Collective expansion in central Au+Au collisions.

Energy spectra for intermediate mass fragments produced in central Au+Au collisions at [ital E]/[ital A]=100MeV indicate a collective expansion at breakup. For the first time, values for this collective expansion energy per nucleon are extracted independently for each charge. Typically, these values are one-third to one-half of the incident kinetic energy per nucleon in the c.m. system, but they decrease with [ital Z][sub [ital f]], suggesting that all fragments do not participate equally in the collective expansion.