Krypton techniques

Our experimental techniques have been described extensively in earlier papers (2, 13). The gamma ray irradiations were carried out in a 50,000-curie source located at the bottom of a pool. The photoionization experiments were carried out by krypton and argon resonance lamps of high purity. The krypton resonance lamp was provided with a CaF2 window which transmits only the 1236 A. (10 e.v.) line while the radiation from the argon resonance lamp passed through a thin ( 0.3 mm.) LiF window. In the latter case, the resonance lines at 1067 and 1048 A. are transmitted. The intensity of 1048-A. line was about 75% of that of the 1067-A. line. The number of ions produced in both the radiolysis and photoionization experiments was determined by measuring the saturation current across two electrodes. In the radiolysis, the outer wall of a cylindrical stainless steel reaction vessel served as a cathode while a centrally located rod was used as anode. The photoionization apparatus was provided with two parallel plate nickel electrodes which were located at equal distances from the window of the resonance lamp. 

The specific surface area is usually determined by the BET technique discussed in Section 6.2.2. For the most reliable BET measurements the adsorbate gas molecules should be small, approximately spherical, inert (to avoid chemisorption), and easy to handle at the temperature in question. For economy, nitrogen is the most common choice with measurements usually made at 77 °K, the normal boiling point of liquid nitrogen. Krypton is another material that is frequently employed. 

For 2PA or ESA spectral measurements, it is necessary to use tunable laser sources where optical parametric oscillators/amplifiers (OPOs/OPAs) are extensively used for nonlinear optical measurements. An alternative approach, which overcomes the need of expensive and misalignment prone OPO/OPA sources, is the use of an intense femtosecond white-light continuum (WLC) for Z-scan measurements [71,72]. Balu et al. have developed the WLC Z-scan technique by generating a strong WLC in krypton gas, allowing for a rapid characterization of the nonlinear absorption and refraction spectra in the range of 400-800 nm [72]. 

Krypton Sorption. Volumetric adsorption using gases with low saturated vapor pressure has been found to be an effective technique to gain detailed structural information for small quantities of porous materials, especially using krypton (Kr).27 The substitution of nitrogen by Kr reduces significantly the amount of unadsorbed molecules in the dead volume, allows for the characterization of small surface areas, and is thus ideal for mesoporous... 

Jensen and Hvitved-Jacobsen (1991) developed a direct method for the determination of the air-water oxygen transfer coefficient in gravity sewers. This method is based on the use of krypton-85 for the air-water mass transfer and tritium for dispersion followed by a dual counting technique with a liquid scintillation counter (Tsivoglou et al 1965,1968 Tsivoglou andNeal, 1976). A constant ratio between the air-water mass transfer coefficients for dissolved oxygen and krypton-85 makes it possible to determine reaeration by a direct method. Sulfur hexafluoride, SF6, is another example of an inert substance that has been used as a tracer for reaeration measurements in sewers (Huisman et al., 1999). 

The off-gas treatment involves primarily iodine, krypton, and xenon. There are a variety of processes for capturing the iodine and disposing of it. Kr and Xe are captured by either cryogenic techniques or selective absorption, such as absorption in chlorofluoromethane. Most of the off-gas volume is due to Xe ( 800 L/Mg fuel) with the activity being mostly 10.7-y 85Kr ( 11,000 Ci/Mg fuel). 

The structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail. 

The gauge has proved equally accurate for constant pressure and blowdown systems, and can also be adapted to vented systems. A typical curve for normalized krypton concn vs the amt of proplnt remaining in the tank is shown in Fig 1. Also shown is the analytical relationship between tracer concn and proplnt remaining in the tank. Statistical error analyses showed the typical average gauging error thruout the entire range of proplnt expulsion to be less than . 3% with a one sigma deviation of less than . 4%. This illustrates the consistency and reproducibility of this measurement technique... 

Villard measured hydrates of Ar, and proposed that N2 and O2 form hydrates first to use heat of formation data to get the water/gas ratio deForcrand and Thomas sought double (W/H2S or H2Se) hydrates found mixed (other than IpSx) hydrates of numerous halohydrocarbons mixed with C2H2, CO2, (pHg de Forcrand first used Clausius-Clapeyron relation for AH and compositions tabulated 15 hydrate conditions Scheffer and Meyer refined Clausius-Clapeyron technique de Forcrand measured hydrates of krypton and xenon... 

The most common method used for the determination of surface area and pore size distribution is physical gas adsorption (also see 1.4.1). Nitrogen, krypton, and argon are some of the typically used adsorptives. The amount of gas adsorbed is generally determined by a volumetric technique. A gravimetric technique may be used if changes in the mass of the adsorbent itself need to be measured at the same time. The nature of the adsorption process and the shape of the equilibrium adsorption isotherm depend on the nature of the solid and its internal structure. The Brunauer-Emmett-Teller (BET) method is generally used for the analysis of the surface area based on monolayer coverage, and the Kelvin equation is used for calculation of pore size distribution. 

Inverse gas chromatography (IGC) is another technique that can be used to measure the specific surface area of a particulate material, as well as to measure a number of surface thermodynamic properties of powders. Such instrumentation operates on a different principle than traditional nitrogen/krypton adsorption using the BET isotherm. 

Fission gas recoil. Another interesting example of recoil separation in the (n,fisslon) reaction is the separation technique for krypton fission products from a uranium foil target (202). The target, an enriched uranium film (0.3 mg/cm ) deposited on a 1.6-cm diameter platinum plate, was mounted as shown in Fig. 1 at one end of a vacuum-tight recoil chamber... 

Selective gas adsorption. The gas chromatographic technique can be cited as another example of rapid radioactive gas separation. One procedure for the separation and detection of argon, krypton and xenon activities In the coolant or exhaust gases from nuclear facilities utilizes such a method (150). 

---