Spelling suggestions: "subject:"mössbauer""
1 |
Mössbauer study of the hyperfine magnetic field and electric field gradient at Fe sites in synthetic diamond.Govender, Nadaraj. January 1992 (has links)
Mossbauer Spectroscopy has been used to investigate the
site of Fe inclusions in a suite of synthetic diamonds (de
Beers MDAS). Information on the hyperfine magnetic fields
and electric field gradients at Fe sites in the diamond
grains were obtained from Mossbauer Spectroscopy of diamond
grains ranging in size from 25 to 250 um. The Fe inclusions
in these samples resulted from the synthesis of the diamond
grains in which Fe was used as a catalytic solvent. The
Mossbauer measurements were carried at room temperature
with a constant acceleration spectrometer operating in
transmission geometry.
The samples with the largest grain size of 180-250 um gave
a well defined six component magnetically split spectrum,
similar to the Zeeman split sextet obtained for natural
iron. As the grain sizes decreased the intensity of
the magnetically split components became greatly reduced
and a strong paramagnetic component appeared. At grain
sizes 105-45 um the spectra are dominated by a central
single line with some evidence of an asymmetric doublet.
For the finest grain size 38-25 um, the reappearance of
the six magnetic hyperfine splitting components together
with the strong central single paramagnetic component was
observed.
The change in the Mossbauer patterns observed with decreasing
grain size suggest that a rapid phase transition of the
Fe inclusions from ferromagnetic to superparamagnetic
takes place.
The analysis of Mossbauer spectra yielded a value of the
hyperfine magnetic field of Bhf = -32.4(4) T and an
electric field gradient in the range of Vzz = 1.4(4) 1.8(
7) X 10'8 V.cm- 2 at the site of the probe s7Fe
nucleus. These values compare favourably with other
measurements. / Thesis (M.Sc.)-University of Durban-Westville, 1992.
|
2 |
Mossbauer spectroscopic and structural studies of tin materialsAbrahams, I. January 1986 (has links)
No description available.
|
3 |
Synthesis and characterisation of metal oxides and metal doped variantsSkinner, Stephen John January 1997 (has links)
No description available.
|
4 |
Quantum coherence phenomena in x-ray opticsAnisimov, Petr Mikhailovich 15 May 2009 (has links)
The effects of quantum coherence in X-ray optics at nuclear transitions are
investigated from a theoretical point of view. First, we introduce the general concept
of the decaying dressed states and present a classification of the quantum coherence
effects in a three-level coherently driven system. Second, we show that the interference
effects may appear in X-ray radiation at the nuclear transitions under the condition of
the nuclear level anti-crossing. This effects are similar to electromagnetically induced
transparency, which has been widely studied earlier at the electronic transitions in
optics. We also suggest a new technique for inhomogeneous line narrowing at nuclear
transitions. This technique is based on the combined action of RF and DC fields
and adopted to be applied in the M¨ossbauer spectroscopy. Numerical simulation of a
simple model with the dipole-dipole interaction is presented in order to demonstrate
the efficiency of the technique. Finally, we study the possibility to suppress the nuclear
elastic forward scattering in the synchrotron experiments using trains of pulses. A
numerical model is developed to confirm this possibility and the main issue of relative
phases of consecutive pulses is discussed.
|
5 |
Small shift Mossbauer spectrometerBeveridge, John Leslie January 1968 (has links)
In this thesis a small shift Mossbauer spectrometer
developed by the author is described.
An automatic multiplexing and printout system for
eight scalers is described along with a digital electronic
control system for the motor drive.
Three-different suspension systems, for the transport
portion of the linear drive --
(1) An air bearing suspension as developed by Wells
(2) An oil supported teflon bearing suspension
(3) A leadscrew suspension
have been constructed. Mossbauer spectra for two sources – CO57
in Armco iron and CO57 in Pt195 -- against an enriched iron
absorber have been taken with the latter two suspensions and
have been compared with each other and with spectra taken on a
commercial Mossbauer spectrometer.
Theoretical calculations of the central Mossbauer line
for the Armco iron source and enriched iron absorber have been
made using the computer program written by Woodrow. These
calculations are compared with the experimental spectra. / Science, Faculty of / Physics and Astronomy, Department of / Graduate
|
6 |
Self-absorption Mössbauer investigation of neutron activated solid krypton /Brown, John Barclay January 1973 (has links)
No description available.
|
7 |
Électrodes négatives pour batteries Li-ion à base de FeSn2 : performances, Mécanismes et Vieillissement. / Negatives electrodes feSn2 based for Li-ion Batteries : performances mechanisms and aging.Chamas, Mohamad 16 December 2010 (has links)
Comme dispositif de stockage de l'énergie, les batteries Li-ion possèdent de nombreux avantages et en particulier une densité d'énergie élevée. Toutefois, la recherche de nouveaux matériaux d'électrode reste nécessaire pour améliorer les performances. Ce travail concerne les matériaux d'électrode négative avec pour objectif l'augmentation de leur capacité. Dans ce but nous nous sommes intéressés à un composé intermétallique à base d'étain : FeSn2. Nous avons effectué la synthèse de ce matériau par différents procédés afin d'obtenir des microparticules et un matériau nanostructuré. L'étude des mécanismes électrochimiques a montré que pour ces deux types de matériaux la première décharge constituait une étape essentielle de restructuration de l'électrode aboutissant à la formation in situ d'un nanocomposite Fe/Li7Sn2. Le suivi quantitatif de la réaction de conversion, responsable de cette transformation, a été effectué par spectrométrie Mössbauer in situ et operando grâce à une nouvelle cellule électrochimique que nous avons développée. D'autres techniques ont été utilisées : DRX et spectrométrie d'impédance in situ, SQUID et XPS. En associant ces différentes techniques nous avons montré que les cycles de charge/décharge étaient basés sur une réaction réversible entre Li7Sn2 et LixSn riche en étain sans reformation de FeSn2. Ce résultat diffère des mécanismes observés pour CoSn2 et Ni3Sn4 et pourrait expliquer la perte progressive de capacité généralement observée avec FeSn2. Toutefois, les performances sont intéressantes avec une capacité de 400-500mAh/g sur 50 cycles entre C/10 et 10C. Enfin, nous avons mis en évidence un phénomène de vieillissement de l'électrode en fin de décharge qui provoque sa délithiation irréversible. / Li-ion batteries are rechargeable energy storage systems with high energy density. However, new electrode materials are needed in order to improve the electrochemical performances. This thesis is devoted to a tin based intermetallic compound as negative electrode for Li-ion batteries: FeSn2. Different synthesis methods were used in order to obtain microsized particles and nanostructured materials. The study of the electrochemical mechanisms shows that for both types of materials the first discharge is an essential restructuring step leading to the in situ formation of a Fe/Li7Sn2 nanocomposite. This transformation is due to a conversion reaction that was quantitatively characterized by Mössbauer spectroscopy from in situ and operando measurements. A new cheap and reliable electrochemical cell was developed for these measurements. Other techniques have also been used: in situ XRD and impedance spectroscopy, XPS and SQUID. By combining these tec hniques we have shown that the charge/discharge cycles were based on a reversible reaction between Li7Sn2 and tin-rich LixSn without back reaction with iron nanoparticles. This result is rather surprising because it differs from the mechanisms observed for CoSn2 and Ni3Sn4 but could explain the progressive loss of capacity usually observed with FeSn2. However, interesting performances were obtained with a capacity of 400-500mAh/g for 50 cycles and lithium rates between C/10 and 10C. Finally, we have identified aging process for the electrode at the end of discharge that causes irreversible delithiation.
|
8 |
The design and construction of a constant acceleration drive system for Mössbauer experimentsRussell, James Donald 01 January 1970 (has links)
An excited nucleus may undergo a transition to its ground state by the emission of a gamma ray. The nucleus, if free to do so, will recoil and take some of the transition energy as recoil energy leaving less energy for the emitted gamma ray. This gamma ray does not have enough energy to excite a similar nucleus and will, therefore, not by resonantly absorbed due to the fact that the natural linewidth of the gamma ray is so much smaller than the energy taken by the emitting atom and the similar energy needed by the absorbing atom.
In 1958 a new effort in the emission and absorption processes of low energy gamma rays was announced by Rudolph L. Mössbauer. His discovery was made while he was doing graduate work at Heidelberg, Germany. Since that time this effect, not known as the Mössbauer effect, has been studied and confirmed in many laboratories. By 1961 the significance and usefulness of this effect was so widely recognized that Rudolph Mössbauer was awarded the Nobel Prize.
The new effect involves recoil free emission and resonant absorption of low energy gamma rays by atoms tightly bound in a crystalline lattice. The characteristics of the Mössbauer effect have led to the feasibility of studies previously not possible in nuclear-. Solid taste-, and atomic physics; chemistry; and biology.
It is the purpose of this research project to design and build a Mössbauer effect apparatus.
|
9 |
Applications of maximum entropy data analysisMcLean, Andrew Lister January 1995 (has links)
No description available.
|
10 |
A Mossbauer Spectroscopy Investigation of Fe enriched WC-CoSufianu, Adeleke Wasiu January 2016 (has links)
A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 2016. / Tungsten carbide cobalt (WC-Co) cemented carbides are widely used for cutting, drilling, machining and as wear resistant materials due to the combination of high hardness and fracture toughness. In this work, we report on as-milled and as-sintered WC-10Co-20Fe samples which were ball milled for 15 hrs and sintered using liquid phase sintering (LPS). These samples were investigated by Vickers hardness test, microstructural analysis, X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and conversion electron Mössbauer spectroscopy (CEMS) techniques.
A mean hardness value of 1160 ± 42 HV was obtained for WC-10Co sample while a value of 776 ± 35 HV was determined for the WC-10Co-20Fe using the Vickers hardness tester. The lower hardness value for WC-10Co-20Fe is attributed to the high volume of the binders (10% Co and 20 %Fe) incorporated in the sample. The microstructural analysis of the as-sintered WC-10Co and WC-10Co-20Fe samples reveals that the light regions represent the WC phases and the dark regions signify the presence of the Co and CoFe phases in the as-sintered WC-10Co and WC-10Co-20Fe samples, respectively. The energy dispersive spectroscopy (EDS) of the as-sintered samples shows the presence of the starting powders used (WC, Co and Fe) and some Cr contamination resulting from either the production process or the starting powders. / GR 2016
|
Page generated in 0.024 seconds