Gamma-Rays from the Alpha-Particle Bombardment of Na, Mg, Al, Si, P, S

Na, Mg, Al, Si, P, S targets have been bombarded by 7.2-Mev helium ions. The emission of gamma-radiation has been observed. Lead absorption coefficients were obtained in all cases. The values lie close to the minimum of the lead absorption curve. In the case of Al, absorption in copper has been measured and, in addition, absorption of Compton recoil electrons by aluminum has been measured by a coincidence method. The results show that a gamma-ray of energy 3.5±{}0.3 Mev is present. This agrees with a transition from the Q₂ to Q₀ state observed in the Al²⁷(αp)Si³⁰ reaction. Unequivocal energy assignments cannot be made for the remaining reactions. However, lead absorption experiments indicate the following probable values: S, 1.6±{}0.3 Mev; Mg, 3.2±{}0.6 Mev; Na, 2.3±{}0.3 Mev. The values for elements Si and P cannot be assigned until it is clear whether the absorption is above or below the minimum. Lead absorption coefficients are given. Since the gamma-ray energies are generally higher than the difference between energy levels obtained from other information, it is likely that in these cases direct transitions are preferred to cascade.