M. Oshima

Prolate and Oblate Shape Coexistence in 188Pt

A standard in-beam γ-spectroscopy experiment for 188Pt is performed via the 176 Yb(18O, 6n) reaction at beam energies of 88 and 95MeV, and the level scheme for 188Pt is established. Prolate and oblate shape coexistence has been demonstrated to occur in 188Pt by applying the projected shell model. The rotation alignment of i13/2 neutrons drives the yrast sequence changing suddenly from prolate to oblate shape at angular momentum 10h, indicating likely a new type of shape phase transition along the yrast line in 188Pt.

Identification of a New Four-Quasiparticle State in Odd-Odd 186Au

The high-spin level structure of 186Au is re-investigated by means of in-beam γ-ray spectroscopy via the 172Yb(19F, 5nγ)186Au reaction. The oblate bands previously reported are revised and extended to higher-spin states. A new Iπ = (20+) excited state has been identified and assigned to the πh−111/2 ⊗ νi−213/2h−19/2 configuration. The total Routhian surface and cranked shell model calculations suggest that the πh−111/2 ⊗ νi−213/2h−19/2 band in 186Au has a non-axial deformation.

Properties of the ν7/2−[503](f7/2) band in 185Pt

High-spin states in 185Pt have been reinvestigated via the reaction 173Yb(16O, 4n) at a beam energy of 90 MeV. The previously known band based on the ν7/2−[503](f7/2) Nilsson orbital has been extended to higher spin states. Properties of the ν7/2−[503](f7/2) band have been discussed with an emphasis on the evolution of configuration while increasing the spin.

Structure evolution along the yrast-line in 101Pd

High-spin states in 101Pd have been investigated experimentally via the 76Ge(28Si, 3nγ)101 Pd reaction. The previously known bands based on the d5/2 and h11/2 neutron orbitals have been extended to higher-spin states, and two new structures have been observed. Spin and parity were assigned to the levels on the basis of the experimental results of the angular distribution of γ rays deexciting the oriented states. For the ground-state band, the E-GOS (E-Gamma Over Spin) curve strongly suggests a structure transition from vibration to rotation while increasing spin.

Study of the vi−113/2 band in 189Pt

High-spin levels of 189Pt have been studied with the in-beam γ-spectroscopy method via the 176Yb(18O,5n) reaction at the beam energies of 88 and 95 MeV. The previously known vi−113/2 band has been confirmed, and its unfavored signature branch extended up to the 31/2+ state. Within the framework of the triaxial particle-rotor model, the vi−113/2 band is suggested to be associated with the 11/2[615] configuration, and to have triaxial deformation.

Identification of a New Band and Its Signature Inversion in ^174Re

High spin states in 174Re are investigated via the 152Sm(27Al,5nγ)174Re reaction and γ−γ coincidence relationships are analysed carefully. A new band is identified due to its spectroscopic connection with the known π1/2−[541]⊗ν1/2−[521] band. This band is proposed to be the ground-state band built on the π1/2−[541]⊗ν5/2−[512] configuration in view of the low-lying intrinsic states in the neighbouring odd-mass nuclei. It is of particular interesting that the new band exhibits a phenomenon of low-spin signature inversion, providing a new situation for theoretical investigations.

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.

Signature inversion in the 7/2−[503] band of 185Pt

High-spin states in 185Pt have been investigated using the 173Yb(16O, 4n) reaction at a beam energy of 90 MeV. The 7/2?[503] band in 185Pt is revised, and particularly the intra-band B(M1)/B(E2) ratios are deduced experimentally. Low-spin signature inversion is revealed in the 7/2?[503] band. The signature inversion can be interpreted if we assume configuration change in this band from the 7/2?[503] orbital to the 7/2?[514] orbital with increasing spin, which is supported by comparing the measured B(M1)/B(E2) ratios with the theoretical values from the semi-classical D?nau and Frauendorf approach.