Results of reaction cross-section measurements on 12 C, 40 Ca, 90 Zr, and 208 Pb at incident proton energies between 80 and 180 MeV and for 58 Ni at 81 MeV are presented. The experimental procedure is described, and the results are compared with earlier measurements and predictions using macroscopic and microscopic models.

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.

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.

No abstract

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 (