Applications of Radioactive Isotopes

We have already described two applications of nuclear chemistry. One was the preparation of elements not available naturally. We noted that the discovery of the transuranium elements clarified the position of the heavy elements in the periodic table. In the section just completed, we discussed the use of radioactivity in dating objects. We will discuss practical uses of nuclear energy later in the chapter. Here we will look at the applications of radioactive isotopes to chemical analysis and to medicine. 

A radioactive tracer is a very small amount of radioactive isotope added to a chemical, biological, or physical system to study the system. The advantage of a radioactive tracer is that it behaves chemically just as a nonradioactive isotope does, but it can be detected in exceedingly small amounts by measuring the radiations emitted. 

As an illustration of the use of radioactive tracers, consider the problem of establishing that chemical equilibrium is a dynamic process. Let us look at the equilibrium 

Melvin Calvin received the Nobel Prize in chemistry in 1961 for his work on photosynthesis. 

In two separate beakers, you prepare saturated solutions of Pbl2 in contact with the solid. One beaker contains only natural iodine atoms with nonradioactive isotopes. The other beaker contains radioactive iodide ion, Some of the solution, but no solid, containing the radioactive iodide ion is now added to the beaker containing nonradioactive iodide ion. Both solutions are saturated, so the amount of solid in this beaker remains constant. Yet after a time the solid lead iodide, which was originally nonradioactive, becomes radioactive. This is evidence for a dynamic equilibrium, in which radioactive iodide ions in the solution substitute for nonradioactive iodide ions in the solid. 

---

Even nowadays the application of radioactive isotopes is the most sensitive method for the analysis of biomolecules or their reaction products. Besides the low detection limits, the replacement of a naturally overbalancing stable isotope by its radioactive analogue does not interfere with the physical or chemical properties of the enzyme (with some exceptions for hydrogens). Figure 6 lists some frequently used radioactive isotopes and their half-life periods. 

Karzinkin, G.S. (1962) Application of Radioactive Isotopes to Fish Culture (In Russian). Pishchepromizdat, Moscow, 71 pp. 

One of the earliest experiments on the application of radioactive isotopes to the study of mechanisms of reactions of metal complexes was that of Ettle and Johnson (22). They added radiochloride ion to solutions of [Co(en)2012] and found that cis-trans isomerization in this system... 

A typical nuclear industry may consist of mining and milling of uranium ore, thorium extraction, fuel fabrication, nuclear reactor operation, and production and application of radioactive isotopes for various industrial medical and research purposes. Almost, in all these steps, waste is generated that needs proper management. Radioactive wastes differ from other industrial wastes due to its radiation exposure and its radiological toxicity to human beings and their environment. Management of radioactive wastes is an important step in a nuclear industry and the objective is to effectively isolate radionuclides from the... 

One very important application of radioactive isotopes is the determination of the ages of archaeological remains. The pioneer in this type of investigation is the American chemist Willard F. Libby. The radioactive isotope carbon-14, was discovered in 1940 by the American biochemists Samuel Ruben and Martin David... 

What are some of the useful applications of radioactive isotopes, including energy production ... 

Chapters 16 (waste disposal). Chapter 17 (radioactive materials transportation), and Chapter 18 (decontamination and decommissioning) are related to many radioactive processes and materials. Radioactive waste is generated wherever radioactive materials are handled and used. This includes medical applications of radioactive isotopes and their production, as well as the facilities and processes involved in nuclear power. This waste must be stored and/or disposed of in a way that isolates it from the environment until the radioactive materials decay. 

Stable isotope dilution assays (SIDAs) can be traced back to the beginning of the 20th century and coincide with the discovery of isotopes by Soddy (1913) and the application of radioactive isotopes to determine the content of lead in rocks and the solubility of lead salts in water (Hevesy and Paneth 1913). Most elements consist of both stable and radioactive isotopes, and examples of natural distributions are listed in Table 25.1. 

Three common quantitative applications of radiochemical methods of analysis are considered in this section the direct analysis of radioactive isotopes by measuring their rate of disintegration, neutron activation, and the use of radioactive isotopes as tracers in isotope dilution. 

The diffusion coefficients of cations in metal oxides are usually measured through the use of radioactive isotopes. Because of the friable nature of oxides it is exU emely difficult to use the sectioning technique employed for metal samples. The need for this can be avoided by the application of radioisotopes which emit radiation having a well established absorption law in matter. Isotopes which emit y radiation are very useful when the cation has a relatively high diffusion coefficient because of the long-range peneU ation of y rays. The absorption law is... 

The application of substrates isotopically labeled in specific positions makes it possible to follow the fate of individual atoms during the microbial degradation of xenobiotics. Under optimal conditions, both the kinetics of the degradation, and the formation of metabolites may be followed— ideally when samples of the labeled metabolites are available. Many of the classical studies on the microbial metabolism of carbohydrates, carboxylic acids, and amino acids used radioactive... 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

The contributions of modern chemistry, including the availability of separated isotopes, the extension of the range of mass spectrometers, and the developments of new chemical methods, which make possible the determination of microgram quantities, have extended the range of application of radioactive age measurements. This extension has been either... 

Another application of radioisotopes is in the oil industry. For example, a small amount of radioisotope is placed into oil pipes in order to observe the circulation of oil. Additionally, if a single pipe is used to transfer more than one petroleum derivative (one after the other) a small amount of radioactive isotope is placed into the last portion of one substance to signal its end and the start of another. 

Special properties of radioactive nuclides (isotopes of an element, Chapter 2) make them useful tracers for following complex processes. Radiochemistry is the branch of chemistry which involves the applications of radioactivity to chemical problems, as well as the chemical processing of radioactive substances. 

W. J. Whitehouse, J. L. Putman, Radioactive Isotopes - An Introduction to their Preparation, Measurement and Use, Clarendon Press, Oxford, 1952 E. Broda, Th. Schonfeld, The Technical Applications of Radioactivity, Vol. 1, Pergamon, Oxford, 1966... 

One application of radioactive tracer techniques of considerable importance in solid state structural problems is the emanation method due to Hahn (21). The method has been employed widely and has been developed recently as a sensitive, quantitative method by Gregory (22), who has employed it for the investigation of structural changes and for the extraction of diffusion data. The procedure in outline is as follows A convenient amount of a radioactive element which decays to an isotope of radon (e.g., radiothorium) is ccprecipitated... 

---