Low-energy dipole response of exotic nuclei

Aumann, T.

doi:10.1140/epja/i2019-12862-7

Cited by 13 publications

(8 citation statements)

References 60 publications

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“…From the ground state, we have considered electric dipole transitions into the continuum. It is known that two-neutron halo nuclei, and in general weakly bound nuclei at the driplines, exhibit large E1 transition probabilities (and therefore large crosssections in Coulomb excitation experiments) [15][16][17] . Since the halo structure is favored by p-wave intruder components, a measurement of the E1 strength could confirm whether 29 F belongs to the island of inversion.…”

Section: Theoretical Approaches and New Experimentsmentioning

confidence: 99%

The 29F nucleus as a lighthouse on the coast of the island of inversion

et al. 2020

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The exotic, neutron-rich and weakly-bound isotope 29 F stands out as a waymarker on the southern shore of the island of inversion, a portion of the nuclear chart where the effects of nuclear forces lead to a reshuffling of the single particle levels and to a reorganization of the nuclear structure far from stability. This nucleus has become very popular, as new measurements allow to refine theoretical models. We review the latest developments and suggest how to further assess the structure by proposing predictions on electromagnetic transitions that new experiments of Relativistic Coulomb Excitation should soon become able to measure. W eakly bound nuclear systems severely test our ability to disentangle the mysteries and oddities of the nuclear interactions and how nuclear systems achieve stability. One of the latest conundrums in this respect is the structure of the exotic 29-fluorine isotope. With nine protons and 20 neutrons, it is located almost on the edge of the stability valley of the nuclide chart, very close to the neutron drip-line, i.e., the dividing line (S n = 0, null separation energy) between bound and unbound neutron-rich nuclei. Pioneering researches on this isotope have recently skyrocketed, as more and more theoretical and experimental papers are being published. The main interest lies in understanding if it belongs to the so-called island of inversion, a portion of the nuclear chart where the standard list of single-particle energy levels (that are filled by nucleons, very similarly to the atomic physics counterpart, in a sort of Aufbauprinzip, a.k.a. the building-up principle, i.e., the rule that states how electronic orbitals are filled up in the atomic shell model) shows an inversion between orbitals belonging to the sdand pf-shells, see Fig. 1. This is crucial to ascertain the presence of a neutron halo (a diffused tail of nuclear matter that spreads around the central core) and its extent. This problem relates also to the disappearance of the N = 20 neutron magic number when moving away from doubly magic nuclei. This shell evolution has profound connections with tensor nuclear interactions 1,2 and with the deformation of the nuclear surface, occurring typically at mid-shell. This system, due to its mass A = 29, is still a hard nut to crack for ab initio approaches exploiting gargantuan numerical calculations. At present, simpler schematic models

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Section: Theoretical Approaches and New Experimentsmentioning

confidence: 99%

The 29F nucleus as a lighthouse on the coast of the island of inversion

et al. 2020

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“…where we adopt the same parameter as Ref. [22]: t 0 = f × (−1100) fm 3 MeV,t 3 = f × 16000 fm 6 MeV, x 0 = 0.5, x 3 = 1, P σ is the spin-exchange operator. The Woods-Saxon parameter is that of Ref.…”

Section: Numerical Example a Settingmentioning

confidence: 99%

“…Examples include the pygmy dipole resonance or the soft dipole excitation, which are considered as a new type of collective excitation or a continuum particle-hole excitations where a neutron is brought into unbound scattering state [1][2][3][4]. In the laboratory experiments, such exotic modes of excita-tion are observed in the excitation reactions such as the photo-absorption or the Coulomb or nuclear dissociation processes [5][6][7]. In the nature, neutron-rich nuclei play important role in the r-process nucleosynthesis, and it has been pointed out that the pygmy or the soft dipole excitations might influence the radiative neutron-capture reaction and resultant abundance of r-process nuclei [8,9].…”

Section: Introductionmentioning

confidence: 99%

Continuum random-phase approximation for gamma transition between excited states in neutron-rich nuclei

Saito,

Matsuo

2021

Preprint

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A characteristic feature of collective and particle-hole excitations in neutron-rich nuclei is that many of them couple to unbound neutron in continuum single-particle orbits. The continuum random phase approximation (cRPA) is a powerful many-body method that describes such excitations, and it provides a scheme to evaluate transition strengths from the ground state. In an attempt to apply cRPA to the radiative neutron capture reaction, we formulate in the present study an extended scheme of cRPA that describes gamma-transitions from the excited states under consideration, which decay to low-lying excited states as well as the ground state. This is achieved by introducing a non-local one-body operator which causes transitions to a low-lying excited state, and describing a density-matrix response against this operator. As a demonstration of this new scheme, we perform numerical calculation for dipole, quadrupole, and octupole excitations in 140 Sn, and discuss E1 and E2 transitions decaying to low-lying 2 + 1,2 and 3 − 1 states. The results point to cases where the branching ratio to the low-lying states is larger than or comparable with that to the ground state. We discuss key roles of collectivity and continuum orbits in both initial and final states.

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“…One way to solve the problem and constrain L stiffly is to find a direct and model-independent correlation between α D and L. Although the previous studies have shown that the model-independent linear correlation only exists between α D J and L, it was only limited to stable nuclei or nuclei near β-stability line. It is well known that exotic phenomena will present when approaching to nuclei far from β-stability line, such as novel shell structures [40][41][42][43][44], new types of excitations [23,45,46], and so on. For E1 excitations, the pygmy dipole resonance (PDR) appears in neutron-rich nuclei [23,45,46], which would cause different characteristics of E1 excitations compared to the ones around β-stability line, and further affect α D .…”

Section: Introductionmentioning

confidence: 99%

“…It is well known that exotic phenomena will present when approaching to nuclei far from β-stability line, such as novel shell structures [40][41][42][43][44], new types of excitations [23,45,46], and so on. For E1 excitations, the pygmy dipole resonance (PDR) appears in neutron-rich nuclei [23,45,46], which would cause different characteristics of E1 excitations compared to the ones around β-stability line, and further affect α D . So an interesting question is if the linear correlation between α D J and L observed in stable nuclei still holds and new correlations would appear in neutron-rich nuclei.…”

Section: Introductionmentioning

confidence: 99%

Electric dipole polarizability in neutron-rich Sn isotopes as a probe of nuclear isovector properties

Li,

Niu,

Long

2021

Preprint

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The determination of nuclear symmetry energy, and in particular, its density dependence, is a long-standing problem for nuclear physics community. Previous studies have found that the product of electric dipole polarizability α D and symmetry energy at saturation density J has a strong linear correlation with L, the slope parameter of symmetry energy. However, current uncertainty of J hinders the precise constraint on L. We investigate the correlations between electric dipole polarizability α D (or times symmetry energy at saturation density J) in Sn isotopes and the slope parameter of symmetry energy L using the quasiparticle random-phase approximation based on Skyrme Hartree-Fock-Bogoliubov. A strong and model-independent linear correlation between α D and L is found in neutron-rich Sn isotopes where pygmy dipole resonance (PDR) gives a considerable contribution to α D , attributed to the pairing correlations playing important roles through PDR. This newly discovered linear correlation would help one to constrain L and neutron-skin thickness ∆R np stiffly if α D is measured with high resolution in neutron-rich nuclei. Besides, a linear correlation between α D J in a nucleus around β-stability line and α D in a neutron-rich nucleus can be used to assess α D in neutron-rich nuclei.

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Low-energy dipole response of exotic nuclei

Cited by 13 publications

References 60 publications

The 29F nucleus as a lighthouse on the coast of the island of inversion

The 29F nucleus as a lighthouse on the coast of the island of inversion

Continuum random-phase approximation for gamma transition between excited states in neutron-rich nuclei

Electric dipole polarizability in neutron-rich Sn isotopes as a probe of nuclear isovector properties

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