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  • Author or Editor: N. Jayadevan x
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Abstract  

Chemical characterization of rubidium uranium(IV) trisulfate, Rb2U(SO4)3, a new chemical assay standard for uranium requires accurate analysis of rubidium. A gravimetric and an X-ray fluorescence method (XRF) for the determination of rubidium in this compound are described. In the gravimetric method, rubidium is determined as Rb2Na[Co(NO2)6].H2O without separating uranium with a precision of the order of ±0.5%. In the XRF method, the concentration ratio of rubidium to uranium, CRb/CU, is determined in the solid samples by the binary ratio method using calibration between intensity ratios (IRb/IU) and concentration ratios (CRb/CU). The concentration of rubidium is derived using the uranium value which is known with a precision better than ±0.05%. The XRF method has a precision better than ±0.8% for rubidium determination.

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Abstract  

An X-ray fluorescence spectrometric method is described for the determination of uranium in liquid samples by absorbing drops of solution on cellulose discs. Internal standards thorium, strontium or yttrium are added in the uranium solution to follow the non-uniform absorption of the liquid on the disc. A precision of better than ±0.5% is obtained for uranium determination with all the three internal standards. The method was also employed to determine uranium in the presence of plutonium and americium without any interference effects.

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Abstract  

An X-ray fluorescence binary ratio method to measure non-destructively the relative percentage of PuO2 in (U, Pu)O2 samples is described. Calibration lines for pellet and microsphere samples are established and evaluated. Independent X-ray measurement of the major component after dissolution leads to the determination of individual concentrations within ±0.5% rel. of the chemical values.

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Thermal decomposition of metal uranyl acetates is one of the best ways of preparation of uranates in crystalline form at low temperatures. Acetates of the type M(UO2)2(OAc)6·7H2O (M=Zn(II), Mg(II) and Ni(II) were prepared and characterised. Their X-ray powder diffraction analysis showed that they all belong to the orthorhombic crystal class.

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Double sulphates of uranium(IV) with Mg, Ni, Cu and Zn with the general formula MU(SO4)3·8H2O were prepared from their respective metal sulphates. All the four compounds are isostructural and belong to monoclinic system. The thermal decomposition at 850 °C results in a single phase of triuranates MU3O10 which on further heating above 980 °C decompose to give the metal oxide and U3O8 in case of Ni and Zn compounds and MUO4 for Mg and Cu compounds. The activation energy for dehydration of these four compounds has been calculated using non-isothermal thermogravimetric data.

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Thermal decomposition of the amorphous coprecipitate of yttrium and aluminium hydroxides forming yttrium aluminium garnet has been investigated employing thermal analyses, X-ray diffraction and IR spectroscopy. On heating, the coprecipitate progressively loses water forming a stable but highly disordered hydroxy garnet which crystallizes at ∼1180 K and decomposes to YAG at ∼1290 K. Nucleation of the crystalline phase appears to begin at ∼800 K.

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Abstract  

Rubidium uranium trisulphate [Rb2U(SO4)3] was prepared as a high purity compound of uranium in different lots of 250 g each. The compound was characterised and evaluated by chemical, atomic spectrosopic, infrared, X-ray diffraction and thermogravimetric methods for its use as a chemical assay standard for uranium. The compound is stoichiometric, pure, homogeneous and stable in atmospheric conditions. The solubility studies showed that Rb2U(SO4)3 is easily soluble in mineral acids. An experiment based on Randomised Block Design was carried out to assign a value to the uranium content in Rb2U(SO4)3 from the statistically analysed chemical data. The assigned value of [34.167±0.042]% to the uranium content is in close agreement with the theoretical value of 34.152%. Based on these studies, Rb2U(SO4)3 is recommended as a chemical assay standard for uranium.

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