Radioactive isotope specification

Radioactive isotopes show excellent properties as tracers since they are detectable in very low concentrations (i.e. high dilution) and with high specificity. Further y-emitting radioactive tracers can be measured in situ, through pipe and vessel walls which enables e.g. studies of processes under high pressures, and processes involving a gaseous phase. 

Nuclear activation analysis (NAA) is a method for qualitatively and quantitatively detg elemental compn by means of nuclear transmutations. The method involves the irradiation or bombardment of samples with nuclear particles or high-energy electromagnetic radiation for the specific purpose of creating radioactive isotopes from the stable or naturally-occurring elements present. From the numbers, types and quantities of radioactive elements or radionuclides, it is possible to deduce information about the elemental compn of the original sample... 

Because exposure to radiation is a health risk, the administration of radioactive isotopes must be monitored and controlled carefully. Isotopes that emit alpha or beta particles are not used for Imaging, because these radiations cause substantial tissue damage. Specificity for a target organ is essential so that the amount of radioactive material can be kept as low as possible. In addition, an Isotope for medical Imaging must have a decay rate that is slow enough to allow time to make and administer the tracer compound, yet fast enough rid the body of radioactivity in as short a time as possible. 

If a known amount of an isotope with a known specific activity is mixed with an unknown amount of the non-radioactive substance, the reduction in the specific activity can be used to determine the degree of dilution of the isotope and, hence, the amount of the non-radioactive isotope present. The isotope and the test substance must be thoroughly mixed before a representative sample of the mixture is purified and its specific activity determined. 

The mixture with the non-radioactive isotope contains the same total activity but the amount of the substance is increased. Hence the specific activity is reduced to ... 

It involves the simultaneous irradiation of the sample and a standard known mass of the same element to produce a radioactive isotope of the element. The activities of both the sample and the standard are then determined and, because their specific activities will be the same, it is possible to calculate the mass of the unknown sample. 

In this type of radiometric analysis, a tracer quantity of a radioactive isotope is added to the analyte, which is then partly extracted using a specific extractant. Since the extractant may be considered as reacting totally with the analyte, the ratio of radioactivity in both phases provides the concentration of analyte in the sample. This method, first developed by Stary [2], has proved to be useful in several 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. 

A second possibility is the modification (conjugation) of an antibody by a label, e.g., biotin, which is detected later on by a specific receptor, e.g., (strept)avidin. In each case the last part of such a cascade has to carry a measurable label. Such labels are enzymes, fluorescent dyes, colloids, radioactive isotopes, paramagnetic substances, and others. 

One of the more important factors affecting the isolation of radioactive waste is the rate of release of the radioactivity from the solid waste form to the environment. The most probable mechanism for release and transport of radioactivity from a solid waste form is by leaching of radioactive isotopes with groundwater. The objective of leach-testing various waste forms is to evaluate the rate at which specific hazardous radionuclides migrate from waste if and when the waste form comes in contact with groundwater. In this paper, measurement of leach rates of radioactive waste by a method which incorporates neutron activation is described. 

It is evident from Table 1 that certain limiting factors exist. For example, experiments with bromine-82 are limited to a duration of about one week because of the short half-life. At the other end of the scale, experiments with stable carbon-13 are limited to dilutions of less than x 500. Even with radioactive isotopes the maximum specific activity available may limit dilution though not to the same extent. Thus, chlorine-36 can stand dilutions up to x 107 but tritium can improve on this to a factor of x 1012. 

A large variety of materials has been used as tracers. Dyes, soluble inorganic compounds such as table salt, radioactive isotopes, and organic compounds having specific detectability are examples. Even changes in physical properties have been used successfully. 

A specific example further clarifies the activation and electron transfer steps. The exchange reaction between solvated Feflll) and Feflll has been studied with radioactive isotopes (Fe ) of iron.36... 

Precipitation of Hafnium Hydroxide. In order to interpret the adsorption data it was necessary to determine the conditions which lead to the precipitation of hafnium hydroxide. It is not usually advisable to depend on the solubility product because the information on this quantity is often unreliable for hydroxides of polyvalent metal ions. In addition, "radiocolloids may apparently form much below saturation conditions in radioactive isotope solutions. In the specific case of hafnium hydroxide only two measurements of the solubility seem to have been reported. According to Larson and Gammill (16) K8 = [Hf(OH)22+] [OH ]2 — 4 X 10"26 assuming the existence of only one hydrolyzed species Hf(OH)22+. The second reported value is Kso = [Hf4+] [OH-]4 = 3.7 X 10 55 (15). If one uses the solubility data by Larson and Gammill (Ref. 16, Tables I and III) and takes into consideration all monomeric hafnium species (23) a KBO value of 4 X 10 58 is calculated. 

All radioactive materials should be stored in well-labeled, glass containers. The label must include your name, the type of isotope, the radioactive compound, the total amount of radioactivity, the specific activity, and the date of measurement. 

It should be stressed that u, as the standard for comparing the masses (weights) of all chemical elements in all kinds of chemical compounds, refers not simply to tlie carbon atom, but rather to one very specific isotope, carbon-12. There are two stable isotopes of carbon, 12C and 13C, and four known radioactive isotopes, 1(,C, 1C, 14C, and 15 C. 

In a specimen of a monomer labelled with carbon-14 or other radioactive isotope, only a small fraction of the molecules actually contain an atom of the isotope if only part of the labelled monomer is polymerized, the specific activity of the part which has reacted may be a little different from that of the residual monomer because of a kinetic isotope effect. The polymerization of a labelled monomer might therefore be regarded as a co-polymerization with a drift in the composition of the feed. This effect has been examined by comparing the polymerizations of unlabelled styrene, a-14C-styrene and /3-14C-styrene in both radical and cationic reactions (18). 

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