M. A. Deleplanque

Shape co-existence in 180Hg and delineation of the midshell minimum

Abstract Excited states in 180Hg have been identified. Yrast states up to spin 16+ are assigned. The decay pattern observed is indicative of a shape co-existence similar to that in the heavier Hg isotopes. The prolate deformed band is higher in energy, relative to the “oblate band”, than in 182Hg, establishing a clear minimum in the prolate-oblate energy difference near N = 103, midshell for the i 13 2 neutrons.

Coulomb excitation of 168Er

Abstract The nucleus 168Er has been Coulomb excited using beams of 40Ca, 58Ni and 208Pb. In addition lifetimes of eight states have been measured by the recoil distance method. About 50 E2 matrix elements in the ground and gamma rotational bands have been determined. The ground-band E2 matrix elements follow the predictions of a quadrupole-deformed rotor model. In the gamma band the measured E2 matrix elements exhibit a reduction of collectivity above spin 6.

High-spin state spectroscopy in 165, 166Yb

Abstract Level schemes of 165Yb and 166Yb are studied up to high spins. Triple γ-ray coincidence spectra are analyzed for the first time. The observed bands in both nuclei are interpreted in terms of the cranked-shell model. In particular, the continuation of the lowest i 13 2 single quasineutron aligned band beyond the first observed backbend is seen in an odd-N nucleus and the interaction strength between this band and the three-quasiparticle band is evaluated. Constancy of the moment of inertia in 166Yb is observed at high spins and interpreted.

Superdeformed bands in Nd nuclei

Abstract Superdeformed bands were found in 134, 136 Nd. Their dynamic moments of inertia are about as large as those of the known superdeformed bands in 135 Nd and 132 Ce, corresponding to β ≈ 0.5. A high probability for staying in band is measured for the discrete superdeformed bands in 134, 136 Nd, in contrast to the unresolved superdeformed ridges.

Loss of collectivity along the yrast line in 158Er

Abstract Lifetimes of yrast states from spin 14 through 40 have been measured in 158Er. The Doppler-shift recoil-distance method was used in conjunction with the multi-Ge detector array HERA, and γγ coincidences were analyzed. The collectivity of the nucleus drops from 200 W.u. to 110 W.u. in the region of the second backbend. By spin 38 it has decreased further to 25 W.u., consistent with a band termination.

New structures at high spin in 159Er

Abstract The nucleus 159 Er was studied with the HERA γ-ray spectrometer. Three rotational bands were extended to higher spins, and three new bands were found. It is shown that specific orbitals rather strongly influence the high-spin behavior, some states remaining collective (somewhat triaxial), others evolving towards a non-collective oblate structure. One of the new bands is a higher- K band, similar to those found in heavier nuclei.

High-spin states in 154Er and parallel proton- and neutron-core breaking

Abstract 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.

Particle-hole states at high spin in 150Dy

Abstract The level scheme of the nucleus 150 Dy up to spin around 40 was obtained using the reaction 114 Cd( 40 Ar, 4n). Above spins 20 to 22 — the highest obtainable from the valence nucleons — the breaking of the 146 Gd pproton and neutron cores occurs in separate parallel cascades.

High-spin spectroscopy of168Hf

The nucleus168Hf was studied up to spin (38+) in the yrast band and to spins (41−) and (38−) in the lowest two negative-parity bands. The onset of a proton alignment (h9/2 or i13/2 quasiparticles) is observed in these three bands for the highest transitions. A new band with even spins and negative parity was found. The interaction strength between the ground-state band and theAB band is measured.