239 research outputs found
Geometry of the shears mechanism in nuclei
5 pages, 3 figures, accepted for publication in Physical Review C, Rapid CommunicationThe geometry of the shears mechanism in nuclei is derived from the nuclear shell model. This is achieved by taking the limit of large angular momenta (classical limit) of shell-model matrix elements
Tidal waves in Pd 102: A phenomenological analysis
Rotational and electromagnetic properties of the yrast band in Pd102 are analyzed in terms of a phenomenological phonon model that includes anharmonic terms. Both the moment of inertia and B(E2)'s are well reproduced by the model, providing an independent confirmation of the multiphonon picture recently proposed. The (empirical) dependence of the phonon-phonon interaction on the phonon frequency, in Ru, Pd, and Ru isotopes, follows the expectations from particle-vibration coupling
Collective T=0 pairing in N=Z nuclei? Pairing vibrations around 56Ni revisited
We present a new analysis of the pairing vibrations around 56Ni, with
emphasis on odd-odd nuclei. This analysis of the experimental excitation
energies is based on the subtraction of average properties that include the
full symmetry energy together with volume, surface and Coulomb terms. The
results clearly indicate a collective behavior of the isovector pairing
vibrations and do not support any appreciable collectivity in the isoscalar
channel.Comment: RevTeX, two-column, 5 pages, 4 figure
The T=0 neutron-proton pairing correlations in the superdeformed rotational bands around 60Zn
The superdeformed bands in 58Cu, 59Cu, 60Zn, and 61Zn are analyzed within the
frameworks of the Skyrme-Hartree-Fock as well as Strutinsky-Woods-Saxon total
routhian surface methods with and without the T=1 pairing correlations. It is
shown that a consistent description within these standard approaches cannot be
achieved. A T=0 neutron-proton pairing configuration mixing of
signature-separated bands in 60Zn is suggested as a possible solution to the
problem.Comment: 9 ReVTex pages, 10 figures, submitted to Phys. Rev.
Degeneracies when T=0 Two Body Matrix Elements are Set Equal to Zero and Regge's 6j Symmetry Relations
The effects of setting all T=0 two body interaction matrix elements equal to
a constant (or zero) in shell model calculations (designated as ) are
investigated. Despite the apparent severity of such a procedure, one gets
fairly reasonable spectra. We find that using in single j shell
calculations degeneracies appear e.g. the and
states in Sc are at the same excitation energies; likewise the
I=,,9 and 10 states in Ti. The
above degeneracies involve the vanishing of certain 6j and 9j symbols. The
symmetry relations of Regge are used to explain why these vanishings are not
accidental. Thus for these states the actual deviation from degeneracy are good
indicators of the effects of the T=0 matrix elements. A further indicator of
the effects of the T=0 interaction in an even - even nucleus is to compare the
energies of states with odd angular momentum with those that are even
Evidence for particle-hole excitations in the triaxial strongly-deformed well of ^{163}Tm
Two interacting, strongly-deformed triaxial (TSD) bands have been identified
in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD
bands have been observed in an element other than the Z = 71 Lu nuclei, where
wobbling bands have been previously identified. The observed TSD bands in
^{163}Tm appear to be associated with particle-hole excitations, rather than
wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental
observables of these bands reasonably well and also provide an explanation for
the presence of wobbling bands in the Lu nuclei, and their absence in the Tm
isotopes.Comment: 13 pages, 7 figure
Empirical investigation of extreme single-particle behavior of nuclear quadrupole moments in highly collective A∼150 superdeformed bands
The intrinsic quadrupole moment Q0 of superdeformed rotational bands in A∼150 nuclei depends on the associated single-particle configuration. We have derived an empirical formula based on the additivity of effective quadrupole moments of single-particle orbitals that describes existing measurements from 142Sm to 152Dy. To further test the formula, the predicted Q0 moments for two superdeformed bands in 146Gd of 14.05eb were confronted with a new measurement yielding 13.9±0.4eb and 13.9 ± 0.3eb, respectively. This excellent agreement provides empirical evidence of extreme single-particle behavior in highly deformed, collective systems
Shape evolution in the superdeformed A ≈ 80-90 mass region
Superdeformed bands in 88Mo, 89Tc, and 91Tc were populated using a 40Ca beam with an energy of 185 MeV, impinging on a backed 58Ni target, γ rays and charged particles emitted in the reactions were detected using the Gammasphere Ge detector array and the CsI(Tl) array Microball. Average transition quadrupole moments Qt, with significantly improved accuracy compared to earlier work, were deduced for the bands using the residual doppler shift technique. The experimental results were included into a systematic study of the Q t values throughout the superdeformed mass 80-90 region. The superdeformed shell gaps are predicted to move towards larger deformations with increasing Z and N in this mass region. This trend is confirmed by the experimental Qt values
Evidence for Shape Co-existence at medium spin in 76Rb
Four previously known rotational bands in 76Rb have been extended to moderate
spins using the Gammasphere and Microball gamma ray and charged particle
detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV.
The properties of two of the negative-parity bands can only readily be
interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model
calculations if they have the same configuration in terms of the number of g9/2
particles, but they result from different nuclear shapes (one near-oblate and
the other near-prolate). These data appear to constitute a unique example of
shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters
High-spin isomers and three-neutron valence configurations in 211Pb
Deep-inelastic reactions between a beam of 1360 MeV 208Pb ions and a thick 238U target have been used to populate the neutron-rich nucleus 211Pb. The observation of its γ decay has allowed identification of excited states up to the highest spin which can be formed from the three valence neutrons, including identification of three high-spin isomers. Level energies and transition strengths are compared to shell-model calculations with empirical interactions and predictions are made for the expected behaviour of more neutron-rich lead isotopes. The evidence for a possible increase in the neutron effective charge moving away from the N=126 shell gap is evaluated
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