Date of Award
Doctor of Philosophy (PhD)
Professor J.C. Waddington
The level structure of ¹⁵⁹Tm has been determined for two different odd-proton bands. The 7/2 [523) band has been constructed up to a spin of I=49/2ˉ (subsequent experiments extending this band up to I=61/2ˉ are referenced and the 7/2  band up to spin I=43/2⁺. In both bands the backbend associated with the i₁₃/₂ neutron alignment is observed. Gamma-ray intensities and angular distribution results are also presented and stretched B(M1)/stretched B(E2) values for transitions in both bands have been calculated.
The nature of the second backbend observed in ¹⁵⁸Er and ¹⁶⁰Yb is examined by considering the blocking effect of the h₁₁/₂ proton in ¹⁵⁹Tm. The measured alignments of the h₁₁/₂ proton band, along with the absence of an observed second crossing in ¹⁵⁹Tm, lead to the conclusion that the second backbend results from h₁₁/₂ proton alignment, in agreement with the theoretical calculations. Band-crossing frequencies in ¹⁵⁹Tm are determined from the experimental Routhians and compared to the crossings predicted in Cranked Shell Model calculations.
Structure effects in the N=90 region are also examined and the influence of the quasiparticle configurations on the core deformation is considered. Before the backbend, the 7/2  band exhibits large signature splitting, the 7/2  band none, which is interpreted as resulting from the very different driving influences of the K=7/2 h₁₁/₂ and g₇/₂ orbits, respectively, on the core triaxiality. The i₁₃/₂ neutron alignment occurring at the first backbend changes the signature splitting in each band as a result of its dominant driving force to positive values of Υ. The measured B(M1;I→-1)/B(E2;I→I-2) values increase dramatically after the backbend and this is explained in terms of calculated increases in the M1 transition rates and decreases in the E2 rates.
Larabee, Arlene Joyce, "Structure Effects and Rotation Alignment in ¹⁵⁹Tm" (1983). Open Access Dissertations and Theses. Paper 1332.