RADIOACTIVE TRACER TECHNIQUES

The use of irradiated particles as tracers provides an accurate way to measure particle velocity it allows one to calibrate low-cost flowmeters such as the capacitive flowmeter. Unfortunately, in most industrial environments, it is not possible to produce short-lived radioactive tracers. At ANL, a nuclear research reactor was available for the production of radioactive particles. Ideally, the density and size of the tracer particles and the solids in the flow should be the same so the tracers can be uniformly distributed in the flow and represent the solids velocity distribution. For that purpose, the sample particles to be activated were fabricated from resin, hardener, and indium oxide powder to closely duplicate the size and density of the glass beads used in the flow tests. The particles, after irradiated in the reactor, had a 54-min half-life of y activity. Twenty particles were injected into the flow stream during the reloading of the feed hopper, becoming randomly mixed with the glass beads. 

The passage of each radioactive particle was registered by nine y detectors (Nal/Tl scintillation detectors), encased in lead shields and placed along the 

FIGURE 6-36 Typical irradiated-particle count rate distribution. 

The accuracy of the radioactive tracer velocity measurement was within 1.5%. Detector separation was measured to 0.02%, and the count rate peak locations were within 0.5% of the reading. The averaging of 15 particle velocity measurements reduced the typical velocity dispersion of 5.8% to 1.5%. 

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Radioactive tracer techniques. In electrochemistry, the procedure is essentially the same as in studies of chemical reactions the electroactive substance or medium (solvent, electrolyte) is labelled, the product of the electrode reaction is isolated and its activity is determined, indicating which part of the electroactive substance was incorporated into a given product or which other component of the electrolysed system participated in product formation. Measurement of the exchange current at an amalgam electrode by means of a labelled metal in the amalgam (see page 262) is based on a similar principle. 

Very few direct measurements of the reaction of surface silanol groups on quartz have been reported. This is apparently caused by the small effects due to the limited surface areas available. Adsorption of sodium ions on quartz was measured by radioactive tracer techniques by Gaudin et al. (293). Saturation was achieved at high pH (>10) and sodium ion concentrations above 0.07 Jlf. The calculated packing density of silanol groups was 4.25/100 A. Goates and Anderson (294) titrated quartz with aqueous sodium hydroxide and alcoholic sodium ethylate. The occurrence of two types of acidic groups was reported. 

Evans, J. C., R. J. Evans, A. Holmes, R. F. Hounam, D. M. Jones, A. Morgan, and M. Walsh (1973). Studies on the deposition of inhaled fibrous materials in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques. 1 UICC Crocidolite Asbestos. Environ. Res. 6 180-201. 

For many systems the equilibrium concentration of monomer is expected to be extremely low and one may attempt to use the radioactive tracer technique to determine its value. The method requires some refinements because even a small isotope effect might affect considerably the final result. The following calculation illustrates this point. 

Inspection of Hand Grenade Fuse Delay Element By A Radioactive Tracer Technique (Ref 14)... 

Helf J.W, McCahill, Recovery of Ammunition Items Using a Radioactive Tracer Technique , PATR 3489 (1967) 13) J.F. Wakeman B. 

Revs 27,199-285( 1940) (ca 600 refs)( Artificial radioactivity) 6)G.vonHevesy, "Radio active Indicators, Interscience, NY(1948) 7)G.K.Schweitzer, "Radioactive Tracer Techniques, Van No strand, MY(1949) 8)... 

Fig. 9.12 Experimental verification of the RTD function in extruder by radioactive tracer techniques with a 44.2-mm-diameter, 24 1 L/D extruder, liquid polyester resin, and a radioactive manganese dioxide tracer Asterisk, Experiment 1 , Experiment 2 smooth curve indicates theoretical prediction. [Reprinted by permission from D. Wolf and D. H. White, Experimental Study of the Residence Time Distribution in Plasticating Screw Extruders, AIChE J., 22, 122-131 (1976).]...

Berthier et al. (84) studied sulfur adsorption on Pt(100), (110), and (111) planes, using LEED, AES, and H235S radioactive tracer techniques. The stable saturated 2-D sulfide phases on the (100), (110), and (111) planes contained 6.6 x 1014, 6.0 x 1014, and 5.5 x 1014 S atoms/cm2, respectively. Although their results suggest surface reconstruction, this question was not resolved in the discussion of results. If in a manner similar to that for Ni, we calculate the site density of surface Pt atoms for the Pt(100) plane, 1.3 x 1015 Pt atoms/cm2 (146), and use it as the basis for calculating 0 for saturation... 

A radioactive tracer technique was ultimately chosen as a mapping tool. The isotope Kr-85 was selected because it can represent the gaseous, vaporous and solid materials in the reactor. Being an inert gas it does not interact chemically with any of the species present. It is readily dispersible... 

Haley TJ, Hunziker J (1974) Instrument for producing standardized skin abrasions. J Pharm Sci 63 106 Mezei M, Sager RW, Stewart WD, DeRuyter AL (1966) Der-matitic effect of nonionic surfactants. I. Gross, microscopic, and metabolic changes in rabbit skin treated with nonionic surface-active agents. J Pharm Sci 55(6) 584-590 Mezei M (1970) Dermatitic effect of nonionic surfactants. V. The effect of nonionic surfactants on rabbit skin as evaluated by radioactive tracer techniques in vivo. J Invest Dermatol 54 510-517... 

A peeling method, in conjunction with a radioactive tracer technique, was used to obtain actual profiles of DOP concentration developed through the matrix of a PVC disc dipped into a limited volume of olive oil. The plasticiser concentration distributions were reproduced to a good approximation using a known model, adjusted by neglecting the (small) amounts of oil which diffused into the polymer. 17 refs. 

Ostergaard and Michelsen104 measured the gas holdup in beds of 0.25-, 1-, and 6-mm glass particles using a radioactive tracer technique. They found that hG °c Uqg, where U0G is the superficial gas velocity, and n took values of 0.88, 0.78, and 0.93, respectively, for three particle sizes. The solid-free bubble-column gave n = 1.05. They also found that, in the solid-free system and in beds of 6-mm particles, the gas holdup decreased with increasing liquid flow rate whereas in beds of 0.25- and 1-mm particles, the gas holdup increased with increasing liquid flow rate. 

Morgan A, Collier CG, Morris KJ, et al. 1993. A radioactive tracer technique to determine in vivo the number of fibers in the lungs of rats following their administration by intratracheal instillation. Environ Res 63(2) 182-190. 

Experimental studies of aging usually employ radioactive-tracer techniques for observation of exchange of ions between precipitate and solution, the adsorption of suitable dyes on the surface of a precipitate to measure the extent of the specific surface, microscopic or x-ray observation of the precipitate, or a combination of these. 

Number of C fCp) and their reactivity in a propagation reaction (propagation rate constant kp). Cp data can be used to determine the mole fraction of active metal centers, the localization of active centers on the surface of the solid catalyst, and the role of individual components of the catalytic system in the formation of active centers. Systematic data on the influence of the catalyst composition and polymerization conditions on Cp and the rate constants of individual steps are important for the determination of the composition of the active centers and the elucidation of the mechanism of these steps. Various methods for determining Cp and kp in catalytic polymerizations of olefins have been reported A direct method for the determination of Cp is the radioactive tracer technique. In this method radioactive compounds react with the AC thus introducing radioactivity into the growing polymer chain. The use of radioactive alcohols is the classical example of this technique... 

One application of radioactive tracer techniques of considerable importance in solid state structural problems is the emanation method due to Hahn (21). The method has been employed widely and has been developed recently as a sensitive, quantitative method by Gregory (22), who has employed it for the investigation of structural changes and for the extraction of diffusion data. The procedure in outline is as follows A convenient amount of a radioactive element which decays to an isotope of radon (e.g., radiothorium) is ccprecipitated... 

An extensive use of radioactive tracer technique permits a deeper insight into the formation of the tropane skeleton in vivo. Hyoscyamine-(methyl-i C) (76), atropine- C, tropic acid-i C (77), and succindi-aldehyde-2,3-i4C (78) were synthesized. The last was not incorporated at all by D. stramonium seedlings (78), while the former feeding experiments with ornithine-a-i4C proved its incorporation into hyoscyamine (79) hjD. stramonium (see Volume VI, pp. 172-173). More recently two independent teams (80, 81) reported that this incorporation takes place asymmetrically. 

Some insight into the mechanisms of the iodine-promoted carbonylation has been obtained by radioactive tracer techniques [17] and low-temperature NMR spectroscopy [18]. The mechanism involves the formation of HI, which in a series of reactions forms with rhodium a hydrido iodo complex which reacts with ethylene to give an ethyl complex. Carbonylation and reductive elimination yield propionic acid iodide. The acid itself is then obtained after hydrolysis. The rate of carboxylation was reported to be accelerated by the addition of minor amounts of iron, cobalt, or manganese iodide [19]. The rhodium catalyst can be stabilized by triphenyl phosphite [20]. However, it is doubtful whether the ligand itself would meet the requirements of an industrial-scale process. 

The existence of such carbonaceous overlayers has also been explored using radioactive tracer techniques.By use of Pd/SiOa, Rh/Si02, and Pd/Al203, it was shown that adsorption of ethylene and acetylene occurred in two distinct stages at 298 K a non-linear irreversible region and a linear second region. The non-linear region was found to correspond to a mono-layer. 

Other than a brief collaboration with S. AronofF, A. Benson, and M. Calvin (1947) on the distribution of label in photosynthesizing plant-tissue, this short sojourn by Hassid in the field of photosynthesis was not continued, and his involvement appears to have been based more on an interest in carbohydrate structural analysis than in the fundamentals of carbon fixation in plants. However, it is apparent from the later turn of events that this introduction to the utility of radioactive-tracer techniques for the elucidation of biochemical processes had a strong influence on his development. 

Solvent extraction (Nd, Eu, Yb, Am) using radioactive tracer techniques. 

Gunnarsson, M. et al.. Sorption studies of cobaltfll) on colloidal hematite using potentiometry and radioactive tracer technique, J. Colloid Interf. Sci., 231, 326, 2000. 

A comprehensive account of the methods used in cellulose chemistry has been published. It includes the preparation and reactions of cellulose and its esters and ethers, chemical and physical anal3rsis, microscopy, and radioactive-tracer techniques. 

Radioactive tracer techniques have been used to study the absorption of various ions by cellulose from salt solutions and from dyebaths. Measurements have been made on the absorption of Na and SO4 ions from Na2S04 solutions at 25°C and at 90 C and from Na2S04 solutions containing a direct dye at 90°C. Measurements of the amount of dye absorbed were made using conventional techniques. The absorption of Br from NaBr solutions was also studied. 

All of the salt absorption measurements were made using radioactive tracer techniques dye uptakes were measured by a change-of-concentration method. Details of each method are given below. 

At present the mechanism of complex processes may be investigated by the more precise radioactive tracer technique. The genetic relationship between individual reaction products may be determined by using this technique together with kinetic studies. The origin of reaction products and the rates of individual reactions involved in the overall process may be established by C14-labeling of the hydrocarbon molecules, or of the products suggested as intermediates. 

It may be considered on the basis of data obtained by means of the radioactive tracer technique that the various stable oxygen-containing products on semiconducting oxides are generated by different routes, through active intermediates. 

The nature of oxygen contribution to the oxidation process may be established by using the radioactive tracer technique. The reduction-oxidation mechanism of reactions is a function of the lattice oxygen mobility. Vainstein and Turovskii (86) investigated the distribution of O18 in the oxidation of carbon monoxide over MnOa and CuO and found that there will be no transfer of the catalyst oxygen to the reaction products, when water is carefully removed from the solid oxides. 

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