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.

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Abstract. Most important for the identification of chiral symmetry in atomic nuclei is to establish a pair of bands that are near-degenerate in energy, but also in B(M 1) and B(E2) transition probabilities. Dedicated lifetime measurements were performed for four bands of 194 Tl, including the pair of four-quasiparticle chiral bands with close near-degeneracy, considered as a prime candidate for best chiral symmetry pair. The lifetime measurements confirm the excellent near-degeneracy in this pair and indicate that a third band may be involved in the chiral symmetry scenario.Chiral systems can exist in nuclei with triaxially deformed shape. Such nuclei rotate collectively predominantly around their intermediate axis. Should the valence nucleons have both particle and hole nature, their singleparticle angular momenta would align along the short and long nuclear axes, respectively. Then the total angular momentum of the nucleus will have large projections along the three major nuclear axes, forming a left-handed or a right-handed systems and exhibiting chiral symmetry.Nuclear chiral symmetry generates a pair of rotational bands with the same parity and with near-degenerate properties; for instance they have similar excitation energies, alignments, and reduced B(M 1) and B(E2) transition probabilities [1]. Most of the chiral bands known to date have been identified based on similarity in the excitation energy and alignments, but very often the most crucial chirality test (see ref.[2]), i.e. the similarity in the B(M 1) and B(E2) transition rates remain outstanding, because it needs dedicated lifetime measurements.The formation of more than one chiral system in the same nucleus is a very rare event. To date chiral multiplets were proposed in only two nuclei, Tl [5], including the only fourquasiparticle chiral pair known to date. This is also the only chiral pair for which chirality persists through a backbend. Furthermore, this chiral pair shows perhaps the best near-degeneracy found to date [6].The 181 Ta( 18 O, 5n) reaction was employed at a beam energy of 91 MeV. The target was a 1 mg/cm 2 181 Ta foil with a thick Bi layer evaporated on the back. The recoils were completely stopped in the Bi backing. The emitted γ-rays were detected with the AFRODITE array [7,8] at iThemba LABS, comprising 9 Compton-suppressed clover detectors, and 6 LEPS detectors. The trigger required 3 coincident γ-rays, with at least two detected in the clovers. Four clover detectors were arranged at 45• , another four were placed at 135• , while the remaining detectors were situated at 90• with respect to the beam direction. Data were sorted into two asymmetric matrices, with the γ-ray energies detected at 45• and at 135• , respectively, stored into one axis, while the coincident γ-ray energies registered at any angle were stored into the second axis. Gated, background-subtracted, forward (45 • ) and backward (135 • ) spectra were used to analyze the Doppler