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[en] There exists a variety of nuclear structure phenomena within the chain of Zr isotopes in the low-excitation regime. While the ground state of 94Zr is spherical in nature, the occurrence of low-lying collective structure has also been observed. The excitation of protons across the Z = 40 sub-shell closure appears to playa dominant role for this collective structure in 94Zr. With the goal of looking for possible competition between proton and neutron excitations in 94Zr, an experiment was carried out at the TRIUMF-ISAC radioactive beam facility. The low-lying states of 94Zr were populated from the β- decay of 94Y. The 8π spectrometer was composed of 20 Compton-suppressed HPGe detectors; details of the experimental setup can be found in earlier literature. Combining the singles and coincidence data, a comprehensive level scheme of 94Zr has been constructed up to Ex ∼ 4.8 MeV, which is very close to the Qβ- value 4.918 MeV. With the revised level lifetimes and the newly found decay branches from the present investigation, the levels could be categorized in terms of proton and neutron excitations. Detailed results obtained from the analysis of the acquired data will be presented
[en] We have studied the fission parameters of hot neutron-rich thermally fissile and nuclei within the temperature dependent effective field theory motivated relativistic mean field (E-TRMF) formalism by using the recently developed FSUGarnet and IOPB-I parameter sets. The results obtained by these two forces are compared with the results of the well known and widely accepted NL3 parameter set. The excitation energy , shell correction energy , single particle energy for neutrons and protons , level density parameter a, neutron skin thickness ΔR, two neutron separation energy , and asymmetry energy coefficient of these neutron-rich thermally fissile nuclei are calculated at finite temperature. The dependency of level density parameter and other observables on the temperature and the force parameters (interaction Lagrangian) are discussed.
[en] The first (namely, inner) fission barriers for even-A N = 152 nuclei have been studied systematically in the framework of macroscopic-microscopic model by means of potential energy surface (PES) calculations in the three-dimensional () deformation space. Their collective properties, such as ground-state deformations, are compared with previous calculations and available observations, showing a consistent trend. In addition, it has been found that the microscopic shell correction energy plays an important role on surviving fission in these N = 152 deformed shell nuclei. The inclusion of non-axial symmetric degree of freedom γ will pull the fission barrier down more significantly with respect to the calculation involving in hexadecapole deformation β 4. Furthermore, the calculated Woods-Saxon (WS) single particle levels indicate that the large microscopic shell correction energies due to low level densities may be responsible for such a reduction on the inner fission barrier. (paper)
[en] New calculations of fission barrier heights in a five-dimensional (5D) deformation space for actinide nuclei have been performed based on a macro-microscopic (MM) model. To calculate potential energy surface (PES), we use the 5D generalized Lawrence shape (GLS) realistic parameterization as the shape description, the Lublin-Strasbourg Drop (LSD) model for the macroscopic energy and the folded-Yukawa model as the single-particle potential. A method to use two-center oscillator basis in calculating Hamiltonian matrix on any kind of shape description was presented. For the pairing energy, we use the SBCS model. Finally, Strutinsky method is used to calculate the microscopic correction energy. To find the fission barriers and fission paths, some concepts, such as basins, edges and neighbors from geography, are extended to identify the topographical structures on the 5D PES and we assume that the fission path follows the line of steepest descent. The fission barriers and double-humped paths of U and Pu isotopes are calculated.
[en] Proxy-SU(3) is an approximate symmetry appearing in heavy deformed nuclei. In SDANCA-2017 the foundation of proxy-SU(3), its parameter-free predictions for the collective deformation parameters β and γ, as well as for B(E2) ratios, have been discussed and its usefulness in explaining the dominance of prolate over oblate shapes in the ground states of even-even nuclei and the point of the prolate over oblate shape transition in the rare earths region has been demonstrated. In the present contribution, preliminary calculations for two-nucleon separation energies within this framework will be discussed.
[en] Full text:Since its discovery in 1939, the nuclear fission process provides much insight into the behavior of nuclei under many different conditions. As part of the nuclear chain reaction, the fission process has had a profound impact on modern society and it has consequently attracted much attention to the field of nuclear physics. In this talk, I will argue that the time is ripe for a resumption of studies of the fission process induced by light, charged particle reactions. Although nuclear fission can be induced in heavy nuclei by several means, in some cases by forming highly excited nuclei by heavy-ion fusion or multi-nucleon transfer reactions, these methods suffer from the complication that fission can occur at several points during the decay chain thus mixing up contributions from different excitation energies. Using instead light charged particle reactions to excite the nuclei in question, the precise excitation energy from which fission takes place, can be determined. In fact, a number of such studies we carried out previously, and a first set of results on fission barrier heights, mass, energy and angular distributions were obtained. Applying detection techniques developed over the last decades, will allow researchers to obtain detailed, high-quality data from which to probe and refine our present understanding of the process. In the meantime, more fundamental theories have been developed that will allow for a deeper understanding of the fission process. Based on these observations, I suggest that substantial advances in the study of this process can be achieved by using simple light, charged-particle reactions. This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract number DEAC02-06CH11357. (author)
[en] The intrinsic Hamiltonian of the Two-Rotors Model as a quantized classical system in which the rotors are abstract rigid bodies has a point symmetry and then its eigenstates come in quadruplets. Only one member of each of the two lowest quadruplets was investigated so far, the ground state and the scissors mode. I determine the whole quadruplets which turn out to contain states of negative parity. When the rotors are made of particles, the symmetry is broken. The actual existence of the new states of the multiplets in atomic nuclei depends on the existence of excited states of the neutron and proton fluids separately odd under inversion of the intrinsic coordinates. The energies of the new states are when one or both rotors have negative parity respectively, where ω is the scissors excitation energy and e is the excitation energy of a single rotor with negative parity. Nonvanishing transitions occur only between states whose energies differ by ω.
[en] Relativistic density functionals provide a powerful phenomenological way to study nuclear structure phenomena. They have been mostly used in describing bulk nuclear properties of ground states and have been also very successful in the description of collective excitations. Nuclear excitations that form due to the inherent structure of nuclei and have a relatively long half-life are called isomers. They play a significant role in recent experimental and theoretical studies of nuclei far from stability, in nuclear fission and in the process of nucleosynthesis relative to astrophysics. In this study we concentrate on the single particle excitations of high K-level isomers that appear mainly at nuclei with well defined axial deformation. We employ the blocking effect to create two quasiparticle states within the relativistic hartree-Bogoliubov framework. We use the Equal filling approximation that respects the time-reversal symmetry breaking caused by blocking. We concentrate our interest in medium mass axially deformed nuclei where there have been several experimentally observed K-level isomers and we can compare directly our results.
[en] We review the current experimental data on collective structures within the pairing gap of even-even deformed nuclei, with emphasis on nuclei near mass number A 150. The essential physics that determines the characteristics of the first excited 0 (0) state in these nuclei has been in dispute for several decades. Interpretation of these states in terms of surface quadrupole vibrations has often been challenged. We examine the role that configuration dependent pairing can play in these levels particularly at the onset of deformation as major shells fill. In all deformed nuclei rotational bands are found experimentally, starting at a state with spin 2 with excitation energies near the middle of the pairing gap. These rotational bands, with quantum number K = 2, are usually referred to as bands and have been identified with quadrupole surface vibrations in the plane perpendicular to the major axis of deformation. However K = 2 bands can also arise due to the breaking of axial symmetry of the quadrupole shape. We discuss data that can help with these different interpretations. (orig.)