279 research outputs found
Simplified approach to the application of the geometric collective model
The predictions of the geometric collective model (GCM) for different sets of
Hamiltonian parameter values are related by analytic scaling relations. For the
quartic truncated form of the GCM -- which describes harmonic oscillator,
rotor, deformed gamma-soft, and intermediate transitional structures -- these
relations are applied to reduce the effective number of model parameters from
four to two. Analytic estimates of the dependence of the model predictions upon
these parameters are derived. Numerical predictions over the entire parameter
space are compactly summarized in two-dimensional contour plots. The results
considerably simplify the application of the GCM, allowing the parameters
relevant to a given nucleus to be deduced essentially by inspection. A
precomputed mesh of calculations covering this parameter space and an
associated computer code for extracting observable values are made available
through the Electronic Physics Auxiliary Publication Service. For illustration,
the nucleus 102Pd is considered.Comment: RevTeX 4, 15 pages, to be published in Phys. Rev.
Phase Transitions in Finite Nuclei and the Integer Nucleon Number Problem
The study of spherical-deformed ground--state phase transitions in finite
nuclei as a function of N and Z is hindered by the discrete values of the
nucleon number. A resolution of the integer nucleon number problem, and
evidence relating to phase transitions in finite nuclei, are discussed from the
experimental point of view and interpreted within the framework of the
interacting boson model.Comment: 8 pages Latex + 8 figs (postscript). In Phys Rev Lett, June 199
Low-lying levels in Xe
The decays of Cs and Cs to Xe have been studied on mass separated samples, using and internal conversion electron measurements. Several new low-lying levels have been established in the Xe level scheme. Half-life evaluations for Cs and Cs have been revisited. The results are compared with other experimental data known in light odd-mass xenon isotopes and with calculations performed in the frame of the multi-shell interacting boson-fermion model
First decay study of the very neutron-rich isotope Br-93
The decay of the mass-separated, very neutron-rich isotope Br-93 has been
studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been
constructed. Level energies, gamma-ray branching ratios and multipolarities
suggest spins and parities which are in accord with a smooth systematics of the
N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to
be effective in Kr isotopes. So far, there is no indication of a progressive
onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin
Projected shell model study of odd-odd f-p-g shell proton-rich nuclei
A systematic study of 2-quasiparticle bands of the proton-rich odd-odd nuclei
in the mass A ~ 70-80 region is performed using the projected shell model
approach. The study includes Br-, Rb-, and Y-isotopes with N = Z+2, and Z+4. We
describe the energy spectra and electromagnetic transition strengths in terms
of the configuration mixing of the angular-momentum projected
multi-quasiparticle states. Signature splitting and signature inversion in the
rotational bands are discussed and are shown to be well described. A
preliminary study of the odd-odd N = Z nucleus, 74Rb using the concept of
spontaneous symmetry breaking is also presented.Comment: 14 pages, 7 figures, final version accepted by Phys. Rev.
In-beam fast-timing measurements in 103,105,107Cd
Fast-timing measurements were performed recently in the region of the
medium-mass 103,105,107Cd isotopes, produced in fusion evaporation reactions.
Emitted gamma-rays were detected by eight HPGe and five LaBr3:Ce detectors
working in coincidence. Results on new and re-evaluated half-lives are
discussed within a systematic of transition rates. The states in
103,105,107Cd are interpreted as arising from a single-particle excitation. The
half-life analysis of the states in 103,105,107Cd shows no change in
the single-particle transition strength as a function of the neutron number
Staggering behavior of the low lying excited states of even-even nuclei in a Sp(4,R) classification scheme
We implement a high order discrete derivative analysis of the low lying
collective energies of even-even nuclei with respect to the total number of
valence nucleon pairs N in the framework of F- spin multiplets appearing in a
symplectic sp(4,R) classification scheme. We find that for the nuclei of any
given F- multiplet the respective experimental energies exhibit a Delta N=2
staggering behavior and for the nuclei of two united neighboring F- multiplets
well pronounced Delta N=1 staggering patterns are observed. Those effects have
been reproduced successfully through a generalized sp(4,R) model energy
expression and explained in terms of the step-like changes in collective modes
within the F- multiplets and the alternation of the F-spin projection in the
united neighboring multiplets. On this basis we suggest that the observed Delta
N=2 and Delta N=1 staggering effects carry detailed information about the
respective systematic manifestation of both high order alpha - particle like
quartetting of nucleons and proton (neutron) pairing interaction in nuclei.PACS
number(s):21.10.Re, 21.60.FwComment: 22 pages and 6 figures changes in the figure caption
Excited States in 52Fe and the Origin of the Yrast Trap at I=12+
Excited states in 52Fe have been determined up to spin 10\hbar in the
reaction 28Si + 28Si at 115 MeV by using \gamma-ray spectroscopy methods at the
GASP array. The excitation energy of the yrast 10+ state has been determined to
be 7.381 MeV, almost 0.5 MeV above the well known \beta+-decaying yrast 12+
state, definitely confirming the nature of its isomeric character. The mean
lifetimes of the states have been measured by using the Doppler Shift
Attenuation method. The experimental data are compared with spherical shell
model calculations in the full pf-shell.Comment: 9 pages, RevTeX, 7 figures include
g factors of coexisting isomeric states in Pb-188
The factors of the , {11}^{\ensuremath{-}}, and {8}^{\ensuremath{-}} isomeric states in were measured using the time-differential perturbed angular distribution method as g({12}^{+})=\ensuremath{-}0.179(6), g({11}^{\ensuremath{-}})=+1.03(3), and g({8}^{\ensuremath{-}})=\ensuremath{-}0.037(7). The factor of the state follows the observed slight down-sloping evolution of the factors of the neutron spherical states with decreasing . The factors of the {11}^{\ensuremath{-}} and {8}^{\ensuremath{-}} isomers proposed as oblate and prolate deformed states, respectively, were interpreted within the rotational model, using calculated and empirical factor values for the involved single-particle orbitals
Extensive investigation of 0<sup>+</sup> states in rare earth region nuclei
The nature of 0+ excitations, especially in transitional and deformed nuclei, has attracted new attention. Following a recent experiment studying 158Gd, we investigated a large group of nuclei in the rare-earth region with the (p,t) pickup reaction using the Q3D magnetic spectrograph at the University of Munich MP tandem accelerator laboratory. Outgoing tritons were recorded at various lab angles, and their angular distributions are compared to those calculated using the distorted-wave Born approximation. Using the unique shape of the L=0 angular distribution, more than double the number of 0+ states than were previously known are identified. The distribution of 0+ energies and cross sections is discussed in terms of collective and noncollective degrees of freedom, and the density of low-lying 0+ states is discussed as a corroboration of a characteristic feature of phase transition regions. The degree of level mixing, as extracted from Brody distribution fits to the energy spacings of adjacent 0+ levels, is also explored.</p
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