α clustering in Si28 probed through the identification of high-lying 0+ states

Abstract

Background: Aspects of the nuclear structure of light $\ensuremath{\alpha}$-conjugate nuclei have long been associated with nuclear clustering based on $\ensuremath{\alpha}$ particles and heavier $\ensuremath{\alpha}$-conjugate systems such as $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$. Such structures are associated with strong deformation corresponding to superdeformed or even hyperdeformed bands. Superdeformed bands have been identified in $^{40}\mathrm{Ca}$ and neighboring nuclei and find good description within shell model, mean-field, and $\ensuremath{\alpha}$-cluster models. The utility of the $\ensuremath{\alpha}$-cluster description may be probed further by extending such studies to more challenging cases comprising lighter $\ensuremath{\alpha}$-conjugate nuclei such as $^{24}\mathrm{Mg}, ^{28}\mathrm{Si}$, and $^{32}\mathrm{S}$.Purpose: The purpose of this study is to look for the number and energy of isoscalar ${0}^{+}$ states in $^{28}\mathrm{Si}$. These states are the potential bandheads for superdeformed bands in $^{28}\mathrm{Si}$ corresponding to the exotic structures of $^{28}\mathrm{Si}$. Of particular interest is locating the ${0}^{+}$ bandhead of the previously identified superdeformed band in $^{28}\mathrm{Si}$.Methods: $\ensuremath{\alpha}$-particle inelastic scattering from a $^{\mathrm{nat}}\mathrm{Si}$ target at very forward angles including ${0}^{\ensuremath{\circ}}$ 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 $^{28}\mathrm{Si}$. 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 $^{28}\mathrm{Si}$ have been identified. The number of states observed in the present experiment shows good agreement with the prediction of the multichannel dynamical symmetry.