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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: 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: 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-Fold Angular Correlation Studies and the Terminating 12+ State of 24Mg.
Creator: Diffenderfer, Eric S., Wiedenhover, Ingo, Steinbock, Oliver, Bonesteel, Nicholas E., Tabor, Samuel L., Volya, Alexander S., Department of Physics, Florida State University
Abstract/Description: A new angular correlation analysis technique for assigning spins to alpha-unbound states of nuclei that feed alpha-unbound states of other nuclei is described. A kinematically complete experiment was performed to study the reaction ¹²C(¹⁶O, alpha)²⁴Mg*, populating alpha-unbound states of ²⁴Mg that decay to alpha-unbound states of ²⁰Ne, where all final state particles were detected. The new analysis technique was used to unambiguously identify the first Ipi = 12+ state of ²⁴Mg at 26.3 MeV. The...
Show moreA new angular correlation analysis technique for assigning spins to alpha-unbound states of nuclei that feed alpha-unbound states of other nuclei is described. A kinematically complete experiment was performed to study the reaction ¹²C(¹⁶O, alpha)²⁴Mg*, populating alpha-unbound states of ²⁴Mg that decay to alpha-unbound states of ²⁰Ne, where all final state particles were detected. The new analysis technique was used to unambiguously identify the first Ipi = 12+ state of ²⁴Mg at 26.3 MeV. The new 12+ state is discussed in the context of the collective and shell models.
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Date Issued: 2007
Identifier: FSU_migr_etd-0081
Format: Thesis

Title: Quantum Tunneling and Scattering of a Composite Object.
Creator: Ahsan, Naureen, Volya, Alexander, Aldrovandi, Ettore, Piekarewicz, Jorge, Crede, Volker, Xiong, Peng, Department of Physics, Florida State University
Abstract/Description: Reaction physics involving composite objects with internal degrees of freedom is an important subject since it is encountered in the context of nuclear processes like fusion, fission, particle decay, as well as many other branches of science. Quantum tunneling and scattering of a composite object are explored in this work. A few model Hamiltonians are chosen as examples where a two-particle system interacts, in one dimension, with a target that poses a delta-potential or an infinite wall...
Show moreReaction physics involving composite objects with internal degrees of freedom is an important subject since it is encountered in the context of nuclear processes like fusion, fission, particle decay, as well as many other branches of science. Quantum tunneling and scattering of a composite object are explored in this work. A few model Hamiltonians are chosen as examples where a two-particle system interacts, in one dimension, with a target that poses a delta-potential or an infinite wall potential. It is assumed that only one of the two components interacts with the target. The study includes the harmonic oscillator and the infinite square well as examples of intrinsic Hamiltonians that do not allow the projectile to break up, and a finite square well and a delta-well as examples of Hamiltonians that do. The Projection Method and the Variable Phase Method are applied with the aim of an exact solution to the relevant scattering problems. These methods are discussed in the context of the pertinent convergence issues related thereto, and of their applicability. Virtual excitations of the projectile into the classically forbidden energy-domain are found to play a dominant and non-perturbative role in shaping reaction observables, giving rise to enhanced or reduced tunneling in various situations. Cusps and discontinuities are found to appear in observables as manifestations of unitarity and redistribution of flux at the thresholds. The intrinsic structure gives rise to resonance-like behavior in tunneling probabilities. It is also shown that there is charge asymmetry in the scattering of a composite object, unlike in the case of a structureless particle.
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Date Issued: 2011
Identifier: FSU_migr_etd-0142
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: 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: Study of Grain Boundaries in Ca-Doped YbBCO Thin Films.
Creator: Li, Pei, Larbalestier, David, Brooks, James, Strouse, Geoffrey, Volya, Alexander, Jaroszynski, Jan, Department of Physics, Florida State University
Abstract/Description: While rare-earth-barium-copper-oxide (REBCO) coated conductor is a promising candidate as a practical superconductor for high magnetic field applications, its performance is largely limited by the depressed current-carrying capability of its grain boundaries (GBs). GBs with misorientation angles beyond relatively low values (3-5o) can substantially reduce the critical current density (Jc) of GBs, which makes the GB problem a critical one, since real, long-length coated conductors are made on...
Show moreWhile rare-earth-barium-copper-oxide (REBCO) coated conductor is a promising candidate as a practical superconductor for high magnetic field applications, its performance is largely limited by the depressed current-carrying capability of its grain boundaries (GBs). GBs with misorientation angles beyond relatively low values (3-5o) can substantially reduce the critical current density (Jc) of GBs, which makes the GB problem a critical one, since real, long-length coated conductors are made on polycrystalline substrates, where GBs are inevitable. The reduced critical current density of GBs has multiple origins, including the existence of non-superconducting dislocation cores, dislocation-strain driven high oxygen vacancies and lowered charge-carrier (hole) density, and excessive local charge due to deviations from stoichiometry that can only be poorly screened due to the low carrier density Since Ca-doping introduces extra holes into the REBCO compounds, it has long been considered a possible method to improve GB transparency. The positive effect of Ca-doping has been verified by a series of studies. Later detailed microstructural study showed that the underlying reason for improved GB properties is not simply due to a uniform Ca-doping because Ca was found to concentrate preferentially at GBs. Furthermore, the Ca distribution along and across the GB is highly non-uniform, especially for low angle grain boundaries that are critical in providing the high-Jc current path. A segregation model was proposed to explain the observed complex GB Ca distribution to dislocation cores and channels characteristic of such low angle grain boundaries (LAGB). This model shows that Ca segregation is driven by the combined effects of local strain and local charge at the grain boundary. This thesis work presents a systematic study of GBs in Ca-doped YbBCO thin films. While a number of works have been done on GBs in Ca-doped YBCO films, this work significantly expands understanding of doped GBs in following aspects. First, the strain and charge model developed in our group predicts a stronger segregation in Ca-doped REBCO for RE elements smaller than Y. We chose YbBCO because Yb is the smallest RE ion possible in REBCO. Second, previous work mainly focused on evaluating the GB properties at high temperatures in the vicinity of 60-80K. This work expands the study of Ca-doped GBs into the low temperature (4-30 K) regime relevant to the growing interest in using REBCO coated conductors for magnetic field applications. Other variables that also affect GB transparency but have been less studied before are also included in this study. These variables include the applied field orientation and the intra-grain oxygen content level. Third, this study uses Low Temperature Scanning Laser Microscopy (LTSLM) to study GB properties. LTSLM is a tool that detects the local electric field, a rather powerful tool for observing where the dominant source of E occurs in a thin film track. Fourth, thin film samples used in this study are grown using carefully optimized conditions. Effects of major parameters are studied systematically. Collectively this new study allows us to more completely evaluate the effect of Ca-doping in samples with both optimized and un-optimized intra-grain properties. The comparison of intra-grain and inter-grain Jc in Ca-doped YbBCO films shows that GBs become more transparent with Ca-doping at high temperatures (T=0.85Tc). For YbBCO, the optimum Ca-doping level is found to be lower than that for YBCO, a result consistent with the charge-segregation model. On the other hand, the beneficial effect of Ca-doping decreases rapidly as the temperature is lowered, becoming then of only marginal value. This temperature dependence is also analyzed in the framework of segregation model, which predicts a depressed segregation in the channels between dislocation where supercurrent is expected to flow. Thus the channels benefit from having a higher local Tc, the effect of such a Tc enhancement being naturally most pronounced at high temperatures. Using the LTSLM to explicitly observe the local electric field, we can for the first time unambiguously distinguish intra-grain and inter-grain Jc These results show that though GB dislocations reduce the current-carrying cross section, they can also act as pinning centers. When the direction of the applied field coincides with the orientation of the GB dislocations, which occurs for H parallel to the c-axis and the perpendicular to the film plane, the GB pinning strength is stronger than the intra-grain pinning due to naturally-occurring defects. More interestingly, depending on the strength of the intra-grain pinning, pinning by GB dislocations can result in the interesting condition of intra-grain Jc being greater than inter-grain Jc. Implied crossovers of this sort have been inferred before but the LTSLM has allowed us to provide the first experimental confirmation of this interesting state. However, pinning by GB dislocations is strongly anisotropic and becomes very weak in parallel field. The optimized film growth conditions for YbBCO are different from those needed for YBCO. YbBCO growth generally requires higher oxygen partial pressure and lower temperature due to its lower melting point. Dependencies of film morphology on different Ca-doping levels and substrate types are also found. An important conclusion of this work is that Ca-doping does not effectively improve GB properties at low temperature, even though it can do so at high temperatures near Tc. Nevertheless, this does not prove that the problem of GB limitation of the critical current density cannot be resolved. In the final part of the thesis, through comparison with literature, we discuss how some naturally-occurring GBs (usually meandered GBs of mixed type, far from the highly idealized [001] tilt geometry studied here) can be better than these artificial straight GBs typical of those grown by PLD, which dominate most present studies of GBs. A concluding recommendation is that future GB studies should focus more on real GBs.
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Date Issued: 2013
Identifier: FSU_migr_etd-7466
Format: Thesis

Title: Experimental Investigations on the Nuclear Structure of the Neutron-Rich Nuclides ⁴⁴S and ²⁰O.
Creator: Santiago-Gonzalez, Daniel, Wiedenhoever, Ingo, Fuelberg, Henry, Bonesteel, Nicholas E., Cottle, Paul D., Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: Experimental results of two independent studies on the nuclear structure of the neutron-rich nuclei 44S and 20O are presented. A short introduction on the context of these studies within nuclear physics is given in chapter 1. Because of the fundamental differences between the experiments and analysis techniques the investigations have been separated in two chapters. The investigation of 44S, extracted via the two-proton knockout reaction from 46Ar with intermediate beam energy, is presented...
Show moreExperimental results of two independent studies on the nuclear structure of the neutron-rich nuclei 44S and 20O are presented. A short introduction on the context of these studies within nuclear physics is given in chapter 1. Because of the fundamental differences between the experiments and analysis techniques the investigations have been separated in two chapters. The investigation of 44S, extracted via the two-proton knockout reaction from 46Ar with intermediate beam energy, is presented in chapter 2. Four new excited states are identified, of which the first 4+state presents evidence of deformation, as suggested by line-shape simulations of the detected γ rays. This is also indicated by a shell-model calculation, where the deformation of the first 4+state originates in a neutron particle-hole configuration which is fundamentally different from the "intruder"configuration producing the ground state deformation and from the configuration describing the relatively long-lived isomeric 0+state. Consequently, not three coexisting shapes, rather three coexisting configurations are found in 44S, corresponding to zero, one and two neutron particle-hole excitations. In chapter 3, results from the analysis of the 19O(d,p)20O reaction in inverse kinematics using the active gas target detector array ANASEN are presented. In order to study the location and fragmentation of the d3/2 orbital in 20O, a beam of the short-lived 19O was produced at the RESOLUT radioactive beam facility of the Florida State University. The ejected protons from the (d,p) reaction were measured with large solid angle coverage and for beam energies between 2.2 and 4.3 MeV/A. Data from the 17O(d,p)18O reaction was acquired to verify our experimental methods and analysis techniques.
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Date Issued: 2013
Identifier: FSU_migr_etd-8631
Format: Thesis

Title: Hadrons with Two Heavy Quarks: Symmetries, Systematics, and Spectroscopy.
Creator: Eakins, Benjamin James, Roberts, Winston, Steinbock, Oliver, Crede, Volker, Owens, Joseph, Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: We explore the symmetries and systematics of the mass spectrum of hadrons with two heavy quarks. We also apply these symmetries to the strong decays of baryons with two heavy quarks. We explore the ramifications of a proposed symmetry that relates heavy diquarks to doubly heavy mesons. We present a method for determining how the excitation energy of a system containing two heavy quarks will scale as one changes the strength of the interactions and the reduced mass of the system. We use this...
Show moreWe explore the symmetries and systematics of the mass spectrum of hadrons with two heavy quarks. We also apply these symmetries to the strong decays of baryons with two heavy quarks. We explore the ramifications of a proposed symmetry that relates heavy diquarks to doubly heavy mesons. We present a method for determining how the excitation energy of a system containing two heavy quarks will scale as one changes the strength of the interactions and the reduced mass of the system. We use this to derive consequences of the heavy diquark-doubly heavy meson symmetry. We compare these consequences to the results of a quark model as well as the experimental data for doubly heavy mesons. We discuss the extension of the superflavor symmetry of Doubly Heavy Baryons (DHBs) to states which contain an excited heavy diquark, and we examine some of the consequences of this symmetry for the spectroscopy of DHBs and heavy mesons. Subsequently, we derive the consequences of this Heavy Diquark Symmetry (HDS) for the decay widths of DHBs. We compare these symmetry constraints to results from the 3P0 model for strong decays. The quark model we implement was not constructed with these symmetries and contains interactions which explicitly break HDS. Nevertheless these symmetries emerge. We argue that the 3P0 model and any other model for strong transitions which employs a spectator assumption explicitly respects HDS. We also explore the possibility of treating the strange quark as a heavy quark and apply these ideas to Ξ, Ξc, and Ξb baryons.
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Date Issued: 2013
Identifier: FSU_migr_etd-8549
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: Structural Changes in ¹⁶¹Tm and ¹¹²Sn as a Function of Increasing Angular Momentum.
Creator: Teal, Charles, Riley, Mark A., Tabor, Samuel L., Volya, Alexander, Ng, Hon-Kie, Department of Physics, Florida State University
Abstract/Description: This dissertation presents the results from three major experiments to investigate angular momentum induced structural or shape changes in A~160 and A~110 atomic nuclei. The basic question we are trying to answer is "How do the excitation modes and deformation of nuclei change with increasing angular momentum or spin?" The First experiment was a high-spin study of 161Tm which lies in the deformed region of the rare-earth region. The second and third experiments have allowed a comprehensive...
Show moreThis dissertation presents the results from three major experiments to investigate angular momentum induced structural or shape changes in A~160 and A~110 atomic nuclei. The basic question we are trying to answer is "How do the excitation modes and deformation of nuclei change with increasing angular momentum or spin?" The First experiment was a high-spin study of 161Tm which lies in the deformed region of the rare-earth region. The second and third experiments have allowed a comprehensive study of the 112Sn nucleus which is close to spherical at low angular momentum values. The high-spin structure of both nuclei were observed using the Gammasphere spectrometer located at Argonne National Laboratory. The low-spin structure of 112Sn was observed using the John D. Fox Superconducting Linear Accelerator Laboratory located at Florida State University (FSU) utilizing the FSU-Pitt Gamma-Ray Array. High-spin states in 161Tm were studied by the reaction 128Te(37Cl, 4n) at a beam energy of 170 MeV. Two rotational bands with high moments of inertia were discovered, one assigned to 160Tm, while the other tentatively assigned to 161Tm. These sequences display features similar to rotational sequences observed in neighboring Er, Tm, Yb, and Lu nuclei which have been discussed in terms of triaxial strongly deformed structures. Cranked Nilsson Strutinsky calculations have been performed that predict well-deformed triaxial shapes at high spin in 160,161Tm. Additionally, significant changes have been made to the normal deformed energy level diagram or level scheme of 161Tm. The changes presented in this dissertation solve the long standing problem of the missing alignment gain of the 7/2+[404] band. At the highest spins evidence is presented for the First observation of the rotational alignment of a pair of h 11/2 protons in this nucleus. A comprehensive energy level diagram of 112Sn is presented. High-spin states (the highest observed so far in any Sn isotope) were populated using the reaction 70Zn(48Ca, 6n) at a beam energy of 202 MeV and utilized the Gammasphere spectrometer. In addition a complementary experiment was performed at FSU using the reaction 100Mo(16O, 4n) at a beam energy of 72 MeV. Combining these data allowed three new additional rotational bands to be added to the level scheme up to a spin of 38 hbar, and many new low-spin states were added compared to previously known work.
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Date Issued: 2009
Identifier: FSU_migr_etd-1640
Format: Thesis

Title: Rare Exclusive Dileptonic and Radiative Decays of ΛB Baryons in Aquark Model.
Creator: Mott, Lonnie J., Roberts, Winston, Ruse, Michael, Volya, Alexander, Crede, Volker, Owens, Joseph, Department of Physics, Florida State University
Abstract/Description: Hadronic form factors for the rare weak transitions Λb→Λ(*) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Both...
Show moreHadronic form factors for the rare weak transitions Λb→Λ(*) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Both sets of form factors are found to satisfy the relationships expecetd from the heavy quark effective theory (HQET). Differential decay rates, branching ratios and forward-backward asymmetries (FBAs) are calculated for the dileptonic decays Λb→Λ(*)ℓ+ℓ , for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. It is found that in the MCN model the Λ(1600) mode is the dominant mode in the μ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable branching ratio to that of the ground state in the μ channel. It has been found that the FBAs for decays to Λ(1115), Λ(1600) and Λ(1405) are less sensitive to the form of the form factors in certain kinematic regions.
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Date Issued: 2011
Identifier: FSU_migr_etd-2223
Format: Thesis

Title: Relativistic Mean Field Models for Finite Nuclei and Neutron Stars.
Creator: Chen, Wei-Chia, Piekarewicz, Jorge, Kopriva, David A., Volya, Alexander, Credé, Volker, Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of...
Show moreChen, Wei-Chia, Piekarewicz, Jorge, Kopriva, David A., Volya, Alexander, Credé, Volker, Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: In this dissertation we have created theoretical models for finite nuclei, nuclear matter, and neutron stars within the framework of relativistic mean field (RMF) theory, and we have used these models to investigate the elusive isovector sector and related physics, in particular, the neutron-skin thickness of heavy nuclei, the nuclear symmetry energy, and the properties of neutron stars. To build RMF models that incorporate collective excitations in finite nuclei in addition to their ground...
Show moreIn this dissertation we have created theoretical models for finite nuclei, nuclear matter, and neutron stars within the framework of relativistic mean field (RMF) theory, and we have used these models to investigate the elusive isovector sector and related physics, in particular, the neutron-skin thickness of heavy nuclei, the nuclear symmetry energy, and the properties of neutron stars. To build RMF models that incorporate collective excitations in finite nuclei in addition to their ground-state properties, we have extended the non-relativistic sum rule approach to the relativistic domain. This allows an efficient estimate of giant monopole energies. Moreover, we have combined an exact shell-model-like approach with the mean-field calculation to describe pairing correlations in open-shell nuclei. All the ingredients were then put together to establish the calibration scheme. We have also extended the transformation between model parameters and pseudo data of nuclear matter within the RMF context. Performing calibration in this pseudo data space can not only facilitate the searching algorithm but also make the pseudo data genuine model predictions. This calibration scheme is also supplemented by a covariance analysis enabling us to extract the information content of a model, including theoretical uncertainties and correlation coefficients. A series of RMF models subject to the same isoscalar constraints but one differing isovector assumption were then created using this calibration scheme. By comparing their predictions of the nuclear matter equation of state to both experimental and theoretical constraints, we found that a small neutron skin of about 0.16 fm in Pb208 is favored, indicating that the symmetry energy should be soft. To obtain stronger evidence, we proceeded to examine the evolution of the isotopic chains in both oxygen and calcium. Again, it was found that the model with such small neutron skin and soft symmetry energy can best describe both isotopic chains, and the resultant values of the neutron-skin thickness and the symmetry energy are consistent with most current constraints. Finally, we addressed the recent tension between dense matter theory and the observation of neutron stars with rather small stellar radii. By employing Lindblom's algorithm, we were able to derive the underlying equation of state for assumed mass-radius relations having the "common radius" feature followed by recent analyses. We found that, in order to support two-solar-mass neutron stars, the typical stellar radii must be greater than 10.7 km—barely compatible with recent analyses—to prevent the underlying equation of state from violating causality.
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Date Issued: 2015
Identifier: FSU_2015fall_Chen_fsu_0071E_12869
Format: Thesis

Title: Experimental Techniques for Rare Isotope Beam Experiments, and a Study of the Breakout from the Hot CNO-Cycle Through the 19Ne(P,γ)20Na Reaction.
Creator: Belarge, Joseph, Wiedenhöver, Ingo, Plewa, Tomasz, Volya, Alexander, Cottle, Paul D. (Paul Davis), Bonesteel, N. E., Florida State University, College of Arts and Sciences,...
Show moreBelarge, Joseph, Wiedenhöver, Ingo, Plewa, Tomasz, Volya, Alexander, Cottle, Paul D. (Paul Davis), Bonesteel, N. E., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The study of exotic nuclei, and their implication for Astrophysics have become a driving force in low-energy nuclear science, nationally recognized by the construction of the Facility for Rare Isotope Beams (FRIB) laboratory. To maximize the potential provided by beams of exotic nuclei, novel detector systems and analysis techniques must be developed, a current focus of the Florida State University (FSU) group. Experimental results from commissioning experiments with the ANASEN and RESONEUT...
Show moreThe study of exotic nuclei, and their implication for Astrophysics have become a driving force in low-energy nuclear science, nationally recognized by the construction of the Facility for Rare Isotope Beams (FRIB) laboratory. To maximize the potential provided by beams of exotic nuclei, novel detector systems and analysis techniques must be developed, a current focus of the Florida State University (FSU) group. Experimental results from commissioning experiments with the ANASEN and RESONEUT detectors at FSU are presented. The neutron deficient ⁹C nucleus was studied through the ⁸B+p resonant elastic scattering reaction. The experiment was conducted during the commissioning of the ANASEN detector in 2012. Due to cryogenics problems, the experiment was stopped prematurely. Through analysis of the partial data set, it was shown that a full analysis could be performed, on complete data sets, for future proton resonance elastic scattering experiments. Results from the ¹⁹O(d,p)²⁰O experiment, also conducted as a part of the commissioning of the ANASEN detector at FSU, will be presented. It was found that heavy ion recoils from the (d,p) reactions were reaching the active zone of the proportional counter, and subsequently producing UV-light radiation that degraded the proportional counter performance. This discovery lead to a re-design of the proportional counter, which is currently being constructed by the ANASEN group at Louisiana State University. An experimental study of low-lying proton resonances in ²⁰Na was performed using the proton transfer ¹⁹Ne(d,n)²⁰Na(p) reaction as part of the commissioning campaign of experiments with the RESONEUT detector. This reaction is comparable to the direct proton capture, ¹⁹Ne(p,ɣ)²⁰Na, which is of astrophysical significance in the breakout from the Hot CNO-cycle. Using protons detected from the decay of ²⁰Na, three resonances were observed, at energies of 0.44 MeV, 0.66 MeV, and 0.82 MeV above the proton threshold. The resonance strengths were determined, and the subsequent ¹⁹Ne(p,ɣ)²⁰Na stellar reaction rate was calculated. A discussion of this reaction rate in the context of the breakout from the Hot CNO-cycle is presented.
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Date Issued: 2015
Identifier: FSU_2015fall_Belarge_fsu_0071E_12826
Format: Thesis

Title: Clustering in Light Nuclei with Configuration Interaction Approaches.
Creator: Kravvaris, Konstantinos, Volya, Alexander, Kopriva, David A., Weidenhoever, Ingo Ludwing M., Capstick, Simon, Reina, Laura, Florida State University, College of Arts and...
Show moreKravvaris, Konstantinos, Volya, Alexander, Kopriva, David A., Weidenhoever, Ingo Ludwing M., Capstick, Simon, Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The formation of sub-structures within an atomic nucleus, appropriately termed nuclear clustering, is one of the core questions of nuclear many-body physics. In this thesis, we put forward a new method for the study of nuclear clustering relying on the completely microscopic Configuration Interaction approach. We construct reaction cluster channels in a Harmonic Oscillator many-body basis that respect the symmetries of the Hamiltonian, are fully antisymmetrized, and carry a separable and...
Show moreThe formation of sub-structures within an atomic nucleus, appropriately termed nuclear clustering, is one of the core questions of nuclear many-body physics. In this thesis, we put forward a new method for the study of nuclear clustering relying on the completely microscopic Configuration Interaction approach. We construct reaction cluster channels in a Harmonic Oscillator many-body basis that respect the symmetries of the Hamiltonian, are fully antisymmetrized, and carry a separable and controlled Center of Mass component. Such channels are then used to explore cluster signatures in Configuration Interaction many-body wavefunctions. The Resonating Group Method is then applied, utilizing the reaction channels as a basis to capture the essential cluster characteristics of the system. We investigate the emergence of nuclear clustering in 2α, 2α+n, 2α+2n and 3α systems using a No Core Shell Model approach from first principles, and traditional Shell Model studies of clustering in heavier nuclei.
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Date Issued: 2018
Identifier: 2018_Su_Kravvaris_fsu_0071E_14611
Format: Thesis

Title: Study of the ¹⁸Ne(α, p)²¹Na Reaction with ANASEN and Its Significance in the Breakout from the Hot-CNO Cycle.
Creator: Anastasiou, Maria, Weidenhoever, Ingo Ludwing M., Albrecht-Schmitt, Thomas E., Huffenberger, Kevin M., Riley, Mark A., Volya, Alexander, Florida State University, College of...
Show moreAnastasiou, Maria, Weidenhoever, Ingo Ludwing M., Albrecht-Schmitt, Thomas E., Huffenberger, Kevin M., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: 18Ne(α,p)21Na reaction is one of the reactions providing a pathway for breakout from the hot CNO cycles to the rp-process in Type I X-ray bursts. The actual conditions under which the breakout occurs depend critically on the thermonuclear reaction rate. This rate has not been sufficiently determined yet over the temperatures present under X-ray burst conditions. We study the direct 18Ne(α,p)21Na reaction with the Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN), using...
Show more18Ne(α,p)21Na reaction is one of the reactions providing a pathway for breakout from the hot CNO cycles to the rp-process in Type I X-ray bursts. The actual conditions under which the breakout occurs depend critically on the thermonuclear reaction rate. This rate has not been sufficiently determined yet over the temperatures present under X-ray burst conditions. We study the direct 18Ne(α,p)21Na reaction with the Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN), using a helium gas target and an 18Ne radioactive beam. ANASEN is an active gas target detection system that uses tracking of the light reaction products in conjunction with energy measurements in Silicon detectors. The position information required for the tracking is provided by a Multi-Anode Proportional Counter in combination with the Silicon detectors. From the tracking the location of the interaction is obtained, which is directly correlated to the energy of the beam particle. While the beam is losing energy while traveling in the gas target, a wide range of reaction energies can be measured simultaneously and without changing the accelerator parameters. The difficulty of this particular experiment lies on the fact that we are trying to detect one single proton from the 18Ne(α,p)21Na reaction per event. Proton background is caused by fusion evaporation reactions of the 18Ne with the CO2 quenching gas added on the 4He target gas. For the first time in the ANASEN setup, we have implemented a cylindrical Ion Chamber for coincident heavy-recoil detection, which was successfully used to suppress such background events. The 18Ne(α,p)21Na cross section was measured in the context of this dissertation. The experiment allows for a determination of the cross section down to reaction energies ∼2 MeV in the center-of- mass system. The results are compared to the previous (α,p) reaction measurement, as well as to the time-inverse (p,α) reaction measurement and theoretically calculated cross sections. Our work resolves significant inconsistencies between the experimental information on the 18Ne(α,p) reaction and the indirect information available, giving larger credence to the use of such indirect methods. At the same time, more sensitive measurements of the 18Ne(α,p) reaction are needed to provide experimental information on the reaction energies below 2 MeV, most important for the break-out phase of X-ray bursts. The experimental techniques developed in this work would have to be applied to a beam of 18Ne with significantly higher quality and intensity.
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Date Issued: 2019
Identifier: 2019_Summer_Anastasiou_fsu_0071E_15357
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: Study of Spin Dynamics by Means of On-Chip SQUIDs.
Creator: Chen, Lei, Chiorescu, Irinel, Zhang, Chuck, Bonesteel, Nicholas, Brooks, James, Volya, Alexander, Xiong, Peng, Department of Physics, Florida State University
Abstract/Description: We developed an on-chip SQUID (Superconducting Quantum Interference Device) measurement technique to study spin dynamics in Single Molecular Magnets (SMMs) and other spin systems. SMMs systems are thought as potential qubit candidates, due to their quantum nature and the possibility to construct superposition of molecular spin states. If spins are enough diluted to minimize dipolar interactions and therefore increase decoherence time, the information carried by each molecular qubit can be...
Show moreWe developed an on-chip SQUID (Superconducting Quantum Interference Device) measurement technique to study spin dynamics in Single Molecular Magnets (SMMs) and other spin systems. SMMs systems are thought as potential qubit candidates, due to their quantum nature and the possibility to construct superposition of molecular spin states. If spins are enough diluted to minimize dipolar interactions and therefore increase decoherence time, the information carried by each molecular qubit can be preserved for sufficiently long times and measured in a single crystal sample. The SQUID, as the most sensitive magnetometer, is used to investigate the magnetization of macroscopic samples containing the spins under study. Traditional SQUID equipment performs magnetization measurements by shielding the SQUID from external magnetic fields, since a high field would destroy its superconductivity. The SQUID-sample coupling in such arrangement is done by a pick-up coil, at the expense of sensitivity. In contrast, the setup implemented by us at NHMFL, uses an ultra thin (~ 3 nm in thickness) niobium SQUID with nano-bridge junctions. Such a SQUID can preserve its superconductivity up to a very high field, as long as the field is perfectly aligned in the film's plane. We conducted experiments at low temperature, in a 3He/4He dilution refrigerator. The measured SQUID switching current is periodically modulated by the magnetic flux, generated only by the studied sample if the field is perfectly aligned with the SQUID plane. Through an initial calibration process, the vectorial magnetic field is aligned with the SQUID plane, for fields up to the maximum field achievable in this setup (7~Tesla). A superconducting feedback coil, placed above the SQUID, is used to compensate the magnetic flux variation caused by the sample. The feedback coil (and its current) can therefore relay information about the sample's magnetization. The control of the experimental setup is accomplished through Labview programs and is ready to incorporate spin excitation done by microwave or laser pulses. We have investigated the molecular paddle-wheel complex of Ru2+5. This molecule shows an enhanced magnetic hysteresis, with a valley of negative differential susceptibility, due to an abrupt spin reversal followed by a phonon avalanche. We simulated the process using the phonon bottleneck effect. Another theoretical model is developed to describe a blending of non-adiabatic spin rotation and the phonon bottleneck effect. Also, using our on-chip SQUID technique, we have observed a spin transition at 1.2K in Gd3N@C80, which is caused by the charge transfer between one of the Gd ions and the carbon cage. In another molecular magnet, Mn12-tBuAc, the influence of the transverse field on the tunneling probability is studied in detail and compared to numerical calculations which we performed using a diagonalization technique.
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Date Issued: 2010
Identifier: FSU_migr_etd-3837
Format: Thesis

Title: 21F Higher Spin Structures in ²⁵Na and ²¹F.
Creator: Vonmoss, Justin Matthew, Tabor, Samuel Lynn, Plewa, Tomasz, Bonesteel, N. E., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences,...
Show moreVonmoss, Justin Matthew, Tabor, Samuel Lynn, Plewa, Tomasz, Bonesteel, N. E., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Two experiments have been performed at Florida State University using the FSU Compton- Suppressed HPGe Array and associated particle telescope. The first experiment used the 9Be(18O, pnγ) reaction at 35 MeV to study the nuclear structure of 25Na. The second experiment used the 9Be(14C, pnγ) reaction at 30, 35, and 45 MeV to study the nuclear structure of 21F. Particle-γ and particle-γ-γ coincidence data were analyzed resulting in the discovery of several new gamma rays and states for both...
Show moreTwo experiments have been performed at Florida State University using the FSU Compton- Suppressed HPGe Array and associated particle telescope. The first experiment used the 9Be(18O, pnγ) reaction at 35 MeV to study the nuclear structure of 25Na. The second experiment used the 9Be(14C, pnγ) reaction at 30, 35, and 45 MeV to study the nuclear structure of 21F. Particle-γ and particle-γ-γ coincidence data were analyzed resulting in the discovery of several new gamma rays and states for both nuclei; this includes resolving a doublet in 25Na which has caused significant confusion in previous works. Angular distributions, lifetimes, and transition strengths have been measured for both nuclei. Shell model calculations have been performed using the USDA and WBP interactions; in addition to 0-particle-0-hole states, 1p1h states have been calculated for both nuclei and, in 21F, 2p2h states have been calculated as well.
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Date Issued: 2015
Identifier: FSU_migr_etd-9478
Format: Thesis

Title: A Configuration Space Monte Carlo Algorithm for Solving the Nuclear Pairing Problem.
Creator: Lingle, Mark, Volya, Alexander, Kopriva, David A., Capstick, Simon, Wiedenhöver, Ingo, Manousakis, Efstratios, Florida State University, College of Arts and Sciences, Department...
Show moreLingle, Mark, Volya, Alexander, Kopriva, David A., Capstick, Simon, Wiedenhöver, Ingo, Manousakis, Efstratios, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Nuclear pairing correlations using Quantum Monte Carlo are studied in this dissertation. We start by defining the nuclear pairing problem and discussing several historical methods developed to solve this problem, paying special attention to the applicability of such methods. A numerical example discussing pairing correlations in several calcium isotopes using the BCS and Exact Pairing solutions are presented. The ground state energies, correlation energies, and occupation numbers are compared...
Show moreNuclear pairing correlations using Quantum Monte Carlo are studied in this dissertation. We start by defining the nuclear pairing problem and discussing several historical methods developed to solve this problem, paying special attention to the applicability of such methods. A numerical example discussing pairing correlations in several calcium isotopes using the BCS and Exact Pairing solutions are presented. The ground state energies, correlation energies, and occupation numbers are compared to determine the applicability of each approach to realistic cases. Next we discuss some generalities related to the theory of Markov Chains and Quantum Monte Carlo in regards to nuclear structure. Finally we present our configuration space Monte Carlo algorithm starting from a discussion of a path integral approach by the authors [2, 3]. Some general features of the Pairing Hamiltonian that boost the effectiveness of a configuration space Monte Carlo approach are mentioned. The full details of our method are presented and special attention is paid to convergence and error control. We present a series of examples illustrating the effectiveness of our approach. These include situations with non-constant pairing strengths, limits when pairing correlations are weak, the computation of excited states, and problems when the relevant configuration space is large. We conclude with a chapter examining some of the effects of continuum states in 24O.
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Date Issued: 2015
Identifier: FSU_migr_etd-9383
Format: Thesis

Title: Detailed Spectroscopic Study of the High-Spin Structures in ¹⁶⁸,¹⁶⁹,¹⁷⁰,¹⁷¹W and ¹⁹⁶Hg and a Systematic Examination of Nuclear Structure Behavior of Rare-Earth Isotopes in the A≈160−180 Region.
Creator: Miller, Scott, Riley, Mark A., Plewa, Tomasz, Tabor, Samuel Lynn, Volya, Alexander, Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of...
Show moreMiller, Scott, Riley, Mark A., Plewa, Tomasz, Tabor, Samuel Lynn, Volya, Alexander, Van Winkle, David H., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: High-spin states in the rare-earth nuclei $^{168,169,170,171}$W (Z=74) were produced via fusion evaporation reactions carried out at Argonne National Laboratory (ANL) using the Argonne Tandem Linear Accelerator System (ATLAS). An additional experiment probing the high-spin structure of $^{196}$Hg was conducted at the Florida State University (FSU) tandem-linac facility. The $\gamma$ rays from these experiments were detected and recorded using the Gammasphere spectrometer at ANL and the FSU $...
Show moreHigh-spin states in the rare-earth nuclei $^{168,169,170,171}$W (Z=74) were produced via fusion evaporation reactions carried out at Argonne National Laboratory (ANL) using the Argonne Tandem Linear Accelerator System (ATLAS). An additional experiment probing the high-spin structure of $^{196}$Hg was conducted at the Florida State University (FSU) tandem-linac facility. The $\gamma$ rays from these experiments were detected and recorded using the Gammasphere spectrometer at ANL and the FSU $\gamma$-ray Array system, respectively. As a result of the analysis, well over 500 new decay transitions and over 300 new energy levels were observed in these nuclei. Whenever possible, the intensities, angular correlations, spins, parities, and rotational behaviors of these newly discovered states were analyzed. Theoretical analysis of the observed structures, including spin, parity, and quasiparticle configurations, was carried out within the framework of the Cranked Shell Model (CSM). Due in part to results obtained from the aforementioned analysis, new systematic data in the A $\approx$ 160 region is also discussed, with an emphasis on the role that pair-blocking effects play during the rotation of the nucleus.
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Date Issued: 2015
Identifier: FSU_migr_etd-9410
Format: Thesis

Title: DC Transport in Two-Dimensional Electron Systems under Strong Microwave Illumination.
Creator: Chakraborty, Shantanu, Engel, Lloyd W., Chiorescu, Irinel, Dalal, Naresh S., Cao, Jianming, Bonesteel, N. E., Volya, Alexander, Florida State University, College of Art and...
Show moreChakraborty, Shantanu, Engel, Lloyd W., Chiorescu, Irinel, Dalal, Naresh S., Cao, Jianming, Bonesteel, N. E., Volya, Alexander, Florida State University, College of Art and Sciences, Department of Physics
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Abstract/Description: At low temperature (T) and weak magnetic field (B), two dimensional electron systems (2DES) can exhibit strong 1/B-periodic resistance oscillations on application of sufficiently strong microwave radiation. These oscillations are known as microwave induced resistance oscillations (MIROs), MIROs appearing near cyclotron resonance (CR) and its harmonics involve single photon processes and are called integer MIROs while the oscillations near CR subharmonics require multiphoton processes and are...
Show moreAt low temperature (T) and weak magnetic field (B), two dimensional electron systems (2DES) can exhibit strong 1/B-periodic resistance oscillations on application of sufficiently strong microwave radiation. These oscillations are known as microwave induced resistance oscillations (MIROs), MIROs appearing near cyclotron resonance (CR) and its harmonics involve single photon processes and are called integer MIROs while the oscillations near CR subharmonics require multiphoton processes and are called fractional MIROs. Similar strong 1/B periodic resistance oscillations can occur due to strong dc current, and are known as Hall-field resistance oscillations (HIROs). Oscillations also occur for a combination of microwave radiation and strong dc current. In one prominent theory of MIROs, known as the displacement model , electrons make impurity-assisted transitions into higher or lower Landau levels by absorbing or emitting one or more (N) photons. In the presence of combined strong dc current and microwave radiation, electrons make transitions between Landau levels by absorbing or emitting photons followed by a space transition along the applied dc bias. The object of the dissertation is to explore how the different resistance oscillations are affected by strong microwave radiation when multiphoton processes are relevant. We used a coplanar waveguide (CPW) structure deposited on the sample, as opposed to simply placing the sample near the termination of a waveguide as is more the usual practice in this field. The CPW allows us to estimate the AC electric field (E_{AC}) at the sample. In much of the work presented in this thesis we find that higher $N$ processes supersede the competing lower N processes as microwave power is increased. We show this in the presence and in the absence of a strong dc electric field. Finally, we look at the temperature evolution of fractional MIROs to compare the origin of the fractional MIROs with that of integer MIROs.
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Date Issued: 2014
Identifier: FSU_migr_etd-9155
Format: Thesis

Title: Ultrafast Dynamics in Laser-Induced Warm Dense Matter and Quantum Dots.
Creator: Zhou, Jun, Cao, Jianming, Yang, Wei, Bonesteel, N. E., Volya, Alexander, Xiong, Peng, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: The dissertation presents the recent development of the 3rd generation femtosecond electron diffractometer in Professor Jim Cao's group. Two techniques, femtosecond electron shadow imaging and deflectometry (FESID) and femtosecond electron diffraction (FED), were developed and applied to study ultrafast dynamics in laser-induced warm dense matter and quantum dots in real time. FESID provides both a global view and local prospect of the transient electric field, associated with laser-induced...
Show moreThe dissertation presents the recent development of the 3rd generation femtosecond electron diffractometer in Professor Jim Cao's group. Two techniques, femtosecond electron shadow imaging and deflectometry (FESID) and femtosecond electron diffraction (FED), were developed and applied to study ultrafast dynamics in laser-induced warm dense matter and quantum dots in real time. FESID provides both a global view and local prospect of the transient electric field, associated with laser-induced electron emission. The research activities cover two main subjects: dynamics of ejected electron expansion from warm dense nanofilms and hyperthermal electron transport mechanisms in warm dense nanofilms. With FED, we measure laser-induced ultrafast structural dynamics of 5-nm PbSe quantum dots (QDs) in real time. In the first project, we conduct ultrafast electron shadow imaging and deflection measurements of the laser-produced warm dense copper nanofilm. The results show that a significant amount of electrons is ejected from the nanofilm , forming electron clouds of hundreds of microns on both sides of the pumped film. Furthermore, even for a thin 30-nm copper film, we find that the electron clouds develop asymmetry between the pumped front side and the rear side at the pump fuence of 4.5 J/cm2. The possible mechanisms leading to this ejected charge asymmetry and its implication are discussed. Next, we report a systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under the high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region followed by the formation of hemispherical clouds of electrons on both sides of the film, which escape into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We also develop a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud. In the second project, we investigate hyperthermal electron transport by single-shot measurements of warm dense gold and aluminum nanofilms using ultrafast electron shadow imaging and deflectometry. The results show a clear fluence limit of 0.26 J/cm2 and 0.83 J/cm2 for ballistic transport of nonthermal electrons for both two metals, respectively. This nonuniform heating is attributed to limited number of ballistic electrons. In addition, we have measured the ultrafast heating induced structural dynamics in 5-nm PbSe QDs in real time with Femtosecond electron diffraction. We observe the picosecond intraband relaxation in PbSe QDs, and tens-of-picosecond heat diffuse process from PbSe QDs to Si3N4 substrate. Except confinement-enhanced Auger-type process, the surface atoms and ligands may play a major role for the fast intraband relaxation.
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Date Issued: 2015
Identifier: FSU_migr_etd-9506
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: Dark Matter Detection in Supersymmetric Models with Non-Universal Gaugino Masses.
Creator: Park, Eun-Kyung, Baer, Howard, Aldrovandi, Ettore, Reina, Laura, Prosper, Harrison, Volya, Alexander, Department of Physics, Florida State University
Abstract/Description: SUSY is one of the most promising new physics ideas, and will soon be tested at high energy accelerators like the CERN LHC. Moreover SUSY provides a good candidate for cold dark matter (CDM). In this dissertation, we investigated phenomenology of SUSY models with non-universal gaugino masses (NUGM) at colliding experiments using event generators such as ISAJET and examined direct and indirect detection rates of relic neutralino CDM in the universe. The motivation of these models is that in...
Show moreSUSY is one of the most promising new physics ideas, and will soon be tested at high energy accelerators like the CERN LHC. Moreover SUSY provides a good candidate for cold dark matter (CDM). In this dissertation, we investigated phenomenology of SUSY models with non-universal gaugino masses (NUGM) at colliding experiments using event generators such as ISAJET and examined direct and indirect detection rates of relic neutralino CDM in the universe. The motivation of these models is that in most of mSUGRA parameter space, the relic density $Omega_{ z_1}h^2$ is considerably larger than the WMAP measurement, and it is well known that if non-universal gaugino masses are allowed, then qualitatively new possibilities arise that are not realized in the mSUGRA model. Our first NUGM attempt is to allow a mixed wino-bino lightest SUSY particle (LSP) by lowering $SU(2)$ gaugino mass $M_2$ at the weak scale from its mSUGRA value while keeping the hypercharge gaugino mass $M_1$ fixed ({it Mixed Wino Dark Matter}). In this model, wino-like $ ilde{Z_1}$ with sufficiently low $M_2$ compared to $M_1$ enhances $ ilde{Z_1} ilde{Z_1} ightarrow W_{1}^{+} W_{1}^{-}$ annihilations to reach the WMAP measured relic density. The second attempt is study on the NUGM model with different signs of $M_1$ and $M_2$ ({it Bino-Wino Co-Annihilation Scenario}). In this case, there is little mixing, so that $ ilde{Z_1}$ remains nearly a pure bino or a pure wino. By increasing $M_1 simeq M_2$, enhanced bino-wino co-annihilation can achieve the relic neutralino abundance. The final attempt of NUGM models is lowering the $SU(3)$ gaugino mass to diminish the effect of the large top quark Yukawa coupling in the running of the higgs mass, so that the value of superpotential $mu$ parameter gets efficiently low to give rise to mixed higgsino dark matter ({it Mixed Higgsino Dark Matter}). Consequences of these NUGM model studies show us that relaxing universality of gaugino masses in SUSY models leads to enhanced direct and indirect dark matter detection rates and reduced $m_{ ilde{Z_2}}-m_{ ilde{Z_1}}$ mass gap so that the LHC and ILC can distinguish each NUGM model from others. Finally, we found that models with well-tempered neutralinos, where the composition of the neutralino is adjusted to give observed relic density, yield target cross sections which are detectable at proposed experiments.
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Date Issued: 2007
Identifier: FSU_migr_etd-2254
Format: Thesis

Title: A Gamma-Ray Spectroscopy Study for Higher Spin Structure of ³¹Si.
Creator: Tai, Pei-Luan, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
Abstract/Description: This work presents a comprehensive gamma-ray spectroscopic study to the higher spin structure of ³¹Si, including its excitation energies, spins, and branching ratios, along with the shell model discussions. ³¹Si was produced through the ¹⁸O(¹⁸O, alpha n) reaction at the beam energy of 25 MeV, which preferentially populates the higher spin states. The alpha particles from the reaction were detected in the Microball detector and the multiple gamma-ray coincidences were detected by GAMMASPHERE....
Show moreThis work presents a comprehensive gamma-ray spectroscopic study to the higher spin structure of ³¹Si, including its excitation energies, spins, and branching ratios, along with the shell model discussions. ³¹Si was produced through the ¹⁸O(¹⁸O, alpha n) reaction at the beam energy of 25 MeV, which preferentially populates the higher spin states. The alpha particles from the reaction were detected in the Microball detector and the multiple gamma-ray coincidences were detected by GAMMASPHERE. The ³¹Si recoil energies and angles were event-by-event kinematically reconstructed by using the information of the energies and angles of the alpha evaporations detected by Microball. The kinematic correction led to a better Doppler correction and allowed us to discover 26 new states and 49 newly-observed gamma transitions in total. 15 gamma-decaying states above the neutron separation energy were identified, and two highest gamma-decaying states are at the energies 9323- and 9216-keV. Spin and parity assignments are based on gamma-ray angular distribution analysis, DCO ratios analysis, branching ratio, and shell model predictions. For the positive-parity states predicted by the shell model calculations using USDA and WBP-a interactions agree well with the measured ones. But for the cross-shell states, the shell model calculations have RMS around 400-500 keV based on testing the lowest three measured negative parity states.
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Date Issued: 2016
Identifier: FSU_2016SU_Tai_fsu_0071E_13321
Format: Thesis

Title: Nuclear Structure Studies of ¹⁹O, ²⁷Mg, and ²⁹Al Using in-Beam γ-Ray Spectroscopy.
Creator: Dungan, Rutger, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department of...
Show moreDungan, Rutger, Tabor, Samuel Lynn, Humayun, Munir, Riley, Mark A., Volya, Alexander, Prosper, Harrison B., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: This dissertation reports the study of three nuclei ¹⁹O, ²⁹Al, and ²⁷Mg at high angular momentum using ɣ-ray spectroscopy. These experiments were performed at the John D. Fox Superconducting Linear Accelerator at Florida State University (FSU). ɣ-radiation and charged particles were detected in coincidence by employing the Compton suppressed FSU ɣ-detector array in conjunction with a silicon ΔE-E particle telescope. The ⁹Be(¹⁴C, ɑɣ) reaction at beam energies of 30 and 35 MeV were used to...
Show moreThis dissertation reports the study of three nuclei ¹⁹O, ²⁹Al, and ²⁷Mg at high angular momentum using ɣ-ray spectroscopy. These experiments were performed at the John D. Fox Superconducting Linear Accelerator at Florida State University (FSU). ɣ-radiation and charged particles were detected in coincidence by employing the Compton suppressed FSU ɣ-detector array in conjunction with a silicon ΔE-E particle telescope. The ⁹Be(¹⁴C, ɑɣ) reaction at beam energies of 30 and 35 MeV were used to populate excited levels of ¹⁹O. The data were sorted for α-ɣ and α-ɣ-ɣ coincidences. A total of eight new ɣ transitions and the addition of one new state in ¹⁹O were identified. Six of these ɣ transitions correspond to neutron unbound states. These results are compared to shell model calculations using the USDA, WBP, and PSDU interactions. The neutron unbound ɣ decaying states are best identified with states having higher spin and small spectroscopic factors. Excited levels were populated in ²⁹Al and ²⁷Mg using the reactions ¹⁸O(¹⁴C,p2n) and ¹⁸O(¹⁴C,α n) at 40 MeV. The data were sorted for p-ɣ-ɣ and α-ɣ-ɣ coincidences for ²⁹Al and ²⁷Mg respectively. The level and decay schemes of both nuclei have been expanded with the addition of several new levels and electromagnetic transitions. The results for both nuclei are compared to shell model calculations using the USDA and WBP interactions.
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Date Issued: 2016
Identifier: FSU_2016SU_Dungan_fsu_0071E_13358
Format: Thesis

Title: Measurement of the ²⁵Al(d,n) ²⁶Si(P) Reaction at RESOLUT.
Creator: Baker, Jessica, Wiedenhöver, Ingo, Fuelberg, Henry E., Tabor, Samuel Lynn, Volya, Alexander, Höflich, Peter A., Florida State University, College of Arts and Sciences,...
Show moreBaker, Jessica, Wiedenhöver, Ingo, Fuelberg, Henry E., Tabor, Samuel Lynn, Volya, Alexander, Höflich, Peter A., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Studies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest l = 0 and l = 1 resonances is the most important step to determine reaction rates in the astrophysical rp– process path. In an experiment performed at the resolut radioactive beam facility of Florida State University, we studied the 25Al(d,n)26Si reaction in inverse kinematics to establish the spectrum of the lowest l = 0 and l = 1 resonances. We observed 4 resonances in 26 Si at 5923 keV, 6357 keV,...
Show moreStudies of rp-process nucleosynthesis in stellar explosions show that establishing the lowest l = 0 and l = 1 resonances is the most important step to determine reaction rates in the astrophysical rp– process path. In an experiment performed at the resolut radioactive beam facility of Florida State University, we studied the 25Al(d,n)26Si reaction in inverse kinematics to establish the spectrum of the lowest l = 0 and l = 1 resonances. We observed 4 resonances in 26 Si at 5923 keV, 6357 keV, 6737 keV, and 7458 keV. We establish the lowest l = 0 resonance at 5.923 keV, 0.409 MeV above proton separation. The result is consistent with the previous experiment performed at FSU by Peplowski et al. however now with significantly larger statistics and detection of the heavy ion decay in coincidence with the proton. We determine upper and lower limits on Γ p and calculate the astrophysical reaction rate. We establish the proton density and temperature conditions in which galactic through the 25Al(d,n)26Sireaction path.
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Date Issued: 2015
Identifier: FSU_2016SP_Baker_fsu_0071E_12983
Format: Thesis

Title: Nuclear Structure Studies of 44S and 26Si.
Creator: Parker, John J. (John Johnston), Wiedenhöver, Ingo, Fuelberg, Henry E., Collins, David C., Tabor, Samuel Lynn, Volya, Alexander, Florida State University, College of Arts and...
Show moreParker, John J. (John Johnston), Wiedenhöver, Ingo, Fuelberg, Henry E., Collins, David C., Tabor, Samuel Lynn, Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Experimental results on the nuclear structure of 44S and 26Si will be reported in this thesis. 44S is studied because of its interest in understanding how nuclei behave far from stability. 26Si is studied because of the impact of understanding its nuclear structure can have on the astrophysical 25Al(p,γ) reaction rate. These are two very differently motivated studies and will be described separately in Chapters 2 and 3, respectively. Chapter 2 focuses on the exotic N=28 nucleus, in 44S....
Show moreExperimental results on the nuclear structure of 44S and 26Si will be reported in this thesis. 44S is studied because of its interest in understanding how nuclei behave far from stability. 26Si is studied because of the impact of understanding its nuclear structure can have on the astrophysical 25Al(p,γ) reaction rate. These are two very differently motivated studies and will be described separately in Chapters 2 and 3, respectively. Chapter 2 focuses on the exotic N=28 nucleus, in 44S. Previous experiments observed a 4+ state and suggested that this state may exhibit a hindered E2-decay rate, inconsistent with being a member of the collective ground state band. We populate this state via a two-proton knockout reaction from a beam of exotic 46Ar projectiles delivered from the coupled cyclotron facility and measure its lifetime using the recoil distance method with the GRETINA γ ray spectrometer. The result, 76(14) stat (20) syst ps, implies a hindered transition of B(E2; 4+ →2+1 ) = 0.61(19) single- particle or Weisskopf units strength and supports the interpretation of the 4 + state as a K = 4 isomer, the first example of a high-K isomer in a nucleus of such low mass. Chapter 3 focuses on resonances above the proton threshold in 26Si. Previous experiments have solidified the placement of 3 resonances thought to contribute to the 25Al(p,γ)26Si reaction. A fourth resonance has been suggested by various experiments, but more recent experiments have suggested that this level has been misidentified. We populate excited states in 26Si via the 24Mg(3He,n) reaction at 10 MeV at the John Fox Lab at FSU. Neutron time-of-flight spectroscopy is used to identify which resonance is populated in 26Si and the γ-array at FSU is used to determine how these levels de-excite. The γ ray sensitivity in this experiment is the highest sensitivity reached to date, but a 4th resonance above the proton threshold was not identified, giving further indication that this state may have been misidentified by past experiments.
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Date Issued: 2017
Identifier: FSU_2017SP_ParkerIV_fsu_0071E_13841
Format: Thesis

Title: ΛC Semileptonic Decays in a Quark Model.
Creator: Hussain, Md Mozammel, Roberts, Winston, Goldsby, Kenneth A,, Volya, Alexander, Crede, Volker, Owens, Joseph F., Florida State University, College of Arts and Sciences,...
Show moreHussain, Md Mozammel, Roberts, Winston, Goldsby, Kenneth A,, Volya, Alexander, Crede, Volker, Owens, Joseph F., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Hadronic form factors for semileptonic decay of the Λ[subscript c] are calculated in a nonrelativistic quark model. The full quark model wave functions are employed to numerically calculate the form factors to all orders in (1/m[subscript c], 1/m[subscript s]). The form factors satisfy relationships expected from the heavy quark effective theory (HQET) form factors. No other semileptonic decays of Λ[subscript c] has been reported other than the decay to the ground state Λ that implies f = B(Λ...
Show moreHadronic form factors for semileptonic decay of the Λ[subscript c] are calculated in a nonrelativistic quark model. The full quark model wave functions are employed to numerically calculate the form factors to all orders in (1/m[subscript c], 1/m[subscript s]). The form factors satisfy relationships expected from the heavy quark effective theory (HQET) form factors. No other semileptonic decays of Λ[subscript c] has been reported other than the decay to the ground state Λ that implies f = B(Λ[subscript c]⁺ → Λl⁺ν[subscript l])/B(Λ[subscript c]⁺ → X[subscript s]l⁺ν[subscript l]) = 1. In this work, the differential decay rates and branching fractions are calculated for transitions to the ground state and a number of excited states of Λ. The branching fraction of the semileptonic decay width to the total width of Λ[subscript c] has been calculated and compared with other theoretical estimates and experimental results. The branching fractions for Λ[subscript c] → Λ*l⁺ν[subscript l] → Σπl⁺ν[subscript l] and Λ[subscript c] → Λ*l⁺ν[subscript l] → NǨl⁺ν[subscript l] are also calculated. Apart from decays to the ground state Λ(1115), it is found that decays through the Λ(1405) provide a significant portion of the branching fraction Λ[subscript c] → X[subscript s]lν[subscript l]. There are various conjectures on the structure of the Λ(1405) while we treated it as a three quark state. A new estimate for f = B(Λ[subscript c]⁺ → Λl⁺ν[subscript l] is obtained.
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Date Issued: 2017
Identifier: FSU_2017SP_Hussain_fsu_0071E_13920
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: 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

Title: Experimental Efforts to Study the Nuclear Structure of ³³P and ³⁸Cl and a Theoretical Endeavor to Develop an Empirical Shell-Model Interaction.
Creator: Lubna, Rebeka Sultana, Tabor, Samuel L., Tripathi, Vandana, Albrecht-Schmitt, Thomas E., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences,...
Show moreLubna, Rebeka Sultana, Tabor, Samuel L., Tripathi, Vandana, Albrecht-Schmitt, Thomas E., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: In this thesis, the excited states ³³P were populated by the ¹⁸O+¹⁸O reaction at E[subscript lab]=24 MeV. The GAMMASPEHRE array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus ³⁶S. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the position and energy of the emitted proton; which eventually helped in calculating more precise...
Show moreIn this thesis, the excited states ³³P were populated by the ¹⁸O+¹⁸O reaction at E[subscript lab]=24 MeV. The GAMMASPEHRE array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus ³⁶S. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the position and energy of the emitted proton; which eventually helped in calculating more precise direction of the recoils to achieve better Doppler corrections. 16 new transitions and 13 new states were observed in ³³P for the first time. The nearly 4π geometry of GAMMASPEHRE allowed the measurement of γ-ray angular distributions leading to spin suggestions for many states. In a separate experiment conducted at the John D. Fox laboratory in Florida State University, the higher-spin structure of ³⁸Cl (N = 21) was investigated following the ²⁶Mg(¹⁴C, pn) reaction at 30 and 37 MeV. The outgoing protons were detected in an E ‒ ΔE Si telescope placed at 0° close to the target with a Ta beam stopper between the target and telescope. Multiple γ rays were detected in time coincidence with the protons using an enhanced version of the FSU γ detection array. A total of 11 new γ transitions and 6 new states were reported for the first time. DCO ratio analysis and measurement of polarization asymmetry for the emitted γ transitions were performed to assign spins and parities to a number of states. The level scheme was extended up to 8420 keV with a likely spin of 10 ħ. A new empirical shell model interaction was developed in the spsdfp model space. This FSU interaction was built by fitting to the energies of 270 experimental states from ¹³C to ⁵¹Ti. Calculations using the FSU interaction reproduced observed energy states of ³³P and ³⁸Cl rather well, including other spectroscopic properties. The interaction has been used to predict the intruder states of other sd-shell nuclei, along with the configurations of the nuclei belong to the Island of Inversion region of the nuclear landscape.
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Date Issued: 2019
Identifier: 2019_Summer_Lubna_fsu_0071E_15247
Format: Thesis

Title: Experimental Investigations of Mass-7 Destruction in Deuteron Induced Reactions with Respect to Standard Big Bang Nucleosynthesis.
Creator: Rijal, Nabin, Weidenhoever, Ingo Ludwing M., Humayun, Munir, Volya, Alexander, Höflich, Peter, Almaraz-Calderon, Sergio J., Florida State University, College of Arts and...
Show moreRijal, Nabin, Weidenhoever, Ingo Ludwing M., Humayun, Munir, Volya, Alexander, Höflich, Peter, Almaraz-Calderon, Sergio J., Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: The Big-Bang theory is the most widely accepted description of the origin of the Universe, creating elementary particles and synthesizing light nuclei up to mass-7 within the first few minutes of the Big-Bang. Its parameters have been recently precisely determined through he multi-years WMAP (Wilkinson Microwave Anisotropy Probe, NASA mission) followed by Planck (ESA mission). These results tightly constrain the baryonic density in the Universe with the highest precision ever achieved,...
Show moreThe Big-Bang theory is the most widely accepted description of the origin of the Universe, creating elementary particles and synthesizing light nuclei up to mass-7 within the first few minutes of the Big-Bang. Its parameters have been recently precisely determined through he multi-years WMAP (Wilkinson Microwave Anisotropy Probe, NASA mission) followed by Planck (ESA mission). These results tightly constrain the baryonic density in the Universe with the highest precision ever achieved, resulting in more constraints in the light element abundance predicted in the Standard Big Bang Nucleosynthesis (SBBN). The observed amount of all other light elements (H, D, 3He, 4He) agrees well with the SBBN calculation but the 7Li is overpredicted by a factor of 3 − 4, which is referred as the Primordial Lithium Problem. The Lithium problem is the disagreement in the theoretical and observed amount of 7Li in the Cosmos which has the key importance in the Big Bang Nucleosynthesis theory which can’t be explained by uncertainties in the main reactions included in the SBBN. In this work, we performed experiments on certain nuclear reactions, 7Be + d and 7Li + d, at energies relevant to SBBN, which could destroy a fraction of the mass-7 nuclei in the conditions of the Big Bang and could offer an explanation of the observed deviation from the prediction of SBBN. In preparation for the main experiment of this dissertation 7Be+d -> p+2 alpha, we performed an experiment for mirror nuclear reaction 7Li + d -> n + 2 alpha, with ANASEN in gas target mode using deuterium as an active gas target and detected 2 -particles in coincidence. In particular, we investigated the 7Be+d reaction at SBBN energies using a radioactive 7Be beam and deuterium gas target, stopping the beam in the target gas inside the ANASEN (Array for Nuclear Astrophysics and Structures with Exotic Nuclei) detector at the Florida State University (FSU). ANASEN is an active target detector system which tracks the charged particles with cylindrical configuration of a position sensitive proportional counter, a Silicon detector array backed up by Caesium Iodide (CsI) detectors; one of the first detectors of its kind. The experiment measured a continuous excitation function by slowing down the beam particles in the target gas down to very low energies into the Gamow window. Our experimental set-up provided a high detection efficiency for all relevant reaction channels focusing on the lowest energies, relevant to the Big Bang Nucleosynthesis (BBN). Results of these experiments after a comprehensive data analysis are documented in this dissertation.
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Date Issued: 2018
Identifier: 2018_Su_RIJAL_fsu_0071E_14658
Format: Thesis

Title: Exploring the Nuclear Structure of the A = 39 Isobars.
Creator: Abromeit, Brittany Lynn, Tabor, Samuel L., Humayun, Munir, Hsiao, Eric Y., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department...
Show moreAbromeit, Brittany Lynn, Tabor, Samuel L., Humayun, Munir, Hsiao, Eric Y., Riley, Mark A., Volya, Alexander, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Investigation of nuclei with neutron and proton imbalance is at the forefront of nuclear physics research today, along with how the nuclear structure varies with the movement of the nucleons. Experimental data and theoretical models work hand-in-hand to understand the structure of these nuclei. Two of the A = 39 isobars, residing in limbo between the sd- and fp-shells are the isotopes of interest for this study. With 24 neutrons, eight neutrons more than the stable isotope of phosphorous, ³⁹P...
Show moreInvestigation of nuclei with neutron and proton imbalance is at the forefront of nuclear physics research today, along with how the nuclear structure varies with the movement of the nucleons. Experimental data and theoretical models work hand-in-hand to understand the structure of these nuclei. Two of the A = 39 isobars, residing in limbo between the sd- and fp-shells are the isotopes of interest for this study. With 24 neutrons, eight neutrons more than the stable isotope of phosphorous, ³⁹P is considered a neutron-rich exotic nucleus, one of which has not been extensively studied until now. Since the late 1990s only two experiments have been conducted, producing the three known gamma-rays and one tentative gamma-ray for ³⁹P. Except for half-life measurements and mass measurements, no further studies of ³⁹P have been done prior to a beta-gamma coincidence experiment conducted in this study at the National Superconducting Cyclotron Laboratory (NSCL) using the Beta Counting System. Continuing up the isobaric chain from ³⁹P toward stability, ³⁹Ar is reached. Unlike ³⁹P, ³⁹Ar is nested between two of the stable isotopes of argon. Being closer to stability, it has been studied more extensively using transfer reactions, however, limited information on high-spin states is produced from only two prior experiments. Despite the more extensive study of ³⁹Ar, the observed gamma transitions are only well known for low-spin states except for one band of high-spin states which have been studied heavily using the gamma spectroscopy setup at the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University. Results for both isotopes, along with comparisons to Shell Model calculations will be presented.
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Date Issued: 2018
Identifier: 2018_Fall_Abromeit_fsu_0071E_14900
Format: Thesis

Title: Exotic Nuclear Deformation and the Evolution of Nuclear Structure with Angular Momentum and Excitation Energy in ¹⁵⁷Ho, ¹⁶⁶Er, and ¹⁶⁹,¹⁷⁰Yb.
Creator: Baron, Jonathan S., Riley, Mark A., Steinbock, Oliver, Tabor, Samuel L., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences, Department of...
Show moreBaron, Jonathan S., Riley, Mark A., Steinbock, Oliver, Tabor, Samuel L., Volya, Alexander, Reina, Laura, Florida State University, College of Arts and Sciences, Department of Physics
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Abstract/Description: Nuclei in the light rare-earth, for values of N ≥ 90, are textbook examples of the evolution of nuclear structure with respect to excitation energy and angular momentum in deformed nuclei. In the high-spin region (J ≥ 10ħ), effects such as backbends and shape changes occur, ending with termination of the lower energy collective structures. First backbends occur before 20ħ Findings also reflect a spectacular return to collectivity in the "ultra-high spin" region (J ≥ 50ħ). Thanks to recent...
Show moreNuclei in the light rare-earth, for values of N ≥ 90, are textbook examples of the evolution of nuclear structure with respect to excitation energy and angular momentum in deformed nuclei. In the high-spin region (J ≥ 10ħ), effects such as backbends and shape changes occur, ending with termination of the lower energy collective structures. First backbends occur before 20ħ Findings also reflect a spectacular return to collectivity in the "ultra-high spin" region (J ≥ 50ħ). Thanks to recent developments in both detectors and accelerators, gamma-ray spectroscopy has been able to probe the upper ends of the high-spin region, and begin probing into the ultra-high spin regime. Data from two experiments form the basis of this work. One study was an ultra-high-spin analysis of the Z=67, N=90 ¹⁵⁷Ho nucleus at Argonne National Laboratory with Gammasphere. The findings were that remarkable correlations were observed to the neighboring isotone, ¹⁵⁸Er, in which termination states and ultra-high spin structures had been previously observed. A high-spin investigation of Ytterbium (Yb) and Erbium (Er) isotopes was performed at FSU. This study used an intense radioactive ¹⁴C beam, available at FSU, in order to study these heavy, neutron-rich nuclei in regions of angular momentum and excitation energy not attainable with stable beams. The reactions of ¹⁷⁰Er(¹⁴C,5n/4n/α4n) generated new information in ¹⁶⁹Yb, ¹⁷⁰Yb, and ¹⁶⁶Er, respectively. Due to the recently upgraded digital FSU Gamma-Ray Array, aided by JBSMILE, triple ᵧ-ray coincidences were able to be viewed in these nuclei for the first time at FSU. The result was the investigation of rotational alignments in both the yrast and non-yrast multi-quasiparticle bands in these nuclei.
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Date Issued: 2018
Identifier: 2018_Fall_Baron_fsu_0071E_14887
Format: Thesis

Physics (29)	+ -
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text (37)	+ -
doctoral thesis (8)	+ -

Department of Physics (37)	+ -
Florida State University (37)	+ -
Volya, Alexander (35)	+ -
College of Arts and Sciences (17)	+ -
Humayun, Munir (9)	+ -

Rogachev, Grigory (9)	+ -
Riley, Mark A. (8)	+ -
Tabor, Samuel L. (8)	+ -
Tabor, Samuel Lynn (6)	+ -
Wiedenhöver, Ingo (6)	+ -
Bonesteel, N. E. (5)	+ -
Reina, Laura (5)	+ -
Crede, Volker (4)	+ -
Xiong, Peng (4)	+ -
Aldrovandi, Ettore (3)	+ -
Capstick, Simon (3)	+ -
Kopriva, David A. (3)	+ -
Piekarewicz, Jorge (3)	+ -
Plewa, Tomasz (3)	+ -
Roberts, Winston (3)	+ -
Steinbock, Oliver (3)	+ -
Weidenhoever, Ingo Ludwing M. (3)	+ -
Wiedenhover, Ingo (3)	+ -
Albrecht-Schmitt, Thomas E. (2)	+ -
Bonesteel, Nicholas (2)	+ -
Bonesteel, Nicholas E. (2)	+ -
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