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Sahin, E. et al, & Algora, A. (2024). Collectivity at the prolate-oblate transition: The 21+ lifetime of 190W. Phys. Lett. B, 857, 138976–8pp.
Abstract: The neutron-rich rare isotope W-190 is discussed as a candidate for a prolate-oblate transitional nucleus with maximum gamma-softness. The collectivity of this isotope is assessed for the first time by the measurement of the reduced E2 transition probability of its first 2(+) state to the ground state. The experiment employed the FAst TIming Array (FATIMA), comprised of 36 LaBr3(Ce) scintillators, which was part of the DESPEC setup at GSI, Darmstadt. The 4(1)(+) and 2(1)(+) states of W-190 were populated subsequently to the decay of its 127(12) μs isomeric J(pi )= 10(-) state. The mean lifetime of the 2(1)(+) state was determined to be tau = 274(28) ps, which corresponds to a B(E2; 2(1)(+ )-> 0(1)(+)) value of 95(10) W.u. The results motivated a revision of previous calculations within an energy-density functional-based interacting boson model-2 approach, yielding E2 transition properties and spectroscopic quadrupole moments for tungsten isotopes. From comparison to theory, the new data suggest that W-190 is at the transition from prolate to oblate structure along the W isotopic chain, which had previously been discussed as a nuclear shape-phase transition.
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Zago, L. et al, Gadea, A., & Algora, A. (2022). High-spin states in Po-212 above the alpha-decaying (18(+)) isomer. Phys. Lett. B, 834, 137457–5pp.
Abstract: The nucleus Po-212 has been produced through the fragmentation of a U-238 primary beam at 1GeV/nucleon at GSI, separated with the FRagment Separator, FRS, and studied via isomer gamma-decay spectroscopy with the RISING setup. Two delayed previously unknown gamma rays have been observed. One has been attributed to the E3 decay of a 21(-) isomeric state feeding the alpha-emitting 45-s (18(+)) high-spin isomer. The other gamma-ray line has been assigned to the decay of a higher-lying 23(+) metastable state. These are the first observations of high-spin states above the Po-212 (18(+)) isomer, by virtue of the selectivity obtained via ion-by-ion identification of U-238 fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high- jproton and neutron orbitals, to which the region around Z similar to 100 is sensitive.
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