Helium diffusion

The most common separators include the Ryhage or jet diffusion separator (74), the Watson-Biemann or pore diffusion separator (75), and the membrane solution diffusion separator originally developed by Llewellyn (75). The first two separators involve direct passage of the sample into the mass spectrometer the low molecular weight helium diffuses more readily and is pumped away. The membrane separator involves diffusion of the sample through a silicone membrane while the carrier gas vents to the atmosphere carrier gas is thus not confined to helium. There is no best separator the choice depends on the nature of the compounds, the temperature range over which it will be operated, and most usually what is available in a particular laboratory. A convenient configuration for a double-beam mass spectrometer such as the AEI MS-30 is two different separators, one into each beam, which permits rapid evaluation of separator performance. 

Jambon A. and Shelby J.E. (1980) Helium diffusion and solubility in obsidians and basaltic glass in the range 200-300°C. Earth Planet Sci. Lett. 51, 206-214. 

Wolf R.A., Parley K.A., and Silver E.T. (1996) Helium diffusion and low-temperature thermochronometry of apatite. Geochim. Cosmochim. Acta 60, 4131-4240. 

C. Leak Detection Using Vacuum Gauges. Reference has already been made to the use of an electronic vacuum gauge in hunting leaks. A cold-cathode gauge is particularly useful because it has rapid response and operates well in the presence of small leaks. Because of this rapid response, acetone or methanol can be squirted on the suspected area. If a hole is present, a momentary pressure drop will be observed because the acetone or methanol molecules are slower than air to diffuse through the hole. Sometimes a helium stream is directed on the suspected leak in this case a pressure rise is noted when the helium passes over the site of the leak, because helium diffuses more rapidly than air. It also is sometimes possible to use a puttylike material, such as Apiezon Q, to cover temporarily a suspected leak. 

Shuster DL, Rowers RM, Farley KA (2006) The influence of natural radiation damage on helium diffusion kinetics in apatite. Earth Planet Sci Lett 249 148-161... 

House, M. A., Farley, K. A., Kohn, B. P. (1999) An empirical test of helium diffusion in apatite Borehole data from the Otway basin, Australia, Earth Planet. Sci. Lett., 170,463-74. 

A standard leak is a small container that leaks helium at a very slow and specific amount. As mentioned before, helium diffuses through borosilicate glass (or through ceramic or capillary tube). This diffusion is very consistent at any given pressure and temperature. Within the standard leak is a thimble of borosilicate glass (see Fig. 7.62) around which is the stored helium. The helium leak rate var-... 

Does Helium Diffuse Through the Upper Crust ... 

The water in each aquifer dissolves all the available helium and shields the overlying aquifers from helium fluxes of the type suggested by the crustal helium diffusion model. 

Measurements of helium diffusion coefficients over the temperature range 25-55 C showed no significant changes in activation energies throughout the drawing range. 

Fig. 56. Variation of helium diffusion coefficient with draw ratio. Hizex 7000F 2 mm feedstock Tj, 115 °C, O Hizex 7000F 2 mm Feedstock Tp 100 °C, X Hizex 7000F 0.5 mm feedstock Tp 115 °C A Rigidex 002-55 0.5 mm feedstock T 115 °C, 006-60 0.5 mm feedstock Tp 75 °C...

Farley K. A. (2000) Helium diffusion from apatite general behavior as illustrated by Durango ffuorapatite. J. Geophys. Res. 105, 2903 -2914. 

Some of the earliest attempts at dating uranium-bearing minerals were made by measuring the accumulation of helium in crystals from the a-decay of uranium and thorium. Two efforts that immediately predated the development of modem geochronology were Hurley (1954) and Damon (1957). Because of the ease of helium diffusion, however, the dates calculated were shown to be too young in most cases and the technique was soon abandoned in favor of... 

A recent attempt to circumnavigate the world in a balloon used a helium-filled balloon wliose volume was 7240 in and surface area was 1800 m. The skin of this balloon is 2 mm thick and is made of a material whose helium diffusion coefficient is 1 X 10 mVs. The molar concentration of the helium at the inner surface of the balloon skin is 0.2 kmol/m and the molar concentration at the outer surface is extremely small. The rale at which helium is lost from this balloon is (a) 0.26kg/li (ft) 1.5 kg/h (c) 2.6kgfli... 

The jet concentrator consisted of a succession of jets that were aligned in series but separated from each other by carefully adjusted gaps. The helium diffused away in the gap between the jets and was removed by appropriate vacuum pumps. In contrast, the solute vapor, having greater momentum, continued into the next jet and, hnally, into the mass spectrometer. The... 

Figure 2. Helium diffusion Arrhenius plot with Otway Basin borehole constraint. The laboratory-measured He diffusion from this sample of Durango apatite defines an extremely linear array (filled symbols), consistent with simple thermally activated volume-diffusion. He age measurements from the Otway Basin provide a completely independent estimate of He diffusivity (open symbol), under natural conditions, which is in excellent agreement with the extrapolated laboratory data. Laboratory data are from Farley (2000). The Otway Basin constraint is from House et al. (1999).

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