Mass distributions of the fragments in the fission of 206 Po and the N=126 neutron shell closed nucleus 210 Po have been measured. No significant deviation of mass distributions has been found between 206 Po and 210 Po, indicating the absence of shell correction at the saddle point in both the nuclei, contrary to the reported angular anisotropy and pre-scission neutron multiplicity results. This new result provides benchmark data to test the new fission dynamical models to study the effect of shell correction on the potential energy surface at saddle point.

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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...

The α-α transition operator-effective interaction, t αα (E, r) has been evaluated using phenomenological α-α optical potentials at several bombarding energies, E α from 77 to 200 MeV. The results are obtained by solving the Schrödinger equation with appropriate optical potentials for various partial waves and then clubbing these with their respective optical potentials and initial state plane waves. The change of the α-α optical potential with or without hard core has been shown to influence the effective α-α t-matrix interactions drastically. The behaviour of the calculated t αα (E, r) effective interaction indicates towards a solution of the large anomalies found in the (α, 2α) reaction analyses.

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