Regular Series

Vol. 32 (2001), No. 9, pp. 2349 - 2725

Rotational Properties of Neutron Drip-Line Nuclei

Acta Phys. Pol. B 32, 2349 (2001)

page 2349 •

abstract

We know very little about the structure of neutron-rich, weakly bound nuclei. We know even less about the way they rotate. In this work, the high-spin behavior of deformed neutron-rich nuclei is studied. In particular, quasi-particle Routhian spectra of heavy Er isotopes are discussed within the deformed shell model, and rotational properties and isovector shape deformations of heavy Ne and Mg isotopes are studied with the self-consistent cranked Skyrme–Hartree–Fock theory.

Collectivity in Light Po Isotopes Revealed in Recoil-Decay-Tagging Experiments

Acta Phys. Pol. B 32, 2365 (2001)

page 2365 •

abstract

It was predicted already more than 20 years ago that coexisting oblate- and prolate-shaped minima should come down in energy in neutron-deficient polonium isotopes around $^{192}$Po. Progress in experimental techniques, and in particular in the use of the Recoil-Decay-Tagging method, has made it possible to verify these predictions. Recent RDT results obtained at the University of Jyväskylä on shape coexistence in very neutron-deficient Po isotopes will be discussed.

Configuration Mixing of Mean-Field Wave-Functions Projected on Angular Momentum and Particle Number; Application to $^{24}$Mg

Acta Phys. Pol. B 32, 2375 (2001)

page 2375 •

abstract

We present in this talk the general framework of a method which permits to restore the rotational and particle number symmetries of wave functions obtained in Skyrme HF+BCS calculations. This restoration is nothing but a projection of mean-field intrinsic wave functions onto good particle number and good angular momentum. The method allows also to mix projected wave functions. Such a configuration mixing is discussed for sets of HF+BCS intrinsic states generated in constrained calculations with suitable collective variables. This procedure gives collective states which are eigenstates of the particle number and the angular momentum operators and between which transition probabilities are calculated. A test application to $^{24}$Mg is presented with mean-field wave functions generated by axial quadrupole constraints. Theoretical spectra and transition probabilities are compared to the experiment. Some preliminary results for $^{32}$Mg and $^{16}$O are also reported.

Quadrupole Collectivity in the Si Isotopes Around $N=20$

Acta Phys. Pol. B 32, 2385 (2001)

page 2385 •

abstract

The angular momentum projected generator coordinate method using the quadrupole moment as a collective coordinate and the Gogny force as the effective interaction is used to describe the properties of the ground and low-lying excited states of the neutron rich light nuclei $^{32,34,36}$Si. It is found that the ground state of the nucleus $^{34}$Si is spherical. However, this is not due only to the $N=20$ shell closure, since the ground state of $^{34}$Si contains a significant amount of the intruder $f_{7/2}$ neutron orbital. A rather good agreement with experimental data for many observables is obtained.

full authors' list

R.M. Lieder, W. Gast, H.M. Jäger, L. Mihailescu, M. Rossewij, J. Eberth, G. Pascovici, H.G. Thomas, D. Weisshaar, F. Beck, D. Curien, G. Duchêne, E. Pachoud, I. Piqueras, C. Rossi Alvarez, D. Bazzacco, M. Bellato, Th. Kroell, Ch. Manea, B. Quintana, R. Venturelli, D.R. Napoli, D. Rosso, P. Spolaore, A. Geraci, A. Pullia, G. Ripamonti, F. Camera, S. Leoni, B. Million, O. Wieland, A. Bracco, M. Pignanelli, S. Brambilla, J. Lisle, A.G. Smith, R. Well, P. Nolan, A. Boston, D. Cullen, M. Descovich, T. Enqvist, B. Cederwall, E. Ideguchi, J. van der Marel, J. Nyberg, B. Herskind, G. Sletten, J. Wilson, B. Redouin, R. Henck, D. Gutknecht, K. Jääskeläinen

Development of $\gamma$-Ray Tracking Detectors

Acta Phys. Pol. B 32, 2395 (2001)

page 2395 •

abstract

The next generation of $4 \pi$ arrays for high-precision $\gamma$-ray spectroscopy AGATA will consist of $\gamma$-ray tracking detectors. They represent high-fold segmented Ge detectors and a front-end electronics, based on digital signal processing techniques, which allows to extract energy, timing and spatial information on the interactions of a $\gamma$-ray in the Ge detector by pulse shape analysis of its signals. Utilizing the information on the positions of the interaction points and the energies released at each point the tracks of the $\gamma$-rays in a Ge shell can be reconstructed in three dimensions on the basis of the Compton-scattering formula.

Structure of $N=Z$ Nuclei from Studies with GASP and Euroball

Acta Phys. Pol. B 32, 2403 (2001)

page 2403 •

abstract

Large $\gamma$-detector arrays coupled with selective ancillary devices has allowed to progress greatly in the nuclear structure studies of $N=Z$ nuclei up to relatively high spin. At GASP and Euroball a series of experiments have been performed ranging from nuclei close to $^{32}$S to the mass $A=90$ region. The new data provide important information on the role of proton neutron pairing correlation, on isospin symmetry and isospin mixing in nuclear states and, for lighter nuclei, constitute an excellent test of the shell model description of nuclear collective motion. Two examples of the work done at Legnaro in this field are presented.

full authors' list

C.E. Svensson, A.O. Macchiavelli, A. Juodagalvis, A. Poves, I. Ragnarsson, S. Åberg, D.E. Appelbe, R.A.E. Austin, C. Baktash, G.C. Ball, M.P. Carpenter, E. Caurier, R.M. Clark, M. Cromaz, M.A. Deleplanque, R.M. Diamond, P. Fallon, M. Furlotti, A. Galindo-Uribarri, R.V.F. Janssens, G.J. Lane, I.Y. Lee, M. Lipoglavsek, F. Nowacki, S.D. Paul, D.C. Radford, D.G. Sarantites, D. Seweryniak, F.S. Stephens, V. Tomov, K. Vetter, D. Ward, C.H. Yu

Fast Rotation of the $N = Z$ Nucleus $^{36}$Ar

Acta Phys. Pol. B 32, 2413 (2001)

page 2413 •

abstract

A highly-deformed rotational band has been identified in the $N=Z$ nucleus $^{36}$Ar. At high spin the band is observed to its presumed termination at $I^{\pi } = 16^{+}$, while at low spin it has been firmly linked to previously known states in $^{36}$Ar. Spins, parities, and absolute excitation energies have thus been determined throughout the band. Lifetime measurements establish a large low-spin quadrupole deformation ($\beta _2 = 0.46 \pm 0.03$) and indicate a decreasing collectivity as the band termination is approached. With effectively complete spectroscopic information and a valence space large enough for significant collectivity to develop, yet small enough to be meaningfully approached from the shell model perspective, this rotational band in $^{36}$Ar provides many exciting opportunities to test and compare complementary models of collective motion in nuclei.

Shell Model Applications to $N=Z$ Nuclei

Acta Phys. Pol. B 32, 2423 (2001)

page 2423 •

abstract

This manuscript reviews recent results of large scale shell model calculations for $N=Z$ nuclei. The topics discussed include the role of the proton–neutron pairing in determining the binding energies of $pf$ shell nuclei and properties of backbending rotors, as well as the Coulomb energy differences and their relationship with alignment. Proton–neutron correlations are found responsible for the characteristic features of the isotopic shifts in calcium, i.e., for the parabolic dependence on $A$ and prominent odd–even staggering.

full authors' list

A. Maj, M. Kmiecik, W. Królas, J. Styczeń, A. Bracco, F. Camera, B. Million, J.J. Gaardhøje, B. Herskind, M. Kicińska-Habior, J. Kownacki, W.E. Ormand

Search for the Jacobi Instability in Rapidly Rotating $^{46}$Ti$^*$ Nuclei

Acta Phys. Pol. B 32, 2433 (2001)

page 2433 •

abstract

The possible existence of Jacobi shape transition in hot $^{46}$Ti at high angular momenta was investigated with the Giant Dipole Resonance exclusive experiments. The GDR spectra and the angular distributions are consistent with predictions of the thermal shape fluctuation model indicating elongated nuclear shapes.

Cranking in Isospace — Towards a Consistent Mean-Field Description of $N=Z$ Nuclei

Acta Phys. Pol. B 32, 2441 (2001)

page 2441 •

abstract

Excitation spectra ${\mit \Delta } E_T$ of $T=0,1,2$ states in even–even (e–e) and odd–odd (o–o) $N=Z$ nuclei are analyzed within a mean-field based model involving isovector and isoscalar pairing interactions and the iso-cranking formalism applied to restore approximately isospin symmetry. It is shown that $T=0$ states in o–o and $T=1$ states in e–e nuclei correspond to two-quasiparticle, time-reversal symmetry breaking excitations since their angular momenta are $I\ne 0$. On the other hand the lowest $T=2$ states in e–e and $T=1$ states in o–o nuclei, which both are similar in structure to their even–even isobaric analogue states, are described as e–e type vacua excited (iso-cranked) in isospace. It appears that in all cases isoscalar pairing plays a crucial role in restoring the proper value of the inertia parameter in isospace i.e. ${\mit \Delta } E_T$.

Rotating $N$=$Z$ Nuclei — a Probe to the $t$=0 and $t$=1 Pairing Correlations

Acta Phys. Pol. B 32, 2457 (2001)

page 2457 •

abstract

A study of heavy $N$=$Z$ nuclei including $t$=1, $t_z$=$\pm$1 pairing only clearly reveals the shortcoming of that model in $T_z$=0 nuclei. We present a simple model in which we study the response of isoscalar $t$=0 and isovector $t$=1 pairing correlations to rotational motion. In particular, we address the role played by the $t$=1 and $t$=0 pair gaps with respect to the band crossing frequency. We argue that the $t$=1 neutron-proton pair field is of limited importance in even-even nuclei. For the $t$=0 pair field, we introduce two different pairing modes. One is invariant with respect to signature symmetry and one is not. The signature conserving mode results in a delay of the band crossing frequency, whereas the signature breaking part enhances the rigidity of the moment of inertia.

Effective Field Theory for Rotational Bands in Deformed and Superdeformed Nuclei

Acta Phys. Pol. B 32, 2469 (2001)

page 2469 •

abstract

An overview is given on the description of rotational bands in normally deformed and superdeformed nuclei in the framework of effective field theories such as the Relativistic Mean Field (RMF) theory and the Relativistic Hartree–Bogoliubov (RHB) theory. In particular we discuss recent investigations for the description of superdeformed bands in the $A\sim 60$, 140–150 and 190 mass regions and compare them briefly with the results obtained in non-relativistic mean field theories.

Effects of Neutron–Proton Interaction in Doubly Odd Deformed Nuclei

Acta Phys. Pol. B 32, 2479 (2001)

page 2479 •

abstract

We have investigated the effects of the neutron–proton interaction in several doubly odd deformed nuclei within the framework of the particle-rotor model. In this paper, we show some selected results of our study which evidence the importance of the tensor-force effects.

full authors' list

R. Kaczarowski, W. Płóciennik, A. Syntfeld, H. Mach, W. Kurcewicz, B. Fogelberg, P. Hoff

Total Routhian Surface Calculations for Neutron-Rich $^{149}$Ce

Acta Phys. Pol. B 32, 2485 (2001)

page 2485 •

abstract

A Total Routhian Surface (TRS) calculations were performed for the $^{149}$Ce nucleus. The equilibrium deformation parameters and total angular momentum values have been calculated as a function of rotational frequency for both signatures of the lowest positive- and negative-parity rotational bands. Theoretical predictions are compared with the results of experimental studies of this nucleus.

Spin Ordering of Nuclear Spectra from Random Interactions

Acta Phys. Pol. B 32, 2491 (2001)

page 2491 •

abstract

Recent developments in many-body quantum chaos have raised the issue of correlations between different families of levels in the spectra of random fermionic systems. It seems that rotational invariance is sufficient to force an otherwise random system to have statistically ordered spectra where the ground state can have zero spin or the maximum spin allowed a huge portion of the time. We have tackled this question and have characterized the role of “geometric chaoticity” and pairing in random systems. We have shown how the geometry gives rise to such a distribution of ground state spins and examined the coexistence of these regularities with chaotic wave functions.

full authors' list

I.Y. Lee, R.M. Clark, D. Ward, M. Cromaz, M.A. Deleplanque, R.M. Diamond, P. Fallon, A. Görgen, G.J. Lane, A.O. Macchiavelli, F.S. Stephens, C.E. Svensson, K. Vetter

Recent Results from Gammasphere

Acta Phys. Pol. B 32, 2499 (2001)

page 2499 •

abstract

Three examples of recent nuclear structure studies using Gammasphere are discussed in this paper. (1) A rotational band has been identified in $^{108}$Cd. Its moment of inertia and quadrupole moment indicate that this band has a shape with an axis ratio larger than 1.8:1. (2) Possible “Jacobi” shape transitions at high spin were investigated from studies of the continuum gamma rays on a number of nuclei. (3) Population of high-spin states in neutron-rich nuclei were studied in target fragmentation reactions. States with spin up to 6–12$\hbar$ were observed in a wide range of nuclei.

full authors' list

M. Pfützner, P.H. Regan, P.M. Walker, Zs. Podolyák, M. Caamaño, J. Gerl, M. Hellström, P. Mayet, M.N. Mineva

Population of High Spin States in Relativistic Fragmentation

Acta Phys. Pol. B 32, 2507 (2001)

page 2507 •

abstract

The population probabilities of isomeric states in the 10 ns to ms regime have been studied following their production via the fragmentation of a $^{208}$Pb beam at 1 GeV per nucleon. Gamma decays from approximately 20 isomeric states, mostly in the $A \sim 180$ region, have been measured. Their corresponding isomeric ratios were compared with theoretical predictions based on the abrasion–ablation model of fragmentation, which appears to provide an upper limit for the measured population probabilities as a function of angular momentum.

full authors' list

N. Amzal, P.A. Butler, P.T. Greenlees, R.-D. Herzberg, R.D. Humphreys, H. Kankaanpää, J. Bastin, F. Becker, P.M. Brew, J.F.C. Cocks, R.A. Cunningham, T. Czosnyka, K. Eskola, J. Gerl, N.J. Hammond, K. Hauschild, P. Heikinen, K. Helariutta, F.-P. Heßberger, A. Hürstel, I. Iwanicki, G.D. Jones, P.M. Jones, R. Julin, S. Juutinen, A. Keenan, H. Kettunen, S. Khlebnikov, T.-L. Khoo, W. Korten, P. Kuusiniemi, Y. LeCoz, M. Leino, M. Muikku, P. Nieminen, T. Page, P. Rahkila, P. Reiter, C.S. Scholey, G. Sletten, O. Stezowski, C. Theisen, H.-J. Wollersheim

The Structure of Heavy Octupole and Superheavy Quadrupole Deformed Nuclei

Acta Phys. Pol. B 32, 2519 (2001)

page 2519 •

abstract

We report here experimental attempts to determine the sign of the electric dipole moment (relative to the electric octupole moment) in the octupole deformed nucleus $^{226}$Ra. Sensitivity to this quantity is observed in the measured yields of $\gamma$-ray transitions following very low energy Coulomb excitation. Recent progress is also reported in the development of new spectroscopic techniques that promise to elucidate the structure of deformed superheavy nuclei in the region of $^{254}$No. The $4^+ \rightarrow 2^+$ transition in $^{254}$No, as well as higher spin transitions, has been identified using recoil-tagged conversion electron spectroscopy.

Fast Nuclear Rotation and Octupole Deformation

Acta Phys. Pol. B 32, 2527 (2001)

page 2527 •

abstract

The $^{150}$Sm nucleus has been studied to high spins in a measurement of $\gamma$ radiation following the $^{136}$Xe ($^{18}$O,$4n)^{150}$Sm, compound-nucleus reaction at beam energy of 76 MeV. The measurement was performed at NBI Risø using the NORDBALL array. Alternating parity, $s\!=\!+1$ band in $^{150}$Sm has been observed up to spin $I\!=\!22$. This band is crossed by two aligned bands, corresponding to a reflection-symmetric shape. After the second crossing the $s\!=\!+1$ band ends abruptly, suggesting that the octupole shape vanishes in $^{150}$Sm above spin $I\!=\!22$, as predicted by calculations. Other explanations, assuming continuation of the $s\!=\!+1$ band past the two alignments are also discussed.

Investigation of the $K^{\pi } = 8^{-}$ Isomers in $N =74$ Isotones on Beam of the Warsaw Cyclotron

Acta Phys. Pol. B 32, 2537 (2001)

page 2537 •

abstract

The decay of the $K^{\pi }$= 8$^{-}$ isomers in $^{132}$Ce and $^{134}$Nd have been investigated on the beam of the Warsaw Cyclotron using OSIRIS array. Reactions $^{120}$Sn($^{16}$O,$4n$)$^{132}$Ce and $^{118}$Sn($^{20}$Ne,$4n$)$^{134}$Nd were used. Two new decay paths have been found in the deexcitation of the 8$^-$ isomer in $^{132}$Ce. The hindrance factors for the E1, M2 and E3 transitions deexciting the isomer have been determined. Similar E3 decay of the 410 $\mu$s isomeric state in $^{134m}$Nd has not been observed in our experiment but nevertheless the reduced hindrance factor $f_3\geq 9$ was determined. The decay properties of the 8$^{-}$ isomers in the $N=74$ isotones are discussed.

full authors' list

I. Hamamoto, S.W. Ødegård, G.B. Hagemann, D.R. Jensen, M. Bergström, B. Herskind, G. Sletten, S. Törmänen, J.N. Wilson, P.O. Tjøm, K. Spohr, H. Hübel, A. Görgen, G. Schönwasser, A. Bracco, S. Leoni, A. Maj, C.M. Petrache, P. Bednarczyk, D. Curien

First Evidence for the Wobbling Mode in a Triaxial Superdeformed Odd-$A$ Nucleus

Acta Phys. Pol. B 32, 2545 (2001)

page 2545 •

abstract

The wobbling mode is uniquely related to rotation of a triaxial body. The Lu–Hf isotopes with $N\sim 94$ provides a possible region of nuclei with pronounced triaxiality. We have investigated $^{163}$Lu through the fusion-evaporation reaction $^{139}$La($^{29}$Si,5n)$^{163}$Lu with a beam energy of 152 MeV. The electromagnetic properties of several connecting transitions between two presumably Triaxial, SuperDeformed (TSD) bands have been studied. New particle-rotor calculations in which an aligned $i_{13/2}$ proton is coupled to a “wobbling” core are presented and evidence for the assignment of the excited TSD band as a wobbling mode built on the yrast TSD band in $^{163}$Lu is given.

Wobbling Motion in the Multi-Bands Crossing Region: Dynamical Coupling Mode Between High- and Low-$K$ States

Acta Phys. Pol. B 32, 2559 (2001)

page 2559 •

abstract

We analyze a mechanism of coupling of high- and low-$K$ bands in terms of a dynamical treatment for nuclear rotations, i.e. , wobbling motion. The wobbling states are produced through the Generator Coordinate Method after Angular Momentum Projection (GCM-after-AMP), in which the intrinsic states are constructed through fully self-consistent calculations by the 2d-cranked (or tilted-axis-cranked) HFB method. In particular, the phenomena of “signature inversion” and “signature splitting” in the t-band (tilted rotational band) are explained in terms of the wobbling model. Our calculations will be compared with new data for in-band E2 transition rates in $^{182}$Os, which may shed light on the mechanism of the anomalous $K=25$ isomer decay, directly to the yrast band.

full authors' list

T. Døssing, B. Herskind, A. Maj, M. Matsuo, E. Vigezzi, A. Bracco, S. Leoni, R.A. Broglia

Gamma-Ray Strength Functions in Thermally Excited Rotating Nuclei

Acta Phys. Pol. B 32, 2565 (2001)

page 2565 •

abstract

A general discussion and illustration is given of strength functions for rotational transitions in two-dimensional $E_{\gamma 1} \times E_{\gamma 2}$ spectra. Especially, a narrow component should be proportional to the compound damping width, related to the mixing of basis rotational bands into compound bands with fragmented transition strength. Three $E_{\gamma 1} \times E_{\gamma 2}$ spectra are made by setting gates on triple coincidences, selecting cascades which feed into specific low-lying bands in the nucleus $^{168}$Hf. In each of the gated spectra, we find a ridge, carrying about 100 decay paths. This ridge is ascribed to rotational transitions in the excitation energy range of 1.0 to 1.5 MeV above the yrast line. The FWHM of the ridges are around 40 keV, about a factor of two smaller than calculated on the basis of mixed cranked mean field bands.

High-Spin States in and around Doubly-Magic Nuclei

Acta Phys. Pol. B 32, 2577 (2001)

page 2577 •

abstract

The study of high-spin states in regions of doubly-magic nuclei performed with the use of deep-inelastic heavy ion reactions is reviewed. New and tentative results concerning high-spin states in the $^{48}$Ca and yrast structures in $^{47}$Ca, $^{47}$K, $^{49}$Ca and $^{49}$Sc isotopes are presented. The status of the high-spin state study in the region of $^{132}$Sn and $^{208}$Pb is outlined, including discussion of recently obtained results in the $^{208}$Pb core and the $^{206}$Hg two-proton-hole nucleus.

Is the Collective IBM Space Exhausted Only by the Valence Shell

Acta Phys. Pol. B 32, 2591 (2001)

page 2591 •

abstract

Interpretation of the $B$(E2) values at energies higher than the first backbending indicates that the maximum boson of IBM has to increase with energy and spin.

High-Spin Terminating Bands Formed from Successive Particle–Hole Excitations Across Closed Shells

Acta Phys. Pol. B 32, 2597 (2001)

page 2597 •

abstract

Observed high spin states in $_{30}$Zn and $_{66}$Dy isotopes with two protons outside the closed shells at $Z=28$ and $Z=64$, respectively, are discussed and compared with cranked Nilsson–Strutinsky calculations. Bands terminating at higher and higher spin values are formed from successive proton excitations across these shells. These bands show very different features depending on the number of excited particles. Very good agreement with experiment is obtained. Special emphasis is put on the formation of M1-bands in configurations with one hole in the $Z=64$ core.

full authors' list

L.L. Riedinger, D.J. Hartley, A. Galindo-Uribarri, B.H. Smith, C. Baktash, M.P. Carpenter, M. Danchev, M. Devlin, C.J. Gross, R.V.F. Janssens, M. Lipoglavsek, S.D. Paul, D.C. Radford, W. Reviol, D.G. Sarantites, D. Seweryniak, C.-H. Yu, O. Zeidan

Signature Inversion in Odd–Odd Nuclei

Acta Phys. Pol. B 32, 2613 (2001)

page 2613 •

abstract

Trends in the energy staggering of the $\pi h_{11/2}\nu i_{13/2}$ and $\pi h_{11/2}\nu h_{11/2}$ bands in the mass 160 and 130 regions, respectively, have been investigated in order to better understand the origin of signature inversion. While the $A\approx 160$ nuclei behave in a consistent manner, a more complicated scenario is observed in the mass 130 region. As a result of our experiments on the lightest Pr nuclei, the systematics of these $Z=59$ nuclei have been extended, which aids in the understanding of the latter region. Triaxial deformation, a $pn$ interaction, and quadrupole pairing are considered as possible contributors to this effect. As all the chiral-twin bands that are known have signature inversion in the favored band, a possible link between the two phenomena should be considered.

Quantum Rotors and Their Symmetries

Acta Phys. Pol. B 32, 2625 (2001)

page 2625 •

abstract

A connection between nuclear symmetries other than those of an ellipsoidal nucleus and the properties of the implied rotational spectra are discussed. The discussion is focused on a few examples of exotic shapes predicted recently by microscopic calculations. Some possible interpretation difficulties related to experiment are shortly mentioned.

Towards Explanation of the “Inertia Anomalies” in Realistic Mean Field Calculations

Acta Phys. Pol. B 32, 2639 (2001)

page 2639 •

abstract

Careful theoretical studies of the nuclear collective inertia based on the non-relativistic mean-field theory and the cranking model [N. El Aouad et al., Nucl. Phys. A676, 155 (2000)] indicate that the moments of inertia of the super-deformed nuclei calculated using various standard methods and parameterizations exceed systematically the experimental values. Similarly, but for other reasons the relativistic cranking calculations based on the relativistic mean field method present, in our opinion, a different class of systematic deviations from experiment. The origin and possible explanations of these deviations are discussed briefly.

Search for Magnetic Rotation in the $A\approx 140$ Region

Acta Phys. Pol. B 32, 2645 (2001)

page 2645 •

abstract

Magnetic dipole bands have been identified in $^{142,143,144}$Gd and $^{141}$Eu nuclei. The observed bands are based on configurations with small oblate deformation involving high-${\mit \Omega }$, $h_{11/2}$ proton particles and low-${\mit \Omega }$, $h_{11/2}$ neutron holes. Information about the strength of the effective interaction between the constituent nucleons has been deduced using a semiclassical scheme of the coupling of two angular momentum vectors. The experimental results are compared with predictions of tilted axis cranking calculations. The transition from irregular dipole band in $^{144}$Gd to more regular ones in lighter Gd nuclei is observed.

full authors' list

D.L. Balabanski, K. Vyvey, G. Neyens, D. Almehed, P. Blaha, D. Borremans, S. Chmel, N. Coulier, R. Coussement, W. de Clercq, S. Frauendorf, G. Georgiev, H. Hubel, S. Pancholi, D. Rossbach, R. Schwengner, S. Teughels, P.M. Walker

Quadrupole Moments of High-Spin Isomers: Test of the Tilted-Axis Cranking Model

Acta Phys. Pol. B 32, 2655 (2001)

page 2655 •

abstract

We report the results of recent measurements of the spectroscopic quadrupole moments of high-spin isomers. For the $K^\pi =\frac {35}{2}^-$ five-quasiparticle isomer in $^{179}$W we measured $Q_s=4.00(^{+0.83}_{-1.06})$ $e$b. It corresponds to a smaller deformation compared to the ground states of the W isotopes and is in disagreement with the current theoretical predictions. We also measured the quadrupole moment of the $I^\pi =11^-$ isomer in $^{196}$Pb, $Q_s=(-)3.41(66)$ eb. It has the same proton $(s^{-2}_{1/2}h_{9/2}i_{13/2})$ configuration as the one suggested for the $I^\pi =16^{(-)}$ magnetic bandhead which allows to deduce the quadrupole moment of the $16^-$ state as $Q_s=-0.316(97)$ eb. This small value proves the near sphericity of the bandhead.

Symmetries of the Rotating Mean Field

Acta Phys. Pol. B 32, 2661 (2001)

page 2661 •

abstract

The discrete symmetries of the rotating mean field lead to a variety of rotational bands with different sequences of spin and parity. We focus on the breaking of chiral symmetry in rotating triaxial nuclei.

Spectroscopy of Superdeformed Pb Isotopes

Acta Phys. Pol. B 32, 2673 (2001)

page 2673 •

abstract

Using the spectrometer arrays Gammasphere and Euroball a detailed spectroscopy of superdeformed $^{193}$Pb and $^{196}$Pb has been performed. In $^{193}$Pb nine superdeformed bands are now known and their quasiparticle assignments are discussed. In $^{196}$Pb evidence for an octupole vibrational excitation is presented.

full authors' list

M.A. Riley, R.W. Laird, F.G. Kondev, D.J. Hartley, D.E. Archer, T.B. Brown, R.M. Clark, M. Devlin, P. Fallon, I.M. Hibbert, D.T. Joss, D.R. LaFosse, P.J. Nolan, N.J. O'Brien, E.S. Paul, J. Pfohl, D.G. Sarantites, R.K. Sheline, S.L. Shepherd, J. Simpson, R. Wadsworth, M.T. Matev, A.V. Afanasjev, J. Dobaczewski, G.A. Lalazissis, W. Nazarewicz, W. Satuła

Global Lifetime Measurements of Highly-Deformed and Other Rotational Structures in the $A\sim$135 Light Rare-Earth Region: Probing the Single-Particle Motion in a Rotating Potential

Acta Phys. Pol. B 32, 2683 (2001)

page 2683 •

abstract

It has been possible, using Gammasphere plus Microball, to extract differential lifetime measurements free from common systematic errors for over 15 different nuclei (various isotopes of Ce, Pr, Nd, Pm, and Sm) at high spin within a single experiment. This comprehensive study establishes the effective single-particle quadrupole moments in the $A\sim$135 light rare-earth region. Detailed comparisons are made with calculations using the self-consistent cranked mean-field theory.

E2 and M1 Strengths in Heavy Deformed Nuclei

Acta Phys. Pol. B 32, 2697 (2001)

page 2697 •

abstract

Energy levels of the four lowest bands in $^{160,162,164}$Dy and $^{168}$Er, $B$(E2) transition strengths between the levels, and the $B$(M1) strength distribution of the ground state, all calculated within the framework of pseudo-SU$_3$ model, are presented. Realistic single-particle energies and quadrupole–quadrupole and pairing interaction strengths fixed from systematics were used in the calculations. The strengths of four rotor-like terms, all small relative to the other terms in the interaction, were adjusted to give an overall best fit to the energy spectra. The procedure yielded consistent parameter sets for the four nuclei.

Effects of Angular Momentum on the Structure of Condensates of Bosonic Atoms Confined in an External Trap

Acta Phys. Pol. B 32, 2711 (2001)

page 2711 •

Selected Aspects of Physics of Fermionic Bubbles

Acta Phys. Pol. B 32, 2713 (2001)

page 2713 •

abstract

We discuss properties of the Fermi system which contain one or more spherical (or almost spherical) objects. The interplay between various effects, such as shell correction and chaotic behavior is considered. We briefly mention the role of the temperature, pairing, and effects associated with bubble dynamics.

full authors' list

A.A. Pasternak, A.D. Efimov, E.O. Podsvirova, V.M. Mikhajlov, J. Srebrny, T. Morek, Ch. Droste, Y. Sasaki, G.B. Hagemann

Electromagnetic E2 Transition Probabilities in $^{120}$Xe and $^{118}$Te — $N$=66 Nuclei

Acta Phys. Pol. B 32, 2719 (2001)

page 2719 •

abstract

Lifetimes of the yrast states in $^{120}$Xe and the ground state band below and above band crossing in $^{118}$Te have been measured by DSAM in the $^{111}$Cd($^{12}$C,$3n$) reaction and by DSAM and RDM in the $^{109}$Ag($^{13}$C,$p3n$) reaction, respectively. The experimental data are compared with calculation done in the framework of the IBM1 model in the O(6) and SU(5) limits.

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