Nuclear Theory·nucl-th

Tuesday·October 6, 2015

20 papers—8 primary·12 cross-listed

01
[Submitted on 2 Oct 2015]
A consistent four-body CDCC model of low-energy reactions: Application to 9Be + 208Pb
M. S. Hussein · P. Descouvemont · L. F. Canto
We investigate the $^{9}$ Be + $^{208}$ Pb elastic scattering, breakup and fusion at energies around the Coulomb barrier. The three processes are described simultaneously, with identical conditions of calculations. The $^{9}$ Be nucleus is defined in an $α + α$ + n three-body model, using the hyperspherical coordinate method. We first analyze spectroscopic properties of $^{9}$ Be, and show that the model provides a fairly good description of the low-lying states. The scattering with $^{208}$ Pb is then studied with the Continuum Discretized Coupled Channel (CDCC) method, where the $α + α$ + n continuum is approximated by a discrete number of pseudostates. Optical potentials for the $α$ + $^{208}$ Pb and n+ $^{208}$ Pb systems are taken from the literature. We present elastic-scattering and fusion cross sections at different energies.
Comments:
8 pages, 3 figures, Proceedings of the International Conference on Nucleus-Nucleus Collisions, NN 2015, Catania-Italy. arXiv admin note: substantial text overlap with arXiv:1410.6410
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1510.00752 [pdf]
EPJ Web Conf.(2016)·1 citation
02
[Submitted on 3 Oct 2015]
Astrophysical S-factor for $^{6}$ Li $(p, γ)$ $^{7}$ Be in the coupled-channel Gamow shell model
G.X. Dong🇫🇷 · K. Fossez🇺🇸 · N. Michel🇫🇷 · M. Płoszajczak🇫🇷
We have applied the Gamow shell model (GSM) in the coupled-channel representation to study the astrophysical $S$ -factor for the proton radiative capture reaction of $^{6}$ Li. Reaction channels are built by coupling the proton wave function expanded in different partial waves with the GSM wave functions of the ground state ( $1^{+}$ ) and the excited states ( $3_{1}^{+}$ , $0_{1}^{+}$ and $2_{1}^{+}$ ) of $^{6}$ Li. All relevant $E 1$ , $M 1$ , and $E 2$ transitions from the initial continuum states in $^{7}$ Be to the final bound states ( $3/2_{1}^{-}$ and $1/2_{1}^{-}$ ) states are included. It is found that the calculated total astrophysical $S$ factor for this reaction agrees well with the experimental data.
Comments:
Presented at the 13th Int. Symposium on Origin of Matter and Evolution of Galaxies (OMEG2015, June 24-27, 2015, Beijing, China
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.00786 [pdf]
EPJ Web Conf.(2016)·0 citations
03
[Submitted on 3 Oct 2015]
Systematic investigations of deep sub-barrier fusion reactions using an adiabatic approach
Takatoshi Ichikawa
To describe fusion hindrance observed in fusion reactions at extremely low incident energies, I propose a novel extension of the standard CC model by introducing a damping factor that describes a smooth transition from sudden to adiabatic processes. I demonstrate the performance of this model by systematically investigating various deep sub-barrier fusion reactions. I extend the standard CC model by introducing a damping factor into the coupling matrix elements in the standard CC model. I adopt the Yukawa-plus-exponential (YPE) model as a basic heavy ion-ion potential, which is advantageous for a unified description of the one- and two-body potentials. For the purpose of these systematic investigations, I approximate the one-body potential with a third-order polynomial function based on the YPE model. Calculated fusion cross sections for the medium-heavy mass systems of $^{64}$ Ni + $^{64}$ Ni, $^{58}$ Ni + $^{58}$ Ni, and $^{58}$ Ni + $^{54}$ Fe, the medium-light mass systems of $^{40}$ Ca + $^{40}$ Ca, $^{48}$ Ca + $^{48}$ Ca, and $^{24}$ Mg + $^{30}$ Si, and the mass-asymmetric systems of $^{48}$ Ca + $^{96}$ Zr and $^{16}$ O + $^{208}$ Pb are consistent with the experimental data. The astrophysical S factor and logarithmic derivative representations of these are also in good agreement with the experimental data. Since the results calculated with the damping factor are in excellent agreement with the experimental data in all systems, I conclude that the smooth transition from the sudden to adiabatic processes occurs and that a coordinate-dependent coupling strength is responsible for the fusion hindrance. In all systems, the potential energies at the touching point $V_{Touch}$ strongly correlate with the incident threshold energies for which the fusion hindrance starts to emerge, except for the medium-light mass systems.
Comments:
19 pages, 20 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1510.00806 [pdf]
PRC(2015)·52 citations
04
[Submitted on 3 Oct 2015]
Bound on the variation in the fine structure constant implied by Oklo data
Leila Hamdan🇰🇼 · Edward D. Davis🇰🇼
Dynamical models of dark energy can imply that the fine structure constant $α$ varies over cosmological time scales. Data on shifts in resonance energies $E_{r}$ from the Oklo natural fission reactor have been used to place restrictive bounds on the change in $α$ over the last 1.8 billion years. We review the uncertainties in these analyses, focussing on corrections to the standard estimate of $k_{α} = α d E_{r} / d α$ due to Damour and Dyson. Guided, in part, by the best practice for assessing systematic errors in theoretical estimates spelt out by Dobaczewski et al. [in J. Phys. G: Nucl. Part. Phys. 41, 074001 (2014)], we compute these corrections in a variety of models tuned to reproduce existing nuclear data. Although the net correction is uncertain to within a factor of 2 or 3, it constitutes at most no more than 25% of the Damour-Dyson estimate of $k_{α}$ . Making similar allowances for the uncertainties in the modeling of the operation of the Oklo reactors, we conclude that the relative change in $α$ since the Oklo reactors were last active (redshift $z ≃ 0.14$ ) is less than $\sim 10$ parts per billion. To illustrate the utility of this bound at low- $z$ , we consider its implications for the string theory-inspired runaway dilaton model of Damour, Piazza and Veneziano.
Comments:
Presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 2015 (Change: footnote added to title page)
Subjects:
Nuclear Theory (nucl-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
arXiv:
1510.00856 [pdf]
1 citation
05
[Submitted on 3 Oct 2015]
Impact of phonon coupling on the radiative nuclear reaction characteristics
Oleg Achakovskiy · Alexander Avdeenkov · Sergei Kamerdzhiev
The pygmy dipole resonance and photon strength functions (PSF) in stable and unstable Ni and Sn isotopes are calculated within the microscopic self-consistent version of the extended theory of finite fermi systems in the quasiparticle time blocking approximation. The approach includes phonon coupling (PC) effects in addition to the standard QRPA approach. The Skyrme force SLy4 is used. A pygmy dipole resonance in 72Ni is predicted at the mean energy of 12.4 MeV exhausting 25.7% of the total energy-weighted sum rule. With our microscopic E1 PSFs in the EMPIRE 3.1 code, the following radiative nuclear reaction characteristics have been calculated for several stable and unstable even-even Sn and Ni isotopes: 1) neutron capture cross sections, 2) corresponding neutron capture gamma-spectra, 3) average radiative widths of neutron resonances. Here, three variants of the microscopic nuclear level density models have been used and a comparison with the phenomenological generalized superfluid model (GSM) has been performed. In all the considered properties, including the recent experimental data for PSF in Sn isotopes, the PC contributions turned out to be significant, as compared with the QRPA one, and necessary to explain the available experimental data. The phenomenological GSM NLD model used in EMPIRE3.1 gives, on the whole, the worse results than the microscopic HFB plus combinatorial NLD model.
Comments:
6 pages, 6 figures. Talk given at the NSRT15 conference (Dubna, 14-18.07.2015)
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1510.00867 [pdf]
EPJ Web Conf.(2016)·2 citations
06
[Submitted on 3 Oct 2015]
An effective method to accurately calculate the phase space factors for $β^{-} β^{-}$ decay
Andrei Neacsu🇺🇸 · Mihai Horoi🇺🇸
Accurate calculations of the electron phase space factors are necessary for reliable predictions of double-beta decay rates, and for the analysis of the associated electron angular and energy distributions. We present an effective method to calculate these phase space factors that takes into account the distorted Coulomb field of the daughter nucleus, yet allows one to easily calculate the phase space factors with good accuracy relative to the most exact methods available in the recent literature.
Comments:
7 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1510.00882 [pdf]
Adv.High Energy Phys.(2016)·29 citations
07
[Submitted on 5 Oct 2015]
Skyrme RPA for spherical and axially symmetric nuclei
Anton Repko · Jan Kvasil · V.O. Nesterenko · P.-G. Reinhard
Random Phase Approximation (RPA) is the basic method for calculation of excited states of nuclei over the Hartree-Fock ground state, suitable also for energy density functionals (EDF or DFT). We developed a convenient formalism for expressing densities and currents in a form of reduced matrix elements, which allows fast calculation of spectra for spherical nuclei. All terms of Skyrme functional were taken into account, so it is possible to calculate electric, magnetic and vortical/toroidal/compression transitions and strength functions of any multipolarity. Time-odd (spin) terms in Skyrme functional become important for magnetic M1 and isovector toroidal E1 transitions. It was also found that transition currents in pygmy region (low-lying part of E1 resonance) exhibit isoscalar toroidal flow, so the previously assumed picture of neutron-skin vibration is not the only mechanism present in pygmy transitions. RPA calculations with heavy axially-symmetric nuclei now become feasible on ordinary PC. Detailed formulae for axial Skyrme RPA are given. Some numerical results are shown in comparison with the approximate approach of separable RPA, previously developed in our group for fast calculation of strength functions.
Comments:
10 pages, 6 figures, corrected typos in eq.(38h,i), for published version see https://fu.sav.sk/wp-content/uploads/uploaded/departments/ojf/events/ISTROS/2015/materials/ISTROS_2015_Proceedings.pdf
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1510.01248 [pdf]
Proceedings of the ISTROS 2015 Internatio…·23 citations
08
[Submitted on 5 Oct 2015]
Initial conditions from the shadowed Glauber model
Sandeep Chatterjee🇮🇳 · Sushant K. Singh🇮🇳 · Snigdha Ghosh🇮🇳 · Md Hasanujjaman🇮🇳 · Jane Alam🇮🇳 · Sourav Sarkar🇮🇳
The two component Monte-Carlo Glauber model predicts a knee-like structure in the centrality dependence of elliptic flow $v_{2}$ in Uranium+Uranium collisions at $s_{N N} = 193$ GeV. It also produces a strong anti-correlation between $v_{2}$ and $d N_{c h} / d y$ in the case of top ZDC events. However, none of these features have been observed in data. We address these discrepancies by including the effect of nucleon shadowing to the two component Monte-Carlo Glauber model. Apart from addressing successfully the above issues, we find that the nucleon shadow suppresses the event by event fluctuation of various quantities, e.g. $ε_{2}$ which is in accordance with expectation from the dynamical models of initial condition based on gluon saturation physics.
Comments:
version accepted for publication in Physics Letters B
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1510.01311 [pdf]
PLB(2016)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE