Noble gases applications

The scope of noble gas applications in groundwater studies is much greater than described thus far, but first we have to check the basic assumption that groundwater provides closed system conditions for dissolved atmospheric noble gases. 

The choice of tracer gas for the measurements is Kr-85 It has a long half-life so that it can be stored for application when needed. It is a noble gas which is chemically inactive giving a low radio toxicity as it is readily removed in case of accidental contamination. 

As indicated in Fig. 21.3, for both atomic absorption spectroscopy and atomic fluorescence spectroscopy a resonance line source is required, and the most important of these is the hollow cathode lamp which is shown diagrammatically in Fig. 21.8. For any given determination the hollow cathode lamp used has an emitting cathode of the same element as that being studied in the flame. The cathode is in the form of a cylinder, and the electrodes are enclosed in a borosilicate or quartz envelope which contains an inert gas (neon or argon) at a pressure of approximately 5 torr. The application of a high potential across the electrodes causes a discharge which creates ions of the noble gas. These ions are accelerated to the cathode and, on collision, excite the cathode element to emission. Multi-element lamps are available in which the cathodes are made from alloys, but in these lamps the resonance line intensities of individual elements are somewhat reduced. 

At first, noble gas chemistry had almost no practical applications. Recently, however, lasers have been developed that are based on the chemical reactions of noble gases. 

The application of matrix isolation to organometallic chemistry has been extensively described elsewhere (4,5,6,7). Two methods have generally been employed. In the first, based on G.C. Pimentel s original development, the solid matrix environment is a frozen noble gas - usually Ar - at 10-20K and the unstable fragment is generated either by photolysis of a parent molecule already trapped in the matrix, or by cocondensation from the gas phase. In the... 

Penning ionization occurs with the (trace) gas M having an ionization energy lower than the energy of the metastable state of the excited (noble gas) atoms A. The above ionization processes have also been employed to construct mass spectrometer ion sources. [21,24] However, Penning ionization sources never escaped the realm of academic research to find widespread analytical application. 

Further designs of ion sources applied in plasma spectroscopy such as electrodeless microwave induced plasmas (MIPs) operating in a noble gas atmosphere at low power (mostly below 200 W) or capacitively coupled microwave plasma using Ar, He or N2 the as plasma gas (at 400-800 W) were described in detail by Broekaert.33 Microwave plasmas produced by a magnetron are operated at 1-5 GHz. Their special application fields for selected elements and/or element species are based (due to the low power applied) in atomic emission spectrometry.33... 

Two points of view are applicable to these species, as they also are to the isoelectronic noble gas fluorides (1) a valence bond approach with promotion of electrons to d orbitals and (2) three-center, four-electron bonds. The same arguments, pro and con. apply as given previously, so they will not be repeated here. Independent of die alternative approaches via VB or MO theory, all are agreed that Madelung energy ( ionic character ) is very important in stabilizing both the polyhalide tons and the polyhalogens.27... 

Fricke, J., Emmerling, A. Aerogels-Preparation, Properties, Applications. Vol. 77, pp. 37-88. Frenking, G., Cremer, D. The Chemistry of the Noble Gas Elements Helium, Neon, and Argon - Experimental Facts and Theoretical Predictions. Vol. 73, pp. 17-96. 

State, M., Schlosser, P. (1993) Principles and applications of the noble gas paleother-mometer. In Climate change in continental isotopic records. Geophysical Monograph, 78, 89-100. 

Radon-222 is an inert noble gas produced by alpha decay of 226Ra with a half-life of 3.85 d. The primary application of 222Rn in estuaries has been in estimating flux rates of pore waters across the sediment-water interface and the rate of gas exchange between the estuary and the atmosphere. 

The application of noble gas based paleotemperature determination is demonstrated in the following sections by case studies, and thereafter some aspects of paleoclimatic feedback are discussed as a requirement of a better understanding of the reconstructed paleotemperatures. Finally, the relevance of paleotemperatures to the topic of global temperature changes is addressed. 

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