Author(s): Yue Shi (石跃), C. L. Zhang (张春莉), J. Dobaczewski, and W. Nazarewicz
Background: For cranked mean-field calculations with arbitrarily oriented rotational frequency vector ω in the intrinsic frame, one has to employ constraints on average values of the quadrupole-moment tensor, so as to keep the nucleus in the principal-axis reference frame. Kerman and Onishi [ Nucl....
[Phys. Rev. C 88, 034311] Published Wed Sep 11, 2013
The evolution of the giant dipole resonance's (GDR) width and shape at finite temperature $T$ and angular momentum $J$ is described within the framework of the phonon damping model (PDM). The PDM description is compared with the established experimental systematics obtained from heavy-ion fusion and inelastic scattering of light particles on heavy target nuclei, as well as with predictions by other theoretical approaches. Extended to include the effect of angular momentum $J$, its strength functions have been averaged over the probability distributions of $T$ and $J$ for the heavy-ion fusion-evaporation reaction, which forms the compound nucleus $^{88}$Mo at high $T$ and $J$. The results of theoretical predictions are found in excellent agreement with the experimental data. The predictions by PDM and the heavy-ion fusion data are also employed to predict the viscosity of hot medium and heavy nuclei.
The current status of the application of covariant density functional theory to microscopic description of nuclear fission with main emphasis on superheavy nuclei (SHN) is reviewed. The softness of SHN in the triaxial plane leads to an emergence of several competing fission pathes in the region of the inner fission barrier in some of these nuclei. The outer fission barriers of SHN are considerably affected both by triaxiality and octupole deformation.
The neutron and proton drip lines represent the limits of the nuclear landscape. While the proton drip line is measured experimentally up to rather high $Z$-values, the location of the neutron drip line for absolute majority of elements is based on theoretical predictions which involve extreme extrapolations. The first ever systematic investigation of the location of the proton and neutron drip lines in the covariant density functional theory has been performed by employing a set of the state-of-the-art parametrizations. Calculated theoretical uncertainties in the position of two-neutron drip line are compared with those obtained in non-relativistic DFT calculations. Shell effects drastically affect the shape of two-neutron drip line. In particular, model uncertainties in the definition of two-neutron drip line at $Z\sim 54, N=126$ and $Z\sim 82, N=184$ are very small due to the impact of spherical shell closures at N=126 and 184.
The transition quadrupole moments, $Q_{t}$, of rotational bands in the neutron-rich, even-mass $^{102-108}$Mo and $^{108-112}$Ru nuclei were measured in the 8 to 16 $\hbar $ spin range with the Doppler-shift attenuation method. The nuclei were populated as fission fragments from $^{252}$Cf fission. The detector setup consisted of the Gammasphere spectrometer and the HERCULES fast-plastic array. At moderate spin, the $Q_{t}$ moments are found to be reduced with respect to the values near the ground states. Attempts to describe the observations in mean-field-based models, specifically cranked relativistic Hartree-Bogoliubov theory, illustrate the challenge theory faces and the difficulty to infer information on $\gamma $ softness and triaxiality from the data.
Author(s): A. Pastore, J. Margueron, P. Schuck, and X. Viñas
Exotic and drip-line nuclei as well as nuclei immersed in a low-density gas of neutrons in the inner crust of neutron stars are systematically investigated with respect to their neutron pairing properties. This is done using Skyrme density-functional and different pairing forces such as a density-de...
[Phys. Rev. C 88, 034314] Published Mon Sep 16, 2013
The synthesis of superheavy elements stimulates the effort to study the peculiarities of the complete fusion with massive nuclei and to improve theoretical models in order to extract knowledge about reaction mechanism in heavy ion collisions at low energies. We compare the theoretical results of the compound nucleus (CN) formation and evaporation residue (ER) cross sections obtained for the $^{48}$Ca+$^{248}$Cm and $^{58}$Fe+$^{232}$Th reactions leading to the formation of the isotopes A=296 and A=290, respectively, of the new superheavy element Lv (Z=116). The ER cross sections, which can be measured directly, are determined by the complete fusion and survival probabilities of the heated and rotating compound nucleus. That probabilities can not be measured unambiguously but the knowledge about them is important to study the formation mechanism of the observed products. For this aim, the $^{48}$Ca+$^{249}$Cf and $^{64}$Ni+$^{232}$Th reactions have been considered too. The use of the mass values of superheavy nuclei calculated in the framework of the macroscopic-microscopic model by Warsaw group leads to smaller ER cross section for all of the reactions (excluding the $^{64}$Ni+$^{232}$Th reaction) in comparison with the case of using the masses calculated by Peter M\"oller {\it et al}.
Author(s): M. Moliner and P. Schmitteckert
We present a novel numerical approach to track the response of a quantum system to an external perturbation that is progressively switched on. The method is applied, within the framework of the density matrix renormalization group technique, to track current-carrying states of interacting fermions i...
[Phys. Rev. Lett. 111, 120602] Published Tue Sep 17, 2013
Author(s): S. Bacca, N. Barnea, G. Hagen, G. Orlandini, and T. Papenbrock
We present a calculation of the giant dipole resonance in 16O based on a nucleon-nucleon (NN) interaction from chiral effective field theory that reproduces NN scattering data with high accuracy. By merging the Lorentz integral transform and the coupled-cluster methods, we extend the previous theore...
[Phys. Rev. Lett. 111, 122502] Published Tue Sep 17, 2013
Author(s): André Mirtschink, Michael Seidl, and Paola Gori-Giorgi
We generalize the exact strong-interaction limit of the exchange-correlation energy of Kohn-Sham density functional theory to open systems with fluctuating particle numbers. When used in the self-consistent Kohn-Sham procedure on strongly interacting systems, this functional yields exact features cr...
[Phys. Rev. Lett. 111, 126402] Published Wed Sep 18, 2013
Author(s): Gerald V. Dunne and Michael Thies
We find the general solution to the time-dependent Hartree-Fock problem for the Gross-Neveu models, with both discrete (GN2) and continuous [Nambu-Jona-Lasinio (NJL2)] chiral symmetry. We find new multibaryon, multibreather, and twisted breather solutions, and show that all GN2 baryons and breathers...
[Phys. Rev. Lett. 111, 121602] Published Wed Sep 18, 2013
Author(s): Satoru Sasabe, Takuma Matsumoto, Shingo Tagami, Naoya Furutachi, Kosho Minomo, Yoshifumi R. Shimizu, and Masanobu Yahiro
It was recently suggested that the odd-even staggering of reaction cross sections is evidence of the pairing anti-halo effect on projectile radii. We define the dimensionless staggering parameters Γrds and ΓR for projectile radii and reaction cross sections, respectively, and analyze the relation be...
[Phys. Rev. C 88, 037602] Published Wed Sep 18, 2013
Author(s): E. Williams, D. J. Hinde, M. Dasgupta, R. du Rietz, I. P. Carter, M. Evers, D. H. Luong, S. D. McNeil, D. C. Rafferty, K. Ramachandran, and A. Wakhle
Background: Quasifission, a fission-like reaction outcome in which no compound nucleus forms, is an important competitor to fusion in reactions leading to superheavy elements. The precise mechanisms driving the competition between quasifission and fusion are not well understood.
Purpose: To understan...
[Phys. Rev. C 88, 034611] Published Wed Sep 25, 2013
Author(s): M. Girod and P. Schuck
The nuclear equation of state (EOS) is explored with the constrained Hartree-Fock-Bogoliubov approach for self-conjugate nuclei. It is found that beyond a certain low, more or less universal density, those nuclei spontaneously cluster into A/4 α particles with A the nucleon number. The energy at the...
[Phys. Rev. Lett. 111, 132503] Published Wed Sep 25, 2013
Author(s): Danilo Gambacurta, Denis Lacroix, and N. Sandulescu
The thermodynamics of pairing phase-transition in nuclei is studied in the canonical ensemble and treating the pairing correlations in a finite-temperature variation after projection BCS approach (FT-VAP). Due to the restoration of particle number conservation, the pairing gap and the specific heat ...
[Phys. Rev. C 88, 034324] Published Fri Sep 27, 2013
Author(s): Nuria López Vaquero, Tomás R. Rodríguez, and J. Luis Egido
Nuclear matrix elements (NME) for the most promising candidates to detect neutrinoless double beta decay have been computed with energy density functional methods including deformation and pairing fluctuations explicitly on the same footing. The method preserves particle number and angular momentum ...
[Phys. Rev. Lett. 111, 142501] Published Mon Sep 30, 2013
We simulate a heavy-ion collision using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory (Cb-TDHFB) treating pairing correlation in the three-dimensional coordinate space. We apply the Cb-TDHFB to 22O+22O collision with a contact-type pairing energy functional, and compare results of Cb-TDHFB and TDHF to investigate the effects of pairing correlations in nuclear fusion. Our results seem to indicate that pairing effects do not increase the fusion cross section in this system.
Isoscalar giant resonances and low spin states in $^{32}$S have been measured with inelastic $\alpha$ scattering at extremely forward angles including zero degrees at E$_{\alpha}$ = 386 MeV. By applying the multipole decomposition analysis, various excited states are classified according to their spin and parities (J$^{\pi}$), and are discussed in relation to the super deformed and $^{28}$Si + $\alpha$ cluster bands.
The density-constrained time-dependent Hartree-Fock (DC-TDHF) theory is a fully microscopic approach for calculating heavy-ion interaction potentials and fusion cross sections below and above the fusion barrier. We discuss recent applications of DC-TDHF method to fusion of light and heavy neutron-rich systems.
Author(s): Andrei N. Andreyev, Mark Huyse, and Piet Van Duppen
This Colloquium reviews the studies of exotic type of low-energy nuclear fission, the β-delayed fission (βDF). Emphasis is made on the new data from very neutron-deficient nuclei in the lead region, previously scarcely studied as far as fission is concerned. These data establish the new region of as…
[Rev. Mod. Phys. 85, 1541] Published Fri Oct 04, 2013
Evidence for a new nuclear ‘magic number’ from the level structure of 54Ca
Nature 502, 7470 (2013). doi:10.1038/nature12522
Authors: D. Steppenbeck, S. Takeuchi, N. Aoi, P. Doornenbal, M. Matsushita, H. Wang, H. Baba, N. Fukuda, S. Go, M. Honma, J. Lee, K. Matsui, S. Michimasa, T. Motobayashi, D. Nishimura, T. Otsuka, H. Sakurai, Y. Shiga, P.-A. Söderström, T. Sumikama, H. Suzuki, R. Taniuchi, Y. Utsuno, J. J. Valiente-Dobón & K. Yoneda
Atomic nuclei are finite quantum systems composed of two distinct types of fermion—protons and neutrons. In a manner similar to that of electrons orbiting in an atom, protons and neutrons in a nucleus form shell structures. In the case of stable, naturally occurring nuclei, large energy gaps exist between shells that fill completely when the proton or neutron number is equal to 2, 8, 20, 28, 50, 82 or 126 (ref. 1). Away from stability, however, these so-called ‘magic numbers’ are known to evolve in systems with a large imbalance of protons and neutrons. Although some of the standard shell closures can disappear, new ones are known to appear. Studies aiming to identify and understand such behaviour are of major importance in the field of experimental and theoretical nuclear physics. Here we report a spectroscopic study of the neutron-rich nucleus 54Ca (a bound system composed of 20 protons and 34 neutrons) using proton knockout reactions involving fast radioactive projectiles. The results highlight the doubly magic nature of 54Ca and provide direct experimental evidence for the onset of a sizable subshell closure at neutron number 34 in isotopes far from stability.
We study the low-energy dipole (LED) strength distribution along the Sn isotopic chain in both the isoscalar (IS) and the isovector (IV, or E1) electric channels, to provide testable predictions and guidance for new experiments with stable targets and radioactive beams. We use the self-consistent Quasi-particle Random-Phase Approximation (QRPA) with finite-range interactions and mainly the Gogny D1S force. We analyze also the performance of a realistic two-body interaction supplemented by a phenomenological three-body contact term. We find that from N=50 and up to the N=82 shell closure (132Sn) the lowest-energy part of the IS-LED spectrum is dominated by a collective transition whose properties vary smoothly with neutron number and which cannot be interpreted as a neutron-skin oscillation. For the neutron-rich species this state contributes to the E1 strength below particle threshold, but much more E1 strength is carried by other, weak but numerous transitions around or above threshold. We find that strong structural changes in the spectrum take effect beyond N=82, namely increased LED strength and lower excitation energies. Our results with the Gogny interaction are compatible with existing data. On this basis we predict that a) the summed IS strength below particle threshold shall be of the same order of magnitude for N=50-82, b) the summed E1 strength up to approximately 12 MeV shall be similar for N=50-82 MeV, while c) the summed E1 strength below threshold shall be of the same order of magnitude for N ~ 64 - 82 and much weaker for the lighter, more-symmetric isotopes. We point out a general agreement of our results with other non-relativistic studies, the absence of a collective IS mode in some of those studies, and a possibly radical disagreement with relativistic models.
Author(s): Guillaume Scamps and Denis Lacroix
The isoscalar (IS) and isovector (IV) quadrupole responses of nuclei are systematically investigated using the time-dependent Skyrme energy density functional including pairing in the BCS approximation. Using two different Skyrme functionals, Sly4 and SkM*, respectively 263 and 324 nuclei have been ...
[Phys. Rev. C 88, 044310] Published Fri Oct 11, 2013
The origin of mass asymmetry in the fission of uranium at a low excitation energy is clarified by a trajectory analysis of the Langevin equation. The positions of the peaks in the mass distribution of fission fragments are mainly determined by fission saddle points originating from the shell correction energy. The widths of the peaks, on the other hand, result from a shape fluctuation around the scission point caused by the random force in the Langevin equation. We found that a random vibration in the oblate direction of fissioning fragments is essential for the fission process. According to this picture, fission does not occur with continuous stretching in the prolate direction, similarly to that observed in starch syrup. This is expected to lead to a new viewpoint of fission dynamics and the splitting mechanism.
Author(s): L. Baguet, F. Delyon, B. Bernu, and M. Holzmann
We calculate the ground state phase diagram of the homogeneous electron gas in three dimensions within the Hartree-Fock approximation and show that broken symmetry states are energetically favored at any density against the homogeneous Fermi gas state with isotropic Fermi surface. At high density, w...
[Phys. Rev. Lett. 111, 166402] Published Mon Oct 14, 2013
Author(s): F. J. Fattoyev and J. Piekarewicz
The Lead Radius Experiment has provided the first model-independent evidence in favor of a neutron-rich skin in 208Pb. Although the error bars are large, the reported large central value of 0.33 fm is particularly intriguing. To test whether such a thick neutron skin in 208Pb is already incompatible...
[Phys. Rev. Lett. 111, 162501] Published Wed Oct 16, 2013
Melting of N=20 shell and development of N = 16 and N = 34 shells for neutron-rich nuclei have been studied extensively through inclusion of tensor interaction in Skyrme Hartree Fock theory optimized to reproduce the splitting neutron 1f states of 40, 48Ca and 56Ni nuclei. Evolution of gap generated by the energy difference of single particle levels neutron 2s1/2 and neutron 1d3/2 state has been found to be responsible for the development of a shell closure at N = 16. The splitting pattern of spin-orbit partners 2p shell model state in Ca, Ti, Cr, Fe and Ni isotopes indicates formation of a new shell at N = 34 region.
Author(s): Paolo Avogadro and Carlos A. Bertulani
We compare the results obtained in the framework of the quasiparticle random-phase approximation on top of a Hartree-Fock-Bogoliubov with the most recent experiments on giant monopole resonances in Pb, Sn, Zr, Sm, Mo, and Cd. Our calculations are fully self-consistent and the density dependence of p...
[Phys. Rev. C 88, 044319] Published Thu Oct 17, 2013
Author(s): B. Alex Brown
The pairing gap for 53Ca obtained from new experimental data on the masses of 52–54Ca has the smallest value yet observed. This is explained in the framework of the nuclear shell model with schematic and realistic Hamiltonians as being due to shell gaps around the low-j orbital 1p1/2. Minima in the ...
[Phys. Rev. Lett. 111, 162502] Published Fri Oct 18, 2013