Krypton abundance

Wider R., Kehm K., Meshik A. P., and Hohenberg C. M. (1996) Secular changes in the xenon and krypton abundances in the solar wind recorded in single lunar grains. Nature 384, 46-49. 

Bogard D. D. and Garrison D. H. (1998). Relative abundances of argon, krypton, and xenon in the Martian atmosphere as measured in Martian meteorites. Geochimica et Cosmochimica Acta, 62(10) 1829-1835. 

Krypton is the 81st most abundant element on Earth and ranks seventh in abundance of the gases that make up Earths atmosphere. It ranks just above methane (CH ) in abundance in the atmosphere. Krypton is expensive to produce and thus has hmited use. The gas is captured commercially by fractional distillation of liquid air. Krypton shows up as an impurity in the residue. Along with some other gases, it is removed by filtering through activated charcoal and titanium. 

Krypton may be analysed most conveniently by GC/MS. The characteristic masses for its mass spectroscopic identification are 84, 86, and 83, the most abundant natural isotopes of the element. It also may be analyzed by gas-sohd chromatography by its retention times. 

The abundances of krypton and xenon are determined exclusively from nucleosynthesis theory. They can be interpolated from the abundances of neighboring elements based on the observation that abundances of odd-mass-number nuclides vary smoothly with increasing mass numbers (Suess and Urey, 1956). The regular behavior of the s-process also provides a constraint (see Chapter 3). In a mature -process, the relative abundances of the stable nuclides are governed by the inverse of their neutron-capture cross-sections. Isotopes with large cross-sections have low abundance because they are easily destroyed, while the abundances of those with small cross-sections build up. Thus, one can estimate the abundances of krypton and xenon from the abundances of. v-only isotopes of neighboring elements (selenium, bromine, rubidium and strontium for krypton tellurium, iodine, cesium, and barium for xenon). 

Noble gases may provide a constraint on the source of water and other volatiles. The abundance pattern of noble gases in planetary atmospheres resembles that of chondrites, perhaps arguing against comets. However, there are some differences, especially in the abundance of xenon. Relative to solar system abundances, krypton is more depleted than xenon in chondrites, but in the planets, krypton and xenon are present in essentially solar relative abundances (Fig. 10.11). This observation has been used to support comets as the preferred source of volatiles (even though measurements of xenon and krypton in comets are lacking). A counter-argument is that the Ar/H20 ratio in comets (if the few available measurements are accurate and representative) limits the cometary addition of volatiles to the Earth to only about 1%. 

Nier, A. O. (1950b) A redetermination of the relative abundances of the isotopes of neon, krypton, rubidium, xenon and mercury. Phys. Rev., 19, 450-4. 

Helium is the second most abundant element in the universe. In the Earth, it is continuously formed by radioactive decay, mostly of uranium and thorium. Its present concentration in the atmosphere is probably the equilibrium concentration between the amount being released from the Earth s crust and the amount of hehum escaping from the atmosphere into space. The atmosphere represents the major source for neon, argon, krypton, and xenon. They are produced as by-products during flactional distillation of liquid air. Radon is obtained from the radioactive decay of radium. 

Clayton D. D. and Ward R. A. (1978) s-Process smdies xenon and krypton isotopic abundances. Astrophys. J. 224, 1000-1006. 

For krypton and xenon abundances were derived from computer hts of aN (neutron capture cross-section times abundance) versus mass number. Nuclei that are shielded from the r-process, so-called s-only nuclei, were used for the ht and the abundances of Kr and Xe were calculated. From these data, and the isotopic composition of the solar wind, the krypton and xenon elemental abundances were calculated (Palme and Beer, 1993) and are listed in Table 1. The meteorite data given in Table 1 will be discussed in a later section. 

For most of the chemical elements, the relative abundances of their stable isotopes in the Sun and solar nebula are well known, so that any departures from those values that may be found in meteorites and planetary materials can then be interpreted in terms of planet-forming processes. This is best illustrated for the noble gases neon, argon, krypton, and xenon. The solar isotopic abundances are known through laboratory mass-spectrometric analysis of solar wind extracted from lunar soils (Eberhardt et al., 1970) and gas-rich meteorites. Noble gases in other meteorites and in the atmospheres of Earth and Mars show many substantial differences from the solar composition, due to a variety of nonsolar processes, e.g., excesses of " Ar and... 

Limitations, (i) As with other radionuclide-based ages, the terrestrial age of the sample must be known, (ii) Concentrations of Kr are quite low in most meteorites, typically just 5 X 10 atomg in chondrites. For this reason, Kr measurements are still scarce and their uncertainties can be relatively large, often —20%. (iii) Production rates for krypton isotopes may vary with the abundances of rubidium, yttrium, and zirconium relative to strontium. It should be understood that the original basis for the calculation of Pgi/Fgs was a set of relative cross-section measurements for the production of krypton from silver (Marti, 1967). 

Besides their presence due to in situ radioactive decay within a given solid sample, radiogenic " He, " Ar, Xe, Pu-fission xenon (and krypton), and likely also U-fission xenon, are also prominent or observable constituents of planetary atmospheres, and their abundance is important in constraining models for planetary atmosphere evolution (see Chapter 4.12). 

Noble gases and nitrogen in martian meteorites reveal several interior components having isotopic compositions different from those of the atmosphere. Xenon, krypton, and probably argon in the mantle components have solar isotopic compositions, rather than those measured in chondrites. However, ratios of these noble gas abundances are strongly fractionated relative to solar abundances. This decoupling of elemental and isotopic fractionation is not understood. The interior ratio in martian meteorites is similar to chondrites. 

In this section we present an overview of the principal means available to sample mantle-derived noble gases, followed by a summary of their main isotope and relative abundance characteristics in the mantle. Mostly, the mantle shows a wide range in noble gas isotope variations serving to impart information on a variety of topics. The only exception is krypton whose isotopic composition is steadfastly air-like in mantle materials. Consequently, we do not consider krypton in this review. 

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