Alpha Particles fromBe9andC12by 25-Mev Alpha-Particle Bombardment

Alpha-particle spectra from thin beryllium and carbon targets have been taken at 47.5° laboratory angle and an alpha energy of 25.41 Mev. The center-of-mass spectra of both nuclei indicate that the four-body reactions ${\mathrm{Be}}^9(\alpha ; 3\alpha , n)$ and ${\mathrm{C}}^{12}(\alpha ; 4\alpha )$ are greatly preferred over the three-body reactions ${\mathrm{Be}}^9(\alpha ; \alpha , n){\mathrm{Be}}^8$ and ${\mathrm{C}}^{12}(\alpha ; 2\alpha ){\mathrm{Be}}^8$. Several inelastic levels of both nuclei appear, and the recoil-decay alpha particles from the 9.61-Mev level of ${\mathrm{C}}^{12*}$ are seen. The Fermi statistical model is invoked in an attempt to establish that the multibody reactions are reasonably representative of the proportions of the two- and three-cluster configurations in the ground states of the two nuclei, and that the three-cluster configurations are preferred.