High-spin states in boson models with applications to actinide nuclei

We use the 1/$N$ expansion formalism in a systematic study of high-spin states in the $sd$ and $sdg$ boson models with emphasis on spin dependence of moment of inertia and E2 transitions. The results are applied to the high-spin states in the actinide nuclei $^{232}$Th, $^{234-238}$U, where the need for $g$ bosons is especially acute but until now, no realistic calculation existed. We find that the $d$-boson energy plays a crucial role in description of the high-spin data.Comment: 11 pages Latex, 4 figures available upon request (to appear in Phys. Lett. B

Analytic Description of Critical Point Actinides in a Transition from Octupole Deformation to Octupole Vibrations

An analytic collective model in which the relative presence of the quadrupole and octupole deformations is determined by a parameter (phi_0), while axial symmetry is obeyed, is developed. The model [to be called the analytic quadrupole octupole axially symmetric model (AQOA)] involves an infinite well potential, provides predictions for energy and B(EL) ratios which depend only on phi_0, draws the border between the regions of octupole deformation and octupole vibrations in an essentially parameter-independent way, and describes well 226-Th and 226-Ra, for which experimental energy data are shown to suggest that they lie close to this border. The similarity of the AQOA results with phi_0=45 degrees for ground state band spectra and B(E2) transition rates to the predictions of the X(5) model is pointed out. Analytic solutions are also obtained for Davidson potentials, leading to the AQOA spectrum through a variational procedure.Comment: LaTeX, 27 pages, including 14 postscript figure

Bonn Potential and Shell-Model Calculations for 206,205,204Pb

The structure of the nuclei 206,205,204Pb is studied interms of shell model employing a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The energy spectra, binding energies and electromagnetic properties are calculated and compared with experiment. A very good overall agreement is obtained. This evidences the reliability of our realistic effective interaction and encourages use of modern realistic potentials in shell-model calculations for heavy-mass nuclei.Comment: 4 pages, 4 figures, submitted to Physical Review

Long-term remnant evolution of compact binary mergers

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae and therefore the free expansion phase of the remnant will be short (~ 1 - 10 yr). In general the remnants will be observable for a considerable time (~ 10^6 - 10^7 yr). Events releasing large amounts of kinetic energy may be responsible for a subsample of observed giant HI holes of unknown origin as compact binaries merge far away from star forming regions. If the ejecta consist primarily of actinides, on long timescales the expelled material will contain mainly the few quasi-stable nuclei in the actinides range. Consequently the abundance of each isotope in the ejecta might be of the order of a few percent. During their decay some actinides will produce observational signatures in form of gamma ray lines. We particularly investigate the gamma ray emission of Am 243, Cm 247, Cm 248 and Bi 208 and estimate their observability in nearby remnants. Detections of the gamma ray lines with INTEGRAL will be possible only in very advantageous cases but these remnants are promising targets for future instruments using focusing optics for soft gamma rays. Due to the low mass expelled in mergers and due to the lack of free electrons in the ejecta, the merger remnants might be significantly fainter in bremsstrahlung and synchrotron radiation than comparable supernova remnants. Hence merger remnants might represent a candidate for very recently discovered 'dark accelerators' which are hard gamma ray sources with no apparent emission in other bands.Comment: 4 pages, 1 figure, accepted for publication in A&A Letter

Analytical description of the Coherent State Model for near vibrational and well deformed nuclei

Analytical formulas for the excitation energies as well as for the electric quadrupole reduced transition probabilities in the ground, beta and gamma bands were derived within the coherent state model for the near vibrational and well deformed nuclei. Numerical calculations were performed for 42 nuclei exhibiting various symmetries and therefore with specific properties. Comparison of the calculation results with the corresponding experimental data shows a good agreement. The parameters involved in the proposed model satisfy evident regularities being interpolated by smooth curves. Few of them, which fall out of the curves, are interpreted as signatures for a critical point in a specific phase transition. This is actually supported also by the figures showing the excitation energy dependence on the angular momentum. The formulas provided for energies and B(E2) values are very simple, being written in a compact form, and therefore easy to be handled to explain the new experimental data.Comment: 9 figures, 50 page

Properties of odd nuclei and the impact of time-odd mean fields: A systematic Skyrme-Hartree-Fock analysis

We present a systematic analysis of the description of odd nuclei by the Skyrme-Hartree-Fock approach augmented with pairing in BCS approximation and blocking of the odd nucleon. Current and spin densities in the Skyrme functional produce time-odd mean fields (TOMF) for odd nuclei. Their effect on basic properties (binding energies, odd-even staggering, separation energies and spectra) is investigated for the three Skyrme parameterizations SkI3, SLy6, and SV-bas. About 1300 spherical and axially-deformed odd nuclei with 16 < Z < 92 are considered. The calculations demonstrate that the TOMF effect is generally small, although not fully negligible. The influence of the Skyrme parameterization and the consistency of the calculations are much more important. With a proper choice of the parameterization, a good description of binding energies and their differences is obtained, comparable to that for even nuclei. The description of low-energy excitation spectra of odd nuclei is of varying quality depending on the nucleus

The level structure of the nucleus 140Ce

Precision energy measurements on 24 gamma-ray lines in the 140La --&gt; 140Ce decay were performed with a 2 m curved-crystal spectrometer and a lithium-drifted germanium spectrometer. The relative intensities of 15 gamma rays were determined. A level scheme for 140Ce is proposed with the inclusion of two new levels at 2516.14 and 2547.5 keV. The new level scheme is compared with recent calculations using the quasi-particle description.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33415/1/0000816.pd

Ground-γ\gamma band coupling in heavy deformed nuclei and SU(3) contraction limit

We derive analytic expressions for the energies and $B(E2)$-transition probabilities in the states of the ground and $\gamma$ bands of heavy deformed nuclei within a collective Vector-Boson Model with SU(3) dynamical symmetry. On this basis we examine the analytic behavior of the SU(3) energy splitting and the B(E2) interband transition ratios in the SU(3) contraction limits of the model. The theoretical analyses outline physically reasonable ways in which the ground-$\gamma$ band coupling vanishes. The experimental data on the lowest collective states of even-even rare earth nuclei and actinides strongly support the theoretical results. They suggest that a transition from the ground-$\gamma$ band coupling scheme to a scheme in which the ground band is situated in a separate irreducible representation of SU(3) should be realized towards the midshell regions. We propose that generally the SU(3) group contraction process should play an important role for such a kind of transitions in any collective band coupling scheme in heavy deformed nuclei.Comment: 24 pages (LaTeX), 7 figures (12 postscript files