Single-Particle and Collective Structures in Tellurium Nuclei.

This dissertation concerns the experimental study of ^{119,121,123}Te populated in (alpha,n) reactions at the Rutgers Tandem Van de Graaff accelerator with alpha beams produced with a duoplasmatron ion source. Even and odd Te isotopes for A = 118-134 are interpreted using the Interacting Boson Approximation Model (IBA) and the Interacting Boson-Fermion Approximation Model, respectively. Excitation function measurements were performed to determine the alpha-beam energies (16-21 MeV) used in these experiments. Three Ge detectors were used in gamma-gamma coincidence measurements, from which gamma-ray cascades were extracted. Gamma-ray multipolarities and relative intensities were determined from gamma -ray angular distribution measurements. The gamma-ray coincidences and multipolarities were used to deduce level schemes for ^ {119,121,123}Te isotopes. Many new transitions were observed, new yrast and non-yrast levels were identified, and new spin-parity assignments were made. The 6_1^+ states in ^{118-134}Te are argued to be two quasiparticle excitations because of the absence of significant interactions between valence neutrons and protons, while the experimental B(E2; 2_1 ^+to 0_1^+) values suggest perfect vibrational structure for the 2_1 ^+ states. IBA calculations for the low -lying levels of ^{122-126}Te suggest a predominantly vibrational structure with a small perturbation. No collective perturbation within the IBA framework conclusively improves the pure vibrational calculations and, in particular, the 6_1^+ states cannot be well described. The Interacting Boson-Fermion Approximation (IBFA) Model describes the odd isotopes in terms of an odd neutron coupled to the states of an even neighbor. The IBFA predictions for the negative-parity levels in ^{121 -125}Te indicate a coupling which is not weak to the vibrational states of the even neighbors, due to the Pauli principle acting between the odd neutron and those in the even cores. In fact, the first excited 7/2 ^- states in the odd isotopes are proposed to arise from an h_{11/2} neutron hole coupled to the 4_1 ^+ and 2_2^+ states in the even cores, rather than the 2_1 ^+ states, which is expected for weak coupling. The states in the odd isotopes that arise from couplings to the 6_1^+ states in the even cores were not well described in the IBFA calculations. This result is consistent with the interpretation of a non-collective nature for the 6_1^+ states.