Study of theMg26(p, p′γ)Reaction Mechanism at Low Energies

Abstract

The angular distribution and ${p}^{\ensuremath{'}}\ensuremath{-}\ensuremath{\gamma}$ angular correlations of the protons inelastically scattered on the first two ${2}^{+}$ excited states of ${\mathrm{Mg}}^{26}$ were measured at several energies of the incident protons between 5.67 and 6.46 MeV. The angular correlation of the inelastically scattered protons on the ${\mathrm{Mg}}^{26}$ second excited state is of the type ${0}^{+}\ensuremath{\rightarrow}{J}^{\ensuremath{\pi}}\ensuremath{\rightarrow}{2}^{+}\ensuremath{\rightarrow}{2}^{+}\ensuremath{\rightarrow}{0}^{+}$, where the heavy arrow indicates the unobserved cascade $\ensuremath{\gamma}$ rays. The angular distributions and correlations corresponding to the second level of ${\mathrm{Mg}}^{26}$ ($Q=\ensuremath{-}2.94$ MeV) are in good agreement with the predictions of the statistical model. In the case of the protons which populate the first level ($Q=\ensuremath{-}1.81$ MeV) the angular distribution varies strongly with the energy, indicating a violation of the hypotheses on which the statistical model is based. The angular correlations corresponding to the excitation of this level likewise agree only in some cases with the predictions of the statistical model. The difference in behavior of the angular distribution and angular correlations on the two levels is attributed to the differences in value of the transmission coefficients ${T}_{l}(E)$. Angular correlations for ${\mathrm{Mg}}^{26}(p, {p}^{\ensuremath{'}}\ensuremath{\gamma})$, $Q=\ensuremath{-}1.81$ MeV at energies higher than 6 MeV also suggest some contribution of the direct-interaction mechanism.