Nuclear Theory·nucl-th

Tuesday·October 30, 2018

14 papers—8 primary·6 cross-listed

01
[Submitted on 28 Oct 2018]
Microscopic quantum ideal rotor model and related self-consistent cranking model, I: uni-axial rotation case
Parviz Gulshani
A microscopic quantum ideal rotor-model Hamiltonian (distinct from that of Bohr's rotational model) is derived for a rotation about a single axis by applying a dynamic rotation operator to the deformed nuclear ground-state wavefunction. It is shown that the microscopic ideal rotor Hamiltonian is obtained only for a rigid-flow prescription for the rotation angle, with the attendant rigid-flow kinematic moment of inertia. (For the center-of-mass motion, the method predicts the correct mass.) Using Hartree-Fock variational and second quantization methods, the ideal rotor-model Hamiltonian is reduced to that of a self-consistent cranking model plus residual terms associated with the square of the angular momentum operator and a two-body interaction. The approximations and assumptions underlying the conventional cranking model are revealed. The resulting nuclear Schrodinger equation, including a residual two-body interaction and the residual part of the square of the angular momentum, is then solved in the Tamm-Dancoff approximation using he eigenstates of the self-consistent cranking model, with a self-consistent deformed harmonic oscillator potential, as the particle-hole basis states. Good agreement is obtained between the predicted and measured ground-state rotational-band excitation energies, including the lowering of the excitation energy with increasing angular momentum, in Ne-20 when the effects of a 3-D rotation are simulated in the model.
Comments:
20 pages, 3 figures, Eq.(32) has been corrected to include the square of the rotation angular velocity. This term was inadvertently omitted in the previous two versions of the article. Eq 24 page 8 is corrected by replacing omega by < J >
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.11836 [pdf]
1 citation
02
[Submitted on 28 Oct 2018]
Particle-hole symmetry breaking due to Pauli blocking
D. Bonatsos · I. E. Assimakis · A. Martinou · S. Sarantopoulou · S. Peroulis · N. Minkov
Particle-hole symmetry has been used on several occasions in nuclear structure over the years. We prove that particle-hole symmetry is broken in nuclear shells possessing the proxy-SU(3) symmetry. The breaking of the symmetry is rooted in the Pauli principle and the short range nature of the nucleon-nucleon interaction. The breaking of the symmetry explains the dominance of prolate over oblate shapes in deformed nuclei and determines the regions of prolate to oblate shape transitions in the nuclear chart. Furthermore, it is related to the existence of specific regions of shape coexistence across the nuclear chart, surrounded by regions in which shape coexistence does not occur.
Comments:
9 pages, 2 figures, to appear in HNPS: Advances in Nuclear Physics: Proceedings of the 27th Annual Symposium of the Hellenic Nuclear Physics Society (Athens, 2018), ed. T. Mertzimekis, G. Souliotis, and E. Styliaris
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.11858 [pdf]
1 citation
03
[Submitted on 28 Oct 2018]
Nucleon numbers for nuclei with shape coexistence
A. Martinou · D. Bonatsos · N. Minkov · T. Mertzimekis · I.E. Assimakis · S. Peroulis · S. Sarantopoulou
We consider two competing sets of nuclear magic numbers, namely the harmonic oscillator (HO) set (2, 8, 20, 40, 70, 112, 168, 240,...) and the set corresponding to the proxy-SU(3) scheme, possessing shells 0-2, 2-4, 6-12, 14-26, 28-48, 50-80, 82-124, 126-182, 184-256... The two sets provide 0+ bands with different deformation and band-head energies. We show that for proton (neutron) numbers starting from the regions where the quadrupole-quadrupole interaction, as derived by the HO, becomes weaker than the one obtained in the proxy-SU(3) scheme, to the regions of HO shell closure, the shape coexistence phenomenon may emerge. Our analysis suggests that the possibility for appearance of shape coexistence has to be investigated in the following regions of proton (neutron) numbers: 8, 18-20, 34-40, 60-70, 96-112, 146-168, 210-240,...
Comments:
8 pages, 1 figure, to appear in HNPS: Advances in Nuclear Physics: Proceedings of the 27th Annual Symposium of the Hellenic Nuclear Physics Society (Athens, 2018), ed. T. Mertzimekis, G. Souliotis, and E. Styliaris
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.11860 [pdf]
Adv.Nucl.Phys.(2018)·9 citations
04
[Submitted on 28 Oct 2018]
Why do Nilsson quantum numbers remain good at moderate deformations?
D. Bonatsos · I.E. Assimakis · A. Martinou · S. Peroulis · S. Sarantopoulou · N. Minkov
The Nilsson model is a simple microscopic model which has been extensively used over the years for the interpretation of a bulk of experimental results. The single particle orbitals in this model are labeled by quantum numbers which are good in the limit of large nuclear deformations. However, it is generally admitted that these quantum numbers remain good even at moderate deformations. We show that this fact is due to the existence of an underlying approximate symmetry, called the proxy-SU(3) symmetry. The implications of proxy-SU(3) on various aspects of nuclear structure will be discussed.
Comments:
11 pages, 1 figure, to appear in Nuclear Theory '37, Proceedings of the 37th International Workshop on Nuclear Theory (Rila 2018), ed. M. Gaidarov and N. Minkov
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.11866 [pdf]
Nucl.Theor.(2018)·1 citation
05
[Submitted on 28 Oct 2018]
Highest weight SU(3) irreducible representations for nuclei with shape coexistence
A. Martinou · D. Bonatsos · N. Minkov · I.E. Assimakis · S. Sarantopoulou · S. Peroulis
The SU(3) irreducible representations (irreps) are characterised by the (lambda, mu) Elliott quantum numbers, which are necessary for the extraction of the nuclear deformation, the energy spectrum and the transition probabilities. These irreps can be calculated through a code which requires high computational power. In the following text a hand-writing method is presented for the calculation of the highest weight (h.w.) irreps, using two different sets of magic numbers, namely proxy-SU(3) and three-dimensional isotropic harmonic oscillator.
Comments:
11 pages, 6 figures, to appear in Nuclear Theory '37, Proceedings of the 37th International Workshop on Nuclear Theory (Rila 2018), ed. M. Gaidarov and N. Minkov
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.11870 [pdf]
Nucl.Theor.(2018)·4 citations
06
[Submitted on 29 Oct 2018]
What can we know about hypernuclei via analysis of bremsstrahlung photons?
Xin Liu (1 and 2)🇨🇳 · Sergei P. Maydanyuk (2 and 3)🇨🇳 · Peng-Ming Zhang (2)🇨🇳 · Ling Liu (1) ((1) College of Physical Science and Technology, Shenyang Normal University, Shenyang, 110034, China, (2) Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, 730000, China, (3) Institute for Nuclear Research, National Academy of Sciences of Ukraine, Kiev, 03680, Ukraine)🇨🇳
We investigate possibility of emission of the bremsstrahlung photons in nuclear reactions with hypernuclei for the first time. A new model of the bremsstrahlung emission which accompanies interactions between $α$ particles and hypernuclei is constructed, where a new formalism for the magnetic momenta of nucleons and hyperon inside hypernucleus is added. For first calculations, we choose $α$ decay of the normal nucleus $^{210} Po$ and the hypernucleus $_{Λ}^{211} Po$ . We find that (1) emission for the hypernucleus $_{Λ}^{211} Po$ is larger than for normal nucleus $^{210} Po$ , (2) difference between these spectra is small. We propose a way how to find hypernuclei, where role of hyperon is the most essential in emission of bremsstrahlung photons during $α$ decay. As demonstration of such a property, we show that the spectra for the hypernuclei $_{Λ}^{107} Te$ and $_{Λ}^{109} Te$ are essentially larger than the spectra for the normal nuclei $^{106} Te$ and $^{108} Te$ . Such a difference is explained by additional contribution of emission to the full bremsstrahlung, which is formed by magnetic moment of hyperon inside hypernucleus. The bremsstrahlung emission formed by such a mechanism, is of the magnetic type. A new formula for fast estimations of bremsstrahlung spectra for even-even hypernuclei is proposed, where role of magnetic moment of hyperon of hypernucleus in formation of the bremsstrahlung emission is shown explicitly. Such an analysis opens possibility of new experimental study of properties of hypernuclei via bremsstrahlung study.
Comments:
25 pages, 2 captured figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1810.11942 [pdf]
5 citations
07
[Submitted on 29 Oct 2018]
Core-polarization effects and effective charges in O and Ni isotopes from chiral interactions
Francesco Raimondi🇬🇧 · Carlo Barbieri🇬🇧
Most nuclear structure calculations, even for full configuration interaction approaches, are performed within truncated model spaces. These require consistent transformations of the Hamiltonian and operators to account for the missing physics beyond the active space, so that several recent efforts have been devoted to find compatible derivations of the effective operators. The effective charges employed in the shell-model calculations, and fitted to reproduce experimental data, can be seen as the phenomenological counterpart of such renormalization for electromagnetic operators. Here, we make a first step to lay the bases for their microscopic derivation in the context of the Self-Consistent Green's Function approach. We compute electric quadrupole (E2) effective charges from microscopic theory by coupling the single-nucleon propagators to core-polarization phonons, derived consistently from a realistic nuclear interaction. The polarization effects are included by evaluating the Feynman diagrams that couple the internal multi-nucleon configurations to the single-particle transitions induced by the electromagnetic operator. The effective charges for E2 static moments and transitions are computed for selected isotopes in the Oxygen ( $^{14} O$ , $^{16}$ O, $^{22}$ O and $^{24}$ O) and Nickel ( $^{48}$ Ni, $^{56}$ Ni, $^{68}$ Ni and $^{78}$ Ni) chains. The values found are orbital dependent especially for the neutron effective charges, which show also a characteristic decreasing trend along each isotopic chain. In general, the values are compatible with the phenomenological ones commonly used for shell-model studies in the $0 p 1 s 0 d$ and $1 p 0 f 0 g_{\frac{9}{2}}$ valence spaces.The phenomenological shell-model effective charges can be explained through \textit{ab initio} approaches, where the sole experimental input comes from the fitting of the realistic nuclear interaction.
Comments:
13 pages, 11 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.12180 [pdf]
PRC(2019)·11 citations
08
[Submitted on 29 Oct 2018]
Quark meson coupling model with $s u (3)$ symmetry within the Bogoliubov independent quark model of the nucleon
Prafulla K. Panda🇮🇳 · Constança Providência🇵🇹 · S.A. Moszkowski🇺🇸 · H. Bohr🇩🇰 · João da Providência🇵🇹
We generalize the Bogoliubov quark-meson coupling model to also include hyperons. The hyperon- $σ$ -meson couplings are fixed by the model and the hyperon- $ω$ -meson couplings are fitted to the hypreon potentials in symmetric nuclear matter. The present model predicts neutron stars with masses above 2 $M_{⊙}$ and the radius of a 1.4 $M_{⊙}$ star equal to 13.83 km.
Comments:
12 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1810.12191 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE