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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Systematics of Giant Impacts in Late-Stage Planet Formation and Active Neutron Experiments on the Surface of Mars

January 2019 (has links)
abstract: Part I – I analyze a database of Smoothed Particle Hydrodynamics (SPH) simulations of collisions between planetary bodies and use the data to define semi-empirical models that reproduce remant masses. These models may be leveraged when detailed, time-dependent aspects of the collision are not paramount, but analytical intuition or a rapid solution is required, e.g. in ‘N-body simulations’. I find that the stratification of the planet is a non-negligible control on accretion efficiency. I also show that the absolute scale (total mass) of the collision may affect the accretion efficiency, with larger bodies more efficiently disrupting, as a function of gravitational binding energy. This is potentially due to impact velocities above the sound speed. The interplay of these dependencies implies that planet formation, depending on the dynamical environment, may be separated into stages marked by differentiation and the growth of planets more massive than the Moon. Part II – I examine time-resolved neutron data from the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) Curiosity rover. I personally and independently developed a data analysis routine (described in the supplementary material in Chapter 2) that utilizes spectra from Monte Carlo N-Particle Transport models of the experiment and the Markov-chain Monte Carlo method to estimate bulk soil/rock properties. The method also identifies cross-correlation and degeneracies. I use data from two measurement campaigns that I targeted during remote operations at ASU. I find that alteration zones of a sandstone unit in Gale crater are markedly elevated in H content from the parent rock, consistent with the presence of amorphous silica. I posit that these deposits were formed by the most recent aqueous alteration events in the crater, since subsequent events would have produced matured forms of silica that were not observed. I also find that active dunes in Gale crater contain minimal water and I developed a Monte Carlo phase analysis routine to understand the amorphous materials in the dunes. / Dissertation/Thesis / Table 1: Giant impact SPH results for Chapter 1 / Table 2: Giant impact SPH results for Chapter 1 / Table 3: Giant impact SPH results for Chapter 1 / Doctoral Dissertation Geological Sciences 2019
52

Weak Boson Production in High Energy Colliders as a Probe of Nucleon Structure

Nam, Jae, 0000-0003-1893-5237 January 2021 (has links)
Presented in this thesis are measurements of W boson production in high energy pp collisions and ep deep inelastic scattering that take place at RHIC and HERA facilities, respectively. These measurements explore the inner structure of the nucleons, in particular, probing the distributions of the light flavor sea which consists of up, down and strange quarks. The W+/W− cross-section ratio, RW , in pp collisions is sensitive to the asymmetry in the ¯d and ¯u flavors in the nucleon sea. This ratio was first measured with the STAR detector at RHIC with the data collected in 2009 and again with the data collected from 2011 to 2013, featuring pp collisions of a center-of-mass energy of √s = 500/510 GeV and an integrated luminosity of ∼ 350 pb−1. The study considered in this thesis further improves the precision of this measurement by analyzing an additional data set collected in 2017 which corresponds to an integrated luminosity of ∼ 350 pb−1. The experimental results are compared to theory predictions generated with various global PDF fits. The measurement performed at HERA searches for the strange quark content in the nucleon via charm production in charged current deep inelastic scattering. This is the first measurement of its kind, using the HERA II data collected with the ZEUS detector. This data set corresponds to e±p collisions at a center-of-mass energy of √s = 318 GeV with an integrated luminosity of 358 pb−1. The results are consistent with expectations from the Standard Model, albeit with large experimental uncertainties arising from the limited statistics. / Physics
53

Precision Møller Polarimetry and Applications at Jefferson Laboratory

Henry, WIlliam Patrick January 2019 (has links)
Jefferson Lab's cutting-edge parity-violating electron scattering program has increasingly stringent requirements for systematic errors. Beam polarimetry is often one of the dominant systematic errors in these experiments. A new Moeller Polarimeter in Hall A of Jefferson Lab (JLab) was installed in 2015 and has taken first measurements for a polarized scattering experiment. Upcoming parity violation experiments in Hall A include CREX, PREX-II, MOLLER and SOLID with the latter two requiring < 0.5% precision on beam polarization measurements, a precision which has not been achieved to date. The polarimeter measures the Moeller scattering rates of the polarized electron beam incident upon an iron target placed in a saturating magnetic field. The spectrometer consists of four quadrupoles and one momentum selection dipole. The detector is designed to measure the scattered and knock out target electrons in coincidence. Beam polarization is extracted by constructing an asymmetry from the scattering rates when the incident electron spin is parallel and anti-parallel to the target electron spin. The largest systematic errors associated with Moeller polarimetry comes from the precision that the target polarization and the detector acceptance is known will be discussed. Other errors including the Levchuk effect, beam stability, and target heating will be addressed. / Physics
54

Measuring the Neutron Spin Asymmetry A1n in the Valence Quark Region in Hall C at Jefferson Lab

Cardona, Melanie Leigh, 0000-0001-5337-9550 January 2023 (has links)
The quest to understand how the nucleon spin is decomposed into its constituent quark and gluon spin and orbital angular momentum (OAM) components has been at the forefront of nuclear physics for decades. Due to the non-perturbative nature of Quantum Chromodynamics (QCD) - the theory describing how quarks and gluons bind together to form protons and neutrons - making absolute predictions of nucleon spin structure is generally difficult, especially as a function of its quark and gluon longitudinal momentum fraction x. Measurements involving nucleon spin structure serve as a sensitive test for QCD, including ab-initio lattice QCD calculations due to the advent of the quasi-PDF formalism, and various predictions that diverge at large-x. The neutron spin asymmetry A1n at high-x is a key observable for probing nucleon spin structure. In the valence domain (x > 0.5), sea effects are expected to be negligible, and so the total nucleon spin is considered to be carried by the valence quarks. The valence region can therefore enable us to study the role of quark OAM and other non-perturbative effects of the strong force. A1^n was measured in the deep inelastic scattering region of 0.40 < x < 0.75 and 6 < Q^2 < 10 GeV^2 in Hall C at Jefferson Lab using a 10.4 GeV longitudinally polarized electron beam, upgraded polarized He-3 target, and the High Momentum Spectrometer (HMS) and Super High Momentum Spectrometer (SHMS). E12-06-110 provides the first precision data in the valence quark region above x = 0.60, and its preliminary results proved consistent with earlier data disqualifying a pQCD model that excluded quark OAM. Combined with previous world proton data, the ratio of the polarized-to-unpolarized up quark momentum distribution (∆u + ∆anti-u)/(u + anti-u) remained positive at large-x, and the down quark (∆d + ∆anti-d)/(d + anti-d) remained negative. / Physics
55

Application de la méthode Monte Carlo à la modélisation d’une source de curiethérapie par diffusion d’émetteurs alpha

Mondor, Julien 12 1900 (has links)
La curiethérapie par diffusion d’émetteurs alpha (DaRT) est un nouveau type de grain interstitiel dont le potentiel thérapeutique pour les tumeurs solides est élevé en raison de l’utilisation de particules alpha. Cette modalité se distingue de la curiethérapie conventionnelle par une contamination des tissus à un niveau thérapeutique. Les radionucléides filles pénètrent la tumeur grâce à l’énergie de recul acquise lors de l’émission d’une particule alpha, puis ils se dispersent par diffusion dans les tissus avoisinants créant un nuage d’émetteurs alpha. Présentement, le \(^{224}\)Ra est la source radioactive utilisée par la modalité car la synergie de ses descendants de courte demi-vie permettent de produire une zone où la mort cellulaire est élevée. De plus, sa longue demie-vie permet de produire des sources thérapeutiques de faible activité. Le modèle de planification dosimétrique Diffusion-Leakage ne permet pas de déterminer la dose livrée à une zone qui seraient étanche aux radionucléides diffusants. Les particules possédant une longue portée, comme les particules beta et gamma, ne sont pas évaluées par le modèle. Pourtant, ces particules secondaires sont les seules qui déposent de l’énergie dans les zones non-traitées par les particules alpha. Le projet cadre est de simuler la distribution de la dose livrée par ces particules à l’aide de la méthode Monte Carlo. Deux distributions sont recherchées. Une première est la dose associée aux descendants du \(^{224}\)Ra qui se sont dispersés autour du grain et la deuxième est associée au \(^{224}\)Ra et à ses descendants distribués quelques nanomètres sous la surface du grain. Ce mémoire présente une méthode permettant de modéliser la distribution interne de la source de \(^{224}\)Ra sous la surface d’un grain DaRT. Des mesures de spectrométrie alpha ont permis de tester le diagramme de flux de travail et de confirmer la faisabilité de l’extraction de la distribution interne pour trois émetteurs alpha. Les distributions permettront d’évaluer la dose provenant exclusivement du grain en plus d’aider à concevoir des simulations du taux de désorption par recul atomique. Ce travail pourrait permettre d’aider à la conception de nouveaux grains et à l’évaluation de la dose beta et gamma entourant un grain DaRT au \(^{224}\)Ra. / Diffusion alpha-emitter Radiation Therapy (DaRT) is a new type of interstitial brachytherapy seed with high therapeutic potential for solid tumors due to the use of alpha particles. This modality differs from conventional brachytherapy by contaminating tissues to a therapeutic level. The daughters penetrate the tumor using the recoil energy acquired when an alpha particle is emitted and they then scatter by diffusion into the surrounding tissue, creating a cloud of alpha emitters. Currently, \(^{224}\)Ra is the radioactive source used by the modality because the synergy of its short half-life progeny allow to produce a zone where cell death is significant. In addition, its long half-life allows the production of therapeutic sources of low activity. The dosimetric planning model Diffusion-Leakage does not allow the determination of the dose delivered to an area that would be impenetrable by diffusing radionuclides. Particles with a long range, such as beta and gamma particles, are not evaluated by the model. However, these secondary particles are the only ones that deposit energy in areas not treated by alpha particles. The framework project is to simulate the dose distribution delivered by these particles using the Monte Carlo method. Two distributions are pursued. The first is the dose associated with the \(^{224}\)Ra progeny that are dispersed around the seed and the second is associated with radium and its progeny distributed a few nanometers below the surface of the seed. This thesis presents a method enabling the modelisation of the internal distribution of the \(^{224}\)Ra source below the surface of a DaRT seed. Alpha spectrometry measurements were used to test the workflow diagram and confirm the feasibility of extracting the internal distribution for three alpha emitters. The distributions will enable an assessment of the dose coming exclusively from the seed, in addition to helping in designing simulations of the desorption rate by atomic recoil. This work could assist in the design of new seeds and in the evaluation of the beta and gamma dose surrounding a \(^{224}\)Ra DaRT seed.
56

Spin distribution in preequilibrium reactions for 48Ti + n.

Dashdorj, D January 2005 (has links)
Thesis (Ph.D.); Submitted to North Carolina State Univ., Raleigh, NC (US); 6 Apr 2005. / Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-TH-211400" Dashdorj, D. 04/06/2005. Report is also available in paper and microfiche from NTIS.
57

Study of 14O as a test of the unitarity of the CKM matrix and the CVC hypothesis

Burke, Jason Timothy January 2004 (has links)
Thesis (Ph.D.); Submitted to the University of California Berkeley, Berkeley, CA (US); 1 Jun 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56278" Burke, Jason Timothy. USDOE Director. Office of Science. Office of High Energy and Nuclear Physics. Division of Nuclear Physics (US) 06/01/2004. Report is also available in paper and microfiche from NTIS.
58

Development of odd-Z-projectile reactions for transactinide element synthesis

Folden III, Charles Marvin January 2004 (has links)
Doctoral Dissertation, Ph.D., University of California, Berkeley, Berkeley, California, USA. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56749" Folden III, Charles Marvin. USDOE Director. Office of Science. Office of Nuclear Physics 11/04/2004. Report is also available in paper and microfiche from NTIS.
59

Measurement of the beta-neutrino correlation in laser trapped {sup 21}Na

Scielzo, Nicholas David January 2003 (has links)
Thesis (Ph.D.); Submitted to Univ. of California, Berkeley, CA (US); 1 Jun 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54350" Scielzo, Nicholas David. USDOE Director. Office of Science. Nuclear Physics (US) 06/01/2003. Report is also available in paper and microfiche from NTIS.
60

Ion Acceleration from the Interaction of Ultra-Intense Lasers with Solid Foils

Allen, M January 2004 (has links)
Thesis (Ph.D.); Submitted to the Univ. of California, Berkeley, CA (US); 24 Nov 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "UCRL-TH-208645" Allen, M. 11/24/2004. Report is also available in paper and microfiche from NTIS.

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