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Title: Pairing Correlations and Phase Transitions in Mesoscopic Systems.
Creator: Sumaryada, Tony Ibnu, Volya, Alexander, Li, Hong, Piekarewicz, Jorge, Rogachev, Grigory, Dobrosavljevic, Vladimir, Department of Physics, Florida State University
Abstract/Description: Pairing correlations and phase transitions in mesoscopic or small systems are studied through out this dissertation. We start our discussion by showing the importance of short range correlations and their role in forming bound Cooper pairs. For a model Hamiltonian, we solved the Schr¨odinger equation in the harmonic oscillator basis analytically, the concept of self consistency is used to get the whole energy spectrum. Using variational methods applied to a trial wave function, we derived the...
Show morePairing correlations and phase transitions in mesoscopic or small systems are studied through out this dissertation. We start our discussion by showing the importance of short range correlations and their role in forming bound Cooper pairs. For a model Hamiltonian, we solved the Schr¨odinger equation in the harmonic oscillator basis analytically, the concept of self consistency is used to get the whole energy spectrum. Using variational methods applied to a trial wave function, we derived the BCS equations, which again should be solved self consistently with particle number to produce the total energy. Some examples of BCS calculations in realistic case like in the Sn isotopes are shown. Various approximations such as one level, two levels and five levels systems are discussed. In the five levels model calculations, we compare our results with the previous works by other authors. We also find a good agreement with the experimental data. We extend our BCS calculations by adding the three body interaction term. This additional term is unlikely to improve our results compared to the experiment. In a separate work, using numerical and analytical methods implemented for different models we conduct a systematic study of thermodynamic properties of pairing correlations in mesoscopic nuclear systems. Various quantities are calculated and analyzed using the exact solution of pairing. An in-depth comparison of canonical, grand canonical, and microcanonical ensemble is conducted. The nature of the pairing phase transition in a small system is of particular interest. We discuss the onset of discontinuities in the thermodynamic variables, fluctuations, and evolution of zeros of the canonical and grand canonical partition functions in the complex plane. The behavior of the Invariant Correlational Entropy is also studied in the transitional region of interest. The change in the character of the phase transition due to the presence of magnetic field is discussed along with studies of superconducting thermodynamics.
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Date Issued: 2007
Identifier: FSU_migr_etd-0406
Format: Thesis

Title: A Precision Measurement of the 1S2S 1S0 – 1S2P 3P1 Interval in Helium-like Silicon Using Fast-Beam Laser Spectroscopy.
Creator: Devore, Thomas Robert, Myers, Edmund, Safron, Sanford, Adams, Todd, Capstick, Simon, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: In this dissertation, we present a precision measurement of the 1s2s 1S0 – 1s2p 3P1 intercombination interval in the moderate-Z helium-like ion, 28Si12+, using a fast-beam laser resonance technique. This experiment is a second-generation measurement designed to surpass the precision of the previous measurement of Redshaw et al. (Phys. Rev. Lett., 88 (2002) 023002), using an improved laser setup designed to cancel the Doppler shift. This was accomplished by incorporating a counter-propagating...
Show moreIn this dissertation, we present a precision measurement of the 1s2s 1S0 – 1s2p 3P1 intercombination interval in the moderate-Z helium-like ion, 28Si12+, using a fast-beam laser resonance technique. This experiment is a second-generation measurement designed to surpass the precision of the previous measurement of Redshaw et al. (Phys. Rev. Lett., 88 (2002) 023002), using an improved laser setup designed to cancel the Doppler shift. This was accomplished by incorporating a counter-propagating laser at 1,450 nm into the previous setup that used a co-propagating laser at 1,319 nm to induce the same transition. Our final result for this energy interval is 7,230.585(6) cm–1 with an overall precision of 0.8 parts-per-million (ppm). This result represents a 30-fold improvement over the previous measurement, and tests QED contributions at the level of 13 ppm. The two-electron atom/ion is a fundamental atomic system, and continues to be the subject of major theoretical work today. Hence, our precise measurement provides a clear test of modern theory, including higher-ordered QED effects.
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Date Issued: 2008
Identifier: FSU_migr_etd-0757
Format: Thesis

Title: The Emergence of Collective Phenomena in Systems with Random Interactions.
Creator: Abramkina, Volha, Volya, Alexander, Okten, Giray, Capstick, Simon, Rogachev, Grigory, Rikvold, Per Arne, Department of Physics, Florida State University
Abstract/Description: Emergent phenomena are one of the most profound topics in modern science, addressing the ways that collectivities and complex patterns appear due to multiplicity of components and simple interactions. Ensembles of random Hamiltonians allow one to explore emergent phenomena in a statistical way. In this work we adopt a shell model approach with a two-body interaction Hamiltonian. The sets of the two-body interaction strengths are selected at random, resulting in the two-body random ensemble ...
Show moreEmergent phenomena are one of the most profound topics in modern science, addressing the ways that collectivities and complex patterns appear due to multiplicity of components and simple interactions. Ensembles of random Hamiltonians allow one to explore emergent phenomena in a statistical way. In this work we adopt a shell model approach with a two-body interaction Hamiltonian. The sets of the two-body interaction strengths are selected at random, resulting in the two-body random ensemble (TBRE). Symmetries such as angular momentum, isospin, and parity entangled with complex many-body dynamics result in surprising order discovered in the spectrum of low-lying excitations. The statistical patterns exhibited in the TBRE are remarkably similar to those observed in real nuclei. Signs of almost every collective feature seen in nuclei, namely, pairing superconductivity, deformation, and vibration, have been observed in random ensembles. In what follows a systematic investigation of nuclear shape collectivities in random ensembles is conducted. The development of the mean field, its geometry, multipole collectivities and their dependence on the underlying two-body interaction are explored. Apart from the role of static symmetries such as SU(2) angular momentum and isospin groups, the emergence of dynamical symmetries including the seniority SU(2), rotational symmetry, as well as the Elliot SU(3) is shown to be an important precursor for the existence of geometric collectivities.
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Date Issued: 2011
Identifier: FSU_migr_etd-0104
Format: Thesis

Title: High-Spin Nuclear Structure of 168,170Ta and Triaxial Strongly Deformed Structure in 160Yb.
Creator: Aguilar, Aaron, Riley, Mark A., Safron, Sanford, Capstick, Simon, Rogachev, Grigory, Adams, Todd, Department of Physics, Florida State University
Abstract/Description: The study of nuclear structure at very high angular momentum requires sensitive detector systems in order to detect weak signals. Large gamma-ray arrays were used in this thesis to study the high-spin states in 166;168;170Ta and 160Yb. These arrays were located at facilities such as: Florida State University (FSU), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), and Yale University. A study utilizing the Gammasphere spectrometer (the world's most powerful...
Show moreThe study of nuclear structure at very high angular momentum requires sensitive detector systems in order to detect weak signals. Large gamma-ray arrays were used in this thesis to study the high-spin states in 166;168;170Ta and 160Yb. These arrays were located at facilities such as: Florida State University (FSU), Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL), and Yale University. A study utilizing the Gammasphere spectrometer (the world's most powerful array) resulted in a dramatic expansion of over 400 new gamma-ray transitions organized into 29 rotational bands in the level scheme of 170Ta. Alignment behavior, an additivity of Routhians analysis, and B(M1)/B(E2) transition strength ratios are used to support the configuration assignments made for this nucleus. The observation of linking transitions between almost all of the bands allowed the relative excitation energies to be determined for nearly the entire level scheme. All of the above work on 170Ta, resulted in the most comprehensive high-spin level scheme in odd-odd nuclei to date. A significant expansion has also been made to the level scheme of 168Ta using the FSU gamma-ray array. An additivity of alignment analysis, along with a B(M1)/B(E2) analysis made it possible to assign band configurations. Although an experiment studying the high-spin structure of 166Ta using the Yale University spectrometer (YRAST Ball) was performed, detailed analysis resulted in the observation of no new information. A new extremely low intensity band structure has also been observed in 160Yb from another Gammasphere experiment. This structure is interpreted as the first observation of a stable triaxial shape in Yb nuclei.
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Date Issued: 2008
Identifier: FSU_migr_etd-0123
Format: Thesis

Title: Thermonuclear Flashes on H/He Accreting Co White Dwarfs and Structure of Exotic Nuclei.
Creator: Mitchell, Joseph P., Hoeﬂich, Peter, Rogachev, Grigory, Humayun, Munir, Gerardy, Christopher, Volya, Alexander, Wiedenhover, Ingo, Department of Physics, Florida State University
Abstract/Description: We studied H-shell flashes on CO WDs accreting Hydrogen rich matter in regimes where they are believed to be on the border of stable accretion and of having dynamical mass loss. These systems are believed to be progenitors of SNe Ia, however, there is still some question of what range of accretion rates and WD masses allow for growth to the Chandrasekhar mass, if any do at all. Flashes that result in mass loss are also of interest as they enrich the Inter Stellar Medium. Initial models are...
Show moreWe studied H-shell flashes on CO WDs accreting Hydrogen rich matter in regimes where they are believed to be on the border of stable accretion and of having dynamical mass loss. These systems are believed to be progenitors of SNe Ia, however, there is still some question of what range of accretion rates and WD masses allow for growth to the Chandrasekhar mass, if any do at all. Flashes that result in mass loss are also of interest as they enrich the Inter Stellar Medium. Initial models are calculated using a stationary evolution code that starts with a 0.5 M WD. Accretion of material of solar metalicity is employed, and nuclear burning is allowed, until the model reaches the desired masses of 0.8 M and 1.0 M for our study. The resultant initial models have structures that are in agreement with the previous works of [93, 26, 96] for accreting hot WD models. The flashes were calculated with an explicit hydrodynamics code that utilizes the PPM method, a second order Godunov scheme, allowing for high time resolution during the flash. This code is used in the co-moving frame to avoid chemical advection over time. Due to a recurrence of flashes of years to thousands of years, however, periods of steady nuclear burning were evolved in a quasi-static method, allowing for longer time steps than are possible in an explicit hydro code. Thus, evolution of the models followed an alternating quasi-static/explicit hydro evolution scheme until flash conditions were met, at which point the explicit hydro was employed. Use of an explicit hydro code has allowed for the observation of a new physical effect from wave dissipation. With our high time resolution, energy transport via waves, and detailed EOS, we found that at the onset of the flash, a reduction in the degeneracy pressure due to electron captures, results in a reduction of the total pressure. With a gravitational acceleration on the order of 108 in the shell, a reduction of the total pressure by 1% results in an in fall acceleration of 10 km . With such a strong in fall, compressional heating results in a hotter flash, with results showing temperatures over a billion degrees in all models. These high temperatures had consequences on the nucleosynthesis, as they allowed for rp-breakout during the flash. The effect of a "double" flash was found in one model. This resulted when the flash stalled in the H-shell, resulting in high temperature burning in only a portion of the shell. Once the H was exhausted in the flash region, cooling occurred and there was contraction of the H exhausted region. This contraction caused an in fall of the un-exhausted region which via compressional heating resulted in the flash to occur in the un-exhausted region. Such an effect may happen in any progenitor system in which the flash stalls and compression afterwards is suitable for a re-start of the flash. This effect may be observable with the current generation of instruments. With the high temperatures found in the flashes, rp-breakout nucleosynthesis was found to occur. Occurrence of rp-nucleosynthesis in these objects may make important sources of the chemical enrichment of isotopes below the iron group that are not know to be synthesized in hydrostatic stellar burning. The existence of rp-breakout in the flashes, shows the importance of nuclear physics in these objects. More precise nuclear reaction rate data are needed for proper energy generation and chemical evolution. With the occurrence of rp-nucleosynthesis in our models, it is especially advantageous to study radioactive proton rich nuclei. These studies are not without many difficulties in the laboratory, as many of the studies require the use of low intensity radioactive beams making clean, high statistic studies difficult. To address this issue, the hybrid target technique was used. This target technique was found to be a great tool for studying resonant proton scattering with exotic beams. It has been used to measure elastic and inelastic excitation functions in the study of 8 B via 7 Be+p scattering, as well as 12 N+p elastic scattering. With such success, the hybrid target technique can be a very useful tool for studying reactions that are important in the rp-process. We have studied the structure of the astrophysically important, radioactive isotope 8 B. Three new resonances have been suggested, a 0+ , 2+ , and 1+ which were predominantly in the inelastic channel and never before seen in previous studies. However, due to their high excitation energies and narrow width, none of the resonances are expected to effect the astrophysically important 7 Be(p,γ) reaction rate. Results were compared to continuum shell model as well as ab initio calculations and found to be in good agreement with both sets of predictions, with the notable exception of the 2+ state. The structure of 13 O, an isotope important in the pp-chain breakout was studied by 12 N+p elastic scattering. This work extended the 13 O excitation function to higher energies than the previous work of [120], however, the cross section was found to be rather flat. Due to the very low intensity of the radioactive 12 N beam, the experiment had very low statistics, 1+ making the observation of any states other than the known 2 very difficult.
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Date Issued: 2012
Identifier: FSU_migr_etd-5408
Format: Thesis

Title: Techniques for Probing the Effects of Three-Dimensional Magneto-Hydrodynamics in Type Ia Supernovae.
Creator: Penney, Robert B., Höﬂich, Peter, Yang, Wei, Gerardy, Chris, Prosper, Harrison, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: Understanding Type Ia Supernovae provides an opportunity to study a wide range of modern physics as well as develop a key tool in cosmology. Here, we identify and investigate new observational signatures of underlying physical processes related to the thermonuclear run- away and the flame propagation and its environment, including three-dimensional effects. Understanding these signatures requires a consistent picture of the nuclear decay processes that power the Supernova and the energy...
Show moreUnderstanding Type Ia Supernovae provides an opportunity to study a wide range of modern physics as well as develop a key tool in cosmology. Here, we identify and investigate new observational signatures of underlying physical processes related to the thermonuclear run- away and the flame propagation and its environment, including three-dimensional effects. Understanding these signatures requires a consistent picture of the nuclear decay processes that power the Supernova and the energy transport of the high-energy particles created by these decays. Therefore we have developed and employed methods for simulating the transport of X-rays, gamma-rays, positrons and of low energy photons through a relativistically expanding envelope. With this, we identify signatures in the light curves, spectra and, in particular, line profiles that are produced in the context of a series of explosion models for Chandrasekhar Mass White Dwarfs. These models use the framework of a delayed detonation scenario in which a deflagration front transitions to a detonation phase. We use models that allow us to separate physical effects due to the flame physics and instabilities, the deflagration to detonation transitions and the initial conditions. Results from within this framework can be used directly for a variety of scenarios for Type Ias including merging White Dwarfs and explosions of sub-Chandrasekhar mass White Dwarfs. We found and developed X-rays as a tool to probe the outer layers of the Supernova envelope. Only models with radioactive material will show significant X-ray line fluxes during the first few months. We show that observations of these can put stringent limits on flame instabilities in delayed-detonation models, and can confirm or rule out mergers and sub-Chandrasekhar mass White Dwarfs as progenitors. Though these observations have not yet been done, the current generation of satellites are capable of observations of these spectra within about 10Mpc. As has been shown previously, optical lightcurves provide a possible diagnostic for mag- netic fields. We confirm previous results that lightcurve changes due to these fields on the order of 0.1 mag are to be expected at 200- 300 days, and changes may be up to 1 mag after 2-3 years. We show that the time evolution of late-time IR line profiles can probe the magentic fields and density and chemical distributions of the Supernova. To separate magnetic field from geometrical effects, we show the need for a time series of observations starting some 3-4 months after maximum light. Up until now, current observational programs commonly take snapshots at one late-time only though, technically, early time spectra are well within reach. Although rare, those observations that have been done show signatures of an off-center deflagration-detonation transition and, at least in some cases, our results strongly suggest the presence of magnetic fields well in excess of 106 G. Fields of this size can be expected to alter the evolution of the nuclear runaway which determines the initial conditions which rule the flame propagation during the explosion. With the upcoming generation of large telescopes on ground and in space, observations can be obtained routinely at distances well beyond the local group of galaxies.
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Date Issued: 2011
Identifier: FSU_migr_etd-5106
Format: Thesis

Title: Experimental Study of the Proton Capture on 25Al Using the 25Al(d,n)26Si Reaction in Inverse Kinematics.
Creator: Rojas, Alexander, Wiedenhöver, Ingo, Humayun, Munir, Volya, Alexander, Rogachev, Grigory, Bonesteel, Nicholas, Department of Physics, Florida State University
Abstract/Description: An experimental examination of low-lying proton resonances in 26Si was conducted using the proton transfer reaction, d(25Al,26Si)n. This reaction is analogous to the direct single proton capture, 25Al(p,g)26Si, of astrophysical significance in the nucleosynthesis calculation of the galactic 26Al. A 30% purity radioactive beam of 25Al at an energy of 5.4 MeV/nucleon was delivered from RESOLUT into a 230 ug/cm**2-thickness CD2 target. Protons from the decay channel of 26Si were measured and...
Show moreAn experimental examination of low-lying proton resonances in 26Si was conducted using the proton transfer reaction, d(25Al,26Si)n. This reaction is analogous to the direct single proton capture, 25Al(p,g)26Si, of astrophysical significance in the nucleosynthesis calculation of the galactic 26Al. A 30% purity radioactive beam of 25Al at an energy of 5.4 MeV/nucleon was delivered from RESOLUT into a 230 ug/cm**2-thickness CD2 target. Protons from the decay channel of 26Si were measured and used to reconstruct the excitation energies. Two 26Si proton resonances, corresponding to the adopted Er(Jpi)=402.9(3+) keV and 1274.3(3-) keV were observed. Cross-section measurement and spin and parity assignments are discussed in the context of DWBA formalism.
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Date Issued: 2011
Identifier: FSU_migr_etd-7221
Format: Thesis

Title: Clustering in ¹⁸O and ANC Measurements Using (⁶Li,D) Reactions.
Creator: Avila, Melina, Rogachev, Grigory, Humayun, Munir, Hoeﬂich, Peter, Volya, Alexander, Wiedenhover, Ingo, Department of Physics, Florida State University
Abstract/Description: Clustering in atomic nuclei is an interesting phenomenon that has been studied extensively in the past. However, most studies were related to clustering in α-like 4N nuclei. This work is focused on clustering in N≠Z non-self-conjugate nuclei. Two experimental approaches are applied. Properties of resonances above the α-decay threshold in 18O are studied using resonance elastic scattering of α-particles on 14C. Asymptotic Normalization Coefficients (ANCs) of near-threshold resonances in 16O,...
Show moreClustering in atomic nuclei is an interesting phenomenon that has been studied extensively in the past. However, most studies were related to clustering in α-like 4N nuclei. This work is focused on clustering in N≠Z non-self-conjugate nuclei. Two experimental approaches are applied. Properties of resonances above the α-decay threshold in 18O are studied using resonance elastic scattering of α-particles on 14C. Asymptotic Normalization Coefficients (ANCs) of near-threshold resonances in 16O, 17O and 20Ne are measured using sub-Coulomb α-transfer (6Li,d) reaction. To investigate the α-cluster states of 18O the α+14C elastic scattering reaction was studied using the Thick Target Inverse Kinematics (TTIK) technique. An exhaustive analysis of the 14C+α excitation functions using multi-channel, multi-level R-matrix approach has been performed. This analysis led to a more complete picture of α-cluster states in 18O. The excitation function was studied in an excitation energy range of 8 MeV-15 MeV. The most remarkable feature found in this analysis is the presence of states with high degree of clustering throughout the whole excitation energy range, including two states with pure α-cluster configuration. To provide a more detailed description of these two broad states, potential model calculations were preformed. These calculations reproduced rather well the excitation energy and width of these states. The Asymptotic Normalization Coefficient (ANC) technique can be used as an effective method to determine the astrophysical S-factor. Combination of the sub-Coulomb α-transfer reaction and application of the ANC technique in the analysis of the experimental data practically eliminates dependence of the result on model parameters, making this approach a very valuable tool for studies of astrophysically important reaction rates. In this study we report the ANC measurements of near threshold states for the reactions: 16O(6Li,d20Ne, 13C(6Li,d)17O and 12C(6Li,d)16O. Two astrophysically important reactions, 13C(α,n) and 12C(α,γ) were studied. The 13C(α,n) reaction is considered to be the main source of neutrons for the s-process in Asymptotic Giant Branch (AGB) stars and the 12C(α,γ) reaction is often regarded as the "holy grail"of nuclear astrophysics, because it enters as a crucial parameter for so many stellar processes. The ANCs of the near α-threshold states were used to calculate astrophysical S-factors and corresponding reaction rates.
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Date Issued: 2013
Identifier: FSU_migr_etd-8525
Format: Thesis

Title: Helium Atom Scattering Study of the Surface Structure and Dynamics of KCl(001) and Potassium Tantalate (KTaO₃) Doped with Lithium and Niobium.
Creator: Fatema, Rifat, Van Winkle, David H., Safron, Sanford A., Flaherty, Francis A., Manousakis, Efstratios, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: The structure and dynamics of the (001) surface of potassium tantalate (KTaO3), doped with lithium (KTL) and niobium (KTN) have been investigated using high resolution helium atom diffraction and single-phonon creation and annihilation, inelastic scattering experiments. This work is the first to investigate the surface structure and dynamics of KTL samples. These experiments are an extension of earlier work done with pure KTaO3 and KTN crystals. As in the previous experiments broad half-order...
Show moreThe structure and dynamics of the (001) surface of potassium tantalate (KTaO3), doped with lithium (KTL) and niobium (KTN) have been investigated using high resolution helium atom diffraction and single-phonon creation and annihilation, inelastic scattering experiments. This work is the first to investigate the surface structure and dynamics of KTL samples. These experiments are an extension of earlier work done with pure KTaO3 and KTN crystals. As in the previous experiments broad half-order diffraction peaks were observed in the <100> azimuth, which may be related to the formation of polar nanoregions that have been reported for bulk KTaO3. However, the condition for the formation of these regions differ somewhat from those reported previously. Drift spectra for these samples, which reveal the step-height distribution of terraces at the surface, show the expected oscillatory behavior for lightly doped KTaO3. Significantly, they also confirm the unusual behavior reported in earlier experiments for the 30% KTN samples. Surface dispersion curves in the two high symmetry directions, namely, <100> and <110>, have been obtained for both KTL and KTN samples. This work compares the above phenomena observed in KTL and KTN to similar phenomena previously observed in pure KTaO3 and KTN. Surface dynamics of KCl(001) is also investigated in this work and compared with reported model calculations. The agreement is generally good for the low-energy Rayleigh mode and for a crossing mode. However, a high energy dispersionless mode, found in the <100> high symmetry direction lies in the region of a shear-horizontal Lucas mode, that cannot in theory be observed by helium atom scattering in our experimental configuration. This disagreement between theory and experiment suggests that further theoretical work is necessary to understand the dynamics of simple ionic-insulator systems like KCl.
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Date Issued: 2009
Identifier: FSU_migr_etd-4495
Format: Thesis

Title: A Study of Rare-Earth Magnetism Through Spectroscopic Studies of Lanthanide-Based Single Crystals.
Creator: Ghosh, Sanhita, Hill, Stephen, Wiebe, Christopher, Dalal, Naresh, Schlottmann, Pedro, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: This dissertation presents a study of rare-earth magnetism using spectroscopic techniques. The features of strong spin-orbit coupling and the presence of hyperfine coupling which lead to coupled electro-nuclear crystal field states are typical of lanthanides, and contribute to distinct magnetic properties. In the work reported here electron paramagnetic resonance (EPR) and neutron scattering techniques have been employed for investigating the ground state magnetic properties of a few...
Show moreThis dissertation presents a study of rare-earth magnetism using spectroscopic techniques. The features of strong spin-orbit coupling and the presence of hyperfine coupling which lead to coupled electro-nuclear crystal field states are typical of lanthanides, and contribute to distinct magnetic properties. In the work reported here electron paramagnetic resonance (EPR) and neutron scattering techniques have been employed for investigating the ground state magnetic properties of a few lanthanide-based single crystalline sample. The two kinds of samples investigated in the course of this work include single molecule magnets (SMMs) and geometrically frustrated systems. EPR studies on mononuclear lanthanide-based SMMs, which have attracted considerable attention due to their potential application in spintronic devices, form a major portion of the research reported in this dissertation. In these systems the magnetization is associated with a single rare-earth ion (holmium) which facilitates mitigation of spin decoherence due to nuclear hyperfine and electron dipolar interactions by dilution and isotope purification. High frequency EPR studies on HoPOM indicate considerable transverse spin orbit anisotropy, which considerably affects the magnetization relaxation properties by giving rise to a tunneling gap between excited electro-nuclear spin states. Electron spin echo measurements at 9 GHz demonstrate long relaxation times (~ 100 ns) for concentrated samples, with much longer values for diluted samples containing deuterated solvent. Besides a detailed study involving the evaluation of the spin Hamiltonian parameters and measurement of transverse relaxation times for HoPOM samples of various concentrations, we also attempt to investigate the mechanism leading to the observed long coherence times. We propose that there is mitigation of decoherence in this system due to the nature of the tunneling gap, which leads to an insensitivity of the spin dynamics to field fluctuations. The other area of focus of the work presented in this dissertation involves studying spin frustrated lattices which give rise to novel ground state properties. The low temperature behavior of the modified honeycomb lattice compound SrHo2O4 has been characterized by dc magnetic susceptibility, heat capacity and neutron scattering experiments indicating lack of long range ordering down to 1.8 K. Elastic neutron scattering measurements show diffuse scattering indicative of short range ordering between nearest neighbor Ho3+ spins. Inelastic neutron scattering experiments carried out at multiple temperatures show the presence of five crystal field levels up to 80 K in energy, which is in agreement with the specific heat measurement on the system. The distorted kagome lattice compounds, Pr3Ga5SiO14 and Nd3Ga5SiO14, were also studied as examples of spin frustrated systems. EPR experiments on single crystals of these isostructural samples show complex multi-peak spectra with strong systematic temperature dependence. The nature of the observed excitations in high frequency EPR measurements indicate that they correspond to collective excitations akin to spin-wave resonances, caused by the formation of spin clusters whose correlation length depends on field and frequency. This study potentially provides an experimental basis to the investigation of antiferromagnetic spin wave - like resonances in the kagome lattice. The two kinds of samples discussed demonstrate interesting ground state properties, which have been probed using spectroscopic techniques for an insight into rare earth magnetism.
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Date Issued: 2012
Identifier: FSU_migr_etd-5656
Format: Thesis

Title: Superconductivity and Quantum Phase Transitions in Ultrathin Amorphous Pb Films.
Creator: Kumar, Ashwani, Xiong, Peng, Strouse, Geoffrey F., Chiorescu, Irinel, Bonesteel, Nicholas, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: This dissertation presents a systematic study of superconductivity and superconducting quantum phase transitions in ultrathin homogeneous Pb films. We have explored the superconductor to insulator quantum phase transitions (SITs) down to 80 mK by tuning several parameter viz: disorder, magnetic field, and magnetic impurity. The experiments have been carried out in a unique experimental setup of a modified dilution refrigerator with in situ thin film growth, magnetic impurity deposition,...
Show moreThis dissertation presents a systematic study of superconductivity and superconducting quantum phase transitions in ultrathin homogeneous Pb films. We have explored the superconductor to insulator quantum phase transitions (SITs) down to 80 mK by tuning several parameter viz: disorder, magnetic field, and magnetic impurity. The experiments have been carried out in a unique experimental setup of a modified dilution refrigerator with in situ thin film growth, magnetic impurity deposition, sample rotation and electrical measurement capabilities. The setup enabled us to increase the film thickness and deposit the magnetic impurities (Cr) incrementally, apply a magnetic field, in both perpendicular and parallel directions, up to 8 T, and perform electrical transport measurements at any film thickness and Cr- impurity density, all under ultrahigh vacuum and at low temperatures. The introduction of magnetic impurity as a new tuning parameter for the SIT provided us with a useful model system in which the microscopic mechanism for the destruction of uperconductivity is well understood, the phase boundary is well-defined, and the insulating state is purely fermionic. Using this as a reference and based on the extensive similarities between the disorder (d)-tuned and magnetic impurity (MI)-tuned transitions, we concluded that the disorder (thickness)-tuned SIT is fermionic in nature, contrary to several popular theoretical models. The magnetic field-tuned transition, on the other hand, appears to be qualitatively different from the magnetic impurity or disorder tuned transitions. When increasingly large perpendicular magnetic field is applied to an ultrathin superconducting film, the resistive transition progressively broadens, leading to an insulating state. There is no well-defined phase boundary between the superconducting and insulating state. In fact, in a range of normal state resistance(RN) near the transition, the sheet resistance, R(T) data exhibit reentrance or even double-reentrance. On the insulating side, increasing magnetic field in fact weakens the temperature dependence of R(T). The overall behavior bears many similarities to the disorder-tuned SIT transition in granular films, a model system for a bosonic transition. We observed a giant enhancement ( 13%) of the mean-field critical temperature (TC) of ultrathin homogeneous pure a-Pb films in parallel magnetic fields as large as 8 T. The magnitude of the TC enhancement was found to vary systematically with the film thickness, showing a nonmonotonic behavior. Most importantly, adding paramagnetic impurities (Cr) on the films always leads to suppression and eventual elimination of the TC enhancement. These observations directly contradict the theories based on the idea that the enhancement effect originates from the magnetic field polarizing the paramagnetic impurities. This dissertation also describes an effort to fabricate on-substrate nanoscale metal stencil masks as well as nanowire templates, using a variety of nanofabrication and assembly techniques. These nanostructures will be used for experiments aiming to extend these studies to the one-dimensional limit.
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Date Issued: 2009
Identifier: FSU_migr_etd-7177
Format: Thesis

Title: Clustering Phenomena in the a = 10 T = 1 Isobaric Multiplet.
Creator: Kuchera, Anthony N., Rogachev, Grigory, Tabor, Samuel, Aldrovandi, Ettore, Prosper, Harrison, Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: Clustering of α particles plays an important role in light atomic nuclei. For example, multicenter structures built on the well-known low-lying states of 8Be can be formed. The addition of nucleons to the system may result in covalent-like bonding between the two α-cores. These structures have been called ''nuclear molecules" because of their analog to atomic molecules. Investigation of these exotic nuclear structures is the main subject of this experimental work. Much of the experimental and...
Show moreClustering of α particles plays an important role in light atomic nuclei. For example, multicenter structures built on the well-known low-lying states of 8Be can be formed. The addition of nucleons to the system may result in covalent-like bonding between the two α-cores. These structures have been called ''nuclear molecules" because of their analog to atomic molecules. Investigation of these exotic nuclear structures is the main subject of this experimental work. Much of the experimental and theoretical work for molecular-like states has been done within the Be isotopes, however, despite of significant effort, our knowledge and understanding of molecular-like structures is still deficient. This is due to limited experimental information on the states of interest. The main goal of this work is to provide this information for the unbound T=1 states in A=10 systems and look for signatures of the exotic α:2N:α configurations. The T=1 states in 10B between Ex = 8.7- 12.1 MeV were studied using the 1H(9Be,α)6Li*(T=1, 0+, 3.56 MeV) reaction. An R-matrix analysis was used to extract parameters for the five resonances observed. The widths of the known 2+ resonance at 8.9 MeV have been measured and support the theoretical predictions that it is a highly clustered state and can be identified as a member of the α-np-α rotational band. The 4+ member was not observed in this reaction channel. In a second experiment, 6He+4He elastic scattering was used to probe resonances in 10Be in search of α-2n-α structures. Using the active target detector system, ANASEN, the excitation function was measured from Ex = 9.6 - 15.4 MeV. This was the first experiment in which the new active target detector, ANASEN, was used in filled (active target) mode. The excitation function shows a strong resonance at 10.2 MeV which was identified as 4+ and assigned to the extremely stretched α:2n:α configuration. A broad structure centered at 13.5 MeV was also observed and it may possibly be the 6+ member of this rotational band.
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Date Issued: 2013
Identifier: FSU_migr_etd-8585
Format: Thesis

Title: Single Crystal Growth and Magnetic and Thermal Properties of Pb₂V₃₀₉.
Creator: Conner, Benjamin S. (Benjamin Scott), Dobrosavljevic, Vladimir, Balicas, Luis, Dalal, Naresh, Brooks, James, Rogachev, Grigory, Schlottmann, Pedro, Department of Physics,...
Show moreConner, Benjamin S. (Benjamin Scott), Dobrosavljevic, Vladimir, Balicas, Luis, Dalal, Naresh, Brooks, James, Rogachev, Grigory, Schlottmann, Pedro, Department of Physics, Florida State University
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Abstract/Description: Electrical insulators provide the opportunity to study the effects of magnetic interactions in the absence of conduction electrons. Since about ten years ago, experiments on a few insulating dimerized antiferromagnets have shown a low temperature, concave-down feature in magnetic susceptibility under magnetic fields larger than a critical value that was difficult to explain. Also, features in heat capacity remnant of the lambda anomaly associated with the superfluid transition in liquid 4He...
Show moreElectrical insulators provide the opportunity to study the effects of magnetic interactions in the absence of conduction electrons. Since about ten years ago, experiments on a few insulating dimerized antiferromagnets have shown a low temperature, concave-down feature in magnetic susceptibility under magnetic fields larger than a critical value that was difficult to explain. Also, features in heat capacity remnant of the lambda anomaly associated with the superfluid transition in liquid 4He were observed after an applied magnetic field was increased beyond the same critical value. These observations are associated with long-range magnetic ordering that has been described as a Bose-Einstein condensation (BEC) of the integer spin excitations, the magnons. Although magnons cannot strictly form a BEC, the BEC description has been qualitatively successful in describing some of the measured quantities of the small number of insulating antiferromagnets that exhibit a field induced low temperature, concave-down susceptibility. Pb2V3O9 is one system that exhibits this field induced low temperature, concave-down magnetic susceptibility and has been ascribed this BEC description. This thesis outlines the following: 1. The floating zone crystal growth of single crystals of Pb2V3O9 is presented. This thesis outlines what is possibly the first successful effort to grow single crystals of Pb2V3O9 via the floating zone method. 2. Measurements of the physical properties of Pb2V3O9 with applied magnetic fields as large as 45 T, specifically those properties associated with the field-induced long range ordered phase, are presented. 3. The observation of glassy magnetic behavior in Pb2V3O9 observed for the first time in off-stoichiometric samples is presented. This glassy magnetic behavior is found to be in competition with the field-induced long range ordered phase.
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Date Issued: 2011
Identifier: FSU_migr_etd-3464
Format: Thesis

Title: The Cluster Structure of Oxygen Isotopes.
Creator: Johnson, Eric D., Rogachev, Grigory V., Humayun, Munir, Blessing, Susan K., Tabor, Samuel L., Volya, Alexander S., Department of Physics, Florida State University
Abstract/Description: The alpha-cluster structure of two oxygen isotopes, 17O and 18O, was studied using two experimental techniques. The first technique measured resonance elastic scattering of alpha particles and the second used the direct alpha-transfer reactions (6Li,d) and (7Li,t) to determine resonance properties. Motivation for this study was two-fold. First, the alpha-cluster structure of N not equal Z nuclei is poorly known and is a subject of intense theoretical discussion . Historically, the alpha...
Show moreThe alpha-cluster structure of two oxygen isotopes, 17O and 18O, was studied using two experimental techniques. The first technique measured resonance elastic scattering of alpha particles and the second used the direct alpha-transfer reactions (6Li,d) and (7Li,t) to determine resonance properties. Motivation for this study was two-fold. First, the alpha-cluster structure of N not equal Z nuclei is poorly known and is a subject of intense theoretical discussion . Historically, the alpha-particle model of the atomic nucleus was the leading model of nuclear structure. As it became clear that nuclei consist of protons and neutrons this model was replaced. The Pauli principle forbids nucleons from different alpha particles to be in the same state since the total wave function of an atomic nucleus must be antisymmetric. However, alpha clusters have been used to explain various nuclear effects including quasi-rotational bands of states with large alpha-particle widths which were observed in light 4N nuclei, 8Be, 12C, 16O and so on. Included here is a report on the observation of the alpha-cluster structure in the N not equal Z nucleus 18O. We measured the alpha-cluster structure of 18O using the Thick Target Inverse Kinematics (TTIK) technique . We found that 18O has a very elaborate alpha-cluster structure, including two unusual states with alpha widths larger than the single particle limit (the Wigner limit ). A comparison of the observed 18O alpha-cluster structure with the predictions of modern theoretical approaches is given. The peculiar nature of the two very broad states is discussed. Second, the alpha-cluster structure of near alpha-threshold excited states in 17O and 18O plays a crucial role in the field of nuclear astrophysics as it determines the rates of the 13C(alpha,n) and 14C(alpha,gamma) reactions. These reactions are thought to play important roles in stellar evolution of Asymptotic Giant Branch (AGB) stars. Unfortunately, direct measurement of these reactions is currently impractical. This has led to the development of indirect methods to determine reaction rates. One such method is the Asymptotic Normalization Coefficient (ANC) technique. We determined the alpha-cluster structure of several near alpha-threshold states in 17O and 18O using this ANC technique. Using this alpha-cluster information we were able to determine the 13C(alpha,n) reaction rate and reduce its uncertainty from approximately 300% to 25%. Also we were able to calculate the 14C(alpha,gamma) reaction rate. Accurately knowing the 13C(alpha,n) reaction rate is crucial to the modeling of AGB stars, and a reliable determination of the 14C(alpha,gamma) reaction rate is needed in order to help understand the unexplained abundance of 19F in the universe.
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Date Issued: 2008
Identifier: FSU_migr_etd-3494
Format: Thesis

Title: An Analytic Approach to Estimating the Required Surplus, Benchmark Profit, and Optimal Reinsurance Retention for an Insurance Enterprise.
Creator: Boor, Joseph A. (Joseph Allen), Born, Patricia, Case, Bettye Anne, Tang, Qihe, Rogachev, Grigory, Okten, Giray, Aldrovandi, Ettore, Paris, Steve, Department of Mathematics,...
Show moreBoor, Joseph A. (Joseph Allen), Born, Patricia, Case, Bettye Anne, Tang, Qihe, Rogachev, Grigory, Okten, Giray, Aldrovandi, Ettore, Paris, Steve, Department of Mathematics, Florida State University
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Abstract/Description: This paper presents an analysis of the capital needs, needed return on capital, and optimum reinsurance retention for insurance companies, all in the context where claims are either paid out or known with certainty within or soon after the policy period. Rather than focusing on how to estimate such values using Monte Carlo simulation, it focuses on closed form expressions and approximations for key quantities that are needed for such an analysis. Most of the analysis is also done using a...
Show moreThis paper presents an analysis of the capital needs, needed return on capital, and optimum reinsurance retention for insurance companies, all in the context where claims are either paid out or known with certainty within or soon after the policy period. Rather than focusing on how to estimate such values using Monte Carlo simulation, it focuses on closed form expressions and approximations for key quantities that are needed for such an analysis. Most of the analysis is also done using a distribution-free approach with respect to the loss severity distribution, so minimal or no assumptions surrounding the specific distribution are needed when analyzing the results. However, one key parameter, that is treated via an exhaustion of cases, involves the degree of parameter uncertainty, the number of separate lines of business involved. This is done for the no parameter uncertainty monoline compound Poisson distribution as well as situations involving (lognormal) severity parameter uncertainty, (gamma/negative binomial) count parameter uncertainty, the multiline compound Poisson case, and the compound Poisson scenario with parameter uncertainty, and especially parameter uncertainty correlated across the lines of business. It shows how the risk of extreme aggregate losses that is inherent in insurance operations may be understood (and, implicitly, managed) by performing various calculations using the loss severity distribution, and, where appropriate, key parameters driving the parameter uncertainty distributions. Formulas are developed that estimate the capital and surplus needs of a company(using the VaR approach), and therefore the profit needs of a company that involve tractable calculations. As part of that the process the benchmark loading for profit, reflecting both the needed financial support for the amount of capital to adequately secure to a given one year survival probability, and the amount needed to recompense investors for diversifiable risk is discussed. An analysis of whether or not the loading for diversifiable risk is needed is performed. Approximations to the needed values are performed using the moments of the capped severity distribution and analytic formulas from the frequency distribution as inputs into method of moments normal and lognormal approximations to the percentiles of the aggregate loss distribution. An analysis of the optimum reinsurance retention/policy limit is performed as well, with capped loss distribution/frequency distribution equations resulting from the relationship that the marginal profit (with respect to the loss cap) should be equal to the marginal expense and profit dollar loading with respect to the loss cap. Analytical expressions are developed for the optimum reinsurance retention. Approximations to the optimum retention based on the normal distribution were developed and their error analyzed in great detail. The results indicate that in the vast majority of practical scenarios, the normal distribution approximation to the optimum retention is acceptable. Also included in the paper is a brief comparison of the VaR (survival probability) and expected policyholder deficit (EPD) and TVaR approaches to surplus adequacy (which conclude that the VaR approach is superior for most property/casualty companies); a mathematical analysis of the propriety of insuring the upper limits of the loss distribution, which concludes that, even if unlimited funds were available to secure losses in capital and reinsurance, it would not be in the insured's best interest to do so. Further inclusions to date include a illustrative derivation of the generalized collective risk equation and a method for interpolating ``along'' a mathematical curve rather than directly using the values on the curve. As a prelude to a portion of the analysis, a theorem was proven indicating that in most practical situations, the n-1st order derivatives of a suitable probability mass function at values L, when divided by the product of L and the nth order derivative, generate a quotient with a limit at infinity that is less than 1/n.
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Date Issued: 2012
Identifier: FSU_migr_etd-4726
Format: Thesis

Title: Sensitivity of Neutron Star Properties to the Equation of State.
Creator: Fattoyev, Farrooh, Piekarewicz, Jorge, Aluf, Paolo, Capstick, Simon, Owens, Joseph F., Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: The subject of this doctoral dissertation is to study the equations of state of nuclear and neutron-star matter. We tackle this problem by employing several models of the relativistic effective interactions. The relativistic effective interactions and their applications to the ground-state properties of medium to heavy nuclei have enjoyed enormous success for the past three decades. With just a few model parameters calibrated to the ground state properties of the closed-shell nuclei, these...
Show moreThe subject of this doctoral dissertation is to study the equations of state of nuclear and neutron-star matter. We tackle this problem by employing several models of the relativistic effective interactions. The relativistic effective interactions and their applications to the ground-state properties of medium to heavy nuclei have enjoyed enormous success for the past three decades. With just a few model parameters calibrated to the ground state properties of the closed-shell nuclei, these models exhibit and encode a great amount of physics. However, theses models are untested far away from their narrow window of applicability. In particular, while these models tend to agree on the saturation properties of symmetric nuclear matter, they largely disagree on its density and isospin dependence, especially in the region of high densities and large proton-neutron asymmetries. In order to better understand the properties of nuclear matter at these extreme regions of isospin asymmetry and high-densities, we will apply these models to predict several neutron star properties. Since the matter in the neutron stars are very neutron-rich, while the density of matter in neutron stars spans over a wide range of magnitudes, these compact objects remain unique laboratories for probing the equation of state of neutron-rich matter under conditions unattainable by terrestrial experiments. Thus it is expected that at least the following neutron star properties must be sensitive to the underlying equation of state: maximum mass, typical radii, moments of inertia (both total and crustal), redshifts, and cooling mechanism. We present numerical solutions and in some cases also analytical solutions to each of the properties above. In particular, the sensitivity of the stellar moment of inertia to the neutron-star matter equation of state is examined using accurately-calibrated relativistic mean-field models. We probe this sensitivity by tuning both the density dependence of the symmetry energy and the high density component of the equation of state, properties that are at present poorly constrained by existing laboratory data. Particularly attractive is the study of the fraction of the moment of inertia contained in the solid crust. Analytic treatments of the crustal moment of inertia reveal a high sensitivity to the transition pressure at the core-crust interface. Motivated by a recent astrophysical measurement of the pressure of cold matter above nuclear-matter saturation density, we compute the equation of state of neutron-star matter using various accurately calibrated relativistic models. We found the predictions of these models to be in fairly good agreement with the measured equation of state. In the effort to explain the observational data we introduce a new relativistic effective interaction that is simultaneously constrained by the properties of finite nuclei, their collective excitations, and neutron-star properties. By adjusting two of the empirical parameters of the theory, one can efficiently tune the neutron skin thickness of $^{208}$Pb and the maximum neutron star mass. The new effective interaction is moderately soft at intermediate densities and relatively stiff at high densities. It is fitted to a neutron skin thickness in $^{208}$Pb of only $R_{rm n} - R_{rm p} = 0.16$ fm and a moderately large maximum neutron star mass of 1.94 $M_{rm Sun}$ consistent with the latest observation. Last, theoretical uncertainties in the predictions of relativistic mean-field models are estimated using a chi-square minimization procedure that is implemented by studying the small oscillations around the chi-square minimum. It is shown that such statistical analysis provides access to a wealth of information that would normally remain hidden. The power of covariance analysis is illustrated in two relativistic mean field models. By performing this analysis one obtains meaningful theoretical uncertainties for both model parameters and predicted observables. Moreover, it is shown, how covariance analysis is able to establish robust correlations between physical observables.
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Date Issued: 2011
Identifier: FSU_migr_etd-4824
Format: Thesis

Title: Search for the Dark Matter Signature in the Lepton Jet Final State √(S) = 7 TeV.
Creator: Gleyzer, Sergei V., Hagopian, Vasken, Safron, Sanford A., Prosper, Harrison B., Berg, Bernd, Rogachev, Grigory, Department of Physics, Florida State University
Abstract/Description: The Large Hadron Collider is pushing high energy physics in to a brand new territory. This extraordinary era may bring discoveries of unprecedented magnitude, delivering validation or extreme dissappointment to the physics theories of the previous decades. By colliding particles at more than 3.5 times the center of mass energy of the Tevatron accelerator at the Fermilab National Accelerator Laboratory, the CERN Large Hadron Collider aims to produce particles in the mass range above those that...
Show moreThe Large Hadron Collider is pushing high energy physics in to a brand new territory. This extraordinary era may bring discoveries of unprecedented magnitude, delivering validation or extreme dissappointment to the physics theories of the previous decades. By colliding particles at more than 3.5 times the center of mass energy of the Tevatron accelerator at the Fermilab National Accelerator Laboratory, the CERN Large Hadron Collider aims to produce particles in the mass range above those that are already known. At the same time, there are exciting possibilities for new physics in the low-mass range that may have gone unnoticed until now. An example of this is a GeV-scale dark sector with a colorful spectrum of new particles. This physics model produces unique signatures of collimated leptons at the Large Hadron Collider energies. In the first part of this work, we describe the interesting astrophysical evidence that motivates a search for lepton jets and focus our attention on a minimal supersymmetric standard model with a GeV-scale dark sector that produces this exciting signature. In the next part of the thesis, we describe a search using the Compact Muon Solenoid (CMS) detector for evidence of dark matter in events containing muonic lepton-jets produced in 7 TeV proton-proton collisions at the Large Hadron Collider. We employ a novel lepton jet algorithm and find no evidence of an excess of such events with respect to the rate predicted by the Standard Model and interpret the null result in terms of a recently developed supersymmetric theory of dark matter. In doing so, we severely constrain the theoretical model and its parameters with the actual data from the Large Hadron Collider. In addition, we report the first observation of double J/ψ production, a new physical process discovery at the next energy frontier.
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Date Issued: 2011
Identifier: FSU_migr_etd-4240
Format: Thesis

Title: Magnetic Field Dependent Properties of the Spin-Peierls Chain in the Organic Conductor Per₂Pt[mnt]₂.
Creator: Green, Elizabeth L. (Elizabeth Lauren), Brooks, James S., Siegrist, Theo, Warusawithana, Maitri, Schlottmann, Pedro, Rogachev, Grigory, Reyes, Arneil, Department of Physics,...
Show moreGreen, Elizabeth L. (Elizabeth Lauren), Brooks, James S., Siegrist, Theo, Warusawithana, Maitri, Schlottmann, Pedro, Rogachev, Grigory, Reyes, Arneil, Department of Physics, Florida State University
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Abstract/Description: Nuclear magnetic resonance (NMR), susceptibility, and magnetic torque measurements were used to investigate the field-dependent properties of the localized magnetic moment in the two chain organic conductor Per2Pt[mnt]2. At 8 K, the conducting (perylene) chain undergoes a lattice distortion resulting in a metal-insulator (M-I) transition and the formation of a charge density wave (CDW). Similarly, the magnetic (Pt[mnt]2) chain undergoes a lattice distortion with the localized electrons...
Show moreNuclear magnetic resonance (NMR), susceptibility, and magnetic torque measurements were used to investigate the field-dependent properties of the localized magnetic moment in the two chain organic conductor Per2Pt[mnt]2. At 8 K, the conducting (perylene) chain undergoes a lattice distortion resulting in a metal-insulator (M-I) transition and the formation of a charge density wave (CDW). Similarly, the magnetic (Pt[mnt]2) chain undergoes a lattice distortion with the localized electrons ordering in an antiferromagnetic manner forming spin-singlet dimers in the spin-Peierls state at 6.5 K. The dimers and tetramers begin to break with increasing magnetic fields. At 20 T the system enters into a metallic state that persists up to 24 T. Dave Graf and his collaborators discovered a field induced charge density wave state (FICDW) from 24 T to 33 T using resisitivity measurements. 1H NMR is a localized probe sensitive to the spin dynamics of the Pt[mnt]2chain. Nuclear relaxation rates (T1-1) and spectra reveal the SP-boundary occurs at a lower temperature than the CDW-boundary indicating the formation of the CDW precedes the dimerization on the Pt[mnt]2 chain. Furthermore, the boundaries at 20 T are concomitant and therefore the two chains are coupled up to high fields. The 45 T hybrid magnet was used to probe the physics of the magnetic chain in the FICDW state. Corresponding high field spectra, measured up to 32.5 T, reveal an increasing electronic spin polarization. Activation energies and magnetic moments were extracted from fitting the temperature dependent T1 and susceptibility data revealing two competing spin systems in the low-temperature ground state; intrinisic behaviour of the dimerized system and a paramagnetic contribution possibly from dangling bonds or unpaired dimers accounting for less than 5 % of the Pt spins. Additional measurements include 195Pt NMR and magnetic torque measurements using a piezoresistive cantilever (PRC). 195Pt NMR results show a strong orientational dependence while the PRC measurements confirm an increasing magnetization in the FICDW state. Finally future experiments will be discussed.
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Date Issued: 2012
Identifier: FSU_migr_etd-4877
Format: Thesis

Title: Search for Large Extra Dimensions via Single Photon Plus Missing Energy Final States at √S =1.96 TeV.
Creator: Carrera, Edgar F. (Edgar Fernando), Gershtein, Yuri, Prosper, Harrison, Schatschneider, Chris, Reina, Laura, Rogachev, Grigory, Wahl, Horst, Department of Physics, Florida State...
Show moreCarrera, Edgar F. (Edgar Fernando), Gershtein, Yuri, Prosper, Harrison, Schatschneider, Chris, Reina, Laura, Rogachev, Grigory, Wahl, Horst, Department of Physics, Florida State University
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Abstract/Description: This dissertation presents a search for large extra dimensions in the single photon plus missing transverse energy final states. We use a data sample of approximately 2.7fb⁻¹ of pp̄ collisions at√s= 1.96 TeV (recorded with the DØ detector) to investigate direct Kaluza Klein graviton production and set limits, at the 95% C.L., on the fundamental mass scale MD from 970 to 816 GeV for two to eight extra dimensions.
Date Issued: 2009
Identifier: FSU_migr_etd-4163
Format: Thesis

Title: The Lowest ℓ = 0 Proton Resonance in Si-26 and Its Implications for the Stellar Nucleosynthesis of Al-26.
Creator: Peplowski, Patrick N. (Patrick Nelson), Wiedenhöver, Ingo, Fuelberg, Henry, Volya, Alexander, Rogachev, Grigory, Höﬂich, Peter, Department of Physics, Florida State University
Abstract/Description: Determining the stellar production site of 26Al is an exciting problem that spans experimental and theoretical nuclear physics, astrophysics, and observational astronomy. This thesis details an experiment to measure the 25Al(d,n)26Si single proton transfer reaction, which can provide information on the astrophysically significant 25Al(p,gamma)26Si reaction. The first 3+ state in 26Si, which is predicted to dominate the stellar nucleosynthesis rate, was observed and characterized. The...
Show moreDetermining the stellar production site of 26Al is an exciting problem that spans experimental and theoretical nuclear physics, astrophysics, and observational astronomy. This thesis details an experiment to measure the 25Al(d,n)26Si single proton transfer reaction, which can provide information on the astrophysically significant 25Al(p,gamma)26Si reaction. The first 3+ state in 26Si, which is predicted to dominate the stellar nucleosynthesis rate, was observed and characterized. The implications for stellar nucleosynthesis are discussed for potential stellar production sites.
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Date Issued: 2009
Identifier: FSU_migr_etd-2032
Format: Thesis

Title: Nuclear Structure of Neutron Rich 34P Using in-Beam Gamma Ray Spectroscopy.
Creator: Bender, Peter C., Tabor, Samuel L., Humayun, Munir, Rogachev, Grigory, Volya, Alexander, Warusawithana, Maitri, Department of Physics, Florida State University
Abstract/Description: Increasing dominance of negative parity intruder states in neutron-rich nuclei in the sd shell as N approaches 20 shows evidence of evolving shell structure. Systematically examining the structure of isotopes with increasing N while filling the vd3/2 level highlights a large number of intruder configurations. These intruder configurations come from the decrease in energy to promote a neutron across the N = 20 shell gap. Such studies are needed to help in the refinement of the shell model and...
Show moreIncreasing dominance of negative parity intruder states in neutron-rich nuclei in the sd shell as N approaches 20 shows evidence of evolving shell structure. Systematically examining the structure of isotopes with increasing N while filling the vd3/2 level highlights a large number of intruder configurations. These intruder configurations come from the decrease in energy to promote a neutron across the N = 20 shell gap. Such studies are needed to help in the refinement of the shell model and increase its predictive power for nuclei far from stability. The presented work chronicles a series of 18O(18O,pn) experiments conducted around the world to study high spin states in 34P, a nucleus in the sd shell bordering the "island of inversion." One of these experiments which was conducted at Argonne National Laboratory where a 24 MeV neutron rich 18O beam impinged on a Ta backed 18O target, is presented here in great detail. The evaporated charged particles were detected with MICROBALL while the γ rays emitted were detected with GAMMASPHERE. A brief discussion of the theory of analysis techniques used in in-beam γ-ray spectroscopy is presented followed by an in depth discussion of the analysis of this experiment. From the analysis of excited states populated in 34P, a number of candidate states including 0p0h and 1p1h configurations are found and identified. A few states are also observed that have strong evidence pointing towards a more exotic 2p2h configuration. One state, the highest ever observed in 34P at 7917 keV may even be of the extremely exotic 3p3h type though the evidence is very speculative. Spins and parities of all levels have been assigned through arguments based on lifetime measurements of individual states measured with Doppler shift attenuation techniques and full γ-ray angular distributions whenever possible. Model dependent assignments have also been used in some spin assignments. In total, 10 newly observed levels are presented along with 23 newly observed transitions. Detailed shell model calculations using both the WBP - a and sdpfnow interactions are also presented. A comparison of theoretically predicted properties of individual states, including occupations, branching ratios and electromagnetic transition strengths is made to the experimentally observed states when applicable. Both interactions show fairly reliable predictive power for the both 0p0h and 1p1h configurations with an approximate root mean squared deviation of 150 keV in energies. States involving 2p2h configurations are discussed, though the current shell model calculations are much less reliable for them.
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Date Issued: 2011
Identifier: FSU_migr_etd-1320
Format: Thesis

Title: A Study of Useful Inflatables.
Creator: Barton, Sean A., Van Winkle, David, Bellenot, Steven, Van Dommelen, Leon, Rogachev, Grigory, Schlottmann, Pedro, Safron, Sanford A., Flaherty, Frank, Department of Physics,...
Show moreBarton, Sean A., Van Winkle, David, Bellenot, Steven, Van Dommelen, Leon, Rogachev, Grigory, Schlottmann, Pedro, Safron, Sanford A., Flaherty, Frank, Department of Physics, Florida State University
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Abstract/Description: It is demonstrated that inflatable structures can provide large amounts of stiffness compared to traditional structures of the same mass. A variety of inflatable structures are investigated theoretically. A pressurized lobed cylindrical wall is shown to be sufficiently lightweight and stiff that it can form a lighter-than-air vacuum chamber. Some prototype inflatables are built. Mechanical and optical tests are performed. Some applications in aerospace and solar energy which require large...
Show moreIt is demonstrated that inflatable structures can provide large amounts of stiffness compared to traditional structures of the same mass. A variety of inflatable structures are investigated theoretically. A pressurized lobed cylindrical wall is shown to be sufficiently lightweight and stiff that it can form a lighter-than-air vacuum chamber. Some prototype inflatables are built. Mechanical and optical tests are performed. Some applications in aerospace and solar energy which require large linear dimension, small mass, or large stiffness are discussed including electromagnetic space launch, airship buoyancy control, solar chimney power plants, and large inflatable mirrors.
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Date Issued: 2011
Identifier: FSU_migr_etd-1120
Format: Thesis

Title: Investigation of the Neutron-Rich Oxygen Isotopes at the Drip Line.
Creator: Hoffman, Calem R., Tabor, Samuel L., Goldsby, Kenneth A., Rogachev, Grigory, Volya, Alexander, Xiong, Peng, Department of Physics, Florida State University
Abstract/Description: To investigate the appearance of a new magic number at neutron number 16, resonance states around the oxygen (Z=8) drip line have been investigated. The neutron unbound states were populated by a nucleon removal reaction from a radioactive 26F ion beam and the invariant mass method was used to reconstruct the resonance decay spectrum. The secondary radioactive 26F beam was created by the fragmentation of a 48Ca beam, produced by the National Superconducting Cyclotron Laboratory's Coupled...
Show moreTo investigate the appearance of a new magic number at neutron number 16, resonance states around the oxygen (Z=8) drip line have been investigated. The neutron unbound states were populated by a nucleon removal reaction from a radioactive 26F ion beam and the invariant mass method was used to reconstruct the resonance decay spectrum. The secondary radioactive 26F beam was created by the fragmentation of a 48Ca beam, produced by the National Superconducting Cyclotron Laboratory's Coupled Cyclotron Facility, and was cleanly selected by the A1900 fragment mass analyzer. A complete kinematic measurement was made of the decay neutron and fragment using the Modular Neutron Array (MoNA) to detect neutrons, and the large gap dipole Sweeper magnet combined with charged particle detectors to select and measure the charged fragments. Resonance spectra were reconstructed for both 24O+n and 23O+n coincidence data to investigate the resonance states in 25O and 24O, respectively. To extract resonance energies and widths from the spectra, a Breit-Wigner line-shape function was input into a Monte Carlo simulation that reflected the experimental response. A fit which minimized chi-squared was completed for each spectrum and for the 24O+n coincidence data a single resonance at a decay energy of Edecay=770(30) keV and with a width of Gamma=172(30) keV was determined. Two resonances of energies Edecay=0.63(4) MeV and Edecay=1.24(7) MeV were found in the fit to the 23O+n coincidence data. The single state in the 24O+n coincidence data is the first mass measurement of the ground state of the lightest neutron unbound oxygen isotope, 25O. The two states in the 23O+n data have been inferred to be the first observation of the 2+ and 1+ neutron unbound excited states in 24O. The ground state mass of 25O was used to determine the location of the 0d3/2 orbital at the oxygen drip line, and hence, determine the size of the N=16 shell gap to be 4.86(13) MeV at this location. Also, the ground state mass measurement provided the one- and two-neutron separation energies for 25O. Each of these observables were compared to shell model calculations using various interactions. Curiously, the interaction which best reproduced the experimental data was the universal sd shell model which calculates a bound 26O ground state, contrary to experiment. The two excited states observed in 24O were also compared to a number of theoretical calculations. The best description of the data was found by a calculation which explicitly included a continuum d3/2 orbital into wave function. The N=16 shell gap was also determined from the two states to be 4.95(16) MeV, in excellent agreement with the 25O result (4.86(13) MeV). Finally, the energy of the first excited 2+ state observed in 24O was systematically compared with the same state in other nearby even-even nuclei. It was determined that 24O is in fact a doubly magic nucleus having a magic number of protons Z=8 and neutrons N=16, due to the relatively high energy of its 2+ excited state.
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Date Issued: 2009
Identifier: FSU_migr_etd-3990
Format: Thesis

Physics (22)	+ -
Mathematics (1)	+ -

Florida State University (23)	+ -
Department of Physics (22)	+ -
Rogachev, Grigory (22)	+ -
Volya, Alexander (9)	+ -
Humayun, Munir (5)	+ -

Capstick, Simon (4)	+ -
Schlottmann, Pedro (4)	+ -
Prosper, Harrison (3)	+ -
Safron, Sanford A. (3)	+ -
Tabor, Samuel L. (3)	+ -
Adams, Todd (2)	+ -
Aldrovandi, Ettore (2)	+ -
Bonesteel, Nicholas (2)	+ -
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