Search Results

You are looking at 51 - 60 of 781 items for :

  • All content x
Clear All

Abstract  

The uptake and distribution of cobalt by filamentous fungus Trichoderma viride has been studied. By means of60Co the cobalt concentrations in conidia and mycelium were determined.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: R.G.V. Hancock, J. McKechnie, S. Aufreiter, K. Karklins, M. Kapches, M. Sempowski, J.-F. Moreau, and I. Kenyon

Abstract  

Chemical analyses were made of royal blue glass trade beads from two early 17th century, archaeological sites in southern Ontario, Canada and from a glass beadmaking house in Amsterdam, The Netherlands. The results confirm that these beads were all mixed alkali — lime — silica glasses, coloured with Co and with opaque varients opacified with Sn. The groupings by chemistry tend to segregate by bead shapes, so that oval beads group together and circular shaped beads group together. Although the 2 Canadian sites are about 190 km apart, they produced 2 different sets of oval beads of similar chemistry, possibly helping confirm the contemporaneity of the people at both sites. An As/Co atomic ratio of about two may fit with the possible source of Co as a cobalt-arsenide ore (of common name smaltite) from the Hartz Mountains of eastern Germany, a source not far from either Amsterdam or Venice, both well known glass beadmaking centres of the period.

Restricted access

Abstract  

Nondestructive activation analysis by proton beam bombardment has been applied to cobalt specimens. Thick target yields were measured on 18 elements for the purpose of quantitative analysis. In order to detect precisely the radionuclides with different half-lives, gamma-ray spectrometry was repeated three times after different cooling times of 1, 15 and 250 hrs from the finish of bombardment for 1 hrby 10.4 MeV proton beam. It was found that Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Nb, Mo, Cd, Sn, Sb, and Te of the order of ppm or less could be detected accurately. Using the proton activation analysis developed, the purification effects of anion exchange, electrolytic extraction, and floating zone-refining have been examined. It was confirmed that the concentrations of the impurity elements contained in the starting material decreased stepwise upon the application of each purification method.

Restricted access
Hungarian Medical Journal
Authors: György T. Szeifert, Hong Xun Han, Lixin Lin, Mi Zhi Quiang, Guang Hua Lou, and István Nyáry

A new digital Cobalt-60 combined stereotactic radiotherapy and radiosurgery system, termed as the GyroKnife, was developed in Shanghai, China in 2004. The equipment integrates advantages of previous generations of gamma radiosurgery techniques and linear accelerators. The technology has the capacity for non-invasive whole-body stereotactic fractionated radiotherapy and single high-dose radiosurgery as well. Using a triple focussing method, high isocenter accuracy (0.5~1.0 mm) and minimal skin (550:1) or normal tissue irradiation dose were achieved with 4 various sizes of collimator sets (5, 15, 25, 50 mm). The first GyroKnife Center in Kang Da Hospital, Xiang Fan, China, has already treated 100 cases with different tumours in the brain and body since November 2006. The technical details of the system will be presented, and the preliminary clinical results will also be discussed.

Restricted access

Abstract  

A57Co doped unsupported CoMo sulfide catalyst with atomic composition ratio r=Co/(Co+Mo)=0.3 was prepared by the homogeneous sulfide precipitation method and exposed to a series of reduction-sulfidation treatments. The treated samples were analyzed by Mössbauer emission spectroscopy using very long accumulation times. Computer decomposition of the spectra revealed the presence of five different cobalt species which were identified as Co9S8, CoS1+x, and three species related to the Co–Mo–S structure. Reduction of the sample under atmospheric pressure of H2 at (and above) 573 K causes an increase of the amount of Co9S8 at the expense of all other species. These results afford a new insight into the stability of the Co–Mo–S structure and of the sulfur rich CoS1+x phase under hydrotreating conditions.

Restricted access

Abstract  

Cobalt(II) complexes of tetradentate Schiff bases of the type CoL [H2L=C20H16N2O2 (H2dsp), C21H18N2O2 (H2dst), C20H15N3O4 (H2ndsp) and C16H16N2O2 (H2salen)] have been synthesized and characterized by UV-visible, IR, and magnetic studies. Various thermodynamic parameters have been calculated for the decomposition step using TG/DTA. C20H14N2O2Co complex has the minimum and C16H14N2O2Co complex has the maximum activation energy.

Restricted access

Abstract  

The retentions of cobalt, copper and zinc recoils were studied in the mixed crystal system of -cobalt phthalocyanine and -zinc phthalocyanine. It was suggested that a part of the retentions of cobalt and zinc recoils was due to a competitive process. The relationship between the retentions of the zinc recoils and their recoil energy in different matrices was discussed.

Restricted access

Abstact  

The reduction process of silica supported cobalt catalyst was studied by thermal analysis technique. The reduction of the catalyst proceeds in two steps:

\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} $$Co_3 O_4 + H_2 \to 3CoO + H_2 O, 3CoO + 3H_2 \to 3Co + 3H_2 O$$ \end{document}
which was validated by the TPR and in-situ XRD experiments. The kinetic parameters of the reduction process were obtained with a comparative method. For the first step, the activation energy, E a, and the pre-exponential factor, A, were found to be 104.35 kJ mol−1 and 1.18�106∼2.45�109 s−1 respectively. The kinetic model was random nucleation and growth and the most probable mechanism function was found to be f(α)=3/2(1−α)[−ln(1−α)]1/3 or in the integral form: g(α)=[−ln(1−α)]2/3. For the second step, the activation energy, E a, and the pre-exponential factor, A, were found to be 118.20 kJ mol−1 and 1.75�107∼2.45 � 109s−1 respectively. The kinetic model was a second order reaction and the probable mechanism function was f(α)=(1−α)2 or in the integral form: g(α)=[1−α]−1−1.

Restricted access

The salicylato complex of cobalt was synthesized and its structure established to be [Co(sal)2] · 4 H2O, where, sal =, from elemental analysis, IR spectroscopy, magnetic susceptibility, cryoscopy and conductivity. The X-ray diffractogram of the complex has been given. Thermal decomposition has been studied in air by thermogravimetry (TG), differential thermal analysis and differential scanning calorimetry. TG shows three main steps of decomposition. The intermediates formed at various stages were collected and analysed. From the TG results and chemical analysis of the intermediates, a mechanism has been proposed for the thermal decomposition of the complex, leading to the oxide formation in the final stage.

Restricted access

Abstract  

Gamma-radiolysis of folic acid and its cobalt complex were studied in aqueous solutions at doses ranged from 2 to 10 krad and from 2 to 10 Mrad using60Co source. The variations in their spectra of IR, UV, and visible due to their radiolysis were shown. Also the change in pH after radiolysis was determined. The results showed that decomposition of folic acid by gamma-radiation occurred without variation of pH. Fine measurements of pH for irradiated CoCl2 and cobalt-folic acid complex solutions can be utilized for dose determination in the studied range of 2–10 Mrad. IR spectra showed that addition of cobalt chloride to folic acid decreased its decomposition by gamma-radiation. This result proved the importance of addition of cobalt chloride in keeping foodstuffs, which contain folic acid, by irradiation. The mechanism for the effect of radiation on cobalt chloride and cobalt-folic acid complex was discussed.

Restricted access