Alpha particle production by molecular single-particle effect in reactions of $^{9}$Be just above the Coulomb barrier

摘要

The $\alpha $-particle production in the dissociation of $^{9}$Be on$^{209}$Bi and $^{64}$Zn at energies just above the Coulomb barrier is studiedwithin the two-center shell model approach. The dissociation of $^{9}$Be on$^{209}$Bi is caused by a molecular single-particle effect (Landau-Zenermechanism) before the nuclei reach the Coulomb barrier. Molecularsingle-particle effects do not occur at that stage of the collision for$^{9}$Be+$^{64}$Zn, and this explains the absence of fusion suppressionobserved for this system. The polarisation of the energy level of the lastneutron of $^{9}$Be and, therefore the existence of avoided crossings with thatlevel, depends on the structure of the target.