Results 1 - 10 of 3478
Results 1 - 10 of 3478. Search took: 0.027 seconds
|Sort by: date | relevance|
[en] Energy in nuclear matter is, in practice, completely characterized at different densities and asymmetries, when the density dependencies of symmetry energy and of energy of symmetric matter are specified. The density dependence of the symmetry energy at subnormal densities produces mass dependence of nuclear symmetry coefficient and, thus, can be constrained by that latter dependence. We deduce values of the mass dependent symmetry coefficients, by using excitation energies to isobaric analog states. The coefficient systematic, for intermediate and high masses, is well described in terms of the symmetry coefficient values of aaV = (31.5-33.5) MeV for the volume coefficient and aaS = (9-12) MeV for the surface coefficient. These two further correspond to the parameter values describing density dependence of symmetry energy, of L∼95 MeV and Ksym∼25 MeV
[en] We investigated the evolution of experimental two-neutron separation energies (S2n) along the isotopic chains for the even-even nuclei. In order to enhance the sensitivity of our search, differential variation of the S2n has been investigated. The emphasis is on finding nonmonotonic behaviors which can be correlated with phase/shape transition. Correlations of the ground state S2n values with the excited states energies R4/2 ratio are also discussed.
[en] In the present investigations we have employed relativistic mean-field plus BCS (RMF + BCS) approach to carry out a systematic study for the ground state properties of even-even C Isotopes. One of the prime reason of this study has been to look into the role of low lying states in neutron rich reason near neutron drip line. It is found that irrespective of whether any resonant state exists or not, the occupancy of weakly bound neutron single particle states having low orbital angular momentum, (l = 0 or 1), with a well spread wave function due to the absence or very small strength of centrifugal barrier, helps to cause the occurrence of nuclei with widely extended neutron density. Such nuclei are found to have characteristically very small two-neutron separation energy and large neutron rms radius akin to that observed in weakly bound systems.
[en] We study the structure of nuclei in the energy region between the ground state and the neutron separation energy, here called warm nuclei. The onset of chaos in the nucleus as excitation energy is increased is briefly reviewed. Chaos implies fluctuations of energies and wave functions qualitatively the same for all chaotic nuclei. On the other hand, large structure effects are seen, e.g. in the level-density function at same excitation energies. A microscopic model for the level density is reviewed and we discuss effects on structure of the total level-density function, parity enhancement, and the spin distribution function. Comparisons to data are performed at the neutron separation energy for all observed nuclei, and structure of the level-density function for a few measured cases. The role of structure effects in the level-density function for fission dynamics is exemplified.
[en] One of the fundamental needs for Mars colonization is an abundant source of energy. The total energy system will probably use a mixture of sources based on solar energy, fuel cells, and nuclear energy. Here we concentrate on the possibility of developing a distributed system employing several unique new types of nuclear energy sources, specifically small fusion devices using inertial electrostatic confinement and portable 'battery type' proton reaction cells
[en] Experimental studies of γ decay of highly excited levels in nuclei started as early as 60 years ago. Soon, it turned out that this decay is strongly dominated by E1 transitions and that it is closely related to the giant electric dipole resonances built not only on the ground state, but also on each excited level, including the levels in the quasicontinuum. These findings brought the first evidence for the electric dipole vibrations coupled to the excited levels and demonstrated viability of Brink's concept. Nevertheless, with growing information on γ rays following neutron capture it emerged that extrapolation of the photonuclear cross sections to the energy region below the neutron separation energy leads in some cases to overpredictions of the E1 photon strength. Several theories were developed, but this disproportion has not yet been satisfactorily accounted for. New information deduced from the data on two-step γ cascades following the thermal neutron capture and from the data yielded by γ-calorimetric (n. γ) measurements at isolated neutron resonances seems promising for further studies of the E1 photon strength functions. The paper is focused on two issues: on the observed deficit of photon strength in transitional nuclei at γ-ray energies above 5 MeV and on the recently observed strong enhancement of the photon strength in nuclei near mass number A≅100 at low energies. The main problems to be solved are formulated.
[en] Fission induced by peripheral heavy-ion collisions at relativistic energies is a powerful experimental approach to determine the dynamical delay of fission (transient time) due to dissipation. The fissioning nuclei produced by this method have small shape distortions, low angular momentum and high excitation energies at which this dynamical delay can be observed. These conditions allow for applying the model of Grange and Weidenmueller to obtain a quantitative value of the transient time. Such approach was followed at GSI where the total and partial fission cross-sections and the widths of the charge distributions of the fission residues from a large number of nuclei were measured. The analysis of these data in the frame of an abrasion-evaporation code has lead to a transient time of 2.1·10-21 s when using a step function to describe the time dependence of the fission width. This result implies that excitation energies larger than 100 MeV are needed to observe this transient time
[en] The recently discovered coexistence of multifragmentation and residue production for the same total transverse energy of light charged particles can be well reproduced in numerical simulations of the heavy ion reactions. We investigate here in detail the origin of the observed sudden transition between the two reaction reaction scenarios and show that another mechanism than a first order phase transition can produce such a phenomenon
[en] The total energies of about 120 nuclei in the Thorium region have been calculated within the macroscopic-microscopic method in the 5-dimensional space of deformation parameters α20, α22, α30, α32 and α40. The macroscopic energy term contains the nuclear surface-curvature dependence as proposed within the LSD approach. The microscopic energies are calculated with the Woods-Saxon single particle potential employing the universal set of parameters.We study a possible presence of the octupole axial and non-axial degrees of freedom all-over in the (β, γ)-plane focussing on the ground-states, secondary minima and in the saddle points. In fact, a competition between axial and tri-axial octupole deformation parameters is obtained at the saddle points and in the secondary minima for many isotones with N > 136. The presence of the tetrahedral symmetry minima is predicted in numerous nuclei in the discussed region, although most of the time at relatively high excitation energies