Proton inelastic scattering experiments at energy E p = 200 MeV and a spectrometer scattering angle of 0 • were performed on 144,146,148,150 Nd and 152 Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150 Nd and 152 Sm, exhibit a pronounced asymmetry rather than a distinct doublehump structure expected as a signature of K-splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data.

Background: Aspects of the nuclear structure of light α-conjugate nuclei have long been associated with nuclear clustering based on α particles and heavier α-conjugate systems such as 12 C and 16 O. Such structures are associated with strong deformation corresponding to superdeformed or even hyperdeformed bands. Superdeformed bands have been identified in 40 Ca and neighboring nuclei and find good description within shell model, mean-field, and α-cluster models. The utility of the α-cluster description may be probed further by extending such studies to more challenging cases comprising lighter α-conjugate nuclei such as 24 Mg, 28 Si, and 32 S. Purpose: The purpose of this study is to look for the number and energy of isoscalar 0 + states in 28 Si. These states are the potential bandheads for superdeformed bands in 28 Si corresponding to the exotic structures of 28 Si. Of particular interest is locating the 0 + bandhead of the previously identified superdeformed band in 28 Si. Methods: α-particle inelastic scattering from a nat Si target at very forward angles including 0• has been performed at the iThemba Laboratory for Accelerator-Based Sciences in South Africa. Scattered particles corresponding to the excitation energy region of 6 to 14 MeV were momentum-analysed in the K600 magnetic spectrometer and detected at the focal plane using two multiwire drift chambers and two plastic scintillators. Results: Several 0 + states have been identified above 9 MeV in 28 Si. A newly identified 9.71 MeV 0 + state is a strong candidate for the bandhead of the previously discussed superdeformed band. The multichannel dynamical symmetry of the semimicroscopic algebraic model predicts the spectrum of the excited 0 + states. The theoretical prediction is in good agreement with the experimental finding, supporting the assignment of the 9.71-MeV state as the bandhead of a superdeformed band. Conclusion: Excited isoscalar 0+ states in 28 Si have been identified. The number of states observed in the present experiment shows good agreement with the prediction of the multichannel dynamical symmetry.

The16 O(α,α ′ ) reaction was studied at θ lab = 0• at an incident energy of E lab = 200 MeV using the K600 magnetic spectrometer at iThemba LABS. Proton decay and α decay from the natural parity states were observed in a large-acceptance silicon strip detector array at backward angles. The coincident charged-particle measurements were used to characterize the decay channels of the 0 Table I). The 0 the four-α-particle breakup threshold and has a large radius of 5 fm, indicating a dilute density structure. Ohkubo and Hirabayashi showed in a study of α + 12 C elastic and inelastic scattering [9] that the moment of inertia of the 0 + 6 state is drastically reduced, which suggests that it is a good candidate for the 4-α cluster condensate state. Calculations performed with the Tohsaki-Horiuchi-Schuck-Röpke (THSR) α-cluster wave function [10] also support this notion with an estimated total width of 34 keV for the 0 + 6 state [11], much smaller than the experimentally determined value of 166(30) keV [12].Recent unsuccessful attempts to measure particle decay widths of the 0 + 6 state in 16 O[17,18] highlighted the need for an experiment that combines α-particle decay measurements with a high-energy-resolution experimental setup and a reaction capable of preferentially populating 0 + states. In contrast to transfer reaction measurements, inelastic α-particle scattering at zero degrees has the advantage that it predominantly excites low-spin natural parity states. A measurement of the 16 O(α,α ′ ) reaction at zero degrees, coupled with coincident observations of the 16 O decay products, was performed at the iThemba Laboratory for Accelerator-Based Sciences (iThemba LABS) (7) 162 (

Background: Inelastic proton scattering at energies of a few hundred MeV and very-forward scattering angles including 0 • has been established as a tool for the study of electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Purpose: Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the isovector giant dipole resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at the iThemba Laboratory for Accelerator Based Sciences in Cape Town, South Africa. The scattering products were momentum-analyzed by the K600 magnetic spectrometer positioned at θ Lab = 0 • . Using dispersion-matching techniques, energy resolutions of E ≈ 40-50 keV (full width at half maximum) were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photoabsorption cross sections using the equivalent virtual-photon method. Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Results: Fine structure of the IVGDR is observed even for the most deformed nuclei studied. Comparisons between the extracted experimental energy scales and those energy scales obtained from the quasiparticlephonon model (QPM) and Skyrme separable random phase approximation (SSRPA) predictions provide insight into the role of different giant-resonance damping mechanisms. It can be seen that the scales in the spherical and most likely also in the deformed nuclei mainly result from the fragmentation of the one-particle-one-hole (1p1h) strength into several dominant transitions serving as doorway states. In cases where calculations beyond the 1p1h level are available, some impact of the spreading due to coupling of the two-particle-two-hole (2p2h) states to the 1p1h doorway states is observed. Conclusions: New virtual-photon absorption data for the chain of stable Nd isotopes and 152 Sm are presented, with a focus on the phenomenon of nonstatistical cross-section fluctuations, referred to as fine structure, in the energy region of the IVGDR. The wavelet-analysis techniques used allowed for the features of the fine structure to be quantified in the form of characteristic scales. Comparisons between experimental results and model predictions indicate that Landau damping seems to be the main source of the fine structure in both the spherical and deformed nuclei, but calculations including 2p2h degrees of freedom would be beneficial to confirm this for the deformed cases.