101 research outputs found
Simple relations among E2 matrix elements of low-lying collective states
A method is developed to derive simple relations among the reduced matrix
elements of the quadrupole operator between low-lying collective states. As an
example, the fourth order scalars of Q are considered. The accuracy and
validity of the proposed relations is checked for the ECQF Hamiltonian of the
IBM-1 in the whole parameter space of the Casten triangle. Furthermore these
relations are successfully tested for low-lying collective states in nuclei for
which all relevant data is available.Comment: 12 pages, 1 figure, RevTeX preprint-styl
Quadrupole shape invariants in the interacting boson model
In terms of the Interacting Boson Model, shape invariants for the ground
state, formed by quadrupole moments up to sixth order, are studied in the
dynamical symmetry limits and, for the first time, over the whole structural
range of the IBM-1. The results are related to the effective deformation
parameters and their fluctuations in the geometrical model. New signatures that
can distinguish vibrator and gamma-soft rotor structures, and one that is
related to shape coexistence, are identified.Comment: 10 pages, ReVTeX, epsf, 2 Postscript figures include
Cluster Interpretation of Properties of Alternating Parity Bands in Heavy Nuclei
The properties of the states of the alternating parity bands in actinides,
Ba, Ce and Nd isotopes are analyzed within a cluster model. The model is based
on the assumption that cluster type shapes are produced by the collective
motion of the nuclear system in the mass asymmetry coordinate. The calculated
spin dependences of the parity splitting and of the electric multipole
transition moments are in agreement with the experimental data.Comment: 29 pages, 10 figure
Quasideuteron states with deformed core
The M1 transitions between low-lying T=1 and T=0 states in deformed odd-odd
N=Z nuclei are analyzed in the frames of the rotor-plus-particle model. Using
the representation of an explicit coupling of angular momenta we show that
strong coupling of the quasideuteron configurations to the axially deformed
core results in a distribution of the total 0+ --> 1+ strength among a few
low-lying 1+ states. Simple analytical formulae for B(M1) values are derived.
The realization of the M1 sum rule for the low-lying 1+,T=0 states is
indicated. The calculated B(M1) values are found to be in good agreement with
experimental data and reveal specific features of collectivity in odd-odd N=Z
nuclei.Comment: 11 pages, 1 figure, LaTe
Partial Dynamical Symmetry in the Symplectic Shell Model
We present an example of a partial dynamical symmetry (PDS) in an interacting
fermion system and demonstrate the close relationship of the associated
Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding
new light on this important interaction. Specifically, in the framework of the
symplectic shell model of nuclei, we prove the existence of a family of
fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction
process for the PDS eigenstates with good symmetry and give analytic
expressions for the energies of these states and E2 transition strengths
between them. Characteristics of both pure and mixed-symmetry PDS eigenstates
are discussed and the resulting spectra and transition strengths are compared
to those of real nuclei. The PDS concept is shown to be relevant to the
description of prolate, oblate, as well as triaxially deformed nuclei.
Similarities and differences between the fermion case and the previously
established partial SU(3) symmetry in the Interacting Boson Model are
considered.Comment: 9 figure
How close to the O (6) symmetry is the nucleus 124Xe?
Excited states in 124Xe have been studied via the 12C(124Xe, 124Xe*) Coulomb excitation reaction. Their population cross-sections relative to the 21+ state have been determined from the γ-ray yields observed with Gammasphere. More than twenty absolute E2 strengths for seven off-yrast, low-spin states of 124Xe have been deduced for the first time. The absolute B (E 2) values indicate pronounced O (5) symmetry, even for the off-yrast states with high O (5) quantum number τ, while the O (6) symmetry is substantially broken
Neutrinoless double beta decay within Self-consistent Renormalized Quasiparticle Random Phase Approximation and inclusion of induced nucleon currents
The first, to our knowledge, calculation of neutrinoless double beta decay
(-decay) matrix elements within the self-consistent
renormalised Quasiparticle Random Phase Approximation (SRQRPA) is presented.
The contribution from the momentum-dependent induced nucleon currents to
-decay amplitude is taken into account. A detailed nuclear
structure study includes the discussion of the sensitivity of the obtained
SRQRPA results for -decay of Ge to the parameters of
nuclear Hamiltonian, two-nucleon short-range correlations and the truncation of
the model space. A comparision with the standard and renormalized QRPA is
presented. We have found a considerable reduction of the SRQRPA nuclear matrix
elements, resulting in less stringent limits for the effective neutrino mass.Comment: 13 pages, 3 figures, 1 tabl
Extended M1 sum rule for excited symmetric and mixed-symmetry states in nuclei
A generalized M1 sum rule for orbital magnetic dipole strength from excited
symmetric states to mixed-symmetry states is considered within the
proton-neutron interacting boson model of even-even nuclei. Analytic
expressions for the dominant terms in the B(M1) transition rates from the first
and second states are derived in the U(5) and SO(6) dynamic symmetry
limits of the model, and the applicability of a sum rule approach is examined
at and in-between these limits. Lastly, the sum rule is applied to the new data
on mixed-symmetry states of 94Mo and a quadrupole d-boson ratio
is obtained in a largely
parameter-independent wayComment: 19 pages, 3 figures, Revte
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