Target fragment distributions were measured using radiochemical techniques for 48 different fragments (28≤A≤185) from the interaction of 85 MeV/nucleon ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ with ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. The laboratory system angular distributions are forward peaked and generally flat beyond 90°. When compared to similar distributions from the 85 MeV/nucleon ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{197}$Au reaction, the U target fragment distributions are less forward peaked, consistent with lower momentum transfer. The (A=80–120) fission fragment distributions were symmetric about 90° in the moving frame, indicative of a ‘‘slow’’ process in which statistical equilibrium has been established. The average fissioning system angular momentum was deduced to be 25-35 ħ. The observation that the fragments with low N/Z showed more anisotropic distributions than fragments with high N/Z was accounted for in firestreak model calculations as being due to a single reaction mechanism with varying amounts of deposition energy. The lightest (A<60) and heaviest (A=139-169) members of the central fission-like bump in the mass distribution had moving frame angular distributions that were asymmetric in the moving frame. Furthermore, the heavy fragment complement of the ${}_{}{}^{46}{}_{}{}^{}\mathrm{Sc}$ distribution was similar in shape to the ${}_{}{}^{146}{}_{}{}^{}\mathrm{Gd}$ distribution, suggesting these fragments were produced in a new intermediate energy reaction mechanism, a fast, non-equilibrium, very asymmetric fission of a heavy nucleus.

• Received 11 July 1985

DOI:https://doi.org/10.1103/PhysRevC.33.885