Populations of excited states and reaction mechanisms in the emission of complex fragments for collisions of 58Ni+58Ni at 11 MeV/nucleon.

Abstract

Cross sections for emission of complex fragments ({ital Z}{gt}2) in their ground and excited states are presented for the reaction {sup 58}Ni+{sup 58}Ni at a bombarding energy of 630 MeV. Measurements of energy spectra, angular distributions, and angle-integrated cross sections were made for fragments of {ital Z}=4 to 20. {gamma} rays emitted in coincidence with the fragments were measured in a 4{pi} geometry using 62 NaI detectors and 8 Compton-suppressed germanium detectors. Data presented are mostly for the cross sections extracted by {gamma}-ray techniques. A simple statistical approach to associate the ratio of cross sections for excited states and ground states to the temperature of the emitter fails to give the expected temperatures. However, it is shown that this is mostly due to the fact that the fragments that {gamma} decay are secondary fragments produced by particle decay of the primary fragments. A Hauser-Feshbach analysis accounts well for the fragment cross sections, energy spectra, and extracted temperatures, provided that evaporation from the primary fragments is included.