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Excited states in 124Xe were populated in the reaction 82Se(48Ca, 6 n)124Xe and γ -ray coincidence relationships were measured with the Gammasphere spectrometer. Two new bands are observed and several of the previously known bands are extended in the high- as well as in the low-spin region. Two irregular high-spin structures are also added. The irregularities are a fingerprint of a transition from collective to non-collective behaviour. Configuration assignments to the new structures are proposed on the basis of systematics and by comparing experimental properties with calculations within the framework of the cranking model. [ABSTRACT FROM AUTHOR]

High-spin states in161Lu were investigated using the EUROBALL spectrometer. A previously known triaxial superdeformed band has been extended to higher spins and a new band with similar characteristics has been discovered. Comparison to systematically occurring wobbling bands in Lu isotopes strongly suggests that these two bands represent thenw = 0 and 1 wobbling excitations in161Lu. [ABSTRACT FROM AUTHOR]

We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in 194Hg, the search for fine structure of the last superdeformed transitions in 194Pb, the primary decay-out strength analysis in 194Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states. [ABSTRACT FROM AUTHOR]

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus 143Eu using &gama;-spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction 37 Cl + 110Pd → 143Eu + 4n. The influence of thermal energy on sup erdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in γ-γ coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of Qt ≈ 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of sup erdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 γ-decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy γ-ray is required, showing the importance of the E1 cooling in the feeding mechanism of the sup erdeformed states. [ABSTRACT FROM AUTHOR]

High-spin states of the nucleus 163Lu have been populated through the fusion-evaporation reaction 139La(29Si, 5n) with a beam energy of 157 MeV. In addition to the two lowest excited triaxial strongly deformed (TSD) bands, recently interpreted as one- and two-phonon wobbling excitations, a third excited TSD band has been firmly established decaying to the yrast TSD band. The assignment of this band as a three-quasiparticle band shows together with the normal deformed (ND) level scheme the presence not only of shape coexistence between ND and TSD structures, but also an interplay of wobbling and quasiparticle excitations in the triaxial strongly deformed potential well of 163Lu. [ABSTRACT FROM AUTHOR]

High-spin properties of the triaxial strongly deformed potential well in 163Lu at excitation energies above resolvable bands have been investigated. Gated Eγ- Eγ spectra display clear ridges with moments of inertia corresponding to those observed for the discrete strongly deformed bands. A fluctuation analysis of the ridges yields a number of two-step paths of ≈ 40 and ≈ 20, when gating on triaxial strongly or normally deformed bands, respectively. These results show that a potential well at large deformation coexists with the normally deformed well, and indicate a mixing between states in the two wells at higher excitation energy. [ABSTRACT FROM AUTHOR]

Lifetimes of states in the yrast superdeformed bands of 163Lu and 164Lu were determined in a Doppler-shift attenuation-method experiment. From fractional Doppler shifts and line shapes, average transition quadrupole moments, Qt = 8.2-0.6 b and 7.1+1.0 b, were deduced for one of the bands in -0.6 +0.5 b, were deduced for one of the bands in 163Lu and 164Lu, respectively. These values are much larger than the quadrupole moment of the normal-deformed yrast band in 163 b, that was also determined in this experiment. Comparison to cranking calculations indicates that both superdeformed bands correspond to a local potential energy minimum with a pronounced triaxiality, γ∼ 20t = 4.9-0.4 +1.3 b, that was also determined in this experiment. Comparison to cranking calculations indicates that both superdeformed bands correspond to a local potential energy minimum with a pronounced triaxiality, γ∼ 20°. [ABSTRACT FROM AUTHOR]

High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h9/2 and an h11/2 quasiproton provide the two signatures of the aligning configuration. [ABSTRACT FROM AUTHOR]

Results from the measurement of the GDR built on excited states of the 147Eu compound nucleus are presented. Data corresponding to restricted regions of angular momenta and more selected data, associated with different residual nuclei are discussed. The behaviour of the GDR width, measured as a function of nuclear spin and temperature, is well described by the predictions of the thermal shape fluctuation model. [ABSTRACT FROM AUTHOR]

The nucleus 166Hf has been populated by the reaction 96Zr(74Ge,4n) using a beam energy of 310MeV. γ-rays were detected with the EUROBALL III detector array. Fourteen new normal-deformed rotational bands, of which six form coupled pairs, have been observed in 166Hf. Four previously known bands have been extended to considerably higher spin, and configurations of the new bands are proposed. Two different bands have been assigned configurations involving the same orbitals at high spin. The two coupling schemes, deformation and rotation alignment, are discussed in connection with this new observation, which calls for a formulation of co-existing coupling schemes in six-quasiparticle structures involving the same orbitals at high spin. [ABSTRACT FROM AUTHOR]

A new superdeformed band has been discovered in a EUROBALL experiment and assigned to 143Eu. It has a maximum intensity of 35% of the 143Eu yrast superdeformed band and the transition energies of the two bands are very similar. Based on comparison with cranked shell model calculations the new band is tentatively assigned the high- N intruder configuration π62ν70 and the parity and signature quantum numbers (π,α) = (−1,+1/2). In addition to the already known high-energy transition at 3361 keV another discrete line at 2715 keV was found to be in coincidence with the yrast superdeformed band. However, it was not possible to connect the decay out of either of the superdeformed bands to known normally deformed states. [ABSTRACT FROM AUTHOR]

A new region of superdeformed shapes with a pronounced triaxiality coexisting with normal deformation exists for nuclei with N ~ 94 and Z ~ 71. Calculations with the Ultimate Cranker have revealed that triaxial SD minima with γ ~ ±20° are expected for all symmetry groups (π, α). In an odd-odd nucleus, the possibility exists to exploit the various combinations of proton and neutron orbitals which are expected to sample the triaxial minima differently. A search for such structures was performed as one of the first Euroball experiments using the reactionLa(Si,4n) with thin self-supporting targets at a beam energy of 145 MeV, provided by the Legnaro XTU tandem accelerator. The preliminary analysis has provided a major extension of the known (normal deformed) level scheme inLu, in addition to ~7 new, presumably triaxial, SD bands inLu. These bands have dynamical moments of inertia similar to those found inLu. The new data are compared to expectations from calculations with the code 'Ultimate Cranker'. [ABSTRACT FROM AUTHOR]

The analysis of the fluctuations of the counts of unresolved γ-γ energy spectra can extend our knowledge of the rotational motion at high angular momentum and excitation energy above the yrast band. Detailed studies of the rotational quasi-continuum built on specific intrinsic nuclear configurations are here discussed. First, the validity of the K-selection rules in the quasi-continuum region is investigated in the case of the normal deformed nucleus Er. The γ cascades feeding into low-K and high-K bands are analyzed studying variance and covariance of the spectrum fluctuations. Low-K bands are found to be fed by a much larger effective number of cascades than high-K bands, while the covariance between pairs of gated spectra shows that the cascades feeding into low-K bands are different from those feeding into high-K bands. These findings suggest a persistence of K-selection rules in the region of excitation energy and angular momentum probed by the rotational decay of Er. As a second case, the existence of a rotational quasi-continuum in the super deformed well of Eu is discussed. An intense bump of rotationally correlated transitions is observed to develop as function of fold in the high spin region of gated spectra. Fold distribution, angular anisotropies, moment of inertia and life time show that the bump consists of fully damped super deformed transitions. This gives experimental evidence of damped rotational motion up to several MeV excitation energy above the super deformed yrast line. [ABSTRACT FROM AUTHOR]

We present shell model calculations for warm rotating nuclei, combining the cranked Nilsson mean field and a residual surface-delta two-body interaction. The model is used to describe the transition from the region of well-defined rotational bands into the region dominated by rotational damping, and the results are in overall agreement with the experimental findings. [ABSTRACT FROM AUTHOR]

Rotational motion loses its coherence as a function of the nuclear internal excitation energy. The damping process does not proceed in a continuous fashion and scars of discrete rotational bands are found, inbedded in a background of damped rotational states, regardless whether the calculations are carried out using effective or 'random' forces. The complexity of the damping mechanism is revealed in the lineshape of the ridges in the γ-γ correlation spectrum. [ABSTRACT FROM AUTHOR]

The strongly shape driving πh[541]l/2 configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ħω, the aligned angular momentum, i, and interaction strength, at the alignment of the first pair of i quasineutrons in several odd-Z rare earth-nuclei. The h[541]1/2 and h[523]7/2 bands have been studied in the stably deformed rare-earth nucleusTm to investigate these features. A difference in band crossing frequency of ∼ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2-29/2 ħ. The γ-decay pattern between the two bands is established in the crossing region and analysed in terms of a moderate shape difference between them. A theoretical estimate of the size of the interaction strength between the two bands is presented and compared to the experimental value. The observed band structure inTm is very similar to that ofLu which has 2 protons and 2 neutrons in addition. This observation is discussed in relation to the similarity of the yrast bands of the two even-even 'core' nucleiEr andYb, for which the γ-transition energies are identical within ∼0.2 keV below the vi crossing. [ABSTRACT FROM AUTHOR]

The γ-decay of the Giant Dipole Resonance (GDR) built on excited nuclear states has been measured for the nucleus143Eu. The reaction110Pd(37Cl, 4 n)143Eu at a beam energy of 165 MeV has been employed. This experiment aimed at searching the γ-decay of the GDR built on the superdeformed143Eu states, populated at high spins. High-energy γ-rays were detected in 8 large BaF2 scintillators in coincidence with discrete transitions measured with the NORDBALL array (in the configuration consisting of 17 HPGe detectors and a 2π multiplicity filter). The spectrum of high-energy γ-rays gated by low-energy transitions between states fed by the superdeformed states shows some excess of yield in the 7–10 MeV region with respect to that gated by transitions between states not populated by the superdeformed states. This excess should be due to the γ-decay of the the giant dipole oscillation along the superdeformed axis of the nucleus that is expected to have a frequency corresponding to ≈9–10 MeV (low-energy component of the GDR strength function). The measured excess, in spite of the large error bars, is found to be of the same order as predicted statistical model values. [ABSTRACT FROM AUTHOR]

The γ-decay of the Giant Dipole Resonance in hot rotating compound nuclei has provided valuable information on the nuclear structure at finite temperature. A number of experimental results showing that the nuclear shapes change with temperature and angular momentum are here reviewed. In particular we concentrate on the temperature interval from 1 to 2 MeV, rotational frequencies from 0.2 to 1.5 MeV and on nuclei in the mass regions A≈160–170 and A≈110, characterized by the prolate-oblate and spherical-oblate phase transitions, respectively. The possibility to study the shapes involved in the compound nucleus formation is also discussed. For this purpose long formation times are required and the nucleus170W formed with the reaction60Ni+110Pd, here studied, seems to be a good candidate. The gamma and particle decays were compared to those of the reaction48Ti+122Te. The comparison shows that in average the energy of the α-particles is larger for the more symmetric reaction, consistent with longer formation times and larger deformations in the pre-equilibrium stage. [ABSTRACT FROM AUTHOR]

The effective lifetimes and the intensity of the discrete transitions of the superdeformed band inDy are described using a statistical model based on a Monte Carlo simulation. The effect of the transition strength in the continuum and the energy dependence of the barrier are investigated. The importance of the mixing of superdeformed and normal states for the resulting feeding times and intensities is emphasized. The calculations are compared to experimental data, and it is shown that the discrete line shapes are sensitive to the transition strength in the continuum. [ABSTRACT FROM AUTHOR]

The linear polarization and angular correlation of continuum γ-rays have been measured for the reactionsSn(Ar, xn)Er andPd(Ar, xn)Gd. From the angular correlation experiments we find that the dominant fractions of the radiation are stretched quadrupoles (50-80%) and stretched dipoles. The linear polarization results are compatible with mainly M1 multipolarity for the dipole part of the continuum in the energy range between 0.5 and 1.6 MeV. [ABSTRACT FROM AUTHOR]

A NaI sum-spectrometer combined with Ge-counters has been used to characterize the members of the island of high spin isomers near N=82. On the basis of half lives, total γ-decay energies and discrete γ-lines, assignments of 22 isomers are given or confirmed. The isomers are localized to the region 82≦ N≦86 and Z≦68, and the excitation energies vary from 3 MeV to 12.2 MeV. An empirical relation between spin and excitation energy is presented and on this basis isomeric spin values up to (33±2)ħ are deduced. The isomers are thought to be due to strong alignment of 2 to 8 shell-model particles in a spherical or possibly weakly oblate potential. [ABSTRACT FROM AUTHOR]

The quadrupole moments of the 3/2 and 5/2 states inRh have been determined by measuring the precession of the gamma-ray angular distribution following Coulomb excitation;O andS beams have been used. The structure of the negative-parity states inRh is found to be in agreement with the model of Arima and Iachello. [ABSTRACT FROM AUTHOR]

The recoil implanation perturbed angular correlation technique, IMPACT, has been used to study the hyperfine interaction inHf in iron and gadolinium. The perturbed angular correlation through the Coulomb excited 4 state was used, thus minimizing the effect of quadrupole interactions. The effective hyperfine fields on Hf in iron and gadolinium are determined to have the same sign, negative, and magnitudes of (507±60) kOe and (304±31) kOe, respectively. Results are compared with values reported from several other experiments ostensibly measuring the same quantity. Problems inherent in the various experimental techniques are considered. [ABSTRACT FROM AUTHOR]

The number of discrete rotational bands in the nucleus 168Yb is obtained by a fluctuation analysis of the rotational ridge structure in double and triple γ coincidence matrices. The data are compared with cranked shell model calculations including a surface delta interaction. It is found that the number of calculated bands strongly depends on the interaction strength V0, and agreement between data and calculations supports the standard value V0= 27.5/A MeV. [ABSTRACT FROM AUTHOR]

A rotational band with 15 transitions has been observed inEu in an experiment with the GASP Ge detector array by thePd(Cl,5) reaction. The average energy spacing between the neighbouring transitions is 60 keV, which is similar to the energy spacings in the superdeformed bands in the mass 140 region. The band has a constant dynamic moment of inertia as suggested by Cranked Shell Model calculations. [ABSTRACT FROM AUTHOR]

Excited states of the nucleus ν123Xe have been investigated with the fusion–evaporation-reaction ν110Pd(ν18O,5n)ν123Xe at 86 MeV beam energy, using the compton-suppressed Nordball-multidetector-system at the Niels-Bohr-Institute in Risø, Denmark. The level scheme of ν123Xe was extended up to a level of tentative 53/2+ħ. Four excited bands of 3-quasiparticle-character were observed. Analyzing the directional correlation information, we could assign spin- and parity-values to all observed bands in ν123Xe. The observed band structures fit well into systematics of the neighboring nuclei ν125Xe and ν127Xe. [ABSTRACT FROM AUTHOR]

The decay of 170W* formed in reactions with two different projectile - target combinations was studied. The observed differences in the average number of emitted neutrons suggest an entrance channel effect at the highest excitation energy and angular momentum. It may be explained by different excitation energies of the equilibrated system, resulting from the emission of pre-equilibrium α-particles during a longer fusion time, in the more symmetric reaction. [ABSTRACT FROM AUTHOR]

The γ-rays following the reaction 105 McV 18O | 28Si have been measured using the EUROBALL IV, HECTOR and EUCLIDES arrays in order to investigate the predicted Jacobi shape transition. The high-energy &gama;-ray spectrum from the GDR decay indicates the presence of large deformations in the hot 46Ti nucleus, in agreement with new theoretical calculations based on the rotating liquid-drop model. [ABSTRACT FROM AUTHOR]

A new high-spin isomer in 145Sm was observed by in-beam γ-ray spectroscopy with the reaction 122Sn(27Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined to be Ex= 11147 keV, and using the generalized centroid-shift method its half-life was found to be T1/2= (7.4 ± 1.0) ns. [ABSTRACT FROM AUTHOR]

Several of the known rotational bands in 164Er are extended considerably (to around 35 h). In addition, a new coupled band is established and found to decay by an isomeric transition with t1/2 ≥ 170 nsec, to the 11t - state of the known Kπ =7− two-quasi-proton band. The new band is interpreted as a four-quasi-particle structure, with measured values of B(M1)/B(E2) consistent with the configuration [7t -] ⊗ ?i13/2[642 5/2+] ⊗ ?h9/2[523 5/2t -], i.e. [7t -]⊗ [AE,AF]. This is supported by the observation of a crossing which resembles the second i13/2 neutron crossing, BC, associated with the two-quasi-neutron band built on the configuration, [AE,AF]. The routhian of the new band is close to the sum of the individual routhians of [AE,AF] and [7−]. The cause of a small gain in energy of 130–272 keV is discussed. [ABSTRACT FROM AUTHOR]

A discrete γ-ray transition with an energy of 3360.6 keV deexciting the second lowest SD state inEu has been discovered. It carries 3.2% of the full intensity of the band and feeds into a nearly spherical state which is above the I=35/2, E=4947 keV level. The exact placement of the single-step link is, however, not established due to the specially complicated level scheme in the region of interest. The energy of the single-step link agrees well with the previously determined two-step links. [ABSTRACT FROM AUTHOR]

We report on new results for the decay of the superdeformed (SD) band inPb. No transitions linking the SD structure with the known level scheme ofPb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given. [ABSTRACT FROM AUTHOR]

The level scheme of Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the Pd( Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity. [ABSTRACT FROM AUTHOR]

An in-beam experiment with the reaction 122Sn(27Al,4np) at 127 MeV was performed at the Nordball multi-detector array in Roskilde. It provided evidence for a new high-spin isomer in 144Sm. This isomer with T1/2= (2.6 ± 0.5) ns at an excitation energy Ex= 9232 keV seems to belong to a family of isomers of similar configuration in neighbouring N= 82 nuclei. [ABSTRACT FROM AUTHOR]

A search for the γ decay of the Giant Dipole Resonance built on superdeformed (SD) nuclear configurations of 143Eu was made, using the reaction 110Pd(37Cl, 4 n)143Eu at 165 MeV. Eight large BaF2 scintillators and the NORDBALL array were used to measure high and low-energy γ-rays. The γ-spectrum gated by transitions populated by the SD states shows an excess yield at 7-10 MeV compared to the spectrum gated by transitions not populated by SD states. The comparison with statistical model predictions indicates that this excess most probably is due to γ-ray emission of the GDR built on superdeformed states. [ABSTRACT FROM AUTHOR]