ENERGY SPECTRA OF α PARTICLES EMITTED FROM THE (p,α) AND (n,α) REACTIONSDepartment of Nuclear Engineering, Kyushu University, Fukuoka 812, Japan We have measured the energy spectra of α particles emitted from (p,α) reactions on 112Cd, 118Sn, 120Sn, Sb, 128Te and 130Te with 18 MeV protons in order to clarify the shell and odd-even effects in the preequilibrium processes of (p,α) and (n,α) reactions. From the experimental results, it was found that there are no appreciable shell and odd-even effects on target nuclei in the gross (p,α) energy spectra lower than 20 MeV in the preequilibrium process. They can be explained well by the α knockout model using the effective Q values which are shell independent. The fine structures of the energy spectra for the (p,α) reactions on nuclei around atomic number 50 can be qualitatively explained using the three-nucleon pickup model under the assumption that the states excited in the (p,α) reaction are formed by the coupling of two-neutron hole states excited in a reaction such as the (p,t) reaction and one-proton hole states excited in a reaction such as the (d,3He) reaction. The similar three-nucleon pickup model can explain qualitatively the fine structures of the energy spectra for the (n,α) reactions on nuclei around neutron numbers 50 and 82. KEYWORDS: (p,α) reaction, (n,α) reaction, energy spectra, α-knockout process, three-nucleon pickup process |