Angular-Momentum Effects in theMg24(α,Be7)andAl27(p,Be7)Reactions at 35-65 MeV

Abstract

The reaction ${\mathrm{Mg}}^{24}(\alpha ,{\mathrm{Be}}^7){\mathrm{Ne}}^{21}$ is investigated with alpha particles in the energy range 35-63 MeV. The measured cross sections are compared with the cross sections for ${\mathrm{Al}}^{27}(p,{\mathrm{Be}}^7){\mathrm{Ne}}^{21}$, a reaction which proceeds through the same compound nucleus, ${\mathrm{Si}}^{28}$. At fixed excitation energy of the compound nucleus (C.N.), the alpha-induced reaction has a higher cross section for $E_{\mathrm{C}.\mathrm{N}.\mathrm{}}>40\mathrm{}$ MeV. The cross-section ratio $\frac{\sigma \left(\alpha \right)}{\sigma \mathrm{}\left(p\right)\mathrm{}}$ increases from 4.4±1.0 at $E_{\mathrm{C}.\mathrm{N}.\mathrm{}}=50\mathrm{}$ MeV to 6.3±1.4 at $E_{\mathrm{C}.\mathrm{N}.\mathrm{}}=60\mathrm{}$ MeV. Part of this significant difference is shown to be due to angular-momentum effects in compound-nuclear processes. The balance is attributed to the multinucleon pickup by the He ion. A similar effect is observed in the reactions ${\mathrm{Al}}^{27}(p,\alpha pn)$ and ${\mathrm{Mg}}^{24}(\alpha ,\alpha pn)$.