Tracer technology

Tracer technology Tracheography Trachoma Track pitch Traction Tractors... 

Many applications ia tracer technology require products of high specific activity, ie, compounds having a high degree of substitution of specific atoms with radioisotopes. For many labeled compounds nearly 100% labeling can be achieved at one or more locations ia a molecule usiag... 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

Concerns over safe handling of radioactive materials and issues around the cost and disposal of low level radioactive waste has stimulated the development of nonradiometric products and technologies with the aim of replacing radioactive tracers in research and medical diagnosis (25). However, for many of the appHcations described, radioactive tracer technology is expected to continue to be widely used because of its sensitivity and specificity when compared with colorimetric, fluorescent, or chemiluminescent detection methods. 

Davenport, J. E., and H. B. Singh, Systematic Development of Reactive Tracer Technology to Determine Hydroxyl Radical Concentrations in the Troposphere, Atmos. Environ., 21, 1969-1981 (1987). 

Stable Activable Tracers. To overcome many of these problems and to open new possibilities of tracer use for the environmental scientist, there has been renewed interest in developing stable activable tracer technologies that will be attractive alternatives to conventional tracers. This chapter reviews some of these developments with illustrative examples from the author s published and impublished work. 

The rare earth tracers, especially those with short-lived activation products, are cost-competitive with other t) es of tracers. Tables I and II show typical rare earth stable activable tracers and the total cost of using them in tracing water pollutants. These cost estimates are, of course, rough approximations and are intended to demonstrate that the costs associated with different tracer technologies are similar. Also note, as shown in Table I, the small amounts of tracer that can be easily detected (give 10 counts). These detection sensitivities are emphasized further when one notes that the natural concentrations of the rare earths in fresh water are (17) in the ppt-ppb range and the atmospheric concentrations (19) are around 10" ng/m . 

Biospheric Applications. The current controversies about the dispersal of herbicides used in forestry have demanded the immediate implementation of tracer techniques that can be used in connection vsdth herbicide dispersal. As a result, we have developed a quick and dirty tracer technology. The success of our eflFort has certain consequences concerning strategies for monitoring herbicide dispersal and for establishing legal responsibility for its consequences. 

With the advent of textbooks and manuals prepared for courses on the subject of tracer technology, the biological scientist has available a considerable literature on radionuclide techniques. Among these are Arena (1971), G. D. Chase and Rabinowitz (1962), G. D. Chase et al. (1964,1971), Fakes and Parks (1973), Hendee (1973a), Tiwari (1974), Wang and Willis (1965), and Wolfe (1964). In addition, a considerable number of literature reviews on the general... 

Many studies have been conducted on the biological uptake and retention of fission and neutron-activation products in organisms, including man and domestic plants and animals. We will consider a limited selection of studies using wild organisms to illustrate this use of tracer technology. 

With the application of isotope tracer technology to this biosynthetic problem, more definitive information regarding precursors and possible routes of synthesis of the three moieties has gradually evolved. 

Photochemical technology Photoconductive polymers Photography Printing processes Radioactive tracers Radiopaques... 

Radiochemical tracers, compounds labeled with radioisotopes (qv), have become one of the most powerful tools for detection and analysis in research, and to a limited extent in clinical diagnosis (see Medical IMAGING TECHNOLOGY). A molecule or chemical is labeled using a radioisotope either by substituting a radioactive atom for a corresponding stable atom in the compound, such as substituting for H, for or for P, and for for... 

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 use of radioactive tracers was pioneered by Georg von Hevesy, a Hungarian physical chemist, who received the Nobel Prize in 1943 for his work on radioactive indicators (1). Radioisotopes have become indispensable components of most medical and life science research strategies, and in addition the technology is the basis for numerous industries focused on the production and detection of radioactive tracers. Thousands of radioactive tracers have been synthesized and are commercially available. These are used worldwide in tens of thousands of research laboratories. 

Technetium-99m coordination compounds are used very widely as noniavasive imaging tools (35) (see Imaging technology Radioactive tracers). Different coordination species concentrate ia different organs. Several of the [Tc O(chelate)2] types have been used. In fact, the large majority of nuclear medicine scans ia the United States are of technetium-99m complexes. Moreover, chiral transition-metal complexes have been used to probe nucleic acid stmcture (see Nucleic acids). For example, the two chiral isomers of tris(1,10-phenanthroline)mthenium (IT) [24162-09-2] (14) iateract differentiy with DNA. These compounds are enantioselective and provide an addition tool for DNA stmctural iaterpretation (36). 

Therefore, fluorescent nano-particles can be used as the tracer in studying micro-fluids. The visualizing approach to nano-flow is not very mature and more experiments should be practiced. Because of its wide connection to modem technologies, the research of the solid-liquid two-phase flow will attract more and more attention. 

Khalil MAK, Rasmussen RA. 1983. Gaseous tracers of arctic haze. Environmental Science and Technology 17 157-164. 

We conclude that recent advances in the use of tracers, albeit C or C, offer a solution to some of the technological difficulties in quantifying and separating microbial from root respiration. Combinations of these tracers may even overcome the last of the problems in discriminating between all three sources of COt released from soil. 

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