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1
Grant, John. "Measuring mesospheric ionisation." Thesis, University of Canterbury. Physics, 2002. http://hdl.handle.net/10092/6072.
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The differential absorption method of retrieving D-region electron density profiles from partially reflected MF radar pulses, has existed in many variants since the original Gardner and Pawsey experiment of 1953. Magnetoionic theory predicts that a pulse propagating within the ionosphere undergoes birefringence two magnetoionic modes. The differential absorption method requires that both the differential absorption and the ratio of the reflection coefficients of those modes are evaluated from a model profile.
In this thesis, a critical review of the differential absorption method is undertaken. Results obtained using the phase shifted correlation polarimeter at the University of Canterbury's Birdlings Flat radar facility near Christchurch, New Zealand, are synthesised to retrieve electron density measurements. The results indicate that over some height ranges, differential absorption method does not account adequately for ionospheric discontinuities and generates reflection coefficient ratios which are in error.
An alternative to the differential absorption method is developed. This alternative uses an optimal estimation inverse method to retrieve both electron density-height and gradient electron density-height profiles. It is asserted that this retrieval, although not resolving small scale discontinuities, does account for them.
The retrieval uses a forward model which includes the physical effects of the ionosphere upon a propagating MF pulse. A feature of the forward model is that as well as using a Fresnel reflection model and parameterising pulse width effects, it includes the effects of both absorption and Faraday rotation upon the magnetoionic modes of propagating pulses.
Hourly mean electron density-height and gradient .electron density-height profiles are generated for the hours of 10:00 to 14:00 every day, over the time period of January 1994 to December 1999, The results of these retrievals are used for internal and external validation as well as to assess geophysical effects upon the distributions of middle atmospheric nitric oxide.
Results of diagnostic tests and the internal validation process indicate that the retrieval consistently converges towards solutions which can be regarded as approximating "true" ionospheric behaviour. The external validation results suggest that the optimal estimation electron densities contain structure which has been observed in other studies and which can be explained in terms of dynamics and chemistry.
Analyses of long term and seasonal variability of nitric oxide transport are facilitated by using a simple photochemical model to derive nitric oxide profiles from optimal estimation electron density profiles. Results show that wintertime enhancement of nitric oxide transport to the mesosphere takes place. The extent of this enhancement varies from year to year with the downward extent of vertical transport of thermospheric nitric oxide showing inter-annual variability.
Gradient electron densities may indicate the presence of mesospheric gravity wave breaking. They also exhibit a strong seasonal variation with large reductions at equinox possibly indicating a lack of breaking gravity waves at this time of year. The ratio of gradient electrons to electrons shows seasonal variability consistent with the notions that gravity wave breaking occurs over a broader range in winter than in summer and upward propagation of orographic gravity waves is favoured in winter.
2
Carruthers, David Robert James. "Quantal threshold ionisation." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333786.
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Dillon, Leonard A. "Electrospray ionisation of volatile analytes : a parametric study of secondary electrospray ionisation." Thesis, University of Huddersfield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.494308.
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With the development of the International Space Station and the planned increase in the duration of spacecraft missions NASA (National Aeronautics and Space Administration) issued a challenge for the development of an on-board environmental monitoring system to analyse air and water within a space station. The response to the challenge within the University of Manchester was the Chip Hyphenation Project which sort to bring together miniaturised sampling, separation and detection systems into a single device. Linking the separation and detection systems was the process of ionisation. This study sought to investigate the potential of using electrospray ionisation as a generic ionisation source for the detection of volatile organic compounds (VOCs) and formed part of the Chip Hyphenation Project.
4
Kara, Vanita. "Positron impact ionisation studies." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394610.
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L'Huillier, Anne. "Ionisation multiphotonique et multielectronique." Paris 6, 1986. http://www.theses.fr/1986PA066268.
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Premiere mise en evidence experimentale d'ions multicharges de gaz rares crees par absorption multiphotonique a 532 et 1064 nm, pour differentes annees de l'impulsion laser (5 a 200 ps). Etude theorique utilisant un formalisme derive de la theorie des perturbations a n corps et des techniques diagrammatiques pour l'ionisation simple et double multiphotonique d'un atome a plusieurs electrons non independants
6
L'Huillier, Anne. "Ionisation multiphotonique et multiélectronique." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375991831.
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Forrest, David Alexander James. "The Muon Ionisation Cooling Experiment." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2839/.
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Outstanding areas of ambiguity within our present understanding of the nature and behaviour of neutrinos warrant the construction of a dedicated future facility capable of investigating the likely parameter space for the theta 1,3 mixing angle, the Dirac CP violating phase and clarifying the neutrino mass hierarchy. A number of potential discovery venues have been proposed including the beta beam, superbeam and neutrino factory accelerator facilities. Of these, the neutrino factory significantly outperforms the others. A neutrino factory will deliver intense beams of 10^21 neutrinos per year, produced from muons decaying in storage rings. This specification, coupled with the constraints of the short muon lifetime warrant the inclusion of a novel cooling channel to reduce the phase space volume of the beam to fall within the acceptance of the acceleration system. Ionisation cooling is the only viable cooling technique with efficacy over the lifetime of the muon, however, it has yet to be demonstrated in practice. In a full cooling channel, a muon beam will traverse a periodic absorber and accelerator lattice consisting of low Z absorbers enclosed by focusing coils and accelerating radio-frequency cavities. Energy loss in the absorbers reduces both transverse and longitudinal momentum. The latter is restored by the accelerating cavities providing a net reduction in transverse momentum and consequently reducing the phase space volume of the muon beam. The Muon Ionisation Cooling Experiment (MICE), under construction at the ISIS synchrotron at Rutherford Appleton Laboratory seeks to provide both a first measurement and systematic study of ionisation cooling, demonstrated within the context of a single cell prototype of a cooling channel. The experiment will evolve incrementally toward its final configuration, with construction and scientific data taking schedules proceeding in parallel. The stated goal of MICE is to measure a fractional change in emittance of order 10% to an error of 1%. This thesis constitutes research into different aspects of MICE: design and implementation of the MICE configuration database, determination of the statistical errors and alignment tolerances associated with cooling measurements made using MICE, simulations and data analysis studying the performance of the luminosity monitor and a first analysis of MICE Step I data. A sophisticated information management solution based on a bi-temporal relational database and web service suite has been designed, implemented and tested. This system will enable the experiment to record geometry, calibration and cabling information in addition to beamline settings (including but not limited to magnet and target settings) and alarm handler limits. This information is essential both to provide an experimental context to the analysis user studying data at a later time and to experimenters seeking to reinstate previous settings. The database also allows corrections to be stored, for example to the geometry, whereby a later survey may clarify an incomplete description. The old and new geometries are both stored with reference to the same period of validity, indexed by the time they are added to the configuration database. This allows MICE users to recall both the best-known geometry of the experiment at a given time by default, as well as the history of what was known about the geometry as required. Such functionality is two dimensional in time, hence the choice of a bi-temporal database paradigm, enabling the collaboration to run new analyses with the most up to date knowledge of the experimental configuration and also repeat previous analyses which were based upon incomplete information. From Step III of MICE onwards, the phase space volume, or emittance, of the beam will be measured by two scintillating fibre trackers placed before and after the cooling cell. Since the two emittance measurements are made upon a similar sample of muons, the measurement errors are influenced by correlations. This thesis will show through an empirical approach that correlations act to reduce the statistical error by an order of magnitude. In order to meet its goals MICE must also quantify its systematic errors. A misalignment study is presented which investigates the sensitivity of the scintillating fibre trackers to translational and rotational misalignment. Tolerance limits of 1 mm and 0.3 mrad respectively allow MICE to meet the requirement that systematic errors due to misalignment of the trackers contribute no more than 10% of the total error. At present, MICE is in Step I of its development: building and commissioning a muon beamline which will be presented to a cooling channel in later stages of MICE. A luminosity monitor has been built and commissioned to provide a measurement of particle production from the target, normalise particle rate at all detectors and verify the physics models which will be used throughout the lifetime of MICE and onwards through to the development of a neutrino factory. Particle identification detectors have already been installed and allow the species of particles to be distinguished according to their time of flight. This has enabled a study of particle identification, particle momenta and simulated and experimental beam profiles at each time of flight detector. The widths of the beam profiles are sensitive to multiple scattering and magnetic effects, providing an opportunity to quantify the success of the simulations in modelling these behaviours. Such a comparison was also used to detect offsets in the beam centre position which can be caused by misalignments of the detectors or relative misalignments in magnet positions causing asymmetrical skew in the magnetic axis. These effects were quantified in this analysis. Particle identification combined with the earlier statistical analysis will be used to show that the number of muons required to meet the statistical requirements of MICE can be produced within a realistic time frame for each beam configuration considered.
8
Back, Trevor. "Ionisation induced collapse of minihaloes." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7608.
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The first stars, galaxies and black holes in the universe produced large quantities of ionising UV radiation; forming H II regions in the neutral gas before the Epoch of Reionisation (EoR). These ionisation fronts will have come into contact with overdensities in the surrounding Intergalactic Medium (IGM), including haloes which were in the process of collapse. Previous studies have shown that the feedback processes on these secondary haloes can either disrupt the gas, or induce further cooling from the formation of molecular hydrogen. The ionising source will eventually die and create a defunct H II region, which expands into the surrounding neutral IGM. Minihaloes at the edge of these defunct H II regions are particularly susceptible to positive feedback due to not having been photoevaporated like their counterparts further inside the ionised volume. In this thesis, numerical simulations of minihaloes at the edges of H II regions formed by the first luminous objects before the EoR are presented. A methodology of including secondary ionisations from high energy photons is also implemented into the radiation hydrodynamical code ZEUS-RT. The interaction of differing spectral index sources with minihaloes including secondary ionisation is discussed. The secondary ionisations show the greatest effect for hard spectral sources with a large fraction of high energy photons; where a decrease in photoheating and an increase in ionisation rate is found at the outer reaches of the ionisation front (I-front). The increased ionisation rate lowers the optical depth of the gas for subsequent photons, and thus reduces the trapping of I-fronts in high densities found in the minihalo cores. The ratio of the free electron fraction to the temperature in the core of the minihaloes is found to constrain the resulting evolution. A high ratio is correlated with the creation of molecular hydrogen, which can then induce further cooling and the collapse of the system.A large parameter suite of 3780 two-dimensional minihalo models utilising radiative hydrodynamical simulations with 12 species and a coupled reaction network, including H2 cooling, HD cooling, Lyman-Werner radiation and secondary ionisation is performed. The parameter space includes: the spectral index representing different sources such as quasars or galaxies, the mass of the minihaloes from 105 - 106 Mʘ, the redshift of ionisation from z ~ 10 - 30, and other factors which denote the position of the minihalo relative to the boundary of the H II region. Minihaloes with average core densities of n0 = 2 - 10 cm-3 show almost unanimous positive feedback, while the majority of minihaloes under this average density are disrupted. Minihaloes with core densities above this value generally would have collapsed in isolation anyway, but are found to not be delayed by the I-front. The H2 fraction in the minihalo gas is also increased in models with no blowout by factors between 2 - 100 times that of an isolated minihalo. This is especially significant for lower redshift, z ≤ 15, minihaloes. Finally, a parameter suite of larger 106 - 107 Mʘ minihaloes results in the creation of self-gravitating clumps of gas moving out of the dark matter potential. The gas core is compressed by the I-front, enriched with molecular hydrogen, and ejected by the pressure front after the source dies. These "baryon bullets" could be progenitors of primordial globular clusters found in the haloes of galaxies today. Properties such as old stellar populations and the lack of dark matter haloes can be explained by this radiative ejection method. The dynamical nature of these interacting systems and diversity of subsequent evolution suggest that minihaloes less than 108 Mʘ are important in the early formation history of the universe, and in determining the constraining parameters of the EoR. The feedback mechanisms investigated, and secondary ionisation physics, should be included in astrophysical simulations and analytical calculations determining the evolution of the universe at this critical epoch.
9
Arcidiacono, C. "Ionisation studies by positron impact." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445268/.
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Differential studies of positron impact ionisation have been performed to understand the energy shift (Kover et al., 2001) of 1.6eV between the theoretical and measured energy spectrum of the ejected electron in the triply-differential cross-section, d*o +1 dE_dQ_dQ+, at 50eV incident energy on H2. Firstly, an absolute energy calibration has been carried out to check for possible contact potential effects in the determination of Kover et al. (2001). Secondly, D2 and He have been investigated at the same residual kinetic energy as in Kover et al. (2001) to probe the occurrence of molecular dissociation or excitation. Finally, the distribution of kinetic energies of scattered positrons from the same collision system (e+-H2) has been measured for the first time. This work shows an unexpected asymmetry in the energy sharing between electron and positron. Possible reasons for this finding are discussed. An extensive study has been carried out also on water vapour ionisation upon positron collision for the first time. Besides their intrinsic interest, ionisation data are essential to provide a measure of the energy released in living matter during radiobiological applications. Preliminary results for the total, o-,+ , and direct, o *, ionisation cross-sections of water have been obtained for collision energies from the threshold to -IkeV. < r* is higher, by up to a factor of 2, than that for electron impact, whereas the dissociative ionisation cross-section, o *, for Yt production is similar to that for electron impact. Under the assumption that the difference between o ,+ and cr,+ is primarily due to positronium formation, o Ps has been extracted. This amounts to a significant fraction contribution of er,+, contrary to the work of Sueoka et al. (1987). Finally, to probe in more detail ionisation in e+-H20 scattering, the doubly differential cross-section, d2a+ ZdE+dQ+, at 0 , for lOOeV positrons colliding with water has been measured. The differential cross-section appears more forward scattered than in Ar. Fragmentation channels are also identified.
10
Ong, Siok Lan. "Impact ionisation in AlInP photodiodes." Thesis, University of Sheffield, 2012. http://etheses.whiterose.ac.uk/3381/.
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11
Whyte, Christopher. "Studies of transition metal carbonyl clusters using laser desorption ionisation and electrospray ionisation mass spectrometry." Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/11569.
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Stable, readily available, transition metal cluster carbonyl compounds, such as Os3(CO)12, Ir4(CO)12, Rh6(CO)16, have been shown to easily aggregate into multi-nuclear supraclusters following exposure to pulsed ultraviolet laser radiation (laser desorption ionisation, LDI) in the source region of a mass spectrometer. The aggregation process has been studied from the resulting mass spectra, using both of time-of-flight mass spectrometry (TOF MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Larger cluster precursors tend to aggregate via the stepwise addition of whole metal cores, whereas the smaller tri-nuclear osmium cluster can produce supraclusters with variable numbers of metal atoms present. Interestingly, laser desorption/ionisation of Os3(CO)12 leads to the formation of prominent dodecaosmium cluster negative ions, such as [Os12(CO)23]-. As far as we are aware, no homoleptic dodecaosmium carbonyl species has been prepared via traditional synthetic methods, highlighting the future potential of this approach if techniques for stabilising these complexes and isolating them can be developed. The LDI spectra also exhibit prominent metastable decay products, corresponding to evaporative carbonyl ligand loss, a phenomenon known as post-source decay. The rates of metastable decay have then been determined for the mono-isotopic rhodium supraclusters. In addition the transition metal carbonyl precursors used in the aggregation experiments have been studied by electrospray ionisation using quadrupole and Fourier transform ion cyclotron resonance mass spectrometers. In this case clusters require derivatisation with an alkoxide agent to produce a carbomethoxy ligand ([COOCH3]-) on the cluster, providing them with the necessary charge for mass spectrometric detection. The recently introduced technique of Energy Dependent Electrospray Ionisation mass spectrometry (EDESI-MS) has been used to investigate the relative strengths of the metal-to-carbonyl bonds using a process known as in-source collision-induced dissociation. From this data bond dissociation energies for the sequential removal of carbonyl ligands from the transition metal cluster precursor have been determined. FT-ICR MS experiments confirm the presence of a second decay channel leading to the formation of metal carbonyl hydride species, produced from the activation of the carbomethoxy ligand. Preliminary studies of these coordinatively unsaturated transition metal carbonyls with hydrocarbons have also been carried out.
12
Dupré, Christophe. "Approche expérimentale des collisions électron-atome à trois électrons actifs. Ionisation et excitation simultanées ; double ionisation." Paris 11, 1990. http://www.theses.fr/1990PA112352.
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L'ionisation de l'helium laissant l'ion residuel dans l'etat he#+ n=2 et la double ionisation de l'argon ont ete etudiees par l'impact d'electrons de haute energie (5500 ev). Des sections efficaces differentielles d'ordre 3, 4 et 5 ont ete mesurees en geometrie coplanaire asymetrique, en utilisant des techniques de coincidence, (e, 2e), (e(3-1)e) et, pour la premiere fois, (e, 3e). Il s'agit d'apporter une information tres detaillee sur les effets des correlations interelectroniques, tant dans les structures atomiques que dans les processus collisionnels. Les resultats des experiences d'ionisation-excitation, comparees a des calculs theoriques, montrent clairement que celles-ci sont a la charniere entre simple et double ionisation: a grand transfert d'impulsion on retrouve des distributions angulaires analogues a celles de l'ionisation simple, faisant surtout ressortir les effets des correlations atomiques. Par contre, a faible transfert d'impulsion, on obtient des distributions tres differentes, qui ne reproduisent pas les calculs theoriques, et dont l'analyse met en evidence la predominance d'effets d'une dynamique a trois corps, notamment l'interaction entre electron ejecte et ion residuel excite. Les experiences de double ionisation sont plus complexes, en raison de la difficulte technique (faibles taux d'evenements coincidents), et egalement a cause de l'absence quasi-complete de points de repere theoriques precis. Le haut degre de differentiation des resultats permet cependant deja de tirer quelques conclusions qualitatives; en particulier, elles excluent une explication en termes de double collision de l'electron incident avec les electrons atomiques
13
Peng, Wei-Xian. "Ionisation studies on some small molecules." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363223.
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Wallace, William Carl. "Strong-field Ionisation of Atomic Hydrogen." Thesis, Griffith University, 2017. http://hdl.handle.net/10072/370427.
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The past two decades have seen advancements in laser technologies wherein laser pulses are
routinely generated with durations on the femtosecond ( 1015 s) timescale. Such pulses
allow only a few cycles (oscillations) of the laser electric eld for lasers with wavelengths
centered in the visible to near-infrared (IR). Not only can there be marked variations in
the peak electric eld value, caused by varying the pulse's carrier-envelope phase (CEP),
but the compression of the pulse energy to within such short durations readily allows
the production of strong laser elds with peak intensities that are well into the petawatt
( 1015 W/cm2) regime.
The strong- eld ionisation of atoms and molecules via light{matter interactions is a
fundamental process across many research elds. Such interactions have previously been
used to reveal the structure and control the dynamics of atoms, molecules and solids, and
to drive processes such as lamentation and to generate attosecond ( 1018 s) pulses.
These interactions are highly non-linear and are di cult to model theoretically, bringing
into question the ability of current theoretical models to capture all of the signi cant
physical processes occurring during said light{matter interactions. Not surprisingly, there
is often a discord between theoretical predictions and experimental data for strong- eld
processes, hampering experiment-theory comparison and, more worryingly, obscuring the
correct physical interpretation of the experimental results. Therefore, an obvious need for
accurate experimental data exists.
The gold standard for target species in atomic physics is atomic hydrogen (H). It is
the simplest atomic system and is the only species for which highly-precise (limited by
numerical accuracy) solutions to the three-dimensional time-dependent Schr odinger (3DTDSE)
equation are possible. Atomic H serves as a test bed for various theoretical models
of ionisation, however it is di cult to produce experimentally. The author of this thesis
was in a unique position of having access to both a source of atomic H and a few-cycle
laser with which to undertake investigations.
This thesis details two investigations of strong- eld ionisation of atomic H using fewcycle
light pulses. The rst investigation explores the e ect that the CEP of a few-cycle
laser pulse has on the directional yield of photoelectrons that are ejected from atomic H
atoms undergoing strong- eld ionisation. These experimental photoelectron yields have been compared to predictions obtained from solving the 3D-TDSE and good experimenttheory
agreement has been achieved without the use of any free t parameters. The results,
which are the rst of their kind in atomic H, pave the way for obtaining CEP-calibrated
reference data across a range of gas species and experimental parameters.
The second investigation explores the e ect that changing the laser peak intensity in
the 1{5 1014 W/cm2 regime has on the yield of photoions arising from strong- eld ionisation
of atomic H atoms. These photoion yields, again the rst of their kind in atomic
H, have been compared to predictions obtained from solving the 3D-TDSE. Quantitative
experiment-theory agreement has been achieved at the few-percent level, proving accurate
knowledge of the photoion yields and permitting the theory-certi ed retrieval of the
true laser peak intensity to better than 1.1 % accuracy. This demonstrably accurate experimental
method has been exploited to measure the photoion yields of the noble gases
argon (Ar), krypton (Kr), and xenon (Xe); such gases are more readily available to other
experimental laboratories. Comparison of the noble-gas yields with solutions to the 3DTDSE
under the single-active electron approximation result in marked discrepancies which
challenge the accuracy of the aforementioned ionisation models.
However, a phenomenological model was developed to t to the noble-gas photoion
yields, permitting a transferrable second-order laser peak intensity calibration standard
that is accurate to 1.3 %, 1.5 %, and 2.5 % in Ar, Kr, and Xe respectively. Not only
does the model allow any laboratory around the world with a few-cycle near-IR laser to
now calibrate their laser peak intensity to the few-percent level, the data presented here
also provides a benchmark for the testing of theoretical models of ionisation in noble-gas
atoms.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Natural Sciences
Science, Environment, Engineering and Technology
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Abbas, Issam. "Ionisation d'atomes, de molécules et de biomolécules par impact des ions multichargés de hautes énergies : comparaison quantique et classique." Thesis, Metz, 2008. http://www.theses.fr/2008METZ007S/document.
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Les processus collisionnels ionisant de type ion-atome ou molécule sont fondamentaux dans plusieurs domaines de la physique et, plus récemment, en médecine nucléaire. Les théories disponibles, quantiques ou semi-classiques, ne peuvent pas traiter de grosses cibles moléculaires comme les biomolécules. Pour résoudre ce problème nous avons développé une méthode purement classique. Dans ce travail, nous présentons notre modèle classique qui est basé sur deux autres approximations classiques¡: Classical Over-Barrier (COB) et Classical Trajectory Monte Carlo (CTMC). Ce modèle est particulièrement conçu à l étude des collisions entre des ions multichargés et des atomes ou molécules. Ce modèle nous permet de calculer les sections efficaces, de capture ou d ionisation, simples ou multiples. Nous l avons appliqué, en premier lieu, sur des cibles atomiques ou moléculaires simples (H, He, H2 et H2O) dont des données expérimentales ou théoriques nombreuses sont disponibles. Ces calculs nous ont permit de vérifier la validité de notre modèle pour des cibles comme les biomolécules. Nous avons appliqué le modèle sur deux des biomolécules constituant de l ADN (Adénine et Cytosine) ce qui est impossible à réaliser avec les approximations actuellement disponiblesThe collisionnal ionizing processes type ion-atom or molecule are fundamental in several fields of physics, and more recently in nuclear medicine. The current theories, quantum or semi-classical, can not deal with large molecular targets as biomolecules. To solve this problem we have developed a method purely classical. In this work we present our model, which is based on two other classical approximations: Classical Over-Barrier (COB) and Classical Trajectory Monte Carlo (CTMC). This model is designed specifically to the study of collisions of multiply charged ions with atoms or molecules. This model allows us to calculate the cross sections, for capture or ionization, singles or multiples. We have applied it, first, on simple atomic or molecular targets (H, He, H2 and H2O) for which many experimental or theoretical data are available. These calculations have allowed us to check the validity of our model for targets like biomolecules. We have applied the model on two of biomolecules constituent of DNA (Adenine and Cytosine), which is impossible to achieve with approximations currently available
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Becher, Marie. "Etude théorique de la double ionisation de la couche L et K du béryllium par impact d'électrons rapides." Thesis, Metz, 2008. http://www.theses.fr/2008METZ035S/document.
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Le mémoire présente une étude théorique sur la double ionisation (e,3e) de la couche L et la couche K du béryllium par impact d électrons rapides, réalisable dans les expériences de détection en coïncidence, qui permettent de sonder la corrélation électron-électron et d observer les mécanismes de la double ionisation. Une procédure de détermination de la section efficace multiplement différentielle est développée dans le cadre d une approche utilisant le premier terme de la série de Born représentant l interaction entre l électron projectile et la cible. Tous les électrons sont pris en compte et décrits par des fonctions d onde comportant différents degrés de corrélation. La fonction 3C est notamment utilisée pour décrire le double continuum des deux électrons éjectés. Le cas particulier de systèmes bi-électroniques doublement excités que représente l ion résiduel lors du processus de double ionisation de la couche K est par ailleurs analysé.Une partie importante du manuscrit est consacrée à la présentation des résultats montrant la variation de la section efficace multiplement différentielle pour différentes situations expérimentales et avec différentes fonctions d onde. Ceci permet d analyser les mécanismes de ce processus quantique complexe et l effet de la corrélation dans les états initial et finalThe document presents a theoretical study of the L shell and K shell double ionization of beryllium by fast electrons, with the coincidence detection of the emerging particles, which represents one of the main tools to probe electron-electron correlation and to observe the mechanisms of the double ionization process. The determination of the fully differential cross section is presented in the frame of a procedure using the first term of the Born series representing the interaction between the incident electron and the target. All the electrons are taken into account. They are described by different more or less correlated wave functions for the bound electrons in the initial and final states, and for the double continuum of the two ejected electrons for which, the well known 3C function is applied. An important part of the document is devoted to the presentation of the results concerning the variation of the fully differential cross section in terms of the different experimental conditions and with different wave functions. This permits to analyse the mechanisms of this complex quantum process and the effect of the initial and final states correlation
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Monti, Juan Manuel. "Le rôle des interactions électroniques pour le processus d'ionisation d'atomes en collisions avec des ions." Thesis, Metz, 2011. http://www.theses.fr/2011METZ004S/document.
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Dans cette thèse, nous étudions les effets des interactions électroniques dans le processus d'ionisation simple des cibles atomiques par impact des ions multichargés, ceux-ci peuvent être nus ou à demi vêtus. Dans le cas des projectiles nus, nous avons étudié l'interaction entre l'électron actif et les électrons passifs, la version post de l'approximation d'onde distordue du continu avec état initial eikonale est reformulé (CDW-EIS pour son sigle anglais), y compris un potentiel résiduel omis de calculs précédents. En addition, nous développons un modèle d'onde distordue de quatre corps pour l'ionisation simple des atomes diélectriques dans lequel les deux électrons sont considérés comme des actifs et à évoluer dans les mêmes temps. Dans le cas de considérer comme projectile des ions partiellement vêtus, nous étudions l'interaction électronique entre l'électron actif du cible et celles liées au projectile par l'élaboration d'un modèle d'onde distordue où le potentiel perturbatif du projectile est séparé en deux termes : une longue distance déterminée par la charge nette du projectile et autre à courte portée donnée par les électrons liés au projectile. Cette dernière est approchée par un potentiel paramétrique type GSZ (Green-Sellin-Zachor)In this thesis the effects of the electronic interactions in the single ionization process of atoms by multiply charged ions impact are studied. The projectiles considered are either fully stripped or partially dressed ions. In the case of fully stripped ions we study the interaction between the target active electron and the passive electrons distribution, the post version of the CDW-EIS (Continuum Distorted Wave-Eikonal Initial State) approximation is revisited and a residual potential neglected in all previous calculations is considered. Also a four-body distorted wave model is developed to investigate the single ionization of dielectronic atoms where both electrons are considered as active ones and evolving in the same time-frame. When considering partially dressed ions as projectiles we investigate the interaction between the target active electron and those bound to the projectile by means of the extension of the CDW-EIS and CDW (Continuum Distorted Wave) models to the case where the projectile is a dressed ion. The projectile potential is described by a analytic parametric GSZ (Green-Sellin-Zachor) one that can be separated in two terms : a long range term determined by the net chargeof the totally screened projectile and a short range term due to the electrons bound to the projectile
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KARGAR, KERMANSHAH TARANEH. "Application de differentes techniques de desorption-ionisation et de desolvatation-ionisation a l'analyse et l'identification de composes pharmaceutiques." Paris 6, 1996. http://www.theses.fr/1996PA066781.
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Les potentialites analytiques de trois techniques d'ionisation recentes : la desorption de plasma (pd), la desorption laser (ld) et l'ionisation par electronebulisation (es) couplees a un spectrometre de masse (ms) sont utilisees pour l'analyse de composes polyfonctionnels d'interet pharmaceutique. Mecanismes de fragmentation de composes azotes polyfonctionnels ionises en pd-ms sont etudies. Des regles generales de fragmentation sont proposees en fonction du degre de substitution des atomes d'azote et de la nature des substituants. L'application de ces regles a l'etude des 1,4-benzodiazepines a permis de realiser leur identification structurale et leur differentition en fonction des substituants. L'etude comparative des techniques citees precedemment, appliquee aux 1,4-benzodiazepines dans differentes conditions experimentales, nous a permis de montrer les differences fondamentales entre ces techniques et de les classer sur une echelle d'energie en fonction des informations structurales fournies par chacune d'elles. Cette classification peut etre utilisee pour orienter le choix de la technique appropriee pour l'analyse de tout compose selon les informations souhaitees. Ces techniques permettent l'analyse directe de melanges de benzodiazepines sans aucune separation prealable et sans perte d'information. Une contribution a la comprehension des mecanismes de desorption et d'ionisation en pd-ms et en ld-ms est apportee par l'etude de deux composes organiques ; un sel d'ammonium quaternaire et une molecule neutre, etudies seuls ou en presence de matrice. La presence d'une matrice judicieusement choisie permet d'augmenter considerablement les rendements d'ionisation.
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MEVEL, ERIC. "Ionisation atomique en champ electromagnetique intense : dynamique des resonances induites, transition vers le regime tunnel et ionisation double." Paris 11, 1994. http://www.theses.fr/1994PA112022.
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Ce travail experimental decrit differents aspects de l'ionisation d'atomes (gaz rares) par des impulsions lasers subpicosecondes (70fs), intenses (10#1#3-10#1#5w. Cm#-#2). Sa motivation est d'etudier le comportement du processus d'ionisation et l'evolution du role de la structure atomique en fonction de l'eclairement du laser. Dans le regime d'ionisation multiphotonique la structure atomique joue un role important a travers les resonances induites par deplacement lumineux qui surviennent inevitablement lorsque ces deplacements sont de l'ordre de grandeur de l'energie du photon. Elles se traduisent par l'apparition, de structures etroites (100mev) dans les spectres d'energie des electrons. Leur evolution en fonction de l'eclairement est en bon accord avec les predictions faites sur la base du modele de floquet a condition de prendre en compte la contribution due a l'ionisation des etats excites peuples lors du croisement des resonances. Lors de la transition du domaine multiphotonique vers le domaine tunnel, qui correspond a un regime d'eclairements ou les deplacements sont de l'ordre du potentiel atomique, nous observons la disparition progressive de la double structure due a l'ionisation au dessus du seuil et aux resonances induites par deplacements lumineux. Cette observation accredite les modeles d'ionisation tunnel qui ne prennent pas en compte ni le role de la structure atomique ni la nature quantique du champ. Dans le domaine tunnel, nous observons la manifestation d'un processus d'ionisation double directe. Son comportement en fonction de la polarisation du champ est correctement decrit par un modele qui traite classiquement le mouvement de l'electron dans le champ. L'ejection du deuxieme electron est provoquee par la collision survenant lors du retour du premier electron sur son ion parent
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Rahman, Mahbubur. "NOx Production by Ionisation Processes in Air." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-6016.
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Koumanov, Assen. "Theoretical prediction of ionisation properties of proteins /." Stockholm, 2003. http://diss.kib.ki.se/2003/91-7349-535-2.
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Gupta, Rajesh. "Electrospray ionisation mass spectrometry of biomolecular complexes." Access electronically, 2003. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20040827.101645/index.html.
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Rogers, Chris. "Beam Dynamics in an Ionisation Cooling Channel." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499277.
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McCormack, Elin A. "Ionisation of hydrogen Rydberg molecules at surfaces." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543033.
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Slater, P. S. "Novel applications of electrospray ionisation mass spectrometry." Thesis, Swansea University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639056.
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Chapters one and two introduce the theory behind electrospray ionisation. Chapter three presents detailed research related to the application of electrospray mass spectrometry to polysulphonates. The correlation between poor sensitivity and the degree of salt contamination held by complex sulphonated compounds is outlined and the initial attempts to remove the salt contamination by different methods discussed. The ability of alkyl-amines to eliminate salt contamination is also discussed. Chapter four discusses direct sample treatment with alkyl-amines, and how closer analysis reveals the presence of alkyl-amine adducts on the decontaminated polysulphonate ions. Further investigations are reported, leading to the discovery that the number of alkyl-amine adducts correlates with the number of sulphonate groups present on the analyte. An ionisation mechanism is also discussed. Chapter five investigates the application of surfactants in electrospray ionisation mass spectrometry. The implications of this theory are discussed, and a mechanism proposed based on extensive experimental and literature research. Chapter six discusses the research performed on a selection of polyphosphated compounds. The improvement observed with treatment by alkyl-amines, the lack of alkyl-amine adduction, and how this observation suggests the theory of bias ion-pairing between the three compound classes discussed so far, is considered. Chapter seven details the research performed into the high performance liquid chromatography of a selection of polyphosphates, and the use of diethylamine as an ion-pairing reagent to assist the separation of these compounds. Chapter eight discusses the research performed on polysulphated-oligo-saccharides, utilising the technique of the sulphate groups. This chapter introduces the electrospray of carbohydrates by investigating the effect of mass spectrometer tuning parameters on the spectra of simple oligosaccharides. The ultimate goal of this chapter is the analysis of glycoaminoglycans, such as chrondroitin sulphate A, and heparin.
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Kaiser, Christian Dieter. "Electron impact ionisation of atoms and molecules." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515113.
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(e,2e) spectroscopy is a versatile tool to investigate the collision dynamics taking place in electron impact ionisation of atoms and molecules as it employs a kinematically complete view of the scattering process. (e,2e) measurements on He and H2 have been carried out from the coplanar to the perpendicular geometry at various impact energies, and these results are compared and discussed. Results for the atomic targets He, Ar and Xe and the molecular targets H2, N2 and CO2 are also presented from measurements in the perpendicular geometry and these are compared. The Ib1 molecular orbital of H20 has been studied at low to intermediate energies in a coplanar symmetric and asymmetric geometry. Where available the experimental data have been compared to theoretical calculations of other research groups located in the USA. A new coincidence spectrometer has been designed, assembled and commissioned which incorporates a pulsed, supersonic beam expansion as well as a continuous, effusive beam expansion. Measurements using supersonically expanded He and H2 demonstrated the feasibility of the new coincidence spectrometer for (e,2e) studies. The supersonic gas expansion provides molecular targets in their ground ro-vibrational states. This spectrometer allows the first steps towards the development of molecular alignment within the target beam. The alignment of diatomic molecules in the experiments would open up a new range of (e,2e) measurements with far-reaching implications for the investigation of collision dynamics from molecules.
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Gingras, Guillaume. "Visualisation de la double ionisation du xénon." Thesis, Université Laval, 2008. http://www.theses.ulaval.ca/2008/25751/25751.pdf.
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Nous avons étudié les processus non linéaires d'ionisation du xénon lors d'interaction avec une impulsion laser ultra-brève et intense de 100fs. (1fs.=1.10-15s). La dépendance de ces processus sur la longueur d'onde du rayonnement laser est investiguée dans le but de mettre en évidence le régime d'ionisation multiphotonique et le régime d'ionisation par effet tunnel. Utilisant un système TOPAS ("Traveling-wave Optical Parametric Amplifier of Superfluorescence"), pompé par un système laser Titane-Saphir (800nm à 100 fs.), nous avons mesuré à l'aide d'une technique de spectroscopie à temps de vol, la production d'ions Xe+ et Xe2+ sur une plage de longueur d'onde s'étalant de 500nm à 2300nm dans un domaine d'intensité de 10TW/cm2 à 1PW/cm2 avec un faisceau laser linéairement polarisé. Les résultats permettent de distinguer les domaines d'ionisation séquentielle et non séquentielle du xénon doublement ionisé en fonction de la longueur d'onde. D'un autre côté, nous avons calculé numériquement les taux d'ionisation du xénon utilisant le modèle PPT (Perelomov et al. (1965)). Il est connu que ce modèle constitue une bonne approximation particulièrement pour les taux d'ionisation du xénon simplement ionisé comme une fonction de la fréquence du rayonnement d'interaction. Ainsi grâce à ce modèle, nous avons pu reconstruire les événements expérimentaux de sorte que nous pouvons directement comparer en fonction de la longueur d'onde et de l'intensité de rayonnement laser le schéma d'ionisation séquentielle prédit par le modèle PPT avec nos résultats expérimentaux. Les résultats nous permettent alors une visualisation directe de la structure du domaine d'ionisation non séquentielle du Xe2+. L'analyse du domaine non séquentiel à plusieurs longueurs d'ondes montre qu'un mécanisme de rediffusion joue un rôle important dans les processus non séquentiels d'ionisation double. Dans ce type de mécanisme, un électron est d'abord éjecté par le champ laser et revient interagir avec un second électron (en se redirigeant vers son ion parent dans l'axe de polarisation du laser) pour ensuite y partager son énergie et ainsi produire une ionisation non séquentielle.We have studied the frequency dependence of single and double ionization of xenon in the multiphoton and tunneling regime by a short laser pulse of 100fs. (1fs.=1.10-15s). We have used a traveling-wave optical parametric amplifier of superfluorescence (TOPAS) pumped by an 800-nm, 100-fs Titane-Sapphire laser system and a time-of-flight spectrometer (TOF). We have measured the ionization yield of Xe+ and Xe2+ in the wavelength range between 500 and 2300nm for intensity between$10TW/cm2 and 1PW/cm2. These results allow us to visualize the non sequential part as well as the sequential part of the ionization process leading to Xe2+. Otherwise, we also have done calculations for the ionization rate of xenon using the PPT model (Perelomov et al. (1965)) which is known to be a good approximation for the ionization rate (which is frequency dependent) for the single ionization of noble gas. Using the fact that the Xe+ yield can be correctly predicted for the single ionization process, we have reconstructed the experimental events in such a way that it allows us to compare directly our measurements to the PPT prediction of a sequential scheme of ionization. Results show clearly the enhancement of the Xe2+ yield charge state (the so call "knee" structure on the ionization curve). The analysis of the non sequential in the wavelength regime show that a rescattering mechanism play an important role in non sequential double ionization. In this type of mechanism, one electron is first ejected by the laser field and come back to interact with a second electron (by redirecting itself toward his parent ion in the direction of the laser polarization) to share his energy and then product a non sequential ionization.
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Armitage, Simon Peter. "Positronium ionisation in collision with He atoms." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270771.
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Spracklen, Edmund Francis. "Inner shell lasing via electron collisional ionisation." Thesis, University of York, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442366.
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Parkes, Michael Anthony. "Ionisation studies of chlorinated and fluorinated compounds." Thesis, University of Birmingham, 2007. http://etheses.bham.ac.uk//id/eprint/74/.
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Ionisation processes in gas-phase polyatomic molecules have been studied using threshold photoelectron photoion coincidence and selected ion flow tube techniques for cations and an electron attachment mass spectrometer for anions. Cation formation has been studied for fluoroform (CHF\(_3\)), octafluorocyclobutane (\(c\)-C\(_4\)F\(_8\)), octafluorocyclopentene (\(c\)-C\(_5\)F\(_8\)), monochloroethene (C\(_2\)H\(_3\)Cl), the three isomers of dichloroethene (C\(_2\)H\(_2\)Cl\(_2\)) (i.e. 1,1-dichloroethene, (\(Z\))-1,2-dichloroethene and (\(E\))-1,2-dichloroethene), trichloroethene (C\(_2\)HCl\(_3\)) and tetrachloroethene (C\(_2\)Cl\(_4\)). Comparison between the data from the photoionisation and the ion-molecule reactions show that the dominant charge-transfer mechanism is long-range in nature. Detailed studies of the reactions of cations with the three dichloroethenes have been performed to look for evidence of isomeric effects. Major differences are seen when the reactant ion is CF\(_3\)\(^+\); when 1,1-dichloroethene is the neutral reactant the only ionic product is C\(_2\)H\(_2\)Cl\(^+\), but if the neutral is 1,2-dichloroethene then the only product is CHCl\(_2\)\(^+\). Only minor differences are seen with other reagent ions. For the reactions of all six chloroethenes with CF\(_3\)\(^+\), product ions are observed which can only be formed by extensive rearrangement across the carbon-carbon double bond. Mechanisms are suggested involving bridged trigonal intermediates to explain the production of the different channels. Studies have been performed on several perfluorocarbons, CHF\(_3\), \(c\)-C\(_4\)F\(_8\) and \(c\)-C\(_5\)F\(_8\), due to their potential for use in industry. They are all excellent at etching substrates and have a lower global warming potential than the currently used gases. CHF\(_3\) shows signs of non-statistical dissociation following photoionisation, and is shown to react via a largely long-range charge transfer mechanism in the ion-molecule reactions studied. For \(c\)-C\(_5\)F\(_8\) the ground electronic state of the ion is found to be very weak under threshold conditions whilst being much more intense when He(I) photons are used. The existing electron attachment mass spectrometer is described, and also extensive modifications which have been made to this apparatus. The use of new electronics and acquisition system give excellent results in the new equipment. The new arrangement has been extensively characterised by studying attachment to seven molecules, including several perfluorocarbon molecules (e.g. the isomers of C\(_4\)F\(_8\)). Some isomeric effects on the measured rate coefficients are observed in the data.
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Poirier, Michel. "Ionisation multiphotonique résonnante et génération d'harmonique trois." Paris 6, 1986. http://www.theses.fr/1986PA066538.
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L'ionisation multiphotonique résonnante d'une vapeur atomique est très sensible à la pression: même en l'absence d'effets collisionnes importants, les processus de génération d'harmonique 3 photons. Développement de plusieurs modèles pour en rendre compte: théorie du champ moyen, approximation quasi statique, approximation de faible dépeuplement. Nouvelle méthode d'analyse de l'effet Stark dynamique, appliquée a une expérience sur hg pour déterminer les paramètres de la génération d'harmoniques. En accord avec l'expérience, disposition des résonances à 4 photons à haute pression.
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Gibbard, Jemma. "Rydberg ionisation into confined and discrete systems." Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:631cf025-c29c-4c46-a219-6f2ae02df4ad.
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The energy levels of a hydrogen Rydberg atom approaching a metallic structure are perturbed by the image-charge interaction with the surface. At small atom-surface separations surface ionisation of the Rydberg electron can occur, whereby the electron is transferred to a metal-localised state. In previous studies investigating surface ionisation at bulk metallic surfaces, this state has been part of a conduction band; however this thesis focuses on metallic and structured surfaces where the Rydberg electron transfers into a discrete image-state or hybrid 'well-image state'. The surface ionisation of hydrogen Rydberg atoms at a Cu(100) projected band-gap surface is investigated experimentally and theoretically. Experimentally, the surface ionisation of an incident beam of hydrogen Rydberg atoms is measured by extraction of the resulting ions. Resonance-enhanced charge transfer is seen for hydrogen Rydberg states that are degenerate with copper-localised image-states. A wavepacket propagation study shows that for on-resonance states the maximum in the surface-ionisation probability is shifted away from the surface by decreasing the collisional velocity. The discrete hybrid 'well-image states' localised along the surface normal of a thin-film change energy with thin-film thickness. The interaction of hydrogen Rydberg atoms with iron thin films deposited on an insulating substrate is investigated. The preference for electron penetration along the surface normal is seen by the resonance-enhancement of charge transfer at energies where the Rydberg state and well-image state are degenerate. By changing the thickness of the thin film, by in situ depositions, the energies of the well-image state are altered and the Rydberg n-values at which resonances occur, change. At a thickness of 30-monolayer the energetic spacings between the well-image states and the Rydberg states become comparable, and the single well-image state resolution is lost. A wavepacket-propagation study investigates the interaction of a nanoparticle and low-n hydrogen Rydberg atoms. The nanoparticle has a fully confined potential which at small radii yields well-spaced, fully discrete well-image states. Resonance-enhanced charge transfer occurs when the Rydberg state and the nanoparticle well-image state energy levels are degenerate. However, when there is poor energy matching between the nanoparticle well-image state and the Rydberg atom, no charge transfer is seen i.e. surface ionisation does not occur. Overall, the work presented here demonstrates the capability of Rydberg-surface studies to identify discrete, high-lying energy levels at specific surfaces.
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Alekou, Androula. "Ionisation cooling lattices for the neutrino factory." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/11183.
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The future accelerator complex of the Neutrino Factory will have an excellent precision and outstanding discovery reach, and is therefore a facility of choice for precise neutrino oscillation measurements. In the Neutrino Factory, muons are accumulated into storage rings and decay to neutrinos. However, due to the fact that the muon beam is produced occupying a large transverse phase-space, it is essential that its emittance is decreased using ionisation cooling. The reference ionisation cooling lattice of the Neutrino Factory has a large magnetic field at the position of the RF cavities, and there is a strong concern this can lead to RF breakdown. Therefore, there lies a great necessity for alternative cooling lattices to be found. This thesis presents several cooling lattices that were designed aiming to mitigate the problem of the RF breakdown in the presence of a magnetic field, that the reference lattice suffers from. In particular, amongst these lattices, a promising new configuration which makes use of a pair of opposite polarity and homocentric coils, named “Bucked Coils”, is presented. The Bucked Coils lattice not only manages to successfully achieve a virtually zero longitudinal magnetic field at the position of the RF cavities, but also obtains a better transmission than the reference lattice. A detailed comparison between the reference and the new lattices is presented with respect to the magnetic field, transmission and cooling efficiency. A possible extension of the work is also discussed. A six-dimensional cooling could be used at a Neutrino Factory but is essential for a Muon Collider. Another novel configuration, which aims to achieve 6D ionisation cooling, is presented in this thesis. This new lattice creates dispersion with the use of dipoles, and a correlation between energy loss and position with the use of wedge absorbers. A detailed description of this lattice configuration and analysis is given, together with preliminary results.
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Poirier, Michel. "Ionisation multiphotonique résonnante et génération d'harmonique trois." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb376004594.
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Ponce, Lino. "Théorie de l'ionisation de l'atome d'hydrogène dans les champs électromagnétiques intenses : lasers et collisions." Paris 6, 2003. http://www.theses.fr/2003PA066476.
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Dupin, Hélène. "Détermination théorique des sections efficaces d'ionisation par impact photonique et électronique." Pau, 2000. http://www.theses.fr/2000PAUU3020.
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C'est dans le cadre général de l'étude théorique de spectres d'ionisation par impact photonique ou électronique dans la région spectrale située au-dessus du premier potentiel d'ionisation, que se situe ce travail. Toute la difficulté de cette examen réside dans la nécessité de traduire les fonctions du continuum, relatives à un potentiel multicentrique de symétrie non sphérique. Trois approches théoriques sont prospectées pour le calcul général de la section efficace d'ionisation : le modèle classique de l'onde plane, la méthode des moments de Stieltjes et la détermination à partir de l'évaluation des polarisabilités dynamiques. Ces trois approximations requièrent le calcul de fonctions d'onde électroniques incluant la corrélation. L'exemple de la molécule d'eau a été choisi pour illustrer les différents aspects du calcul des sections efficaces. Différents aspects sont alors abordés : l'influence du choix des bases atomiques, de la prise en compte de la corrélation intercanal et de l'énergie de la source excitatrice. Le travail souligne très nettement la possibilité de rendre compte correctement du continuum en utilisant une base susceptible de le discrétiser; cette base doit en particulier être constituée de fonctions diffuses (Rydberg) et de fonctions de polarisation convenablement choisies.
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Walter, Michael. "Photo(doppel)ionisation von Helium und einfachen Molekülen." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961295074.
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Siedschlag, Christian. "Mechanismen der Ionisation atomarer Systeme in intensiven Laserpulsen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2002. http://nbn-resolving.de/urn:nbn:de:swb:14-1027510747000-39142.
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Die Dissertation besteht aus zwei Teilen: im ersten Teil wird das Verhalten von kleinen Edelgasclustern in intensiven Laserfeldern theoretisch untersucht. Im zweiten Teil wenden wir die Bohmsche Mechanik auf die Untersuchung von Helium und des Wasserstoffmolkülions (H_2^+) in intensiven Pulsen an. Im ersten Teil wird zunaechst ein numerisches Modell entwickelt, welches es erlaubt, unter Mitnahme aller Elektronen die die Dynamik kleiner Edelgascluster in starken Feldern zu simulieren. Anschliessend wird detailliert untersucht, wie die Expansion eines Clusters Einfluss auf dessen Absorptionseigenschaften nimmt. Wir verallgemeinern dabei den aus der Molekuelphysik bekannten "enhanced-ionization" Mechanismus auf den Bereich der Clusterphysik. Im zweiten Teil wird die in der Bohmschen Mechanik gegebene Moeglichkeit einer mikroskopischen Untersuchung der Wellenfunktionsdynamik verwendet, um atomphysikalische Prozesse unter einem neuen Aspekt zu betrachten. Der Ionisationsprozess des Wasserstoffmolekuelions im starken Lichtfeld wird eingehend untersucht, insbesondere die Frage, bei welchen Kernabstaenden die Ionisation stattfindet. Fuer das Heliumatom liefert die Analyse der zur Einfach- bzw. Doppelionisation fuehrenden Anfangszustaende der Bohmschen Testteilchen neue Einblicke in das nichtsequentielle Ionisationsverhalten.
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Czajkowski, Igor Kajetan. "Impact ionisation in bulk semiconductors and superlattice devices." Thesis, University of Surrey, 1990. http://epubs.surrey.ac.uk/842982/.
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This thesis reports results of experimental and theoretical investigations of impact ionisation in semiconductors. The impact ionisation rates for electrons and holes (alpha and beta respectively) are important parameters which determine the performance of several high-field semiconductor devices, including avalanche photodiodes (APDs). These ionisation rates depend on the threshold energies for ionisation, which are determined by the details of the band-structure for a semiconductor material. However, little is known about the band-structure features responsible for the favourable noise-performance of some materials (eg. Si) or relatively poor noise-performance of others (eg. Ge and most III-V materials). A better understanding of the relation between the band-structure and the resulting ionisation thresholds and rates would help guide the search for materials and structures with desirable properties. Impact ionisation in Si and Ge has been studied both experimentally and theoretically. Threshold energies in Si and Ge were calculated from pseudopotential band-structures. The key band-structure features leading to a large asymmetry in the ratio of thresholds for electrons and holes in Si, and the small ratio in Ge have been identified. The breakdown voltages in Si and Ge APDs have been measured under hydrostatic pressure. The results for Si and Ge are very different, and reflect the difference in the dominant ionisation processes calculated in these materials. Threshold energies have also been calculated for a selection of relaxed and strained GexSi1-x alloys. The relaxed alloys are expected to exhibit "Si-like" characteristics for a Ge mole fraction of 0 < X < 0.35. The effects of uniaxial strain on GexSi1-x alloys lead to a significant increase in the lowest-threshold ratio, making GexSi1-x/Si APDS an attractive proposition. However, a first-order Monte Carlo simulation of the effect of strain on ionisation rates indicates that the enhancement may be less than expected, as a result of the extreme softness of the ionisation process in Si. The role of satellite valleys in ionisation rate enhancement in multiple quantum well APDs has been studied using a Monte Carlo simulation. It is shown that the enhancement of the electron ionisation rate in multiple quantum well (MQW) APDs is determined by band-edge discontinuities in the satellite valleys, rather than in the r valley as previously assumed for semiconductors where the threshold field for the Gunn effect is lower than that for impact ionisation. Simulations of a model GaAs/Al0.45Ga0.55As MQW show no enhancement attributable to the band-edge discontinuities.
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Tantot, Laurent. "Modelling ionisation chamber response to nonstandard beam configurations." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18748.
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For patient-specific quality assurance of IMRT, a point dose measurement with an ionisation chamber and a relative dose distribution with film are performed. The use of ionisation chambers follows dosimetry protocols that only deal with reference beams, for which Spencer-Attix cavity theory is valid. However, IMRT and other recent radiation delivery techniques do not comply with these protocols. Therefore, the conversion of the dose to the chamber cavity to the dose to water becomes uncertain; and the geometrical details of the chamber, as well as the details of the delivery, are expected to be significant. In this thesis, a realistic model of the Exradin A12 Farmer chamber is simulated. A framework is applied for the calculation of ionisation chamber response to arbitrarily modulated fields as a summation of responses to pencil beams. This approach is used with the chamber model and tested against measurements in static open fields and dynamic MLC IMRT fields. As a benchmark test of the model, quality conversion factors values calculated by Monte-Carlo simulation with the chamber model are in agreement within 0.1 % and 0.4 % with those in the AAPM TG-51, for 6 MV and 18 MV photon beams, respectively. Pencil-beam kernels show a strong dependence on the geometrical details of the chamber. Kernel summations with open fields show a relative agreement within 4.0 % with experimental data ; the agreement is within 2.0 % for dynamic MLC IMRT beams. Simulations show a strong sensitivity of chamber response on positioning uncertainties, sometimes leading to dose uncertainties of 15 %.Pour le contrôle de qualité spécifique au patient en IMRT, on pratique une mesure ponctuelle de dose avec une chambre à ionisation et une mesure relative de distribution de dose avec un film. L'utilisation de chambres à ionisation suit les protocoles de dosimétrie qui ne traitent que de faisceaux de référence pour lesquels la théorie de Spencer-Attix est valide. Cependant, la radiothérapie à modulation d'intensité, ainsi que d'autres techniques récentes de radiothérapie, ne se conforme pas à ces protocoles. Par conséquent, la conversion de la dose dans la chambre à la dose dans l'eau devient incertaine ; et on s'attend à ce que les détails géométriques de la chambre, ainsi que les détails de l'émission des faisceaux, soient significatifs. Dans cette thèse, la chambre Exradin A12 de type Farmer a été modélisée de façon réaliste. Un formalisme a été utilisé pour la simulation de la réponse de la chambre à des champs modulés de façon arbitraire, où la réponse était calculée en sommant les réponses à des faisceaux-pinceaux. Cette approche est utilisée avec le modèle de la chambre et contrôlée par comparaison avec des mesures de champs statiques ouverts et de champs d'IMRT délivrés avec un collimateur multilame (CML) en mode dynamique. Comme test de référence du modèle de la chambre, les facteurs de conversion de qualité ont été calculés avec la chambre par Monte-Carlo et les résultats montrent un accord à mieux que 0.1 % et 0.4 % avec les valeurs du TG-51 de l'AAPM pour des faisceaux de photons de 6 MV et 18 MV, respectivement. Les noyaux de faisceaux-pinceaux montrent une forte dépendance aux détails géométriques de la chambre. Les sommations des noyaux avec les champs ouverts montrent un accord relatif à mieux que 4 % avec les résulats expérimentaux ; cet accord est à mieux que 2 % pour les faisceaux d'IMRT délivrés en mode dynamique avec le CML. Les simulations ont montré une force sensibilité d
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Leake, James Edward. "Effects of partial ionisation in the solar atmosphere." Thesis, University of Warwick, 2006. http://wrap.warwick.ac.uk/53967/.
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In this thesis techniques are developed for the simulation of partially ionised plasmas in the fluid approximation. These techniques are used to model the evolution of magnetic fields in the partially ionised regions of the solar atmosphere. Single fluid equations for a partially ionised plasma are derived based on the individual equations for each species. A Lagrangian Remap MHD code is then adapted to simulate a plasma of arbitrary degree of ionisation. The effects of the presence of neutrals on the propagation and damping of Alfv´en waves in the solar atmosphere are investigated. Ion-neutral collisions are shown to be an efficient damping mechanism for outwardly propagating Alfv´en waves of frequencies greater than 0.1 Hz, showing that high frequency waves in the outer solar atmosphere cannot originate at the surface of the Sun. Next simulations to show the effects of neutrals on the emergence of magnetic flux from beneath the solar surface into the outer atmosphere are performed. Results from 2D and 3D numerical experiments show that the presence of neutrals increases the amount of magnetic flux that can emerge into the corona. Furthermore, ion-neutral collisions are strong enough to dissipate currents perpendicular to the magnetic field as it emerges. This shows that ion-neutral collisions are a viable mechanism for the formation of force-free (j ∧B = 0) coronal magnetic field from sub-surface field, which is not the case when the plasma is assumed to be fully ionised.
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Dunseath, Kevin Murray. "Transfer and ionisation processes in ion-atom collisions." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335336.
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Houston, Christine Margaret. "Laser ionisation studies : applications in nuclear waste monitoring." Thesis, University of Glasgow, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481125.
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Scott, Colin Thomas Joseph. "A characterisation of matrix-assisted laser desorption ionisation." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388567.
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Towrie, Michael. "Multiphoton resonant ionisation : applications to high energy physics." Thesis, University of Glasgow, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280015.
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Williams, Christopher John. "Impact ionisation and Auger recombination in SiGe heterostructures." Thesis, University of Newcastle Upon Tyne, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295073.
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HernaÌndez, BeleÌn. "Ultratrace analysis by resonance ionisation mass spectrometry (RIMS)." Thesis, Manchester Metropolitan University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396526.
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Ness, Karen Margaret Montgomery. "Multiphon ionisation and laser-induced autoionisation in xenon." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47426.
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Price, H. "Multi-electron ionisation in driven atoms and molecules." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1448567/.
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In this thesis we formulate sophisticated quasiclassical techniques to describe corre- lated electron dynamics in atoms and diatomic molecules that are either absorbing a single photon or are driven by strong infrared laser fields. The first part of this thesis concerns the multi-electron ionisation in atoms following single-photon absorption. For excess photon energies close to threshold, the Wannier threshold law predicts that the electrons escape in the most symmetric way. We describe the single-photon quadru- ple ionisation from the ground state of beryllium. Surprisingly, we find that close to threshold the four electrons escape on the apexes of a triangular pyramid, while Wan- nier threshold law predicts a regular tetrahedron. We explain this unexpected breakup pattern using non-linear analysis for the fixed points of the Coulomb four-body sys- tem. We then focus on time-resolving the attosecond collision sequences that underlie single-photon multi-electron ionisation. We formulate how to time resolve intra-atomic correlated electron dynamics during the escape of two electrons. Specifically, we show how to compute the “collision” time, using the inter-electronic angle as a function of the phase between the triggering and the streaking laser fields. We also demonstrate how this two-electron streak camera captures the different ionisation dynamics for different electron energy sharings. We then proceed to generalise the two electron streak camera to account for realistic experimental conditions. In the final part of this thesis, we ad- dress correlated electron dynamics during the breakup of diatomic molecules driven by intense infrared laser fields. We concentrate on the two pathways leading to the forma- tion of highly excited neutral atoms. In particular, we show how for high ellipticites of the infrared laser field two-electron effects are “switched” off. Moreover, we find that the two dimensional momentum distribution of the escaping electron, in the formation of highly excited neutral atoms, carries the imprint of one-electron effects with increasing ellipticity of the infrared laser field.
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Vaupré, Solenn. "Ionisation des nuages moléculaires par les rayons cosmiques." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY049/document.
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Les rayons cosmiques (RC) ont un rôle fondamental sur la dynamique et l'évolution chimique des nuages moléculaires interstellaires, qui sont le lieu de formation stellaire et planétaire. Les RC sont probablement accélérés dans les enveloppes en expansion des rémanents de supernova (SNR), ainsi les nuages moléculaires situés à proximité peuvent être soumis à d'intenses flux de RC. Les protons relativistes ont principalement deux effets sur les nuages moléculaires : 1) en rencontrant le milieu dense, les protons de haute énergie (>280 MeV) induisent via la désintégration des pions l'émission de photons gamma. à cause de ce processus, les associations SNR-nuages moléculaires sont des sources intenses d'émission GeV et/ou TeV présentant des spectres similaires à celui des protons incidents. 2) à plus basse énergie, les RC pénètrent le nuage et ionisent le gaz, induisant la formation d'espèces moléculaires caractéristiques appelées traceurs de l'ionisation. L'étude de ces traceurs permet de déduire des informations sur les RC de basse énergie inaccessibles aux autres méthodes d'observation. J'ai étudié l'ionisation des nuages moléculaires par les RC près de trois SNR : W28, W51C et W44. Il existe des preuves observationnelles d'interaction avec le nuage voisin pour chaque SNR (présence de gaz choqué, masers OH, émission gamma). Mon travail repose sur la comparaison d'observations millimétriques des traceurs de l'ionisation à des modèles de chimie appliqués à ces nuages denses. Dans chaque région, nous avons déterminé un taux d'ionisation supérieur à la valeur standard, confortant l'hypothèse d'une origine des RC dans l'enveloppe du SNR voisin. L'existence d'un gradient d'ionisation en s'éloignant de l'onde de choc du SNR apporte des contraintes précieuses sur les propriétés de propagation des RC de basse énergie. La méthode utilisée repose sur l'observation des ions moléculaires HCO+ et DCO+, qui montre des limitations importantes à haute ionisation. C'est pourquoi j'ai également cherché à identifier des traceurs alternatifs de l'ionisation, par un effort croisé de modélisation et d'observation. En particulier, dans la région W44, les observations de N2H+ ont permis de mieux contraindre les conditions physiques, les abondances volatiles dans le nuage et l'état d'ionisation du gaz. Ce projet de recherche a amené une meilleure compréhension de la chimie induite par les RC dans les nuages moléculaires. Il a également ouvert de nouvelles perspectives de recherche interdisciplinaire vers la compréhension des RC, des observations millimétriques aux observations gammaCosmic rays (CR) are of tremendous importance in the dynamical and chemical evolution of interstellar molecular clouds, where stars and planets form. CRs are likely accelerated in the shells of supernova remnants (SNR), thus molecular clouds nearby can be irradiated by intense fluxes of CRs. CR protons have two major effects on dense molecular clouds: 1) when they encounter the dense medium, high-energy protons (>280 MeV) create pions that decay into gamma-rays. This process makes SNR-molecular cloud associations intense GeV and/or TeV sources whose spectra mimic the CR spectrum. 2) at lower energies, CRs penetrate the cloud and ionise the gas, leading to the formation of molecular species characteristic of the presence of CRs, called tracers of the ionisation. Studying these tracers gives information on low-energy CRs that are unaccessible to any other observations. I studied the CR ionisation of molecular clouds next to three SNRs: W28, W51C and W44. These SNRs are known to be interacting with the nearby clouds, from the presence of shocked gas, OH masers and pion-decay induced gamma-ray emission. My work includes millimeter observations and chemical modeling of tracers of the ionisation in these dense molecular clouds. In these three regions, we determined an enhanced CR ionisation rate, supporting the hypothesis of an origin of the CRs in the SNR nearby. The evolution of the CR ionisation rate with the distance to the SNR brings valuable constraints on the propagation properties of low-energy CRs. The method used relies on observations of the molecular ions HCO+ and DCO+, which shows crucial limitations at high ionisation. Therefore, I investigated, both through modeling and observations, the chemical abundances of several other species to try and identity alternative tracers of the ionisation. In particular, in the W44 region, observations of N2H+ bring additional constraints on the physical conditions, volatile abundances in the cloud, and the ionisation state. This research brought valuable insight into the CR induced chemistry in the interstellar medium. It also brought new perspectives of interdisciplinary research towards the understanding of CRs, from millimeter to gamma-ray observations