"Ionizing radiation is produced as the result of the decay of an unstable nucleus. The standard measure of radioactivity is quantified according to the rate of disintegration of the unstable nucleus. This method of quantification does not incorporate the total amount of ionizing radiation that is associated with each disintegration of the radionuclide. The ionizing radiation that is produced as a result of decay is specific to a given radionuclide. A radionuclide can be conceptualized as a source of ionizing radiation. Disintegration of the unstable nucleus will therefore result in the continual release of ionizing radiation throughout the fixed existence of the radionuclide. This thesis will present a reasonable and practical adjustment to the current mechanism regarding the quantification of radionuclides. This adjustment will provide a basis to which the specific decay attributes of radionuclides can be normalized. Such a normalization will allow for direct comparisons among important inventories of radionuclides. This adjustment will be used to formulate a characterization of common radionuclides that exist in the environment. Such a characterization can provide a control inventory of ionizing radiation to which more specific systems of radionuclides can be compared."

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Scanning probe microscopy (SPM) allows us to directly measure the interactions between a probe and a sample at the atomic scale. Techniques such as non-contact atomic force microscopy (NC-AFM), allows us to to characterize the forces present on a surface, resolve the atomic structure of molecules or examine their chemical properties, while scanning tunneling microscopy (STM) allows their electronic properties to be characterized. As the interactions take place at the atomic scale, the atomistic state of the probe apex plays a crucial role. In AFM, it is the atomic scale forces between the outermost atoms of the probe and surface that are dominant, while for STM the density of states (DOS) that contribute to tunneling are crucial. Therefore, understanding and controlling the tip termination is crucial to derive meaningful interpretations from experimental data. In this thesis, the role of the tip termination is examined for various surfaces and situations. We find that determining the "right" tip state depends critically on the experiment and several general strategies for shaping the tip apex into a preferred state are therefore outlined. H:Si(100) surfaces were used as a substrate for lithographic patterning using STM. We have successfully implemented an automated extraction routine for performing large scale patterning with high fidelity and single atom specificity. Our ultimate goal is to combine the extraction routine with SPM image recognition software to allow analysis and manipulation of atomic scale features without human intervention. To perform manipulations reliably, the tip influence on "what we see" (tip imaging states), or specifically on what the recognition software can identify, needs to be considered. We find, counter-intuitively, that atomic scale manipulation with the highest fidelity occurs when silicon dimers are observed as rows as opposed to when atomic resolution imaging occurs. The tip state influence on measuring surface diffusion of PTCDA on Ag(110) surfaces, was also investigated. We find that the adsorption kinetics of diffusing molecules can only be detected for specific tip imaging states. To allow examination with no-human intervention, the tip state needs to be carefully considered, and a combination of analytical and spectroscopic tools needs to be implemented in conjunction with the experiment. Additionally, characterization of the tip apex was investigated at the tunnel junction between a STM tip and a metal surface using field emission measurements. Our results suggest that field emission measurements performed at the tunnel junction are sensitive to changes in the nanoscopic/mesoscopic tip apex structure, thus opening up the possibility of automating the process of characterization the tip apex.

A search for the electroweak production of charginos and neutralinos decaying into final states involving three electrons or muons is presented. The analysis is based on 36.1 fb^-1 of √s = 13TeV proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Scenarios considered are based on simplified models with the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons. No significant deviations from Standard Model expectations are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles. For a massless lightest neutralino, masses up to 1.13TeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming slepton mediated decays, whereas for gauge-boson-mediated decays, masses up to 380 GeV are excluded.

Phase transitions and critical phenomena are of central importance in quantum field theory and statistical physics. We investigate the low energy properties of O(N) symmetric scalar field theories using functional renormalisation group methods for all N. This modern formulation of Wilson's renormalisation group allows a continuous interpolation between short and long distance physics without resorting to a weak coupling expansion. To leading order in the derivative expansion, we study the phase transition and the approach to convexity in the deep infrared limit. In the limit of infinite N, the fluctuations of the Goldstone modes dominate allowing for a complete analytical discussion of the effective potential. For finite N, the radial fluctuations become important and we resort to systematic series expansions. In both cases a systematic and thorough analysis of the diverse fixed point solutions is carried out. This leads to a comprehensive picture of the scaling potential for a large number of universality classes. We also study the dependence of our results on the regularisation scheme. Finally, we establish that the infrared completion of the effective potential in the broken phase is driven by a fixed point that leads to the flattening of the non-convex part of the potential.

The work in this thesis extends the applications of the Electric Potential Sensor (EPS) designed by the Sensor Research Technology Centre. Combined is work undertaken in two areas related by their application in security systems: low-field nuclear magnetic resonance with electric-field acquisition, and particle detection for alpha, beta and neutron radiation. In both these areas the EPS is used as to acquire signals. The first half of the thesis consists of the work undertaken to design a low-field Nuclear Magnetic Resonance spectrometer to detect drugs and explosives. In doing so, the use of the electric field detection technique - patented by Sussex University - is extended to low-field NMR work. The eventual negative results in this field lead first to the design of a simpler proton magnetometer apparatus, a design which would confirm the use of the EPS at low frequencies, and eventually to a change in direction of the research: particle detection. Detailed in this first section are a theoretical explanation of NMR in chapter 2, and a chapter covering the design and testing of the equipment in chapter 3. The particle detection part of the thesis covers modifications made to the EPS in order to detect particles and experiments conducted to confirm their operation. As in the NMR section, the work is split into a theory chapter which underpins the work, providing context for the experiments chapter. Chapter 5 covers the detection of alpha, beta and neutron radiation and the use of feedback to control the RC time constant of the front end of the sensor. The work in this thesis concludes negative results in the NMR area, but proves the EPS particle detector as a viable, cost effective alternative to conventional detectors.

This thesis presents a search for the electroweak production of supersymmetry using the dataset taken by the ATLAS detector at the Large Hadron Collider with √8 = 8 TeV during 2012. Events with three leptons are selected and required to satisfy additional kinematic criteria that define optimised signal regions. In these signal regions, Standard Model processes are discriminated against, whilst retaining a large fraction of events produced by specified compressed supersymmetry scenarios. Compressed refers to near massdegeneracy between the decaying gauginos and the final state gauginos. The expected number of Standard Model events are estimated using a combination of Monte Carlo and data-driven methods, where the predictions are tested against data in specifically designed validation regions. Exclusion limits are then set at 95% confidence level (CL) on via ℓ`L- and via WZ-decay scenarios for the decaying charginos and neutralinos. With the ℓ`L halfway between the decaying charginos and neutralinos and the final state neutralinos, there is a new sensitivity up to 250 GeV. In scenarios with large mass splitting, the decaying chargino and neutralino masses are excluded up to 740 GeV. Looking forward to the 13 TeV data-taking, a search for the electroweak production of supersymmetry with threelepton final states is presented, with a first look at an optimisation strategy to improve sensitivity to charginos and neutralinos.

This thesis introduces a novel technique for resummation of a wide class of observables to next-to-next-to-leading-logarithmic accuracy in e+e− annihilation, and potentially beyond. The method is applicable to observables that exhibit recursive infrared and collinear (rIRC) safety and continuous globalness. A systematic analysis of logarithmic counting in emission phase space reveals the contributions necessary to achieve NNLL-accurate results. A detailed description of the derivation and subsequent calculation of these effects is given. A framework of computer code (called ARES) has been developed to carry out automated numerical implementation of each of the NNLL contributions. ARES (Automated Resummer of Event Shapes) provides the user with an efficient determination of the resummed result for a desired observable. New results for several observables are presented, including the first NNLL resummation of the two-jet rate in the Durham and Cambridge algorithms which is crucial for determination of the strong coupling of Quantum Chromodynamics (QCD). This work as a whole presents an important addition to phenomenological precision calculations. Validation of the obtained predictions is performed, using both matching to NNLO fixed order calculations and comparison to data from the Large Electron-Positron collider at CERN.

The thesis presents the results of two searches for the direct pair-production of third generation scalar quarks, the stop and the sbottom, in proton-proton collisions at √s = 13 TeV delivered by the Large Hadron Collider (LHC) and recorded by the ATLAS detector. Third generation squarks are studied in the context of natural supersymmetric extensions of the Standard Model, highlighting their role in the solution of the Higgs hierarchy problem and considering both R-parity conserving and violating decay scenarios. The signal models of interest produce final states characterised by the presence of two bottom quarks, and the identification of the hadronic jets generated by their fragmentation plays a crucial role in the analyses. The performance of b-jet identification algorithms is studied in detail, and a novel approach for the estimate of the associated systematic uncertainties is presented. The first analysis in the thesis is a search for a pairproduced sbottom with two-body decays into Standard Model third generation quarks and quasi-degenerate electroweakinos, while the second targets the pair-production of the stop followed by R-parity violating decays into a bottom quark and a lepton. No evidence of SUSY particles is found, and exclusion limits are set on the relevant signal models using dedicated statistical tools.

This thesis presents a search for supersymmetry using the dataset taken by ATLAS at the Large Hadron Collider with ps =8 TeV during 2012. Events with four or more leptons are selected and required to satisfy additional kinematic criteria that define optimised signal regions. These criteria are chosen to reject the majority of events produced by Standard Model processes, whilst retaining a large fraction of events produced by a variety of proposed supersymmetry scenarios. The expected number of Standard Model events are estimated using a combination of Monte Carlo and data-driven methods, the predictions of which are tested against data in specifically designed validation regions. No significant deviations from the Standard Model estimations are observed within statistical and systematic uncertainties. Exclusion limits are then set at 95% confidence level (CL) on a wide range of R-parity conserving and R-parity violating supersymmetry simplified models, as well as models of general gauge mediated supersymmetry. In R-parity violating models, 95% CL exclusion limits of 1350 GeV and 750 GeV are set on the masses of gluinos and charginos respectively. Exclusion limits are also set at 95% CL up to 620 GeV on the mass of heavy neutralinos for an R parity conserving scenario with decays via righthanded sleptons. Results are also presented for the combination of the four lepton analysis with another lepton-rich supersymmetry search.