| 1. |
- Ojala, Joonas, et al.
(författare)
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Reassigning the shapes of the 0+ states in the 186Pb nucleus
- 2022
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Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- 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 02+ state and the interband 22+→21+ 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;21+→02+) value of 190(80) W.u., the transitional quadrupole moment ∣Qt(21+→02+)∣=7.7(33) eb and intensity balance arguments provide evidence to reassign the 02+ and 03+ 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.
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| 2. |
- Zhang, Wei, et al.
(författare)
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Observation of the proton emitter 11657La59
- 2022
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Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental “smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope 1165757116La59, 23 neutrons away from the only stable isotope 1395757139La82, is reported. 116La nuclei were synthesised in the fusion-evaporation reaction 58Ni(64Zn, p5n)116La and identified via their proton radioactivity using the mass spectrometer MARA (Mass Analysing Recoil Apparatus) and the silicon detectors placed at its focal plane. Comparisons of the measured proton energy (Ep = 718 ± 9 keV) and half-life (T1/2 = 50 ± 22 ms) with values calculated using the Universal Decay Law approach indicate that the proton is emitted with an orbital angular momentum l = 2 and that its emission probability is enhanced relative to its closest, less exotic, odd-even lanthanum isotope (1175757117La60) while the proton-emission Q-value is lower. We propose this to be a possible signature for the presence of strong neutron-proton pair correlations in this exotic, neutron deficient system. The observations of γ decays from isomeric states in 116La and 117La are also reported.
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