Radiometric techniques

Another valiant on the basic isotope dilution technique is that of double isotope dilution, or valiants thereof, as first proposed by Block and Anker (1948). It is used in reverse IDA where the specific activity of the original unknown radioactive material A cannot be measured for some reason. Hence a second dilution is made to determine the specific activity of the original sample. 

Consider a system containing an unknown amount q of some active substance A whose specific activity A cannot be measured. Take two equal aliquots of this unknown substance A. Add r milligrams of inactive A to one aliquot and p milligrams of inactive A to the other aliquot. Measure the specific activities of the two aliquots, Sr and SPi respectively. For the first sample of specific activity Sn we have 

A major difficulty with double isotope dilution analysis is that, because of the double dilution, the specific activities involved become low and therefore more uncertain. 

The central idea in all radiometric techniques of analysis is to have a radioactive reagent R of known activity combine quantitatively with some unknown amount of material U to form a radioactive addition product R U. By measuring the activity of the product R U, the original amount of unknown material U is deduced. The advantages of such techniques are the high sensitivity due to the use of radioactivity and the requirement that the product R U need not be chemically pure. All that is required is the R U not contain any spurious radioactivity. The disadvantages of these techniques are that the reaction between R and U must be quantitative, and 

One of the radiometric techniques is precipitation with a radioactive reagent. For example, the halides can be precipitated with 110Ag, silver precipitated with 131I, the sulfates and chromates precipitated with 212Pb or 131Ba, while Al, Be, Bi, Ga, In, Th, U, Zr, and the rare-earth elements can be precipitated with 32P04. This method suffers from the lack of selectivity and the need to make careful corrections for self-absorption in counting the samples. 

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A large number of radiometric techniques have been developed for Pu analysis on tracer, biochemical, and environmental samples (119,120). In general the a-particles of most Pu isotopes are detected by gas-proportional, surface-barrier, or scintillation detectors. When the level of Pu is lower than 10 g/g sample, radiometric techniques must be enhanced by preliminary extraction of the Pu to concentrate the Pu and separate it from other radioisotopes (121,122). Alternatively, fission—fragment track detection can detect Pu at a level of 10 g/g sample or better (123). Chemical concentration of Pu from urine, neutron irradiation in a research reactor, followed by fission track detection, can achieve a sensitivity for Pu of better than 1 mBq/L (4 X 10 g/g sample) (124). 

Hereia optical spectroscopy for laboratory analysis, giving some attention to remote sensing usiag either active laser-based systems (13—16) or passive (radiometric) techniques (17—20), is emphasized. 

Highly sensitive determination of "Tc is possible using today s advanced mass spectroscopic methods. However, orthodox determination methods of "Tc involving radiometric techniques or even activation analysis are still used because they are simple and can be done without expensive machines. The detection limits of typical analytical methods are listed in Table 1. 

Radiometric detection technology, 21 271 Radiometric ore sorting, 16 626 Radiometric techniques, for plutonium analysis, 19 699-700 Radiometry, 23 142-143 Radionuclide removal... 

A radiometric technique for estimating the rates of intracellular synthesis and/or turnover of a metabolite. To measure the rates of synthesis, cells are exposed to a radioisotopically labeled precursor (such as pH]-,... 

One of the most popular radiometric techniques is that of radiometric titrations. In a radiometric titration, the unknown is titrated with a radioactive reagent, and the radioactivity of the product or supernate, formed by the chemical reaction of the reagent and the unknown material, is monitored as a function of titrant volume to determine the endpoint. This means that the radioactive component being followed must be isolated during the titration and its activity measured—that is, a discontinuous titration. 

Saelens et al. measured choline, acetylcholine, and their metabolites by combined enzymatic and radiometric techniques [219]. Choline and acetylcholine were isolated from tissue extracts by a low voltage... 

Lotzsch, K. R., Reng, A. K., Gantz, D., and Quack, J. M., The radiometric technique. Explained by the example of absorption and desorption of C-labelled distearyl-dimethylammonium chloride on human hair, in Hair Research Status and Future Aspects, Orfanos, C. E., Montagna, W., and Stuttgen, G., Eds., Springer-Verlag, Berlin, 1981, 638. 

As with most foram records, the atmospheric record cannot be dated with radiometric techniques. Dating of the record has been accomplished by correlation with the orbitally tuned deep-sea record (Sowers et al., 1993), using estimates of ice accumulation rates, ice flow models, and estimates of offsets between snowfall and gas closure ages (Petit et al., 1999), and by direct orbital tuning of the atmospheric oxygen record itself (Shackleton, 2000). Separate tuning of the marine and atmospheric records establishes independent chronologies for the two. 

Precise times of duration of certain Cretaceous stages (dehned by their diagnostic faunas) seem to be possible, based on integration of orbital chronometry with radiometric techniques. Orbital chronometry is a signihcant component in relatively precise Pliocene-Pleistocene age analyses (Berggren et al., 1995, pp. 131-132). 

Radiometric techniques, essentially alpha and gamma spectrometry, allow the determination of a number of fissile and fission product isotopes. 

Here is how SAL works Samples are received in a reception and storage room, then routed to the appropriate wet chemical analysis laboratory. There, they are analysed for uranium, thorium or plutonium content, and purified aliquots (portions of the sample) are prepared for the isotopic analysis of three elements. Isotopic analyses are performed routinely by mass spectrometry, and radiometric techniques are used for back-up. Emission spectrography serves to detect the presence of impurities which could interfere with the measurements and thus distort the results of the chemical and isotopic analysis of uranium, thorium and plutonium. Complex calculations and quality checks are performed on minicomputers, which are connected in a network to a central laboratory mini-computer. A central laboratory data system stores and provides analytical reports and enables the quality of the analyses and the status of the flow of samples through the laboratory at any time to be monitored. 

In principle, radiometric techniques are most suitable for the shorter-lived radio-nuclides, whereas at longer half-lives (-100 years or more) techniques based on mass spectrometry or neutron activation analysis start to become more sensitive. This is shown in Table 12.10. 

Levinson, A.A. and Coetzee, G.L., 1978. Implications of disequilibrium in exploration for uranium ores in the surficial environment using radiometric techniques - a review. Min. Sci. Eng., 10 19-27. 

Samples of all ICE were submitted for analysis. Plutonium and americium were determined by radiometric techniques and other elements were determined by atomic absorption. 

Whereas interval dating can be carried out by counting annual layers (e.g. Baldini et al., 2002), radiometric techniques are needed to provide the... 

Radiometric techniques, among the most sensitive analytical techniques, are very well known in clinical analysis and diagnosis. For sodium assay a neutron activation analysis (NAA)319 is proposed in the place of a spectro-metric method. This reduces the uncertainty value considerably because of the high selectivity and sensitivity of NAA. 

Optical or radiometric techniques for measuring solids concentration are based on the dependence of attenuation and scattering of an optical beam or radiation on the number of particles in the optical path. The theory that guides these techniques assumes a single-scattering process thus, it is only valid for low concentrations of solids. These techniques require special optical windows, which sometimes are impractical and limiting. 

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