Structural Changes in ¹⁶¹Tm and ¹¹²Sn as a Function of Increasing Angular Momentum

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 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.