abstract

Tunneling along the \(\gamma \) path between prolate and oblate axial shapes of even–even nuclei, being in the ground state, is analyzed. Mixing of two \(0^+\) states and splitting of their energies are calculated in the quasi-classical approximation. Expressions for the E0 transition rates between these \(0^+\) levels are derived and compared with the experiment for Kr isotopes. Mixing of the prolate and oblate shapes in these nuclei is found to reach 50%. Tunneling between states of the nucleus with the same axial shape but with the angular momentum parallel and perpendicular to the symmetry axis is also studied. The hindrance factor for decay of the \(25^+\) isomeric level of \(^{182}\)Os, provided by \(\gamma \) tunneling, is estimated.

abstract

The algebraic approach which allows for simulation of symmetries of a nucleus with respect to the laboratory and intrinsic frames is presented. The formalism is based on the partner groups (a group and the corresponding intrinsic group) idea. An illustrative example is related to the successful SU(3) Elliot nuclear model. An example of schematic Hamiltonian is chosen to have tetrahedral or octahedral symmetry.

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We present a description of Wheeler’s delayed choice experiment. Unlike the usual approach, we concentrate on the possible time structure of the process. We stress that both the test particle and the apparatus have non-trivial temporal parts of their wave functions, which opens a new channel of interaction. Our calculations show that the temporal overlap between the quantum states is enough to account for the observed results. The description is based on the formalism of the projection time evolution.

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An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability: Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations, the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree–Fock–Bogoliubov (HFB) calculations; this indicates a nuclear Jahn–Teller effect. We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.

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We compare the characteristics of the charged-current quasielastic neutrino and antineutrino scattering obtained in two different nuclear models, the phenomenological SuperScaling Approximation and the model using a realistic spectral function \(S(p,{\cal E})\) that gives a scaling function in accordance with the (\(e,e'\)) scattering data, with the recent data published by the MINER\(\nu \)A Collaboration. The spectral function accounts for the nucleon–nucleon (\(NN\)) correlations by using natural orbitals from the Jastrow correlation method and has a realistic energy dependence. Both models provide a good description of the data without the need of an ad hoc increase of the value of the mass parameter in the axial-vector dipole form factor.

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An experiment to investigate the \(^{1}\)H\((d,pp)n\) breakup reaction using a deuteron beam of 300, 340, 380 and 400 MeV and the WASA detector has been performed at the Cooler Synchrotron COSY-Jülich. As a first step, the data collected at the beam energy of 340 MeV are analysed, with a focus on the proton–proton coincidences registered in the Forward Detector. Elastically scattered deuterons are used for precise determination of the luminosity. The main steps of the analysis, including energy calibration, particle identification (PID) and efficiency studies, and their impact on the final accuracy of the result, are discussed.

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We apply, for the first time, the importance-truncation (IT) procedure based on the many-body perturbation theory for the multi-shell SU(3) scheme basis of the ab initio symmetry-adapted no-core shell model (SA-NCSM). It is shown that the IT method can yield a quantitative justification for the symmetry-based truncation of the SA-NCSM approach. Furthermore, we demonstrate that the IT algorithm can be applied in a symmetry-truncated model space and it leads to even more dramatic reduction in dimensionality of the nuclear eigenvalue problem.

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Possibilities of discriminating neutrons and gamma rays in the Moroccan TRIGA Mark II reactor have been investigated with the aim of reducing intensity causes pile-ups of the pulses in the fission chamber preamplifier’s output signals, the effect of the electronic noise and the unwanted background of the gamma radiation. This background may become a significant problem especially in neutron detection. To remedy this problem, we applied NTF2 model as Nonnegative Tensor Factorization (NTF) method to extract useful neutron signal from recorded mixture and thus to obtain clearer neutron flux spectrum. In this study, a full simulation of a WL-7657 fission chamber detector based on the Geant4/Garfield++ interface has been developed and the verification of the code through comparison with the results of pyFC (python-based simulation of Fission Chambers). Since we have achieved the separation task, the power spectral densities and the normalized cross-correlation of each extracted independent components computed by NTF2 algorithm from Geant4/Garfield++ interface output was compared to those computed from pyFC suite output. The results show that the computed Geant4/Garfield++ interface results are in a good agreement with the pyFC results.

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Sets of near-degenerate rotational bands built on configurations involving \(\pi h_{9/2}\) particle and \(\nu i_{13/2}\) holes were observed in the neighbouring \(^{193,194}\)Tl isotopes. Such sets of bands, involving particle and hole configurations and occurring in nuclei with triaxial shape, are caused by chiral symmetry formed in angular momentum space. Each nuclear chiral system is expected to generate a pair of near-degenerate partner bands. However, several sets of three partner bands were observed in these Tl isotopes, raising questions whether one or two chiral systems are formed, and which two bands are partners in the chiral pair. Many-particle-rotor model calculations reproduce well the features of the observed negative-parity bands in \(^{193,194}\)Tl and support the suggested chiral geometry of the angular momenta.

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The study focuses on spontaneous chiral symmetry breaking in odd–odd nuclei in \(A\sim 130\) mass region. The work presents a comparison of experimentally obtained values of \(S(I)\), \(B\)(M1), \(B\)(E2), \(B\)(M1)/\(B\)(E2) for \(^{132}\)La and \(^{124,126,128,130}\)Cs. This comparison is used to estimate a spin in Cs isotopes at which critical frequency occurs.

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Angular distributions for \(^{15}\)N elastically scattered from \(^{10, 11}\)B nuclei were measured at the energy of 43 MeV. The experimental data for the \(^{11}\)B+\(^{15}\)N system showed a remarkable increase in differential cross sections at large angles which cannot be explained within the framework of the optical model. Such behavior of the cross sections can be reproduced only by taking into account the contribution of the \(\alpha \)-cluster transfer mechanism. Although the experimental data for \(^{10}\)B+\(^{15}\)N system showed an increase in differential cross sections at backward angles, it can be described by optical model calculations.

abstract

The hot rotating nuclei could be formed in the complete and incomplete fusion reaction of two heavy ions. At low bombarding energies, the reaction goes via compound nucleus formation and subsequent evaporation of charged particles, neutrons and \(\gamma \) rays. However, with increasing the energy of the projectile, the emission of particles during the equilibration process becomes more and more probable. This effect can be estimated by the Heavy-Ion Phase-Space Exploration (HIPSE) code which describes the production of clusters of various size from nucleons initially in the target or projectile. This dynamic evolution finalizes with the compound nuclei, quasi-fission or multi-fragmentation products. The hot rotating nuclei produced in fusion reaction can de-excitate by evaporation of particles and emission of \(\gamma \) rays from the Giant Dipole Resonance, or by fission into two fragments. These processes, evaporation and fission, are described within statistical codes such as GEMINI++ or in dynamical approaches by solving the transport equations of Langevin type. In the present article, we will concentrate on the possible effect of the pre-equilibrium emission on the strength function of the effective Giant Dipole Resonance, which can be described within Thermal Shape Fluctuation Model (TSFM) approach.

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The chiral geometry of the angular momentum in the intrinsic frame is extracted from angular momentum projected wave functions in the laboratory frame by the \(K\)-Plot and Azimuthal-Plot. The method is demonstrated by an application to the chiral doublet bands in \(^{128}\)Cs, based on the standard pairing-plus-quadrupole Hamiltonian. The observed energy spectra and the electromagnetic transitions are well-reproduced, and the \(K\)-Plot and Azimuthal-Plot obtained give evolution of angular momentum geometry with spin, by which the chirality is demonstrated.

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The self-consistent quasiparticle random phase approximation (QRPA) plus quasiparticle-vibration coupling (QPVC) with Skyrme interactions is used to describe the Gamow–Teller (GT) response in open-shell nuclei. The effect of superfluidity, including both the isoscalar spin-triplet and the isovector spin-singlet pairing interactions, is taken into account in both the ground state and the excited states. Zero-range pairing forces of volume-type and surface-type are both used in our investigation. The phonon properties and GT strength distributions obtained with either type of force are compared, by taking the superfluid nucleus \(^{120}\)Sn as an example. In both cases, a spreading width is developed, and the agreement with experimental data of the strength distribution in \(^{120}\)Sn is improved with the inclusion of QPVC effect.

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Nuclear deformation-energy landscapes are presented in a shape parametrization which allows to describe the vast variety of nuclear deformations through a recently developed Fourier expansion. It is shown that, together with the macroscopic–microscopic model, one is thus able to give a good description of nuclear deformation-energy landscapes. Using a new collective model for the fission process, we are then able to make predictions for the fission-fragment mass yields and kinetic-energy distributions that turn out to reproduce the experimental data quite nicely. Investigating the quantum effects of nuclei in the region of super-heavy nuclei, one finds that these are specially favourable in the region of atomic number \(Z\!=\,\)118, whereas the fission barrier height turns out to be quite large in the region of \(Z\!=\,\)110 which will make the survival probability of these nuclei quite important.

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Multi-particle-plus-triaxial-rotor (MPR) model calculations were performed for chiral partner bands associated with the multi-particle \(\pi g_{9/2}^{-1} \otimes \nu h_{11/2}^{2}\) nucleon configuration in the 100 mass region. Multiple chiral systems were found, but they may not necessarily form well-defined pairs of near-degenerate bands.

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Analysis of rich experimental data on four negative parity bands of \(^{119}\)I in frame of the CQPC (Core-Quasiparticle Coupling) model with the \(h_{11/2}\) proton coupled to a collective quadrupole core is presented. Confrontation of results obtained for two kinds of the even–even core: \(\gamma \)-soft and \(\gamma \)-rigid does not show distinct difference. This conclusion confirms hypothesis that a chiral structure in odd–odd nuclei can be equally well-explained with a rigid triaxial core as well with a soft triaxial core. Possible occurrence of a transverse wobbling motion is also briefly discussed.

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We study the nuclear properties of even–even superheavy \(Z=120\) isotopes and \(N=184\) isotones with the Skyrme–Hartree–Fock–Bogoliubov (HFB) approach. Within this model, we examine the deformation energy surfaces and two paths to fission: a reflection-symmetric path with elongated fission fragments (sEF) and a reflection-asymmetric path corresponding to elongated fission fragments (aEF). Furthermore, we explore the energy surfaces in the region of very large oblate deformations with toroidal nuclear density distributions. While the energy surfaces of toroidal \(Z=120\) isotopes and \(N=184\) isotones do not possess energy minima without angular momenta, local energy minima (toroidal high-spin isomeric states) appear for many of these superheavy nuclei with specific angular momenta about the symmetry axis. We have theoretically located the toroidal high-spin isomers (THSIs) of \(^{302}\)Og\(_{184}\), \(^{302}120_{182}\), \(^{306}120_{186}\), and \(^{306}122_{184}\).

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The medium- and high-spin band structure of \(^{103}\)Rh, \(^{104}\)Rh and \(^{105}\)Pd has been studied in order to search for new multiple chiral doublet bands and bands corresponding to the recently predicted transverse wobbling motion. Several new band structures have been identified and their properties compared with constrained covariant density functional theory and particle rotor model calculations. Based on this comparison, three chiral band pairs were identified in \(^{103}\)Rh, of which two belong to the same configuration. Several new positive- and negative-parity bands in \(^{104}\)Rh can form chiral band pairs according to their experimental properties and to the preliminary calculations, thus the existence of multiple chiral doublet bands in this nucleus is possible. Experimental properties of one of the observed negative-parity bands in \(^{105}\)Pd are characteristic of transverse wobbling motion, predicted also by calculations in this nucleus.

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In heavy-ion collisions at low energy, the decay mode of the compound nucleus formed in fusion reactions can be strongly influenced by the isospin degree of freedom, strictly connected to the isotopic ratio \(N/Z\) of the system. The competition among the disintegration modes of \(^{118,134}\)Ba\(^{*}\) produced in \(^{78,86}\)Kr\(+^{40,48}\)Ca reactions at 10 \(A\) MeV has been studied in the framework of the ISODEC experiment, and experimental data have been compared with the prediction of GEMINI++ and DiNuclear System (DNS) models.

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The significant progresses of chirality in atomic nuclei from both experimental and theoretical sides are briefly reviewed. The recent progress of collective Hamiltonian for chiral modes is introduced. The results of collective Hamiltonian for an asymmetric particle–hole configuration \(\pi g^{-1}_{9/2}\otimes \nu h_{11/2}\) coupled to a triaxial rotor are presented.