Helium atmospheric concentration

Oil Contamination of Helium Gas. For more than 20 years, helium gas has been used in a variety of nuclear experiments to collect, carry, and concentrate fission-recoil fragments and other nuclear reaction products. Reaction products, often isotropically distributed, come to rest in helium at atmospheric concentration by coUisional energy exchange. The helium is then allowed to flow through a capillary and then through a pinhole into a much higher vacuum. The helium thus collects, carries, and concentrates products that are much heavier than itself, electrically charged or neutral, onto a detector... 

Combustion tests were carried out by heating the sample to the desired temperature in a helium atmosphere and then exposing it to a pre-selected O2 concentration by diluting air with helium. In some cases the samples were first subjected to high temperatures (800-1050 K) in either a helium or CO2 atmosphere in order to effect changes in the mineral compositions and then cooled to the desired combustion temperature. Combustion activities were evaluated for O2 partial pressures between 5 and 20 kPa and at temperatures between 700 and 825 K. 

Fig. 2 reports the X-ray diffraction patterns of the prepared samples and Table 1 gives the corresponding cobalt content. An evolution of the solid structure with cobalt content is observed. At low cobalt concentration poorly crystallized hydrotalcites are obtained with a precipitation of NaNOs (Fig. 2b and 2c), while good crystallized hydrotalcites are obtained for higher cobalt concentrations (Fig. 2d to 2g). At least an amorphous product is obtained for a cobalt content of about 1.0910 mol g (Fig. 2b). Table 1, gives the interlayer spacing measured for planes (003). Even working under helium atmosphere to minimize contamination by atmospheric CO2, the obtained doo3 is about 7.8 A, as generally reported for hydrotalcites containing CO in the interlayer [20,24].

The second procedure that has been widely used is that of Grassman and Hannig (29,31) and of McDonald and associates (48,49). Here the filter paper is stretched taut in a horizontal position and placed under a cover. The paper is stretched between two rolls at each end in one method (31), with the ends dipping in the electrode vessels. Excellent resolutions can be achieved by this arrangement. Conditions for reproducibility of experiments are perhaps somewhat improved by this arrangement but evaporation and electrolyte concentration gradients still exist. McDonald (49) has recently employed a helium atmosphere to minimize these effects. 

Of the gases neon, sulfur dioxide, helium, oxygen, and nitrogen, which shows the most variation in its atmospheric concentration ... 

To achieve the very low initial fluorine concentration in the LaMar fluorination process initially a helium or nitrogen atmosphere is used in the reactor and fluorine is bled slowly into the system. If pure fluorine is used as the incoming gas, a concentration of fluorine may be approached asymptotically over any time period (Fig. 3). It is possible to approach asymptotically any fluorine partial pressure in this manner. The very low initial concentrations of fluorine in the system greatiy decreases the probabiUty of simultaneous fluorine coUisions on the same molecules or on adjacent reaction sites. 

He is present in natural gases with a concentration of MO-7 of that of 4He and 1(T6 of the helium in the atmosphere. The separation is very expensive. Hence 3He is instead obtained as by-product of tritium production in nuclear reactors. Tritium in fact produces, by beta decay (the half life is 12.26 years), 3He the separation of 3He is obtained through a diffusion process. 

Xenon is an odourless, colourless, non-explosive gas present in the atmospheres of both Earth and Mars in concentrations of approximately 0.08 ppm. Its density is approximately three times and its viscosity twice that of nitrous oxide. Like other noble gases, such as helium and argon, its outer electron shell contains the maximum number of electrons (8) making the molecule highly stable chemically. Despite this, its anaesthetic activity indicates that xenon binds to cell proteins and cell membrane constituents. 

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