Y. D. Fang

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.

High-spin states in Au-188: Further evidence for nonaxial shape

The high-spin level structure of {sup 188}Au has been investigated via the {sup 173}Yb({sup 19}F,4n{gamma}) reaction at beam energies of 86 and 90 MeV. The previously reported level scheme has been modified and extended significantly. A new I{sup {pi}}=20{sup +} state associated with {pi}h{sub 11/2}{sup -1} x {nu}i{sub 13/2}{sup -2}h{sub 9/2}{sup -1} configuration and two new rotational bands, one of which is built on the {pi}h{sub 9/2} x {nu}i{sub 13/2} configuration, have been identified. The prolate-to-oblate shape transition through triaxial shape has been proposed to occur around {sup 188}Au for the {pi}h{sub 9/2} x {nu}i{sub 13/2} bands in odd-odd Au isotopes. Evidence for {pi}h{sub 11/2}{sup -1} x {nu}i{sub 13/2}{sup -1} structure of nonaxial shape with {gamma}<-70 deg. has been obtained by comparison with total Routhian surface and cranked-shell-model calculations.

High-spin level structure in deformed odd-odd ~(186)Au

High-spin states in deformed odd-odd 186Au have been reinvestigated via the 172Yb(19F,5nγ) fusion-evaporation reaction.Detailed analysis of γ-γ coincidence relationships leads to a revised high-spin level scheme for 186Au.New spin values are assigned to the prolate πh9/2i13/2 and πi13/2i13/2 bands in 186Au according to the level spacing systematics as well as the existing knowledge in odd-odd neighboring nuclei.Based on the new spin assignments,both bands exhibit the characteristics of low-spin signature inversion.The properties of signature splitting for the prolate πh9/2i13/2 and πi13/2i13/2 and oblate πh-111/2νi-131/2 bands in Au isotopes have been discussed.A new rotational band built on Ix=(20+) state has been identified and assigned as the oblate πh-111/2  νi-232h-19/12 configuration.

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.

Properties of the {pi}h{sub 11/2} band in the stable nucleus {sup 193}Ir

Excited states in the stable nucleus {sup 193}Ir have been investigated through an in-beam {gamma}-ray spectroscopic technique following the {sup 192}Os({sup 7}Li, {alpha}2n) reaction at a beam energy of 44 MeV. A level scheme built on the {pi}h{sub 11/2} isomer has been extended to high-spin states using eleven newly observed {gamma} transitions. The {pi}h{sub 11/2} band is proposed to be formed by coupling an h{sub 11/2} proton to a core with large triaxial deformation. Three-quasiparticle states are suggested in {sup 193}Ir on referring to the similar states in {sup 187}Ir. The features of signature splitting in the {pi}h{sub 11/2} bands of {sup 187-193}Ir are discussed with the help of total Routhian surface calculations.

Microscopic examination of N{sub p}N{sub n} dominance in the evolution of nuclear structure

The proton-neutron interaction in determining the evolution of nuclear structure has been studied by using the Brillouin-Wigner perturbation expansion. The particle-hole and particle-particle p-n interactions are unifiedly described in the theory. The obtained formulas of level energies and excitation energies scaled in the small- and large-N{sub p}N{sub n} limits can well explain the linearity of the extracted proton-neutron interaction energies and the attenuation of the 2{sub 1}{sup +} excitation energies against the valence nucleon product N{sub p}N{sub n}for five mass regions from A=100-200.

Band properties of the transitional nucleus 189Pt

High‐spin states in 189Pt have been studied with the in‐beam γ‐spectroscopy method via the 176Yb(18O,5n) reaction at beam energies of 88 MeV and 95 MeV. A new level scheme of 189Pt has been established. Rotational bands based on the υi13/2−1, υf5/2(p3/2) and υi13/2−2υf5esol2(p3/2) configurations, as well as several structures with irregular level spacings, have been observed. Properties of rotational bands have been analyzed in the framework of triaxial particle‐rotor model. A γ~−30° triaxial shape and a near prolate shape have been proposed to the υi13/2−1 and υf5/2(p3/2) bands, respectively. Two ΔI = 2 transition sequences with similar energies have been observed, and they have been proposed to be associated with the υi13/2−2υf5/2(p3/2) configuration. According to the relevant Nilsson orbitals, the bands built on the υi13/2−2υf5/2(p3/2) configuration could be interpreted as a pair of pseudo‐spin partner.