A.O. Macchiavelli

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.

Neutron transfer reactions with very heavy ions

Abstract We have studied neutron transfer reactions induced by 132Xe on three rare-earth targets at E V C ∼ 1.1 . By using particle-particle-γ coincidence techniques we were able to identify final products and states populated in the one- and two-neutron reactions. The dependence of the transfer probabilities on the distance of closest approach is discussed in terms of effective penetration factors. The results seem to indicate the importance in two-neutron transfer of intermediate states with ≳ 6 MeV of excitation energy. The effect of excitation energy on the enhancement of the two-neutron transfer is discussed. A qualitative interpretation of the spin dependence of the one-neutron γ-ray yields in terms of the spatial localization of the wave functions involved is given.

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.

Shapes and alignments at high spin in some rare-earth nuclei

Abstract Properties of quasirotational rare-earth nuclei at high spins are studied with continuum γ-ray spectra. It is shown that the height of these spectra at each rotational frequency gives an effective moment of inertia which includes both collective and alignment effects. At high frequencies it is necessary to correct these spectra for incomplete population of the highest spin states. This feeding correction method is presented and studied in detail. It is shown that, in quasirotational nuclei, it can in general be applied successfully. The results are discussed in terms of an interplay between alignment and deformation effects. At high spins, the highly aligned orbitais from the first empty major shell (above the valence shell) play a major role. When they reach the Fermi surface, they produce large alignments visible in our spectra. The effect of the Fermi level position and of the softness toward deformation are discussed.

Mass dependence of shell effects at high rotational frequencies

Abstract The continuum γ-ray spectra from the reactions 40 Ar(170–185 MeV) + 50 Ti, 68 Zn, 82 Se, 100 Mo → 90 Zr ∗ , 108 Cd ∗ , 122 Te ∗ , 140 Nd ∗ , respectively have been studied by using a sum-energy technique. The evolution of the γ-ray spectra with sum energy (spin) suggests the presence of rotational motion at high spins. A method to correct for incomplete feeding was applied to the γ-ray spectra and effective moments of inertia were determined. The results indicate the appearance of a new source of angular momentum at high rotational frequencies. We interpret this as the alignment of high- j orbitals from the next major shell. Simple arguments, as well as cranked-shell-model calculations, are consistent with this picture. Data on band moments of inertia, from E γ − E γ correlation experiments, are also in accord with our interpretation.