Nuclear Theory·nucl-th

Monday·December 18, 2017

11 papers—8 primary·3 cross-listed

01
[Submitted on 15 Dec 2017]
A 4-dimensional Langevin approach to low-energy nuclear fission of $^{236}$ U
Chikako Ishizuka · Mark D. Usang · Fedir A. Ivanyuk · Joachim A. Maruhn · Katsuhisa Nishio · Satoshi Chiba
We developed a four-dimensional Langevin model which can treat the deformation of each fragment independently and applied it to low energy fission of 236U, the compound system of the reaction n+ $^{235}$ U. The potential energy is calculated with the deformed two-centerWoods-Saxon (TCWS) and the Nilsson type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments $ν$ (A). Furthermore, the measured total kinetic energy TKE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several long-standing open problems in fission such as the sharing of the excitation energy between the fragments.
Comments:
9 pages, 10 figures, 1 table, accepted to PRC
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1712.05488 [pdf]
PRC(2017)·70 citations
02
[Submitted on 15 Dec 2017]
Hauser-Feshbach fission fragment de-excitation with calculated macroscopic-microscopic mass yields
Patrick Jaffke · Peter Moller · Patrick Talou · Arnold J. Sierk
The Hauser-Feshbach statistical model is applied to the de-excitation of primary fission fragments using input mass yields calculated with macroscopic-microscopic models of the potential energy surface. We test the sensitivity of the prompt fission observables to the input mass yields for two important reactions, $^{235}$ U $(n_{th}, f)$ and $^{239}$ Pu $(n_{th}, f)$ , for which good experimental data exist. General traits of the mass yields, such as the location of the peaks and their widths, can impact both the prompt neutron and $γ$ -ray multiplicities, as well as their spectra. Specifically, we use several mass yields to determine a linear correlation between the calculated prompt neutron multiplicity $ν ˉ$ and the average heavy-fragment mass $⟨ A_{h} ⟩$ of the input mass yields $\partial ν ˉ / \partial ⟨ A_{h} ⟩ = \pm 0.1 n / f / u$ . The mass peak width influences the correlation between the total kinetic energy of the fission fragments and the total number of prompt neutrons emitted $ν ˉ_{T} (TKE)$ . Typical biases on prompt particle observables from using calculated mass yields instead of experimental ones are: $δ ν ˉ = 4%$ for the average prompt neutron multiplicity, $δ M ˉ_{γ} = 1%$ for the average prompt $γ$ -ray multiplicity, $δ ϵ ˉ_{n}^{LAB} = 1%$ for the average outgoing neutron energy, $δ ϵ ˉ_{γ} = 1%$ for the average $γ$ -ray energy, and $δ ⟨ TKE ⟩ = 0.4%$ for the average total kinetic energy of the fission fragments.
Comments:
12 pages, 8 figures, 2 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1712.05511 [pdf]
PRC(2018)·22 citations
03
[Submitted on 15 Dec 2017]
Massive neutron stars and $Λ$ -hypernuclei in relativistic mean field models
Ting-Ting Sun🇨🇳 · Cheng-Jun Xia🇨🇳 · Shi-Sheng Zhang🇨🇳 · M. S. Smith🇺🇸
Based on relativistic mean field (RMF) models, we study finite $Λ$ -hypernuclei and massive neutron stars. The effective $N$ - $N$ interactions PK1 and TM1 are adopted, while the $N$ - $Λ$ interactions are constrained by reproducing the binding energy of $Λ$ -hyperon at $1 s$ orbit of $_{Λ}^{40}$ Ca. It is found that the $Λ$ -meson couplings follow a simple relation, indicating a fixed $Λ$ potential well for symmetric nuclear matter at saturation densities, i.e., around $V_{Λ} = - 29.786$ MeV. With those interactions, a large mass range of $Λ$ -hypernuclei can be well described. Furthermore, the masses of PSR J1614-2230 and PSR J0348+0432 can be attained adopting the $Λ$ -meson couplings $g_{σ Λ} / g_{σ N} ≳ 0.73$ , $g_{ω Λ} / g_{ω N} ≳ 0.80$ for PK1 and $g_{σ Λ} / g_{σ N} ≳ 0.81$ , $g_{ω Λ} / g_{ω N} ≳ 0.90$ for TM1, respectively. This resolves the Hyperon Puzzle without introducing any additional degrees of freedom.
Comments:
5 figures, 1 table, to be published in Chinese Physics C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1712.05569 [pdf]
CPC(2018)·37 citations
04
[Submitted on 15 Dec 2017]
The three-pion decays of the $a_{1} (1260)$
Xu Zhang🇨🇳 · Ju-Jun Xie🇨🇳
We investigate the decay of $a_{1}^{+} (1260) \to π^{+} π^{+} π^{-}$ with the assumption that the $a_{1} (1260)$ is dynamically generated from the coupled channel $ρ π$ and $K ˉ K^{*}$ interactions. In addition to the tree level diagrams that proceed via $a_{1}^{+} (1260) \to ρ^{0} π^{+} \to π^{+} π^{+} π^{-}$ , we take into account also the final state interactions of $π π \to π π$ and $K K ˉ \to π π$ . We calculate the invariant $π^{+} π^{-}$ mass distribution and also the total decay width of $a_{1}^{+} (1260) \to π^{+} π^{+} π^{-}$ as a function of the mass of $a_{1} (1260)$ . The calculated total decay width of $a_{1} (1260)$ is significantly different from other model calculations and tied to the dynamical nature of the $a_{1} (1260)$ resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the $ρ π$ component in the $a_{1} (1260)$ wave function.
Comments:
Published version
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1712.05572 [pdf]
Commun.Theor.Phys.(2018)·12 citations
05
[Submitted on 15 Dec 2017]
Analysis of the total kinetic energy of fission fragments with the Langevin equation
Mark Dennis Usang · Fedir Ivanyuk · Chikako Ishizuka · Satoshi Chiba
We analyzed the total kinetic energy (TKE) of fission fragments with three-dimensional Langevin calculations for a series of actinides and Fm isotopes at various excitation energies. This allowed us to establish systematic trends of TKE with $Z^{2} / A^{1/3}$ of the fissioning system and as a function of excitation energy. In the mass-energy distributions of fission fragments we see the contributions from the standard, super-long, and super-short (in the case of $^{258}$ Fm) fission modes. For the fission fragments mass distribution of $^{258}$ Fm we obtained a single peak mass distribution. The decomposition of TKE into the prescission kinetic energy and Coulomb repulsion showed that decrease of TKE with growing excitation energy is accompanied by a decrease of prescission kinetic energy. It was also found that transport coefficients (friction and inertia tensors) calculated by a microscopic model and by macroscopic models give drastically different behavior of TKE as a function of excitation energy. The results obtained with microscopic transport coefficients are much closer to experimental data than those calculated with macroscopic ones.
Comments:
Article has been accepted for publication in Physical Review C on 20 November 2017
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1712.05616 [pdf]
PRC(2017)·55 citations
06
[Submitted on 15 Dec 2017]
Onset of $η$ nuclear binding
Nir Barnea🇮🇱 · Betzalel Bazak🇮🇱 · Eliahu Friedman🇮🇱 · Avraham Gal🇮🇱 · Aleš Cieplý🇨🇿 · Jiří Mareš🇨🇿 · Martin Schäfer🇨🇿
Recent studies of $η$ nuclear quasibound states by the Jerusalem-Prague Collaboration are reviewed, focusing on stochastic variational method self consistent calculations of $η$ few-nucleon systems. These calculations suggest that a minimum value Re $a_{η N} \approx 1$ fm (0.7 fm) is needed to bind $η^{3}$ He ( $η^{4}$ He).
Comments:
presented by A. Gal at EXA2017, Vienna, Sept. 2017; written up for EPJ Web of Conferences
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1712.05643 [pdf]
EPJ Web Conf.(2018)·2 citations
07
[Submitted on 15 Dec 2017]
An Alpha Particle Model for Carbon-12
J. I. Rawlinson
We introduce a new model for the Carbon-12 nucleus and compute its lowest energy levels. Our model is inspired by previous work on the rigid body approximation in the $B = 12$ sector of the Skyrme model. We go beyond this approximation and treat the nucleus as a deformable body, finding several new states. A restricted set of deformations is considered, leading to a configuration space $C$ which has a graph-like structure. We use ideas from quantum graph theory in order to make sense of quantum mechanics on $C$ even though it is not a manifold. This is a new approach to Skyrmion quantisation and the method presented in this paper could be applied to a variety of other problems.
Comments:
New figures added. Revised version to appear in Nuclear Physics A
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th)
arXiv:
1712.05658 [pdf]
NPA(2018)·26 citations
08
[Submitted on 15 Dec 2017]
Hypernuclear No-Core Shell Model
Roland Wirth🇩🇪 · Daniel Gazda🇸🇪 · Petr Navrátil🇨🇦 · Robert Roth🇩🇪
We extend the No-Core Shell Model (NCSM) methodology to incorporate strangeness degrees of freedom and apply it to single- $Λ$ hypernuclei. After discussing the transformation of the hyperon-nucleon (YN) interaction into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group transformation applied to it to improve model-space convergence, we present two complementary formulations of the NCSM, one that uses relative Jacobi coordinates and symmetry-adapted basis states to fully exploit the symmetries of the hypernuclear Hamiltonian, and one working in a Slater determinant basis of HO states where antisymmetrization and computation of matrix elements is simple and to which an importance-truncation scheme can be applied. For the Jacobi-coordinate formulation, we give an iterative procedure for the construction of the antisymmetric basis for arbitrary particle number and present the formulae used to embed two- and three-baryon interactions into the many-body space. For the Slater-determinant formulation, we discuss the conversion of the YN interaction matrix elements from relative to single-particle coordinates, the importance-truncation scheme that tailors the model space to the description of the low-lying spectrum, and the role of the redundant center-of-mass degrees of freedom. We conclude with a validation of both formulations in the four-body system, giving converged ground-state energies for a chiral Hamiltonian, and present a short survey of the $A \leq 7$ hyper-helium isotopes.
Comments:
17 pages, 8 figures; accepted version
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1712.05694 [pdf]
PRC(2018)·47 citations

Affiliations

first authorsco-authorsvia INSPIRE