Tonev, D. et al, & Gadea, A. (2021). Transition probabilities in P-31 and S-31: A test for isospin symmetry. Phys. Lett. B, 821, 136603–6pp.
Abstract: Excited states in the mirror nuclei P-31 and S-31 were populated in the 1p and 1n exit channels of the reaction Ne-20 + C-12, at a beam energy of 33 MeV. The Ne-20 beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident gamma-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A = 31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction.
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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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Pasqualato, G. et al, Gadea, A., & Jurado, M. (2023). An alternative viewpoint on the nuclear structure towards 100Sn: Lifetime measurements in 105Sn. Phys. Lett. B, 845, 138148–7pp.
Abstract: This work aims at presenting an alternative approach to the long standing problem of the B(E2) values in Sn isotopes in the vicinity of the N=Z double-magic nucleus Sn-100, until now predominantly measured with relativistic and intermediate-energy Coulomb excitation reactions. The direct measurement of the lifetime of low-lying excited states in odd-even Sn isotopes provides a new and precise guidance for the theoretical description of the nuclear structure in this region. Lifetime measurements have been performed in Sn-105 for the first time with the coincidence Recoil Distance Doppler Shift technique. The lifetime results for the 7/2(1)(+) first excited state and the 11/2(1)(+) state, 2(+)(Sn-104) circle times nu 1g(7/2) multiplet member, are discussed in comparison with state-of-the-art shell model and mean field calculations, highlighting the crucial contribution of proton excitation across the core of Sn-100. The reduced transition probability B(E2) of the 11/2(1)(+) core-coupled state points out an enhanced staggering with respect to the B(E2; 2(1)(+) -> 0(1)(+)) in the even-mass Sn-104 and Sn-106 isotopes.
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Gottardo, A. et al, Gadea, A., & Algora, A. (2012). New Isomers in the Full Seniority Scheme of Neutron-Rich Lead Isotopes: The Role of Effective Three-Body Forces. Phys. Rev. Lett., 109(16), 162502–5pp.
Abstract: The neutron-rich lead isotopes, up to Pb-216, have been studied for the first time, exploiting the fragmentation of a primary uranium beam at the FRS-RISING setup at GSI. The observed isomeric states exhibit electromagnetic transition strengths which deviate from state-of-the-art shell-model calculations. It is shown that their complete description demands the introduction of effective three-body interactions and two-body transition operators in the conventional neutron valence space beyond Pb-208.
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Taprogge, J. et al, Gadea, A., & Montaner-Piza, A. (2014). 1p(3/2) Proton-Hole State in Sn-132 and the Shell Structure Along N=82. Phys. Rev. Lett., 112(13), 132501–6pp.
Abstract: A low-lying state in In-131(82), the one-proton hole nucleus with respect to double magic Sn-132, was observed by its gamma decay to the I-pi 1/2(-) beta-emitting isomer. We identify the new state at an excitation energy of E-x = 1353 keV, which was populated both in the beta decay of Cd-131(83) and after beta-delayed neutron emission from Cd-132(84), as the previously unknown pi p(3/2) single-hole state with respect to the Sn-132 core. Exploiting this crucial new experimental information, shell-model calculations were performed to study the structure of experimentally inaccessible N = 82 isotones below Sn-132. The results evidence a surprising absence of proton subshell closures along the chain of N = 82 isotones. The consequences of this finding for the evolution of the N = 82 shell gap along the r-process path are discussed.
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