Neck emission of intermediate-mass fragments in the fission of hot heavy nuclei

An unusual low-energy component has been observed in the spectrum of equilibriumlike intermediate-mass fragments (IMFs) emitted from systems formed in high-linear-momentum-transfer reactions of 270-MeV ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ with ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$. The properties of this component include strong focusing of IMFs at an angle perpendicular to the fission fragment separation axis, kinetic energies about one-half those for normal IMFs, and a preference for neutron-excess fragments. This behavior is consistent with emission of IMFs from the neck region of a fissioning nucleus.