Nuclear Theory·nucl-th

Monday·November 30, 2020

13 papers—8 primary·5 cross-listed

01
[Submitted on 26 Nov 2020]
A Dynamical Study of Fusion Hindrance with Nakajima-Zwanzig Projection Method
Yasuhisa Abe🇯🇵 · David Boilley🇫🇷 · Quentin Hourdillé🇫🇷 · Caiwan Shen🇨🇳
A new framework is proposed for the study of collisions between very heavy ions which lead to the synthesis of Super-Heavy Elements (SHE), to address the fusion hindrance phenomenon. The dynamics of the reaction is studied in terms of collective degrees of freedom undergoing relaxation processes with different time scales. The Nakajima-Zwanzig projection operator method is employed to eliminate fast variable and derive a dynamical equation for the reduced system with only slow variables. There, the time evolution operator is renormalised and an inhomogeneous term appears, which represents a propagation of the given initial distribution. The term results in a slip to the initial values of the slow variables. We expect that gives a dynamical origin of parameter "injection point $s$ " introduced by Swiatecki et al in order to reproduce absolute values of measured cross sections for SHE. Formula for the slip is given in terms of physical parameters of the system, which confirms the results recently obtained with a Langevin equation.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13119 [pdf]
PTEP(2021)·2 citations
02
[Submitted on 26 Nov 2020]
Deformed Halo of ^{29}_{9}F_{20}
Ikuko Hamamoto
Using a simple model based on the knowledge of spherical and deformed Woods-Saxon potentials, it is shown that the recent observation of halo phenomena in $^{29}$ F can be interpreted as an evidence for the prolate deformation of the ground state of $^{29}$ F. The prolate deformation is the result of the shell structure, which is unique in one-neutron resonant levels, in particular near degeneracy of the neutron 1 $f_{7/2}$ and 2 $p_{3/2}$ resonant levels, together with the strong preference of prolate shape by the proton number $Z$ = 9. On the other hand, in oxygen isotopes spherical shape is so much favored by the proton number $Z$ = 8 that the presence of possible neutron shell-structure may not make the system deformed. Thus, the strong preference of particular shape by the proton numbers 8 and 9, respectively, together with a considerable amount of the energy difference between the neutron $1 d_{3/2}$ and $2 s_{1/2}$ orbits in oxygen isotopes seems to play an important role in the phenomena of oxygen neutron drip line anomaly, as was suggested by H. Sakurai {\it et al.} in 1999.
Comments:
11 pages, 2 figures,
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13139 [pdf]
PLB(2021)·11 citations
03
[Submitted on 26 Nov 2020]
Perturbative chiral nucleon-nucleon potential for the $^{3} P_{0}$ partial wave
Rui Peng🇨🇳 · Songlin Lyu🇨🇳 · Bingwei Long🇨🇳
We study perturbativeness of chiral nuclear forces in the $^{3} P_{0}$ channel. In previous works, the focus has been on one-pion exchange, and the applicable window of perturbative pion exchanges has been shown to span from threshold to the center-of-mass momentum $k ≃$ 180 MeV. We will examine, instead, whether cancellation of short and long-range parts can sufficiently soften the $^{3} P_{0}$ chiral force to make it more amenable to perturbation theory. The result is encouraging, as the combined $^{3} P_{0}$ force is shown to be perturbative up to $k ≃$ 280 MeV, covering many nuclear-structure calculations.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13186 [pdf]
Commun.Theor.Phys.(2020)·15 citations
04
[Submitted on 26 Nov 2020]
Covariant density functional theory input for r-process simulations in actinides and superheavy nuclei: the ground state and fission properties
A. Taninah · S.E. Agbemava · A.V. Afanasjev
The systematic investigation of the ground state and fission properties of even-even actinides and superheavy nuclei with $Z = 90 - 120$ from the two-proton up to two-neutron drip lines with proper assessment of systematic theoretical uncertainties has been performed for the first time in the framework of covariant density functional theory (CDFT). These results provide a necessary theoretical input for the r-process modeling in heavy nuclei and, in particular, for the study of fission recycling. Four state-of-the-art globally tested covariant energy density functionals (CEDFs), namely, DD-PC1, DD-ME2, NL3* and PC-PK1, representing the major classes of the CDFT models are employed in the present study. Ground state deformations, binding energies, two neutron separation energies, $α$ -decay $Q_{α}$ values and half-lives and the heights of fission barriers have been calculated for all these nuclei. Theoretical uncertainties in these physical observables and their evolution as a function of proton and neutron numbers have been quantified and their major sources have been identified. Spherical shell closures at $Z = 120$ , $N = 184$ and $N = 258$ and the structure of the single-particle (especially, high- $j$ ) states in their vicinities as well as nuclear matter properties of employed CEDFs are two major factors contributing into theoretical uncertainties. However, different physical observables are affected in a different way by these two factors. For example, theoretical uncertainties in calculated ground state deformations are affected mostly by former factor, while theoretical uncertainties in fission barriers depend on both of these factors.
Comments:
28 pages, 18 figures, Physical Review C, in press
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13368 [pdf]
PRC(2020)·35 citations
05
[Submitted on 27 Nov 2020]
Shell evolution in neutron-rich nuclei: the single particle perspective
Weiqiang Ma · Yibin Qian
The shell evolution has been studied extensively within the framework of interacting shell model, while the studies from the single particle viewpoint is relatively lacking or neglected. In particular, the isospin dependence of spin-orbit splitting has become increasingly important as $N / Z$ increases in neutron-rich nuclei. Following the initial independent-particle strategy towards explaining the occurrence of magic numbers, we have systematically investigated the isospin effect on the shell evolution of neutron-rich nuclei within the Woods-Saxon (WS) mean-field potential plus the spin-orbit term. It is found that new magic numbers $N = 14$ and $N = 16$ may emerge in neutron-rich nuclei if one changes the sign of the isospin-dependent term in the spin-orbit coupling while the traditional magic number $N = 20$ may disappear. The magic number $N = 28$ is expected to be destroyed despite the sign choice of the isospin part in spin-orbit splitting, while $N = 50$ may disappear and $N = 82$ persists within the single particle scheme. Besides, an appreciable amount of energy gap appears at $N = 32$ and 34 in neutron-rich Ca isotopes. All these results are more consistent with those of the interacting shell model, when the sign of the isospin term of the WS potential is different from that of the corresponding spin-orbit coupling part. The present study may provide a more reasonable starting point for not only the interacting shell but also other nuclear many-body calculations towards the neutron-dripline.
Comments:
8 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13540 [pdf]
0 citations
06
[Submitted on 27 Nov 2020]
Modified empirical formulas and machine learning for $α$ -decay systematics
G. Saxena · P. K. Sharma · Prafulla Saxena
Latest experimental and evaluated $α$ -decay half-lives between 82 $\leq$ Z $\leq$ 118 have been used to modify two empirical formulas: (i) Horoi scaling law [J. Phys. G \textbf{30}, 945 (2004)], and Sobiczewski formula [Acta Phys. Pol. B \textbf{36}, 3095 (2005)] by adding asymmetry dependent terms ( $I$ and $I^{2}$ ) and refitting of the coefficients. The results of these modified formulas are found with significant improvement while compared with other 21 formulas, and, therefore, are used to predict $α$ -decay half-lives with more precision in the unknown superheavy region. The formula of spontaneous fission (SF) half-life proposed by Bao \textit{et al.} [J. Phys. G \textbf{42}, 085101 (2015)] is further modified by using ground-state shell-plus-pairing correction taken from FRDM-2012 and using latest experimental and evaluated spontaneous fission half-lives between 82 $\leq$ Z $\leq$ 118. Using these modified formulas, contest between $α$ -decay and SF is probed for the nuclei within the range 112 $\leq$ Z $\leq$ 118 and consequently probable half-lives and decay modes are estimated. Potential decay chains of $^{286 - 302}$ Og and $^{287 - 303}$ 119 (168 $\leq$ N $\leq$ 184: island of stability) are analyzed which are found in excellent agreement with available experimental data. In addition, four different machine learning models: XGBoost, Random Forest (RF), Decision Trees (DTs), and Multilayer Perceptron (MLP) neural network are used to train a predictor for $α$ -decay and SF half-lives prediction. The prediction of decay modes using XGBoost and MLP are found in excellent agreement with available experimental decay modes along with our predictions obtained by above mentioned modified formulas.
Comments:
24 Pages, 6 Figures, Accepted in Journal of Physics G (Nucl. and Part. Physics)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2011.13566 [pdf]
J.Phys.G(2021)·45 citations
07
[Submitted on 27 Nov 2020]
Quark-hadron crossover equations of state for neutron stars: constraining the chiral invariant mass in a parity doublet model
Takuya Minamikawa🇯🇵 · Toru Kojo🇨🇳 · Masayasu Harada🇯🇵
We construct an equation of state (EOS) for neutron stars by interpolating hadronic EOS at low density and quark EOS at high density. A hadronic model based on the parity doublet structure is used for hadronic matter and a quark model of Nambu--Jona-Lasinio type is for quark matter. We assume crossover between hadronic matter and quark matter in the the color-flavor locked phase. The nucleon mass of the parity doublet model has a mass associated with the chiral symmetry breaking, and a chiral invariant mass $m_{0}$ which is insensitive to the chiral condensate. The value of $m_{0}$ affects the nuclear EOSs at low density, and has strong correlations with the radii of neutron stars. Using the constraint to the radius obtained by LIGO-Virgo and NICER, we find that $m_{0}$ is restricted as $600 MeV ≲ m_{0} ≲ 900 MeV$ .
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2011.13684 [pdf]
PRC(2021)·66 citations
08
[Submitted on 27 Nov 2020]
Triaxial rigidity of $^{166}$ Er and its Bohr-model realization
Yusuke Tsunoda · Takaharu Otsuka
The triaxial nature of low-lying rotational bands of $^{166}$ Er is presented from the viewpoint of the Bohr Hamiltonian and from that of many-fermion calculations by the Monte Carlo shell model and the constrained Hartree-Fock method with projections. A recently proposed novel picture of those bands suggests definite triaxial shapes of those bands, in contrast to the traditional view with the prolate ground-state band and the $γ$ -vibrational excited band. Excitation level energies and E2 transitions can be described well by the Bohr Hamiltonian and by the many-fermion approaches, where rather rigid triaxiality plays vital roles, although certain fluctuations occur in shell-model wave functions. Based on the potential energy surfaces with the projections, we show how the triaxial rigidity appears and what the softness of the triaxiality implies. The excitation to the so-called double $γ$ -phonon state is discussed briefly.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2011.13717 [pdf]
PRC(2021)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE