Anomalies in Yield Curves over the 992-kevAl27(p, γ)Si28Resonance

Gamma-ray yields from the ${\mathrm{Al}}^{27}(p, \gamma ){\mathrm{Si}}^{28}$ reaction have been investigated at the 992-kev resonance using ${\mathrm{H}}_1^{+}$ and ${\mathrm{H}}_2^{+}$ ions on thick and thin aluminum targets. Thick-target yield curves due to proton bombardment show a prominent peak a few hundred ev above the resonance energy. This structure was predicted by Lewis and is caused by the discrete nature of the energy losses suffered by the protons as they penetrate the target. A Monte Carlo calculation gives good agreement with the general form of the experimental curve. Diatomic ion thick-target yield curves are more complex in structure than those found with protons. The largest effect here is due to Coulomb repulsion between the two protons as they pass through the target. Internal kinetic energy of the ions makes a contribution to the structure. The Lewis effect also appears to contribute. Some information regarding the relative populations of the vibrational levels of the ions was obtained from ${\mathrm{H}}_2^{+}$ ion thin-target yield curves.