Radioactive tracers to study

One effective method of obtaining information about zinc metabolism Is the use of radioactive tracers to study absorption, kinetics and body distribution following oral administration. Of course, as in all cases in which radionuclides are administered to human subjects, the hazard of such administration must be considered and balanced against the value of information expected from the study. The administered activity should be as low as possible consistent with obtaining adequate measurements. The studies reported here were carried out in accordance with approved protocols which followed relevant guidelines for studies of human subjects and with the informed consent of the participating subjects. 

There are a number of tracers that have been used to help understand chemical reactions and interactions. Historically, development of modem tracer methods began with the pioneering work of the Hungarian physical chemist, George Charles de Hevesy, in the early 1900s. De Hevesy s work focused on the use of radioactive tracers to study chemical processes, for which he was awarded the Nobel Prize in Chemistry in 1943. Radioactive tracers, also known as radioactive labels, are based on the use of a given radioisotope. However, it is important to note that there are also isotopic tracers (or isotopic labels). Isotopes are forms of a chemical element with different atomic mass, which have nuclei with the same atomic number (i.e. number of protons) but different numbers of neutrons. Examples include H, " C, and which are radioactive forms of stable elements... 

Overall, similar improvements in wear in engines have also been found Shadow et al used radioactive tracers to study the wear in piston engines. They found a consistent decrease in piston wear in engines when a dispersion of molybdenum disulphide in the engine oil was used. Figure 13.3 shows the effect on wear rate when the molybdenum disulphide was added, and the reduction in wear rate of the bearings was over 40%. 

In May 1938, Sam received the degree of Doctor of Philosophy in Chemistry. The title of his doctoral dissertation is Studies in Artificial Radioactivity. It has three sections (i) One involves fimdamental physics of iodine and neutrons, (ii) The second section concerned chemical reaction rates using radioactive iron, (iii) The third and longest section used radioactive tracers to study a fundamental problem in biology. It involved stomach-feeding radioactive phosphorus to rats, and after an elapsed period of time he killed the rats to determine which organs of the body had taken up the radioactivity. Ruben published six articles from his thesis research. 

In all of these investigations it should be noted that even when we characterize an isotopic effect as large, it is still quite small by normal reaction criteria except for hydrogen isotopes. For all but the very lightest elements we can assume in most chemical experiments that there is no isotope effect. This assumption forms a basis of the use of radioactive tracers to study chemical systems. 

Hall, Kokes, and Emmett (24), who used radioactive tracers to study the Fischer-Tropsch reaction, suggested that besides stepwise growth with single-carbon intermediates, multiple build-in could and probably did occur in the synthesis. They also showed that multiple build-in could not be distinguished from single-carbon stepwise growth below C12-C16 hydrocarbons, and thus the effect of multiple build-in could only be seen if detailed product distributions up to large carbon numbers were obtained. 

Scientific research is another major application of radionuclides. Chemists use tagged atoms as radioactive tracers to study the mechanism, or series of individual steps, in complicated reactions. For example, by using water containing radioactive oxygen, scientists have determined that the oxygen in the glucose, CgHi20g, formed in photosynthesis... 

Radiometric detection technology offers high sensitivity and specificity for many appUcations in scientific research. The radioactive emission of the labeled compound is easily detected and does not suffer from interference from endogenous radioactivity in the sample. Because of this unique property, labeled compounds can be used as tracers to study the localization, movement, or transformation of molecules in complex experimental systems. 

The radioactive isotope calcium-45 is deposited in bones and teeth as well as other plant and animal tissues. Because our bodies cannot distinguish between Ca-45 and the stable Ca-40, the radioactive isotope Ca-45 is used as a tracer to study diseased bone and tissue. At the same time, a massive overexposure to Ca-45 can displace the stable form of Ca-40 in animals and can cause radiation sickness or even death. 

Cell cultures offer many advantages over intact animals when it comes to incorporation of radioactive tracers and studying the effects of drugs or hormones. Thus the tracer or drug may be added and removed at known times, its extracellular concentration and specific activity maintained constant and there is no interference in its metabolism by cells of other organs. This does not mean to say, however, that there are no pitfalls to the use of isotopes in cell cultures. 

One radioactive isotope of zinc, zinc-65, has some practical importance. Zinc-65 is used as a tracer to study physical and biological events. A tracer is an isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system. 

Condit and Holt have reviewed the use of radioactive tracers in the study of oxidation. Radioactive platinum has been used to study the oxidation of cobalt and radioactive silver to study the oxidation of molybdenum. If the tracer element remains at the surface it indicates that the oxygen is diffusing into the metal, and if it is located some distance from the surface shows diffusion of the metal through the oxide. The tracer can be detected by autoradiography and its distribution studied by gradual removal of the oxide layer. Its distance from the surface can also be estimated by measurement of the energy of the emitted radiation at some point outside the surface . ... 

To study how living species interact with the environment, ecology, one can use radioactive tracers to follow the uptake of a trace metal (e.g. cobalt) from the soil by plants, and by animals after having eaten the plant. In agriculture, this is useful in studying the uptake of trace elements necessary for plant growth. For exan >le, it has been found that sheep need plants containing selenium in order to combat white muscle disease. The... 

Radiochemical methods of analysis are used in a wide range of analytical applications. Not only can these methods be used to obtain information regarding the nature and quantities of substances present in materials of interest, but radioactive elements can also be employed as tracers to study various physicochemical processes. Radioactive substances can be used to follow the movement of elements or of specific compounds in soils and plants, the absorption of elements in the body, and the selfdiffusion of lead atoms in metallic lead, among other applications. Although these tracer applications are of great practical value, the present chapter will be concerned only with applying radioactivity to determining the presence and quantity of elements and compounds in various materials—that is, the use of radioactivity in chemical analysis. 

For medical purposes, an enormous collection of techniques is accumulated regarding production of short-Kved nuclides mainly by cyclotrons. The technique should undoubtedly be usefiil for appKcation of radioactive tracers to other fields. Such nucKdes include F, and also many nucKdes of metals, halogens, and rare gases. Reactor and cyclotron production of medical radioisotopes is described in Chaps. 38 and 39 of VoL 4, respectively. Basic data for production of short-Kved nucKdes by cyclotron were compfled with substantial references by Qaim (1982). Another review by Waters and Silvester (1982) emphasizes cyclotron-produced nuclides useful for inorganic studies with many references, too. 

Distribution ratios. An example of the determination of distribution ratio in solvent extraction will show the simplicity of application of radioactive tracers to the study of chemical equilibrium. 

Uses of Isotopes Isotopes, especially radioactive isotopes, are used as tracers to study the mechanisms of chemical and biological reactions and as medical diagnostic tools. 

The study of atomic structure and the nucleus produced a new field of medicine called nuclear medicine. Describe the use of radioactive tracers to detect and treat diseases. 

Recently, Fahland and Herrmann (4) have studied the electrolytic deposition of metals from dilute solutions using radioactive tracers to follow concentration changes with the objective of checking the validity of equation (2.7). The concentration of metal ions in solution was found to decrease exponentially with time even for 10" m solutions of bismuth. As predicted, the electrolysis was accelerated by high temperatures, large cathode areas and small electrolyte volumes. 

The most widely used experimental method for determining surface excess quantities at the liquid-vapor interface makes use of radioactive tracers. The solute to be studied is labeled with a radioisotope that emits weak beta radiation, such as H, C, or One places a detector close to the surface of the solution and measures the intensity of beta radiation. Since the penetration range of such beta emitters is small (a ut 30 mg/cm for C, with most of the adsorption occurring in the first two-tenths of the range), the measured radioactivity corresponds to the surface region plus only a thin layer of solution (about 0.06 mm for C and even less for H). 

Special techniques for experimentation with the actinide elements other than Th and U have been devised because of the potential health ha2ard to the experimenter and the small amounts available (15). In addition, iavestigations are frequently carried out with the substance present ia very low coaceatratioa as a radioactive tracer. Such procedures coatiaue to be used to some exteat with the heaviest actinide elements, where only a few score atoms may be available they were used ia the earHest work for all the transuranium elements. Tracer studies offer a method for obtaining knowledge of oxidation states, formation of complex ions, and the solubiHty of various compounds. These techniques are not appHcable to crystallography, metallurgy, and spectroscopic studies. 

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