We develop a method of directly incorporating additional Shell Model (SM) components in the One-Body Density Matrix (OBDM) by treating Core Polarization (CP) as a two-body operator in a limited SM space. We show that inclusion of such SM configurations in CP through the use of first-order Perturbation Theory in a calculation of the OBDM can be accomplished by the introduction of segmented Two-Body Density Matrices (TBDM) between the appropriate inital and final SM states. Comparisons between "exact" SM calculations and the CP approach are presented, as are attempts to assess the role of spuriosity and different treatments of the Hartree-Fock condition in the latter.

A description of the measurement of quasielastic interference structure functions for the nucleus $\sp{12}$C is presented. Longitudinally polarized electrons with an average polarization of 39 $\pm$ 4% and an initial energy of 660.0 MeV were scattered through 33.4 degrees from a graphite target. The scattered electrons were detected with a large magnetic spectrometer in coincidence with the knockout protons which were detected simultaneously by either of two small magnetic spectrometers placed out of the electron scattering plane. The forward-backward asymmetry A$\sb{91}$ and the beam helicity induced asymmetry A$\sbsp{01}{\prime}$ were measured, and the longitudinal-transverse interference structure functions $f\sb{01}$ and $f\sbsp{01}{\prime}$ were extracted for the $\sp{12}$C p-shell knockout reaction at a missing momentum of 115.0 MeV/c and a Q$\sp2$ of 0.13 (GeV/c)$\sp2$. This experiment was the first attempt in a series of $(\vec e,e\sp{\prime}p)$ experiments using multiple out-of-plane spectrometers to detect hadrons in isolating several interference structure functions simultaneously through precise asymmetry and cross section measurements. The equipment for these measurements was installed from 1995 to 1996 at the Bates Linear Accelerator Center in Middleton, Massachusetts, and this experiment was carried out in September of 1996.

While the agreement between theory and experiment is excellent for the π 0 → 2γ reaction, other reactions that proceed through the axial anomaly have been poorly tested. For example the existing measurement of the γ → 3π amplitude, F3π, is in poor agreement with theory. In the limit of low s and t, the γp → π+π 0n reaction is sensitive to F 3π. In this thesis preliminary cross sections for the γp → π +π0n reaction are presented using the CLAS with tagged photon energies between 1 and 2 GeV and over a range in s and t up to 1 GeV2. The π+ was detected using the time-of-flight and tracking systems. The π0 was detected via reconstruction of the invariant mass of its two decay photons, which were detected by an electromagnetic calorimeter. The presence of the neutron was inferred via missing mass. The sensitivity of these cross sections to F3π in the low t region is studied for s = [special characters omitted] and s = [special characters omitted] at Eγ = 2 GeV. The results show a momentum dependence of the F3π and are consistent with a calculation that includes the effects of ππ final state interactions on the chiral perturbation prediction for F 3π.

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 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. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 19, 2018. / Includes bibliographical references. / Mark A. Riley, Professor Directing Dissertation; Oliver Steinbock, University Representative; Samuel L. Tabor, Committee Member; Alexander Volya, Committee Member; Laura Reina, Committee Member.

No description available.

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 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. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2019. / May 7, 2019. / Higher spin, Intruder states, Nuclear Structure, particle hole excitation, Shell evolution, Shell model / Includes bibliographical references. / Samuel Tabor, Professor Co-Directing Dissertation; Vandana Tripathi, Professor Co-Directing Dissertation; Thomas Albrecht-Schmitt, University Representative; Alexander Volya, Committee Member; Laura Reina, Committee Member.

No description available.

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 $\gamma$-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. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2015. / March 2, 2015. / backbend, configuration, mercury, parity, quasiparticle, tungsten / Includes bibliographical references. / Mark A. Riley, Professor Directing Dissertation; Tomasz Plewa, University Representative; Samuel L. Tabor, Committee Member; Alexander Volya, Committee Member; David Van Winkle, Committee Member.

In this dissertation, we introduce a new approach in building a hybrid nuclear model that combines some existing theoretical models and a \universal" approximator. The goal of such an approach is to obtain new predictions of nuclear masses and charge radii. We begin our study by investigating nuclear masses based on theoretical and experimental values. Nuclear masses are essential for astrophysical applications, such as r-process nucleosynthesis and neutron-star structure. To overcome the intrinsic limitations of the existing ``state-of-the-art" mass models, a renement is generated based on a Bayesian Neural Network (BNN) formalism. A novel BNN approach is applied with the aim of optimizing mass residuals between theory and experiment. A signicant improvement (of about 40%) in the mass predictions of existing models is obtained after BNN renement. Moreover, these improved results are accompanied by proper statistical errors. By constructing a \world average" of these predictions, we obtained a unied mass model that is used to predict the composition of the outer crust of a neutron star. In order to get a better description of nuclear structure, a similar procedure is also implemented in the nuclear charge radius. A class of relativistic energy density functionals is used to provide robust predictions for nuclear charge radii. In turn, these predictions are rened through the BNN approach to generate predictions for the charge radii of thousands of nuclei throughout the nuclear chart. The neural networks function is trained using charge radii residuals between theoretical predictions and experimental data. Although the predictions obtained with density functional theory provide a fairly good description of the experiment, our results show signicant improvement (better than 40%) after BNN renement. Despite the improvement and robust predictions, we failed to uncover the underlying physics behind the intriguing behavior of charge radii along the calcium isotopic chain. Overall, we have successfully demonstrated the ability of the BNN approach to signicantly increase the accuracy of nuclear models in the predictions of nuclear masses and charge radii. Extension to other nuclear observables is a natural next step in asserting the eectiveness of the BNN method in nuclear physics. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2016. / November 9, 2016. / Bayesian Neural Network, Neutron Star, Nuclear Structure / Includes bibliographical references. / Jorge Piekarewicz, Professor Directing Dissertation; Washington Mio, University Representative; Harrison Prosper, Committee Member; Simon Capstick, Committee Member; Volker Cred´e, Committee Member.

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. 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. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / April 5, 2017. / Includes bibliographical references. / Ingo Wiedenhöver, Professor Directing Dissertation; Henry Fuelberg, University Representative; David Collins, Committee Member; Sam Tabor, Committee Member; Alexander Volya, Committee Member.