Effect of Weak Binding on the Apparent Spin-Orbit Splitting in Nuclei

Kay, B. P.; Hoffman, C. R.; Macchiavelli, A. O.

doi:10.1103/physrevlett.119.182502

Cited by 16 publications

(25 citation statements)

References 14 publications

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“…Further studies on the neutron 2p 3/2 -2p 1/2 splitting of the same nuclei has been made recently (Kay et al, 2017), where the change of this splitting was interpreted in terms of loose binding effects. It, however, can be described in terms of the monopole effect of the 2b-LS force, as described in Supplemental Material Sec.…”

Section: Spectroscopy Of the Nuclear Wave Function Through Direct Reamentioning

confidence: 95%

Evolution of shell structure in exotic nuclei

et al. 2020

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The atomic nucleus is a quantum many-body system whose constituent nucleons (protons and neutrons) are subject to complex nucleon-nucleon interactions that include spin-and isospin-dependent components. For stable nuclei, already several decades ago, emerging seemingly regular patterns in some observables could be described successfully within a shell-model picture that results in particularly stable nuclei at certain magic fillings of the shells with protons and/or neutrons: N,Z = 8, 20, 28, 50, 82, 126. However, in short-lived, so-called exotic nuclei or rare isotopes, characterized by a large N/Z asymmetry and located far away from the valley of beta stability on the nuclear chart, these magic numbers, viewed through observables, were shown to change. These changes in the regime of exotic nuclei offer an unprecedented view at the roles of the various components of the nuclear force when theoretical descriptions are confronted with experimental data on exotic nuclei where certain effects are enhanced. This article reviews the driving forces behind shell evolution from a theoretical point of view and connects this to experimental signatures.

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Section: Spectroscopy Of the Nuclear Wave Function Through Direct Reamentioning

confidence: 95%

Evolution of shell structure in exotic nuclei

et al. 2020

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“…[18].As zero binding is approached, the energies of s orbitals increase less rapidly than those of states with higher angular momenta [19]. This behavior has been studied for light nuclei [20,21] and, in the vicinity of N = 126, it is likely to play an important role in neutron-capture reactions. Direct measurements of properties of nuclei in the r-process path in this region will not be possible for many years, if not decades.…”

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confidence: 99%

First Exploration of Neutron Shell Structure below Lead and beyond N=126

Tang¹,

Kay²,

Hoffman³

et al. 2020

Phys. Rev. Lett.

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The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical r-process in producing nuclei heavier than A ∼ 190. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in 207 Hg have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of 206 Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of 207 Hg marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the r-process.The nucleus 207 Hg lies in the almost completely unexplored region of the nuclear chart below proton number 82 and just above neutron number 126, both "magic" numbers representing closed shells in the nuclear shell model [1]. The doubly-magic nucleus 208 Pb is the cornerstone of this region, a benchmark nucleus in our understanding of the single-particle foundation of nuclear structure. This region, highlighted on the nuclear chart in Fig. 1, is unique in that its single-particle structure remains unexplored.The nucleosynthesis of heavy elements via the rapid neutron-capture (r-) process path [2] crosses this region, as shown in Fig. 1. The robustness of the N = 126 neutron shell closure plays a crucial role in the nucleosynthesis of the actinides [3][4][5][6][7]. The recent observation of a neutron star merger has provided a new focus of interest [8,9], suggesting a possible astrophysical environment for r-process nucleosynthesis [10-13].Approaching the r-process path along the N = 126 isotonic chain from Pb, the binding energies (the degree to which neutrons are bound by the mean-field potential created by the decreasing number of all other nucleons) decrease, eventually crossing zero binding and becoming unbound. Near closed shells, the level density is low, so the usual statistical assumptions of many resonances participating in neutron capture is not valid, and specific nuclear-structure properties become important. Knowledge of ground-state binding energies of nuclei with N = 126 + n is important in defining the waiting point caused by the N = 126 closure, the bottleneck which is responsible for the third peak in solar system elemental abundances at nuclear mass A ∼ 195 [14]. The binding energies are critical to how the r-process evolves. The energies of ground and excited states have significant consequences for the rate at which direct s-, p-, (and possibly d-) wave neutron-capture (n,γ) reactions proceed [15][16][17]. This was discussed recently in the context of the N = 82 shell closure in Ref. [18].As zero binding is approached, the energies of s orbitals increase less rapidly than those of states with higher angular momenta [19]. This behavior has been studied for light nuclei [20,21] and, in the vicinity o...

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“…Figure 8 shows that the possible significant change in the neutron 2p 3/2 -2p 1/2 gap between 35 Si and 37 S is explained to a good extent by the shell evolution due to the two-body spin-orbit force. 39 Ar [50], and 41 Ca [50,51]. The horizontal bars are the energy differences between relevant highest peaks [50,52].…”

Section: Monopole Interaction Of the Two-body Spin-orbit Forcementioning

confidence: 99%

Emerging Concepts in Nuclear Structure Based on the Shell Model

Otsuka

2022

Physics

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Some emerging concepts of nuclear structure are overviewed. (i) Background: the many-body quantum structure of atomic nucleus, a complex system comprising protons and neutrons (called nucleons collectively), has been studied largely based on the idea of the quantum liquid (à la Landau), where nucleons are quasiparticles moving in a (mean) potential well, with weak “residual” interactions between nucleons. The potential is rigid in general, although it can be anisotropic. While this view was a good starting point, it is time to look into kaleidoscopic aspects of the nuclear structure brought in by underlying dynamics and nuclear forces. (ii) Methods: exotic features as well as classical issues are investigated from fresh viewpoints based on the shell model and nucleon–nucleon interactions. The 70-year progress of the shell–model approach, including effective nucleon–nucleon interactions, enables us to do this. (iii) Results: we go beyond the picture of the solid potential well by activating the monopole interactions of the nuclear forces. This produces notable consequences in key features such as the shell/magic structure, the shape deformation, the dripline, etc. These consequences are understood with emerging concepts such as shell evolution (including type-II), T-plot, self-organization (for collective bands), triaxial-shape dominance, new dripline mechanism, etc. The resulting predictions and analyses agree with experiment. (iv) Conclusion: atomic nuclei are surprisingly richer objects than initially thought.

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Effect of Weak Binding on the Apparent Spin-Orbit Splitting in Nuclei

Cited by 16 publications

References 14 publications

Evolution of shell structure in exotic nuclei

Evolution of shell structure in exotic nuclei

First Exploration of Neutron Shell Structure below Lead and beyond N=126

Emerging Concepts in Nuclear Structure Based on the Shell Model

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