Inelastic Scattering of 12-Mev Protons on Lithium, Carbon, Magnesium, and Silicon

Abstract

The angular distributions of protons from the reactions ${\mathrm{Li}}^{7}(p, {p}^{\ensuremath{'}}){\mathrm{Li}}^{7*}$ ($Q=\ensuremath{-}4.61$ Mev), ${\mathrm{C}}^{12}(p, {p}^{\ensuremath{'}}){\mathrm{C}}^{12*}$ ($Q=\ensuremath{-}4.43$ Mev), ${\mathrm{Mg}}^{24}(p, {p}^{\ensuremath{'}}){\mathrm{Mg}}^{24*}$ ($Q=\ensuremath{-}1.36$ Mev), and ${\mathrm{Si}}^{28}(p, {p}^{\ensuremath{'}}){\mathrm{Si}}^{28*}$ ($Q=\ensuremath{-}1.78$ Mev) have been measured, and the cross sections for the reactions have been obtained.The lithium distribution has been analyzed in terms of (a) inelastic scattering proceeding through formation and decay of the compound nucleus, and (b) direct inelastic scattering of the Austern, Butler, McManus theory. An assignment of $J=\frac{5}{{2}^{\ensuremath{-}}}$ to the 4.61-Mev level of ${\mathrm{Li}}^{7}$ is consistent with all the experimental evidence to date; however, the intermediate coupling shell model prediction of $\frac{7}{{2}^{\ensuremath{-}}}$ should not be ruled out completely. The carbon, magnesium, and silicon distributions indicate that the statistical theory of the compound nucleus does not apply and, also, that the direct-interaction type of scattering is negligible. It appears that the reactions involving these nuclei proceed through only a few or several levels of the intermediate nuclei.For each reaction, the cross section has been compared with estimates of the cross sections for formation of the compound nucleus. The results are in qualitative agreement with the theory of decay of the compound nucleus through competing channels.