3,707 research outputs found
Description of nuclear octupole and quadrupole deformation close to the axial symmetry: Octupole vibrations in the X(5) nuclei 150Nd and 152Sm
The model, introduced in a previous paper, for the description of the
octupole and quadrupole degrees of freedom in conditions close to the axial
symmetry, is used to describe the negative-parity band based on the first
octupole vibrational state in nuclei close to the critical point of the U(5) to
SU(3) phase transition. The situation of 150Nd and 152Sm is discussed in
detail. The positive parity levels of these nuclei, and also the in-band E2
transitions, are reasonably accounted for by the X(5) model. With simple
assumptions on the nature of the octupole vibrations, it is possible to
describe, with comparable accuracy, also the negative parity sector, without
changing the description of the positive-parity part.Comment: 8 pages, 5 figure
Description of nuclear octupole and quadrupole deformation close to the axial symmetry: Critical-point behavior of 224Ra and 224Th
The model, introduced in a previous paper, for the description of the
octupole and quadrupole degrees of freedom in conditions close to the axial
symmetry, is applied to situations of shape phase transitions where the
quadrupole amplitude can reach zero. The transitional nuclei 224,226Ra and
224Th are discussed in the frame of this model. Their level schemes can be
reasonably accounted for assuming a square-well potential in two dimensions.
Electromagnetic transition amplitudes are also evaluated and compared with
existing experimental data.Comment: 11 pages, 9 figure
Description of nuclear octupole and quadrupole deformation close to the axial symmetry and phase transitions in the octupole mode
The dynamics of nuclear collective motion is investigated in the case of
reflection-asymmetric shapes. The model is based on a new parameterization of
the octupole and quadrupole degrees of freedom, valid for nuclei close to the
axial symmetry. Amplitudes of oscillation in other degrees of freedom different
from the axial ones are assumed to be small, but not frozen to zero. The case
of nuclei which already possess a permanent quadrupole deformation is discussed
in some more detail and a simple solution is obtained at the critical point of
the phase transition between harmonic octupole oscillation and a permanent
asymmetric shape. The results are compared with experimental data of the
Thorium isotopic chain. The isotope Th-226 is found to be close to the critical
point.Comment: 17 pages, 5 figures, 8 tables; 3 new references added, misprints
correcte
Transition probabilities in the X(5) candidate Ba
To investigate the possible X(5) character of 122Ba, suggested by the ground
state band energy pattern, the lifetimes of the lowest yrast states of 122Ba
have been measured, via the Recoil Distance Doppler-Shift method. The relevant
levels have been populated by using the 108Cd(16O,2n)122Ba and the
112Sn(13C,3n)122Ba reactions. The B(E2) values deduced in the present work are
compared to the predictions of the X(5) model and to calculations performed in
the framework of the IBA-1 and IBA-2 models
Isospin symmetry violation in mirror E1 transitions: Coherent contributions from the giant isovector monopole resonance in the 67As-67Se doublet
The assumption of an exact isospin symmetry would imply equal strengths for mirror E1 transitions (at least, in the long-wavelength limit). Actually, large violations of this symmetry rule have been indicated by a number of experimental results, the last of which is the 67As-67Se doublet investigated at GAMMASPHERE. Here, we examine in detail various possible origins of the observed asymmetry. The coherent effect of Coulomb-induced mixing with the high-lying giant isovector monopole resonance is proposed as the most probable process to produce a large asymmetry in the E1 transitions, with comparatively small effect on the other properties of the parent and daughter levels. © 2012 American Physical Society.Financial support from the Spanish Ministry of Economy and Competitiveness, via the Project Consolider Ingenio (CPAN) (CSD2007-42).Peer Reviewe
Parity shift and beat staggering structure of octupole bands in a collective model for quadrupole-octupole deformed nuclei
We propose a collective model formalism which describes the strong parity
shift observed in low-lying spectra of nuclei with octupole deformations
together with the fine rotational band structure developed at higher angular
momenta. The parity effect is obtained by the Schroedinger equation for
oscillations of the reflection asymmetric (octupole) shape between two opposite
orientations in an angular momentum dependent double-well potential. The
rotational structure is obtained by a collective quadrupole-octupole rotation
Hamiltonian. The model scheme reproduces the complicated beat staggering
patterns observed in the octupole bands of light actinide nuclei. It explains
the angular momentum evolution of octupole spectra as the interplay between the
octupole shape oscillation (parity shift) mode and the stable
quadrupole-octupole rotation mode.Comment: 16 pages, 7 figure
Transition rates and nuclear structure changes in mirror nuclei 47Cr and 47V
Lifetime measurements in the mirror nuclei 47Cr and 47V were performed by
means of the Doppler-shift attenuation method using the multidetector array
EUROBALL, in conjunction with the ancillary detectors ISIS and the Neutron
Wall. The determined transition strengths in the yrast cascades are well
described by full pf shell model calculations.Comment: Latex2e, 11 pages, 3 figure
Relativistic and Binding Energy Corrections to Direct Photon Production In Upsilon Decay
A systematic gauge-invariant method is used to calculate the rate for an
upsilon meson to decay inclusively into a prompt photon. An expansion is made
in the quark relative velocity v, which is a small natural parameter for heavy
quark systems. Inclusion of these O(v^2) corrections tends to increase the
photon rate in the middle z range and to lower it for larger z, a feature
supported by the data.Comment: 13 pages, LateX, One figure (to be published in Phys. Rev. D, Sept.
1, 1996
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