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A high-spin study of the shape transitional nucleus 188 Pt reveals the unusual coexistence of both shapeand K -isomeric states. Reduced B(E2) transition probabilities for decays from these states inferred from the data clearly establish their hindered character. In addition to other excited structures, a rotational band built upon the K isomer is identified, and its configuration has been assigned through an analysis of alignments and branching ratios. The shape evolution with spin in this nucleus has been inferred from both experimental observables and cranking calculations. The yrast positive parity structure appears to evolve from a near-prolate deformed shape through triaxial at intermediate excitation, and eventually to oblate at the highest spins.Shape coexistence is an important theme in nuclear structure research, and has been reported in many nuclei in the chart of nuclides [1]. The most extensive manifestation of this nuclear phenomenon known anywhere on the nuclear mass surface is found in the neutron-deficient isotopes at and near Z = 82 [1]. The shape coexistence and/or shape evolution in the Pt nuclei with Z = 78 has generated a lot of research interest in recent years. It has been observed that with increasing proton and neutron numbers, beyond Z = 72 and N = 106, the nuclear shape becomes more prone to non-axial fluctuation, induced by multi-quasiparticle excitation. Indeed, in the self-consistent Relativistic Hartree-Bogoliubov (RHB) calculations, the gradual transition from the prolate deformed 186 Pt, through the region of triaxially deformed [188][189][190][191][192][193][194][195][196][197][198] Pt, to the slightly oblate 200 Pt, and finally the spherical 202-204 Pt isotopes has been revealed [2]. Again, in the self-consistent Hartree-FockBogoliubov (HFB) calculations using non-relativistic Skyrme and Gogny interactions, a sudden prolate to oblate shape change was observed in the Pt chain of isotopes around A = 188 [2]. A good agreement was found when the latter calculation was compared * Corresponding author. E-mail address: somm@barc.gov.in (S. Mukhopadhyay).with a recent study on the evolution of the total energy surface and the nuclear shape in the isotopic chain Pt in the framework of the interacting boson model, including configuration mixing (IBM-CM) [3]. All these different theoretical approaches point towards the common fact that the lightest Pt isotopes are slightly deformed and prolate. With increasing neutron number, those attain more strongly deformed shape, while at the same time the γ deformation increases, leading to a triaxial nuclear shape. Eventually, the triaxial shape becomes oblate with the addition of more neutrons.The presence of isomeric states is also well established in the A ≈ 180 mass region both in experiment and theory. The occurrence of these metastable states can be interpreted in terms of both protons and neutrons in high-Ω orbitals. In axially symmetric nuclei, transitions involving large changes in the projection of angular momentum on the symmetry axis, K...

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The excited states in the odd-A 197 Tl nucleus have been studied by populating them using the 197 Au(α, 4n) 197 Tl reaction at a beam energy of 48 MeV. The γ -γ coincidence data were taken using a combination of clover, low-energy photon spectrometer (LEPS), and single-crystal high-purity germanium (HPGe) detectors. Precise spin and parity assignments of the excited states have been done through polarization and directional correlation from oriented states (DCO) measurements. A new band structure has been identified and evidence for a possible intruder πi 13/2 state has been found for the first time. Possible configurations of the observed bands have been discussed. The total Routhian surface calculations have been performed to study the shape of 197 Tl for different configurations.