26 Mg(α, α ) 26 Mg reaction -probing astrophysically important states in 26 Mg. 26 Mg reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the s-process.

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: The 22 Ne(α, n) 25 Mg reaction is an important source of neutrons for the s-process. Direct measurement of this reaction and the competing 22 Ne(α, γ) 26 Mg reaction are challenging due to the gaseous nature of both reactants, the low cross section and the experimental challenges of detecting neutrons and high-energy γ rays. Detailed knowledge of the resonance properties enables the rates to be constrained for s-process models.Purpose: Previous experimental studies have demonstrated a lack of agreement in both the number and excitation energy of levels in 26 Mg. In order to try to resolve the disagreement between different experiments, proton and deuteron inelastic scattering from 26 Mg have been used to identify excited states.Method: Proton and deuteron beams from the tandem accelerator at the Maier-Leibnitz Laboratorium at Garching, Munich were incident upon enriched 26 MgO targets. Scattered particles were momentum-analysed in the Q3D magnetic spectrograph and detected at the focal plane.Results: Reassignments of states around Ex = 10.8 − 10.83 MeV in 26 Mg suggested in previous works have been confirmed. In addition, new states in 26 Mg have been observed, two below and two above the neutron threshold. Up to six additional states above the neutron threshold may have been observed compared to experimental studies of neutron reactions on 25 Mg but some or all of these states may be due to 24 Mg contamination in the target. Finally, inconsistencies between measured resonance strengths and some previously accepted J π assignments of excited 26 Mg states have been noted.Conclusion: There are still a large number of nuclear properties in 26 Mg which have yet to be determined and levels which are, at present, not included in calculations of the reaction rates. In addition, some inconsistencies between existing nuclear data exist which must be resolved in order for the reaction rates to be properly calculated. I. ASTROPHYSICAL BACKGROUND AND SUMMARY OF PREVIOUS EXPERIMENTAL STUDIESThe slow neutron-capture process (s-process) is one of the nucleosynthetic processes responsible for the production of elements heavier than iron [1]. The neutrons which contribute to the s-process result mainly from two reactions: 13 C(α, n) 16 O and 22 Ne(α, n) 25 Mg. The 13 C(α, n) 16 O reaction is active in thermally pulsing lowmass asymptotic giant branch stars. The 22 Ne(α, n) 25 Mg reaction is active during thermal pulses in low-and intermediate-mass asymptotic giant branch (AGB) stars and in the helium-burning and carbon-shell burning stages in massive stars (see Ref.[1] and references therein). The 22 Ne(α, n) 25 Mg reaction is slightly endothermic (Q = −478.29 keV, S n = 11.093 MeV) and does not strongly operate until slightly higher temperatures are reached during either the thermal pulse in AGB stars or, in massive stars, at the end of helium burning *

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.