The goal of nuclear structure experiments is to understand how properties of nuclei evolve as a function of key observables such as proton and neutron numbers, deformation, angular momentum and excitation energy, to name a few. In order to investigate how the nuclear structure evolves with these parameters, γ-ray spectroscopy can be utilized, which requires efficient γ-ray detection systems. This thesis details γ-ray spectroscopy to investigate the nuclear structure in a series of rare-earth nuclei using state of the art γ-ray detector systems. In the first part of this thesis, high-spin states in ¹⁷⁹, ¹⁸⁰W (Z=74) produced via fusion-evaporation reactions carried out at Florida State University's John D. Fox Laboratory are discussed. The reaction used to produce excited states in these nuclei was a 14C beam on an enriched ¹⁷⁰Er target, and the 5n and 4n evaporation channels were studied to investigate ¹⁷⁹, ¹⁸⁰W respectively. The emitted γ-rays were detected using three Compton-suppressed clover detectors and seven single element Compton-suppressed high-purity germanium detectors. In this experiment, 852 million γ-γ coincidences and 82 million γ-γ-γ coincidences at 75 MeV beam energy were collected. Additionally, at a beam energy of 68 MeV, 119 million γ-γ coincidences and 9.6million γ-γ-γ coincidences. The primary purpose of this experiment was to add to a systematic investigation of band crossing frequencies in heavy tungsten nuclei in order to observe the effect of quasiparticle seniority and high rotational frequencies on pairing correlations. Additionally, due in part to results obtained from the first part of this analysis, new systematic data in the A ≈ 160 − 180 region is also discussed, with an emphasis on the role that pair-blocking effects play during the rotation of the nucleus. This systematic investigation builds upon the classic findings of Garrett et al. [1] who investigated systematically the critical band crossing frequencies resulting from the rotational alignment of the first pair of i₁₃/₂ neutrons (AB) in rare-earth nuclei. In that study, evidence was found for an odd-even neutron number dependence attributed to changes in the strength of neutron pairing correlations. The present work carries out a similar investigation at higher rotational frequencies for the second pair of aligning i₁₃/₂ neutrons (BC), advancing the work started by Scott Miller, formerly of the Riley group [2]. Again, a systematic difference in band crossing frequencies is observed between odd-N and even-N Er, Yb, Hf, and W nuclei, but in the BC case, it is opposite to the AB neutron-number dependence. These results are discussed in terms of a reduction of neutron pairing correlations at high rotational frequencies and of the effects of Pauli blocking on the pairing field by higher-seniority configurations. Also playing a significant role are the changes in deformation with proton and neutron number, the changes of location of single-particle orbitals as a function of quadrupole deformation, and the position of the Fermi surface with regard to the various Ω (projection of total angular momentum I onto the symmetry axis) components of the neutron i₁₃/₂ shell. The second part of this thesis discusses in detail the nuclear structure of ¹⁶⁰Gd and highlights some new band structures in ¹⁵⁵Sm and ¹⁶¹Gd. Two reactions were carried out to produce a multitude of neutron-rich isotopes performed at the Argonne Tandem Linear Accelerator System (ATLAS) at Argonne National Laboratory (ANL). Firstly, a ¹⁶⁰Gd beam of energy at 1000 MeV was impinged on a ¹⁵⁴Sm target and then in a second experiment on a ¹⁶⁴Dy target. The goal of the deep-inelastic collisions was to provide a mechanism to reach a number of neutron-rich isotopes, in particular those from the mid-shell region in rare-earth nuclei. Although many neutron-rich nuclei were produced, they were not populated strongly enough to see new results. However, a byproduct of the reactions was the strong Coulomb excitation of the 160 Gd beam. Many excited states in ¹⁶⁰Gd were produced, and as a result, a spectroscopic analysis of 160Gd was carried out, and will be discussed in detail in this thesis. Additionally, new γ-ray transitions in other isotopes such as ¹⁵⁵Sm and ¹⁶¹Gd were also produced and will be discussed. The Gammasphere detector array was used to detect γ-rays from the excited nuclei, because of its sensitivity to cleanly delineate the vast number of multi-nucleon transfer reaction channels. As a result of both analysis, many new decay transitions and new energy levels were observed in the aforementioned nuclei. Whenever possible, the intensities, angular correlations, spins, parities, and rotational behaviors of these newly discovered states were analyzed.
