Recoil Range Evidence for the Compound-Nucleus Mechanism in Reactions between Complex Nuclei

We have measured the recoil-range distributions of 4.1-h Tb¹⁴⁹ produced in a variety of complex nuclear reactions. The targets were Pr¹⁴¹, Ce¹⁴⁰, La¹³⁹, and Ba¹³⁸; projectiles were C¹², N¹⁴, N¹⁵, O¹⁶, O¹⁸, F¹⁹, and Ne²⁰. In every case the range distributions could be fitted to a Gaussian function. The average range values give evidence for total momentum transfer, and the range straggling is consistent with nuclear evaporation. We conclude that these reactions are pure compound-nucleus reactions. Excitation energies were approximately 50 to approximately 150 MeV, corresponding to incident energies of 5 to 10.4 MeV per nucleon.