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Lifetimes have been measured for four quadrupole bands in 142Gd with EUROBALL using the Doppler-shift attenuation method. The deduced B(E2) values have been compared with results of Interacting Boson Model calculations.

To investigate the interplay between collective and single particle degrees of freedom in odd nuclei, Recoil distance Doppler-shift and Doppler-shift attenuation lifetime measurements were carried out for levels in 155 Dy in coincidence detection of gamma-rays. 26 lifetimes were determined using the Differential decay curve method. Particle plus triaxial rotor model (PTRM) calculations were performed to compare the experimental level scheme and transition strengths with theoretical ones in order to get information on the quadrupole deformation (ǫ,γ) of the bands. As a result, different quadrupole deformations for the one-quasineutron bands at low and medium spins are deduced.

Transitions linking the highly deformed (HD) bands to states of normal deformation in 137 Sm and 139 Gd have been identified in experiments performed at GASP. The spins deduced for the HD bands in these N = 75 isotones support the previously assigned νi 13 2 [660] 1 2 + configuration. The different decay-out patterns of the two otherwise similar HD bands are tentatively explained by the difference in pairing between the Z = 62 and Z = 64 proton systems.

The four-quasiparticle magnetic dipole band in {sup 128}Ba has been investigated with the {sup 96}Zr({sup 36}S,4n){sup 128}Ba reaction at the GASP spectrometer of the Laboratori Nazionali di Legnaro. Linking transitions to the previously known positive parity states have been observed for the first time in this mass region and new transitions on top of the band have been found. The experimental results are compared to previously made tilted axis cranking calculations. {copyright} {ital 1997} {ital The American Physical Society}

The high-spin structure of 137Nd has been studied through the 110Pd(30Si,3n) and the 123Sb(19F,5n) reactions at beam energies of 125 and 97 MeV, respectively. A very complex level scheme has been established up to spin 97 2 + and 23.9 MeV of excitation energy. Regular bands are observed at high-spin, consisting of either M1 and E2 crossover transitions, or of stretched M1 or E2 transitions. Calculations have been performed in the framework of the interacting boson-fermion model with broken pairs for the relatively strong ΔI = 1 regular structures observed above spins 27 2 − and 31 2 − , which are well described by the (νh 11 2 ) 3 and νh 11 2 ⊗(πh 11 2 ) 2 configurations, respectively.

High-spin states in the doubly odd nucleus Br-76 have been investigated using the Mn-55(Si-30,2 alpha n) reaction at a beam energy of 130 MeV. Five bands have been established to high spin. The features of the level scheme, particularly the signature inversion and the band crossings in the yrast band as well as proton and neutron alignments in the negative-parity bands, are discussed in the framework of the cranked shell model. (C) 1997 Elsevier Science B.V.

The feeding mechanism of the superdeformed bands in ${}^{147}$Gd and ${}^{148}$Gd has been studied via the ${}^{124}$Sn + ${}^{29}$Si reaction at a beam energy of 157 MeV. Using the BGO inner ball of the GASP array, high-energy $\ensuremath{\gamma}$ rays have been detected in coincidence with discrete transitions deexciting normal-deformed (ND) and superdeformed (SD) states in the final product nuclei. The slope of the measured high-energy $\ensuremath{\gamma}$-ray spectra depends strongly on the number of emitted neutrons and is somewhat lower for spectra in coincidence with SD bands than for those in coincidence with ND structures. Both observations are qualitatively reproduced by statistical model Monte Carlo calculations, which point out the importance of angular momentum effects in the emission of energetic $\ensuremath{\gamma}$ rays. The present data exclude the enhanced population of SD bands when fed through high-energy $E1$ transitions.

The decay out of the yrast and excited highly deformed (HD) bands in ${}^{134}$Nd has been investigated via the ${}^{28}\mathrm{Si}{+}^{110}\mathrm{Pd}$ reaction at 130 MeV using the GASP array. Several deexcitation pathways have been established for both the yrast and excited HD bands. The resulting spins remove previous ambiguities in the assignment of the excited HD band and confirm the structure assigned to the yrast HD band. The decay out is understood in terms of mixing between the normal-deformed and HD states, which is triggered by the crossing between the $\ensuremath{\nu}{i}_{13/2}$ and $\ensuremath{\nu}{d}_{5/2}$ orbitals.

High-spin structures in 136Nd have been investigated via the 110Pd(30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i 13 2 - h 9 2 f 7 2 configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this γ-soft nucleus, can be also generated through successive pairs of h 11 2 protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported γ-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

Lifetimes have been measured in 139Sm with the DSAM method, using the reaction 62Ni(81Br,p3n)139Sm at 350 MeV. In the negative-parity regular dipole band based on the 25 2 − state at 3325 keV values of 0.60(21), 0.40(14) and 0.25(8) ps were found for the 337, 409 and 473 keV transitions, respectively. The deduced B(M1) and B(E2) are in agreement with the predictions of the tilted axis cranking model, allowing a triaxial equilibrium shape for the assumed νh 11 2 ⊗ πh 11 2 2 configuration.

The Coulomb excitation experiment to study electromagnetic structure of low-lying states in Ca-42 with a focus on a possible superdeformation in this nucleus was performed at the Laboratori Naziona ...

Expérience GANIL/VAMOS/EXOGAM; International audience; Lifetimes of first 4+ and 6+ states have been measured in neutron-rich isotopes of Zr, Mo, Ru and Pd using the recoil distance Doppler shift method at GANIL. The nuclei were produced through a fusion-fission reaction in inverse kinematics. The fission fragments were fully identified in the large-acceptance VAMOS spectrometer and -rays were detected in coincidence with the EXOGAM germanium array. Lifetimes of excited states in the range of 1-100 ps were measured with the Cologne plunger. Preliminary lifetime results are presented as well as a discussion on the evolution of the collectivity in this region.

High spin states have been observed for the first time in the odd-odd nucleus80Y, by using the24Mg(58Ni,pn) reaction at 180 MeV. Eight rotational bands have been established, indicating a nucleus with appreciable deformation.

The nuclear structure of 145Gd has been investigated via the 114Cd(36S,5n) reaction. Three superdeformed bands have been discovered, consisting of 17, 16 and 10 transitions, respectively. The first excited superdeformed band shows two band crossings which are assigned to the subsequent alignment of an i 13 2 proton pair and a crossing of the i 13 2 and i 11 2 neutron orbitals, respectively. Such a double band crossing has been observed for the first time. The second excited superdeformed band is assigned as the signature partner of the previous band but shows no band crossing in the observed frequency range. The band crossing behaviour of the SD bands has been described theoretically.

High-spin states of the neutron-rich vibrational nucleus 114 Cd have been studied using the incomplete fusion reaction 110 Pd(7Li, p2n) and the GASP spectrometer in conjunction with the ISIS Si ball. About 50 new states with excitation energies up to 7 MeV and angular momentum $I \le (18^ + )$ were observed and for many of them, spin and parity could be firmly assigned. The band-like stuctures in 114 Cd are compared to the corresponding ones in the even-even neighbour 112 Cd.

Neutron-rich Co isotopes from N = 34 to 40 were studied through multinucleon transfer by bombarding a 238U target with a 460 MeV 70Zn beam at the Legnaro National Laboratories. Gamma-recoil coincidences were recorded identifying the ions by using a high-acceptance magnetic spectrometer (PRISMA) and detecting the gamma radiation by using an array of HPGe clover detectors (CLARA). The results are discussed in comparison with the predictions of large-scale shell-model calculations.

Lifetimes of excited states in 155Dy were measured by means of the Recoil Distance Doppler-shift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne plunger using the reaction 124Sn(36S,5n)155Dy at a beam energy of 155 MeV. The Differential decay-curve method was applied for the lifetime determination. The measured transition probabilities in 155Dy and the energy spectrum are compared to the predictions of the Particle plus rotor model. The comparison indicates slightly different quadrupole deformations characterizing the low-lying one-quasineutron bands which may point to a shape coexistence.

Unfavored components of doubly decoupled bands are reported. They can be interpreted as having the pseudospin flipped relative to the orientation in the favored components, i.e., antialigned with respect to the rotation axis. In addition, the differences in consecutive transition energies along the favored and unfavored sequences are strikingly similar among them up to [ital I][sup [pi]]=15[sup +] and 14[sup +], respectively. This feature arises from a cancellation of differences in alignments and moments of inertia.

Fusion cross sections and mean angular momenta have been measured for 16 O + 112 Cd around the Coulomb barrier. The experimental results are well reproduced by coupled- channels calculations, confirming the validity of this model for mass-asymmetric systems. The predicted asymptotic behaviour of the mean angular momentum at low energies has been observed.

Neutron-rich nuclei beyond N = 126 in the lead region were populated by fragmenting a 238U beam at 1 GeV A on a Be target and then separated by the Fragment Separator (FRS) at GSI. Their isomeric decays were observed, enabling study of the shell structure of neutron-rich nuclei around the Z=82 shell closure. Some preliminary results are reported in this paper.

The Coulomb excitation experiment to study electromagnetic properties of low-lying states in 42Ca with a focus on a presumably superdeformed band was performed at the Laboratori Nazionali di Legnaro in Italy using the \gamma -ray spectrometer AGATA Demonstrator coupled to the DANTE charged particle detector array. First results are presented, including the refinement of the 42Ca level scheme.

Using the 20Ne + 12C fusion-evaporation reaction at E20Ne = 33 MeV and the multidetector array GASP in conjuction with the EUCLIDES charged particle detector, angular correlations of coincident pairs of γ transitions and lifetimes in mirror nuclei 31S and 31P have been measured at the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. A comparison of the determined B(E1) strengths of the analog mirror 7/2− → 5/2+ transitions indicates the presence of a violation of isospin symmetry.

A great deal of research work has been undertaken in the alpha-clustering study since the pioneering discovery, half a century ago, of 12C+12C molecular resonances. Our knowledge of the field of the physics of nuclear molecules has increased considerably and nuclear clustering remains one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. In this work, the occurence of "exotic" shapes in light N=Z alpha-like nuclei is investigated. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures are presented. Results on clustering aspects are also discussed for light neutron-rich Oxygen isotopes.

Transitions linking the highly deformed band to low deformation states have been unambiguously established in 133 Nd in the very first experiment performed with the GASP array. the highly deformed band becomes yrast at 29 2 + , where it mixes with the positive parity band built upon the [404] 7 2 Nilsson state. The experimentally deduced interaction amounts to 13 keV. The measurement of the spins in the highly deformed intruder band sheds some light upon the reported backbend anomaly in this mass region.

We report here on the measurements of one-particle transfer cross sections and quasi-elastic scattering of 32S+64Ni at energies around and well-below the Coulomb barrier. The experiment has been perormed with the Legnaro Recoil Mass Spectrometer. We have measured the excitation function at θcm = 170° from Elab = 68.3 to 92.4 MeV and the angular distribution at Elab = 81.3 MeV from θcm = 120° to 170°. The results have been analysed in the framework of the complex WKB theory and the semiclassical approach based on Coulomb trajectories.

Pure elastic scattering cross sections for the systems 58Ni+90,94Zr have been measured at energies of 247.5 and 232.5 MeV, making use of the ENMA spectrograph which is particularly suited for heavy‐ion reactions. Also the differential cross sections for the excitation of the first 2+ inelastic state of 58Ni in the 58Ni+90Zr combination were extracted. Simple coupled channel calculations successfully reproduce the data at 247.5 MeV while some improvement is needed for the lower energy. Calculations with the code CC‐FUS, based on the real optical model parameters extracted from the elastic scattering measurements, are compared with the previously measured fusion cross sections at energies near and below the Coulomb barrier.

In-beam γ-rays in neutron-rich sdfp shell nuclei, produced in deep-inelastic collisions of 48Ca projectiles on 48Ca target nuclei, have been studied using Ge multidetector array EU-ROBALL III. New yrast states in heavy argon isotopes have been identified.

The 24Mg + 24Mg reaction has been studied at the Legnaro Tandem at a CM bombarding energy of 45.7 MeV where a narrow and high spin resonance has been reported previously. The decay of the resonance into the inelastic and fusion-evaporation channels has been investigated. The ON and OFF resonance decay yields have been measured using, for the inelastic channels, the fragment spectrometer PRISMA and the γ array CLARA, and, for the fusion-evaporation channels, the Si array EUCLIDES and the γ array GASP The resonant effects observed in both experiments are discussed and it is suggested that the resonance populates a deformed 48Cr after a Jacobi shape transition.

Angular distributions of fragments emitted in the reaction {sup 19}F+{sup 63}Cu measured in the range {theta}{sub lab}=10{degree} to 120{degree} at incident energy between 100 to 108 MeV (lab) have been analyzed according to available models for deep inelastic collisions with the aim to evidence different mechanisms contributing to such reactions. The analysis was performed in the framework of Strutinsky model taking into account both the development of Kun and of Abul-Magd and Simbel. To determine the interaction times, previously published excitation functions were also analyzed in the framework of Kun's model of cross section statistical fluctuations and near-side and far-side scattering were taken into account separately. It was pointed out that the rotational energy dissipation occurs in a limited angular range around the grazing angle. The presence of two distinct reaction mechanisms, each of them characterized by an interaction time, was also evidenced by comparing the energy averaged angular distributions to the Abul-Magd and Simbel model for dissipative collisions.

The mean life of the 12+ level at 4195 keV in146Sm has been measured with the Recoil Distance method. The reduced strength of the E3 decay 12+→9−, about 60 W.u., confirms the collectivedouble-octupole character of the 12+ level.

Two-phonon γ-vibrational states in166Er have been populated using Coulomb excitation. The Kπ=4+ component of the vibration appears to be fragmented over several states, whereas only one Kπ=0+ state is observed.

High-spin states in 124Xe were populated by means of the 110Pd(18O,4n) reaction. In-beam γ rays were measured using the GASP spectrometer. A dipole band, similar to those previously found in other nuclei of this mass region, was identified in 124Xe.

New results on the high spin structure of the N=Z nuclei 48Cr and 52Fe are presented. Experiments were performed using the GASP array in coincidence with the 4π charged particle detector ISIS which allows a better selection of the reaction channel by γ-γ-particles and γ-γ-γ-particles coincidences.

High-spin states in the nucleus123Te have been populated by the116Cd(11B,p3n) reaction. γ-ray energies, intensities, γ-γ coincidences and DCO ratios have been measured. The level sequence build on the h11/2 isomeric state has been extended to an excitation energy of about 7 MeV.

High spin rotational bands in 162 Lu and 164 Lu have been studied through the 139 La( 28 Si,5n) and 139 La( 29(30) Si,4(5)n) reactions respectively. For both nuclei the yrast sequence which is associated with the πh 11/2 ⊗νi 13/2 configuration shows the signature inversion feature.

High-spin states in 196Pb have been populated using the reaction 170Er(30Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin.

High-spin states in the nucleus121Te have been populated by the110Pd(18O,α3n) reaction. γ-ray energies, intensities,γ-γ coincidences and DCO ratios have been measured. The level sequence build on the h11/2 isomeric state has been extended to spin I ≥51/2 and to an excitation energy of about 8.5 MeV.

High spin states of 146 Dy above the 10+ isomer have been identified by means ofγ- recoil andγ }-γ coincidences through the reaction90 Zr(58 Ni, 2pat a bombarding energy of 250 Me V. The level scheme is discussed in terms of the coupling of 2h11/2 protons to the N=80 core vibrations.

The population strengths of excited states in nuclei produced via transfer reactions in the 185 MeV32S +208Pb reaction have been investigated by heavy-ion-γ coincidence techniques. The cross sections extracted from the γ spectra, have been analyzed in the framework of the Complex WKB approximation theory.

Cold fragmentation and hot fission processes are analyzed from the viewpoint of the maximum entropy principle (MEP), which is seen to provide a good description of the main features that characterize these phenomena.

The conservation of the number of nucleons is shown to be an important constraint that governs the nuclear fission process. Both cold and energy-rich fission processes are analyzed. Particular attention is paid to the role of pairing effects in governing the fine structure in the mass and charge distributions. Symmetric and asymmetric fission processes are studied using a maximal entropy procedure. The interpretation of the results in terms of the Planck potential of the nucleons is discussed.

A simple method to separate the K X-ray emitted from fragments in flight or trapped in the backing of the source is developed, for those cases in which a transmission source is not available.