Radioisotope A radioactive isotope

Radioisotope A radioactive isotope of an element. Radionuclide A radioactive nuchde. 

A radioactive isotope (radioisotope) is an unstable isotope of an element that decays into a more stable isotope of the same element. They are of great use in medicine as tracers (to help monitor particular atoms in chemical and biological reactions) for the purpose of diagnosis (such as imaging) and treatment. Iodine (-131 and -123) and Technetium-99 are used for their short half-lives. 

The half-life is the time it takes for half of a given amount of a radioactive isotope to undergo decay. Half-life, which is symbolized ti/2, is easy to measure and has been determined for many different radioisotopes, some of which have important uses. Some half-lives are only fractions of a second, whereas others are billions of years. Half-lives for some of the most commonly used radioisotopes are listed in Table 21.1. The concept of half-life is illustrated in the graph in Figure 21.7. 

Radioisotopes used as tracers solve scientific mysteries Radioactive and nonradioactive isotopes of the same element act the same way in a chemical reaction. When scientists want to put tags on a compound, they substitute a radioactive isotope for a nonradioactive one in the compound. Then they can use radiation detectors to track and locate the radioisotope tracer. 

The term radiometric analysis is often used in a broad sense to include all methods of determination of concentrations using radioactive tracers. In a more restricted sense it refers to a specific analytical method which is based on a two-phase titration in the presence of a radioactive isotope. The endpoint of the titration is indicated by the disappearance of the radioisotope from one of the phases. Figure 9.4 illustrates two cases, (a) the determination of Ag in a solution by titration with Nal solution containing ( y t 1.57x10 y),and (b) the determination of Fe in an aqueous solution, to which trace amounts of radioactive Fe (EC 2.73 y) has been added. In case (a) the Agl precipitate is radioactive but the solution has little radioactivity until all the Ag has been precipitated. The activity of the solution is measured by a liquid flow GM-detector (Ch. 8). In the latter case (b) a two-phase liquid-liquid analytical technique is used ( 9.2.6) the titrant contains a substance (oxine) which extracts Fe(II) from the aqueous to the chloroform phase. The radioactivity of the organic phase is followed by liquid scintillation (sampling) to determine the end point of the titration. 

Radionuclide is a shortened form of radioactive nuclide , practically synonymous with radioisotope or radioactive isotope . A particular chemical element may consist of a number of nuclides, some of which may be radionuclides, characterized by the name of the chemical element followed by a number denoting the atomic mass of the nuclide in question, e.g. cobalt-60 and uranium-235. IMO Class 7, 2.20... 

For instance, a common technique to measure diffusion coefficient D is to deposit a very thin layer of a radioactive isotope (or mass isotope) on a flat surface of a thick sample, which is then annealed at a given temperature for a given time duration. By measuring the concentration of the diffusing species as a function of distance, the diffusion coefficient can be determined. In this case, the experimental system is a semi-inflnite solid. If the initial thickness of the radioisotope layer is sufficiently small as compared with the diffusing distance of the radioisotope, the solution of Eq. (5.37) is given by ... 

In neutron activation analysis, an activation of a sample material is accomplished by placing the sample in some position within the neutron environment. At the time the sample is exposed to neutrons, a compound nucleus is formed as the result of the interaction of a neutron with the nucleus of a stable isotope of the element being determined. The compound nucleus i.e. the end-product of an excitation process caused by both the kinetic and binding energy of the neutron with the nucleus, instantaneously loses its excess energy by a transformation to a more stable isotope by emitting prompt radiations. As a result of this event, another stable nuclide or a radioactive isotope is formed. This radioisotope then becomes the activation, or isotopic, indicator of the element of interest. 

Today, many radioisotopes are prodneed in small amounts by converting stable, nonradioaclive isotopes into radioactive ones. In a process called transmutation, a stable nucleus is bombarded by high-speed particles such as alpha particles, protons, neutrons, and small nuclei. When one of these particles is absorbed, the stable nucleus is converted to a radioactive isotope and usually some type of radiation particle. 

What is a radioisotope When a combination of neutrons and protons, which does not already exist in nature, is produced artificially, the atom will be unstable and is called a radioactive isotope or radioisotope. There are also a number of unstable natural isotopes arising from the decay of primordial uranium and thorium. Overall there are some 1800 radioisotopes. At present there are up to 200 radioisotopes used on a regular basis, and most must be produced artificially. 

Gamma-ray sources can also be used without the need for an elaborate power supply, allowing use in small portable instruments. The sources include a radioactive isotope which supply gamma rays with characteristic energy and can supply an X-ray or gamma-ray beam with the flux of 10 photons s sr . The main advantages of radioisotope excitation over X-ray tube excitation are the monoenergetic character of radioisotope-emitted X-rays, and that it is an inexpensive technique that is easily commercially available. 

It is not necessary that there be two isotopes in both the sample and the spike. One isotope in the sample needs to be measured, but the spike can have one isotope of the same element that has been produced artificially. The latter is often a long-lived radioisotope. For example, and are radioactive and all occur naturally. The radioactive isotope does not occur naturally but is made artificially by irradiation of Th with neutrons. Since it is commercially available, this last isotope is often used as a spike for isotope-dilution analysis of natural uranium materials by comparison with the most abundant isotope ( U). 

Radiocarbon dating (43) has probably gained the widest general recognition (see Radioisotopes). Developed in the late 1940s, it depends on the formation of the radioactive isotope and its decay, with a half-life of 5730 yr. After forms in the upper stratosphere through nuclear reactions of... 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

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