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No description available.

Single Event Gate Rupture (SEGR) induced by an energetic ion traversing a MOSFET may cause catastrophic failure of the device. The mechanism for SEGR in a power MOSFET structure is investigated in this work. A simple analytical prediction method is introduced. This prediction method allows evaluation of device SEGR sensitivity through 2-D computer simulations and therefore avoids the need for time consuming and costly experiments on an ion accelerator. A thorough investigation of SEGR sensitivity dependence is shown for a variety of influencing factors such as (i) device parametric variations, (ii) ion strike characteristics, and (iii) device operation temperature. Based on knowledge of the physical model for the SEGR mechanism and the utilization of simulation results and experimental SEGR data, useful SEGR hardening techniques are suggested.

A new spherical-shell radiative transfer model has been developed, with particular emphasis on the accurate calculation of the scattered radiance in the limb of the atmosphere. The model accounts for the spherical geometry of the atmosphere for all orders of scattering, but neglects the influence of polarization and refraction. Solutions are obtained by the successive orders of scattering method for several solar zenith angles simultaneously, using the inherent symmetry of the radiation field about the sub-solar point. The model is described by comparing and contrasting it with the model previously presented by Thome (1990) and Herman et al. (1994). The new model is tested against independent calculations to demonstrate the accuracy of the method. Its results are compared with the Monte Carlo calculations presented by Adams and Kattawar (1978) and Kattawar and Adams (1978) for a homogeneous atmosphere. Agreement is observed to within the stated statistical error of the Adams and Kattawar (1978) and Kattawar and Adams (1978) results for all lines of sight, including those in the limb. Comparisons are also made to the results obtained by the Herman et al. (1994) code for a more realistic atmospheric profile. These comparisons reveal excellent agreement outside the limb of the atmosphere, but some significant disagreement in the limb, which must be investigated further. Finally, preliminary results are presented that demonstrate the sensitivity of limb scattered radiances to changes in the ozone profile. Limb radiances are shown to be sensitive to a relatively small change in the ozone abundance in a thin layer of the atmosphere. However, the observed sensitivity is shown to decrease when aerosol scattering is added to the model atmosphere.

Current electron beam treatment planning algorithms are inadequate to calculate dose distributions in heterogeneous phantoms. Fast Monte Carlo algorithms are accurate in general but their clinical implementation needs validation. Calculations of electron beam dose distributions performed using the fast Monte Carlo system XVMC and the well-benchmarked general-purpose Monte Carlo code EGSnrc were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from the Clinac 18 accelerator with standard conditions. Percent depth doses and lateral profiles were measured with thermoluminescent dosimeter and electron diode respectively. The accelerator was modelled using EGS4/BEAM, and using an experiment-based beam model. All measurements were corrected by EGSnrc calculated stopping power ratios. Overall, the agreement between measurement and calculation is excellent. Small remaining discrepancies can be attributed to the non-equivalence between physical and simulated lung material, precision in energy tuning, beam model parameters optimisation and detector fluence perturbation effects.

The goal of Total Skin Electron Therapy (TSET) is to deliver a uniform dose to the patient's entire skin to a limited depth while sparing the body organs. Due to the laborious commissioning process, it is helpful to use the Monte Carlo (MC) method for the procedure and treatment planning. Calculations of dosimetric quantities were performed with EGSnrc/BEAM MC codes as well as with the fast MC code XVMC. The linac model for a 6 MeV Varian CL21EX accelerator was established by measuring the electron focal spot size with a slit camera. Using this measured focal spot value in our proposed divergent beam model, an improved result for large field profiles can be achieved. Measured PDDs and profiles under standard set-up and TSET conditions were compared to MC calculations. Overall, satisfactory results were obtained except for simulations with an additional scattering filter, suggesting the composition, density and dimensions of the filter need to be confirmed.

The goal of conformal radiation techniques is to improve local tumor control through dose escalation to target volumes while at the same time sparing surrounding healthy tissue. Accurate target volume delineation is essential in achieving this goal to avoid inadequate tumor coverage and/or irradiation of an unnecessary volume of healthy tissue. Respiratory motion is known to be the largest intra-fractional organ motion and the most significant source of uncertainty in treatment planning for chest lesions. A method to minimize effects of respiratory motion is to use four-dimensional (4D) radiotherapy. / A novel scanning procedure for 4D CT data acquisition is described in this work. Three single-slice helical scans are acquired simultaneously with the real-time tracking of several markers placed on a moving phantom. At the end of the three scans. CT data is binned into different respiratory phases according to the externally recorded respiratory signal and the scanned volume is reconstructed for several respiratory phases. The 4D CT images obtained show an overall improvement when compared to conventional CT images of a moving phantom.

<p> The main motivation of the Compact Muon Solenoid (CMS) experiment is to explore and to discover physics underlying electro-weak asymmetry breaking. Beside this, CMS detector provides an opportunity to do various experiments for detecting new physics signatures beyond the Standard Model (SM). Investigation of these signatures requires the identification and precise energy and moment measurement of electrons, muons, photons, and jets. The objective of this thesis is the calculation of the efficiencies for the measurement of W charge asymmetry in inclusive <i>pp</i> &rarr; <i>W</i> (&mgr;&upsi;) production. The charge asymmetry is defined to be the difference between W⁺ and W^&minus; bosons, normalized to the sum. This asymmetry is sensitive to the u-quark and d-quark ratios in the proton and precise measurement of the W charge asymmetry can provides new insights to the proton structure functions. Therefore, to improve understanding of SM backgrounds in search for new physics, the moun trigger, isolation, reconstruction, identification efficiencies has been studied using partial data collected by the CMS detector during pp collisions at the LHC in 2011. The dataset corresponds to an integrated luminosity of 2.31 fb^&minus;1. The efficiencies are measured as functions of the decay muon pseudo rapidity and transverse momentum based on "tag and probe" method. The efficiency measurements are compared to their estimated value from the Monte Carlo simulations so as to provide scaling factors to correct to the residual mis-modeling of the CMS muon performance. The comparison with simulations based on MC simulations opens a gate for validation of the detector simulation and optimization of selection strategies.</p>

The work of this thesis describes the experimental set-up and measurements for spectroscopic and kinetic studies of ionized helium gas. An injection-controlled KrF 248nm laser beam focussed to an intensity of 3 $\times$ 10$\sp{11}$ Wcm$\sp{-2}$ was used to generate highly ionized tantalum plasma. Helium gas was photoionized by the broadband soft x-ray flux from the laser-produced Ta plasma. The possibilities for realizing a short wavelength laser (below 2000A) have been investigated. The spectra of He$\sp+$ transitions 4 $\to$ 2 and 3 $\to$ 2 were experimentally measured by an optical multichannel analyzer, and the time evolution of the fluorescences were observed by a fast response photomultiplier. The effects of helium pressure on the fluorescence were also studied. In addition to the experiments, a kinetic model was developed. The properties of ionized helium predicted by this model are in relatively good agreement with the experimental results.