Intermediate mass fragments from the reactions 486, 550, 640, and 730 MeVKr86+63Cu

Intermediate mass fragments have been studied from the reaction ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$ ${+}^{63}$Cu for ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$ beam energies of 486, 550, 640, and 730 MeV. Average center-of-mass (c.m.) energies are nearly constant with the c.m. angle and vary little with incident energy. Furthermore, the angular distributions are well approximated by 1/sin${\mathrm{\theta }}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$. From this and other evidence we conclude that equilibration has occurred prior to fissionlike asymmetric binary breakup of the composite nucleus in the predominant mechanism for IMF production.