Formation and decay of hot nuclei have been studied in 64 Zn 1 nat Ti collisions between 35 and 79 MeV͞nucleon. The mass and excitation energy of excited quasiprojectiles are reconstructed from the kinematical characteristics of their decay products. In central collisions, excitation energies larger than 10 MeV͞nucleon are reached. Comparisons with theoretical predictions indicate that a fraction of the excitation energy is associated with an isotropic radial flow. [S0031-9007(96)00539-X] PACS numbers: 25.70.Lm, 21.65.+f, 25.70.Mn, 25.70.Pq One of the presently most debated questions in heavyion physics at intermediate energies focuses on the properties of hot nuclear matter and, in particular, on the so-called multifragmentation process as well as on the search for a liquid-gas phase transition. A very often invoked scenario is the occurrence of a compressionexpansion phase at the beginning of the interaction between projectile and target. In the course of such a process, after an initial compression, the hot nuclear matter expands towards low density regions where it can break up into fragments [1][2][3][4]. An alternative to this scenario is the occurrence of an expansion just arising from the pressure induced by the thermal energy [5]. From the fragment kinetic energies, we expect to gain information about the magnitude of the collective radial flow resulting from the expansion phase. Indeed, recent results show evidence for a collective energy of a few MeV͞nucleon at bombarding energies lower than 100 MeV͞nucleon [6-11], and reaching even higher values (.10 MeV͞nucleon) at higher bombarding energies [11][12][13][14][15].This Letter reports on the properties of hot nuclei formed in the 64 Zn 1 nat Ti reaction, which was investigated at GANIL at several bombarding energies between 35 and 79 MeV͞nucleon [16]. Light charged particles (LCP's: Z 1 and 2) and intermediate mass fragments (IMF's: Z $ 3) were detected in two plastic multidetectors covering a total solid angle of 84% of 4p, between 3 ± and 150 ± [17,18]. Detection of LCP's and IMF's was achieved for energies above 2.5 MeV͞nucleon. Identification of IMF's was possible only above 15-20 MeV͞nucleon. Heavier fragments were detected and identified in an additional set of seven DE-E telescopes between 3 ± and 30 ± .The events were sorted according to the violence of the collision measured by the total transverse momentum, taken as the sum of the moduli of transverse momenta of all particles detected in an event. It was assumed that the transverse momentum is maximum for head-on collisions and is a decreasing function of the impact parameter. The experimental impact parameter b exp has been derived from the measured differential cross section [16]. Results of simulations exhibit a linear relationship between b exp and the true impact parameter with a standard deviation of 1-1.5 fm [19].The correlation between the total multiplicity of charged products detected in an event and the corresponding total parallel momentum displays two distinct regions [16]. Low...
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