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

COEXISTENCE DES FORMES ALLONGÉE ET APLATIE DANS 187Au

187Au a été étudié simultanément par réaction 175Lu(16O, 4n)l87Au au cyclotron à énergie variable d'Orsay, et par étude de la désintégration radioactive de 187Hg (T½ = 133 ± 13 ns) à l'aide du séparateur Isocèle en ligne sur le synchrocyclotron de l'IPN d'Orsay. Les résultats obtenus ont été comparés à ceux du coeur pair-pair 186Pt formé par réaction 174Yb(16O, 4n)186Pt. On a ainsi mis en évidence deux bandes découplées construites dans les couches h 11/2 et h 9/2 indiquant des déformations respectivement oblate et prolate comme dans 189Au [1]. Dans la bande h 9/2, bien développée, de même que dans le coeur 186Pt, on a pu mettre en évidence un effet de backbending : ceci permet de penser qu'il est essentiellement dû à une paire de protons h 11/2 (blocking du proton h 9/2 aligné sur le cœur)

Superdeformation in 198^{198}Po

The $^{174}$Yb($^{29}$Si,5n) reaction at 148 MeV with thin targets was used to populate high-angular momentum states in $^{198}$Po. Resulting $\gamma$ rays were observed with Gammasphere. A weakly-populated superdeformed band of 10 $\gamma$-ray transitions was found and has been assigned to $^{198}$Po. This is the first observation of a SD band in the $A \approx 190$ region in a nucleus with $Z > 83$. The ${\cal J}^{(2)}$ of the new band is very similar to those of the yrast SD bands in $^{194}$Hg and $^{196}$Pb. The intensity profile suggests that this band is populated through states close to where the SD band crosses the yrast line and the angular momentum at which the fission process dominates.Comment: 10 pages, revtex, 2 figs. available on request, submitted to Phys. Rev. C. (Rapid Communications

Chaos in Axially Symmetric Potentials with Octupole Deformation

Classical and quantum mechanical results are reported for the single particle motion in a harmonic oscillator potential which is characterized by a quadrupole deformation and an additional octupole deformation. The chaotic character of the motion is srongly dependent on the quadrupole deformation in that for a prolate deformation virtually no chaos is discernible while for the oblate case the motion shows strong chaos when the octupole term is turned on.Comment: 6 pages LaTex plus 4 figures available by contacting the authors directly, published in PHYS.REV.LETT. 72(1994) 235

Spin-rotor Interpretation of Identical Bands and Quantized Alignment in Superdeformed A ≈\approx 190 Nuclei

The ``identical'' bands in superdeformed mercury, thallium, and lead nuclei are interpreted as examples of orbital angular momentum rotors with the weak spin-orbit coupling of pseudo-$SU(3)$ symmetries and supersymmetries.Comment: 15 pages, revtex 3.0, 7 figures available upon request from [email protected]

Band structure of 235 U

Over a period of several years we have performed three separate experiments at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron in which 235U (thick target) was Coulomb-excited. The program involved stand-alone experiments with Gammmasphere and with the 8pi Spectrometer using 136Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with a 40Ca beam at 184 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g., [631]1/2, [624]7/2, and [622]5/2) strongly populated by E3 excitation. The CHICO data have been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many M1 matrix elements could be extracted from the γ-ray branching ratios. A number of new features have emerged, including the unexpected attenuation of magnetic transitions between states of the same Nilsson multiplet, the breakdown of Coriolis staggering at high spin, and the effect of E3 collectivity on Coriolis interactions