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  • Author or Editor: Van Nguyen x
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Abstract.

Let be a convex combination space as defined by Terán and Molchanov [13]. By using their definition of mathematical expectation of an -valued random variable, we state several new variants of strong laws of large numbers for double arrays of integrable -valued random variables under various assumptions. Some related results in the literature are extended.

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Abstract  

Zircon separated from samples of monazite in beach sand have been analyzed for Zr, Hf, U, Th, Sc and REE concentration by the neutron activation analysis technique. After irradiation, the rare earth elements were separated from Zr and Hf by oxalate precipitation, using La as a carrier, from239Np/U/ by ion-exchange chromatographic method and from233Pa/Th/ by co-precipitation with MnO2. The chondritic normalized REE pattern of two zircon samples show negative Eu anomalies with a slope increasing at the heavy rare earths.

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Abstract  

A procedure for separation of Au, Ag, Pt, and Pd in geological samples has been developed. After irradiation, samples were fused with Na2O2 and silver was separated by filtering through a PbCl2 filter in 4M nitric acid solution. Au, Pt and Pd were concentrated with rhodium and thiourea as rhodium sulfide and the separation process of these elements was carried out by a chromatographic method. Au, Pt and Pd were retained on a Dowex-1×8 anion column in 1M HCl. Pd was eluted from the column by using a mixture of 75% HCl acid-25% acetone. Au was eluted by using a mixture of 10% HCl-90% acetone. In the gold fraction, Pt was also determined through the photopeak of199Au radionuclide (158 keV). The method was simple and rapid.

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Abstract  

Cerium trace impurity in high purity lanthanum oxide (99.99%) has been determined by NAA after pre-separation of La matrix. In this method, the sample was dissolved in conc. nitric acid and diluted with water. The final concentration of solution is about 0.1M of nitric acid. It was passed through a MnO2 column. Under these conditions cerium is retained on the column quantitatively without retaining lathanum. Cerium is eluted with 4M nitric acid. The recoveries of Ce were checked with tracers and by standard addition to lanthanum oxide matrices. Results obtained on a high purity lanthanum oxide are reported here.

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Abstract  

A method is described for the simultaneous determination of tin and tungsten in cassiterite ores by photon activation analysis using both elements and zirconium and zinc as internal standards. By using a 15-MeV photon beam, some interfering reactions with higher threshold energies can be eliminated. Thus the data processing becomes simpler and more accurate. The proposed procedure can be used for the routine analysis of tin and tungsten in cassiterite samples.

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Abstract  

Radiochemical neutron activation analysis (RNAA) has been applied for determination of rare earth elements (REE) in Vietnamese monazite. The chemical separation procedure used is based on the chromatographic elution of rare earth groups, after the separation of233Pa(Th) in irradiated monazite samples by coprecipitation with MnO2, the rare earth elements were retained by Biorad AG1×8 resin column in 10% 15.4M HNO3-90% methanol solution. The elution of heavy rare earth (HREE) and middle rare earth (MREE) groups was carried out with 10% 1M HNO3-90% methanol and 10% 0.05M HNO3-90% methanol solution, respectively; while the light rare earths (LREE) were eluted from the column by 0.1M HNO3 solution. The accuracy of the method was checked by the analysis of granodiorite GSP-I and the rare earth values were in good agreement.

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Abstract  

Neutron activation analysis has been applied for the determination of Hg and As in freshwater samples. Preconcentration of Hg and As from the samples before irradiation by using active carbon for scavenging the chelate complex of Hg with dithizone at pH 1 and Fe(OH)3 for co-precipitating arsenic was used. After irridiation, mercury was determined by direct counting of the irradiated active carbon. Arsenic was separated from Fe(OH)3 by precipitating arsenic in the metal form after removing122Sb by extraction in 2N HCl with Ni-diethyldithiophosphoric acid in carbon tetrachloride. The method is simple and reliable.

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