Matching Items (20)

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Implementation of a Prototype Aerogel RICH detector for Testing the Performance of Aerogels

Description

Our group has constructed a ring-imaging Cherenkov (RICH) detector with the goal of testing the performance of aerogel tiles in charged particle detectors. In previous work, tiles produced by Aspen

Our group has constructed a ring-imaging Cherenkov (RICH) detector with the goal of testing the performance of aerogel tiles in charged particle detectors. In previous work, tiles produced by Aspen Aerogels were tested as radiators in Cherenkov threshold counters and compared to commercial-grade samples. As an extension of this work we built a counter of the RICH type, which is used in practice to extract more particle identification information than threshold counters, and we have studied the images resulting from various aerogel samples.
The detector was designed for use in table-top experiments in which our particle source would be cosmic rays. Due to the vast energy range of cosmic rays, the window in which we can discriminate velocities is relatively small. Since the particles we do detect generally have β≈1, the relativistic limit β→1 motivates imaging by the Focusing Aerogel RICH (FARICH) technique, in which photons from multiple tiles are focused together at a detection plane.
Our detection plane is an array of flat-panel, multi-anode photomultiplier tubes (PMTs). Readout consists of multiplexing the anode outputs, recording the digitized signal, and converting this into a matrix of integrated charge values. The charge distribution in that matrix should directly imply the particle's speed; however, in practice, final recorded images are the influenced by many intermediate processes, so we have attempted to make meaningful measurements by averaging over numerous events.
For a given configuration and data collection, we produce the spatial distribution of observed signals relative to the cosmic ray's point of impact. These distributions have the expected form of a ring and their characteristics compare favorably with the predictions of geometric optics. Our confidence in the images is increased by verifying that changes to the configuration are reflected by the changes in the rings. We find that FARICH improves the sharpness of our ring images, but tiles must be used individually for actual aerogel analysis. So far we have shown that the Aspen tiles behave as one would expect for the purposes of RICH. Their images do resemble those produced by commercial-grade tiles, but we do not have tiles sufficiently similar for side-by-side comparison. A method of quantifying tile performance has proven difficult and is the only remaining task for our group.

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  • 2014-05

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Determination of Renal Stone Composition with Dual-Energy CT

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This research evaluates the capabilities of typical radiological measures and dual-energy systems to differentiate common kidney stones materials: uric acid, oxalates, phosphates, struvite, and cystine. Two different X-ray spectra (80

This research evaluates the capabilities of typical radiological measures and dual-energy systems to differentiate common kidney stones materials: uric acid, oxalates, phosphates, struvite, and cystine. Two different X-ray spectra (80 kV and 120 kV) were applied and the dual-energy ratio of individual kidney stones was used to figure out the discriminability of different materials. A CT cross-section with a prospective kidney stone was analyzed to see the capabilities of such a technique. Typical radiological measures suggested that phosphates and oxalate stones can be distinguished from uric acid stones while dual-energy seemed to prove similar effectiveness.

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  • 2020-05

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Proton Therapy Patient Log File Analysis for Machine Performance Evaluation

Description

Treatment log files for spot scanning proton therapy provide a record of delivery accuracy, but they also contain diagnostic information for machine performance. A collection of patient log files can

Treatment log files for spot scanning proton therapy provide a record of delivery accuracy, but they also contain diagnostic information for machine performance. A collection of patient log files can identify machine performance trends over time. This facilitates the identification of machine issues before they cause downtime or degrade treatment quality. At Mayo Clinic Arizona, all patient treatment logs are stored in a database. These log files contain information including the gantry, beam position, monitor units (MUs), and gantry angle. This data was analyzed to identify trends, which were then correlated with quality assurance measurements and maintenance records.

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  • 2021-05

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Spectral Analysis of Four Times Ionized Iron and Nickel in the Vacuum Ultraviolet with Applications in Astrophysics

Description

Observations of four times ionized iron and nickel (Fe V & Ni V) in the G191-B2B white dwarf spectrum have been used to test for variations in the fine structure

Observations of four times ionized iron and nickel (Fe V & Ni V) in the G191-B2B white dwarf spectrum have been used to test for variations in the fine structure constant, α, in the presence of strong gravitational fields. The laboratory wavelengths for these ions were thought to be the cause of inconsistent conclusions regarding the
variation of α as observed through the white dwarf spectrum. This thesis presents 129 revised Fe V wavelengths (1200 Å to 1600 Å) and 161 revised Ni V wavelengths (1200 Å to 1400 Å) with uncertainties of approximately 3 mÅ. A systematic calibration error
is identified in the previous Ni V wavelengths and is corrected in this work. The evaluation of the fine structure variation is significantly improved with the results
found in this thesis.

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  • 2016-05

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Analysis of Different Detector Layouts for Proton Beam Tomography

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Professor Alarcon’s lab is producing proton beam detectors, and this project is focused on informing the decision as to which layout of detector is more effective at producing an accurate

Professor Alarcon’s lab is producing proton beam detectors, and this project is focused on informing the decision as to which layout of detector is more effective at producing an accurate backprojection for an equal number of data channels. The comparison is between “square pad” detectors and “wire pad” detectors. The square pad detector consists of a grid of square pads all of identical size, that each collect their own data. The wire pad detector consists of large rectangular pads that span the entire detector in one direction, with 2 additional layers of identical pads each rotated by 60° from the previous. In order to test each design Python was used to simulate Gaussian beams of varying amplitudes, position and size and integrate them in each of the two methods. They were then backprojected and fit to a Gaussian function and the error between the backprojected parameters and the original parameters of the beam were measured.

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  • 2019-05

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Quantum Monte Carlo studies of strongly interacting fermionic systems

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In this dissertation two kinds of strongly interacting fermionic systems were studied: cold atomic gases and nucleon systems. In the first part I report T=0 diffusion Monte Carlo results for

In this dissertation two kinds of strongly interacting fermionic systems were studied: cold atomic gases and nucleon systems. In the first part I report T=0 diffusion Monte Carlo results for the ground-state and vortex excitation of unpolarized spin-1/2 fermions in a two-dimensional disk. I investigate how vortex core structure properties behave over the BEC-BCS crossover. The vortex excitation energy, density profiles, and vortex core properties related to the current are calculated. A density suppression at the vortex core on the BCS side of the crossover and a depleted core on the BEC limit is found. Size-effect dependencies in the disk geometry were carefully studied. In the second part of this dissertation I turn my attention to a very interesting problem in nuclear physics. In most simulations of nonrelativistic nuclear systems, the wave functions are found by solving the many-body Schrödinger equations, and they describe the quantum-mechanical amplitudes of the nucleonic degrees of freedom. In those simulations the pionic contributions are encoded in nuclear potentials and electroweak currents, and they determine the low-momentum behavior. By contrast, in this work I present a novel quantum Monte Carlo formalism in which both relativistic pions and nonrelativistic nucleons are explicitly included in the quantum-mechanical states of the system. I report the renormalization of the nucleon mass as a function of the momentum cutoff, an Euclidean time density correlation function that deals with the short-time nucleon diffusion, and the pion cloud density and momentum distributions. In the two nucleon sector the interaction of two static nucleons at large distances reduces to the one-pion exchange potential, and I fit the low-energy constants of the contact interactions to reproduce the binding energy of the deuteron and two neutrons in finite volumes. I conclude by showing that the method can be readily applied to light-nuclei.

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Date Created
  • 2018

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Two-flavor color superconductivity in magnetic field

Description

Quark matter at sufficiently high density and low temperature is expected to be a color superconductor, and may exist in the interior of neutron stars. The properties of two simplest

Quark matter at sufficiently high density and low temperature is expected to be a color superconductor, and may exist in the interior of neutron stars. The properties of two simplest possible color-superconducting phases, i.e., the color-flavor-locked (CFL) and two-flavor superconducting (2SC) phases, are reviewed. The effect of a magnetic field on the pairing dynamics in two-flavor color-superconducting dense quark matter is investigated. A universal form of the gap equation for an arbitrary magnetic field is derived in the weakly coupled regime of QCD at asymptotically high density, using the framework of Schwinger-Dyson equation in the improved rainbow approximation. The results for the gap in two limiting cases, weak and strong magnetic fields, are obtained and discussed. It is shown that the superconducting gap function in the weak magnetic field limit develops a directional dependence in momentum space. This property of the gap parameter is argued to be a consequence of a long-range interaction in QCD.

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Date Created
  • 2012

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True muonium on the light front

Description

The muon problem of flavor physics presents a rich opportunity to study beyond standard model physics. The as yet undiscovered bound state (μ+μ-), called true muonium, presents a unique opportunity

The muon problem of flavor physics presents a rich opportunity to study beyond standard model physics. The as yet undiscovered bound state (μ+μ-), called true muonium, presents a unique opportunity to investigate the muon problem. The near-future experimental searches for true muonium will produce it relativistically, preventing the easy application of non-relativistic quantum mechanics. In this thesis, quantum field theory methods based on light-front quantization are used to solve an effective Hamiltonian for true muonium in the Fock space of |μ+μ-> , |μ+μ-γ> , |e+e->, |e+e-γ>, |τ+τ-> , and |τ+τ-γ> . To facilitate these calculations a new parallel code, True Muonium Solver With Front-Form Techniques (TMSWIFT), has been developed. Using this code, numerical results for the wave functions, energy levels, and decay constants of true muonium have been obtained for a range of coupling constants α. Work is also presented for deriving the effective interaction arising from the |γγ sector’s inclusion into the model.

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Date Created
  • 2016

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Holography in Rindler space

Description

This thesis addresses certain quantum aspects of the event horizon using the AdS/CFT correspondence. This correspondence is profound since it describes a quantum theory of gravity in d + 1

This thesis addresses certain quantum aspects of the event horizon using the AdS/CFT correspondence. This correspondence is profound since it describes a quantum theory of gravity in d + 1 dimensions from the perspective of a dual quantum field theory living in d dimensions. We begin by considering Rindler space which is the part of Minkowski space seen by an observer with a constant proper acceleration. Because it has an event horizon, Rindler space has been studied in great detail within the context of quantum field theory. However, a quantum gravitational treatment of Rindler space is handicapped by the fact that quantum gravity in flat space is poorly understood. By contrast, quantum gravity in anti-de Sitter space (AdS), is relatively well understood via the AdS/CFT correspondence. Taking this cue, we construct Rindler coordinates for AdS (Rindler-AdS space) in d + 1 spacetime dimensions. In three spacetime dimensions, we find novel one-parameter families of stationary vacua labeled by a rotation parameter β. The interesting thing about these rotating Rindler-AdS spaces is that they possess an observer-dependent ergoregion in addition to having an event horizon. Turning next to the application of AdS/CFT correspondence to Rindler-AdS space, we posit that the two Rindler wedges in AdSd+1 are dual to an entangled conformal field theory (CFT) that lives on two boundaries with geometry R × Hd-1. Specializing to three spacetime dimensions, we derive the thermodynamics of Rindler-AdS space using the boundary CFT. We then probe the causal structure of the spacetime by sending in a time-like source and observe that the CFT “knows” when the source has fallen past the Rindler horizon. We conclude by proposing an alternate foliation of Rindler-AdS which is dual to a CFT living in de Sitter space. Towards the end, we consider the concept of weak measurements in quantum mechanics, wherein the measuring instrument is weakly coupled to the system being measured. We consider such measurements in the context of two examples, viz. the decay of an excited atom, and the tunneling of a particle trapped in a well, and discuss the salient features of such measurements.

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  • 2012

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Development of dose verification detectors towards improving proton therapy outcomes

Description

The challenge of radiation therapy is to maximize the dose to the tumor while simultaneously minimizing the dose elsewhere. Proton therapy is well suited to this challenge due to the

The challenge of radiation therapy is to maximize the dose to the tumor while simultaneously minimizing the dose elsewhere. Proton therapy is well suited to this challenge due to the way protons slow down in matter. As the proton slows down, the rate of energy loss per unit path length continuously increases leading to a sharp dose near the end of range. Unlike conventional radiation therapy, protons stop inside the patient, sparing tissue beyond the tumor. Proton therapy should be superior to existing modalities, however, because protons stop inside the patient, there is uncertainty in the range. “Range uncertainty” causes doctors to take a conservative approach in treatment planning, counteracting the advantages offered by proton therapy. Range uncertainty prevents proton therapy from reaching its full potential.

A new method of delivering protons, pencil-beam scanning (PBS), has become the new standard for treatment over the past few years. PBS utilizes magnets to raster scan a thin proton beam across the tumor at discrete locations and using many discrete pulses of typically 10 ms duration each. The depth is controlled by changing the beam energy. The discretization in time of the proton delivery allows for new methods of dose verification, however few devices have been developed which can meet the bandwidth demands of PBS.

In this work, two devices have been developed to perform dose verification and monitoring with an emphasis placed on fast response times. Measurements were performed at the Mayo Clinic. One detector addresses range uncertainty by measuring prompt gamma-rays emitted during treatment. The range detector presented in this work is able to measure the proton range in-vivo to within 1.1 mm at depths up to 11 cm in less than 500 ms and up to 7.5 cm in less than 200 ms. A beam fluence detector presented in this work is able to measure the position and shape of each beam spot. It is hoped that this work may lead to a further maturation of detection techniques in proton therapy, helping the treatment to reach its full potential to improve the outcomes in patients.

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Date Created
  • 2019