Stable and radioactive isotopes

All elements, by definition, have a unique proton number, but some also have a unique number of neutrons (at least, in naturally occurring forms) and therefore a unique atomic weight - examples are gold (Au Z = 79, N = 118, giving A =197), bismuth (Bi Z = 83, N = 126, A = 209), and at the lighter end of the scale, fluorine (F Z = 9, N = 10, A = 19) and sodium (Na Z = 11, N= 12, A = 23). Such behavior is, however, rare in the periodic table, where the vast majority of natural stable elements can exist with two or more different neutron numbers in their nucleus. These are termed isotopes. Isotopes of the same element have the same number of protons in their nucleus (and hence orbital electrons, and hence chemical properties), but 

In addition to these stable isotopes, many elements have one or more radioactively unstable isotopes, which are produced either as a result of specific nuclear processes (such as 14C, which is the result of the interaction of neutrons produced by cosmic radiation with 14N in the atmosphere) or as daughter 

The following particles are involved in natural radioactive decay. 

The nucleus of a helium atom ( He) is ejected from the parent nucleus, leaving it four mass units lighter, and its charge reduced by two protons  

This results in the transmutation of parent element X into daughter Y, which has an atomic number two less than X. The particular isotope of element Y which is formed is that with an atomic mass of four less than the original isotope of X. Note that, as in chemical reactions, these nuclear reactions must be numerically balanced on either side of the arrow. Many of the heavy elements in the three naturally occurring radioactive decay chains (see below) decay by a-emission. 

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Half-time, Biological—Time required for an organ, tissue, or the whole body to eliminate one-half of any absorbed substance by regular processes of elimination. This is the same for both stable and radioactive isotopes of a particular element, and is sometimes referred to as half-time, symbolized as tbiol or Tb. 

In the case of radioactive materials contained in living organisms, an additional consideration is made for the reduction in observed activity due to regular processes of elimination of the respective chemical or biochemical substance from the organism. This introduces a rate constant called the biological half-life (Tbioi) which is the time required for biological processes to eliminate one-half of the activity. This time is virtually the same for both stable and radioactive isotopes of any given element. 

The penetration depth of cosmic radiation is of the order of 1 m and therefore isotopes are produced by spallation only in the surface layers of meteorites and the moon. After collisions of meteorites with each other or with the moon, newly formed surfaces get exposed to cosmic radiation and production of stable and radioactive isotopes starts. If P is the production rate of a... 

Wolfe has presented an excellent description of the systematic application of stable and radioactive isotope tracers in determining the kinetics of leucine metabolism and other amino acids in living systems. 

Wolfe has presented an excellent description of the systematic application of stable and radioactive isotope tracers in determining the kinetics of substrate oxidation, carbon dioxide formation (including C02 breath tests), glucose oxidation, and fat oxidation in normal and diseased states. Quantification of the rate and extent of substrate oxidation can be achieved by using a specific or C-substrate which upon oxidation releases radioactive carbon dioxide. 

When discussing stable and radioactive isotopes, what is meant by the valley of P stability ... 

We can now construct a model that describes the evolution of the abundances of stable and radioactive isotopes in the gas phase of the galaxy as a function of time. Such as model provides an estimate of the abundances of the radioactive nuclides that should have been available in the average interstellar medium at the time the solar system formed. By comparing these predictions with the abundances inferred for the early solar system from meteorites, we can investigate the environment in which the solar system formed. 

Mazor, E., Verhagen, B. Th. (1983) Dissolved ions, stable and radioactive isotopes and noble gases in thermal waters of South Africa. J. Hydro ., 63, 315-29. 

While adequate Intestinal absorption Is clearly required to maintain zinc sufficiency, a number of different methods are presently used for Its measurement. Intestinal absorption has been measured by clinical balance studies, tracers (using both stable and radioactive Isotopes) and serum levels after Ingestion of pharmacologic doses of stable zinc compounds. Each can be useful, but each also has limitations and It Is Important to note that different methods. In reality, measure different aspects of absorption. While results are often reported as absorption, specific nomenclature has been developed to specify the results from each method of measurement(13,14). 

E, Tracer Methods. With the availability of both stable and radioactive isotopes and equipment for their analytic determination, a new method presents itself for the study of kinetic systems, in particular for equilibrium systems in which equilibrium has already been established. To avoid ambiguity, let us consider a specific system in which equilibrium has been established ... 

The differences between the radioactive and stable nuclide concentration factors may be due to the presence in the organism of slowly exchangeable or nonexchangeable compartments. Steady-state conditions of stable and radioactive isotopes would not be reached in such compartments during the period of most laboratory experiments, and the contribution of these compartments to the concentration factor would be overlooked. Because most stable element analyses do not distinguish compartments but give the total amount in all compartments, the concentration factor of a stable isotope would be larger than... 

Differences in concentration factors between stable and radioactive isotopes may result also from other factors. If more than one chemical form of the element are present in the environment, they may be subject to different turnover and concentration processes. Seasonal effects could result if different physicochemical forms dominate during parts of the year. 

Classical feeding experiments with both stable and radioactive isotopic labels (7) enabled the biosynthetic origin of the polyethers to be elucidated and for a general stereochemical model to be proposed (1). More recent work on this class of compounds has focused on a genetic approach, and unusual and interesting genes specific to polyether biosynthesis have been isolated from these clusters. 

Radioactivity is a part of nature—in the process of element formation by nuclear reactions taking place in stars, both stable and radioactive isotopes of elements are formed. The isotopic composition of elements is characterized by properties of nuclear reactions that led to the formation of the elements. Elemental composition of the planet Earth, thought to be about 4.5x 10 years old, although not yet in chemical equilibrium, reflects the composition of the material from which it was formed. Therefore, a number of radionuclides occur in nature, having long half-lives (longer than the age of Earth). In addition there are natural processes which continuously produce new radioisotopes. Recently, human activities have also contributed to the increased concentration of some of the radionuclides. 

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