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An oblate rotational sequence, built on an aligned, two-quasineutron isomeric state has been established in 196Pt. The isomer has a half-life of 7.7(7) ns and is associated with the Iπ = 12+, (i13/2)² neutron configuration. Excited states, with angular momentum generated primarily through successive nucleon alignments, have been populated through 1p transfer from 197Au. The nucleus 196Pt is the most neutron-rich Pt isotope for which high-spin states, beyond the 12+ isomeric state, have been established thus far. Cranked shell model calculations have been performed to understand shape evolution with spin, and the role of nucleons occupying specific Nilsson orbitals in generating aligned angular momentum for both prolate and oblate deformations has been explored. [ABSTRACT FROM AUTHOR]

The decay of K isomers in Cm (Z = 96) isotopes has been studied using inelastic and transfer reactions. The half-life of a previously identified 2-quasiparticle (qp) Kπ=8- isomer in 246Cm has been measured. A new 2-qp isomer is observed in 248Cm, its half-life measured and its decay scheme established. The reduced K hindrances extracted for the decay transitions from the isomers in 246,248Cm indicate K to be a robust quantum number and validate axial symmetry in these nuclei. The excitation energies of the 2-qp isomers in 246Cm (N = 150) and 248Cm (N = 152) support the persistence of a deformed subshell gap at N = 152 in the Z≈100 region down to Z = 96 nuclei. [ABSTRACT FROM AUTHOR]

A six-quasiparticle isomer with T1/2 = 57(2) ns has been established in the doubly-odd isotope 200Tl and its level scheme is significantly extended. Half-lives of previously reported isomers in 200Tl and 201,202Pb have been determined and revised values are reported in a few cases, with T1/2 = 397(17) ns and 7.0(5) ns for the Iπ = 5+ and 7- states in 200Tl, 52(2) ns for the 41/2+ level in 201Pb, and 93(4) ns for the 16+ state in 202Pb. Configurations for the isomers have been assigned and these predominantly involve intrinsic excitations of neutrons from the i13/2 subshell. The inferred transition rates for the decay of these isomers compare well with single-particle estimates attesting to their intrinsic character. [ABSTRACT FROM AUTHOR]

The structure of decoupled positive-parity and semidecoupled negative-parity bands up to high spin in 197,199Hg has been studied using multinucleon transfer reactions with the Gammasphere array. A positive-parity band in 199Hg with the (νi13/2)³ decoupled configuration that deexcites to levels in the negative-parity sequences is newly established. The semidecoupled sequences in both isotopes are extended to higher spin. Rotation-aligned angular momenta and crossing frequencies determined from experiment are in fair agreement with those from cranking calculations. A transition from oblate collective rotation at low spin to triaxial noncollective shapes at high spin is indicated. [ABSTRACT FROM AUTHOR]

Multi-quasiparticle high-K states, several of which are isomeric, were observed in 180Hf with the Gammasphere array. Lifetimes in the ns-μs range were determined using centroid-shift and decay measurements within a μs coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ=(18-) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well. [ABSTRACT FROM AUTHOR]

The decay of a Kπ=8- isomer in 244Pu and the collective band structures populating the isomer were studied using deep inelastic excitations with 47Ti and 208Pb beams, respectively. Precise measurements of M1/E2 branching ratios in the band confirm a 9/2-[734]ν⊗7/2+[624]ν configuration assignment for the isomer, validating the systematics of Kπ=8-, two-quasineutron isomers observed in even-Z, N=150 isotones. These isomers around the deformed shell gap at N=152 provide critical benchmarks for theoretical predictions of single-particle energies in this gateway region to superheavy nuclei. [ABSTRACT FROM AUTHOR]

High spin states in 73As have been investigated through the fusion-evaporation reaction 64Ni(12C,p2n)73As with an incident beam energy of 55 MeV. The level scheme has been extended up to Jπ=(37/2-) and excitation energy ~8.7 MeV with the addition of 30 new γ-ray transitions. The microscopic origins of the observed positive- and negative-parity band structures are discussed in the context of the particle rotor model. Nucleon alignments and shape evolution with increasing angular momentum are discussed in the framework of the cranked shell model and relativistic mean-field calculations. The results offer insight into the nature of the observed band structures and indicate prolate-oblate shape coexistence between positive- and negative-parity bands at low spin. [ABSTRACT FROM AUTHOR]

Parity doublet structures are established in 216Fr, which lies at the lower boundary of enhanced octupole collectivity in the trans-lead region. The newly identified levels are established as the simplex partner of a previously reported band leading to parity doublets with small (~55 keV) average energy splitting, a feature typical of nuclei with near-static octupole deformation. The observed levels do not follow a regular pattern of rotational bands, indicating low quadrupole collectivity. However, enhanced octupole correlations are evident from the small energy splitting and large B(E1)/B(E2) values. Staggering in E1 transition energies and B(E1)/B(E2) ratios is noted. The enhancement of octupole correlations in 216Fr is attributed to the availability of a neutron orbital with a K = 3/2 component. [ABSTRACT FROM AUTHOR]

High-spin states in the 188Pt nucleus have been investigated employing the 174Yb(18O,4n)188Pt reaction. The level scheme has been significantly extended with the addition of several new γ rays. The Indian National Gamma Array (INGA) spectrometer consisting of eighteen clover Ge detectors facilitated angular correlation and linear polarization measurements for spin-parity assignment of levels. The Iπ=5- semi-decoupled band has been investigated in detail, and the long-standing ambiguity regarding the correct ordering of associated γ rays is now removed with the new observation of transitions linking the even-spin levels to the odd-spin ones. A weak, ΔI=2 sequence of γ rays with alignment and moment of inertia similar to the yrast, even-spin, rotation-aligned neutron i13/2 band has been newly observed. Cranking calculations suggest that this new odd-spin sequence arises from the excitation of a valence quasineutron to the next i13/2 level. [ABSTRACT FROM AUTHOR]

Negative parity high-spin states of 107Cd have been investigated using the reaction 94Zr(18O,5n), from the γ-ray coincidence events recorded by the Indian National Gamma Array. A magnetic dipole (M1) band structure was established for the first time in this nucleus decaying to the low-spin states via several paths. Lifetimes of five in-band levels in this band have been measured using the Doppler shift attenuation method. The experimentally deduced B(M1) values are found to decrease with increasing spin. The experimental observations, interpreted by the tilted axis cranking calculations, suggest that the M1 band is developed from the shears mechanism based on the 5qp configuration π(g9/2-2) ⊗ ν(h11/2g7/2²), which is then crossed by another 5qp configuration π(g9/2-2) ⊗ ν(h11/2³). The semiclassical model of the shears mechanism also reasonably reproduces the decreasing trend of the observed B(M1) values as a function of spin, supporting the above interpretation. The present work highlights the unique coexistence of both magnetic and antimagnetic (observed by us earlier) rotation bands in one nucleus arising from the same proton configuration, but different neutron configurations. [ABSTRACT FROM AUTHOR]

The structure of 70Ge has been studied through in-beam γ-ray spectroscopy. A new band structure is identified that leads to forking of the ground-state band into two excited bands. Band structures have been investigated using the microscopic triaxial projected shell-model approach. The observed forking is demonstrated to result from almost simultaneous band crossing of the two-neutron aligned configuration and the γ band built on this two-quasiparticle configuration with the ground-state band. [ABSTRACT FROM AUTHOR]