Tracer emissions

Bour ne and Le Calvd used pulse radiolysis to study the quenching of metastable Ar states by a wide range of reagents these workers monitored the excited atoms by tracer emission from added Na,... 

Validating the final experimental protocol was accomplished by running a model study in which Nd was released into the atmosphere from a 100-MW coal utility boiler. Samples were collected at 13 locations, all of which were 20 km from the source. Experimental results were compared with predictions determined by the rate at which the tracer was released and the known dispersion of the emissions. 

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. 

A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

The methods for detection and quantitation of radiolabeled tracers are deterrnined by the type of emission, ie, y-, or x-rays, the tracer affords the energy of the emission and the efficiency of the system by which it is measured. Detection of radioactivity can be achieved in all cases using the Geiger counter. However, in the case of the radionucHdes that emit low energy betas such as H, large amounts of isotopes are required for detection and accurate quantitation of a signal. This is in most cases undesirable and impractical. Thus, more sensitive and reproducible methods of detection and quantitation have been developed. 

The detection and determination of traces of cobalt is of concern in such diverse areas as soflds, plants, fertilizers (qv), stainless and other steels for nuclear energy equipment (see Steel), high purity fissile materials (U, Th), refractory metals (Ta, Nb, Mo, and W), and semiconductors (qv). Useful techniques are spectrophotometry, polarography, emission spectrography, flame photometry, x-ray fluorescence, activation analysis, tracers, and mass spectrography, chromatography, and ion exchange (19) (see Analytical TffiTHODS Spectroscopy, optical Trace and residue analysis). 

The neutron activation technique mentioned in the preceding paragraph is only one of a range of nuclear methods used in the study of solids - methods which depend on the response of atomic nuclei to radiation or to the emission of radiation by the nuclei. Radioactive isotopes ( tracers ) of course have been used in research ever since von Hevesy s pioneering measurements of diffusion (Section 4.2.2). These techniques have become a field of study in their own right and a number of physics laboratories, as for instance the Second Physical Institute at the University of Gottingen, focus on the development of such techniques. This family of techniques, as applied to the study of condensed matter, is well surveyed in a specialised text... 

European Standard EN 1093-4. Safety of machinery—Evaluation of the emission of airborne hazardous substances. Part 4 Capture efficiency of an exhaust system— Tracer method. 1996. 

Experiments on the scale of 1 to 1 are often used to study the local ventilation around an operator s workplace. Tracer gas is used to simulate the contaminant transport, and a high concentration level of the model tracer gas makes it possible to work with a convenient level of concentration for the measurements. Figure 12.31 shows an enclosure with an emission source S and a laboratory. setup with a model source 5,. The dimensionless concentration c/cg is... 

Its terrestrial abundance has been estimated as 2x10" ppm, which corresponds to a total of only 15g in the top 1km of the earth s crust. Other isotopes have since been produced by nuclear reactions but all have shorter half-lives than Fr, which decays by energetic emission, t j2 21.8 min. Because of this intense radioactivity it is only possible to work with tracer amounts of the element. 

Positron emission tomography (PET) A medical imaging technique that helps physicians locate tumors and other growths in the body. A radioactive tracer isotope which emits a positron is incorporated into a metaholically active molecule. A scanner locates the tissues where the radioactive substance winds up. 

Methane emission from ruminants can be estimated by using the ERUCT technique (Emissions from Ruminants Using a Calibrated Tracer). The tracer can either be isotopic or nonisotopic. Isotopic tracer techniques generally require simple experimental designs and relatively straightforward calculations [31]. Isotopic methods involve the use of (3H-)CH4 or (14C-)CH4 and ruminally cannulated animals. 

Whitaker, J.E., fdaugland, R.P., Moore, P.L., Hewitt, P.C., Reese, M., and Haugland, R.P. (1991) Cascade blue derivatives Water soluble, reactive, blue emission dyes evaluated as fluorescent labels and tracers. 

Elution volume calibrations were performed using radioactive tracers of the rare earth elements and 133Ba, with atomic-absorption or flame-emission analysis of iron, sodium, potassium, calcium, and magnesium. As shown in Fig. 5.14, any barium added to the second columns is eluted at the start of the light rare earth element fraction . To ensure barium removal the sample can be put through the first column again. 

Klunk, W. E., Engler, H., Nordberg, A. et al. Imaging brain amyloid in Alzheimer s disease using the novel positron emission tomography tracer, Pittsburgh Compound-B. Ann. Neurol. 55 1-14, 2004. 

Radical trapping studies, 14 277 Radicidation, 8 655 Radioactive decay, 21 287—288 particles associated with, 21 291 Radioactive decay properties of uranium isotopes, 25 393 Radioactive emission, interaction with tracer molecules, 21 276 Radioactive iodine, protection from,... 

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