Preequilibrium emission in central collisions of the mass-symmetric system 40Ar+ 40Ca at 20 MeV/u

Abstract

In the mass symmetric system 40Ar+ 40Ca the emission of neutrons and light charged particles produced in central collisions was studied at an incident energy of 20 MeV/u. Heavy reaction products and light particles were measured inclusively as well as exclusively. The heavy reaction product data allow a separation of central and peripheral collisions. The mass difference between the observed heavy fragments and the compound system can be explained by the emission of light particles with Z ⩽ 2. For the neutrons clear evidence for preequilibrium effects is found from the shape of the energy spectra and angular distributions. The preequilibrium and equilibrium multiplicities and nuclear temperatures are extracted from the data. The experimental results are compared to various models. From a quantal phase-space model an average equilibration time is derived.