Nuclear Theory·nucl-th

Friday·January 12, 2024

15 papers—8 primary·7 cross-listed

01
[Submitted on 10 Jan 2024]
Predicting nucleon-nucleus scattering observables using nuclear structure theory
Aaina Thapa🇺🇸 · Jutta Escher🇺🇸 · Emanuel Chimanski🇺🇸 · Marc Dupuis🇫🇷 · Sophie Péru🇫🇷 · Walid Younes🇺🇸
Developing a predictive capability for inelastic scattering will find applications in multiple areas. Experimental data for neutron-nucleus inelastic scattering is limited and thus one needs a robust theoretical framework to complement it. Charged-particle inelastic scattering can be used as a surrogate for $(n, γ)$ reactions to predict capture cross sections for unstable nuclei. Our work uses microscopic nuclear structure calculations for spherical nuclei to obtain nucleon-nucleus scattering potentials and calculate cross sections for these processes. We implement the Jeukenne, Lejeune, Mahaux (JLM) semi-microscopic folding approach, where the medium effects on nuclear interaction are parameterized in nuclear matter to obtain the nucleon-nucleon $(N N)$ interaction in a medium at positive energies. We solve for the nuclear ground state using the Hartree-Fock-Bogliubov (HFB) many-body method, assuming the nucleons within the nucleus interact via the Gogny-D1M potential. The vibrational excited states of the target nucleus are calculated using the quasi-particle random phase approximation (QRPA). We demonstrate our approach for spherical nuclei in the medium-mass region, showing scattering results for the $^{90}$ Zr nucleus.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2401.05505 [pdf]
EPJ Web Conf.(2024)·7 citations
02
[Submitted on 11 Jan 2024]
Inference of Parameters for Back-shifted Fermi Gas Model using Feedback Neural Network
Peng-Xiang Du · Tian-Shuai Shang · Kun-Peng Geng · Jian Li · Dong-Liang Fang
The back-shifted Fermi gas model is widely employed for calculating nuclear level density (NLD) as it can effectively reproduce experimental data by adjusting parameters. However, selecting parameters for nuclei lacking experimental data poses a challenge. In this study, the feedforward neural network (FNN) was utilized to learn the level density parameters at neutron separation energy $a (S_{n})$ and the energy shift $Δ$ for 289 nuclei. Simultaneously, parameters for nearly 3000 nuclei are provided through the FNN. Using these parameters, calculations were performed for neutron resonance spacing in $s$ and $p$ waves, cumulative number of levels, and NLD. The FNN results were also compared with the calculated outcomes of the parameters from fitting experimental data (local parameters) and those obtained from systematic studies (global parameters), as well as the experimental data. The results indicate that parameters from the FNN achieve performance comparable to local parameters in reproducing experimental data. Moreover, for extrapolated nuclei, parameters from the FNN still offer a robust description of experimental data.
Comments:
11 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2401.05622 [pdf]
PRC(2024)·8 citations
03
[Submitted on 11 Jan 2024]
From NS observations to nuclear matter properties: a machine learning approach
Valéria Carvalho · Márcio Ferreira · Constança Providência
This study is devoted to the inference problem of extracting the nuclear matter properties directly from a set of mass-radius observations. We employ Bayesian neural networks (BNNs), which is a probabilistic model capable of estimating the uncertainties associated with its predictions. To simulate different noise levels on the $M (R)$ observations, we create three different sets of mock data. Our results show BNNs as an accurate and reliable tool for predicting the nuclear matter properties whenever the true values are not completely outside the training dataset statistics, i.e., if the model is not heavily dependent on its extrapolating capacities. Using real mass-radius pulsar data, the model predicted, for instance, $L_{sym} = 39.80 \pm 17.52$ MeV and $K_{sym} = - 101.67 \pm 62.86$ MeV ( $2 σ$ interval). Our study provides a valuable inference framework when new NS data becomes available.
Comments:
15 pages, 12 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2401.05770 [pdf]
PRD(2024)·21 citations
04
[Submitted on 11 Jan 2024]
Quadrupole dynamics of carbon isotopes and 10Be
H. Li · D. Fang · H. J. Ong · A. M. Shirokov · J. P. Vary · P. Yin · X. Zhao
Electric quadrupole (E2) moments and transitions provide measures of nuclear deformation and related collective structure. However, matrix elements of the E2 operator are sensitive to the nuclear wave function at large distances and are poorly convergent within the ab initio no-core shell model approach. We demonstrate for the first time that the ratio of neutron to proton quadrupole transition matrix elements, Mn/Mp, is well-converged in the ab initio no-core shell model and provides a new and robust tool for comparing with experimental results. We find that our parameter-free results for Mn/Mp for the carbon isotopes and 10Be compare well with experiment, where available, and offer new insight into the quadrupole dynamics of nuclear response.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2401.05776 [pdf]
PRC(2024)·8 citations
05
[Submitted on 11 Jan 2024]
Impact of the molecular resonances on the 12C+12C fusion reaction rate
Yasutaka Taniguchi · Masaaki Kimura
The properties of the low-energy 12C+12C molecular resonances, which potentially enhance the fusion reaction rate at low temperatures, have been investigated by a full-microscopic nuclear model employing various nuclear energy density functionals. We show that some density functionals plausibly describe the observed high-spin 12C+12C molecular resonances and predict many 0+ and 2+ resonances at low energies, which enhance the reaction rate. We also discuss how the uncertainty in the nuclear energy density functionals propagates to that of the reaction rate.
Comments:
6 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2401.05803 [pdf]
PLB(2024)·17 citations
06
[Submitted on 11 Jan 2024]
Axially Symmetric Quadrupole-Octupole Model incorporating Sextic Potential
M. Chabab · A. El Batoul · L. El Ouaourti
We present an extended application of the analytic quadrupole octupole axially symmetric model, originally employed to study the octupole deformation and vibrations in light actinides using an infinite well potential (IW). In this work, we extend the model's applicability to a broader range of nuclei exhibiting octupole deformation by incorporating a sextic potential instead of the Davidson potential.Similarly to conventional models, such as AQOA-IW (for infinite square potential) and AQOA-D (for the Davidson potential), our proposed model is referred to as AQOA-S. By employing the sextic potential, phenomenologically represented as $v (β ~) = a_{1} β ~^{2} + a_{2} β ~^{4} + a_{3} β ~^{6}$ , we can derive analytical expressions for the energy spectra and transition rates (B(E1), B(E2), B(E3)). The energy spectra of the model are essentially governed by two critical parameters: $ϕ_{0}$ , indicating the balance between octupole and quadrupole strain, and $α$ , a key factor in adjusting the shape and behavior of the spectra through the sextic potential. In terms of applications, the study encompasses five isotopes, namely $^{222 - 226}$ Ra and $^{224, 226}$ Th. Significantly, our model demonstrates remarkable agreement with the corresponding experimental data, particularly for the recently determined B(EL) transition rates of $^{224}$ Ra, surpassing the performance of the model that employs the Davidson potential. The stability of the octupole deformation in $^{224}$ Ra adds particular significance to these findings.
Comments:
10 pages, 1 figure, accepted in Null. Phys. A
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2401.05985 [pdf]
NPA(2024)·2 citations
07
[Submitted on 11 Jan 2024]
Implications of comprehensive nuclear and astrophysics data on the equations of state of neutron star matter
Sk Md Adil Imam · Tuhin Malik · Constança Providência · B. K. Agrawal
The equations of state (EoSs) governing neutron star (NS) matter obtained for both non-relativistic and relativistic mean-field models are systematically confronted with a diverse set of terrestrial data and astrophysical observations within the Bayesian framework. The terrestrial data, spans from bulk properties of finite nuclei to the heavy-ion collisions, constrain the symmetric nuclear matter EoS and the symmetry energy up to twice the saturation density ( $ρ_{0}$ = 0.16 fm $^{- 3}$ ). The astrophysical observations encompass the NS radius, the tidal deformability, and the lower bound on maximum mass. Three distinct posterior distributions of EoSs are generated by gradually updating the priors with different constraints: (i) only the maximum NS mass, (ii) incorporating additional terrestrial data, (iii) combining both the terrestrial data and astrophysical observations. These EoS distributions are then compared using the Kullback-Liebler divergence which highlights the significant constraints imposed on the EoSs by the currently available lower bound of NS maximum mass and terrestrial data. The remaining astrophysical observations marginally refine the EoS within the density range $\sim$ 2-3 $ρ_{0}$ . It is observed that the relativistic mean field model yields stiffer EoS around the saturation density, but predict smaller values of the speed of sound and proton fraction in the interior of massive stars.
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
arXiv:
2401.06018 [pdf]
PRD(2024)·27 citations
08
[Submitted on 11 Jan 2024]
Landscape of nuclear deformation softness with spherical quasi-particle random phase approximation
Le-Anh Nguyen · Minh-Loc Bui · Panagiota Papakonstantinou · Naftali Auerbach
We investigate the stability and softness of nuclei against quadrupole, octupole, and hexadecapole deformation. By applying the spherical Skyrme-force Hartree-Fock Bardeen-Cooper-Schrieffer quasi-particle random phase approximation, we diagnose ground-state deformation when imaginary solutions are obtained, i.e., the spherical ground state {\em collapses}. We also calculate the multipole polarizability in spherical nuclei with no collapse, as a measure of softness. This numerically light and theoretically sound method is found able to capture deformation patterns across the nuclide chart. The connection between the intrinsic shape of nuclei and the dynamics of their low-lying collective states is established and the role of shell structure is discussed.
Comments:
8 pages, 8 figures, accepted for publication in Physical Review C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2401.06117 [pdf]
PRC(2024)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE