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  • Author or Editor: M. Vasconcellos x
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Abstract  

The radiotracer method was applied to evaluate the precision of themeasurements of abrasivity data obtained for dentifrice samples and for abrasiveagents (silica and calcium carbonate). This method consists of measuring 32P transferred to a dentifrice or abrasive slurry when an irradiated dentinis submitted to a brushing simulation. Results obtained for abrasivity indiceshad good precision with relative standard deviations lower than 11.8%. Comparisonsmade between our abrasivity index data with those obtained at the Oral HealthResearch Institute of Indiana University also showed a good agreement.

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Abstract  

Several radiochemical separations have been employed at the Radiochemistry Division of the Institute of Nuclear and Energy Research-Brazilian Nuclear Energy Commision, for the analysis of a number of elements in different kinds of matrices. In the present paper some of these separations applied to the analysis of geological samples, geological and biological reference materials and Brazilian foodstuffs are described. The separation procedures utilized are mainly ion exchange, retention in inorganic exchangers like HAP, TDO and HMD and solvent extraction.

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Abstract  

This paper describes an evaluation of activation analysis by delayed neutron counting to determine uranium and thorium simultaneously in geological materials and to measure235U/238U isotopic ratios. A procedure to isolate the thorium before the irradiation was studied and adapted for use when the interference of uranium makes the nondestructive thorium analysis impossible.235U/238U ratios were determined in standards with235U abundances from about 0.5 to 93%, in milligram size samples. Discussion on precision, accuracy and total error of the method is presented.

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Abstract  

The concentrations of Na, Cl, Mn, Br, Fe, Zn, Rb, Sb, Sc, Cr, Al and Mg were determined in some types of bread and in some brands of milk powder consumed in the city of São Paulo (SP—Brasil), by instrumental neutron activation analysis. Radiochemical separations were carried out by means of retention of24Na on hydrated antimony pentoxide (HAP) from a 8N HCl solution, after digestion of the organic matter. It was possible in this way to determine the radioisotopes64Cu,69mZn and140La in the effluent solution. The detection limits of the trace elements analyzed in bread and milk powder samples were determined using the Currie and Girardi criterions.

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Abstract  

Kinetic decay of paramagnetic species formed in the radiolysis of tetracycline hydrochloride in powder form, at 77 K, shows that most of the H· is not able to migrate. Geminate recombination between H· and its partner is the main reaction: H·+TC· TCH, although a few H· succeed in diffusing slowly. But when H· acquires enough kinetic energy to migrate, it reacts preferentially with species different from its partner. The e is not observed by ESR, at 77 K, although tetracycline hydrochloride is a chemical trap for e in methanol, benzyl alcohol and alkaline aqueous solutions. In the radiolysis of tetracycline hydrochloride in powder form, the dimethylammonium group blocks H· abstraction reaction at 77 K.

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Abstract  

The present study deals with the radiolysis of tetracycline hydrochloride dissolved in aerated alkaline aqueous solutions containing 0.1, 0.5 and 1M NaOH, at 77 K, as followed by ESR. The rate constants for the reactions between the electron and physical and chemical traps which are present in these solutions are calculated. These values are kph= =9.6·1015 l·mol–1·s–1 and kch=1.3·1010 l·mol–1·s–1. The reactivity of electrons that are formed in the radiolysis of water decreases in the following proportions: physical traps: chemical traps: molecules of water: 4.8·1014: 6.5·108: 1.0. The electrons react preferentially with the solute instead of the solvent.

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Abstract  

The radiolysis of tetracycline hydrochloride dissolved in benzyl alcohol has been studied at 77 K by ESR. The H. and e which are formed in the radiolysis of benzyl alcohol at 77 K migrate over a distance corresponding to about 95 and 995 molecules of solvent, respectively, before they are captured by the tetracycline hydrochloride solute. This distance corresponding to H. is smaller than the distance that it migrates in a neopentane matrix. The migration of H. in neopentane matrix is more favoured than in benzyl alcohol matrix. When the mole ratio between solute and solvent is 110000, the reactivity of H. observed by ESR is the following: a) 20% of H. reacts preferentially with solute because EH(sin )2 < (Emp)solvent; b) 80% of H. reacts exclusively with the solvent in the firsst collision because EH(sin )2 > (Emp)solvent. The crystal structure of benzyl alcohol presents inherent factors which do not favour the migration of H. at 77 K.

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Abstract  

The United States Geological Survey reference sample AGV-1 andesite, and three alkaline rocks from the apatite mine of Jacupiranga, Brasil, were analyzed by thermal neutron activation analysis using destructive and non-destructive methods, and high resolution Ge(Li) gamma-ray detectors. One of the rocks, a carbonatite, was also analyzed by instrumental activation analysis with epithermal neutrons. A greater number of elements can be determined using the radiochemical separation, but the precision and accuracy attained by INAA and RNAA were of the same order for most of the elements analyzed. Epithermal activation was more advantageous for tantalum, terbium and holmium. Comparison of the analytical results for USGS reference sample (AGV-1) with the data published by others gave good agreement. Statistical tests used for comparison of the results of destructive and non-destructive methods, as well as other results are presented.

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Abstract  

Instrumental neutron activation analysis was applied to the determination of the elements Na, K, Br, As, Rb, Zn, Co, Fe and Sc in Brazilian rice samples and in biological standards. Hg and Se concentrations were determined by using a simple radiochemical separation. The chemical procedure was carried out by means of distillation of Hg and Se in HBr medium and subsequent precipitation of selenium by sodium metabisulfite and mercury by thioacetamide. The accuracy of the instrumental and radiochemical methods was evaluated by means of analysis of the Reference Materials NBS-Bovine Liver, Bowen's Kale and NBS-Rice Flour.

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Summary  

Missouri University, a recipient of a U.S. Department of Energy Radiochemistry Education Award Program (REAP) grant in 1999, has significantly expanded its education and research mission in radiochemistry. While MU had a viable radiochemistry program through existing faculty expertise and the utilization of the Missouri University Research Reactor, the REAP award allowed MU to leverage its resources in significantly expanding capabilities in radiochemistry. Specifically, the grant enabled the: (1) hiring of a new faculty member in actinide radiochemistry (Dr. Paul Duval); (2) support of six graduate students in radiochemistry; (3) purchase of new radiochemistry laboratory equipment; (4) more extensive collaboration with DOE scientists through interactions with faculty and graduate students, and (5) revised radiochemical curriculum (joint courses across disciplines and new courses in actinide chemistry). The most significant impact of this award has been in encouraging interdisciplinary education and research. The proposal was initiated by a joint effort between Nuclear Engineering and Chemistry, but also included faculty in biochemistry, radiology, and molecular biology. Specific outcomes of the REAP grant thus far are: (1) increased educational and research capabilities in actinide chemistry (faculty hire and equipment acquisition); (2) increased integration of biochemistry and radiochemistry (e.g., radiochemical analysis of uranium speciation in biological systems); (3) stronger interdisciplinary integration of molecular biology and radiochemical sciences (alpha-emitters for treating cancer); (4) new and more extensive interactions with national laboratory facilities (e.g., student internships at LANL and LLBL, faculty and lab scientist exchange visits, analytical measurements and collaboration with the Advanced Photon Source), and (7) new research funding opportunities based on REAP partnership.

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