Incipient octupole and 26-pole deformation in the mass region 220 < A < 230

The increase in calculated binding energies of nuclides in the mass region 220<A<230 due to varying the 2⁶-pole deformation parameter is found to be ∽1.0 MeV. The implications of this finding for octupole deformation are discussed.     

Nuclear dynamical octupole deformation in heavy-ion reactions

Within the quantum molecular dynamics (QMD) model, the dynamical octupole deformation is studied as a function of the central distance between the projectile and target in the approaching process of heavy-ion fusion reactions. The dependence of the maximum dynamical octupole deformations on the incident energies is also investigated. The dynamical octupole deformations can be observed during the approaching process, and the maximum dynamical octupole deformations become more significant with decreasing incident energies. The distributions of the proton and neutron centers in the projectile and target are also investigated, respectively. In the approaching process of heavy-ion fusion reactions, the separation between proton centers for two nuclei is larger than that between neutron centers because of the strong Coulomb potential.     

On the geometric structure of a parity-conserving relativistic quantum field theory

Wheeler's conjecture that there might exist a ‘principle’ which rules out parity-non-conserving spaces is analysed. The following result has been obtained: A local relativistic quantum field theory is parity-conserving if the following conditions hold:

1. The fields are derived from geometry, i.e. they are represented by quantised currents (in the sense of de Rham); and
2. The theory may be defined on a connected and, under certain restrictions, on a disconnected orientable space-time continuumM ⁴.

     

Search for octupole deformation in neutron-rich Xe isotopes

A search for octupole deformation in neutron-rich Xe isotopes has been conducted through prompt gammaray spectroscopy of secondary fragments produced in the spontaneous fission of²⁴⁸Cm. The spectrometer consisted of the Eurogam 1 array and a set of 5 LEPS detectors. Level schemes were constructed for Xe isotopes with mass number ranging from 140 to 144 and excited states for^143,144Xe nuclei were observed for the first time. None of the level schemes exhibit an alternating parity quasimolecular band, a feature usually expected in nuclei in which octupole correlation effects are strong enough to produce stable octupole deformation. For several isotopes, structures observed in the level schemes are consistent with an octupole softness of the nuclei.     

Rotational consequences of stable octupole deformation in nuclei

The characteristic features of high-spin spectra of octupole-deformed nuclei are demonstrated by means of Woods-Saxon-Bogolyubov cranking calculations. The rotational spectra of Ra and Th nuclei are studied. The experimental data suggests shape changes with increasing neutron number from N ? 130 (nearly spherical shapes) through N ? 134 (octupole-deformed shapes) to N ? 140 (well-deformed reflection-symmetric shapes). The octupole mixing between the high-j intruder states and normal-parity orbitals leads to specific patterns of quasiparticle spectra characterised by a quantum number referred to as simplex. The influence of octupole deformation on high-spin properties of nuclear spectra like spin alignment, band interaction, etc. are discussed.     

Possible evidence for static octupole deformation in128,129Ba

It is demonstrated that recent experimental results on high spin states of^128,129Ba offer substantial new evidence for static octupole deformation in these nuclei.     

Quadruplet spectroscopy in the region of strong nuclear octupole correlations

Experimental evidence from the spectroscopy of¹⁵⁵Gd and¹⁵³Sm for the theoretically predicted quadruplet band structure, with band parity sequences (+––+) and (–++–), is examined.We wish to thank Dr. R. Piepenbring for illuminating discussions on the differences between octupole correlations in the actinides and in the rare earths. These investigations were supported by the National Science Foundation under contract number PHYS9-06613 with the Florida State University.     

Influence of angular momentum in axially symmetric potentials with octupole deformation

The chaotic classical single-particle motion in an oblate octupole deformed potential with a nonzero z-component of angular momentum Lz is investigated. The stability analysis of the trajectories shows that with increasing rotation of the system, the unstable negative curvature regions of the effective potential surface decrease, which converts the chaotic motion of the system into a regular one.     

Influence of angular momentum in axially symmetric potentials with octupole deformation

The chaotic classical single-particle motion in an oblate octupole deformed potential with a non-zero z-component of angular momentum Lz is investigated. The stability analysis of the trajectories shows that with increasing rotation of the system, the unstable negative curvature regions of the effective potential surface decrease, which converts the chaotic motion of the system into a regular one.     

Magnetic octupole order in : A polarized neutron diffraction study

Recently, in phase IV of Ce_xLa_1-xB₆, weak but distinct superlattice reflections from the order parameter of phase IV have been detected by our unpolarized neutron scattering experiment [K. Kuwahara, K. Iwasa, M. Kohgi, N. Aso, M. Sera, F. Iga, J. Phys. Soc. Japan 76 (2007) 093702]. The scattering vector dependence of the intensity of superlattice reflections is quite unusual; the intensity is stronger for high scattering vectors. This result strongly indicates that the order parameter of phase IV is the magnetic octupole. However, the possibility that the observed superlattice reflections are due to lattice distortions could not be completely ruled out only on the basis of the unpolarized neutron scattering experiment. To confirm that the superlattice reflections are magnetic, therefore, we have performed a single crystal polarized neutron diffraction experiment on Ce_0.7La_0.3B₆. The obtained result has clearly shown that the time reversal symmetry is broken by the order parameter of phase IV. This is further evidence for the magnetic octupole order in Ce_xLa_1-xB₆.     

Enhanced octupole collectivity at double subshell closure in the96Zr region

A value of 84 ± 44 ps has been established for the half-life of the first 3^? state of⁹⁶Zr, using the centroid shift method. It is shown that the corresponding large electric octupole transition strength is in accordance with systematics, suggesting largest octupole collectivity when both the 1g_9/2 Proton and 1h_11/2 neutron orbitals are nearly empty due to the Z=40, N=56 double subshell closure.     

A study of collective octupole states in barium in the interacting boson model

We analyze low-lying collective negative parity states in ^140–148Ba in terms of the interacting spdf boson model. We point out the crucial role played by p bosons in describing E1 transitions. We discuss the rather unusual properties of the nucleus ¹⁴⁶Ba.     

Some progress in research on octupole deformation around Z=56, N=88 nuclei

Recent progress in research on octupole deformation around Z=56, N=88 neutron-rich nuclei by our cooperative groups of Tsinghua University, Vanderbilt University and Lawrence Berkeley National Laboratory has been introduced. The experiment was carried out by measuring the prompt γ-rays in spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The new results of     

A microscopic study of the octupole degree of freedom at high angular momentum

A microscopic parity and number projected calculation after the variation was used to describe the rotational bands of the octupole deformed nuclei ¹⁴⁴Ba, ¹⁴⁶Ce and ²²⁴Ra. The states obtained in a cranked Hartree-Fock-Bogoliubov approach are taken as intrinsic states for the parity and number projection. Dipole moments, deformation parameters, B(E1), B(E2) and B(E3) transition probabilities along the band are obtained and compared with the available experimental data. The calculations have been done with the finite range density dependent Gogny force.     

Octupole deformation in the actinide region

Properties of nuclei exhibiting the features of intrinsic reflection asymmetry, identified and studied at ISOLDE and ISOLDE PSB, are reviewed. This revised version was published online in July 2006 with corrections to the Cover Date.