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  • Author or Editor: A. Figueiredo x
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Abstract  

Radiochemical neutron activation method is presented for the determination of iridium in geological materials. The procedure consisted of thermal neutron irradiation of an 500 mg sample followed by sinterization with sodium peroxide, precipitation with tellurium and high resolution gamma-spectrometry with a hyper-pure Ge-detector. The procedure was evaluated by the analysis of the certified reference materials SARM-7 and W-1. The detection limit for the analytical conditions employed was 0.004 ng·g–1 Ir. The procedure was applied to the reference materials TDB-1 and WGB-1, which present provisional values for Ir concentration, and GXR-3, GXR-5 and GXR-6, which do not present any reported data for Ir contents.

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Abstract  

We have determined the concentrations of eight REE elements by instrumental neutron activation analysis (INAA) (La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu) in plant leaves of the species Solanum lycocarpum, a typical Brazilian "cerrado" plant widely distributed around the country, and in the soils in which they grow. Three different ecosystems were studied. Very similar chondrite normalized patterns were observed in the soil and in the plant, presenting an enrichment of the light REE, indicating a typical absorption of these elements by this species.

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Abstract  

Procedures for the determination of traces of rare earth elements (REE) in geological samples by instrumental neutron activation analysis (INAA) and high resolution liquid chromatography (HPLC) are presented. The international standard reference materials AGV-1, GSP-1 and G-2 (USGS) were tested for the determination of REE concentrations using both techniques. The results obtained showed good agreement with certified values, giving relative errors less than 10%. By using INAA, the REE La, Ce, Nd, Sm, Eu, Tb, Yb and Lu were determined. All the REE, except Dy and Y, were determined when HPLC was employed. The application of INAA and HPLC to the determination of REE in geological samples is also discussed.

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Abstract  

A radioreagent method of analysis was developed and applied to the determination of trace quantities of lead in several types of samples. The method is based on the extraction of radioactive cobalt, displaced by lead from the cobalt chelate of ethylenediaminetetraacetate labelled with60Co, into a tetracycline-benzyl alcohol solution. The radioactivity of the released cobalt, extracted into the organic phase, is proportional to the lead concentration. Interference caused by some elements was eliminated by means of a previous separation of lead using dithizone. The method was applied for lead determination in aerosol samples, gasoline and samples from the International Atomic Energy Agency, namely: simulated-air filter (Air-3), fresh water (W-3), dried animal whole blood (A-2) and calcined animal bone (A-3/1). The sensitivity, accuracy and precision of the method were also studied.

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Abstract  

NAA and UV laser ablation ICP-MS were used to determine platinum group elements (PGEs) and gold in the geological reference materials UMT-1, WPR-1, WMG-1, GPT-4 and GPt-6, after NiS fire assay. Both methods presented results were good agreement with the recommended values. NAA gave more accurate values for Ir (relative errors between 0 to 9%) and UV-LA-ICP-MS presented better results for Pt (relative errors less than 12%, except for WPR-1). UV-LA-ICP-MS showed better sensitivity than NAA for Pd and Os. On the other hand, NAA showed lower detection limits for Ir and Au. Advantages and disadvantages of each method are discussed.

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Summary  

Instrumental neutron activation analysis (INAA) was used to determine metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), semi-metals (As, Sb), actinides (U, Th) and rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in bottom sediments from one of the ponds of the Sewage Treatment Plant (STP) in São Paulo, Brazil. The results obtained were compared with the concentration determined in a soil profile and in a rock sample, in natura, representing the lithologies of the region, and indicated that only As, Cr and Zn can have their origin associated with the residues disposed around the pond.

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Abstract  

Epiphytic bromeliadTillandsia usneoides was used as a biomonitor of metal atmospheric pollution in the city of São Paulo, Brazil. The samples were collected from an unpolluted area and were exposed for 8 weeks in 10 sites of the city and in a control site. The data obtained showed that the control site presented lower concentration for most elements analyzed and the highest concentrations of Na, Cl, Br, K. The highest concentrations of Zn, Cu and V were observed in stations submitted to industrial and vehicular sources. The results obtained for rare earth elements, Al, Fe, Mg, Mn, Rb and Sc indicate mineral dust origin. The elements Ba, As and Sb presented higher values in stations near streets with heavy traffic.

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Abstract  

Instrumental neutron activation analysis was applied to determine La, Ce, Nd, Sm, Eu, Tb, Yb, Lu and Sc in two biological reference materials: NIST 1575 Pine Needles and BCR-CRM 101 Spruce Needles. The purpose was to contribute to the reference data for these two reference materials. The results were obtained with a good precision (relative standard deviations less than 15%). For the Pine Needles reference material there are already some proposed values and our results showed, in general, a good agreement with the data published. The contribution of uranium fission products to La, Ce, Nd and Sm was evaluated and considered in the determination of these elements. Interferences in the determination of rare earth elements in biological materials are also discussed.

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Abstract  

Comparisons were made between the results obtained for elements accumulated by Tradescantia pallidaplant exposed in sites with different pollution levels: Cerqueira César and Congonhas districts, considered polluted areas of São Paulo city, and Caucaia do Alto county, considered a non polluted site. Statistical test applied to the results indicated that plant samples from polluted areas presented higher concentrations of Ba, Ce, Cr, Co, Fe, La, Sb and Sc than those found for ones from a non-polluted site. Discriminant analysis applied to the results obtained revealed three groups of results corresponding to sites with different levels of pollution.

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Abstract  

In the present work, a comparative study is made among nuclear methods for235U/238U ratios determination: activation analysis followed by high-resolution gamma-ray spectrometry, delayed neutron counting, passive gamma-ray and alpha spectrometry. Activation analysis followed by high-resolution gamma-ray spectrometry yielded a relative standard deviation down to 0.1% and a relative error of about 1% for standards of uranium enriched to 14%. Passive gamma-ray spectrometry using Ge(Li) detectors yielded a relative error down to 0.1% for enriched uranium and values even lower for the standard deviation. Passive gamma-ray spectrometry using Low Energy Photon Detector (LEPD) yielded a precision of 0.2% and a still better accuracy for enriched standards. In the case of alpha spectrometry, a relative error down to 0.5% and a precision of about 1% were obtained, also for enriched uranium standards. Delayed neutron counting allowed a relative standard deviation of about 7% and a relative error of about 2%, for standards of depleted uranium.

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