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Title: In-Beam Test of the TIGRESS Prototype Detector, Author: Lesley M .Watters, Location: Thode This thesis describes the preparations for the first in-beam test of a new type of gamma-ray detector, which will be part of the TIGRESS array of segmented high-purity Germanium clover detectors. Gamma rays emitted from a moving nucleus are Doppler-shifted leading to a broadening of the measured photo-peak. Through a determination of the interaction position in the crystal, it is anticipated that most of the resolution may be recovered with these detectors. In order to test this prediction, the detector has been tested in an experiment. Prior to this test, a "pre-test" was done with a conventional detector. The reasons for the choice of the reaction for the pre-test, the description of the experiment and its results and the lessons learned will be presented. Thesis Master of Science (MS)

The proton-rich nuclei in the A ? 60 mass region provide an excellent laboratory for studying the interplay between single-particle and collective nuclear excitations. In order to increase the sensitivity of spectroscopic studies of these nuclei, a new method of channel selection based on the measurement of the total energy of all ? rays and charged particles emitted in fusion-evaporation reactions has been developed. This method has been used to identify and study deformed and superdeformed (SD) rotational bands in 62 Zn and the N = Z nucleus 60 Zn. Two sets of strongly coupled rotational bands have been identified in 62 Zn and have been observed up to the terminating states of their respective configurations. Lifetime measurements indicate that the transition quadrupole moments in these bands decrease as termination is approached. These results represent the first observation of the terminating states of rotational bands in the A ? 60 mass region and confirm the predicted loss of collectivity associated with the phenomenon of smooth band termination. The first superdeformed rotational band in the A ? 60 mass region has also been identified in 62 Zn, establishing a new region of superdeformation for nuclei with neutron and proton numbers N , Z [approximate] 30. The doubly-magic superdeformed band in the N = Z nucleus 60 Zn has been identified. This band corresponds to filling the single-particle orbitals up to the large SD shell gaps at N , Z = 30 and is the natural reference core for the study of A ? 60 superdeformation. In addition, the observation of linking transitions connecting this band to normal deformed (ND) states provides the first spin, parity, and excitation energy measurements for A ? 60 SD states. The stretched- E 2 character and relatively large B (E 2) values of these linking transitions indicate that the decay-out mechanism in 60 Zn differs significantly from that observed in heavier nuclei. Doctor of Philosophy (PhD)

When some nuclei are excited to tens of MeV above their ground state, with angular momenta so high that they are on the verge of fissioning, they can take on cigar-like shapes with axis ratios of 2 : 1, so-called superdeformed shapes. These superdeformed nuclei de-excite by the emission of cascades of γ rays (a superdeformed band). One of the most puzzling aspects of this emission is the phenomenon called ΔI = 4 bifurcation, or staggering, in which every second γ-ray energy in a given superdeformed band is shifted upward relative to the other energies in the band. Very little is known about this phenomenon, making a systematic investigation necessary. In this thesis, ΔI = 4 bifurcation has been studied in twenty-two bands in europium and gadolinium nuclei with mass numbers A near 150. The results obtained include the observation that the staggering patterns in three identical bands (bands with identical moments of inertia) are very highly correlated. This result seems to agree with what one might expect from a restrictive interpretation of the model of Hamamoto and Mottelson, and the staggering patterns in these three bands are used to constrain the model parameters for this triplet of bands. This systematic survey of ΔI = 4 bifurcation has been used to rigorously test the model of Pavlichenkov, and that of Hamamoto and Mottelson. It is demonstrated that neither of these models is capable of explaining the results presented. Finally, a statistical analysis of the staggering patterns presented in this thesis is proposed and carried out. This analysis underlines the highly non-statistical nature of the staggering phenomenon, but also emphasizes the importance of independent verification of these results. Doctor of Philosophy (PhD)

As part of a systematic survey of superdeformation in nuclei in the vicinity of ¹⁴³Eu, six superdeformed bands in ¹⁴²Sm, ¹⁴²Eu and ¹⁴⁴Eu have been studied by their Υ-ray decay following heavy-ion fusion-evaporation reactions. All of these bands are based on a "second minimum" shell gap associated with the superdeformed (2:1 prolate ellipsoid of rotation) nuclear shape at neutron number N=80 and proton number Z=63. The first band in ¹⁴²Sm and the band in ¹⁴²Eu have been studied with the 8π spectrometer, while the bands in ¹⁴⁴Eu and the excited band in ¹⁴²Sm have been discovered with the GAMMASPHERE array. The Υ-ray decays of these superdeformed structures are compared to collective rotational models, and specifically to state-of-the-art Cranked Shell Model (CSM) calculations for Nilsson, Woods-Saxon, and Hartree-Fock models of the nuclear potential. The predicted roles of specific orbitals in the A~140 mass region are compared to quantities derived from the experiments and where possible, configurations with respect to an ¹⁴³Eu core are proposed. The first ¹⁴²Sm band consists of 19 Υ-ray transitions with an intensity of 0.5% of the reaction channel, and its behaviour is best described in the calculations as an ¹⁴³Eu superdeformed core with a hole in an Nosc=5 proton orbital. The second excited band consists of 15 transitions with an intensity ~ 20% that of the first band, of which the transitions above ~ 1 MeV are identical in energy to those in a ¹⁴⁶Gd band. This new band, which represents the second example of a two-proton, two-neutron identical bands pair, is most likely a ¹⁴⁶Gd superdeformed core with four holes in low Nosc orbitals. Structures based on simple excitations of the proton hole of the first band likely comprise a quasi-continuum ridge structure. The ¹⁴²Eu band has 15 transitions and an intensity of 1.2%. The detailed behavior of this band suggests that its configuration is an Nosc=5 neutron hole in the ¹⁴³Eu core. Such a configuration is not predicted to be energetically favourable. The three ¹⁴⁴Eu bands all have population intensities of < 0.2 % relative to the reaction cross-section. Two of the ¹⁴⁴Eu bands, with 17 and 18 transitions respectively, are quite likely Nosc=6 neutron particle states coupled to the ¹⁴³Eu core. The behavior of the third band indicates occupation of an Nosc=7 neutron intruder which does not influence the shape of the ¹⁴³Eu core. Doctor of Philosophy (PhD)

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 [404] 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 [523] band exhibits large signature splitting, the 7/2 [404] 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. Doctor of Philosophy (PhD)

The level structures of the odd and odd-odd deformed nuclei ¹⁷⁷Ta and ¹⁷⁶Ta have been studied by means of (Heavy, Ion, xn) reactions. Gamma singles, Υ-angular distribution, delayed gamma singles, ϒ-ϒ prompt, coincidence, ϒ-ϒ delayed coincidence and delayed conversion electron measurements were used. Isomeric states with half-lives of 78 ns and 3.8 μs were established at (1309.0) keV and 2826.8 KeV in ¹⁷⁶Ta and ¹⁷⁷Ta, respectively. The interpretation of the high spin states has been carried out within the framework of the quasiparticle model, these states being assigned many-quasiparticle configurations. Experimentally deduced energy levels in ¹⁷⁷Ta were found to agree well with calculated values using the experimentally determined energies of lower-order many-quasiparticle states in ¹⁷⁶Hf and ¹⁷⁷Ta and a zero-range interaction between unpaired nucleons. Doctor of Philosophy (PhD)