Isotopic contamination

The main assumption in this model is that matrix carbonate in solution is the principle agent for alteration of carbonates in biological apatites. Although the liquid and solid carbonate phases differ isotopically (the latter is enriched by about 8%o relative to former, under equilibrium conditions), the isotopic relationship between phases is well-defined (Emrich et al. 1970) hence values obtained from solid are at least representative of the dissolved phase. As shown in the model in Fig. 5.3, isotopic contamination of... 

The paradox of the spatial decoupling between isotopic contamination and LILE and LREE enrichment was resolved with a numerical simulation of isotopic variations during reactive porous flow (Bodinier et al., 2004). This confirmed that the isotopic contamination (e.g., " Nd/ " Nd) by the infiltrated melt is restricted to the domain between the melt source ( = dike) and the chromatographic front of the element (neodymium)—i.e., —20 cm from the dike in the studied wall rock. Numerical experiments also showed that the fractional solidification of infiltrated melt (due to amphibole cpx precipitation) accounts for the systematic increase in thorium, uranium, LREE, and P2O5, that reach a maximum in the distal apatite-bearing wall rock (>50 cm from the... 

Spooner E. T. C., Chapman H. J., and Smewing J. D. (1977) Strontium isotopic contamination, and oxidation during... 

Thompson R. N., DicMn A. P., Gibson I. L., andMorrison M. A. (1982) Elemental fingerprints of isotopic contamination of Hebridean Palaeocene mantle-derived magmas by Archaean sial. Contrib. Mineral. Petrol. 79, 159—168. 

The Group noted the problems in translating these radiation protection limits into intervention levels based on the specific activity of foodstnffs bnt in September 1986 recommended new limits, listed in Table 8.3. The Group proposed intervention limits for I and Sr isotopic contamination and for Pn, as well as Cs. These proposals did not find favonr with the Commission which discussed internally its own recommendations in autumn 1986 (see Table 8.3). 

In order to insure accurate and reproducible isotopic analyses, the compounds to be analyzed must be rigorously purified. The usual methods of purification of organic and inorganic materials are used, bearing in mind that often only very small quantities are available. Thus microtechniques (Cheronis, 1954) are usually employed for distillation or even recrystallization. In recrystallization as in extraction, hydroxylic solvents should not be used in order to reduce the possibility of exchange, and to reduce isotopic contamination in analysis. 

For the naturally occurring elements, many new artificial isotopes have been made, and these are radioactive. Although these new isotopes can be measured in a mass spectrometer, this process could lead to unacceptable radioactive contamination of the instrument. This practical consideration needs to be considered carefully before using mass spectrometers for radioactive isotope analysis. 

Plutonium (Pu) is an artificial element of atomic number 94 that has its main radioactive isotopes at 2 °Pu and Pu. The major sources of this element arise from the manufacture and detonation of nuclear weapons and from nuclear reactors. The fallout from detonations and discharges of nuclear waste are the major sources of plutonium contamination of the environment, where it is trapped in soils and plant or animal life. Since the contamination levels are generally very low, a sensitive technique is needed to estimate its concentration. However, not only the total amount can be estimated. Measurement of the isotope ratio provides information about its likely... 

Special sample inlet devices such as nebulizers, furnaces, and gas inlets are commonly used to avoid cross-contamination and accidental fractionation of isotopes. 

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

The implanted ion can be singly or multiply charged and can be any isotope. The mass separation system is used to avoid contamination. As an example, when implanting silicon the isotope is often used instead of to avoid contamination from the signals. After mass... 

Production-Scale Processing. The tritium produced by neutron irradiation of Li must be recovered and purified after target elements are discharged from nuclear reactors. The targets contain tritium and He as direct products of the nuclear reaction, a small amount of He from decay of the tritium and a small amount of other hydrogen isotopes present as surface or metal contaminants. 

A SSIMS spectrum, like any other mass spectrum, consists of a series of peaks of dif ferent intensity (i. e. ion current) occurring at certain mass numbers. The masses can be allocated on the basis of atomic or molecular mass-to-charge ratio. Many of the more prominent secondary ions from metal and semiconductor surfaces are singly charged atomic ions, which makes allocation of mass numbers slightly easier. Masses can be identified as arising either from the substrate material itself from deliberately introduced molecular or other species on the surface, or from contaminations and impurities on the surface. Complications in allocation often arise from isotopic effects. Although some elements have only one principal isotope, for many others the natural isotopic abundance can make identification difficult. 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

The isotopes hsted in Table 5 are the ones most frequently employed They are all weak ) -emitters with a relatively long half-hfe, so that they can unfortunately contaminate the orgamsm in medical investigations... 

Corrosion products include iron oxide (Fe203), ferrosoferric oxide (Fe304), nickel oxide (NiO), cobalt oxide (CoO), and complex Fe, Ni, and Co oxides. Cobalt in particular may present a problem (as cobalt59, a naturally occurring isotope), and when present as a contaminant in nickel alloys (such as Inconel 800), may enhance the development of an outer-core radiation field (see Section 7.4.1). 

Atmospheric testing of nuclear bombs resulted in contamination of the surface of the ocean with various isotopes including H, °Sr, Pu, and " °Pu. These isotopes are slowly being mixed through the ocean... 

Bones of 19 individuals were analyzed for strontium, rubidium and zinc. The number of samples was limited by the availability of bone after the stable isotope analyses were completed. Strontium was analyzed in order to test for trophic level, and to compare to other results obtained in the region on prehistoric peoples (Katzenberg 1984). Rubidium is not expected in human bone, so its presence acts as a measure of contamination. The use of zinc as a paleodi-etary indicator has been questioned recently (Ezzo 1994) and we were interested to see if there was any relationship between zinc content in food and bone. 

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