No abstract

The cross sections of the 117 Sn(α, γ ) 121 Te and 117 Sn(α, p) 120 Sb reactions have been measured in the effective center of mass energy from 11.5 to 14.6 MeV. Highly enriched self-supporting 117 Sn (90%) foils were bombarded with an α beam delivered by the Bucharest IFIN-HH tandem accelerator. The induced activity of 121 Te and 120 Sb was measured with two large-volume high-purity Ge detectors in close geometry to maximize the detector efficiency. The experimental cross section and astrophysical S factor are compared with statistical model predictions for different global α-nucleus optical potentials.

The low-lying excited states in 132,134 Ba isotopes have been studied with high-resolution (p,t) reactions. The experiments were performed at the Munich Q3D spectrograph with a 25-MeV proton beam and the 1.5-m-long focal plane detector. The high-resolution triton spectra allowed the observation of levels up to ∼4 MeV. The experimental results revealed 75 excited states in 134 Ba and 79 in 132 Ba, many of them observed for the first time. The measured angular distributions compared with distorted-wave Born approximation calculations allowed spin assignments for these levels in most cases. The systematics of the monopole and quadrupole two-neutron transfer strengths is compared with the prediction of the interacting boson approximation model. The results indicate a transitional structure in 132 Ba and 134 Ba and contribute additional evidence in favor of a description between the U(5) and O(6) symmetries of the model.

No abstract

No abstract

A simple compact correlation of the energies of the lowest 0 ϩ excitation with the yrast energy ratio R 4/2 (g.s.)ϵE(4 1 ϩ )/E(2 1 ϩ ) is found to characterize all collective nuclei, regardless of structure. This correlation can be reproduced by interacting bosom approximation calculations. Collective signature observables for the states based on 0 2 ϩ excitations indicate a different structure than for the ground state configuration but systematic inconsistencies in their global behavior and discrepancies with calculations prevent a definite interpretation.Two recent areas of interest in the study of collective nuclei have been the evolution of structure with nucleon ͑especially valence nucleon͒ number, in particular the correlations of collective observables, and the structure of intrinsic excitation modes, in particular the nature of 0 ϩ modes. In the former case, recent work ͓1,2͔ has focused on the bilinear correlation of E(4 1 ϩ ) with E(2 1 ϩ ) or of the two neutron separation energies S 2n with E(2 1 ϩ ). Both these correlations basically pertain to the structural evolution of the equilibrium configuration, not that of intrinsic excitation modes. In the latter case, numerous studies of the 0 2 ϩ ͑first excited 0 ϩ state͒ have focused on possible interpretations in terms of multiphonon ͑double ␥-vibrational͒ ͓3-5͔, ␤-vibrational ͓6,7͔, or shape coexisting structures ͓8,9͔.It is the purpose of the present paper to link these two subjects by studying the correlation of the 0 2 ϩ excitation energies with the collective shape signature observable R 4/2 (g.s.)ϵE(4 1 ϩ )/E(2 1 ϩ ), and to compare the properties of the states based on the 0 2 ϩ state with those based on the ground state. The main results will be the discovery of robust simplicities in these poorly understood 0 2 ϩ excitations and evidence that their global properties are seemingly inconsistent and are not easily reproduced by model calculations.The first result is shown in Fig. 1͑a͒ for nuclei from Z ϭ8Ϫ98 where, to compare widely different nuclei, the 0 2 ϩ energies are given on the scale of E(2 1 ϩ ) values. The figure shows a remarkably simple and compact trajectory as a function of R 4/2 (g.s.). Note that the well known difficulties in attempting to understand the nature of 0 2 ϩ excitations in deformed nuclei are not resolved by this simplicity: they are still reflected in the wide range of values of the 0 2 ϩ energies for R 4/2 (g.s.)տ3.2. Nevertheless, the simplicity and robustness of the correlation argues for a simple underlying interpretation. Most of the handful of points above the main trajectory are for light actinide nuclei while the two isolated points below the trajectory are for nuclei ( 184 Hg and 98 Sr) where deformed intruder states have descended into the lowlying spectrum.To try to understand this correlation, we carried out an extensive mesh of interacting boson approximation ͑IBA͒ ͓10͔ calculations, as representative of a collective model approach. The calculations were done with the scaled Hamiltonian (2) . For 0рр1 and Ϫ...

No abstract

No abstract