Effect of octupole and higher deformations on Coulomb barrier

The effect of octupole deformation, β₃, and the higher multipole deformations, β₆ and β₈, on the distribution of barriers in orientation degrees of freedom, is studied. Coulomb barriers are derived in the frame work of the double folding model with the realistic M3Y nucleon–nucleon interaction and its density dependent version. ⁴⁸Ca + ²⁴⁴Pu spherical-deformed nuclear interacting pair is considered, as an example, to study the effect of deformation parameters on the height and position of the Coulomb barrier. Although the dependence of the Coulomb barrier parameters on the higher deformations is complicated, numerically, if it is treated in microscopic way, we found a simple linear variation of barrier parameters with the different orders of deformation. We found that the variation of the barrier parameters with deformation exactly follows the change of the half density radius of the deformed nucleus in the direction of the separation vector between the centers of mass of the interacting nuclei. This suggests a simple and straightforward way to predict the behavior of the barrier parameters with different orders of deformations. We compared the results of present work with a similar recent study of the same quantities based on simple expression derived by Wong for the Coulomb part and proximity approach for the nuclear part of heavy ion potential, respectively.     

Triaxial deformation in the 1p shell

Triaxial deformation is found to be important in ¹⁰Be. It lowers the ground-state energy and explains, with a reasonable spin-orbit strength, the strong E₂-transition from the first excited state.     

Nonlinear deformations of a radiating shell moving with acceleration

The two-dimensional nonstationary motion of a cold dense shell accelerated under the action of rarefied hot gas pressure is modeled. The influence of radiative processes on manifestations of cumulative effects predicted by the inertia model is analyzed. It is assumed that the major medium component is hydrogen with small admixtures of oxygen, nitrogen, carbon, silicon, and iron. Radiative energy loss caused by photorecombinations and excitation followed by impurity ion metastable level deexcitation is taken into account. An approximation to the cooling function is suggested and implemented. This approximation can be used to perform calculations over wide ionization degree and gas temperature ranges. The formation of a shell during gas expansion ionized and heated by a source of ultraviolet radiation is studied. The characteristic time of shell appearance and its gas dynamic parameters are determined. The distribution of plasma temperature is shown to be nonmonotonic and have a maximum close to the ionization front. An increase in small perturbations of the velocity of a shell is shown to cause the formation of radial fibers and the concentration of gas mass and momentum in them. The structure of condensates formed is, however, much more complex than that predicted by the model of a thin layer of incompressible matter. In particular, condensation includes “fingerlike” thickening and a more extended region with a lower density. It also follows from the calculations that radiative cooling contributes to shell expansion in the radial direction but does not change the integral characteristics of condensations substantially.     

Triaxial projected shell model study of chiral rotation in odd-odd nuclei

Chiral rotation observed in ¹²⁸Cs is studied using the newly developed microscopic triaxial projected shell model (TPSM) approach. The observed energy levels and the electromagnetic transition probabilities of the nearly degenerate chiral dipole bands in this isotope are well reproduced by the present model. This demonstrates the broad applicability of the TPSM approach, based on a schematic interaction and angular-momentum projection technique, to explain a variety of low- and high-spin phenomena in triaxial rotating nuclei.     

The octupole response function

The octupole response function for ²⁰⁸Pb, ¹²⁰Sn, ⁹⁰Zr and ⁴⁰Ca, is calculated in the RPA. Of the order of 60–70% of the EWSR is found around an energy of 3?ω₀, spread over an energy interval of ～ 15 MeV. About half of this strength (～ 30%) lies in a single peak. Based on the excitation of surface vibrations, the widths of these states are estimated within the framework of the nuclear field theory. They are found to be of the order of 6 MeV. The results seem to be consistent with recent data.     

Estimates of the influence of nuclear deformations and shell effects on the lifetimes of exotic radioactivities

We estimate the influence on the lifetimes of exotic radioactivities of nuclear ground-state deformations and of the attenuation of fragment shell effects by the fragments' interaction. These corrections are generally of the order of one power of ten, representing modifications of the barrier penetrabilities amounting to a few percent. The corrections to the lifetimes do not ruin the current reasonable correspondence between theory and experiment. In fact, the fit is improved slightly.     

Inner shell structure of heavy atoms

The inner-shell structure of some heavy atoms is examined using a self-consistent relativistic local density method. Ar(K), Kr(K) and Xe (K,L ₁,L ₂ andL ₃) binding energies and {ie863-1} (hyper-satellite) energies of Tl, Hg and Tm are calculated. The results are compared with available experimental data. A part of this work was presented byMPD at the Trieste International Symposium on “Core level excitations in atoms, molecules and solids,” 22–26 June 1981, Extended Abstracts (ed.) E Tosatti, ICTP Report No. 89/81 p. 11.     

On octupole alignment in actinides

The alignment of the octupole angular momentum in the rotational states of the K^π = 0⁻ band is analysed in the microscopic model. The model describes qualitatively the branching ratio for the E1-transitions from these states to the ground band states.     

Periodic-orbit bifurcation and shell structure at exotic deformation

We have investigated the semiclassical origin of superdeformed shell structure and also of reflection-asymmetric deformed shapes by means of the periodic orbit theory and the deformed cavity model. Systematic analysis of the quantum-classical correspondence reveals that bifurcation of equatorial orbits into three-dimensional ones play predominant role in the formation of these shell structures. Presented by K. Matsuyanagi at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Electronic shell and supershell structure in graphene flakes

We use a simple tight-binding (TB) model to study electronic properties of free graphene flakes. Valence electrons of triangular graphene flakes show a shell and supershell structure which follows an analytical expression derived from the solution of the wave equation for triangular cavity. However, the solution has different selection rules for triangles with armchair and zigzag edges, and roughly 40?000 atoms are needed to see clearly the first supershell oscillation. In the case of spherical flakes, the edge states of the zigzag regions dominate the shell structure which is thus sensitive to the flake diameter and center. A potential well that is made with external gates cannot have true bound states in graphene due to the zero energy band gap. However, it can cause strong resonances in the conduction band.     

Particle octupole multiplet in147Gd

The rotational properties of the odd-odd¹⁶⁸Tm have been studies by means of the¹⁶⁵Ho(α, 3n)¹⁶⁶Tm reaction. The existence of five rotational bands has been established.     

Quadrupole and octupole collectivity in light Po isotopes

The level structure of¹⁹⁶Po has been studied using a¹⁶⁰Dy(⁴⁰Ar, 4n) reaction and a recoil-catcher technique to reduce fission. The results showed a sharp drop off in the first (2⁺) and (4⁺) energies relative to systematics implying an abrupt increase in the quadrupole collectivity at N=112. In addition, second (2⁺) and(4⁺) states were identified at 859 and 1388 keV, respectively, suggesting the discovery of a 4p2h deformed band in Po isotopes which is related to known 2p2h proton bands in several Pb isotopes. A prompt¹⁸³W(²⁰Ne, 5n@#@) experiment located similar second 2⁺ and 4⁺ states at 1039 and 1483 keV in¹⁹⁸Po providing corroboration and extended information on the properties of the new Po deformed bands. A measured halflife of 850 (90) ns for the 2491 keV (11^?) state in¹⁹⁶Po implied collective E3 contributions to the extractedB (@#@ E3; 11^?→8⁺)=27(5) W.u.     

Multiple octupole excitations in 148Gd

The lifetime and the -decay to the 0⁺ ground state of the lowest 3^- state in ¹⁴⁸Gd has been determined. The reduced strength B(E3, 3^- 0⁺)=41 (6) W.u. agrees well with the theoretical value from empirical shell model calculations and can be directly compared with the 12⁺ 9^- two-octupole-phonon one-octupole-phonon strength obtained in the same Recoil Distance Method lifetime measurement. The results of our search for a three octupole-phonon state built on the state is also reported. Received: 7 March 2000 / Accepted: 12 May 2000     

Quadrupole and octupole electron-phonon coupling in acoustoelectric effects

We propose an experiment to determine the quadrupole and octupole electron-phonon coupling in germanium and silicon. The experiment consists in measuring the electroacoustic absorption and/or the acoustoelectric field in uniaxially stressed n-type crystals. From theoretical values, quadrupole coupling should be well-measurable.     

Clustering aspects of nuclei with octupole and superdeformation

Extreme nuclear shapes are considered from the clustering point of view. General aspects of light nuclei which possess very exotic, elongated shapes (“α-strings”) are given. The relation between superdeformation and di-molecules is considered, and it is shown that nuclear di-molecules have the same magic numbers and orbits filled as the ellipsoidal superdeformations for light nuclei, while for heavier nuclei they are expected in different mass-regions. The structure of possible octupole-unstable 3∶1 nuclear shapes (“hyperdeformations”) is discussed. Indications and consequences of a four-fold symmetry of the nuclear hamiltonian are briefly discussed.