This thesis investigates the use of Monte Carlo methods to study several imaging applications. Studies are based on the EGS4 code system, and some of these used a low energy electron expansion for this software package that was developed during this work. The code is firstly used to gain some insight into one-sided imaging techniques making use of megavoltage radiation. The method explored is based on induced positron annihilation. The dependence of annihilation yields on atomic number demonstrates that the technique is suitable for the inspection of high-Z inclusions in low-Z, less dense, matrices. Results obtained with the EGS4 code were found to be in good agreement with experimental data. Several applications have been considered via the simulation approach, showing that areas like civil engineering and nuclear material inspection can benefit from this novel inspection technique. The limited accuracy of EGS4 in the simulation of X-ray tubes operating at diagnostic energies led to an expansion of the code to be developed. The enhanced code incorporates a generalized oscillator strength (GOS) model for electron atom inelastic collisions, where atomic bound effects are considered. An enhanced version of this model has been developed so that K-shell ionisation events could be reproduced realistically. The accuracy of low energy bremsstrahlung emissions has also been assessed, and an improved scheme for the angular sampling of newly created photons suggested. The low energy electron expansion of EGS4 (the EGS4/GOS code) is described, and used to simulate photon spectra from diagnostic X-ray tubes. The results were compared with experimental data, showing an accuracy of the order of 15% near the Ka line. Some X-ray tube design studies were carried out using the EGS4/GOS code. The importance of the different physical interactions was analysed. The results show that better fluorescence-to-bremsstrahlung ratios can be obtained with thinner targets, but a factor 2 increase in this ratio is achieved at the expense of a decrease of 40 times in efficiency. The need for low-Z substrates in thin-target applications is also discussed.

Le contrôle des états quantiques de la lumière est une étape nécessaire pour la transmission et le traitement quantiques des informations. Un nuage d'atomes froids constitue un milieu optiquement non-linéaire très intéressant pour créer et manipuler des états photoniques. Le sujet de cette thèse est l'étude expérimentale de telles non-linéarités, induites entre des photons optiques par leur couplage avec des atomes de Rydberg. Les états de Rydberg sont des états atomiques très excités (n>30), qui permettent de créer des interactions photon-photon par l'intermédiaire de leurs interactions dipôle-dipôle à longue distance (>10µm). Nous utilisons une cavité de faible finesse pour transformer ces interactions en effets observables sur un faisceau de très faible intensité, ce qui peut permettre de produire des états non-classiques de lumière. / The control of quantum states of light is a necessary step for quantum information transportation and processing. Cold atomic memories are one of the prime candidates for storing and manipulating photonic states. This thesis is a study of optical non-linear effects created using Rydberg states. Rydberg states are highly excited states (n>30) of atoms, which are useful in realizing photon-photon interactions because of their long distance (>10µm) dipole-dipole interactions. We utilize a low finesse cavity to transform phase shifts into intensity correlations which would allow one to generate arbitrary non-classical states of light

The non-invasive measurement of the mass of bone is a clinically relevant problem. The bone is one component of a composite system. At the spine it may include fat, lean and bone mineral. At a hip prosthesis it may include soft tissue, bone mineral and metal. The measurement of the attenuation of photons of different energies can be used to determine the mass of one or all of the components of the composite system. The first system is currently measured using only two photon energies by assuming that it is a two component system. A model was developed which predicts the effect of the third component, fat, and was validated using phantom measurements. Typical parameters for the volume and spatial distribution of fat 𝘪𝘯 𝘷𝘪𝘷𝘰 were determined using CT scans. In combination with the model a median error of 8% is introduced by the third component. The feasibility of using a third energy to correct for the error was investigated. A model for the variance of the bone measurement normalized to emitted photon flux was developed. The optimal set of photon energies yielded a minimum value for the variance. However, this variance was excessively high, requiring a radiation dose 3000 times that for dual photon absortiometry. For the second system a triple photon absorptiometry technique was developed using the isotopes 203-Hg and 141-Ce. The technique was shown to be valid, but the variance was high due to cross-over of high energy photons in the detector and by scattering. In order to make measurements with a precision of 1%, counting times of 70 hours are required. Monte Carlo simulations were performed to determine the optimal geometry to reduce cross-over from scattering. However, cross-over cannot be reduced sufficiently with 203-Hg and 141-Ce. A three isotope source is required to make clinical bone measurements at a prosthesis. / Thesis / Doctor of Philosophy (PhD)

A ¹⁵³Sm source was used with a dual photon absorptiometry technique in vitro to determine the feasibility of using this isotope as an alternative source to ¹⁵³Gd for further in vivo studies. The source activity was typically .4 Ci (i.e., at the source collimator exit) with a half life of 46.8 hours and photon energies of "103" keV and ¹⁵³Eu X-rays at "42.5" keV. The system was evaluted using phantom measurements of water, aluminum and polyethylene to simulate soft tissue, bone and fat respectively. During stationary measurements, a total absorber thickness between 15 and 22.5 cm. was used in conjunction with an aluminum thickness range of .314 to 1.91 em. (.848-5.16 g/cm²). The coefficient of variation and the accuracy at most total absorber thicknesses was less than 2%. This showed that ¹⁵³Sm could produce precision and accuracy comparable to ¹⁵³Gd. When polyethylene (fat) was present, as the amount of polyethylene in the RST measurement increased, the error due to a difference in the amount of polyethylene between the RST and the BMC measurements increased. For a percent difference in polyethylene thickness between the RST and BMC measurement of less than 50% at 16.3% RST polyethylene content, measurements of aluminum (bone) above 1.8 g/cm²(.662 cm. of aluminum) produced results accurate to within 10% of the true aluminum (BMC) value for this experimental geometry. Motional studies were performed using a modified OHIO NUCLEAR rectilinear scanner. The optimal scan speed was shown to be in the range of 4-6 mm./sec. with a sample space of between .5 to .7 cm.. The worst-case dose using the optimal scan parameters was determined as 6.2 and 1. 4 mRad per scan of approximately 24 minutes for bone and soft tissue respectively. The combination of stationary and motional in vitro studies indicated that ¹⁵³Sm could be an economical and effective alternative to ¹⁵³Gd for clinical studies. A Monte Carlo simulation was implemented to determine the optimal detector collimator entrance size. Simulation of the experimental geometry indicated that the .6 cm. detector collimation used experimentally was near the optimal size to produce efficient results in terms of accuracy and precision. A brief summary of Monte Carlo methods and radiation theory is also included. / Thesis / Master of Engineering (ME)

L'expérience HPS (Heavy Photon Search) au Jefferson Lab (USA)recherche un nouveau boson de jauge vecteur, nommé "photon lourd" ou "photon sombre", dans une fourchette de masse allant de 20 à 1000 MeV. Une telle particule couplerait avec le photon du modèle standard par effet de "kinetic mixing" et pourrait ainsi être émis par l'intermédiaire d'électrons. En utilisant un faisceau d'électron de haute intensité d’un à six GeV envoyé sur une cible de tungstène, HPS cherche à détecter une fine résonance dans le bruit de fond produit par les processus QED qui serait la signature d'un photon lourd. HPS exploitera aussi le fait qu'à très petit couplages, le photon lourd se désintègrera après une distance détectable, fournissant ainsi une seconde signature sous la forme d'un vertex éloigné de la cible. Dans cette thèse, je présente les motivations pour une telle recherche de photon lourd dans ce domaine spécifique de l'espace de phase, puis je présente le spectromètre HPS, en détaillant en particulier le calorimètre électromagnétique qui a été l'un de mes sujets d'étude. Ensuite, je présente mon travail utilisant une intégration Monte-Carlo pour calculer la section efficace des processus QED attendus dans l'expérience HPS. Finalement, je présente dans cette thèse mon analyse de donnée pour la recherche d'un pic sur le bruit de fond QED dans les données acquises au printemps 2015. / The heavy photon search (HPS) experiment in Jefferson Lab (USA) is looking for a new vector gauge boson, called "heavy photon" or "dark photon", in a mass range of 20 MeV to 1000 MeV. Such particle can couple to the standard model photon through kinetic mixing and therefore can be radiated in electron scatterings. Using a high intensity, one to six GeV electron beam sent onto a tungsten target, HPS will look for a narrow resonance above the QED background that would be a signature of a dark photon. HPS will also exploit the fact that for small couplings, this dark photon would also travel a detectable distance before decaying, providing a second signature in the form of a vertex away from the target. In this thesis, I will present the motivations to look for such a dark photon in this particular domain of phase space, then present the HPS spectrometer, with a particular focus on the electromagnetic calorimeter which was a focus of my work. Then, I will present my work using a Monte-Carlo integration to calculate the cross section of the expected background QED processes for the HPS experiment. The final part of my work presented in this thesis will be focused on my data analysis, looking for a bump on the QED background, I carried out using data taken in Spring 2015.

本論文包括對 Jaynes-Cummings-Hubbard (JCH) 系統的研究。在這個系統中，每個耦合光學腔之內都放置了一顆雙態原子，偶極相互作用導致系統有激發光子和原子的自由度。對量子電動力學系統的研究，使我們對光子與原子間的相互作用以及量子相變有更深的認識。 / 我們研究了一維JCH系統中有兩個激發子的本徵態。我們發現當真空拉比頻率與腔間穿隧率之比超過某一臨界值，兩個激發子的束縛態就會出現。 / 我們還為兩個腔的JCH系統之演化作出研究，並指出系統的量子態在一定條件下可演變成薛丁格貓態。從相干態演化到薛丁格貓態所需的時間亦被估計。 / 最後，我們使用主方程來探討驅動JCH系統的去相干。在這篇論文中，我們提出了一些低激發量的穩態的例子。許多不同的穩態系統的光子統計將被討論。 / This thesis comprises of an investigation of the Jaynes-Cummings-Hubbard (JCH) system. In such a system, single two-level atoms are embedded in each coupled optical cavity, and the dipole interaction leads to dynamics involving photonic and atomic degrees of freedom. The investigation of quantum electrodynamics in the system provides insight about the behaviour of strongly interacting photons and atoms and quantum phase transition. / We examine the eigenstates of the one-dimensional JCH system in the two-excitation subspace. We discover that two-excitation bound states emerge when the ratio of vacuum Rabi frequency to the tunnelling rate between cavities exceeds a critical value. / We also study for the time evolution of a two-cavity JCH system, and indicate that the evolved state can be a Schrödinger's cat state under certain conditions. The time required for evolving a coherent state into a Schrödinger's cat state is also estimated. / Finally, we investigate the decoherence of a driven JCH system by using the master equation. In this thesis we present several examples of steady state when the total number of excitation is low. The photon statistics of the steady state of the system will be discussed. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wong, Tsz Ching Max = Jaynes-Cummings-Hubbard模型的課題 / 黃子澄. / "November 2012." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 79-84). / Abstracts also in Chinese. / Wong, Tsz Ching Max = Jaynes-Cummings-Hubbard mo xing de ke ti / Huang Zicheng. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Basic Description of the Jaynes-Cummings-Hubbard Model --- p.4 / Chapter 2.1 --- Jaynes-Cummings Model --- p.4 / Chapter 2.1.1 --- Hamiltonian --- p.5 / Chapter 2.1.2 --- Energy Eigenstates --- p.6 / Chapter 2.2 --- Coupled-cavity System without Atoms --- p.8 / Chapter 2.2.1 --- A One-dimensional Coupled-cavity Chain --- p.8 / Chapter 2.2.2 --- Normal Modes --- p.9 / Chapter 2.3 --- Jaynes-Cummings-Hubbard Model --- p.10 / Chapter 2.3.1 --- Eigenstates of Single Excitation --- p.11 / Chapter 2.3.2 --- Dynamics of Single Excitation --- p.12 / Chapter 2.3.3 --- Single Excitation in the Weak Coupling Limit --- p.15 / Chapter 2.3.4 --- Single Excitation in the Strong Coupling Limit --- p.16 / Chapter 3 --- Solution of the JCH Model with Two Excitations --- p.17 / Chapter 3.1 --- Two-particle Bound States in the Bose-Hubbard Model --- p.17 / Chapter 3.2 --- Two-polariton Bound States in the JCH Model --- p.19 / Chapter 3.2.1 --- Bound State Eigenvectors --- p.24 / Chapter 3.2.2 --- Bound State Eigenvalues --- p.26 / Chapter 3.2.3 --- Critical Coupling --- p.28 / Chapter 3.2.4 --- Analytic Approximations in Strong Coupling Regime n≫k --- p.30 / Chapter 3.3 --- Dynamics of Two Excitations in Strong Coupling Regime --- p.33 / Chapter 3.3.1 --- Initial Condition: --- p.33 / Chapter 3.3.2 --- Initial Condition: Superposition of j2; gin in Gaussian Distribution --- p.34 / Chapter 3.3.3 --- Initial Condition: Superposition of j1; gin j1; gim in Gaussian Distribution --- p.39 / Chapter 3.3.4 --- Initial Condition: Superposition of j1;+in j1; ¡im in Gaussian Distribution --- p.39 / Chapter 4 --- JCH Model in a Two-cavity Con¯guration --- p.41 / Chapter 4.1 --- Generation of SchrÄodinger's Cat State: Numerical Simulation --- p.41 / Chapter 4.2 --- Generation of SchrÄodinger's Cat States: Analytic Solution --- p.45 / Chapter 4.2.1 --- Estimation of Optimum Parameters --- p.53 / Chapter 4.3 --- Coherent States as Initial Conditions --- p.55 / Chapter 5 --- Decoherence of a Weakly Driven JCH Model --- p.60 / Chapter 5.1 --- Master Equation --- p.60 / Chapter 5.2 --- Driven JCH Model: N-cavity Configuration --- p.61 / Chapter 5.2.1 --- One-excitation Approximation --- p.63 / Chapter 5.2.2 --- Simple Harmonic Oscillator Limit --- p.66 / Chapter 5.3 --- Driven JCH Model: Two-cavity Configuration --- p.69 / Chapter 6 --- Conclusion --- p.76 / Bibliography --- p.79

The characterization and measurement of the spatial, temporal and energy emission of air-scattered photons, electrons and neutrons generated near 10 MV or greater accelerator-based bremsstrahlung photon sources is becoming important in many applications. The national and homeland security research community is interested in developing technologies which can detect illicit materials at substantial standoff distances in outdoor environments. These systems are referred to as "active" interrogation systems and are defined as inspection systems that take advantage of an externally applied "source" to perform traditional imaging of, or to stimulate characteristic emissions from, an inspected object. A key concern in the development of these systems is the ability to effectively predict the dose equivalents at long standoff distances from these sources in order to ascertain the operational radiation safety of said systems. Current computational radiation transport simulation tools have the ability to effectively model these systems; however, a paucity of experimental data exists in comparing the results of these simulations. A methodology to assess the radiation dose surrounding a high-energy bremsstrahlung-based accelerator system for national defense applications was developed. Fluence-to-dose conversion coefficients for the International Commission on Radiation Units and Measurements operational quantity ambient dose equivalent were calculated for photons and electrons up to 25 MeV utilizing the Los Alamos National Laboratory Monte Carlo N-Particle code, MCNP5 Version 1.51. Special consideration was given to the treatment of secondary charged particle equilibrium in all simulations. An extensive set of system simulations was performed to model a prototype high-energy bremsstrahlung-based accelerator system to obtain photon, electron and neutron fluence spectra. These fluence data were folded with the calculated ambient dose equivalent conversion coefficients as well as previously published effective dose conversion coefficients. A set of integral air-scatter measurements for accelerator-generated primary and secondary radiations (photon and neutron) were performed around the prototype system in order to provide a comparative data set from which to determine the total dose equivalent both in the beam (on-axis) and outside of the beam (off-axis).

No description available.

Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2005. / Includes bibliographical references (leaves 20-24).

Universiẗat, Diss., 2000--Freiburg.