Quasi-Free Alpha-Alpha Collisions in Be9 and C12 at 28 MeV

Abstract

In the reactions Be 9 (α, 2α)He 5 and C 12 (α, 2α)Be 8 at 28 MeV, the single and summed energy spectra of emitted alpha-particles have been measured at several pairs of angle in order to investigate the quasi-free collision between incident alpha-particles and alpha-clusters in Be 9 and C 12 . The summed energy spectrum of the alpha-particles from the reaction Be 9 (α, 2α)He 5 shows a peak corresponding to the ground state of He 5 at the angles at which the emitted particles come from the collision between incident alpha-particles and nearly zero-momentum alpha-clusters in Be 9 . The momentum spread of the alpha-cluster in Be 9 coupled with He 5 (ground state) is estimated to be 0.3 fm -1 from the angular correlation of the peak in the summed energy spectrum, and the probability of finding an alpha-cluster in this state is 0.12, if a plane wave impulse approximation is assumed. In the reaction C 12 (α, 2α)Be 8 g'nd , the yield has a minimum at the angles expected from the quasi-free collision between incident alpha-particles and nearly zero-momentum alpha-clusters in C 12 . The state in which an alpha-cluster is bound to Be 8 (ground state) in C 12 seems to be very different from that for Be 9 .