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The successes of the nuclear shell model in explaining the stability properties of magic nuclei are challenged by the observation of rotational bands for which the sequential filling of single-particle energy levels of the spherical shell model are not respected. This Letter proposes criteria for identifying the shell-model configurations appropriate for describing such bands of states.

By means of the ͑p , t͒ reaction we study the excitation spectra of 0 + states in the deformed nuclei 228 Th, 230 Th, and 232 U, using the Q3D magnetic spectrograph facility at the Munich tandem accelerator. At small reaction angles the 0 + transfer angular distributions have steeply rising cross sections which allow us to identify these states in otherwise very complicated and dense spectra. For each of these nuclei we resolve typically about ten excited states with safe 0 + assignments. The studied excitation energies range up to 2.5, 2.7, and 2.3 MeV, respectively, and the summed transfer strengths add to more than 60% of the ground state strength. As in a recent study of 158 Gd we compare with interacting boson approximation (IBA) calculations in the spdf boson space. This highly schematic collective model description, including octupole collectivity, but neglecting other relevant degrees of freedom, gives numbers of excited 0 + states in these actinide nuclei that are rather close to the observed ones.

The excitation function for the elastic scattering reaction p(18 Ne,p) 18 Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a dedicated solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus 19 Na. In addition, two-proton emission events have been identified and are discussed. PACS. PACS-key discribing text of that key-PACS-key discribing text of that key

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Lifetimes of intermediate-spin states in two rotational bands of 99 Zr have been measured. These states were populated following the neutron-induced fission of 235 U at the PF1B beamline of the Institut Laue-Langevin, Grenoble, during the EXILL-FATIMA campaign. The nucleus 99 Zr 59 exhibits shape coexistence and lies precisely on the border of an abrupt change in ground-state deformation when going from N = 58 to N = 60, making its study interesting for understanding the mechanisms involved in the rapid onset of deformation here. The B(E 2) values extracted for decays in the ν3/2[541] band allow quadrupole deformations of β 2 = 0.34(1) and 0.26(3) to be determined for the 821.6-and 1236.6-keV members, whereas β 2 = 0.32(3) was found for the 850.5-keV member of the ν3/2 [411] band. Some of the excited states known in 99 Zr have been reasonably described with interacting boson-fermion model (IBFM) calculations. Type-II shell evolution is proposed to play a major role in modifying single-particle energies in 99 Zr.

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