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An isomeric state (T1/2=4.0±0.2ns, E*=9.915 MeV,Iπ=61/2+)has been found in149Tb by measuring the half-life of the K internal conversion line of the 184 keV E2 deexciting transition. The breaking of the neutron core is theoretically expected at that spin resulting in sizeable increase of the oblate deformation.

The nucleus 146Tb was studied from in beam γγ-and conversion electron measurements. The level scheme was established up to ∼5MeV above the (πh11/2vd3/2−1)5−β-isomer. In addition to the known (πh11/2vh11/2−1)10+ E3-isomer, the 8+ and 11+ members of this configuration were located. The levels at the yrast line are dominated by the couplings of the πh11/2vh11/2−1 valence nucleons to the collective 3− octupole state and to the πh11/2d5/2−1 and πh11/2g7/2−1 particle-hole excitations of 146Gd.

The EUROGAMarray has been used to investigate the decay out of the yrast superdeformed (SD) band in 194Pb. Eigth single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy (4877 ± 1.5 keV) and the spin (6+) of the lowest observed SD state in 194Pb are established.

The nucleus 193Pb was populated via the 168Er(30Si, 5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole ΔI = 1 cascades have been found. The 193Pb dipole bands are discussed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two-quasiproton excitation coupled to rotation aligned quasineutrons. Parallel to the dipole bands the six superdeformed bands have been discussed in the framework of microscopic mean-field calculations. The bands are interpreted as three pairs of signature partners based on quasineutron excitations. Cross-talk transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, a mean B(M1)/B(E2) ratio value of 0.15±0.04 μ N 2 /e2b2 has been extracted.

We have carried out an experiment using the reaction168Er (30Si, 5n)193Pb at a beam energy of 159MeV with EUROGAM 2 to study the superdeformed (SD) bands in193Pb. We have observed some discreteγ rays which are possible candidates for links between the yrast SD band and the low-lying levels in this odd lead isotope. These data suggest for the lowest state of the SD band 1 an excitation energy of 4217±2 keV and a spin of (23/2−).

Above-yrast states in the one-ptoton nucleus147Tb were studied in144Sm(6Li,3n)γ- and electron-measurements at the Coulomb barrier. Together with data from a separate study of147Dyβ-decay, members of all ten particle×phonon configurations of147Tb were identified, including the completeπh11/2×3− and πs1/2×3− octupole multiplets.

The 192Hg nucleus has been produced via the 36S(160Gd, 4n) reaction at a beam energy of 159 MeV. The γ-rays have been detected with the multi-detector array EUROGAM phase 1. The level scheme has been extended up to 10.4 MeV excitation energy and spin 34. Two new structures, composed of competing ΔI = 1 and ΔI = 2 transitions, have been observed and, for the first time in Mercury isotopes, some links with the previously known low-lying states have been established. These experimental results are discussed in terms of mean-field Hartree-Fock plus BCS calculations and the new bands are proposed to originate from deformation-aligned quasi-proton excitations. π(i13/2 * h9/2)kπ=11 and π(h9/2)2kπ=8+ coupled to rotation-aligned quasi-neutrons v(i13/2)n and quasi-proton π(h11/2)2 excitations.

New results on the192Hg superdeformed band have been obtained with EUROGAM. The experiment has been performed with the160Gd(36S,4n) reaction at 159 MeV. Above 800 keV the γ-ray energies differ from the previously published ones. Thus the rise of the dynamical moment of inertia\(\mathfrak{F}^{(2)} \) above ħω=0.4 MeV is no longer observed. This is in better agreement with recent cranked Hartree-Fock-Bogoliubov calculations.

Recent data from the EUROGAM array have revealed the population of the yrast superdeformed (SD) band of192Hg in the α4n exit channel of the16O+184W reaction at 113 MeV beam energy. The nucleus assignment was made on the basis of the SD band transition energies, and the observation of characteristic X-rays and lowlying yrast γ-transition of192Hg in coincidence with the SD band γ-rays. Both the feeding and decay-out patterns of the observed SD band have been found similar to the ones previously measured in the (36S,4n) reaction.

Both the magnitude and alignment of the transferred angular momentum in the reaction {sup 165}Ho + {sup 165}Ho have been measured as a function of Q value via continuum {gamma}-ray multiplicity and anisotropy techniques. Two regimes are observed: A low-Q-value regime where the aligned angular momentum component dominates over the random components, and a large-Q-value regime where the random components dominate and decrease the spin alignment.

The decay scheme of 185m + g pt has been investigated using isotopically separated samples produced by the ISOLDE facility. A level scheme of 185 Ir has been established. The 3 2 + [402] and 1 2 + [400] positive parity bands have been observed. The negative parity levels belonging to the h 9 2 and h 11 2 orbitals are discussed in the framework of the asymmetric rotor-plus-particle model.

Both the magnitude and alignment of the transferred angular momentum in the reaction 165Ho + 165Ho have been measured as a function of Q-value via continuum γ-ray multiplicity and anisotropy techniques. The spin transfer and the continuum γ-ray anisotropy increase throughout the quasi-elastic region. The spin transfer as a function of Q-value saturates at ~ 35ħ/fragment, the anisotropy peaks at a value of ~2 and then decreases to near unity for the largest Q-values. The observed anisotropies are in good agreement with predictions from an equilibrium statistical model in which thermal excitation of angular-momentum-bearing collective modes and neutron evaporation give rise to in-plane components of the angular momentum.

The structure of nuclei at very high spins can be studied by measuring correlations between ..gamma..-ray energies in the unresolved spectrum emitted. Collective rotations have been shown to produce characteristic features in such correlation spectra. The features produced by the noncollective alignment effects in some high spin Er nuclei are shown here.

The decay 187 Au → 187 Pt has been studied using on-line mass-separated sources produced at ISOCELE (ORSAY) and ISOLDE (CERN). Lifetime measurements were performed with a Gerholm spectrometer and precise conversion electron determination with a 180° spectrograph. A decay scheme is proposed. Low-lying low-spin states in 187 Pt are discussed. Special attention is given to four highly converted transitions (260.3, 262.5, 498.2 and 498.8 keV) which are tentatively considered to have large E0 components.

Erbium nuclei around N=86, which are weakly collective at spins below about 40h, have been studied at higher spin using techniques recently developed for studying continuum ..gamma.. rays. A strong collective structure appears to develop above spins aroung 40h, which can explain why no discrete lines have been observed beyond 36h. The similarity of the spectra for heavier and lighter erbium nuclei at spins (40--60) h suggests the same shape (prolate) for both.

Level properties of 185Ir were investigated by in-beam γ-spectroscopy using (α, 4n) and (α, 6n) reactions with E, ranging from 41 to 77 MeV. A well-developed system of levels built on the h 9 2 Subshell is excited. A band built on the 11 2 − isomeric state is also observed. In distinction from heavier Ir isotopes, only a single positive parity band is developed to high-spin states. Two isomers with T 1 2 = 120 ns and 40 ns are found for excitation energies above 2.2 MeV. The experimental results are discussed in terms of rotational models including the Coriolis coupling and providing for a stable triaxial shape of the 185Ir nucleus.

High-spin states of 154Er have been studied using the 21 Compton-suppressed detector array HERA following the 118Sn(40Ar, 4n) reaction at 180 MeV. A detailed analysis of the triple coincidences was performed and the level scheme of 154Er could be built up to spin 42ℏ. Calculations were performed using the deformed Woods-Saxon cranking approximation, taking into account the pairing forces. The decay scheme evolves from a weakly collective rotational structure at the lower spins to a typical non-collective one including a few characteristic multiplet-sequences: (f 7 2 2 )6,4,2,0 and (h 11 2 4 )16,14,12,10. The most striking feature seems to be the existence, above the Iπ = 36+ state (which has the maximum angular momentum available from alignment of the valence particles), of two parallel unconnected decay paths involving the separate breaking of the neutron and proton cores.

High-spin states in 187, 188 Hg have been investigated via the 163, 164 Dy ( 28 Si , x n ) reactions by in-beam γ-ray spectroscopic techniques using the “Chateau de Cristal” 4π-multidetector array. Level schemes have been established. Spins and parities of the states have been deduced from transition multipolarities obtained from measurements of the angular distribution and linear polarization of the γ-rays. The shape coexistence of both prolate and oblate band structures has been observed for the first time in 187 Hg. In 188 Hg negative-parity bands are well developed. The band structure is interpreted within the frame of the Strutinsky method with the deformed Woods-Saxon average field. Pairing behaviour with increasing spin and general features of shape coexistence in mercury nuclei are illustrated.

Excited states of187Hg have been investigated via the164Dy (28Si,5n) reaction by means of in- beam gamma-ray spectroscopy using the multidetector 4π away “Ckāteau de. Cristal”. Different bands were populated up to spin I- 45/2. Coexistence of both prolate and oblate structures is observed for the first time in an odd- A Hg isotope. The crossing of aligned and strongly coupled sequences of levels built on the vi13/2 orbital infers the near degeneracy of oblate and prolate structures in187Hg.

Rotational bands, characteristic of a superdeformed prolate shape ( e ≈0.6) and extending to above spin 60 h , have been observed in both 150 Gd and 151 Tb. The magnitudes of the moments of inertia I (2) were found to vary with frequency and the variation greatly exceeded that seen in 148,149 Gd and 151,152 Dy. The differences in the I (2) 's are attributed to the occupation of particular high- N orbitals. Moreover, contrary to the previous examples the bands in both 150 Gd and 151 Tb de-excited at a much higher rotational frequency of h ω≈0.4 MeV and this may indicate that the pair gap extends to higher frequencies in 150 Gd and 151 Tb.

Spectra of ..gamma.. rays in the 2--30-MeV range have been observed following /sup 40/Ar-induced reactions leading to the /sup 122/Te, /sup 150/Gd, and /sup 164/Er systems. Shoulders in the spectra for E/sub ..gamma../>10 MeV are interpreted as arising from the giant dipole resonance and are consistent with statistical-model calculations using the giant-dipole-resonance strength function. Their observation offers the possibility of studying nuclear shapes and dynamics as functions of temperature and spin.

Three rotational sequences in 165Yb have been extended to high spins by using the 130Te(40Ar, 5n) and 150Nd(20Ne, 5n) reactions. Evidence is presented for a reduction of the neutron pairing correlations at the highest rotational frequencies (hω > 0.40 MeV), but no quantitative measure of this reduction can be made. There appears to be a conflict with the expectations of simple CSM calculations.

A discrete γ-ray study of 155 Er has been performed. A level scheme up to spin 85/2 has been established and interpreted using the deformed Woods-Saxon cranking approximation, taking into account pairing forces. Interpretation in terms of shape coexistence, band termination and breaking of the ( Z =64, N =82) core is proposed.

The yrast superdeformed (SD) structure of 194Pb has been studied using the EUROGAM γ-ray spectrometer. New results have been obtained at low as well as at high spin values. At low frequency, the SD band has been extended to the lowest-spin SD state ever observed in the A ∼ 190 region. The energies of 194Pb and 192Hg SD bands are identical for ω < 0.25 MeV. However, they diverge for higher frequency, which rules out the idea that these two SD bands are identical. Moreover, the SD band of 194Pb is populated at lower spin values than that of 192Hg and de-excites towards normally-deformed (ND) states at a spin value lower than that of 192Hg. This suggests that the barrier separating the SD and ND minima in the potential energy surface is higher in 194Pb than in 192Hg.