Abstract: The multi-nucleon transfer reaction mechanism was used to produce and study nuclei in the vicinity of 208Pb. This mass region is a test case for the nuclear shell model. The mass identification of the fragments was performed with the large acceptance magnetic spectrometer VAMOS++ coupled to the AGATA gamma-tracking array. This experiment aimed to determine both lifetimes and gyromagnetic ratios of excited states with the Cologne plunger device. The analysis indicates promising results with the possibility to determine several new lifetimes in this region.

Abstract: The structure of As-83,As- 85, and As-87 have been studied in fusion-fission reaction( 238)U+9Be. Fission fragments were identified in mass and atomic number using the VAMOS++ spectrometer and the coincident gamma rays were detected in the gamma-ray tracking array AGATA. New transitions in 83As and 85As are reported and placed in the level schemes. A level scheme of the excited states in 87As is proposed for the first time. The data are interpreted in frame of large-scale shell-model calculations, SU3 symmetries, and beyond mean-field frameworks. A spherical regime at magic number N = 50 is predicted and the location of the proton g9/2 orbital is proposed for the first time. Development of collectivity in a prolate deformed, gamma-soft regime in the open shell cases 85As and 87As, most neutron-rich isotopes beyond N = 50, is concluded. Data and theoretical calculations give confidence to a relatively high extrapolated excitation energy about 4 MeV of the 9/2+ state in 79Cu, one proton above 78Ni.

Abstract: A gamma-ray spectroscopic study of Po-212 was performed at the Grand Accelerateur National d'Ions Lourds, using the inverse kinematics alpha-transfer reaction C-12(Pb-208, Po-212) Be-8 and the AGATA spectrometer. A careful analysis based on gamma gamma coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of 1(-) and 2(-) and excitation energies below 2.1 MeV, which have been predicted by recent alpha-cluster model calculations. A systematic comparison of the experimentally established excitation scheme of Po-212 with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4(-)), 1751 (8(-)), 1787 (6(-)), 1946 (4(-)), 1986 (8(-)), and 2016 (6(-)) keV, which previously were interpreted as alpha-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of Po-212 is supported by experimental information with respect to the linear polarization of gamma rays, which suggests a magnetic character of the 432-keV gamma ray decaying from the state at an excitation energy of 1787 keV to the 6(1)(+) yrast state, and exclusive reaction cross sections.

Abstract: Lifetime measurements of excited states of the light N = 52 isotones Kr-88, Se-86, and Ge-84 have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2; 2(+)-> 0(+)) and B(E2; 4(+)-> 2(+)) were obtained for the first time for the hard-to-reach 84Ge. While the B(E2; 2(+)-> 0(+) ) values of Kr-88, Se-86 saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g(7/2), 1h(11/2)) space of an inert Ni-78 core, the value obtained for Ge-84 largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N less than or similar to 49, extend beyond N = 50. The onset of collectivity at Z = 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector rho field in shell-structure evolution.

Abstract: Background: The Z = 50 shell closure, near N = 82, is unique in the sense that it is the only shell closure with the spin-orbit partner orbitals, pi g(9/2) and pi g(7/2), enclosing the magic gap. The interaction of the proton hole/particle in the above-mentioned orbitals with neutrons in the nu h(11)(/2) orbital is an important prerequisite to the understanding of the nuclear structure near N = 82 and the nu pi interaction. Purpose: To explore the structural similarity between the high-spin isomeric states in In (Z = 49), Sn (Z = 50), and Sb (Z = 51) isotopes from a microscopic point of view. In addition, to understand the role of a proton hole or particle in the spin-orbit partner orbitals, pi g(9/2) and pi g(7/2), respectively, with neutron holes in the nu h(11)(/2) orbital on these aforementioned isomers. Methods: The fusion and transfer induced fission reaction Be-9(U-238, f) with 6.2 MeV/u beam energy, using a unique setup consisting of AGATA, VAMOS ++, and EXOGAM detectors, was used to populate through the fission process and study the neutron-rich In-119,In-121 isotopes. This setup enabled the prompt-delayed gamma-ray spectroscopy of isotopes in the time range of 100 ns-200 μs. Results: In the odd-A In-119,In-121 isotopes, indications of a short half-life 19/2(-) isomeric state, in addition to the previously known 25/2(+) isomeric state, were observed from the present data. Further, new prompt transitions above the 25/2(+) isomer in In-121 were identified along with reevaluation of its half-life. Conclusions: The experimental data were compared with the theoretical results obtained in the framework of large-scale shell-model calculations in a restricted model space. The <pi g(9/2)nu h(11/2); I vertical bar H vertical bar pi g(9/2) nu h(11/2);I > two-body matrix elements of residual interaction were modified to explain the excitation energies and the B(E2) transition probabilities in the neutron-rich In isotopes. The (i) decreasing trend of E(29/2(+))-E(25/2(+)) in odd-In (with dominant configuration pi g(9/)(2)(-1) nu h(11/2)(-2) and maximum aligned spin of 29/2+) and (ii) increasing trend of E(27/2(+)) – E(23/2(+)) in odd-Sb (with dominant configuration pi g(7/)(2)(+1) nu h(11/2)(-2) and maximum aligned spin of 27/2(+)) with increasing neutron number could be understood as a consequence of hole-hole and particle-hole interactions, respectively.