Abstract
Multifragmentation of the system
α +
197
Au
has been studied at incident energies of 1 and 3.6 GeV/nucleon with the new 4π setup, “FASA”. A very high mean IMF multiplicity of 〈
M〉
IMF
=5.1 ± 0.8 is observed at the higher incident energy. Applying the statistical multifragmentation model of Gross, a breakup density
ϱ
ϱ
0
of about
1
7
is deduced from the relative velocity between two IMFs at large relative angles. The excitation energy increases from 4.5 MeV/nucleon at the lower beam energy to 5.5 MeV/nucleon at the higher beam energy. The time difference between the emission of two IMFs is less than 100 fm/c, justifying to call this process a simultaneous breakup.