The single-particle structure and shell gap of 100Sn as inferred from previous in-beam γ-ray spectroscopy has been confirmed in recent studies of seniority and spin-gap isomers by γγ, βγ, βpγ, pγ and 2pγ spectroscopy. The results for 94,95Ag, 98Cd and its N=50 isotones 96Pd and 94Ru stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations, seniority mixing and E2 polarisation of the 100Sn core. The strong monopole interaction of the Δl=0, 1 spin/isospin-flip partners πg 9/2-νg 7/2 along the N=50 isotones and the πf 5/2-νg 9/2 pair of nucleons along the Z=28 Ni isotopes are decisive for the evolution of the shell structure towards 100Sn and 78Ni. It can be traced back to the tensor force in the effective nucleon-nucleon interaction and provides a straightforward explanation for new shells in neutron-rich light nuclei, implying qualitative predictions for new N=32, 34 subshells in Ca isotopes, persistence of the 78Ni proton and neutron shell gaps and non-equivalence of the g 9/2 valence mirror Ni isotopes and N=50 isotones. This is corroborated by recent experimental data on 56,58Cr and 70–76Ni. The implication of monopole driven shell evolution for apparent spin-orbit splitting towards N ≫ Z and structure along the astrophysical r-path between N=50 and N=82 is discussed

https://link.springer.com/content/pdf/10.1140%2Fepja%2Fi2006-08-040-7.pdf

Nuclear structure far off stability —Implications for nuclear astrophysics

Is seniority a partial dynamic symmetry in the first νg9/2 shell?

Partial conservation of seniority and its unexpected influence on E2 transitions in g 9/2 nuclei

Direct lifetime measurements via γ−γ coincidences using a fast timing detector array consisting of LaBr3(Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N=50) nucleus Ru94. The experiment was carried out as the first in a series of “FAIR-0” experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru94 were populated primarily via the β-delayed proton emission of Pd95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe124 beam impinging on a 4 g/cm2Be9 target. While the deduced E2 strength for the 2+→0+ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4+→2+ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the fpg proton hole space with respect to doubly magic Sn100. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority ν=2, Iπ=4+ state and that of a close-lying ν=4 state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive 6+→4+ transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.Received 17 October 2021Revised 17 January 2022Accepted 11 March 2022DOI:https://doi.org/10.1103/PhysRevC.105.L031304Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasIsomer decaysProton emissionProperties90 ≤ A ≤ 149Nuclear bindingTechniquesGamma ray spectroscopyNuclear structure & decaysRadiation detectorsRadioactive beamsSpectrometers & spectroscopic techniquesNuclear PhysicsAccelerators & Beams 

/pdf/nature-of-seniority-symmetry-breaking-in-the-semimagic-et8sdmf7.pdf

Nature of seniority symmetry breaking in the semimagic nucleus 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ru</mml:mi><mml:mprescripts /><mml:none /><mml:mn>94</mml:mn></mml:mmultiscripts></mml:math>

The seniority symmetry is known to be partially conserved in two special cases in the ${(9/2)}^{4}$ system, which can lead to striking features in the corresponding structure and electromagnetic transition properties. However, it is still quite difficult to derive those kind of solvable states, in general, especially towards higher-$j$ orbits. We have developed a novel and effective way to confront this challenge by starting from the $m$ scheme and making use of the angular momentum projection method. It also allows us to explore another special family of seniority conserving states in the midshell besides the specific case of the ${(9/2)}^{4}$ configuration. Moreover, we have studied systemically all states in single-$j$ systems up to $j=15/2$ and derived the analytic expressions for the eigenvalues of all solvable states with a focus on those in $j=9/2$ and $j=11/2$. Such studies can also be useful for the experimental search of relevant states and for the understanding of their electromagnetic transition properties.

Partial seniority conservation and solvability of single-j systems

Swedish Research Council; European Community [HPRI-CT 1999-00019]; Spanish MINECO [FPA2015-65035-P]

/pdf/ultrafast-timing-lifetime-measurements-in-ru-94-and-pd-96-2jur5m6ytr.pdf

Ultrafast-timing lifetime measurements in Ru 94 and Pd 96 : Breakdown of the seniority scheme in N = 50 isotones

Nuclear structure studies of exotic nuclei via the strength of E2 transitions; advanced time-delayed γγ spectroscopy at the extreme

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Ultrafast-timing lifetime measurements in Ru 94 and Pd 96 : Breakdown of the seniority scheme in N = 50 isotones

Nuclear structure studies of exotic nuclei via the strength of E2 transitions; advanced time-delayed γγ spectroscopy at the extreme