547 research outputs found
Transition Rates between Mixed Symmetry States: First Measurement in 94Mo
The nucleus 94Mo was investigated using a powerful combination of
gamma-singles photon scattering experiments and gamma-gamma-coincidence studies
following the beta-decay of 94mTc. The data survey short-lived J^pi=1+,2+
states and include branching ratios, E2/M1 mixing ratios, lifetimes, and
transition strengths. The mixed-symmetry (MS) 1+ scissors mode and the 2+ MS
state are identified from M1 strengths. A gamma transition between MS states
was observed and its rate was measured. Nine M1 and E2 strengths involving MS
states agree with the O(6) limit of the interacting boson model-2 using the
proton boson E2 charge as the only free parameter.Comment: 9 pages, 3 PostScript figures included, ReVTeX, accepted for
publication in Physical Review Letters, tentatively scheduled for August 9,
199
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
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Low-Spin Spectroscopy of 50Mn
The data on low spin states in the odd-odd nucleus 50Mn investigated with the
50Cr(p,ngamma)50Mn fusion evaporation reaction at the FN-TANDEM accelerator in
Cologne are reported. Shell model and collective rotational model
interpretations of the data are given.Comment: 7 pages, 2 figures, to be published in the proceedings of the
"Bologna 2000 - Structure of the Nucleus at the Dawn of the Century"
Conference, (Bologna, Italy, May 29 - June 3, 2000
Symmetries of Quadrupole-Collective Vibrational Motion in Transitional Even-Even 124−134Xenon Nuclei
Projectile-Coulomb excitation of Xe isotopes has been performed at ANL using the Gammasphere array for the detection of γ-rays. The one-quadrupole phonon 2+ 1,ms mixed-symmetry state (MSS) has been traced in the stable N=80 isotones down to 134Xe. First, the data on absolute E2 andM1 transition rates quantify the amount of F-spin symmetry in these nuclei and provide a new local measure for the pn-QQ interaction. Second, the evolution of the 2+ 1,ms state has been studied along the sequence of stable even-even 124−134Xe isotopes that are considered to form a shape transition path from vibrational nuclei with vibrational U(5) symmetry near N=82 to γ-softly deformed shapes with almost O(6) symmetry. Third, our data on more than 50 absolute E2 transition rates between off-yrast low-spin states of 124,126Xe enable us to quantitatively test O(6) symmetry in these nuclei. As a result we find that O(6) symmetry is more strongly broken in the A=130 mass region than previously thought. The data will be discussed
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