Basic Principles of Radioactivity

The experimentally measured rates of decay of radioactive atoms shows that their decay is first order, where the number of atoms decomposing in a unit of time is proportional to the number present—this can be expressed in the following equation (Faure, 1986)  

We can then substitute into equation 7.2 to obtain the following equation  

In addition to X, another term used for characterizing rate of decay is half-life (ty2), the time required for half of the initial number of atoms to decay. If we substitute t = ty2 and N = Nq 2 into equation 7.5 we obtain the following equation  

Finally, the term used to examine the average life expectancy, or mean life (rm), of a radioactive atom is expressed as follows  

On the assumption that the radioactive parent atom produces a stable radiogenic daughter (D ), that is zero at t = 0, we can describe the number of daughter atoms at any time with the following equation  

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The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

Powsncr, E.R. (1994) Basic principles of radioactivity and its measurement. In Tietz Textbook of Clinical Chemistry (C.A. Burtis, and E.R. Ashwood, eds.), pp. 256-282. Saunders, Pennsylvania, Philadelphia. 

With the development of radioimmunoassays (RIAs) in the 1960s that used radioactive isotopes as labels (see Chapter 9), the measurement of radioactivity became a common and important practice in clinical laboratories. However, concerns about, and problems with, the safe handhng and disposal of radioactive reagents and waste have led to the development of immunoassays that use nonisotopic labels (see Chapter 9). The rapid acceptance and extensive use of nonisotopic immunoassays by the clinical laboratory have resulted in a decreased use of RIA and ultimately a decreased requirement for them to measure radioactivity. Because of this deemphasis on the necessity to measure radioactivity, only a brief discussion of the topic is presented here. Readers requiring more detail on this topic are referred to the chapter entitled Basic Principles of Radioactivity and Its Measurement that is included in a prior edition of this textbook, ... 

Powsner ER, Widman JC. Basic Principles of Radioactivity and Its Measurement. In Burtis CA, Ashwood ER, eds. Tietz textbook of clinical chemistry, ed. Philadelphia W B Saunders, 1999 113-132. 

The principle of supercritical wet oxidation can be applied to several areas, including municipal waste treatment, chemical waste treatment, polymeric waste treatment, and the treatment of mildly radioactive waste. Since the basic principle of wet oxidation involves the rapid oxidation of organic material, any substance which is mildly oxidative can be subjected to this process. With such high temperature operation, the remaining fraction of inorganic material can be simply precipitated as a salt and then easily collected from the bottom of the oxidation vessel. 

All absolute dating methods that have proven dependable are based on radioactive decay. Virtually all of the methods depend on the methodical decrease in the amount of the radioactive nuclide and the growth of the corresponding daughter product. The one exception is in the area of radiation-induced damage in solids, which is the basis of thermoluminescence or ESR dating. This latter scheme will be dealt with later in the chapter. Here the basic principles of canonical radioactive geochronometry as applied to marine deposits is reviewed. 

Gray, Harry B., John D. Simon, and William C. Trogler. Braving the Elements. Sausalito, Calif. University Science Books, 1995. This book is an introduction to the basic principles of chemistry, with elementary explanations of radioactive decay, chemical bonding, oxidation-reduction reactions, and acid-base chemistry. Practical applications of specific chemical compounds and classes of compounds are presented. 

Microbalances used to be very tridqr instruments and only very skilled workers could hope to obtain reproducible results. The basic principle of most types is the torsion of a fiber (steel or quartz), its deflection being read with special optics. Cefola (C5) described a fish-pole balance which has been used in the isolation of plutonium. (A great number of ultramicro techniques now generally known originate from research on radioactive chemicals.) The development of these balances and the use of new principles (electric balances) bring the possibility of accurate weighing to the level of the laboratory technician. 

In 1903, with the scientist Frederick Soddy, Rutherford concluded that radiation was caused by atoms of radioactive material breaking apart. The tiny bits that broke off were the a and (3 rays. This was a revolutionary idea, since it had been a basic principle of physics and chemistry that atoms were the smallest possible particles of matter and therefore indivisible. Rutherford went on to demonstrate that a-particles were, in fact, a form of the helium atom. He did this by placing a delicate glass bulb containing radon gas, which emitted a-particles, in an evacuated tube. The particles would penetrate the glass of the bulb but not escape the tube, and could then be analyzed. 

The basic principle of the VK-300 safety design is consistent implementation of the defence-in-depth concept based on a system of physical barriers to ionizing radiation and radioactive substance propagation to the environment. The system of barriers incorporates ... 

Radioactive waste management is a quite mature field of application of basic geoscientific disciplines. As we will discuss in forthcoming sections, the long-term performance and henceforth the safety of radioactive waste disposal systems, deeply relies on the basic principles that control the release, mobility, and transport of the chemical elements in the geosphere. In the context of radioactive waste disposal, the waste matrix constitutes the innermost of the barriers that may control the release and ulterior transport of radionuclides through the ground-water systems. 

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. 

To reliably perform qualitative and quantitative analyses on body fluids and tissue, the clinical laboratorian must understand the basic principles and procedures that affect the analytical process and operation of the clinical laboratory. These include the knowledge of (1) the concept of solute and solvent, (2) units of measurement, (3) chemicals and reference materials, (4) basic techniques, such as volumetric sampling and dispensing, centrifugation, measurement of radioactivity, gravimetry, thermometry, buffer solution, and processing of solutions, and (5) safety. ... 

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