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Across the physics disciplines, the 186Pb nucleus is the only known system, where the two first excited states, together with the ground state, form a triplet of zero-spin states assigned with prolate, oblate and spherical shapes. Here we report on a precision measurement where the properties of collective transitions in 186Pb were determined in a simultaneous in-beam γ-ray and electron spectroscopy experiment employing the recoil-decay tagging technique. The feeding of the 0+2 state and the interband 2+2→2+1 transition have been observed. We also present direct measurement of the energies of the electric monopole transitions from the excited 0+ states to the 0+ ground state. In contrast to the earlier understanding, the obtained reduced transition probability B(E2;2+1→0+2) value of 190(80) W.u., the transitional quadrupole moment |Qt(2+1→0+2)|=7.7(33) eb and intensity balance arguments provide evidence to reassign the 0+2 and 0+3 states with predominantly prolate and oblate shape, respectively. Our work demonstrates a step-up in experimental sensitivity and paves the way for systematic studies of electric monopole transitions in this region. These electric monopole transitions probe the nuclear volume in a unique manner and provide unexploited input for development of the next-generation energy density functional models. peerReviewed

The mean lifetimes of the lowest energy 2+, 8+ and 9− states in 166Os have been measured using the recoil distance Doppler-shift method in conjunction with a selective recoil-decay tagging technique. These measurements extend studies into the most neutron-deficient mass region accessible to current experimental methods. The B(E2; 2+ → 0+) = 7(2) W.u. extracted from these measurements is markedly lower than those observed in the heavier even-mass Os isotopes. The 8+ and 9− states yield reduced transition probabilities that are consistent with single-particle transitions. While these values may indicate a departure from collective structure, the level scheme and the underlying nuclear configurations can also be interpreted in terms of a simple collective picture. This contrasting behaviour suggests an intriguing dichotomy in the description of heavy transitional nuclei. peerReviewed

Two experiments aiming to study the shape coexistence and competing structures in 193Bi and 195Bi isotopes have been performed at the Accelerator laboratory of the University of Jyv askyl a, Finland (JYFL). Many new states have been found, hugely extending the previously known level schemes for both isotopes. The i13=2 bands were extended up to I = 45/2+ in both the 193;195Bi isotopes. In case of 193Bi, the I = 31/2+ member of the i13=2 band was found to de-excite also to a long-lived isomeric state. This link determines the energy of the isomeric state to be 2350(1) keV and suggests a spin and parity of 29/2+. The half-life of the isomeric state was measured to be 85(3) s. A level structure on top of this isomeric state was constructed. The newly observed 49 keV E2 transition provides a link between the (29/2􀀀) isomeric state and lower-lying structures in 193Bi. A superdeformed band almost identical to that present in the neighboring isotope 191Bi has been identified. Both the 29/2+ and (29/2􀀀) isomeric states, together with the full decay-paths have also been identified in 195Bi. In both isotopes, the decay cascades from 31/2+ states to the 29/2+ isomeric states are surprisingly similar. Compared to 193Bi, measured half-lives of these isomeric states are considerably shorter in 195Bi. Experimental evidence is given proving the smaller quadrupole deformations in 195Bi when compared to 193Bi nucleus. Moreover, several new rotational collective structures have been identified in 195Bi, even though their variety is not as rich as in 193Bi. This is the first time the collective structures have been observed up to a high spins and excitation energies in 195Bi. Strong manifestation of shape coexistence is thus proved to be present also in 195Bi. Keywords