VIOLENT COLLISIONS AND MULTIFRAGMENT FINAL-STATES IN THE CA-40-40 REACTION AT 35 MEV(CA)NUCLEON/

The 4pi multidetector AMPHORA has been used to measure yield distribut ions and energy spectra for products of the collisions in the reaction s of Ca-40 with Ca-40 at 35 MeV/nucleon. Events of high multiplicity ( greater-than-or-equal-to 10) for which greater-than-or-equal-to 85% of the total entrance channel atomic number is detected have been isolat ed and found to result from the most violent collisions which lead to excitation energies near 6 MeV/nucleon. A large fraction of these coll isions lead to multifragment final states. A detailed comparison of th e experimental data with results of various models indicates that stat istical models which allow for expansion of the system or treat the mu ltifragmentation process as a simultaneous disassembly are more succes sful than normal sequential binary models at reproducing the yield dat a and the event complexity inherent in the multifragment events. Quant um molecular dynamic (QMD) calculations are found to provide generally good agreement with the data but overestimate the proton and neutron emission. The agreement is significantly improved if an appropriate af terburner is used to deexcite the separated primary QMD fragments. The sensitivity of such hybrid calculations to the assumed matching time between the dynamical calculation and the afterburner has been explore d. The experimentally filtered QMD calculations which provide good agr eement with the experimental observables suggest that the most complex events observed in this work come not from the most central collision s, which decay more by light particle emission, but from a region of i mpact parameter b/b(max) = 0.5. This suggests that angular momentum ef fects play an important role in the multifragment decay modes. A compa rison of the present results with those for projectile fragmentation i n intermediate impact parameter collisions of 600 MeV/nucleon Au-197 w ith Cu indicates that a similar multifragmenting system is produced in the two very different reaction systems.