvent, 2) char the solid residue, and finally 3) atomize the analyte, creating the atomic vapor. 

Mercury is the only metal that is a liquid at room temperature and is therefore the only metal that has a significant vapor pressure such that an atomic vapor can be created without heat. 

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. 

Sorokin and Lankard illuminated cesium and rubidium vapors with light pulses from a dye laser pumped by a ruby giant-pulse laser, and obtained two-step excitation of Csj and Rbj molecules (which are always present in about 1 % concentration at atomic vapor pressures of 10" - 1 torr) jhe upper excited state is a repulsive one and dissociates into one excited atom and one ground-state atom. The resulting population inversion in the Ip level of Cs and the 6p level of Rb enables laser imission at 3.095 jum in helium-buffered cesium vapor and at 2.254 pm and 2.293 /zm in rubidium vapor. Measurements of line shape and frequency shift of the atomic... 

To produce this type of atomic emission in a pyrotechnic system, one must produce sufficient heat to generate atomic vapor in the flame, and then excite the atoms from the ground to various possible excited electronic states. Emission intensity will increase as the flame temperature increases, as more and more atoms are vaporized and excited. Return of the atoms to their ground state produces the light emission. A pattern of wavelengths, known as an atomic spectrum, is produced by each element. This pattern - a series of lines - corresponds to the various electronic... 

Fig. 5 Diagram showing the major aspects of metal atom vapor deposition on a SAM...

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