16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

Abstract

The (α, 12C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A t −5 ± 1. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ T < 10 −34 cm 2 consistent with present experimental limits. The data for 24Mg(α, 12C) 16O has been studied in more detail and indicates a selective population of final states including 16O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct 8Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2 +, E x ≈ 7 MeV; 4 +, E x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated 8Be cluster overlaps and the calculated and measured (α, 12C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.