Radiochemical techniques

Radiochemistry is defined as the chemical study of radioactive elements, both natural and artificial, and their use in the study of chemical processes (Random House Dictionary, 1984). Operationally, radiochemistry is defined by the activities of radiochemists, that is, (a) nuclear analytical methods, (b) the application of radionuclides in areas outside of chemistry, such as medicine, (c) the physics and chemistry of the radioelements, (d) the physics and chemistry of high-activity-level matter, and (e) radiotracer studies. We have dealt with several of these topics in Chapters 4, 13, 15, and 16. In this chapter, we will discuss the basic principles behind radiochemical techniques and some details of their application. 

Modem Nuclear Chemistry, by W.D. Loveland, D.J. Morrissey, and G.T. Seaborg Copyright 2006 John Wiley Sons, Inc. 

In addition to the discussions of these topics in textbooks such as this, there are excellent textbooks that focus primarily on radiochemistry (Adlofif and Guillamont, 1984 Lieser, 1997 Ehmann and Vance, 1991). 

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Prior to working with radioactive materials, the scientist should attend a pertinent training course or consult a standard source of information on radioisotope methodology to become familiar with the precautions used in the safe handling of radiochemicals in the laboratory (e.g., DuPont, 1988a Shapiro, 1972 Stewart, 1981). As much as possible, experiments should be carried out, and plates with radioactive zones stored, in a fume hood. 

Commercial glass-backed TLC and HPTLC plates, which contain flat, uniform layers, are best to use for instrumental TLRC. Plates with plastic or aluminum backing can be cut into sections, thereby facilitating zonal analysis by scintillation counting or preparative isolation of compounds. Layers must be clean and free from dust and other particles in order to measure radioactivity accurately. Samples should be spotted manually or automatically with an instrument (see Chapter 5) as small spots or narrow bands sufficiently far apart (minimum of 1.5 cm) to avoid measurement of radioactivity from adjacent lanes. Complete resolution of sample components is required for accurate quantification there- 

In metabolism studies by TLRC, one- and two-dimensional development has been used for qualitative identification and quantitative estimation of metabolites. Cochromatography with reference standards can help to confirm structures of unknown components. Isolation of larger quantities of metabolites for identification by spectrometry can be carried out by streaking a band of sample across an analytical or preparative layer (Chapter 11). 

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There are many potential advantages to kinetic methods of analysis, perhaps the most important of which is the ability to use chemical reactions that are slow to reach equilibrium. In this chapter we examine three techniques that rely on measurements made while the analytical system is under kinetic rather than thermodynamic control chemical kinetic techniques, in which the rate of a chemical reaction is measured radiochemical techniques, in which a radioactive element s rate of nuclear decay is measured and flow injection analysis, in which the analyte is injected into a continuously flowing carrier stream, where its mixing and reaction with reagents in the stream are controlled by the kinetic processes of convection and diffusion. 

Baur, J. P. Gibbs, H. L. Wadsworth, M. E., Initial-Stage Sulfuric Acid Leaching Kinetics of Chalcopyrite Using Radiochemical Techniques, 1974, United States Bureau of Mines Report of Investigations 7823, Washington, D.C. 

A well known radiochemical technique which provides reliable data involves the use of a mixture of many elements in the same aqueous solution (9). This technique... 

For work with solutions, and in particular with solid materials, precautions against electrostatic charging and the effects of air currents have to be taken, and standard radiochemical techniques should be used. The handling techniques required for other technetium isotopes such as Tc are described below (Scheme 2). 

Fig. 6.26. Two electrode positions in a radiochemical technique. On the left, the electrode is lifted up for adsorbate equilibration and bulk counting rate measurement. On the right, the electrode is pressed down (squeezed) against the scintillator for surface counting rate measurement. (Reprinted with permission from M. E. Gamboa-Aldeco, K. Franaszczuk, and A. Wieckowski, Radiotracer Study of Electrode Surfaces, in Surface Imaging and Visualization, A. T. Hubbard, ed., Ch. 46, CRC Press, Boca Raton, FL, p. 635,1995, Fig. 46.4.)...

In contrast to poisoning with water vapor, the poisoning of ammonia synthesis catalysts by hydrogen sulfide is irreversible. It was studied using H2S labeled with H 5S (123) that made the radiochemical technique applicable to the determination of sulfur content in catalysts. 

Basic Radiochemical Techniques Applied to Uranium-Thorium Separation Precipitation, Solvent Extraction, and Ion Exchange... 

Basic Radiochemical Techniques Applied to Uranium-Thorium Separation... 

Mossbauer spectroscopy with the iodine isotopes is not a practical method for identification or quantification of organic compounds (nor of inorganics). It is most applicable for discerning electronic effects and charge states. For these applications, 129I gives far better results, and allows the separation of superposed subspectra. It is unfortunate that its use requires radiochemical techniques and very small scales. 

For the development of concepts of kinetics and of thermodynamics, considered in this chapter, the single atom was assumed to be stable. In fact, the probability for a unique atom to exist in specific specie can only be determined in a chemical experiment if the atom is radioactive. Therefore, if the atom is stable or has a large half-life, any radiochemical techniques can be used for single atom chemistry. 

Each study of the chemical property of a transactinide element requires the development of radiochemical technique that allows collecting data relevant to the scale of one atom. Experimental approaches are therefore severely limited. 

The authors are indebted to S. Carangelo for instruction in the radiochemical techniques. 

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