4,221 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 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
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
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
coupling determined beyond the chiral limit
Within the conventional QCD sum rules, we calculate the coupling
constant, , beyond the chiral limit using two-point correlation
function with a pion. We consider the Dirac structure, , at
order, which has clear dependence on the PS and PV coupling schemes
for the pion-nucleon interactions. For a consistent treatment of the sum rule,
we include the linear terms in quark mass as they constitute the same chiral
order as . Using the PS coupling scheme for the pion-nucleon
interaction, we obtain , which is very close to the
empirical coupling. This demonstrates that going beyond the chiral
limit is crucial in determining the coupling and the pseudoscalar coupling
scheme is preferable from the QCD point of view.Comment: 8 pages, revtex, some errors are corrected, substantially revise
First results from an aging test of a prototype RPC for the LHCb Muon System
Recent results of an aging test performed at the CERN Gamma Irradiation
Facility on a single--gap RPC prototype developed for the LHCb Muon System are
presented. The results are based on an accumulated charge of about 0.45
C/cm, corresponding to about 4 years of LHCb running at the highest
background rate. The performance of the chamber has been studied under several
photon flux values exploiting a muon beam. A degradation of the rate capability
above 1 kHz/cm is observed, which can be correlated to a sizeable increase
of resistivity of the chamber plates. An increase of the chamber dark current
is also observed. The chamber performance is found to fulfill the LHCb
operation requirements.Comment: 6 pages, 9 figures, presented at the International Workshop on Aging
Phenomena in Gaseous Detectors'', DESY-Hamburg (Germany), October 200
Preliminary results of an aging test of RPC chambers for the LHCb Muon System
The preliminary results of an aging test performed at the CERN Gamma
Irradiation Facility on a single--gap RPC prototype developed for the LHCb Muon
System are presented. The results are based on an accumulated charge density of
0.42 C/cm^2, corresponding to about 4 years of LHCb running at the highest
background rate. We observe a rise in the dark current and noise measured with
source off. The current drawn with source on steadily decreased, possibly
indicating an increase of resistivity of the chamber plates. The performance of
the chamber, studied with a muon beam under several photon flux values, is
found to still fulfill the LHCb operation requirements.Comment: 4 pages, 6 figures, presented at RPC2001, VIth Workshop on Resistive
Plate Chambers and Related Detectors, November 26-27 2001, Coimbra, Portuga
- …