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1
Ansbro, Simon. « Molecular nanomagnets probed by inelastic neutron scattering ». Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/molecular-nanomagnets-probed-by-inelastic-neutron-scattering(8206c00e-50bf-48e4-888d-6161791e8159).html.
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Molecular nanomagnets have the potential to address many technological challenges whilst also giving insights into fundamental quantum behaviours. In order to accomplish this it is crucial that a determination of the magnetic properties of these nanoscopic objects is established. Inelastic neutron scattering (INS) is at the forefront of these investigations and is a technique capable of unravelling vast amounts of information that can enable a detailed understanding and tailoring of the properties of these molecules. This thesis demonstrates the application of this state-of-the-art technique to a number of different yet important nanomagnets in the field, pushing the technique to the limit to yield new insights into the underlying physics in these systems. The potential of this technique is finely displayed in the unravelling of the spin dynamics in a supramolecular (Cr7Ni)2 dimer, where the intermolecular entanglement is portrayed in the vast 4D phase space extracted. This work also harnesses the full power of the 4D-INS technique to resolve the long standing issue of the spin Hamiltonian in the archetypal single molecule magnet (SMM) Mn12, which after hundreds of papers since the realisation of its magnetic properties some 25 years ago had still not been convincingly settled. A little utilised avenue to building on Mn12 and generating better SMMs is also suggested and the evolution of the technique demonstrated by 8 characterising the magnetic properties in a tiny quantity of nanomagnet dimers.
2
Baker, Michael Lloyd. « Antiferromagnetic wheels probed by inelastic neutron scattering ». Thesis, University of Manchester, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542789.
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Bryan, Matthew S. « Inelastic Neutron Scattering of Nanoconfined Superfluid Helium ». Thesis, Indiana University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10842052.
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The dynamics of liquid 4He confined in a mesoporous powder FSM-16 are reported in this dissertation, including the roton linewidth, excitation spectrum, and Compton profile. With an ordered triangular lattice structure, FSM-16 is a high surface area porous glass with hexagonal pores a few nanometers in diameter. Neutron backscattering results examined the roton linewidth as a function of temperature. Observed linewidths in confinement are consistent with the theoretical and experimental results of the bulk liquid. The temperature-filling phase diagram was explored at intermediate fillings and low temperatures. The maxon and roton excitations are used as indicators of density for a thin-film that transitions into a three dimensional confined fluid. The resulting excitation spectrum at low fillings does not correspond to the bulk liquid at any pressure. The deep inelastic neutron scattering results found an enhanced single particle kinetic energy, with full pore and thin film liquid deviating from the bulk momentum distribution in shape.
4
Tait, Kimberly. « Inelastic Neutron Scattering and Neutron Diffraction Studies of Gas Hydrates ». Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194926.
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Gas hydrates (clathrates) are elevated-pressure (P) and low-temperature (T) solid phases in which gas molecule guests are physically incorporated into hydrogen-bonded, cage-like ice host frameworks. Natural clathrates have been found worldwide in permafrost and in ocean floor sediments, as well as in the outer solar system (comets, Mars, satellites of the gas giant planets). Diffraction patterns have been collected of gas hydrates at various methane and ethane compositions by preparing samples in an ex situ gas hydrate synthesis apparatus, and CO₂ gas hydrates were prepared in situ to look at the kinetics of formation. Storage of hydrogen in molecular form within a clathrate framework has been one of the suggested methods for storing hydrogen fuel safely, but pure hydrogen clathrates H₂(H₂O)₂ form at high pressures. It has been found that mixed clathrates (a stabilizer molecule in the large cage) and hydrogen gas together can reduce the pressures and temperatures at which these materials form. In situ neutron inelastic scattering experiments on hydrogen adsorbed into a fully deuterated tetrahydrofuran water ice clathrate show that the adsorbed hydrogen has three rotational excitations (transitions between J = 0 and 1 states) at approximately 14 meV in both energy gain and loss. These transitions could be unequivocally assigned the expected slow conversion from ortho- to para-hydrogen resulted in a neutron energy gain signal at 14 meV, at a temperature of 5 K (kT= 0.48 meV). A doublet in neutron energy loss at approximately 28.5 meV are interpreted as J = 1 → 2 transitions. In situ neutron inelastic scattering experiments on hydrogen adsorbed into ethylene oxide, a structure I former, were also carried out at the Los Alamos Neutron Scattering Center (LANSCE). There is convincing evidence (shifted rotational mode of molecular hydrogen) that hydrogen is capable of diffusing in the small cages of ethylene oxide clathrate. Values are also obtained for the librational modes of enclathrated ethylene oxide and several water translation modes. Also reported for the first time are the internal modes (higher frequencies) of ethylene oxide in ethylene oxide clathrate as measured by inelastic neutron scattering.
5
Needham, Lyn Michelle. « High energy inelastic scattering by condensed matter ». Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238373.
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Fagerstroem, C. Peter. « Leading neutron production in deep inelastic scattering at HERA ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ50059.pdf.
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Inoue, Rintaro. « Dynamics in Polymer Thin Films by Inelastic Neutron Scattering ». 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/57278.
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Fabiani, Elisa. « Dynamics in strong glasses : an inelastic neutron scattering analysis ». Université Joseph Fourier (Grenoble), 2005. http://www.theses.fr/2005GRE10031.
Texte intégralRésumé :
Le but principal de cette thèse est d'effectuer une recherche systématique sur la dynamique des matériaux vitreux à des températures T beaucoup plus petites que la température de transition vitreuse Tg. Des études théoriques et expérimentales, exécutées pendant les deux dernières décennies sur différents aspects de l'état vitreux, ont établi un certain nombre de propriétés particulières qui concernent le dynamique à basse énergie et qui se manifestent dans la chaleur spécifique à basse température, dans la conductivité thermique, et dans la diffusion inélastique expérimentale. Certaines questions fondamentales dans ce domaine, relatives à la nature microscopique de la dynamique et à l'origine des caractéristiques "universelles" de la densité des états vibrationnels (VDOS) dans les verres, n'ont pas trouvé actuellement une réponse généralement admise. Afin d'expliquer certaines caractéristiques des verres, nous avons étudié deux verres forts, le quartz fondu (v-SiO2) et l'oxyde de germanium vitreux (v-GeO2). La technique utilisée est la dispersion inélastique des neutrons. Les études de ces échantillons avaient pour objectifs : i) le développement d'une nouvelle procédure pour extraire la VDOS à partir des systèmes cohérents en étendant l'approximation incohérente habituelle ; ii) l'étude de la diffusion quasiélastique de nos échantillons dans la région de très de basse fréquence ; iii) la comparaison des données de dispersion précédemment mentionnées, afin de calculer la fonction de couplage Raman C(w) et sa limite à basse fréquence ; iv) l'étude du v-GeO2 afin de prouver que les branches acoustiques longitudinales et transversales sont aussi définies dans le système vitreuxThe main task of this thesis is to perform a systematic investigation of the dynamics of glassy materials at temperatures T much smaller than Tg, the glass transition temperature. Both theoretical and experimental studies performed over the last two decades on different aspects of the glassy state, have established a number of peculiar properties that concem low energy dynamics and manifest themselves in low temperature specifie heat, thermal conductivity, and inelastic scattering experiments. Sorne of the fundamental questions in this field, in particular about the microscopie nature of the dynamics and the origin of the "universal" features concerning the density of vibrational states in glasses, have not found a generally accepted answer. Ln order to explain some features of strong glasses, different systems have been investigated. Here we present new results on two strong glasses, vitreous silica (v-SiO2) and vitreous germania (vGeO2). The technique employed was inelastic Neutron Scattering (lNS). The studies of these sam pies have been done in order to : i) develop a new procedure to extract the density of states from coherent systems extending the usual Incoherent approximation ; (ii) study the QES of our samples at very low frequency range (in order to compare with Brillouin data and to asses a correlation with the mechanism causing the sound attenuation) ; (iii) compare of the previous scattering data above-mentioned, in order to calculate the Raman coupling function C(w) and its low frequency limit ; (iv) finally, investigate v-GeO2 to asses that both longitudinal and transverse acoustic branches are still somewhat defined also in glassy system
9
Hayward, Richard Laurence. « Inelastic neutron scattering spectroscopy of polypeptides and molecular crystals ». Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/21296.
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A predictive and practical theory for a fundamental biological problem - the relation between a protein's three dimensional folded form and its function - will rest on an accurate description of the potential energy surface as a function of the protein configuration, and, thereby, on an accurate description of dynamic and thermodynamic properties. A successful theory of this sort will provide the means for rational design of proteins and ligands with desirable properties. Modern computational chemistry techniques have been applied, with qualitative success, to the calculation of protein potential energy functions, and resulting dynamics and ligand binding properties. These calculations have led to suggestions for new drug design. Improvement in the accuracy of predictions from such calculations will require a consistent program of refinement of parameterisation and approximation schemes, by comparison with experimental data. This thesis describes the application to this task of inelastic neutron scattering experiments on samples of polypeptides (collagen, (prolylprolylglycine)10 and polyproline II) and molecular crystals of biological relevance (acetanilide and two isotopmers). The experimental data were analysed for each of the samples in the context of models for their dynamics on the picosecond time scale. Improvements of the form and parameters of the dynamical models are suggested by comparison of the experimental data with the results of numerical calculations. An appendix described an idea I have had for the model independent exploitation of neutron scattering data, and a second appendix records inelastic neutron scattering data collected for two further molecular crystals of biological relevance, 1-alanine and acetyl-alanyl-methylamide.
10
Adams, Mark Anthony. « Vibrational spectroscopy at high pressures using incoherent inelastic neutron scattering ». Thesis, Brunel University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263518.
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Roach, Daniel Lee. « Computational investigations of polycrystalline systems using inelastic neutron scattering techniques ». Thesis, University of Salford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492433.
Texte intégralRésumé :
Coherent Inelastic Neutron Scattering (CINS) cross-sections are usually measured using single crystal samples and triple axis spectrometers; the resulting dispersion curves can then be analysed in terms of Born-von Karman force constant models or IS often very difficult (if not impossible) to obtain single crystal samples of sufficient size. Also, the development of pulsed neutron sources means that data may be collected over a wide range of energies and momentum transfer (Q). These two factors mean that we are now dealing with a vastly greater data set, which contains a demonstrably greater information density.
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Evans, Alan Charles. « The study of condensed matter by deep inelastic neutron scattering ». Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387343.
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Lemishko, Tetiana. « Inelastic neutron scattering study of Brønsted acidity in LTA zeolite ». Doctoral thesis, Universitat Politècnica de València, 2019. http://hdl.handle.net/10251/119966.
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[ES] En esta tesis se realiza un estudio de acidez de zeolita LTA con la relación Si/Al 5 y 40 utilizando la técnica de dispersión inelástica de neutrones (INS) en combinación con otras tecnicas como la modelización computacional y la espectroscopía de resonancia magnética nuclear (RMN).
Las zeolitas son aluminosilicatos altamente cristalinos que forman parte de un grupo importante de los materiales funcionales. Las zeolitas son extremadamente útiles como catalizadores para muchas reacciones importantes con moléculas orgánicas. Las más importantes son craqueo, isomerización y síntesis de hidrocarburos.
Las propiedades catalíticas de una zeolita dependen principalmente de su acidez y ésta depende de tres factores: el número totál de los sitios ácidos, sus fuerzas individuales y su localización individual, estando estos tres factores relacionados. Los parámetros geométricos definidos por localización de los sitios ácidos (es decir, la longitud y los ángulos de enlaces entre los átomos alrededor del sitio ácido) contribuyen de una manera importante a la fuerza ácida.
En la literatura hay muchos trabajos de estudios de acidez en zeolita utilizando la espectrometría infrarroja (IR), sin embargo, con esta técnica es imposible medir las vibraciones de flexión (bending modes, 200-1200 cm-1), las bandas más sensibles al entorno local de los centros ácidos, ya que estas bandas se superponen con las bandas de vibración de la red de zeolite (300-1800 cm-1).
En esta tesis se realiza un estudio de acidez utilizando la tecnica de INS, que nos permite medir principalmente los modos de vibración de los átomos de H y también nos permite medir todas las bandas de vibración (incluido el bending).
Este estudio muestra que la combinación de la alta calidad de las muestras y la sensibilidad del instrumento utilizado permite detectar con alta precisión los sitios ácidos y obtener la información sobre su posición que a su vez nos perimte obtener la posición de los átomos de Al. Con el fin de interpretar los espectros INS se ha realizado un estudio computacional (cálculos ab-initio) con el objetivo de comparar los espectros cálculados con los resultados experimentales y definir el modelo que reproduce la posición mas probable de los centros ácidos en la muestra.[CAT] En aquesta tesi es realitza un estudi d'acidesa de zeolita LTA amb la relació Si / Al 5 i 40 utilitzant la tècnica de dispersió inelastica de neutrons (INS) en combinació d'altres tècniques com la modelització computacional i la espectroscòpia de ressonància magnètica nuclear (RMN ). Les zeolites són aluminosilicats altament cristal·lins que formen part d'un grup important dels materials funcionals. Les zeolites són extremadament útils com a catalitzadors per a moltes reaccions importants amb molècules orgàniques. Les més importants són craqueig, isomerització i síntesi d'hidrocarburs. Les propietats catalítiques d'una zeolita depenen principalment de la seva acidesa i aquesta depèn de tres factors: el nombre total dels llocs àcids, les seves forces individuals i la seva localització individual, estant aquests tres factors relacionats. Els paràmetres geomètrics definits per localització dels llocs àcids (és a dir, la longitud i els angles d'enllaços entre els àtoms al voltant del lloc àcid) contribueixen d'una manera important a la força àcida. En literatura hi ha molts treballs d'estudis d'acidesa en zeolita utilitzant l'espectrometria infraroja (IR), però és impossible mesurar les vibracions de flexió (bending modes, 200-1200 cm-1) amb aquesta tècnica ja que aquestes bandes es superposen amb les bandes de vibració de la xarxa de zeolita (300-1800 cm-1). La tècnica de dispersió inelastica de neutrons (Inelastic neutron scattering) ha estat utilitzada per estudiar l'acidesa de la zeolita LTA amb diferents relacions Si / Al (per tant diferents c.ontinguts de H en la zeolita). En aquesta tesi es realitza un estudi d'acidesa utilitzant la tècnica de INS, que ens permet mesurar principalment els modes de vibració dels àtoms d'H i també ens permet mesurar totes les bandes de vibració (inclòs el bending). Aquest estudi mostra que la combinació de l'alta qualitat de les mostres i la sensibilitat del instrument utilitzat permet detectar amb alta precisió els llocs àcids i obtenir la informació sobre la seva posició que en el seu lloc ens perimte obtenir la posició d'Al. Per tal de interpretar els espectres INS s'ha realitzat un estudi computacional (càlculs ab-initio) amb la comparació dels espectres calculats amb els resultats experimentals.
[EN] This thesis is dedicated to the study of acidity of LTA zeolites with Si/Al ratios 5 and 40 by using the technique of inelastic neutron scattering (INS) in combination with other techniques such as computational modeling and nuclear magnetic resonance (NMR) spectroscopy. Zeolites are crystalline and microporous aluminosilicates which form one of the most important groups of functional materials. Zeolites are widely used as solid acid catalysts for the wide range of important processes regarding organic molecules. The most important are cracking, isomerization reaction and synthesis of hydrocarbons. The catalytic properties of a zeolite depend strongly on its acidity, and this in turns depends on: the total number of acid sites, their individual strength, and their individual location. These three factors are strongly correlated. Geometric parameters that are defined by the location of the acid site (i.e., bond angles and lengths around the acid site) make a remarkable contribution to the acid strength. There are several studies, found in literatures, typically done by Infrared (IR) or Nuclear magnetic resonance (NMR) technique and dedicated to acidity of zeolites. However, the hydrogen bending modes (200-1200 cm-1), which are found to be more sensitive to local environment, cannot be observed by this technique, since these bands overlap with strong bands of the vibrations of zeolitic framework (300-1800 cm-1). INS technique used in this study allows to detect the bands of vibrations of hydrogen atoms in zeolites (including bending modes). Moreover, this study shows that the combination of an extremely high quality of the samples and the sensitivity of the instrument allows to detect with high precision the acid sites of both high-silica and low-silica zeolites and obtain information about their position. This in its turn gives us the possibility to obtain the aluminium location in zeolites. In order to fully understand the INS spectra we performed ab-initio calculations that allow to interpret the experimental bands and choose a structural model that reproduces the probable location of acid sites in the sample.
Lemishko, T. (2019). Inelastic neutron scattering study of Brønsted acidity in LTA zeolite [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/119966
TESIS
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McFarlane, Andrew Robert. « The application of inelastic neutron scattering to investigate methane reforming catalysts ». Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/4098/.
Texte intégralRésumé :
Hydrocarbonaceous overlayers formed on a range of nickel alumina and gold-doped nickel alumina catalysts during both the H2O and CO2 reforming of methane has been examined using a number of techniques including thermal studies, XRD, TEM IR and Raman spectroscopy. These techniques have allowed both qualitative and quantitative analysis of the carbon and hydrogen components of coke to be achieved. Both amorphous carbon and filamentous carbon has been observed. Results show that changing the catalyst preparation routine effects the morphology of the carbon in both the CO2 and H2O reforming reactions. The “dry” and steam reforming reactions were also studied by inelastic neutron scattering. This technique has permitted quantitative measurements of the extent of hydrogen retention for the first time and has allowed elementary steps associated with the reaction to be explored from a new perspective. As well as determining the nature and quantity of the hydrocarbonaceous overlayers, the source of the coke has also been considered in the CO2 reforming reaction. Isotopic substitution reactions have been employed to achieve this. Temperature programmed oxidation measurements using a 13CO2 feedstream identify a clear role for the oxidant in the carbon retention process. The combination of techniques outlined above has permitted a series of elementary reactions to be proposed for both reforming reactions. Elementary surface reactions involving hydrogen are shown to be fast and efficient compared to those involving carbon. Furthermore, oxidation of carbon to CO is slower than that of carbon polymerisation. These statements are true for both CO2 and H2O reforming and suggest the CO2 reforming reaction has the potential to represent a environmentally friendly alternative to the industrially preferred steam reforming process. As well as increasing the understanding of these two highly relevant reaction systems, a range of inelastic neutron scattering reactors have been designed, built and tested under reforming conditions in order to accomplish the quantitative hydrogen measurements. An evaluation of these reactors, as well as a description of the development of the INS technique as a quantitative tool is given.
15
Rivera, Sharon A. « Inelastic neutron scattering and quantum mechanical calculations of polymorphic organic crystals ». Related electronic resource : Current Research at SU : database of SU dissertations, recent titles available full text, 2008. http://wwwlib.umi.com/cr/syr/main.
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Resler, David Alan. « Structure of 14C via Elastic and Inelastic Neutron Scattering from 13C : Measurement, R-matrix Analysis, and Shell Model Calculations ». Ohio University / OhioLINK, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1472558171.
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Öhrn, Angelica. « Neutron Scattering at 96 MeV ». Doctoral thesis, Uppsala universitet, Tillämpad kärnfysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8425.
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Data on elastic scattering of 96 MeV neutrons from 56Fe, 89Y and 208Pb in the angular interval 10-70° are presented. The previously published data on 208Pb have been extended, as a new method has been developed to obtain additional information at the most forward angles. The results are compared with phenomenological and microscopic optical potentials. The theory predictions are in general in good agreement with the experimental data. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. The data on 208Pb are in agreement with Wick's limit, while those on lighter nuclei overshoot the limit significantly. A novel analysis method has been developed to obtain the inelastic neutron emission cross sections from the existing 56Fe data. The method is based on folding a trial spectrum with the response of the detector setup. The data cover the angular interval 26-65° and an excitation energy range of 0-45 MeV, ranges hitherto not studied. The results are compared with nuclear model predictions and found to be in good agreement with the experimental data.
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Jenkins, Timothy Andrew. « Short strong hydrogen bonds studied by inelastic neutron scattering and computational methods ». Related Electronic Resource : Current Research at SU : database of SU dissertations, recent titles available full text, 2003. http://wwwlib.umi.com/cr/syr/main.
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Darko, J. B. « Development of neutron inelastic scattering analysis as an associated particle imaging technique ». Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636348.
Texte intégralRésumé :
An in vivo neutron inelastic scattering activation analysis based on the associated particle timing method is being developed with imaging capability. A proposed imaging system, the Associated Particle Imaging System (APIS) has been described. The APIS is based on identifying the spatial origin, of a measured neutron induced prompt gamma ray, by a position sensitive detection of the associated particle (the helium nucleus). Using the D-D reaction at neutron energy of 2.8 MeV elemental analysis of bulk samples has been demonstrated with the timing technique. Initial results of gamma ray measurements showed a significant reduction in the background. However, losses did occur with the generation of the timing signals, which was improved with the use of a Timing Single Channel Analyser TSCA. The timing method has also been used to measure aluminium in a hand phantom. Unlike some other techniques for measuring aluminium in bone, this technique eliminates the possible interference usually encountered with the presence of phosphorus. The minimum detection limit obtained with the use of the timing showed a significant improvement to that without the timing technique. Further improvements and optimising of the system to higher detection efficiency of the gamma rays have been considered. A detection limit of about 5 mg of aluminium in the hand for a dose of 10 mSv is achievable with the improved system.
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Biniskos, Nikolaos Verfasser], Thomas [Akademischer Betreuer] [Brückel et Georg [Akademischer Betreuer] Roth. « Inelastic neutron scattering on magnetocaloric compounds / Nikolaos Biniskos ; Thomas Brückel, Georg Roth ». Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1189332469/34.
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Allen, Jonathan Paul. « Magnetism in uranium and praseodymium intermetallic compounds studied by inelastic neutron scattering ». Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446566/.
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The dispersion of magnetic excitations in PrNiSn has been studied using inelastic neutron scattering. The dispersion relations along [0 0 Q] and [Q 0 0] have been determined for the excitations observed at 1.5, 2.5 and 5.2 meV. The two lower excitations are proposed to be modes originating from the 2 meV level predicted by earlier inelastic measurements. Additional measurements of the 3.5 meV excitation already studied were performed to provide higher resolution data and improved statistics. Preliminary measurements on NdNiSn were also made. Searches have been made using inelastic neutron scattering to look for crystalline electric field (CEF) excitations in the uranium-based intermetallics UPdSn, UCu2Sn and U3Pd20Si6. In UPdSn, a distinct CEF excitation has been observed at 50 meV in the paramagnetic phase. On cooling, the excitation shifts to lower energies and its temperature dependence exhibits marked changes at the antiferromagnetic transition temperatures of TN =25 and 40 K. The quasielastic scattering below 20 meV is found to increase significantly below the lower transition temperature. A set of Stevens parameters have been proposed to account for the observed data. The magnetic scattering observed in UCu2Sn is a broad, asymmetric peak centred at 7 meV which disappears above the quadrupolar ordering temperature of TQ = 16.5 K. The temperature dependence of the peak has been determined and comparisons with two different energy level schemes have been made. Three clear CEF excitations, which are visible in both the paramagnetic and ordered phase, have been observed at energies of 14.3, 23.9 and 31.6 meV in U3Pd20Si6. The temperature dependence of the excitations has been followed and a tentative level scheme proposed. A sharp, intense peak at 3 meV is visible at low temperatures and has been attributed to the exchange induced splitting of the 8c ground state below TN =19 K.
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Warringham, Robbie. « An investigation of iron-based Fischer-Tropsch catalysts using inelastic neutron scattering ». Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6364/.
Texte intégralRésumé :
The primary objective of this study was to characterise standard iron based Fischer- Tropsch catalysts by using the hydrogenation of CO at elevated temperatures and ambient pressure as a test reaction. The reaction test data is supplemented by the following analytical techniques; X-ray diffraction (XRD), Raman scattering, temperature programmed oxidation (TPO), transmission electron microscopy (TEM) and also inelastic neutron scattering (INS). The aim of these studies is to characterise the hydrocarbonaceous species present on the catalyst surface after reaction and to propose what role these hydrocarbonaceous species may play in the Fe/CO/H2 surface chemistry; be it active or not. These initial characterisation studies of the reacted iron catalysts were then extended to study the temporal dependence of these species with increasing reaction time. The application of inelastic neutron scattering is shown to provide a great deal of information regarding the hydrocarbonaceous component present in these types of systems. Therefore the application of INS and the subsequent result constitute the majority of the discussion of this study. The research objectives for this study can be listed as follows; 1. To prepare an iron oxide catalyst using a reproducible and controlled method and to characterise this material using the methods outlined previously. 2. To react the iron oxide catalysts using a representative test reaction for the purpose of characterising the surface species present after reaction. 3. To use inelastic neutron scattering to probe and gain a vibrational spectroscopic insight to the hydrocarbonaceous species present. 4. To study the temporal dependence of the hydrocarbonaceous species and how they alter with increasing time-on-stream. The thesis will begin with an introduction to Fischer-Tropsch catalysis, with a focus on iron-based Fischer-Tropsch catalysis. The discussion will move to some heightened analysis of some previously reported INS measurements of iron Fischer-Tropsch catalysts. This prelude will be followed by the main discussion of results, that is the characterisation of the reacted iron oxide catalyst using inelastic neutron scattering and the temporal study with increasing time-on-stream. The thesis will then finish with a discussion on a brief study investigating the role of promoters in iron based Fischer-Tropsch catalysts, which constitutes future work.
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Biniskos, Nikolaos [Verfasser], Thomas [Akademischer Betreuer] Brückel et Georg [Akademischer Betreuer] Roth. « Inelastic neutron scattering on magnetocaloric compounds / Nikolaos Biniskos ; Thomas Brückel, Georg Roth ». Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://nbn-resolving.de/urn:nbn:de:101:1-2019062706541954675594.
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Johnston, Kyle. « Polarized He-3 as an Effective Neutron Target for Deep Inelastic Scattering ». Master's thesis, Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/318281.
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PhysicsM.S.
In undergraduate physics courses, we are all taught that a proton and a neutron both have a quantity called 'spin' which has a simple value of 1/2 in units of ℏ. It was first naively understood that this value comes from the addition of the spins of the basic constituents, quarks and gluons. However, experiments revealed that it is not enough. The value of 1/2 has yet to be reconciled with the addition of not only the spins of the constituents but also their orbital motion. Clearly, the spin structure in terms of the basic constituents needs more investigation. This thesis aims to describe the polarization and calibration of a polarized ³He target, which can be used for probing the spin structure of the neutron in terms of its constituents, quarks and gluons.
Temple University--Theses
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Kaiser, Ralf Bernd. « Measurement of the spin structure of the neutron using polarised deep inelastic scattering ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24319.pdf.
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Hamilton, Neil G. « The application of inelastic neutron scattering to the investigation of industrial heterogeneous catalysts ». Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2164/.
Texte intégralRésumé :
Vibrational spectroscopy has been used to probe the surface chemistry of two heterogeneous catalysts. This has principally involved the application of infrared (IR) spectroscopy and inelastic neutron scattering (INS), with a much reduced role for Raman scattering. Firstly, the activation of high surface area alumina catalysts has been investigated. IR spectroscopy is able to discern the presence of a recently postulated active site. Moreover, INS measurements indicate the potential of this technique to provide additional insight into the surface Lewis acidity of this substrate. The second part of this project uses the reaction of carbon monoxide and hydrogen over an Fe-based catalysts to discern some of the fundamental processes that are likely to contribute to the more complex Fischer-Tropsch synthesis (FTS) process. Ancillary measurements on an industrial grade FTS catalyst validate the procedure adopted.
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Federico, Mazza. « First Principle Calculations & ; Inelastic Neutron Scattering on the Single-Crystalline Superconductor LaPt2Si2 ». Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278071.
Texte intégralRésumé :
This work presents a comprehensive study on single crystalline LaPt2Si2, in which superconductivity and a charge density wave (CDW) coexist. The usage of density functional theory (DFT) modeling and Inelastic Neutron Scattering has been the primary form of investigation, in order to determine all the characteristic features of the sample taken under consideration. From the results one can observe that the Fermi surface nesting is the primary contributor for the CDW wavevector ~qCDW = (1/3, 0, 0). In addition, the phonon density of states present two typical energy levels, with soft modes in the Pt3-Pt4 layer coherent with the presence of a CDW. The superconducting temperature has been estimated at Tc = 1.6 K. The experimental data from the inelastic instrument High Resolution Chopper Spectrometer (HRC) at the J-PARC neutron source are in good agreement with the theoretical simulations, showing the same energy levels for the polarization phonon modes (from 4 to 18 meV and from 32 to 42 meV).Denna rapport presenterar en omfattande studie av enkristalls LaPt2Si2 i vilken supraledning och en laddningsdensitetsvåg (CDW) samexisterar. Användandet av DFT-modellering och neutronspridning har varit de huvudsakliga undersökningsmetoderna, för att bestämma alla karakteristiska drag hos det undersökta provet. Från resultaten kan observeras att den inneslutna Fermiytan är den huvudsakliga bidragaren till CDW-vågvektorn~qCDW = (1/3, 0, 0). Vidare visar den närvarande fonontillståndsdensiteten två typiska energinivåer, med mjuka lägen i Pt3-Pt4-skiktet, som stämmer överens med närvaron av en CDW. Den supraledande temperaturen har uppskattats till Tc = 1.6 K. Experimentella data från det inelastiska instrumentet HRC vid J-PARCs neutronkälla stämmer väl överens med teoretiska simuleringar, som visar samma energinivåer för polarisationsfononlägena (från 4 till 18 meV och från 32 till 42 meV).
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Elhami, Esmat. « STUDIES OF LOW-LYING STATES IN 94ZR EXCITED WITH THE INELASTIC NEUTRON SCATTERING REACTION ». UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/624.
Texte intégralRésumé :
The aim of nuclear structure studies is to observe and describe the structures and associated symmetries in nuclei, which in turn help us in understanding the nature of nucleon-nucleon interactions in a nucleus as a many-body quantum system. The protons and neutrons as constituents of a nucleus and their interactions are responsible for nuclear properties. The evolution of nuclear structure as a function of valence nucleon number, i.e., the number of nucleons beyond a magic number, can be inferred from the experimental level scheme and transition rates. In particular, the studies of low-lying, low-spin excited states in stable nuclei provide valuable information on the interplay of valence neutrons and protons in nuclear structure. The decay scheme and knowledge of transition strengths in the low-lying states become a benchmark for testing theoretical model predictions and understanding the underlying microscopic foundations of nuclear structure. Along with the experimental techniques, theoretical models have been developed to explain and describe the observed nuclear properties, e.g., shell model, Fermi-gas model, optical and liquid-drop models, and several “collective” models.
94/40Zr50 nucleus with 2 protons and 4 neutrons above the shell closures of the 88/38Sr50 core nucleus is considered as a nearly spherical nucleus. Such nuclei present a vibrational structure; surface vibration of the nucleus about a spherical shape. In addition to the symmetric excitations, in which proton and neutron oscillations are in phase, there are another class of excitations in which the wave function is not fully symmetric with respect to the exchange of protons and neutrons. These states are so called mixed-symmetry (MS) states. Such excitations have been observed in the N= 52 neighboring isotones. In this study, the low-lying structure of 94/40Zr has been studied with the (n, n'ƴ) reaction at the University of Kentucky and Triangle Universities Nuclear Laboratories (TUNL) facilities, to identify symmetric and MS excitations in this nucleus.
A decay scheme has been established based on excitation function and coincidence measurements. Branching ratios, multipole mixing ratios, and spin assignments have been determined from angular distribution measurements at En= 2.3, 2.8, and 3.5 MeV. Lifetimes of levels up to 3.4 MeV were measured by the Doppler-shift attenuation method (DSAM), and for many transitions reduced transition probabilities were determined. The experimental results were used for the identification of collective symmetric and mixed-symmetric (MS) multiphonon excitations. The 2+/2 state at 1671.4 keV has been identified as the lowest MS state in 94Zr; B(M1; 2+/ms → 2+/1 ) = 0.31(3) μ2/N. This state has an anomalous decay behavior, i.e., B(E2; 2+/ ms → 0+/1 ) = 7.8(7) W.u., which is unusually large compared to the B(E2; 2+/1 → 0+/1 ) = 4.9(3) W.u. More anomalies were identified in the states above the 2+/ms state. For example, the 4+/2 state at 2330 keV decays strongly to the 2+/1 state, B(E2; 4+/2 → 2+/1 ) = 20+3/−2 W.u., compared to the 4+/1 state at 1469 keV, B(E2; 4+/1 → 2+/1 ) = 0.878(23) W.u. The experimental results revealed additional interesting and unusual properties of the low-lying states in 94Zr. Shell model calculations were performed with the Oxbash code, using the Vlow k interaction. Also, the IBM-2 predictions in the vibrational limit were compared with the experimental results. The results from neither of these nuclear models were in good agreement with the observed transition strengths, e.g., the B(E2; 2+/ms → 0+/1 ) value. These observations may indicate that the contributions of valence nucleons in the low-lying excited states of 94Zr differ from what has been perscribed by the shell model and the IBM-2 model. The effects of the Z = 40 and N = 56 subshell closures should be also considered. In a simple interpretation, the excited states are classified in two distinct categories, i.e., those populating the 2+/2 state and those decaying to the 2+/1 state. This approach suggests that in 94Zr the low-lying states may be related to two-configurations coexistence.
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Elhami, Esmat. « Studies of low-lying states in ⁹⁴Zr excited with the inelastic neutron scattering reaction ». Lexington, Ky. : [University of Kentucky Libraries], 2008. http://hdl.handle.net/10225/894.
Texte intégralRésumé :
Thesis (Ph. D.)--University of Kentucky, 2008.Title from document title page (viewed on October 29, 2008). Document formatted into pages; contains: xii, 142 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 135-139).
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ROMANELLI, GIOVANNI. « On the quantum contributions to phase transitions in Water probed by inelastic neutron scattering ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2013. http://hdl.handle.net/2108/202107.
Texte intégralRésumé :
This Thesis on the Physics of condensed matter collects some of my research activities performed
during my Doctorate devoted to the measurement of nuclear quantum effects on the dynamics of
hydrogen and oxygen in the water molecule. Indeed, the single-particle motion and in particular
the kinetic energy are effective thermometers representing the probe to measure the deviations
from classical or first-order quantum mechanics.
In the introduction, I present the scientific case and highlight the complexity of the mechan
ical and thermodynamic properties of water and their physical modelling. I also explain why
neutron scattering has been chosen as the experimental technique to study this subject and
how inelastic scattering at high energy and momentum transfers can access the single-particle
motion in the case of the nuclear constituents of the molecule i.e., oxygen and hydrogen, the
latter as a proton or deuteron.
Then, a discussion on momentum distributions in statistical classical and quantum systems
is presented, introducing models enabling a physical interpretation in the case of water or
similar molecules. In particular, the use of multivariate distributions allows the measurement
of the anisotropy of the effective potential which determines the nuclear motion. In particular,
i) I optimized the data reduction and analysis routines reducing their running times and ii)
I increased the reliability of the fitting parameters describing the shapes of the momentum
distributions, reducing the number of free parameters through physical constraints. This leads
to the determination of the components of the nuclear kinetic energy matrix.
A harmonic model is then proposed to relate these observables to the translational, ro
tational and vibrational frequencies of the molecule. This calculation is based on the model
proposed by Moreh and co-workers for the interpretation of gamma nuclear resonance scatter
ing from excited nuclear levels. I derived the analytical generalization to a molecule in any phase
through knowledge of vibrational frequencies and molecular geometrical parameters. Moreover,
I implemented the model in the data analysis routines in order to predict, guide or compare with experimental results.
The results of inelastic neutron scattering experiments on the melting of light and heavy wa
ter are then presented. Changes in the components of the kinetic-energy matrix are discussed
in the case of phase transitions and the relevance of nuclear quantum effects is highlighted.
The experimental results are compared to the harmonic model and to computer simulations
based on path-integral molecular dynamics. Another set of experiments is presented on the
measurement of the dynamic structure factor of supercritical water in thermodynamic states
across the pseudo-critical line, i.e., the locus of points with a pressure greater than the critical
pressure corresponding to a maximum of the specific heat for a temperature greater than the
critical temperature. Moreover, the changes in the dynamic structure factor are studied in the
amorphous-solid water phase across the transition from very-high-density to high-density amor
phous ice, and then from the high-density to the low-density amorphous ice. I have been directly
involved in the experiment preparation and set-up, measurements, analysis and interpretation
of the experiments on heavy water, supercritical water and amorphous ice. I contributed to
the data analysis and interpretation of inelastic neutron scattering experiments in super-cooled,
stable liquid, supercritical water and poly-crystalline ice.
This work has been carried out at the ISIS Neutron and Muon Pulsed Source at the Ruther
ford Appleton Laboratory in the UK for about four months for the experiments and data
analysis, at the SNS Spallation Neutron Source at Oak Ridge National Laboratory in the US
for data reduction and analysis, and in Tor Vergata for the data analysis, interpretation and
modelling.
During the three years of Doctorate I attended to the School of Neutron Scattering Francesco
Paolo Ricci (XI Edition) on the neutron investigation of bio-systems in Taormina as a student; I
participated in the International Neutron Scattering Instrumentation School at the Laboratori
Nazionali di Frascati as a student and local organizer; I attended the International Conference
on Neutron Scattering 2013 in Edinburgh contributing to the poster session with the results on
the oxygen dynamics that was for the first time measured through neutron Compton scattering;
I contributed to the VI Workshop in Electron-Volt Neutron Spectroscopy meeting in Abingdon
(UK) with a talk on competing quantum effects on the melting of heavy water. Since September 1st, I steadily work at ISIS in Rutherford Appleton Laboratory to the computational and experimental development of eV neutron scattering techniques.
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Thomas, Rowena. « Development of resonant inelastic X-ray metal catalysts scattering spectroscopy for 4d and 5d transition metal catalysts ». Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/354566/.
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Atter, Glenn David. « The study and refinement of vibrational force fields using optical and inelastic neutron scattering spectra ». Thesis, University of York, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319456.
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Osborn, Raymond. « Neutron inelastic scattering studies of magnetic exitations in rare earth compounds and transition metal alloys ». Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292435.
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Bircher, Roland. « Studies of single-molecule magnets and spin clusters by inelastic neutron scattering and magnetic measurements / ». Bern : [s.l.], 2005. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Lorne, Thomas. « Contribution of inelastic neutron scattering to the characterization of the grafting of fluorophores onto double-walled carbon nanotubes ». Thesis, Toulouse 3, 2017. http://www.theses.fr/2017TOU30363/document.
Texte intégralRésumé :
Face à la recrudescence de l'utilisation des nanotubes de carbone (NTCs) pour des applications de pointe, leur impact potentiel sur la santé et sur l'environnement est devenu une question centrale. Afin d'évaluer les risques liés à l'exposition accidentelle des êtres-vivants à ces nanoparticules de nombreuses études de toxicité ont été réalisées. Pour certaines, il est important de pouvoir déterminer précisément où et comment les NTCs s'accumulent dans les organismes aquatiques ou dans les cellules. Un des moyens habituel pour réaliser de telles expériences consiste à fonctionnaliser les NTCs avec des molécules fluorescentes, qui seront par la suite mises en évidence sous un rayonnement de longueur d'onde appropriée, permettant ainsi de localiser les nanotubes. Malgré le fait que cette technique soit bon marché et facilement mise en œuvre, elle souffre d'un défaut majeur: elle présuppose en effet que les molécules fluorescentes resteront attachées aux nanotubes de façon définitive. Cependant, cette supposition peut être sérieusement questionnée car les fluorophores possèdent généralement un ou plusieurs cycles aromatiques pouvant facilement conduire à l'adsorption de ces derniers sur les parois des NTCs. Dès lors, une fois que les NTCs atteignent l'environnement chimique complexe d'une cellule, on peut s'attendre à une désorption des molécules fluorescentes, pouvant de fait conduire à de mauvaises interprétations des résultats expérimentaux. Il est par conséquent essentiel d'évaluer l'efficacité du protocole de greffage et de déterminer les différentes proportions de molécules greffées de façon covalente et non-covalente (adsorbées). Bien entendu, la fonctionnalisation des NTCs étant une problématique clef dans le développement de leurs applications en science des matériaux, les questions soulevées ici dépassent le simple cadre de la santé et de l'environnement. Pour y répondre, nous avons décidé de nous intéresser à la fonctionnalisation de nanotubes de carbone double-parois (DWNTs) par deux molécules fluorescentes, l'Isothiocyanate de Fluorescéine (FITC) et la cyanine 5Me(Net2)2. Nous avons, pour ce faire, réaliser le greffage des fluorophores sur des DWNTs oxydés purifiés à l'aide d'un procédé de fonctionnalisation en 3 étapes. Enfin, nous avons caractérisé nos échantillons au moyen de deux techniques différentes de spectroscopie, la spectroscopie de photoélectron X (XPS) et la spectroscopie de diffusion inélastique de neutrons (INS). En complément de la spectroscopie de neutrons, nous nous sommes appuyés sur des simulations numériques, telle que la théorie de la fonctionnelle de la densité (DFT) pour les analyses de nos données expérimentales. Les résultats ainsi obtenus, ont permis de montrer que, contrairement à ce qui était communément attendu lors d'un greffage covalent, une part non négligeable des marqueurs fluorescent restait adsorbée à la surface des NTCs, et ce, en dépit de lavages consciencieux par des solvants appropriés. La présence de ces marqueurs fluorescents adsorbés montre, dans le cadre des études de toxicité, qu'il existe une certaine probabilité que ces derniers se détachent des NTCs lors de leur voyage dans un organisme ou dans une cellule, ce qui conduirait l'établissement de conclusions potentiellement erronées quant au destin de ces nanoparticulesFacing the growing use of carbon nanotubes (CNTs) in state-of-the-art applications, the question of their potential impact on health and environment became a central one. In order to evaluate the risks related to living being exposure to those nanoparticles, several toxicity studies have been performed aiming at knowing the exact location of the CNTs accumulating inside organisms or cells. A very common way to track them in such conditions is to functionalize the CNTs with fluorescent molecules which would be highlighted afterwards under a light with appropriate exciting wavelength. Despite the fact that these fluorescence techniques are very cheap and easy to operate, they suffer from a major drawback: they assumes that the fluorescent molecule is permanently linked to the CNTs. It is however reasonable to question this assumption as the fluorescent molecules are usually constituted by one or more 6-carbon rings that can easily also simply adsorb on the surface of the CNTs. This non-covalent binding could lead to the desorption of the fluorophore once the CNTs reach the complex chemical environment of a living cell or organism. Therefore, the fluorescence data could lead to wrong information about the CNTs location. Therefore, it is fundamental to understand the grafting mechanisms in order to estimate the efficiency of the covalent functionalization of the CNTs as well as the amount of simply adsorbed fluorophores. Of course, the impact of such a question clearly exceeds the field of the health and the environment, because the functionalization of CNTs is a key for their application is Materials Science in general. In order to answer to these questions, we chose to study the functionalization of Double-Walled carbon Nanotubes (DWNTs) with two different fluorophores, the Fluorescein Isothiocyanate (FITC) and the STREPTOcyanine 5Me(Net2)2. We used a three-step functionalization process to graft the fluorophores on highly-purified oxidized DWNTs. Finally, both the surface and the bulk of the sample have been investigated using two different spectroscopic techniques, the X-ray photoelectron spectroscopy (XPS) and the inelastic neutron scattering spectroscopy (INS). In addition to neutron techniques we also used computational techniques such as Density Functional Theory (DFT) calculations for a better analysis of our results. The results obtained by means of this two powerful techniques highlighted that, although the fluorescent markers is always considered to be strongly bonded onto carbon nanotubes when using a covalent strategy, a non-negligible part may in fact be only adsorbed, even after thorough washings in appropriate solvents. This is likely, in the particular field of toxicology, to lead to a release of the fluorescent marker at some point along the journey of the nanoparticle throughout the cells or the whole organism, and thus to partially wrong conclusions in terms of their fate in terms of biodistribution, accumulation or excretion
36
Crider, Benjamin P. « Nuclear Structure Relevant to Double-beta Decay : Studies of ⁷⁶Ge and ⁷⁶Se using Inelastic Neutron Scattering ». UKnowledge, 2014. http://uknowledge.uky.edu/physastron_etds/17.
Texte intégralRésumé :
While neutrino oscillations indicate that neutrino flavors mix and that neutrinos have mass, they do not supply information on the absolute mass scale of the three flavors of neutrinos. Currently, the only viable way to determine this mass scale is through the observation of the theoretically predicted process of neutrinoless double-beta decay (0νββ). This yet-to-be-observed decay process is speculated to occur in a handful of nuclei and has predicted half-lives greater than 10²⁵ years. Observation of 0νββ is the goal of several large-scale, multinational efforts and consists of detecting a sharp peak in the summed β energies at the Q-value of the reaction. An exceptional candidate for the observation of 0νββ is ⁷⁶Ge, which offers an excellent combination of capabilities and sensitivities, and two such collaborations, MAJORANA and GERDA, propose tonne-scale experiments that have already begun initial phases using a fraction of the material. The absolute scale of the neutrino masses hinges on a matrix element, which depends on the ground-state wave functions for both the parent (⁷⁶Ge) and daughter (⁷⁶Se) nuclei in the 0νββ decay and can only be calculated from nuclear structure models. Efforts to provide information on the applicability of these models have been undertaken at the University of Kentucky Accelerator Laboratory using gamma-ray spectroscopy following inelastic scattering reactions with monoenergetic, accelerator-produced fast neutrons. Information on new energy levels and transitions, spin and parity assignments, lifetimes, multipole mixing ratios, and transition probabilities have been determined for ⁷⁶Se, the daughter of ⁷⁶Ge 0νββ, up to 3.0 MeV. Additionally, inaccuracies in the accepted level schemes have been addressed.
Observation of 0νββ requires precise knowledge of potential contributors to background within the region of interest, i.e., approximately 2039 keV for ⁷⁶Ge. In addition to backgrounds resulting from surrounding materials in the experimental setup, ⁷⁶Ge has a previously observed 3952-keV level with a de-exciting 2040-keV γ ray. This γ ray constitutes a potential background for 0νββ searches, if this level is excited. The cross sections for this level and, subsequently, for the 2040-keV γ ray has been determined in the range from 4 to 5 MeV.
37
Maynard, Stephen Charlrs Payne. « Adsorption of gases on inorganic solids and the characterisation of the solids by inelastic neutron scattering ». Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294001.
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Ziegler, Fabian. « Investigation of the Structure and Dynamics of Multiferroic Systems by Inelastic Neutron Scattering and Complementary Methods ». Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E5A6-5.
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Gaw, Stephen Michael. « Cooperative spin excitations in quantum materials studied by neutron spectroscopy ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c20676e1-b927-4ee5-a3fe-97f0f80cb141.
Texte intégralRésumé :
This thesis describes the experimental investigation of three different strongly correlated transition-metal oxide systems. The magnetic behaviour of each has been probed using inelastic neutron spectroscopy. A distinctive hour-glass excitation spectrum has been observed in the layered cobaltate La1.75Sr0.25CoO4. This spectrum is similar to that measured in a related cobaltate La1.67Sr0.33CoO4, although it appears broader. The spectrum has been reproduced using a spin wave model derived from a disordered cluster spin glass ground state. Signatures of spin glass behaviour have also been observed in bulk magnetisation measurements of La1.75Sr0.25CoO4. These findings, once more, demonstrate the emergence of an hour-glass spectrum from a ground state that combines quasi-one dimensional magnetic correlations and disorder. Additionally, this study shows that charge and magnetic stripe order persists to lower dopings in La2-xSrxCoO4 than previously thought. The complete magnetic excitation spectrum of the multiferroic compound CuO has been measured for the first time. A high energy, one-dimensional magnetic spectrum is observed and modelled using the Muller ansatz derived for the S=1/2 Heisenberg antiferromagnetic chain. At lower energies, a three-dimension spectrum is observed. The measured spectrum is inconsistent with all previous theoretical estimates of the dominant inter-chain exchange interactions in CuO. The inter-chain dispersion is successfully described by a phenomenological model based on linear spin wave theory. The third material investigated, LuFe2O4 demonstrates complex charge and magnetic order, the precise nature of which is still under debate. The full spectrum of in-plane excitations in LuFe2O4 has been measured and a complicated dispersion consistent with six magnetic modes is observed. These findings are compatible with structures described by a magnetic unit cell containing six spins. The dispersion can be described by a spin wave model derived from a bilayer structure comprised of charge-rich and charge-poor monolayers. This structure is consistent with the original site-specific model for the 3D magnetic ordering in LuFe2O4.
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Kargl, Florian. « The interplay of structure and microscopic dynamics in oxidic melts observed by means of inelastic neutron scattering ». [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978975618.
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Barratt, Julian P. « Neutron scattering studies of heavy fermion behaviour in YbNiâ†2Bâ†2C ». Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365688.
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Nadel-Turonski, Pawel. « Experimental Studies of Neutron Emission Induced by Heavy-Ion Scattering ». Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3570.
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PARMENTIER, ALEXANDRA. « FOLLOW THE WATER : an insight into proton quantum dynamics of selected phases of water by inelastic neutron scattering ». Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2016. http://hdl.handle.net/2108/201939.
Texte intégralRésumé :
The present PhD thesis stems from 36 months of intensive experimental investigation and data analysis of quantum dynamics of the hydrogen nucleus in various amorphous solid states (AIs) and supercritical phase (SCW) of water by inelastic neutron scattering. This doctoral effort places this work into the apparently inexhaustible stream of studies on water, at the same time offering an evidence of the role of density in shapingthesingle-particlepotential-energysurfaceintermsofcurvatureandanharmonicity,ashighlightedbyarecenthigh-impactpublicationinJ. Phys. Chem. Lett. [1]. The layout of the monograph has been thought for a broad audience, with an eye to making it both agile and exhaustive. After a brief introduction on the why and how of water and neutron spectroscopy, two separate chapters are dedicated to the properties of amorphous ices and the supercritical fluid, followed by the presentation of the fundamentals of inelastic (INS) and deep-inelastic (DINS) neutron techniques, and a sketch of the instrumentation employed, which is functional to the full understanding of the development of data reduction and analysis. Thesubsequentchapteronthepotentialofmeanforce(PMF)introducesanalternativeandpossiblyeasier-to-managewaytointerpretDINSoutputs. Thearrangement of related data and their interpretation into a scientific paper for a special issue of Front. Phys. is currently afoot. The work closes with a clean report of experimental results and relative discussion, which allows for inferring new insights into the function and effects of the H-bond environmentthemoleculesareimmersedin, aswellaspicturingfutureinvestigation scenarios. All INS and DINS experiments described in the following sections were performed at MARI and VESUVIO spectrometers, respectively, both located at ISIS Neutron and Muon Pulsed Source at the Rutherford Appleton Laboratory in the UK, with later data analysis and interpretation developed at the Department of Physics of Tor Vergata University of Rome, Italy. Theexperimentalworkwasaccompaniedbytheparticipationbypostercontribution in the 2013 International Conference on Neutron Scattering in Edinburgh, UK, the VI Workshop in eV Neutron Spectroscopy (2014) in Abingdon, UK, and the 2016 Erice School (’Water and Water Systems’) held in Erice (TP), Italy, and promoted by the School of Neutron Scattering (SoNS) entitled to Francesco Paolo Ricci.The second meeting called for my personal involvement into the coordination of the final scientific discussion, which is currently included in the proceedings of the conference [2–4]. A fruitful introduction to the PhD route was for sure the pre-doctorate course on general neutron scattering held by ILL in summer 2012 (Giornate Didattiche). As to present, I am about to start a full-immersion training as a McStas professional user, in order to participate in the development of the VESPA Project at the European Spallation Source (ESS). A parallel collaboration is in progress with a team based in Sapienza University of Rome in order to investigate anomalous transport properties of ultraconfined water by quasi-elastic neutron scattering (QENS) [5] and other spectroscopic techniques.
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Ciezak, Jennifer A. Hudson Bruce S. « Organic charge transfer complexes and an open-shell organic radical studied by inelastic neutron scattering spectroscopy and DFT methods ». Related electronic resource : Current Research at SU : database of SU dissertations, recent titles available full text, 2004. http://wwwlib.umi.com/cr/syr/main.
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Nakatsuka, Noritsugu. « Isoscalar and Isovector strengths of low-energy dipole excitations in neutron-rich unstable 20O ». Kyoto University, 2018. http://hdl.handle.net/2433/232241.
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Liu, Yun 1973. « Studies of structure and dynamics of biological macro-molecular assemblies by low angle neutron diffraction and inelastic X-ray scattering ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34438.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005.Includes bibliographical references (leaves 141-148).
This thesis is organized into two parts which focus on the studies of the dynamic structure factor and static inter-particle structure factor respectively. In the first part, we have measured and analyzed the dynamic structure factors of aligned 40 wt% calfthymus Na-DNA molecules with the inelastic X-ray scattering (IXS). In the second part, we have developed a new efficient method to calculate the inter-particle structure factor in a simple fluid interacting with a two-Yukawa term potential and apply it to study the kinetic phase diagram and analyze the small angle neutron scattering (SANS) intensity distribution of colloidal systems. By analyzing the dynamic structure factor measured with IXS, the phonon dispersion relations of 40 wt% calf-thymus Na-DNA with different counterion atmosphere are constructed. It is found that the addition of extra counterions will increase phonon damping at small scattering wave vector, Q. At the intermediate Q range (12.5 nm- < Q < 22.5 nm-l), it may even overdamp the phonon so that the phonon feature can not be extracted from the IXS spectra. The measured sound speed is 3100m/s, which is much higher than the sound speed, - 1800m/s, obtained by Brillouin light scattering. This difference shows that the atoms of DNA molecules are closely coupled to the surrounding water molecules.
(cont.) Therefore, the different dynamic response of water molecules in different Q range affects the overall dynamic response of the hydrated DNA molecules. By analyzing the IXS spectra, the intermediate scattering function is extracted and shows a clear two step relaxation with the fast relaxation time ranging from 0.1 to 4 ps and the slow relaxation time ranging from 2 to 800 ps. In order to understand the phase behavior and the interactive potential of a colloidal system, we have developed a new and efficient method to calculate the inter-particle structure factor of a simple fluid interacting with a two-Yukawa term potential. We have applied this method to study the kinetic phase diagram of a system interacting with a short-range attraction and a long-range repulsion. A new glass phase, cluster glass, is determined through the theoretical analysis by the mode coupling theory (MCT). The SANS intensity distribution of cytochrome C protein molecules in solutions is measured and analyzed with our method. A sharp rising intensity at very low Q value has been consistently observed, which is named zero-Q peak. The existence of the zero-Q peak implies that a weak long-range attraction between protein molecules in solutions exists and has a even longer range than the electrostatic repulsion.
by Yun Liu.
Ph.D.
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Weber, Frank. « Probing electronic phase transitions with phonons via inelastic neutron scattering : superconductivity in borocarbides, charge and magnetic order in manganites$nElektronische Ressource / ». [S.l. : s.n.], 2007. http://digbib.ubka.uni-karlsruhe.de/volltexte/1000007516.
Texte intégral
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Peters, Erin Elizabeth. « Nuclear Structure in Transitional Regions : Studies of ¹³²,¹³⁴Xe and Lifetimes in the Stable Zr Nuclei with the (n,n′γ) Reaction ». UKnowledge, 2014. http://uknowledge.uky.edu/chemistry_etds/34.
Texte intégralRésumé :
Nuclei at closed shells tend to be spherical and are well-described by the shell model, while those between closed shells are deformed and better described by collective models. The nuclei which are in transitional regions between spherical and deformed may be studied to gain insight into the nature of this transition. The stable isotopes of zirconium and xenon span such transitional regions and are the subject of this dissertation. Gamma-ray spectroscopy following inelastic neutron scattering has been performed on the stable isotopes of Zr as well as 132,134Xe at the University of Kentucky Accelerator Laboratory. Level lifetimes have been measured using the Doppler-shift attenuation method, which allow the determination of transition probabilities that are of utmost importance in elucidating the structure of these nuclei. The lifetime measurements were the focus of the study of the Zr isotopes. Previously measured level lifetimes in 94Zr by our group were called into question by recent electron scattering experiments. This motivated a re-measurement of these lifetimes and led to a study of the role of the chemical properties of the scattering samples employed in the measurements. Various Zr-containing compounds were characterized with powder X-ray diffraction and scanning electron microscopy and were employed as scattering samples. These studies revealed the impact of using amorphous materials and those composed of small particles as scattering samples on the resulting lifetimes, and has important implications for future lifetime measurements employing the Doppler-shift attenuation method. For the xenon experiments, highly enriched (>99.9%) 132Xe and 134Xe gases were converted to solid 132XeF2 and 134XeF2, and were used as scattering samples. The xenon isotopes have not been particularly well-studied as elemental targets are gases under ambient conditions, which introduces difficulties into the measurements. Much new information was obtained for these nuclei, including the placement of many new transitions and levels, and measurement of many new level lifetimes, allowing the determination of reduced transition probabilities. This additional information provided important insight into the structure of these two transitional nuclei.
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Kauth, Maximilian [Verfasser], et F. [Akademischer Betreuer] Weber. « Phonon renormalization in La-cobaltate and Fe-based superconductors investigated by inelastic neutron and x-ray scattering / Maximilian Kauth ; Betreuer : F. Weber ». Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/1174992255/34.
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Allada, Kalyan C. « Measurement of Single Spin Asymmetries in Semi-Inclusive Deep Inelastic Scattering Reaction n↑(e, éπ+)X at Jefferson Lab ». UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/31.
Texte intégralRésumé :
What constitutes the spin of the nucleon? The answer to this question is still not completely understood. Although we know the longitudinal quark spin content very well, the data on the transverse quark spin content of the nucleon is still very sparse. Semi-inclusive Deep Inelastic Scattering (SIDIS) using transversely polarized targets provide crucial information on this aspect. The data that is currently available was taken with proton and deuteron targets.
The E06-010 experiment was performed at Jefferson Lab in Hall-A to measure the single spin asymmetries in the SIDIS reaction n↑(e,éπ±/K±)X using transversely polarized 3He target. The experiment used the continuous electron beam provided by the CEBAF accelerator with a beam energy of 5.9 GeV. Hadrons were detected in a high-resolution spectrometer in coincidence with the scattered electrons detected by the BigBite spectrometer. The kinematic coverage focuses on the valence quark region, x = 0.19 to 0.34, at Q2 = 1.77 to 2.73 (GeV/c)2. This is the first measurement on a neutron target. The data from this experiment, when combined with the world data on the proton and the deuteron, will provide constraints on the transversity and Sivers distribution functions on both the u and d-quarks in the valence region. In this work we report on the single spin asymmetries in the SIDIS n↑(e,éπ+)X reaction.