Nonequilibrium emission of neutrons from fusion-like reactions of 152-MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$

Neutron time-of-flight spectra and angular correlations were obtained in coincidence with $\gamma$ rays characteristic of the $\mathrm{xn}(x=8,9,10\mathrm{})\mathrm{}$ and $\alpha \mathrm{xn}(x=7,8\mathrm{})\mathrm{}$ fusion-like products in reactions of 151.9 MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ with ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}$. The spectra at all angles (20°, 70°, 100°, 151°) clearly indicate the presence of nonequilibrium neutron emission. The energy spectra can be represented in terms of isotropic emission in the rest frames of two moving sources. The slower of these moves with the speed of the center of mass; its emission corresponds to a temperature of ∼1.7 MeV. The faster source, characterized by a temperature of 5 to 6 MeV, has a velocity of ∼0.4 of that corresponding to the projectile energy above the Coulomb barrier. The yield of fast neutrons as a function of the exit channel is found to be in good agreement with the predictions of an extended incomplete fusion model. Comparisons are made with other models that lead to emission of fast neutrons.

NUCLEAR REACTIONS ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},xn){}_{}{}^{170-x}{}_{}{}^{}\mathrm{Yb}$ $x=8\mathrm{}-10$; ${}_{}{}^{154}{}_{}{}^{}\mathrm{Sm}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},\alpha xn){}_{}{}^{166-x}{}_{}{}^{}\mathrm{Er}$, $x=7,8\mathrm{}$; $E=151.9\mathrm{}$ MeV; measured $\sigma (E_n,{\theta }_n)$; deduced temperatures, source velocities and yields of equilibrium and pre-equilibrium neutrons, interaction times; compared with incomplete fusion, PEP, and hot-spot models.