^9Be + ^(12)C, ^9Be + ^(16)O,^9Be + ^(19)F reactions at energies below the barrier

Abstract

The ^(16)O + ^9Be reactions have been studied from E_(c.m.) = 2.0 MeV to 5.1 MeV, an energy near the top of the Coulomb barrier. The cross section for the neutron transfer reaction ^9Be(^(16)O,^(17)O^∗ (0.87 MeV))^8Be has been measured over this range by detecting the prompt 0.87 MeV γ-rays. The total fusion cross section has been determined from E_(c.m.) = 2.8 to 5.1 MeV by observing individual γ-ray transitions in the evaporation residues with a Ge(Li) detector, and then summing the separate yields. Direct processes are found to dominate the reaction yield below E_(c.m.) = 4 MeV. A comparison of the energy dependence of the fusion cross section for this reaction and the ^(12)C + ^(13)C reaction, which proceeds via the formation of the same compound nucleus, ^(25)Mg, reveals differences at sub-barrier energies. Optical model and incoming-wave boundary condition calculations are presented. Data have also been obtained for the near optimum Q-value neutron-transfer reactions ^9Be(^(12)C, ^(13)C^∗)^8Be and ^9Be(^(19)F, ^(20)F)^8Be, and these are discussed in terms of a simple model of sub-barrier direct reactions.

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