Y. H. Qiang

Characteristics of a CsI(Tl) Compton-suppressed clover detector

The performance of a four fold segmented clover detector coupled to a CsI-suppressed shield has been tested using several standard radioactive sources. The summing characteristics, hit patterns and absolute efficiency were measured in both crystal and clover modes. Peak-to-total ratios of 57.3% and 45.6% in suppressed clover mode have been determined for 137Cs and 60Co sources, respectively. A Geant4 simulation of the suppressed clover detector, including the segmentation of the germanium crystals, has been created, and the simulation results agreed very well with the experimental data.

Rotational band properties in {sup 165}Er

High-spin states in {sup 165}Er have been studied experimentally using the {sup 160}Gd({sup 9}Be, 4n) reaction at beam energies of 42 and 45 MeV. The previously known bands based on the 5/2{sup +}[642], 5/2{sup -}[523], and 11/2{sup -}[505] configurations are extended to (49/2{sup +}), (45/2{sup -}), and (31/2{sup -}) states, respectively. The rotational bands in {sup 165}Er generally show gradual alignment processes, indicating strong band interactions associated with the i{sub 13/2} neutron alignments. The band properties are compared with those in the neighboring nuclei and discussed within the framework of the cranked shell model.

Properties of the rotational bands in {sup 161}Er

High-spin states in {sup 161}Er have been studied experimentally using the {sup 150}Nd({sup 16}O,5n) reaction at a beam energy of 86 MeV. The 5/2{sup +}[642], 3/2{sup -}[521], and 11/2{sup -}[505] bands are extended up to high-spin states, and particularly the {alpha}=-1/2 branch of the ground state 3/2{sup -}[521] band is revised significantly. The relatively enhanced E1 transitions from the 3/2{sup -}[521] band to the 5/2{sup +}[642] band are observed. The band properties are analyzed within the framework of a triaxial particle-rotor model, and near-prolate shape and triaxial deformation are proposed to the 3/2{sup -}[521] and 5/2{sup +}[642] bands, respectively. Signature inversion occurs in the 3/2{sup -}[521] band after the band crossing in {sup 161}Er, and the systematics of the signature inversion associated with the 3/2{sup -}[521] configuration are discussed. By analyzing the properties of the relatively enhanced E1 transitions, it is found that the R(E1/E2) values show angular momentum dependence before the band crossing, and these enhanced E1 transitions could be attributed to octupole softness.

Identification of the {gamma}-vibrational band built on the 11/2{sup -}[505] orbital in {sup 165}Er

Excited states in {sup 165}Er have been populated using the {sup 160}Gd({sup 9}Be, 4n) reaction at beam energies of 42 and 45 MeV. A band consisting of two levels at excitation energies of 1317.6 and 1505.9 keV, both of which decay strongly to the 11/2{sup -}[505] band, is observed and assigned as the {gamma}-vibrational band built on the 11/2{sup -}[505] configuration. In addition, a newly identified level is proposed as a three-quasiparticle state.