Committee Feed
https://feeds.library.caltech.edu/people/Koonin-S-E/committee.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 15:31:05 +0000Cascade of Negative Muons in Atoms
https://resolver.caltech.edu/CaltechTHESIS:03012018-141215522
Authors: {'items': [{'id': 'Akylas-Victor-R', 'name': {'family': 'Akylas', 'given': 'Victor R.'}}]}
Year: 1978
DOI: 10.7907/7VND-MP91
<p>The subject of this thesis is the study of the evolution of a negative muon captured in an atom and the formalism of energy loss associated with the muonic atom. The principal goals are to calculate reliably the muon x-ray intensities, given .the initial population of the muonic orbits, to invert the problem and deduce the initial distribution from the x-ray intensities, to provide the experimentalist with a reasonably simple and convenient tool to correlat·e his observations, and finally, to systematize some questions of theoretical interest. The early part of the history of the muon in matter, including the atomic capture and classical phase of the atomic cascade are reviewed. In the quantal treatment of the transition rates, both radiative and electron Auger transitions are considered. In general, multipolarities up to <i>E</i>3 and K, L, and M electronic shells are fully investigated. Multipole radiation is treated in the conventional way and presents no special problems . Magnetic type transitions between states with different principal quantum numbers are shown to be small. Auger electron ejection rates are more complicated and several approximations have been adopted. The basic results have been computed in terms of elementary functions. The relativistic retardation effect is significant at high transition energies, where Auger rates are unimportant. Similarly, the effect of the electron screening of the muon has no significant influence on the results. The calculation of the penetration makes the transition rates reliable . In the Auger transitions we have shown that magnetic multipoles can be safely neglected. The relative sizes of the rates corresponding to different multipoles are systematically studied. The <i>E</i>1 Auger rates are generally largest, but the <i>E</i>0 and <i>E</i>2 transitions are also substantial. Penetration usually decreases rates, being mostly important for transitions with small continuum electron momentum. A comparison of our results is made with atomic photoelectric effect data and with the nuclear internal conversion coefficients. A general agreement is found, except around shell thresholds. The existing data of muonic x-ray intensities in iron and thallium are analyzed in a systematic way. The data are fitted with an initial Z-distribution and some other derived physical parameters. The quality of the fits is good. It is found that for Fe the initial Z-distribution is almost flat, whereas that for T1 is weighted toward s the high Z values, sharper than statistical. As a result of the investigations and in order to make our findings usable, a computer program has been developed. This program is superior to the present standard one, including more precise calculation of transition rates , wider choice of parameters, and a flexible input/output section.</p>https://thesis.library.caltech.edu/id/eprint/10742Application of TDHF Methods to Nuclear Physics
https://resolver.caltech.edu/CaltechTHESIS:03022018-134310889
Authors: {'items': [{'id': 'Flanders-Bradley-A', 'name': {'family': 'Flanders', 'given': 'Bradley A.'}}]}
Year: 1981
DOI: 10.7907/vakw-ws15
<p>Part I presents results for TDHF calculations of realistic heavy-ion reactions. Results for a separable approximation, neglecting motion normal to the scattering plane, agree very well with the results of the full 3-D calculation. Results for the fusion cross section of two systems leading to the compound nucleus <sup>56</sup>Ni are compared with experimental data. The <sup>16</sup>O + <sup>40</sup>Ca results agree quite well with the experimental data, and the <sup>28</sup>Si + <sup>28</sup>Si results agree quite well with experimental data for the similar <sup>32</sup>S + <sup>27</sup>Al system. Results of calculations with the separable approximation for <sup>86</sup>Kr + <sup>139</sup>La are compared with both axially symmetric calculations and experimental results. All three show substantial agreement.</p>
<p>Part II presents a stability criterion for the validity of TDHF solutions based on a time-dependent generalization of RPA theory. Results are tested in an exactly soluble model, the SU(3) generalization of the Lipkin model. Unfortunately, the exact solution could not be computed for a large enough number of particles to permit quantitative testing of this criterion. However, it does seem to correctly indicate the stability or instability of the TDHF path.</p>https://thesis.library.caltech.edu/id/eprint/10747A Proximity Formulation of Nuclear Dynamics
https://resolver.caltech.edu/CaltechTHESIS:12082010-110205851
Authors: {'items': [{'email': 'gjball@gmail.com', 'id': 'Ball-Gregory-John', 'name': {'family': 'Ball', 'given': 'Gregory John'}, 'show_email': 'NO'}]}
Year: 1981
DOI: 10.7907/0H2W-T919
<p>The nuclear potential, the transfer-induced dissipation, and the mass diffusion coefficient in heavy-ion collisions are investigated in a proximity formulation. An energy-dependent nuclear potential is calculated in the frozen wave function approximation using two slabs of symmetric nuclear matter, each described by Hartree-Fock single-particle wave functions. Corrections to the inertia parameter are also evaluated from this potential. The flux entering the window formula for the friction between two heavy ions is calculated in a simple barrier penetration model. The classically forbidden flux is found to make a significant contribution. The transfer flux arising from both the relative motion and finite temperature of the nuclei is calculated and the latter is used to estimate the mass diffusion coefficient. Using the mean trajectories from time-dependent Hartree-Fock calculations the charge variance is calculated for the reaction <sup>84</sup>Kr(712 MeV) + <sup>209</sup>Bi and is found to be in agreement with experiment.</p>https://thesis.library.caltech.edu/id/eprint/6198Nuclear Weak Interaction Rates During Stellar Evolution and Collapse
https://resolver.caltech.edu/CaltechTHESIS:06052013-092608399
Authors: {'items': [{'email': 'gfuller@ucsd.edu', 'id': 'Fuller-George-Michael', 'name': {'family': 'Fuller', 'given': 'George Michael'}, 'show_email': 'YES'}]}
Year: 1981
DOI: 10.7907/Y2W8-MB57
<p>Nuclear weak interaction rates, including electron and positron emission rates, and continuum electron and positron capture rates, as well as the associated ν and ⊽ energy loss rates are calculated on a detailed grid of temperature and density for the free nucleons and 226 nuclei with masses between A = 21 and 60. Gamow-Teller and Fermi discrete-state transition matrix element systematics and the Gamow-Teller T<sup><</sup> ⇄ T<sup>></sup> resonance transitions are discussed in depth and are implemented in the stellar rate calculations. Results of the calculations are presented on an abbreviated grid of temperature and density and comparison is made to terrestrial weak transition rates where possible. Neutron shell blocking of allowed electron capture on heavy nuclei during stellar core collapse
is discussed along with several unblocking mechanisms operative at high temperature and density. The results of one-zone collapse calculations are presented which suggest that the effect of neutron shell blocking is to produce a larger core lepton fraction at neutrino trapping which leads to a larger inner-core mass and hence a stronger post-bounce shock.</p>https://thesis.library.caltech.edu/id/eprint/7840Topics in Perturbative Field Theory
https://resolver.caltech.edu/CaltechTHESIS:03132018-144734173
Authors: {'items': [{'id': 'Terrano-Anthony-Emerson', 'name': {'family': 'Terrano', 'given': 'Anthony Emerson'}}]}
Year: 1981
DOI: 10.7907/7w28-px32
<p>This thesis discusses several results in perturbative field theory. The first two sections present a calculation of the order α<sup>2</sup><sub>s</sub> corrections to the event shape in e<sup>+</sup>e<sup>-</sup> annihilation into hadrons. A technique for the calculation of Feynman diagrams based upon a generalization of the multipole expansion of a potential is discussed in the third section. Computer programs which can be used evaluate the traces which arise in the evaluation of Feynman diagrams are described in an Appendix.</p>https://thesis.library.caltech.edu/id/eprint/10776Mass-Gaps in Lattice Field Theories
https://resolver.caltech.edu/CaltechTHESIS:05152018-114910943
Authors: {'items': [{'id': 'Gupta-Rajan', 'name': {'family': 'Gupta', 'given': 'Rajan'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/w3cz-2v27
<p>In this thesis we discuss two methods for calculating the mass-spectrum in field theories using Monte Carlo Methods. A Hamiltonian variational method is developed and checked on the 0(3) non-linear sigma model in 1+1 dimensions. The mass-gap is also· found from the 2-point correlation function and some improvements to this method are suggested. Both methods give reliable results for the lattice theory. The connection between the lattice 0(3) spin-model and the continuum theory is explored in detail.</p>https://thesis.library.caltech.edu/id/eprint/10889Do Helium Monolayer Films Melt by Unbinding of Dislocations?
https://resolver.caltech.edu/CaltechTHESIS:07122018-101312147
Authors: {'items': [{'id': 'Greif-Jeffrey-Mark', 'name': {'family': 'Greif', 'given': 'Jeffrey Mark'}, 'show_email': 'NO'}]}
Year: 1982
DOI: 10.7907/7cwm-xp02
<p>The Kosterlitz-Thouless-Nelson-Halperin-Young theory of melting in two dimensions by unbinding of thermally excited dislocation pairs is tested against thermodynamic data on monolayer films of <sup>3</sup>He and <sup>4</sup>He on graphite. It is shown using a new analysis of the theory in the asymptotic region that a definitive test is not possible with these data because the theory is expected to be most accurate in a regime very close to the melting transition which is inaccessible to experiments that are not performed on extremely long time and length scales.</p>
<p>One of the two unknown parameters of the theory, that which measures the resistance to twist of the monolayer with respect to the periodic substrate, is calculated, along with the equilibrium angle, to moderate accuracy using the most recent information about the helium graphite potential from atomic scattering experiments. The other parameter, which characterizes the energy of a dislocation core, is provisionally determined by finding what values make the heat capacity of the film, computed from the theory and elastic data on the film, are consistent with experimental results.</p>
<p>These computations are carried out using the full renormalization group equations, crossing the transition from the solid into into the region where those equations break down, by cutting off the integration at a finite value characteristic of the size of a graphite platelet, which works until the mean distance between free dislocations decreases to approximately the size of the patch. The core parameter falls in a range considerably larger than previously estimated for classical Lennard-Jones solids and other materials. Only at large values can the dislocation heat capacity be suppressed enough not to be inconsistent with experiment.</p>
<p>Non-rigorous interpolation methods were developed to try to include some quantum effects in the heat capacity calculations, but these improved the agreement between the theory and the experiments only slightly.</p>
<p>Also appearing for the first time are extensive tables of the thermodynamic functions of <sup>3</sup>He for coverages ranging from .001 to 1 layer and temperatures from 50mK to 10K.</p>https://thesis.library.caltech.edu/id/eprint/11115General Methods for Analyzing Higgs Potentials
https://resolver.caltech.edu/CaltechTHESIS:07122018-154521178
Authors: {'items': [{'email': 'jsk@postech.ac.kr', 'id': 'Kim-Jai-Sam', 'name': {'family': 'Kim', 'given': 'Jai Sam'}, 'show_email': 'YES'}]}
Year: 1982
DOI: 10.7907/RAFF-A683
<p>This thesis is based on several papers published by the author and some more work to be published. We explain the technical problem of minimizing Higgs potentials using group theoretical concepts. Three mathematical results which belong to distinct areas are used to analyze the Higgs potential in an abstract way. The problem reduces to one of finding "contours" of directional minima and thus our method is geometrical. It is explained in detail and demonstrated for some simple cases. We show that the Michel-Radicati conjecture and the Gell-Mann-Slansky conjecture have geometrical significance besides predicting the most likely symmetry groups of the absolute minimum of the potential. We also apply the method to a non-monotonic potential.</p>https://thesis.library.caltech.edu/id/eprint/11118Topics in Supersymmetry Theory: 1. A Superspace Action for Ten-Dimensional Supersymmetric Yang-Mills Theory in Terms of Four-Dimensional Superfields; 2. Gauge Groups for Type-I Superstrings
https://resolver.caltech.edu/CaltechTHESIS:10232019-170411829
Authors: {'items': [{'id': 'Sagnotti-Augusto', 'name': {'family': 'Sagnotti', 'given': 'Augusto'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/qrfw-nf31
This thesis is an account or most of the work that I did in Supersymmetry and Supergravity over the last two years. It deals with two major topics. the construction of a new superspace action for ten-dimensional supersymmetric Yang-Mills theory in terms of four-dimensional superfields. and the classification of the gauge groups allowed at the classical level in the type-I superstring theory. In addition, it contains a discussion of work that I did showing the uniqueness of supergravity in eleven dimensions and the uniqueness of the free Rarita-Schwinger action for massless and massive spin-³/₂ fields.https://thesis.library.caltech.edu/id/eprint/11853Semiclassical Quantization in Many Dimensions
https://resolver.caltech.edu/CaltechTHESIS:10312019-103914805
Authors: {'items': [{'id': 'Williams-Roy-David', 'name': {'family': 'Williams', 'given': 'Roy David'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/ezwt-k047
<p>We examine the semiclassical limit of the quantum energy spectrum in many dimensions: by means of a WKB-like ansatz leading to Einstein-Brillouin-Keller (EBK) quantization, by means of a path integral, hence associating a bound state with a particular classical periodic trajectory, and by the Birkhoff-Gustavson (BG) transformation to action-angle variables. We extend the EBK method to many-fermion systems using coherent states; and apply both EBK using surfaces of section, and the BG transformation to an SU(3) schematic nuclear shell model. We describe a new algorithm for finding periodic trajectories of a Lagrangian system with polynomial potential. It is applied to the Henon-Heiles system with good results, and these trajectories are used to quantize the system. The EBK and BG methods have some success, while periodic trajectory quantization fails. We discuss possible reasons for this failure and future approaches to these problems.</p>https://thesis.library.caltech.edu/id/eprint/11876Monte Carlo Methods in Lattice Gauge Theories
https://resolver.caltech.edu/CaltechTHESIS:10222019-172150505
Authors: {'items': [{'id': 'Otto-Steve-William', 'name': {'family': 'Otto', 'given': 'Steve William'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/hv52-v269
<p>In this work, we study various Monte Carlo methods for lattice gauge theories. The mass of the 0<sup>+</sup> glueball for SU(2) gauge theory in 4 dimensions is calculated. This computation was done on a prototype parallel processor and the implementation of gauge theories on this system is described in detail. Using an action of the purely Wilson form (trace of plaquette in the fundamental representation), we obtain results with high statistics . We conclude that these results are not consistent with scaling according to the continuum renormalization group. Using actions containing higher representations of the group, we search for one which is closer to the continuum limit. Our choice is based upon the phase structure of these extended theories and also upon the Migdal-Kadanoff approximation to the renormalization group on the lattice . We obtain the mass of the 0<sup>+</sup> glueball for this improved action and find that the mass divided by the square root of the string tension is a constant as the lattice spacing is varied. We conclude that scaling has set in and that this lattice theory is closer to the continuum limit than the simple Wilson version.</p>
<p>The other topic studied is the inclusion of dynamical fermions into Monte Carlo calculations via the pseudo fermion technique. Monte Carlo results obtained with this method are compared with those from an exact algorithm based on Gauss-Seidel inversion. We first apply the methods to the Schwinger model (QED in 1 + 1 dimensions) and show, in a coupling regime where the dynamical fermions have a nontrivial effect, that the mass gap is obtained with the correct value . After giving simple arguments explaining why the method works better than expected, we turn to a study of SU(3) in 4 dimensions (although on small lattices). Comparing with the exact algorithm, we again find encouraging agreement with the pseudo fermion technique. Evidence is given which shows that any systematic bias, associated with the breaking of the Markov process which generates the field configurations, is small.</p>https://thesis.library.caltech.edu/id/eprint/11845Realistic Calculations of Excitations in Nuclear Matter
https://resolver.caltech.edu/CaltechTHESIS:10182019-162452942
Authors: {'items': [{'id': 'Kwong-Nai-Hang', 'name': {'family': 'Kwong', 'given': 'Nai-Hang'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/wcb1-mh63
<p>A numerical method has been developed to solve the RPA equation, exchange term included, in nuclear matter. The dynamic form factor S(q, ω) is extracted for several v4 and v6 phenomenological potentials, including the d1-potential of Gogny et al. The limits of validity of the long-wavelength (Landau) approximation and the often adopted local-kernel approximation are discussed. Substantial disagreements with the exact results are found for the latter. The method is then applied to solve a Jastrow-correlated extension of the RPA equation, using the hardcore OMY potential. Results of calculations performed in two-body cluster approximation and Fermi-Hypernetted-Chain (FHNC) approximation are compared. The two-body results predict an instability against density fluctuations, which disappears at the FHNC level. The validity and consequences of employing the FHNC effective potential within the self-consistent HF/RPA framework are discussed. Future developments include applying the method to other Fermi systems such as liquid <sup>3</sup>He and the microscopic calculation of Landau parameters.</p>https://thesis.library.caltech.edu/id/eprint/11828Carbon Isotope Fusion
https://resolver.caltech.edu/CaltechTHESIS:06292010-142221703
Authors: {'items': [{'id': 'Trentalange-Stephen', 'name': {'family': 'Trentalange', 'given': 'Stephen'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/9P3E-5D41
<p>The <sup>13</sup>C + <sup>13</sup>C total fusion cross section has been determined in the range 3.26 ≤ <i>E<sub>c.m.</sub></i> ≤ 8.0 MeV using Ge(Li) detector measurements of low-lying transitions in the residual nuclei and a statistical model calculation of excited state populations. Six different residual nuclei have been observed and their production yields are given. To constrain the parameters in fusion models for these reactions, we have also taken elastic scattering data at <i>υ<sub>c.m.</sub></i> = 60°, 70°, 80°, and 90° for 4.5 ≤ <i>E<sub>c.m.</sub></i> ≤ 8.5 MeV, as well as angular distributions at <i>E<sub>c.m.</sub></i> = 7 and 8 MeV. The relationship of low energy scattering and reaction cross sections among the carbon isotopes is discussed.</p>https://thesis.library.caltech.edu/id/eprint/5963The ³He(α,γ)⁷Be Reaction at Low Energies
https://resolver.caltech.edu/CaltechTHESIS:10222019-162722254
Authors: {'items': [{'id': 'Osborne-John-Lawrence', 'name': {'family': 'Osborne', 'given': 'John Lawrence'}, 'show_email': 'NO'}]}
Year: 1983
DOI: 10.7907/jjbj-9188
<p>Cross sections for the <sup>3</sup>He(α,γ)<sup>7</sup>Be reaction have been measured at several energies from <i>E<sub>cm</sub></i> = 165 to 1200 keV by counting prompt γ rays from a windowless, differentially pumped, recirculating, <sup>3</sup>He gas target. The cross-section factor <i>S</i><sub>34</sub>(<i>E<sub>cm</sub></i>) and branching ratio γ<sub>1</sub>/γ<sub>0</sub> were determined at each energy. Absolute cross sections were measured at <i>E<sub>cm</sub></i> = 947 and 1255 keV by counting the γ rays from the <sup>7</sup>Be produced in a <sup>3</sup>He gas cell with a Ni entrance foil. The inferred zero-energy intercept of the cross-section factor is <i>S</i><sub>34</sub>(0) = 0.52 ± 0.03 keV-barn. This value is in good agreement with the previous measurements of Parker and Kavanagh and Nagatani et al., but disagrees substantially with the recently published measurement of Kräwinkel et al. from Münster. The relationship between the present measurements and several theoretical calculations, and the effect of the extrapolated cross section on the solar neutrino problem are discussed.</p>https://thesis.library.caltech.edu/id/eprint/11844Chiral Anomalies and the Chiral Lagrangian
https://resolver.caltech.edu/CaltechTHESIS:01312019-173857612
Authors: {'items': [{'id': 'Sonoda-Hidenori', 'name': {'family': 'Sonoda', 'given': 'Hidenori'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/xg77-hd79
<p>The subject of this thesis is some implications of chiral anomalies for chiral Lagrangians. The thesis consists of three parts:</p>
<p>In the first part, a somewhat heuristic discussion of the topological meaning of anomalies is given in the framework recently introduced by Alvarez. Its application to the sigma model anomalies is also given.</p>
<p>In the second part, the incorporation of chiral anomalies into the chiral Lagrangian is discussed in a simple manner. The Wess-Zumino term and the sigma model anomalies for the effective theory are explained.</p>
<p>Finally in the third part, as an implication of chiral anomalies, the chiral soliton model is described. Its relation to QCD in large N is discussed in detail. Quantization of the soliton is done in the path integral formalism.</p>https://thesis.library.caltech.edu/id/eprint/11376Monte Carlo Calculation of Three-Body Scattering
https://resolver.caltech.edu/CaltechTHESIS:01252019-102522205
Authors: {'items': [{'id': 'Mahale-Narayan-Krishna', 'name': {'family': 'Mahale', 'given': 'Narayan Krishna'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/09kg-d808
<p>We construct an eigenvalue problem by confining many-body system to a bounded domain with the boundary condition that the wave function vanishes. By changing the boundary, however, the eigenvalues of the energy can be varied continuously. The D-matrix is defined for a series of bounded problems with the same value for the ground state energy. The D-matrix is related to the S-matrix, enabling us to calculate the S-matrix at a given energy. The Schrodinger equation for the system is transformed to a diffusion equation by regarding time as imaginary. Initial ensemble, representing an approximate wave function, is evolved, through Monte Carlo simulation of random walks and branching, to the ground state ensemble. The limitations of investigation are: 1. Ingoing and outgoing channels have two fragments. 2. The interaction between the fragments is negligible outside the boundary mentioned above. 3. The particles are bosons or we know the zeros of the wave function.</p>
<p>First we consider the scattering of a particle by a potential, which is equivalent to the two-body problem, in one dimension. Here we use the Poschl-Teller potential for which the exact solution is known. We use this case to investigate a new sampling method and study of various parameters. Next we consider three particles in one dimension. Here we take interaction to be a potential well, where at least one of the interactions is attractive so that a two-body bound state is possible.</p>https://thesis.library.caltech.edu/id/eprint/11362The ²⁶Mg(p,n)²⁶Al and ²³Na(α,n)²⁶Al Reactions
https://resolver.caltech.edu/CaltechTHESIS:02012019-083752423
Authors: {'items': [{'id': 'Skelton-Robert-Thomas', 'name': {'family': 'Skelton', 'given': 'Robert Thomas'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/z85k-2k90
<p>Cross sections for the <sup>26</sup>Mg (p ,n)<sup>26</sup>AI reaction have been measured from threshold at E<sub>p</sub> = 4.988 MeV to E<sub>p</sub> = 5.820 MeV. Cross sections for the <sup>23</sup>Na (α,n)<sup>26</sup>AI reaction have been measured from threshold at E<sub>α</sub> = 3.483 MeV to E<sub>α</sub> = 4.597 MeV. In each case separate measurements have been to the ground state and to the first and second excited states of <sup>26</sup>AI. Cross sections for the inverse reactions have been calculated and reaction rate factors relating to the destruction of <sup>26</sup>AI in a supernova environment have been determined. Astrophysical implications relating to the observation of live and extinct <sup>26</sup>AI are discussed. Excitation functions for several additional exit channels for the <sup>26</sup>Mg + p and <sup>26</sup>Na + α reactions are reported.</p>https://thesis.library.caltech.edu/id/eprint/11377Auxiliary Field Monte-Carlo for Quantum Many-Body Systems
https://resolver.caltech.edu/CaltechTHESIS:01072019-110818820
Authors: {'items': [{'id': 'Sugiyama-Gayle-A', 'name': {'family': 'Sugiyama', 'given': 'Gayle A.'}, 'show_email': 'NO'}]}
Year: 1985
DOI: 10.7907/t9kp-qe57
<p>An algorithm is developed for determining the exact ground state properties of quantum many-body systems which is equally applicable to bosons and fermions. The Schroedinger eigenvalue equation for the ground state energy is recast into the form of a many-dimensional integral through the use of the Hubbard-Stratonovitch representation of the imaginary time many- body evolution operator. The resulting functional integral is then evaluated stochastically. The algorithm is tested for an exactly soluble boson system and is then extended to include fermions and repulsive potentials. Importance sampling is crucial to the success of the method, particularly for more complex systems. Improved computational efficiency is attained by performing the calculations in momentum space.</p>https://thesis.library.caltech.edu/id/eprint/11335Subbarier Fusion of the Oxygen Isotopes
https://resolver.caltech.edu/CaltechTHESIS:06302010-080153741
Authors: {'items': [{'id': 'Pönisch-Volker', 'name': {'family': 'Pönisch', 'given': 'Volker'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/KZX1-P789
<p>The subbarrier fusion process is studied for systems involving oxygen isotopes. A one-channel incoming wave boundary condition (IWBC) calculation gives an excellent fit to fusion cross section data for <sup>16</sup>O+<sup>16</sup>O. An IWBC coupled channels calculation for <sup>17</sup>O+<sup>16</sup>O that includes inelastic excitations as well as one-neutron transfer with formfactors calculated in a consistent single-particle framework reproduces the subbarrier enhancement down to four fifths the barrier height, but not below that. The calculation does not invoke the adiabatic approximation, which would create non-unitarity in the coupled channels equations. The measured subbarrier fusion cross section for <sup>18</sup>O+<sup>16</sup>O is well reproduced by an IWBC coupled channels calculation with two-neutron transfer, but the calculation disagrees with the above-barrier data.</p>
https://thesis.library.caltech.edu/id/eprint/5966Thermal Desorption of Helium Films: Theory and Experiment
https://resolver.caltech.edu/CaltechTHESIS:10302019-173639293
Authors: {'items': [{'id': 'Weimer-Michael-Ben', 'name': {'family': 'Weimer', 'given': 'Michael Ben'}, 'show_email': 'NO'}]}
Year: 1986
DOI: 10.7907/e8ag-j914
<p>The desorption kinetics of helium films is explored in the context of a phenomenological model wherein the film is assumed to have the thermodynamic properties of bulk liquid and the vapor is described by simple kinetic theory. When supplemented by the condition that desorption proceed at the maximum rate permitted by detailed balance, equations for energy and mass conservation completely determine the dynamics of the system.</p>
<p>The model is applied to the specific problem of characterizing the time response of an adsorbed film when the equilibrium between it and the ambient vapor is perturbed by a sudden change in substrate temperature and the system subsequently evolves toward a new steady state. Analysis reveals that for infinitesimal perturbations from equilibrium the equations of motion are linear and result in exponential solutions for the time dependence of the desorption flux. For finite temperature elevations and realistic adsorption isotherms, however, the equations of motion are highly nonlinear. In either case, isothermal desorption at the temperature of the substrate is shown to be a general feature of the solutions under usual experimental conditions and this considerably simplifies interpretation of the nonlinear problem. Under these circumstances one can identify a continuous succession of coverage-dependent relaxation time scales which are given in terms of instantaneous properties of the adsorption system. These time scales are distinct from, and in general unrelated to, the coverage-dependent mean lifetime of an atom on the surface. To characterize the overall time scale of the nonlinear evolution towards steady state, a global measure is defined in terms of both instantaneous and steady-state properties and used to summarize experimental data.</p>
<p>A direct method for measuring the relaxation time of monolayer helium films flash desorbed from evaporated metal-film substrates is described and used to test the model. The technique is based on a rapid heating scheme made possible by the unique properties of ballistic phonon propagation in single crystals at low temperature. Global time constants extracted from the data in the near-equilibrium regime agree well with the predictions of the model. When these results are combined with earlier data at higher substrate temperatures and different ambient conditions, the picture is consistent with scaling properties implied by the theory. It is shown how the particular dependence on initial conditions of the exponent in a Frenkel-Arrhenius parameterization of the global time constant may be traced to the curvature of the equilibrium adsorption isotherm. This curvature is substantiated by the behavior of the instantaneous relaxation time scales, the time-of-flight spectrum of the desorbing flux, and the kinetics of readsorption.</p>https://thesis.library.caltech.edu/id/eprint/11875The β Spectrum Following Fission from ²⁵²Cf
https://resolver.caltech.edu/CaltechTHESIS:01052012-145244894
Authors: {'items': [{'id': 'Wark-David-Lee', 'name': {'family': 'Wark', 'given': 'David Lee'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/747M-2F73
<p>The β spectrum from the fission products of <sup>252</sup>Cf has been measured using a flat-field magnetic spectrometer. The active entrance aperture to the magnetic field region consisted of an annular plastic scintillator to veto slit scattering and a thin wire chamber to signal electrons on a good trajectory. The electrons exited the magnetic field through a position sensitive wire chamber capable of three dimensional track reconstruction. The energy calibration and relative efficiency of the spectrometer were determined using the β decays of <sup>12</sup>B, <sup>20</sup>F, and <sup>90</sup>Sr. The shape of the β spectrum from <sup>252</sup>Cf was measured at 5 field settings and the results combined to form a complete spectrum from 2.0 to 9.0 MeV (β total energy) with a total error of 3% at 3 MeV, rising to 6% at 5 MeV, 9% at 7 MeV, 15% at 8 MeV and 25% at 9 MeV. This experiment was motivated by the need to know the ν̅<sub>e</sub> spectrum from the β decays of fission products in order to interpret the results of reactor based neutrino oscillation experiments. The ν̅<sub>e</sub> spectrum can be calculated directly or converted from a measured β spectrum. This experiment is an additional check of these calculations and constitutes a complementary check of previous measurements of the β spectrum from other fissioning nuclei <sup>235</sup>U, <sup>239</sup>Pu, and <sup>241</sup>Pu. We find a softer spectrum fewer β's at high momenta) than predicted by the calculations, in agreement with earlier measurements in other nuclei by Schreckenbach et al.. but in disagreement with earlier measurements by Borovoi et al. in <sup>252</sup>Cf. Possible sources of the disagreement with the calculations and the earlier experiment and possible improvements to the experiment are discussed.</p>
https://thesis.library.caltech.edu/id/eprint/6762Two Problems in Many Body Physics: I. Photon Production: A Probe of Heavy Ion Collisions. II. Structure of Matter in Strong Magnetic Fields
https://resolver.caltech.edu/CaltechTHESIS:10222019-115047089
Authors: {'items': [{'id': 'Neuhauser-Daniel', 'name': {'family': 'Neuhauser', 'given': 'Daniel'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/dn5s-g690
<p>In Part 1 we examine the theoretical framework for the use of photon spectra to probe heavy ion collisions. We first calculate single photon emission spectra from nuclear matter in the incoherent limit and combine them with the simplified participant-spectator model and with the semiclassical VUU model, to predict photon production cross sections in heavy ion collisions. The spectra differ from previous estimates based on a classical soft-photon approximation and lead to good agreement with experiment, except for an overall normalization factor of order (2-5), which we interpret as direct evidence for medium effects.</p>
<p>We then proceed to examine the Hanbury-Brown-Twiss correlation of high-energy photons emitted from heavy ion collisions. We find that both the polarization average and a possible coherent component complicate the extraction of the size and lifetime of the emitting source from the correlation function.</p>
<p>In Part 2 we calculate the binding energies of atoms and molecular chains in 10<sup>12</sup> G magnetic fields using the Hartree-Fock method. Our calculations are the first self-consistent ones treating exchange properly for atoms heavier than helium in high fields. For <i>Z</i> > 2 at 10<sup>12</sup>G and <i>Z</i> > 4 at 5 x 10<sup>12</sup>G the isolated atom is energetically favored over the molecular chains.</p>https://thesis.library.caltech.edu/id/eprint/11840Lattice Gauge Theory on a Parallel Computer
https://resolver.caltech.edu/CaltechTHESIS:10112019-085854195
Authors: {'items': [{'id': 'Flower-Jonathan-William', 'name': {'family': 'Flower', 'given': 'Jonathan William'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/zhdg-qp82
<p>The results of several numerical simulations of QCD by Monte Carlo lattice gauge theory are presented. Studying the mesonic potential on a 20<sup>4</sup> lattice, we conclude that asymptotic scaling does not hold over the range 6.1 ≤ β ≤ 6.7, although we are not able to quantify the discrepencies. The effect of discrete rotational symmetry on physical parameters is examined and seems to modify the string tension by 15 % at β = 6.1, while at β = 6.3 the change was less than 1 %. The potential between three charges is studied and yields a string tension of .18 GeV<sup>2</sup>, consistent with mesonic calculations and relativised potential models. Contributions to the potential from low-energy string vibrations appear small in the range x ≾ .5 fm. We perform energy density measurements in the colour fields surrounding both mesons and baryons, which provide strong evidence in favour of the dual superconductor picture of confinement. It is also suggested that the confining strings in the baryon meet at a central point rather than joining the quarks pairwise.</p>
<p>Several algorithms are explored in an attempt to develop simulation methods which are able to directly account for the currents generated by colour sources. The extension of the Langevin equation to complex degrees of freedom is derived leading to a Fokker-Planck equation for a complex 'Probability distribution'. Using this technique we are then able to calculate energy densities in U(1) gauge theory at-large charge separations. The extension of the method to non-Abelian theories comes up against an unresolved problem in segregation for certain types of observable.</p>
<p>We discuss methods for the simulation of full QCD, including the effects of dynamical fermions. The Langevin approach is analysed in detail, and the systematic error associated with the discretisation of the equations of motion is derived. We propose a mixed Langevin/Metropolis algorithm and explore its properties on a small lattice. Finally, the method is tested on the finite temperature deconfinement transition and applied to the mesonic potential. It is found that shielding effects lead to deconfinement at β = 6.1 on a lattice of size 12<sup>2</sup> x 16<sup>2</sup>.</p>https://thesis.library.caltech.edu/id/eprint/11811Quantum Chaos: Spectral Fluctuations and Overlap Distributions of the Three Level Lipkin-Meshkov-Glick Model
https://resolver.caltech.edu/CaltechTHESIS:02202019-120226199
Authors: {'items': [{'id': 'Meredith-Dawn-Christine', 'name': {'family': 'Meredith', 'given': 'Dawn Christine'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/7y5k-ex17
<p>We test the prediction that quantum systems with chaotic classical analogs have spectral fluctuations and overlap distributions equal to those of the Gaussian Orthogonal Ensemble (GOE). The subject of our study is the three level Lipkin-Meshkov-Glick model of nuclear physics. This model differs from previously investigated systems because the quantum basis and classical phase space are compact, and the classical Hamiltonian has quartic momentum dependence. We investigate the dynamics of the classical analog to identify values of coupling strength and energy ranges for which the motion is chaotic, quasi-chaotic, and quasi-integrable. We then analyze the fluctuation properties of the eigenvalues for those same energy ranges and coupling strength, and we find that the chaotic eigenvalues are in good agreement with GOE fluctuations, while the quasi-integrable and quasichaotic levels fluctuations are closer to the Poisson fluctuations that are predicted for integrable systems. We also study the distribution of the overlap of a chaotic eigenvector with a basis vector, and find that in some cases it is a Gaussian random variable as predicted by GOE. This result, however, is not universal. </p>
https://thesis.library.caltech.edu/id/eprint/11406Hydrodynamics of Ultra-Relativistic Heavy-Ion Collisions
https://resolver.caltech.edu/CaltechTHESIS:08302019-142642675
Authors: {'items': [{'id': 'Chu-Ming-chung', 'name': {'family': 'Chu', 'given': 'Ming-chung'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/kq9w-6f74
<p>Relativistic hydrodynamic calculations are presented to describe the dynamics
of ultra-relativistic heavy-ion collisions. In contrast to the "standard picture" of
the field, our calculations do not assume scaling symmetry, and in fact we find
large scaling violations near the fragmentation regions. In our 1+1-dimensional
calculations, we find that while the hydrodynamic evolution is very sensitive to the
formation and thermalization time and to the models of the source terms, the effects
of changing the viscosity and the equation of state are small. Our 2+1-dimensional
calculations show that transverse expansion is not important in the central rapidity
region. We also present a brief review of the proposed signatures of the formation of
quark-gluon plasma in high energy heavy-ion collisions, as examples of applications
of hydrodynamics.</p>https://thesis.library.caltech.edu/id/eprint/11780Doublewell Tunneling via the Feynman-Kac Formula
https://resolver.caltech.edu/CaltechETD:etd-09062005-152643
Authors: {'items': [{'email': 'askell@ma.is', 'id': 'Hardarson-Askell', 'name': {'family': 'Hardarson', 'given': 'Askell'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/34ks-xy63
<p>We discuss asymptotics of the heat kernel [equation; see abstract in scanned thesis for details] and its x-derivatives when T, λ → ∞ and (T/λ) → 0 where H(λ) = - ((Δ/2) + λ²V) and where V is a double well. When the groundstate is localized in both wells for λ large we derive, by the Feynman-Kac formula, W.K.B. expansions of the groundstate, the first excited state and their gradients.</p>
<p>As a consequence we get a general asymptotic formula for the splitting of the two lowest eigenvalues, E₀(λ) and E₁(λ).</p>
<p>This formula allows us, in principle, always to go beyond the leading order given by [equation; see abstract in scanned thesis for details] where C is the action of a classical instanton.</p>
https://thesis.library.caltech.edu/id/eprint/3352Absence of a Scott Correction for the Total Binding Energy of Noninteracting Fermions in a Smooth Potential Well
https://resolver.caltech.edu/CaltechETD:etd-09062005-101909
Authors: {'items': [{'email': 'bhuxtable@usersystems.com', 'id': 'Huxtable-Barton-Duane', 'name': {'family': 'Huxtable', 'given': 'Barton Duane'}, 'show_email': 'YES'}]}
Year: 1988
DOI: 10.7907/87FQ-5X29
<p>It is shown, for V in a particular class of smooth functions, that the total binding energy, E(Z), of Z noninteracting Fermions in the potential well Z<sup>4/3</sup>V(Z<sup>1/3</sup>x), obeys E(Z) = c<sub>TF</sub>(V)Z<sup>7/3</sup> + 0(Z<sup>5/3</sup>) as Z → ∞. Here c<sub>TF</sub>(V) is the coefficient predicted by the Thomas-Fermi theory. This result is consistent with the conjectured Scott correction, which occurs at order Z<sup>2</sup>, to the total binding energy of an atom of atomic number Z. This correction is thought to arise only because V(x) ~ - |x|<sup>1</sup> near x - 0 in the atomic problem, and so V is <i>not</i> a smooth function.</p>
https://thesis.library.caltech.edu/id/eprint/3349¹⁸O + ¹⁸O Reactions
https://resolver.caltech.edu/CaltechTHESIS:03112013-110625162
Authors: {'items': [{'id': 'Yuan-Ren-Feng', 'name': {'family': 'Yuan', 'given': 'Ren-Feng'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/0rf5-z473
<p>Cross sections for the ¹⁸O + ¹⁸O reactions (fusion, inelastic excitation and transfer reactions ) have been determined in the range 6.73 ≤ E<sub>c.m</sub> ≤ 13.24 MeV by measuring the low- lying γ-ray transitions in the residual nuclei with a high resolution Ge detector. A statistical model calculation of the populations of the residual nuclear states was employed in deducing cross sections from the measured γ-yields. γ-ray angular distributions were determined at E<sub>lab</sub> = 20.0 MeV. The total fusion cross sections were compared with an IWBC calculation employing a parameter set obtained from fitting elastic scattering data. The interaction barrier shape has been obtained by means of the BKN inversion procedure and compared with the barriers for other oxygen isotopes. The inelastic scattering cross section and the two-neutron transfer reaction cross section are reproduced well by the DWBA approach.</p>
https://thesis.library.caltech.edu/id/eprint/7506Scaling Violations in Quasielastic Electron Scattering
https://resolver.caltech.edu/CaltechTHESIS:01172013-133508860
Authors: {'items': [{'id': 'Butler-Malcolm-Nicholas', 'name': {'family': 'Butler', 'given': 'Malcolm Nicholas'}, 'show_email': 'NO'}]}
Year: 1988
DOI: 10.7907/pp3m-h071
<p>We study the phenomenon of y-scaling in inclusive quasielastic electron scattering. Emphasis is placed on the approach to scaling at finite four-momentum transfers, and the effects of final state interactions. Brueckner-Goldstone perturbation theory for nuclear matter is used to perform a detailed, microscopic calculation of the dynamic structure function of nuclear matter. This is compared to the naive prediction of the Impulse approximation, and we find that the approach to scaling is quite different. The Brueckner-Goldstone approach reproduces the trends seen experimentally (Impulse approximation does not); however, there is still not good quantitative agreement with the data. We take this to be a possible sign of problems in the conventional nucleon-nucleon interactions studied.</p>https://thesis.library.caltech.edu/id/eprint/7404Exchange Interactions in Solid ³He on a Parallel Computer
https://resolver.caltech.edu/CaltechETD:etd-06072007-135648
Authors: {'items': [{'id': 'Callahan-Sean-Macauley', 'name': {'family': 'Callahan', 'given': 'Sean Macauley'}, 'show_email': 'NO'}]}
Year: 1989
DOI: 10.7907/4dxb-6t85
<p>We have developed a method of calculating the Gruneisen parameter, γ ≡ ∂lin<i>J</i>/∂lnν (J - exchange splitting; ν - molar volume), for energy splittings that are due to atoms exchanging lattice sites in fermionic systems for which the exchange splittings are small compared with the lattice kinetic and potential energies. The method involves making two separate path integral Monte Carlo calculations, one for a path (sequence of particle positions in time) that doesn't involve atoms exchanging lattice sites, and one for a path in which the atoms do exchange lattice sites. The difference between a quantity calculated for the two systems is related to the Gruneisen parameter.</p>
<p>The central results of this thesis are firstly, that there is no significant variation of the Gruneisen parameters for two, three and four particle exchange (γ₂, γ₃ and γ₄, respectively) for solid ³He, in going from 24 cm³/mole, which is near melting, to 22 cm³/mole. This result was extended to 20 cm³/mole for γ₂. Since no significant variation was observed, the values calculated for different molar volumes were combined to give best estimates for the Gruneisen constants, γ₂ = 15.9 ± .8, γ₃ = 16.4 ± 1.4 and γ₄ = 13.8 ± 1.5. The second result is that the magnitudes of the Gruneisen parameters are very similar for the three types of exchange despite their significantly different geometry. Some very limited runs were done for a system of hard spheres. It is interesting that for the hard sphere diameter chosen, the Gruneisen parameters are of the same order as for solid ³He, γ₂ = 21.7 ± .8, γ₃ = 16.8 ± 2.1 and γ₄ = 19.3 ± 1.9 for the small test systems checked. The final result relates to ³He deposited on a graphite surface. The Gruneisen parameter for three particle exchange for a two-dimensional system with a triangular mesh is found to be consistent with γ₃ = 50 ± 5 for a range of nearest-neighbor, lattice spacings from 3.2 Å to 3.6 Å. This is inconsistent with experiment, indicating that three particle exchange confined to two dimensions does not account for the ferromagnetic properties of this system, as was claimed previously.</p>https://thesis.library.caltech.edu/id/eprint/2511A Path Integral Monte Carlo Method for the Quasielastic Response
https://resolver.caltech.edu/CaltechETD:etd-06072007-080221
Authors: {'items': [{'email': 'Carraro@berkeley.edu', 'id': 'Carraro-Carlo', 'name': {'family': 'Carraro', 'given': 'Carlo'}, 'orcid': '0000-0002-3482-9226', 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/mkyz-4067
<p>We formulate the quasielastic response of a non-relativistic many-body system at zero temperature in terms of ground state density matrix elements and real time path integrals that embody the final state interactions. While the former provide the weight for a conventional Monte Carlo calculation, the latter require a more sophisticated treatment. We argue that the recently developed Stationary Phase Monte Carlo technique can be used to study the approach to "Y-scaling." We perform calculations for a particle in a potential well in one and three dimensions and compare them to the exact results available for these models. We then derive an eikonal approximation to the Path Integrals. This method is suitably generalized to treat strongly repulsive interactions, and allows comparison to Silver's theory of final state interactions in a straightforward way. We also give an exact prescription to calculate the scaling limit for potentials comprising a hard core. Finally, we study the approach to scaling in a model ⁴He nucleus, and find good agreement with experimental data.</p>https://thesis.library.caltech.edu/id/eprint/2498Shell Model Monte Carlo for Gamow-Teller Strengths and Two-Neutrino Double Beta Decay
https://resolver.caltech.edu/CaltechTHESIS:10312019-172947012
Authors: {'items': [{'id': 'Bahukutumbi-Radha-Pillapakkam', 'name': {'family': 'Bahukutumbi', 'given': 'Radha Pillapakkam'}, 'show_email': 'NO'}]}
Year: 1996
DOI: 10.7907/xg95-wy83
<p>In this thesis, a method to calculate two-neutrino double beta decay matrix elements employing the Shell Model Monte Carlo is presented. This method is validated against direct-diagonalization for the decay of <sup>48</sup>Ca. The first realistic calculation of the nuclear matrix element within the shell model for <sup>76</sup>Ge is performed; the result is in reasonable agreement with experiment.</p>
<p>The sensitivity of the shell model results to the nuclear Hamiltonian has been studied for the case of <sup>48</sup>Ca where the Hamiltonian used is known to be an optimal one. While one cannot make the nuclear matrix element arbitrarily small, the uncertainty in certain pieces of the Hamiltonian such as the monopole isovector pairing, provides room for at least a factor of two in the matrix element (and hence a factor of four in the half-life) from such calculations.</p>
<p>A Maximum Entropy method to obtain realistic strength functions from imaginary time response functions has been applied to Gamow-Teller response functions calculated using the Shell Model Monte Carlo and the results are validated against direct-diagonalization and experiment.</p>
<p>Future prospects for double beta decay calculations and astrophysical applications of the Gamow-Teller strength functions are briefly discussed.</p>https://thesis.library.caltech.edu/id/eprint/11879Stabilizer Codes and Quantum Error Correction
https://resolver.caltech.edu/CaltechETD:etd-07162004-113028
Authors: {'items': [{'email': 'dgottesman@perimeterinstitute.ca', 'id': 'Gottesman-Daniel-Eric', 'name': {'family': 'Gottesman', 'given': 'Daniel Eric'}, 'show_email': 'YES'}]}
Year: 1997
DOI: 10.7907/rzr7-dt72
Controlling operational errors and decoherence is one of the major challenges facing the field of quantum computation and other attempts to create specified many-particle entangled states. The field of quantum error correction has developed to meet this challenge. A group-theoretical structure and associated subclass of quantum codes, the stabilizer codes, has proved particularly fruitful in producing codes and in understanding the structure of both specific codes and classes of codes. I will give an overview of the field of quantum error correction and the formalism of stabilizer codes. In the context of stabilizer codes, I will discuss a number of known codes, the capacity of a quantum channel, bounds on quantum codes, and fault-tolerant quantum computationhttps://thesis.library.caltech.edu/id/eprint/2900