| 1. |
- Albertsson, Martin, et al.
(författare)
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Calculated fission-fragment mass yields and average total kinetic energies of heavy and superheavy nuclei
- 2020
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 56:2
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Tidskriftsartikel (refereegranskat)abstract
- Fission-fragment mass and total-kinetic-energy (TKE) distributions following fission of even-even nuclides in the region 74 ≤ Z≤ 126 and 92 ≤ N≤ 230 , comprising 896 nuclides have been calculated using the Brownian shape-motion method. The emphasis is the region of superheavy nuclei. To show compatibility with earlier results the calculations are extended to include earlier studied regions. An island of asymmetric fission is obtained in the superheavy region, 106 ≤ Z≤ 114 and 162 ≤ N≤ 176 , where the heavy fragment is found to be close to 208Pb and the light fragment adjusts accordingly. Most experimentally observed α-decay chains of superheavy nuclei with Z> 113 terminate by spontaneous fission in our predicted region of asymmetric fission. In these cases, the pronounced large asymmetry is accompanied by a low TKE value compatible with measurements.
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| 2. |
- Albertsson, M., et al.
(författare)
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Formation of transfermium elements in reactions with 208Pb
- 2024
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Ingår i: Physical Review C. - 2469-9985. ; 110:1
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Tidskriftsartikel (refereegranskat)abstract
- Within the Langevin framework, we investigate the dynamics of the fusion process for production of transfermium elements in reactions of 48Ca, 50Ti, 54Cr, and 58Fe with 208Pb. After the reacting nuclei have made contact, the early dynamical stage is dominated by the dissipation of the initial radial kinetic energy, while the subsequent shape evolution is diffusive. The probability for surmounting the inner barrier and forming a compound system is obtained by simulating the evolution as a Metropolis random walk in a five-dimensional potential-energy landscape. Good agreement with the available data is obtained, especially for the maximal formation probability.
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| 3. |
- Almosly, W., et al.
(författare)
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Charged-current neutrino and antineutrino scattering off Cd-116 described by Skyrme forces
- 2014
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 89:2, s. 024308-
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Tidskriftsartikel (refereegranskat)abstract
- We perform calculations of the cross sections for charged-current neutrino and antineutrino scattering off Cd-116 using ten different Skyrme interactions, at energies typical of supernova neutrinos. We use the quasiparticle random-phase approximation in its charged-changing mode (pnQRPA) to construct the required nuclear wave functions for the participant initial and final states. We compare the results of these calculations with the results of calculations based on the Bonn one-boson-exchange potential. The response of Cd-116 to supernova neutrinos is calculated by folding the obtained cross sections with suitably parametrized Fermi-Dirac distributions of the electron-neutrino and electron-antineutrino energies.
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| 4. |
- Almosly, W., et al.
(författare)
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Theoretical estimates of supernova-neutrino cross sections for the stable even-even lead isotopes : Charged-current reactions
- 2016
-
Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 94:4
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the charged-current supernova electron neutrino and electron antineutrino scattering off the stable even-mass lead isotopes A=204, 206, and 208 is reported in this work. The proton-neutron quasiparticle random-phase approximation (pnQRPA) is adopted to construct the nuclear final and initial states. Three different Skyrme interactions are tested for their isospin and spin-isospin properties and then applied to produce (anti)neutrino-nucleus scattering cross sections for (anti)neutrino energies below 80 MeV. Realistic estimates of the nuclear responses to supernova (anti)neutrinos are computed by folding the computed cross sections with a two-parameter Fermi-Dirac distribution of the electron (anti)neutrino energies. The computed cross sections are compared with earlier calculations and the analyses are extended to take into account the effects coming from the neutrino oscillations.
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| 5. |
- Andersson, Lise-Lotte, et al.
(författare)
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Classification of Superdeformed Bands in the Mass A~60 Region
- 2008
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Ingår i: Nuclear Physics and Astrophysics. - : AIP. - 9780735406032 ; 1072, s. 211-214
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Konferensbidrag (refereegranskat)abstract
- The experimental knowledge of the Cu-61(29)32 and Zn-61(30)31 nuclei has been largely extended via the joint results from three experiments. The fusion-evaporation reaction used a Ar-36 beam and a Si-28 target foil to produce the two nuclei via the evaporation of either three protons (Cu-61) or two protons and a neutron (Zn-61). The experimental set-ups comprised the Ge-array GAMMASPHERE as well as neutron and charged-particle detectors placed around the target position. The resulting level schemes include around ten rotational superdeformed structures in each isotope. Most of them are linked to normally deformed states and in many cases spins and parities of the low-lying states in each structure have been determined. The collective structures are compared with results from configuration dependent Cranked Nilsson-Strutinsky calculations. The different structures are in general well understood from the calculation but the results do also suggest modifications of the standard Nilsson parameters in the mass A similar to 60 region.
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| 6. |
- Andersson, Lise-Lotte, et al.
(författare)
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Extensive Gamma-ray Spectroscopy of Normally and Superdeformed Structures in 61Cu
- 2008
-
Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 36:3, s. 251-278
-
Tidskriftsartikel (refereegranskat)abstract
- A largely extended experimental knowledge of the Cu-61(29)32 nucleus has been obtained from three experiments. Excited states in Cu-61 were produced via the fusion-evaporation reaction Si-28(Ar-36, 3p)Cu-61. In addition to the Ge array GAMMASPHERE, neutron and charged-particle detectors placed around the target position were used for high-performance particle spectroscopy. The constructed level scheme includes more than 160 energy levels and 320 gamma-ray transitions belonging to both normally deformed as well as superdeformed rotational structures. The multipolarities have been determined for the gamma-ray transitions and as a result spin-parity assignments are given for nearly all energy levels. Experimental results in the normally deformed region are compared with predictions from large-scale shell model calculations. The collective structures are compared with results from cranked Nilsson-Strutinsky calculations. The results reveal the need to modify the standard Nilsson parameters in the mass A similar to 60 region.
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| 7. |
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| 8. |
- Carlsson, Gillis, et al.
(författare)
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Calculating the nuclear mass in the very high angular momentum regime
- 2006
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 74:1
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Tidskriftsartikel (refereegranskat)abstract
- Macroscopic-microscopic methods are applied in the high-spin regime to calculate the nuclear binding energy ("mass") as a function of proton number, neutron number, and angular momentum. Masses at high spin are calculated using the cranked Nilsson-Strutinsky model together with two different liquid drop models, the Lublin-Strasbourg drop model and the finite range liquid drop model. When comparisons are made with experimental data, a similar agreement between theory and experiment is obtained as for ground-state masses.
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| 9. |
- Carlsson, Gillis, et al.
(författare)
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Calculations of nuclear masses at finite angular momenta
- 2006
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Ingår i: Physica Scripta. - 0031-8949. ; T125, s. 130-133
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Tidskriftsartikel (refereegranskat)abstract
- The macroscopic-microscopic method to calculate nuclear masses is extended into the high-spin regime in order to calculate the nuclear binding energy as a function of proton number, neutron number and angular momentum. We describe the method and exemplify it on recent experimental data.
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| 10. |
- Carlsson, Gillis, et al.
(författare)
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Collective vibrational states within the fast iterative quasiparticle random-phase approximation method
- 2012
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- An iterative method we previously proposed to compute nuclear strength functions [Toivanen et al., Phys. Rev. C 81, 034312 (2010)] is developed to allow it to accurately calculate properties of individual nuclear states. The approach is based on the quasiparticle random-phase approximation (QRPA) and uses an iterative non-Hermitian Arnoldi diagonalization method where the QRPA matrix does not have to be explicitly calculated and stored. The method gives substantial advantages over conventional QRPA calculations with regards to the computational cost. The method is used to calculate excitation energies and decay rates of the lowest-lying 2(+) and 3(-) states in Pb, Sn, Ni, and Ca isotopes using three different Skyrme interactions and a separable Gaussian pairing force.
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| 11. |
- Carlsson, Gillis, et al.
(författare)
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Fluctuating parts of nuclear ground-state correlation energies
- 2013
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 87:5
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Tidskriftsartikel (refereegranskat)abstract
- Background: Heavy atomic nuclei are often described using the Hartree-Fock-Bogoliubov (HFB) method. In principle, this approach takes into account Pauli effects and pairing correlations while other correlation effects are mimicked through the use of effective density-dependent interactions. Purpose: Investigate the influence of higher-order correlation effects on nuclear binding energies using Skyrme's effective interaction. Methods: A cutoff in relative momenta is introduced to remove ultraviolet divergencies caused by the zero-range character of the interaction. Corrections to binding energies are then calculated using the quasiparticle-random-phase approximation and second-order many-body perturbation theory. Result: Contributions to the correlation energies are evaluated for several isotopic chains and an attempt is made to disentangle which parts give rise to fluctuations that may be difficult to incorporate on the HFB level. The dependence of the results on the cutoff is also investigated. Conclusions: The improved interaction allows explicit summations of perturbation series, which is useful for the description of some nuclear observables. However, refits of the interaction parameters are needed to obtain more quantitative results.
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| 12. |
- Carlsson, Gillis, et al.
(författare)
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How to calculate α-decay rates in the future?
- 2016
-
Ingår i: Nobel Symposium NS 160 - Chemistry and Physics of Heavy and Superheavy Elements. - : EDP Sciences. - 9782759890118 ; 131
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Konferensbidrag (refereegranskat)abstract
- New elements discovered during past decades have been created in fusion reactions where a lighter nucleus is collided with a heavier one. The new elements created often decay by emitting α particles. From the half-lives of the decays and the energies of the emitted particles one may extract some properties of the new elements. In this talk the recent work performed by the Lund group to model α decay starting from nuclear density-functional theory is reviewed and a possible extension is mentioned.
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| 13. |
- Carlsson, Gillis, et al.
(författare)
-
Low-lying states in near-magic odd-odd nuclei and the effective interaction
- 2014
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:5
-
Tidskriftsartikel (refereegranskat)abstract
- The iterative quasiparticle random-phase approximation (QRPA) method we previously developed [Phys. Rev. C 81, 034312 (2010); 86, 024303 (2012); 86, 014307 (2012)] to accurately calculate properties of individual nuclear states is extended so that it can be applied for nuclei with odd numbers of neutrons and protons. The approach is based on the proton-neutron QRPA (pnQRPA) and uses an iterative non-Hermitian Arnoldi diagonalization method where the QRPA matrix does not have to be explicitly calculated and stored. The method is used to calculate excitation energies of proton-neutron multiplets for several nuclei. The influence of a pairing interaction in the T = 0 channel is studied.
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| 14. |
- Carlsson, Gillis, et al.
(författare)
-
Many-particles-plus-rotor description of magnetic bands at high spin
- 2006
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 74:4
-
Tidskriftsartikel (refereegranskat)abstract
- The high-spin parts of shears bands observed in Pb-198,Pb-199 are described by coupling several valence particles to a deformed rotor core. To give the model enough freedom so that both the proton and the neutron spin vectors can find their preferred direction, the use of five to six valence particles and holes is found to be necessary. Effective parameters characterizing the rotor are deduced from the cranking model. The method is described and results are presented concerning transition probabilities and energies in the high-spin regime for several rotational bands in Pb-199. The possible termination of the rotational bands is also discussed.
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| 15. |
- Carlsson, Gillis
(författare)
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Models for Rotating Nuclei - Cranking and Rotor + Particles Coupling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation investigates properties of rotating atomic nuclei. Studies are performed using the cranking model and in the particles + rotor model. Properties studied are energy spectra and electromagnetic transition probabilities. The thesis also investigates the use of different liquid drop models at high spin values and studies the use of the particle + rotor approximation for the description of different 'exotic' ways of rotating. The dissertation comprises six original papers, which are presented following an introduction to the fields of research and the methods used and the systems studied. Paper I investigates the use of different meanfield parameters for the description of experimental high-spin states in 86Nb. A better agreement with experimental data could be found, however some experimental features proved hard to explain. In Paper II new experimental data on high-spin states in 58Ni was presented and compared with cranking calculations. A good agreement with calculation led to a clear interpretation of all observed states. The interaction and transitions between two of the rotational bands are analyzed and found to be sensitive to the deformation of the nucleus. In Paper III the average pairing energy is removed from the parameters of the liquid-drop model by performing a refitt to nuclear groundstate masses. The modified model is then used to calculate the total energy of the nucleus at high-spin values. Two different models are compared and one is found to be more reliable for light nuclei. In Paper IV the usual particle plus rotor model is extended to incorporate an arbitrary number of particles coupled to the rotor. This model is then used to describe the so called shears bands where states are formed by the coupling of perpendicular neutron and proton spin vectors. The same model is employed in Paper V for the description of collective wobbling excitations in nuclei. In Paper VI, new experimental data on quadrupole transitions in 142Gd are presented. These data are compared to the result of cranking calculations employing a monopole pairing interaction. Based on the calculations the relatively small transition probabilities are interpreted as being the result of the rotation taking place around the longest principal axis of the mass distribution.
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| 16. |
- Carlsson, Gillis, et al.
(författare)
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Nuclear binding energy at high spin
- 2006
-
Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. ; 831, s. 60-64
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Konferensbidrag (refereegranskat)abstract
- A method to calculate absolute values of the total nuclear binding energy in the high-spin regime is briefly described. Applications to test the position of specific orbitals are examplified on Z = 36 Kr isotopes with N = 36 - 38. Calculated binding energies of possible configurations for one dipole band in 199Pb are compared with experiment
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| 17. |
- Carlsson, Gillis, et al.
(författare)
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Nuclear shell structure and rotational bands in Nb-86
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 70:2
-
Tidskriftsartikel (refereegranskat)abstract
- The high spin structures in Nb-86 are analyzed using the cranked Nilsson-Strutinsky model. Energy versus spin curves as well as deformations and electric transition quadrupole moments are considered. It is concluded that different single-particle parameters compared with the standard values lead to better agreement with recent experimental results.
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| 18. |
- Carlsson, Gillis
(författare)
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Structure of wobbling excitations in Lu-163
- 2007
-
Ingår i: International Journal of Modern Physics E. - 0218-3013. ; 16:2, s. 634-642
-
Tidskriftsartikel (refereegranskat)abstract
- Using a many-particles plus rotor model, wobbling excitations built on top of a triaxial superdeformed band in Lu-163 are investigated. By extracting all parameters for the rotor from a mean field calculation a good correspondence with calculations based on the random-phase approximation is achieved.
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| 19. |
- Forsberg, U., et al.
(författare)
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Recoil-α-fission and recoil-α-α-fission events observed in the reaction 48Ca + 243Am
- 2016
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Ingår i: Nuclear Physics, Section A. - : Elsevier BV. - 0375-9474. ; 953, s. 117-138
-
Tidskriftsartikel (refereegranskat)abstract
- Products of the fusion-evaporation reaction 48Ca + 243Am were studied with the TASISpec set-up at the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. Amongst the detected thirty correlated α-decay chains associated with the production of element Z=115, two recoil-α-fission and five recoil-α-α-fission events were observed. The latter five chains are similar to four such events reported from experiments performed at the Dubna gas-filled separator, and three such events reported from an experiment at the Berkeley gas-filled separator. The four chains observed at the Dubna gas-filled separator were assigned to start from the 2n-evaporation channel 289115 due to the fact that these recoil-α-α-fission events were observed only at low excitation energies. Contrary to this interpretation, we suggest that some of these recoil-α-α-fission decay chains, as well as some of the recoil-α-α-fission and recoil-α-fission decay chains reported from Berkeley and in this article, start from the 3n-evaporation channel 288115.
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| 20. |
- Forsberg, Ulrika, et al.
(författare)
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Spectroscopic Tools Applied to Element Z = 115 Decay Chains
- 2014
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X .- 2101-6275. - 9782759811755 - 9782759811762 ; 66, s. 02036-02036
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Konferensbidrag (refereegranskat)abstract
- Nuclides that are considered to be isotopes of element Z = 115 were produced in the reaction 48Ca + 243Am at the GSI Helmholtzzentrum für Schwerionenforschung Darmstadt. The detector setup TASISpec was used. It was mounted behind the gas-filled separator TASCA. Thirty correlated α-decay chains were found, and the energies of the particles were determined with high precision. Two important spectroscopic aspects of the offline data analysis are discussed in detail: the handling of digitized preamplified signals from the silicon strip detectors, and the energy reconstruction of particles escaping to upstream detectors relying on pixel-by-pixel dead-layer thicknesses.
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| 21. |
- Gellanki, Jnaneswari, et al.
(författare)
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Comparative Study of Rotational Bands in the A~60 Mass Region: Modification of Nilsson Parameters
- 2014
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:2
-
Tidskriftsartikel (refereegranskat)abstract
- The large number of high-spin bands that have been observed in A=56-62 nuclei are analyzed systematically within the cranked Nilsson-Strutinsky approach. Optimized Nilsson single-particle parameters are derived from investigations of energy differences between experimental and calculated rotational bands. Specifically, the relative energies of bands in neighboring nuclei whose configurations differ by having a high-j orbital either filled or empty are analyzed. The level schemes calculated with the new Nilsson parameters are compared with those using standard Nilsson parameters. Some configuration assignments are revised.
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| 22. |
- Kardan, Azam, et al.
(författare)
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Interpretation of normal-deformed bands in Lu 167
- 2020
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Ingår i: Physical Review C. - 2469-9985. ; 101:1
-
Tidskriftsartikel (refereegranskat)abstract
- With the aim to get a general understanding of rotational bands in the deformed rare-earth region or in deformed nuclei in general, the observed normal-deformed rotational structures in Lu167 are interpreted within the unpaired and paired cranked Nilsson-Strutinsky formalisms, cranked Nilsson-Strutinsky and cranked Nilsson-Strutinsky-Bogoliubov. Particular attention is devoted to the band crossings. For this nucleus with the Fermi surface high up in the h11/2 shell, we conclude that except for the paired AB and BC crossings in configurations with an even and odd number of i13/2 neutrons, respectively, the observed band crossings can be understood within the unpaired formalism. Especially, it means that above the AB and BC crossings, the evolution with spin is described as a gradual alignment of the spin vectors of the particles outside closed shells. Consequently, the configurations can be characterized by the number of particles occupying open j shells or groups of j shells. In the present study, we revise the interpretation of some experimental bands and also the nature of the crossings while some previous configuration assignments are confirmed.
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| 23. |
- Lantz, Victor, et al.
(författare)
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Deep learning for inverse problems in quantum mechanics
- 2021
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 121:9
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Tidskriftsartikel (refereegranskat)abstract
- Inverse problems are important in quantum mechanics and involve such questions as finding which potential give a certain spectrum or which arrangement of atoms give certain properties to a molecule or solid. Inverse problems are typically very hard to solve and tend to be very compute intense. We here show that neural networks can easily solve inverse problems in quantum mechanics. It is known that a neural network can compute the spectrum of a given potential, a result which we reproduce. We find that the (much harder) inverse problem of computing the correct potential that gives a prescribed spectrum is equally easy for a neural network. We extend previous work where neural networks were used to find the electronic many-particle density given a potential by considering the inverse problem. That is, we show that neural networks can compute the potential that gives a prescribed many-electron density.
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| 24. |
- Ma, Hai-Liang, et al.
(författare)
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Interpretation of the high spin states in Lu-161: A paired and unpaired study
- 2014
-
Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:1
-
Tidskriftsartikel (refereegranskat)abstract
- A paired cranked Nilsson-Strutinsky-Bogoliubov (CNSB) model is presented, which employs the same method to calculate the liquid-drop energy and moment of inertia as the unpaired cranked Nilsson-Strutinsky (CNS) model. In the CNSB model, the energy minimization is carried out in the mesh of pairing gaps Delta and Fermi levels lambda as well as deformation parameters. The high spin states in Lu-161 are then investigated with the CNSB and CNS models. The terminating structure shows a striking similarity with these two models. Combining the CNSB and CNS models, a complete understanding of high spin structures, including the normal deformed (ND) and triaxial strongly deformed (TSD) bands and observed side bands in Lu-161, is achieved. It appears that the only important paired crossings are the first i(13/2) neutron crossing and the first h(11/2) proton crossing. For the description of the unpaired high spin crossings, it is important to be able to distinguish between the pseudospin partners in the proton N = 4 shell, (d(5/2), g(7/2)) and (d(3/2), s(1/2)). The yrast bands are predicted to terminate, which explains the structure of a TSD-like band X2. A band crossing at I approximate to 36.5 for the TSD band in Lu-161, unique within the chain of even-N Lu isotopes, is well described by the CNSB model.
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| 25. |
- Masiteng, P. L., et al.
(författare)
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Close near-degeneracy in a pair of four-quasiparticle bands in Tl-194
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 83-88
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Tidskriftsartikel (refereegranskat)abstract
- A pair of rotational bands associated with the pi h(9/2) circle times nu i(13/2)(-1) configuration at lower spins and with the pi h(9/2) circle times nu i(13/2)(-3) configuration at higher spins is found in Tl-194. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. Such close near-degeneracy probably indicates chiral geometry in the angular momentum space. (c) 2013 Elsevier B.V. All rights reserved.
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| 26. |
- Moeller, P., et al.
(författare)
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Axial and reflection asymmetry of the nuclear ground state
- 2008
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Ingår i: Atomic Data and Nuclear Data Tables. - : Elsevier BV. - 0092-640X. ; 94:5, s. 758-780
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Tidskriftsartikel (refereegranskat)abstract
- More than a decade ago we published a calculation of nuclear ground-state masses and deformations in Atomic Data and Nuclear Data Tables [P. Moller, J.R. Nix, W.D. Myers, W.J. Swiatecki, At. Data Nucl. Data Tables 59 (1995) 185]. In this study, triaxial nuclear shapes were not considered. We have now enhanced our model and studied the influence of triaxial shape degrees of freedom on the nuclear ground-state potential-energy (mass) and ground-state shape. It turns out that a few hundred nuclei are affected to a varying degree with the largest effect, about 0.7 MeV, occurring near Ru-108. We provide here a table of the calculated effects of triaxial shape degrees of freedom. Although axial-asymmetry effects were not considered in the 1995 mass calculation, it did study the effects of reflection-asymmetric shape degrees of freedom (epsilon(3)) on nuclear masses. However, the magnitude of the effect was not tabulated. Here, we provide such a table. In addition we calculate the effect in a much improved fashion: we search a four-dimensional deformation space (epsilon(2), epsilon(3), epsilon(4), and epsilon(6)). This is now possible because the computational resources available to us today are more than 100,000 times better than at the time we calculated the mass table published in 1995. (C) 2008 Elsevier Inc. All rights reserved.
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| 27. |
- Moller, Peter, et al.
(författare)
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Global calculations of ground-state axial shape asymmetry of nuclei
- 2006
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Ingår i: Physical Review Letters. - 1079-7114. ; 97:16
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Tidskriftsartikel (refereegranskat)abstract
- Important insight into the symmetry properties of the nuclear ground-state (gs) shape is obtained from the characteristics of low-lying collective energy-level spectra. In the 1950s, experimental and theoretical studies showed that in the gs many nuclei are spheroidal in shape rather than spherical. Later, a hexadecapole component of the gs shape was identified. In the 1970-1995 time frame, a consensus that reflection symmetry of the gs shape was broken for some nuclei emerged. Here we present the first calculation across the nuclear chart of axial symmetry breaking in the nuclear gs. We show that we fulfill a necessary condition: Where we calculate axial symmetry breaking, characteristic gamma bands are observed experimentally. Moreover, we find that, for those nuclei where axial asymmetry is found, a systematic deviation between calculated and measured masses is removed.
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| 28. |
- Mustafa, M., et al.
(författare)
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Diverse collective excitations in Er-159 up to high spin
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:5
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Tidskriftsartikel (refereegranskat)abstract
- A spectroscopic investigation of the gamma decays from excited states in Er-159 has been performed to study the changing structural properties exhibited as ultrahigh spins (I > 60 (h) over bar) are approached. The nucleus of Er-159 was populated by the reaction Cd-116(Ca-48, 5n gamma) at a beam energy of 215 MeV, and the resulting gamma decays were studied using the Gammasphere spectrometer. New rotational bands and extensions to existing sequences were observed, which are discussed in terms of the cranked shell model, revealing a diverse range of quasiparticle configurations. At spins around 50 (h) over bar, there is evidence for a change from dominant prolate collective motion at the yrast line to oblate non-collective structures via the mechanism of band termination. A possible strongly deformed triaxial band occurs at these high spins, which indicates collectivity beyond 50 (h) over bar. The high-spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.
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| 29. |
- Papoulia, Asimina, et al.
(författare)
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Effect of realistic nuclear charge distributions on isotope shifts and progress towards the extraction of higher-order nuclear radial moments
- 2016
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 94:4
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Tidskriftsartikel (refereegranskat)abstract
- Atomic spectral lines from different isotopes display a small shift in energy, commonly referred to as the line isotope shift. One of the components of the isotope shift is the field shift, which depends on the extent and the shape of the nuclear charge density distribution. The purpose of this work is to investigate how sensitive field shifts are with respect to variations in the nuclear size and shape and what information of nuclear charge distributions can be extracted frommeasurements.Nuclear properties are obtained from nuclear density functional theory calculations based on the Skyrme-Hartree-Fock-Bogoliubov approach. These results are combined with multiconfiguration Dirac-Hartree-Fock methods to obtain realistic field shifts and it is seen that phenomena such as nuclear deformation and variations in the diffuseness of nuclear charge distributions give measurable contributions to the isotope shifts.Using a different approach,we demonstrate the possibility to extract information concerning the nuclear charge densities from the observed field shifts. We deduce that combining methods used in atomic and nuclear structure theory gives an improved description of field shifts and that extracting additional nuclear information from measured isotope shifts is possible in the near future with improved experimental methods.
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| 30. |
- Ragnarsson, Ingemar, et al.
(författare)
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Building angular momentum beyond band termination in 157,158Er
- 2006
-
Ingår i: ; , s. 66-75
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Our present understanding of the terminating bands in the I=40-50 spin range of 157,158Er is reviewed briefly. It is only recently that it has been possible to study states at higher spin in these nuclei, beyond band termination. Firstly, a large number of weak high-energy transitions feeding the terminating states were observed. Secondly, some collective structures that extended discrete spectroscopy in these nuclei beyond I= 60 hbar were identified.
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| 31. |
- Ragnarsson, Ingemar, et al.
(författare)
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Shape Coexistence, Triaxial Shape and Band Terminations at High Spin
- 2015
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 46:3, s. 477-486
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Tidskriftsartikel (refereegranskat)abstract
- Selected high-spin bands in A = 120-170 nuclei are interpreted within the configuration-constrained Cranked Nilsson-Strutinsky formalism with pairing neglected (CNS) and with pairing included (CNSB). A few bands in Lu/Hf nuclei which have been interpreted as formed at large triaxial deformation are reinterpreted as rotational bands at small deformation approaching termination. The differences between the linked high-spin rotational bands in Xe-125,Xe-126 are explored, suggesting that the bands in Xe-126 terminate high above yrast at close to spherical shape.
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| 32. |
- Ragnarsson, Ingemar, et al.
(författare)
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Terminating States In Z=71 Lu Nuclei With N Approximate To 90
- 2010
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Ingår i: International Journal of Modern Physics E. - 0218-3013. ; 19:4, s. 590-600
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Tidskriftsartikel (refereegranskat)abstract
- The high-spin yrast states in Lu-161 are calculated in a Cranked Nilsson-Strutinsky approach keeping track of configurations and their evolution with spin. The outcome from calculations neglecting pairing and including pairing are compared. It is predicted that several yrast region configurations terminate at a very favored energy around I = 50 and that one of the observed bands is two transitions short of termination.
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| 33. |
- Raimondi, F., et al.
(författare)
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Continuity equation and local gauge invariance for the (NLO)-L-3 nuclear energy density functionals
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:6
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Tidskriftsartikel (refereegranskat)abstract
- Background: The next-to-next-to-next-to-leading order ((NLO)-L-3) nuclear energy density functional extends the standard Skyrme functional with new terms depending on higher-order derivatives of densities, introduced to gain better precision in the nuclear many-body calculations. A thorough study of the transformation properties of the functional with respect to different symmetries is required as a step preliminary to the adjustment of the coupling constants. Purpose: We determine to what extent the presence of higher-order derivatives in the functional can be compatible with the continuity equation. In particular, we study the relations between the validity of the continuity equation and the invariance of the functional under gauge transformations. Methods: We derive conditions for the validity of the continuity equation in the framework of time-dependent density functional theory. The conditions apply separately to the four spin-isospin channels of the one-body density matrix. Results: We obtained four sets of constraints on the coupling constants of the (NLO)-L-3 energy density functional that guarantee the validity of the continuity equation in all spin-isospin channels. In particular, for the scalar-isoscalar channel, the constraints are the same as those resulting from imposing the standard U(1) local-gauge-invariance conditions. Conclusions: The validity of the continuity equation in the four spin-isospin channels is equivalent to the local-gauge invariance of the energy density functional. For vector and isovector channels, such validity requires the invariance of the functional under local rotations in the spin and isospin spaces.
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| 34. |
- Raimondi, F., et al.
(författare)
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Effective pseudopotential for energy density functionals with higher-order derivatives
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 83:5
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Tidskriftsartikel (refereegranskat)abstract
- We derive a zero-range pseudopotential that includes all possible terms up to sixth order in derivatives. Within the Hartree-Fock approximation, it gives the average energy that corresponds to a quasilocal nuclear energy density functional (EDF) built of derivatives of the one-body density matrix up to sixth order. The direct reference of the EDF to the pseudopotential acts as a constraint that divides the number of independent coupling constants of the EDF by two. This allows, e. g., for expressing the isovector part of the functional in terms of the isoscalar part, or vice versa. We also derive the analogous set of constraints for the coupling constants of the EDF that is restricted by spherical, space-inversion, and time-reversal symmetries.
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| 35. |
- Randrup, Jørgen, et al.
(författare)
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Fission dynamics with microscopic level densities
- 2018
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Ingår i: Scientific Workshop on "Nuclear Fission and the Emission of Prompt Neutrons and Gamma Rays", THEORY 2017. - : EDP Sciences. - 9782759890316 ; 169
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Konferensbidrag (refereegranskat)abstract
- Working within the Langevin framework of nuclear shape dynamics, we study the dependence of the evolution on the degree of excitation. As the excitation energy of the fissioning system is increased, the pairing correlations and the shell effects diminish and the effective potential-energy surface becomes ever more liquid-drop like. This feature can be included in the treatment in a formally well-founded manner by using the local level densities as a basis for the shape evolution. This is particularly easy to understand and implement in the Metropolis treatment where the evolution is simulated by means of a random walk on the five-dimensional lattice of shapes for which the potential energy has been tabulated. Because the individual steps between two neighboring lattice sites are decided on the basis of the ratio of the statistical weights, what is needed is the ratio of the local level densities for those shapes, evaluated at the associated local excitation energies. For this purpose, we adapt a recently developed combinatorial method for calculating level densities which employs the same single-particle levels as those that were used for the calculation of the pairing and shell contributions to the macroscopic-microscopic deformation-energy surface. For each nucleus under consideration, the level density (for a fixed total angular momentum) is calculated microscopically for each of the over five million shapes given in the three-quadratic-surface parametrization. This novel treatment, which introduces no new parameters, is illustrated for the fission fragment mass distributions for selected uranium and plutonium cases.
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| 36. |
- Rudolph, Dirk, et al.
(författare)
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58Ni: An Unpaired Band Crossing at New Heights of Angular Momentum for Rotating Nuclei
- 2006
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Ingår i: Physical Review Letters. - 1079-7114. ; 96:9
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states in Ni-58 have been investigated by means of the fusion-evaporation reaction Si-28(S-32,2p)Ni-58 at 130 MeV beam energy. Discrete-energy levels are observed in Ni-58 at record-breaking 42 MeV excitation energy and angular momenta in excess of 30h. The states form regular rotational bands with unprecedented high rotational frequencies. A comparison with configuration dependent cranked Nilsson-Strutinsky calculations reveals an exceptional two-band crossing scenario, the interaction strength of which is strongly shape dependent.
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| 37. |
- Rudolph, Dirk, et al.
(författare)
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Alpha-Photon Coincidence Spectroscopy Along Element 115 Decay Chains
- 2014
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 45, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Produced in the reaction 48Ca+243Am, thirty correlated α-decay chains were observed in an experiment conducted at the GSI Helmholzzentrum für Schwerionenforschung, Darmstadt, Germany. The decay chains are basically consistent with previous findings and are considered to originate from isotopes of element 115 with mass numbers 287, 288, and 289. A set-up aiming specifically for high-resolution charged particle and photon coincidence spectroscopy was placed behind the gas-filled separator TASCA. For the first time, γ rays as well as X-ray candidates were observed in prompt coincidence with the α-decay chains of element 115.
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| 38. |
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| 39. |
- Rudolph, Dirk, et al.
(författare)
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Selected Spectroscopic Results on Element 115 Decay Chains
- 2015
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Ingår i: Journal of Radioanalytical and Nuclear Chemistry. - : Springer Science and Business Media LLC. - 0236-5731 .- 1588-2780. ; 303:2, s. 1185-1190
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Tidskriftsartikel (refereegranskat)abstract
- Thirty correlated alpha-decay chains were observed in an experiment studying the fusion-evaporation reaction 48Ca + 243Am at the GSI Helmholtzzentrum f¨ur Schwerionenforschung. The decay characteristics of the majority of these 30 chains are consistent with previous observations and interpretations of such chains to originate from isotopes of element Z = 115. High-resolution alpha-photon coincidence spectroscopy in conjunction with comprehensive Monte-Carlo simulations allow to propose excitation schemes of atomic nuclei of the heaviest elements, thereby probing nuclear structure models near the ‘Island of Stability’ with unprecedented experimental precision.
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| 40. |
- Rudolph, Dirk, et al.
(författare)
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Spectroscopy of Element 115 Decay Chains
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:11
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Tidskriftsartikel (refereegranskat)abstract
- A high-resolution , X-ray and gamma-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated alpha-decay chains were detected following the fusion-evaporation reaction 48Ca + 243Am. The observations are consistent with previous assignments of similar decay chains to originate from element Z = 115. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements Z > 112. Comprehensive Monte-Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.
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| 41. |
- Shi, Yue, et al.
(författare)
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Structure of Superheavy Nuclei Along Decay Chains of Element 115
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 90:1
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Tidskriftsartikel (refereegranskat)abstract
- A recent high-resolution α, X-ray, and γ-ray coincidence-spectroscopy experiment offered the first glimpse of excitation schemes of isotopes along α-decay chains of Z=115. To understand these observations and to make predictions about shell structure of superheavy nuclei below 288-115, we employ two complementary mean-field models: the self-consistent Skyrme energy density functional approach and the macroscopic-microscopic Nilsson model. We discuss the spectroscopic information carried by the new data. In particular, candidates for the experimentally observed E1 transitions in Mt276 are proposed. We find that the presence and nature of low-energy E1 transitions in well-deformed nuclei around Z=110,N=168 strongly depends on the strength of the spin-orbit coupling; hence, it provides an excellent constraint on theoretical models of superheavy nuclei. To clarify competing theoretical scenarios, an experimental search for E1 transitions in odd-A systems Mt277, Hs275, and Ds277 is strongly recommended.
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| 42. |
- Shirinda, O., et al.
(författare)
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Can a Chiral System Be Built on a Strongly Asymmetric Nucleon Configuration?
- 2013
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 44:3, s. 341-344
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Tidskriftsartikel (refereegranskat)abstract
- The multi-particle-plus-triaxial-rotor (MPR) model calculations were performed for several nuclei in the 100, 130 and 190 mass regions. It was found that chiral geometry can form even for very asymmetric nucleon configurations. However, the near-degeneracy of the partner bands may not be as good as the one observed for symmetric or slightly asymmetric configurations. DOI:10.5506/APhysPolB.44.341
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| 43. |
- Stefanescu, I, et al.
(författare)
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High-spin states and band terminations in As-69
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- Excited levels in As-69 were studied using the Ca-40(S-32,3p)As-69 reaction at 95 and 105 MeV beam energy. Gamma rays were detected with the EUROBALL spectrometer operated in conjunction with the Neutron Wall and the charged-particle detector array EUCLIDES. New level sequences with positive and negative parity were identified from 3p-gammagamma and gammagammagamma coincidences. Spins were assigned to many of the levels on the basis of directional correlations of oriented states measurements. The previously observed positive-parity band was extended to spin 45/2(+) and it was found to exhibit a crossing with another configuration identified up to spin 53/2(+). Three negative-parity bands were observed for the first time up to spins (43/2(-)), 39/2(-), and (41/2(-)). The previously known band was extended to spin (49/2(-)). No evidence for superdeformation was found, despite very high counting statistics. Configurations were assigned to each of the observed bands through comparisons to the cranked Nilsson-Strutinsky calculations.
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| 44. |
- Såmark-Roth, Anton, et al.
(författare)
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Spectroscopy along flerovium decay chains: Discovery of 280Ds and an excited state in 282Cn
- 2021
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Ingår i: Physical Review Letters. - 1079-7114. ; 126:3
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Tidskriftsartikel (refereegranskat)abstract
- A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions 48Ca+242Pu and 48Ca+244Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to 286Fl and 288Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α-particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely 282Cn. Spectroscopy of 288Fl decay chains fixed Qα=10.06(1) MeV. In one case, a Qα=9.46(1)-MeV decay from 284Cn into 280Ds was observed, with 280Ds fissioning after only 518 μs. The impact of these findings, aggregated with existing data on decay chains of 286,288Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.
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| 45. |
- Tarpanov, D., et al.
(författare)
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Polarization corrections to single-particle energies studied within the energy-density-functional and quasiparticle random-phase approximation approaches
- 2014
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 89:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Models based on using perturbative polarization corrections and mean-field blocking approximation give conflicting results for masses of odd nuclei. Purpose: We systematically investigate the polarization and mean-field models, implemented within self-consistent approaches that use identical interactions and model spaces, to find reasons for the conflicts between them. Methods: For density-dependent interactions and with pairing correlations included, we derive and study links between the mean-field and polarization results obtained for energies of odd nuclei. We also identify and discuss differences between the polarization-correction and full particle-vibration-coupling (PVC) models. Numerical calculations are performed for the mean-field ground-state properties of deformed odd nuclei and then compared to the polarization corrections determined using the approach that conserves spherical symmetry. Results: We have identified and numerically evaluated self-interaction (SI) energies that are at the origin of different results obtained within the mean-field and polarization-correction approaches. Conclusions: Mean-field energies of odd nuclei are polluted by the SI energies, and this makes them different from those obtained using polarization-correction methods. A comparison of both approaches allows for the identification and determination of the SI terms, which then can be calculated and removed from the mean-field results, giving the self-interaction-free energies. The simplest deformed mean-field approach that does not break parity symmetry is unable to reproduce full PVC effects.
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| 46. |
- Tarpanov, D, et al.
(författare)
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Spectroscopic properties of nuclear skyrme energy density functionals.
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 113:25
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Tidskriftsartikel (refereegranskat)abstract
- We address the question of how to improve the agreement between theoretical nuclear single-particle energies (SPEs) and observations. Empirically, in doubly magic nuclei, the SPEs can be deduced from spectroscopic properties of odd nuclei that have one more or one less neutron or proton. Theoretically, bare SPEs, before being confronted with observations, must be corrected for the effects of the particle vibration coupling (PVC). In the present work, we determine the PVC corrections in a fully self-consistent way. Then, we adjust the SPEs, with PVC corrections included, to empirical data. In this way, the agreement with observations, on average, improves; nevertheless, large discrepancies still remain. We conclude that the main source of disagreement is still in the underlying mean fields, and not in including or neglecting the PVC corrections.
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| 47. |
- Vesely, P., et al.
(författare)
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Giant monopole resonances and nuclear incompressibilities studied for the zero-range and separable pairing interactions
- 2012
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 86:2
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Tidskriftsartikel (refereegranskat)abstract
- Background: Following the 2007 precise measurements of monopole strengths in tin isotopes, there has been a continuous theoretical effort to obtain a precise description of the experimental results. Up to now, there is no satisfactory explanation of why the tin nuclei appear to be significantly softer than Pb-208. Purpose: We determine the influence of finite-range and separable pairing interactions on monopole strength functions in semimagic nuclei. Methods: We employ self-consistently the quasiparticle random phase approximation on top of spherical Hartree-Fock-Bogoliubov solutions. We use the Arnoldi method to solve the linear-response problem with pairing. Results: We found that the difference between centroids of giant monopole resonances measured in lead and tin (about 1 MeV) always turns out to be overestimated by about 100%. We also found that the volume incompressibility, obtained by adjusting the liquid-drop expression to microscopic results, is significantly larger than the infinite-matter incompressibility. Conclusions: The zero-range and separable pairing forces cannot induce modifications of monopole strength functions in tin to match experimental data.
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| 48. |
- Wadsworth, R., et al.
(författare)
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Evidence for shape coexistence at medium spin in Rb-76
- 2011
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 701:3, s. 306-312
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Tidskriftsartikel (refereegranskat)abstract
- Four previously known rotational bands in Rb-76 have been extended to moderate spins using the Gammasphere and Microball gamma ray and charged particle detector arrays and the Ca-40(Ca-40,3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g(9/2) particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape coexisting structures at medium spins. (C) 2011 Elsevier B.V. All rights reserved.
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| 49. |
- Ward, Daniel, et al.
(författare)
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alpha-decay calculations of heavy nuclei using an effective Skyrme interaction
- 2013
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 88:6
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Tidskriftsartikel (refereegranskat)abstract
- Background: For nuclei heavier than Pb-208 alpha decay is a dominating decay mode, and in the search of new superheavy elements one often observes chains of alpha decays. Purpose: Explore and test microscopic descriptions of alpha decay based on theories with effective nuclear interactions. Methods: The nuclear ground states are calculated with the Hartree-Fock-Bogoliubov (HFB) method using the Skyrme interaction. Microscopic alpha-decay formation amplitudes are calculated from the HFB wave functions, and the R-matrix formalism is utilized to obtain decay probabilities. Results: Using a large harmonic-oscillator basis we obtain converged alpha-decay widths. A comparison with experiment including all spherical even-even alpha emitting nuclei shows that the model consistently predicts too small formation amplitudes while relative values are in good agreement with experiment. Conclusions: The method was found to be numerically practical even with a large basis size. The comparison of formation amplitudes suggests that the pairing type correlations included in the HFB approach cannot produce sufficient a-particle clustering.
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| 50. |
- Ward, Daniel, et al.
(författare)
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Alpha-particle formation and decay rates from Skyrme-HFB wave functions
- 2014
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 89:5
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Tidskriftsartikel (refereegranskat)abstract
- alpha decay is treated microscopically, where the unstable mother nucleus and residual daughter nucleus are described using Hartree-Fock-Bogoliubov (HFB) wave functions, obtained with the Skyrme effective interaction. From these wave functions the amplitude for forming alpha particles in the mother nucleus is computed. Two different Skyrme parametrizations with different pairing properties are compared, and we find good agreement with experiment for relative decay rates in both cases. The absolute values of the decay rates are underestimated.
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