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The energy at which collective transverse flow in the reaction plane disappears, the balance energy ${E}_{\mathrm{bal}}$, is found to depend on the isospin of the system using the reactions ${}^{58}\mathrm{Fe}{+}^{58}\mathrm{Fe}$ and ${}^{58}\mathrm{Ni}{+}^{58}\mathrm{Ni}$. The more neutron-rich system exhibits higher balance energies for all measured impact parameters, in agreement with the predictions of a transport model which incorporates an isospin dependent mean field and isospin dependent in-medium nucleon-nucleon cross sections.

The disappearance of collective flow in nucleus-nucleus collisions occurs at an incident energy ([ital E][sub bal]) where the attractive scattering dominant at low energies balances the repulsive scattering dominant at high energies. We have performed the first systematic study of the entrance-channel mass dependence of the disappearance of flow and hence [ital E][sub bal]. The new data presented for the C+C, Ne+Al, Ar+Sc, and Kr+Nb systems show that [ital E][sub bal] scales as [ital A][sup [minus]1/3] where [ital A] is the mass of the combined system. Boltzmann-Uehling-Uehlenbeck model calculations show trends which are in qualitative agreement with these new results.

We have measured two-fragment reduced-velocity correlation functions of the intermediate mass fragments (IMF: 3\ensuremath{\le}Z\ensuremath{\le}7) produced in multifragment final states for the Kr+Nb system (E/A=35, 45, 55, 65, and 75 MeV). From the measured correlation functions we extract mean IMF emission lifetimes (\ensuremath{\tau}) which are observed to decrease from \ensuremath{\tau}\ensuremath{\approxeq}400 fm/c at E/A=35 MeV to \ensuremath{\tau}\ensuremath{\approxeq}125 fm/c at E/A=55 MeV. For beam energies in excess of E/A=55 MeV, no further decrease in \ensuremath{\tau} is observed, indicating a possible saturation of the mean emission lifetime for IMF produced in multifragment exit channels.

We present Z distributions for fragments with 1\ensuremath{\le}Z\ensuremath{\le}12 from central collisions of $^{40}$ Ar${+}^{45}$Sc at incident energies ranging from 35 to 115 MeV/nucleon. We find that the Z distributions can be described by a power law or an exponential and steepen with increasing incident energy. Over the range of incident energies studied, the average number of intermediate mass fragments decreases while the average number of particles increases. When combined with previous results for the charge distributions, a minimum is observed in the extracted power-law parameter.

The Michigan State University 4{pi} array has been used to select central-impact-parameter events from the reaction {sup 40}Ar+{sup 51}V at incident energies from 35 to 85 MeV/nucleon. The event shape in momentum space is an observable which is shown to be sensitive to the dynamics of the fragmentation process. A comparison of the experimental event-shape distribution to sequential- and simultaneous-decay predictions suggests that a transition in the breakup process may have occurred. At 35 MeV/nucleon, a sequential-decay simulation reproduces the data. For the higher energies, the experimental distributions fall between the two contrasting predictions.

Multifragment azimuthal correlation functions have been measured as a function of beam energy and impact parameter for the Ar+Sc system ([ital E]/[ital A]=35 to 115 MeV). The observed azimuthal correlation functions---which do not require corrections for dispersion of the reaction plane---exhibit strong asymmetries which are dependent on impact parameter and beam energy. Rotational collective motion and flow seem to dominate the correlation functions at low beam energies. It is proposed that multifragment azimuthal correlation functions can provide a useful probe for intermediate energy heavy ion reaction dynamics.

Cross sections have been measured for the production of /sup 6/He, /sup 6/Li, /sup 7/Li, and /sup 7/Be in the ..cap alpha.. + ..cap alpha.. reaction between 61.5 and 158.2 MeV. The insignificance of these measurements for theories of lithium nucleosynthesis is discussed.

Production of various nuclei following bombardment of medium-mass nuclei with intermediate-energy protons is determined by observing both prompt and delayed ..gamma.. rays. The variation of production cross section with target mass and with bombarding energy over the range 80 to 160 MeV implies that between one and two nucleons are emitted in the pre-equilibrium phase of the interaction.