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Dosage du molybdene et du tungstene dans les plantes par activation neutronique

Methode radiochimique adaptee aux vegetaux riches en calcium

Journal of Radioanalytical and Nuclear Chemistry
Authors: M. Neuburger and A. Fourcy

Abstract  

A method for the determination of molybdenum and tungsten in plant material using neutron activation analysis was developed. The considered reaction are:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\begin{gathered} {}^{98}Mo(n,\gamma )^{99} Mo \hfill \\ {}^{186}W(n,\gamma )^{187} W \hfill \\ \end{gathered}$$ \end{document}
The separation for tungsten and molybdenum was carried out using anion exchange separation (Dowex 1×10; 200–400 mesh). Irradiation was carried out in a swimming pool reactor at a thermal flux of about 1–2×1013 n·cm−2·sec−1 for 15 hours. The samples and standard were allowed to cool for 5–6 hours before chemical processing. the high concentration of calcium in plants (up to 40 mg/g dry material), the use of hydrofluoric acid for a good absorption and quantitative recovery of tungsten led us to dissolve the samples with Ht−H2O2 mixtures containing boric acid to prevent the precipitation of fluorides.

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Abstract  

The long-lived -radionuclidic impurities in the columns of spent99Mo/99mTc generators one year after the calibration date have been determined by -spectrometry. Three radionuclidic impuritiesfission products (103Ru,106Ru and125Sb) were detected. Also in the majority of samples three radioisotopes of tungsten (181W,185W and188W) were also present. The contents of the impurities were found to vary greatly. According to the activity, energy and half-life, the main contribution to the residual activity in the spent generators is due to the presence of125Sb.

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Abstract  

Uranium analysis at trace levels from geological samples was performed by K X-ray fluorescence using a semiconductor detector and radioisotope excitation. The exciting57Co-source was constructed in such a way as to produce a high peak to background ratio. Using 10 minutes counting times the detection limit with a 0.26 GBq source was 24 μg/g improving to about 9 μg/g with a ten times stronger source. The detection limits for tin, cerium, tungsten and thorium were also measured.

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Abstract  

A simple neutron-activation method for the determination of rhenium based on a preliminary extractive separation of the latter from molybdenum and tungsten is described. The sample is decomposed with sodium peroxide, a small amount of water is added and the resulting pulp is extracted with pyridine. The extract is evaporated to dryness, the residue is dissolved in water and the solution is passed through a column packed with Dowex 50WX8 in H+ form to eliminate the metal impurities. The HReO4 passed, after neutralization with ammonia, is evaporated to dryness in penals, which then are irradiated with thermal neutrons.

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Abstract  

An analytical method, SSMS, for the determination of trace impurities in cobalt is described. This element is used as raw material for the production of60Co in Embalse Nuclear Power Station. Tin, aluminum, lead, silicon, molybdenum, calcium, vanadium, boron, chromium, zirconium, tungsten, nickel, magnesium, iron, zinc and copper were determined. Manganese, analyzed by AAS, was used as an internal standard. The measurements were semiquantitative. The accuracy of the results was compared with that of emission spectrography and atomic absorption spectrometry, the agreement was found to be satisfactory.

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Abstract  

INAA technique for the determination of impurities (O, F, Na, Mg, Al, Si, P, S, K, Sc, Cr, Mn, Fe, Co, Ni, etc.) and of some doping elements in molybdenum and tungsten with detections limits between 10–12 and 10–6g/g by using a nuclear reactor and a neutron generator have been developed. The methods have been used to control the products of processing of refractory materials, to study the dynamics of impurities and doping elements at all stages of the production process.

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Abstract  

Pt/WOx–ZrO2 bifunctional catalysts were synthesized using impregnation and polymeric precursor methods. After the synthesis process the samples were calcined at 600, 700 and 800C and characterized by X-ray diffraction, nitrogen adsorption and temperature programmed reduction study by thermogravimetry. DTG-TPR profiles showed between three and five reduction events at different temperatures attributed to platinum reduction and to different stages of tungsten species reduction. A comparative study of the synthesis method influence on the DTG-TPR curves was accomplished.

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Abstract  

A technique named ‘apparent thermogravimetry’ (ATG) has been developed for studying infiltration phenomena. It has been used for investigating of infiltration of copper, cast iron, and cobalt alloys into porous tungsten, sintered steel, and tungsten carbide. A description of ATG signal behaviour has been obtained, taking into account ‘internal’ (capillary, viscous, gravitational, end-drag) and ‘external’ (wetting, buoyancy, Archimedean) forces. Dependencies of Archimedean foroe and wetting angle on different parameters are described in relation to the infiltration mechanism. The ATG method can be used to determine surface tension or contact angle.

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Abstract  

In recent years, -particle surface applicators (such as32P,90Sr) have been widely used in treating some diseases of dermotology, ophthalmology, otolaryngology etc. in China. The powder metallurgy and metal rolling technology of strontium-90/yttrium-90 () sources and the manufacture process of90Sr/90Y surface applicators are described in this paper. For this kind of radioactive sources, the strontium-90 insoluble compound is incorporated in a silver matrix which is sandwiched between the gold (or silver) face and the silver backing. The external surface of strontium-90 foil source is then protected by palladium or tungsten-nickel alloy coating. The characteristics of strontium-90 surface applicator are of uniform dose rate, small self-absorption and safety in use, so it can satisfy the requests of medical care.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: N. Shigeta, H. Matsuoka, A. Osa, M. Koizumi, M. Izumo, K. Kobayashi, K. Hashimoto, T. Sekine, and R. Lambrecht

Abstract  

No-Carrier-Added186Re was produced using the186W(p,n)186Re nuclear reaction with 13.6 MeV protons on thick targets of 99.79% isotopically enriched186WO3. The theoretical excitation functions for producing186Re, and possible radionuclidic impurities of182Re,183Re, and184Re were calculated using the ALICE code. Cross-sections of the186W(p,n)186Re reaction were measured up to 20 MeV using the stacked target method with thin foils of natural composition tungsten metal. The experimental and theoretical excitation functions were in good agreement. Targetry used at the TIARA cyclotron, and a radiochemical separation scheme for186Re are described.

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