Alpha-Gamma Reaction

The cross section of the reaction ${\mathrm{Ni}}^{58}(\alpha , \gamma ){\mathrm{Zn}}^{62}$ was measured as a function of the incident alpha-particle energy from ∼10 to 17 Mev. The cross section at 17 Mev is about 0.4 mb and decreases gradually with decreasing energy. The experimental curve is compared with calculations assuming the formation of the compound nucleus. Two different gamma-ray width formulas are used; one is Weisskopf's single-particle formula for electric dipole radiation and the other is obtained from the known gamma-ray width derived from photonuclear absorption cross sections. The former has about the right order of magnitude at the middle of the range investigated but behaves quite differently from the experimental curve. The latter shows fairly good agreement with the experiment, indicating the existence of the giant resonance. A calculation is also made for the reaction ${\mathrm{Ni}}^{60}(p, \gamma ){\mathrm{Cu}}^{61}$ cross section and the results fit quite well again with the experimental cross section reported by B. L. Cohen et al., indicating the possibility of explaining the reaction cross section without the assumption of the "capture of the proton from the orbit." In both cases, the calculated values are too low at the high-energy side. This may be explained by some failure of the assumptions in the calculations.