The first three moments of the γ-ray multiplicity distribution were measured for individual αxn exit channels of the reactions 85-MeV ${}_{}{}^{12}{}_{}{}^{}$C${+\mathrm{}}^{154}$Sm, 109-MeV ${}_{}{}^{12}{}_{}{}^{}$C${+\mathrm{}}^{154}$Sm, and 115-MeV ${}_{}{}^{14}{}_{}{}^{}$N${+\mathrm{}}^{159}$Tb, in which massive transfer had been studied previously. The average γ multiplicity (first moment) was found to be almost constant, independent of yrast spin for fast α-particle emission, while it increases with yrast spin for slow α-particle emission as is common in complete fusion. The variance (second moment) is also independent of yrast spin. For fast α-particle emission, the average γ multiplicity decreases monotonically with increasing α-particle energy, and simultaneously the skewness (third moment) tends to be positive. This indicates that massive transfer accompanied by fast α-particle emission is similar to a quasielastic process in heavy-ion reactions. A statistical model calculation has been made to study the dependence of the γ-ray multiplicity distribution on angular momentum and excitation energy. The results are consistent with the experimental data. It is found that the sign of skewness depends on the widths of angular-momentum and excitation-energy distributions.

• Received 15 July 1985

DOI:https://doi.org/10.1103/PhysRevC.32.1539