Helium versus

Fig. 4.26. Plot of the ratio aPS/aH for positron and proton collisions with helium, versus the velocity of the projectiles (following Schultz and Olson, 1988). The curve is the result of their classical trajectory Monte Carlo calculation. The triangles are based on the positron data of Fromme et al. (1986) whilst the circles are from Diana et al. (1986b).

After you inhale helium your voice might sound higher, but the pitch (or frequency of the sound waves) is exactly the same. Your vocal cords vibrate at the same frequency because your body doesn t adjust for the presence of a less-dense gas in your throat. What does change is the speed of sound in helium versus air—because helium has a lower molecular weight than air, the speed of sound is higher. You ve probably heard this is because helium is less dense—that s not technically correct, but let s not go there. 

For monatomic species, the heavier substance has the greater entropy (for example, helium versus neon). 

Higher performance is always obtained using a non-condensable pressurant gas such as helium versus pressurizing with a condensable vapor. 

RIE Rieder, K. H. Surface structural research with atom beam diffraction helium versus neon Surf. Rev. Lett. 1 (1994) 51. 

The ions or cluster ions are thermalized by collisions with an inert carrier gas (usually helium), although often argon or even nitrogen is employed. Neutral reactant gas is added through a reactant gas inlet at an appropriate location downstream in the flow tube, and allowed to react with the injected ions. Rate coefficients, k, are determined by establishing pseudo-first-order reaction conditions in which the reactant ion concentration is small compared to the reactant neutral concentration. Bimolecular rate coefficients, k, are obtained from the slope of the natural logarithm of the measured signal intensity, /, of the reactant ion versus the flow rate (2b of reactant gas 45,48-50... 

Ti content in the polymer films was measured with a Princeton Gamma Tech System 4 x-ray Fluorescence Spectrometer. The conditions employed were Cr target, 50 keV source operating at 3 mA, 0.75 mm aperture, 4.8 mm beam stop, helium atmosphere and 100 sec. counting time. A calibration curve was constructed by plotting the fluorescence counts versus the amount of Ti in HB-HPR 206 films determined by Rutherford Backscattering Spectroscopic (RBS) analysis. 

In ISS, like in SIMS, gas ions such as helium or neon are bombarded on the sample surface at a fixed angle of incident. The ISS spectrum normally consists of a single peak of backscattered inelastic ion intensity at an energy loss that is characteristic of the mass of surface atom. From the pattern of scattered ion yield versus the primary ion energy, information about elements present on the sample surface can be obtained at ppm level. 

Fig. 4. Potential energy versus distance from the surface. Data is appropriate for He and tungsten. E, is the ionization potential for helium and ( > is the work function of tungsten. E (e") is the kinetic energy of an emitted secondary electron. The symbol He + nej implies a system composed of an helium ion and n conduction electrons in tungsten. The lower potential curve results from an Auger neutralization process where both electrons were originally at the Fermi level. (The figure is similar to one published in Ref. )...

A plot of density versus pore radius, from the data in Table 21.2, is shown in Fig. 21.3. The horizontal line indicates the true density obtained by helium pycnometry. This higher density by gas displacement reflects the volume of pores smaller than about 18 A. 

This requirement is fulfilled in gas chromatography (GC), where nitrogen or helium is used as the carrier gas. The low density of gases correlates with their high diffusion coefficients, and therefore in GC fast separations at high flow rates can be achieved when compared with LC. In Figure 7.2.1, the diffusion coefficient versus density diagram shows the areas occupied by the mobile phases in HPLC and GC. 

Enrichment of the preferred gas, helium in this case, is most productively displayed as a plot of the feed concentration of this gas relative to the remainder gases (or to a less preferred gas in the mixture) versus the equivalent ratio in the permeate. This is thus a plot of feed ratio vs. flux ratio. If this is done for several feed compositions representing a significant preferred-gas composition ran e, enrichment curves can be generated, such as those displayed in Figures 6 and 7. Here it can be seen that the lower pressure differentials are more desirable from a permeate quality standpoint. 

Fig. 7.24. Positronium-beam production efficiencies versus gas pressure at positronium kinetic energies of 30 eV, 60 eV, 90 eV and 120 eV for (o) helium, (A) argon and ( ) molecular hydrogen gases. The curves are polynomial fits to the data, which were performed by Garner, Laricchia and Ozen (1998).

Figure 1.2. A/H for deuterium, helium-3, lithium-7 and Yp versus fif, - the four curves show the predicted abundances by the sBBN model, - the horizontal boxes show the various measurements, - the vertical band covers the D/H data. From Kirkman et al. 2003...

In addition to the shaft power needed to raise the water heat transfer medium from the low to high loop pressure, additional compressor power is needed to overcome frictional pressure drop around the loop. The power associated with this loss has been compared with that of the high temperature process loop in the reference design. To understand the role of the different heat transport fluid -water in the alternate design versus helium in the reference design - the pumping power is expressed as a fraction of the pumping power per unit thermal power transported. This permits a consistent comparison between the two loops even if they differ in total thermal power transported. 

The pumping power for a water-based versus helium-based loop was calculated at the full power condition. The fluid properties in the respective loops were used to calculate the friction loss power per unit megawatt of thermal power transported for the water-based loop as a fraction of the same in the helium-based loop. The result derived in Vilim (2009) shows that the power in the water loop is insignificant to the power in the helium loop. In the helium loop the circulating power needed is about 7 MWe or 14 MWt out of a reactor thermal capacity of 600 MWt. Thus an advantage of a water-based loop is that the pumping power to overcome frictional losses is significantly less and results in an efficiency increase. 

Fig. 4. Plots of mobility versus E/p for ions in helium (originally published in the article of Mitchell and...

Fig. 3. First successful observation of laser resonance of antiprotonic helium, now attributed to the (n, l) = (39,35) —> (38,34) transition. (Left) Observed time spectra of delayed annihilation of antiprotons with laser irradiation of various vacuum wavelengths near 597.2nm. Spikes due to forced annihilation through the resonance transitions are seen. (Upper right) Enlarged time profile of the resonance spike. (Lower right) Normalized peak count versus vacuum wavelength in the resonance region. From Morita et al. [11]...

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