Rotation-aligned isomeric states and associated oblate collective sequences are established in even Pt isotopes. Reduced E2 transition probabilities for the deexcitation of the 12 + isomers indicate an abrupt and unexpected quenching of oblate collectivity around neutron number N = 120. Structure and shape evolution at high spin in the heaviest stable isotopes is found to be markedly different from observations in the lighter ones.

An oblate rotational sequence, built on an aligned, two-quasineutron isomeric state has been established in 196 Pt. The isomer has a half-life of 7.7(7) ns and is associated with the I π =12 + , (i 13/2 ) 2 neutron configuration. Excited states, with angular momentum generated primarily through successive nucleon alignments, have been populated through 1p transfer from 197 Au. The nucleus 196 Pt 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.

The excited level structures of 202 Tl and 203 Pb, above the 7 + and 29/2 − isomers, respectively, have been studied. An isomer with I π = 20 + and T 1/2 = 215(10) μs has been established in 202 Tl, and the level scheme extended from I = 10 to 20 h with the placement of fifteen new transitions. In 203 Pb, the I π = 37/2 + state is established to be metastable, with T 1/2 = 2.5(3) ns. Levels in both nuclei arise from intrinsic excitations, with likely particle-hole character for the higher-lying states in 203 Pb. The 20 + isomer in 202 Tl is most likely associated with a π h −1 11/2 ⊗ ν(i −2 13/2 , f −1 5/2 ) configuration, while the 37/2 + state in 203 Pb results from the excitation of five neutrons. Calculations, using both an empirical approach and the OXBASH code, have been performed to aid in the description of the excited level structure.

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