Nuclear Theory·nucl-th

Wednesday·April 3, 2019

12 papers—6 primary·6 cross-listed

01
[Submitted on 1 Apr 2019]
Neutron skins as laboratory constraints on properties of neutron stars and on what we can learn from heavy ion fragmentation reactions
C.A. Bertulani · J. Valencia
The equation of state (EOS) of infinite nuclear matter with a small proton/neutron fraction is a crucial input to determine the properties of neutron stars and compare model predictions to astronomical observations. The so-called `symmetry energy' is the part of the EOS accounting for the difference in the number of neutrons and protons. Numerous experiments have been devised to assess the symmetry energy and constrain its functional dependence with the nucleon density. Further constraints follow from a stellar modeling using the EOS to reproduce astronomical observations such as neutron star masses and radii. The recent detection of gravitational waves emitted from neutron star mergers and the nucleosynthesis ensuing from these events caused a surge of interest for such studies. Several types of nuclear reactions have been proposed to study the symmetry energy part of the EOS. Some of them consist in determining the neutron skin in nuclei and exploit its correlation with the slope parameter of the symmetry energy. In this article we explore a particular set of reactions using high energy ( $E_{l ab} \sim 1$ GeV/nucleon) neutron-rich projectiles. We explore measurements of all reaction fragments (a) in the same isotopic chain, i.e., only by removal of neutrons, (b) in all charge-changing channels, and (c) total interaction cross sections. Using Hartree-Fock-Bogoliubov (HBF) predictions for neutron and proton densities with Skyrme interactions, we explore the sensitivity of these cross sections with the neutron skin in nuclei.
Comments:
11 pages, 8 figures, published version in the Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.01078 [pdf]
PRC(2019)·28 citations
02
[Submitted on 2 Apr 2019]
$A b ini t i o$ description of collectivity for $s d$ shell nuclei
A. Saxena · A. Kumar · V. Kumar · P.C. Srivastava · T. Suzuki
In the present work, we have reported shell model results for open shell nuclei Ne, Mg and Si isotopes with $10 \leq N \leq 20$ in $s d$ -shell model space. We have performed calculations in $s d$ shell with two $ab ini t i o$ approaches: in-medium similarity renormalization group (IM-SRG) and coupled-cluster (CC) theory. We have also performed calculations with phenomenological USDB interaction and chiral effective field theory based CEFT interaction. The results for rotational spectra and $B (E 2; 2_{1}^{+} \to 0_{1}^{+})$ transitions are reported for even-mass isotopes. The IM-SRG and CC results are in reasonable agreement with the experimental data except at $N$ =20. This demonstrates a validity of $ab ini t i o$ description of deformation for doubly open-shell nuclei for $s d$ shell. To see the importance of $p f$ orbitals, we have also compared our results with SDPF-MU interaction by taking account of $2 p - 2 h$ and $4 p - 4 h$ configurations in $s d$ - $p f$ -shell model space.
Comments:
Hyperfine Interactions (Springer) - Accepted
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.01225 [pdf]
Hyperfine Interact.(2019)·4 citations
03
[Submitted on 2 Apr 2019]
Microscopic study of K-Selection Rule Violation in $^{182}$ W K=10 $^{+}$ Isomer Decay
C. R. Praharaj · Swagatika Bhoi · Z. Naik · S. K. Ghorui · S. K Patra
In this paper we study the microscopic mechanism for the retarded decay of K-isomers to lower K bands. We do angular momentum projection from suitable intrinsic states. The retardation arises from poor overlap between the low K and high K bands in the integral over Euler angles. Deformed HF and angular momentum projection calculations are done for the decay of the $K = 1 0^{+}$ isomer band to the ground band of $^{182} W$ . K-mixing is unimportant and the K quantum numbers of the bands are quite good. There is significant difference in the reduced matrix elements of transition operators in our formalism and that in the rotational model. Angular momentum projection gives J-selection rule but there is no K selection rule for reduced matrix elements of electromagnetic multipole operators. Thus, E2 and M1 transitions from the K isomer to the ground band of $^{182} W$ are finite but retarded in angular momentum projection theory, as in experiments. This provides a theoretical basis for the study of K-isomers and their decay modes. Quantitative results are presented. The microscopic model gives J-selection rule and angular momentum conservation for combined matter and radiation systems.
Comments:
7 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.01229 [pdf]
1 citation
04
[Submitted on 2 Apr 2019]
Effect of shell structure on the fission of sub-lead nuclei
Guillaume Scamps · Cédric Simenel
Fission of atomic nuclei often produces mass asymmetric fragments. However, the origin of this asymmetry was believed to be different in actinides and in the sub-lead region [A. Andreyev {\it et al.}, Phys. Rev. Lett. {\bf 105}, 252502 (2010)]. It has recently been argued that quantum shell effects stabilising pear shapes of the fission fragments could explain the observed asymmetries in fission of actinides[G. Scamps and C. Simenel, Nature {\bf 564}, 382 (2018)]. This interpretation is tested in the sub-lead region using microscopic mean-field calculations of fission based on the Hartree-Fock approach with BCS pairing correlations. The evolution of the number of protons and neutrons in asymmetric fragments of mercury isotope fissions is interpreted in terms of deformed shell gaps in the fragments. A new method is proposed to investigate the dominant shell effects in the pre-fragments at scission. We conclude that the mechanisms responsible for asymmetric fissions in the sub-lead region are the same as in the actinide region, which is a strong indication of their universality.
Comments:
Accepted as a rapid communication by Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1904.01275 [pdf]
PRC(2019)·91 citations
05
[Submitted on 2 Apr 2019]
Two-neutron transfer reactions and quantum-chaos measure of nuclear spectra
A.I. Levon · A.G. Magner
A new statistical interpretation of the nuclear collective states is suggested and applied recently in rare earths and actinide nuclei by the two-neutron transfer reactions in terms of the nearest neighbor-spacing distributions (NNSDs). Experimental NNSDs were obtained by using the complete and pure sequences of the collective states through an unfolding procedure. The two-neutron transfer reactions allow to obtain such a sequence of the collective states that meets the requirements for a statistical analysis. Their theoretical analysis is based on the linear approximation of a repulsion level density within the Wigner-Dyson theory. This approximation is successful to evaluate separately the Wigner chaos and Poisson order contributions. We found an intermediate behavior of NNSDs between the Wigner and Poisson limits. NNSDs turn out to be shifted from a chaos to order with increasing the length of spectra and the angular momentum of collective states. Perspectives for the statistical analysis of the symmetry breaking of states with the fixed projection of angular momenta $K$ are discussed.
Comments:
15 pages, 16 figures
Subjects:
Nuclear Theory (nucl-th); Data Analysis, Statistics and Probability (physics.data-an)
arXiv:
1904.01347 [pdf]
Nucl.Phys.Atom.Energy(2019)·1 citation
06
[Submitted on 2 Apr 2019]
Description of the mass-asymmetric fission of the Pt isotopes, obtained in the reaction $^{36}$ Ar + $^{142}$ Nd within the two-stage fusion-fission model
V. L. Litnevsky · F. A. Ivanyuk · G. I. Kosenko · S. Chiba
The two stages dynamical stochastic model developed earlier for description of fusion-fission reactions is applied to the calculation of mass- and energy-distributions of fission fragments of platinum isotopes in reaction $^{36} Ar +^{142} Nd \to^{178 - x} Pt + xn$ . The first stage of this model is the calculation of the approaching of projectile nucleus to the target nucleus. On the second stage of the model, the evolution of the system formed after the touching of the projectile and target nuclei is considered. The evolution of the system on both stages is described by three-dimensional Langevin equations for the shape parameters of the system. The mutual orientation of the colliding ions and tunneling through the Coulomb barrier in the entrance channel are also taken into account. The potential energy of the system is calculated within the macroscopic-microscopic approach. The calculated mass-energy distributions of fission fragments are compared with the available experimental data. The impact of shell effects, rotation of the system and neutron evaporation on the calculated results is discussed.
Comments:
8 pages, 12 figures, submitted to PRC
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.01492 [pdf]
PRC(2019)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE

Neutron skins as laboratory constraints on properties of neutron stars and on what we can learn from heavy ion fragmentation reactions

Ab initio description of collectivity for sd shell nuclei

Microscopic study of K-Selection Rule Violation in 182W K=10+ Isomer Decay

Effect of shell structure on the fission of sub-lead nuclei

Two-neutron transfer reactions and quantum-chaos measure of nuclear spectra

Description of the mass-asymmetric fission of the Pt isotopes, obtained in the reaction 36Ar + 142Nd within the two-stage fusion-fission model

Affiliations

$A b ini t i o$ description of collectivity for $s d$ shell nuclei

Microscopic study of K-Selection Rule Violation in $^{182}$ W K=10 $^{+}$ Isomer Decay

Description of the mass-asymmetric fission of the Pt isotopes, obtained in the reaction $^{36}$ Ar + $^{142}$ Nd within the two-stage fusion-fission model