Search

A major drawback of most quantum mechanical measurements is that they produce only quantities averaged over coordinates or time; nuclear physics is no exception. There is, however, an observable (the angular distribution with respect to the deformation axis of single nucleons emitted from metastable states in oriented nuclei) that is directly related to the spatial distribution of the single-particle wave function, as will be shown in this paper. It will also be argued that measuring probability densities of nucleons in nuclei (not only matrix elements) is more promising and that it should become a new trend in evaluating our understanding of nuclear structure in the future.

The low-spin collective excitations of even-even Pd nuclei in the A ≈ 110 mass region indicate a structural transition from an anharmonic vibrator to a gamma-soft rotor. This observation is supported by recent calculations of the potential energy surfaces using different types of mean field approaches. In particular, prolate-to-oblate shape transition has been predicted at 111Pd [1]. Experimental evidence for a shape change or shape coexistence can be obtained by high-spin studies of these transitional nuclei. Band crossings in the odd-N Pd nuclei are especially important to understand the origin of the alignments. No band structures built on the low-lying states were known in heavier odd Pd nuclei (A≥109). High-spin states in these nuclei cannot be populated using fusion-evaporation reactions. The heavier neutron-rich 112,114,116Pd nuclei have been studied from spontaneous fission of 252Cf [2]. In this work the less neutron-rich Pd nuclei have been produced as fission fragments following the fusion reactions 28Si + 176Yb at 145 MeV. The 28Si beam was provided by the Vivitron accelerator in Strasbourg. Gamma rays were recorded with the EUROGAM2 array [3]. The level schemes were constructed by examining γ- spectra extracted from two and three dimensional matrices.

The structure of nuclei far from stability can be investigated by means of in-beam gamma spectroscopy using both stable and radioactive beams. Two such experiments have been recently performed at GANIL. i) Secondary beams of neutron-rich Ge, Zn and Ni isotopes around N=40 were produced from the fragmentation of a primary 86 Kr beam, and analyzed by means of the LISE3 spectrometer. For the transitions between the 0+ ground state and the first 2+ state, B(E2) values have been extracted from Coulomb excitation cross-section measurement. Some of the obtained results related to the effectiveness of the N=40 spherical sub-shell closure are discussed. ii) In-beam γ-spectroscopy of neutron-rich nuclei around 32Mg produced by fragmentation of 36S have been performed recently. Gamma decay of relatively higher excited states have been measured in a large number of exotic light nuclei. Preliminary results obtained in a number of neutron-rich nuclei around N=20 are presented.