Properties of Very Hot Nuclei Formed in64Zn+natTiCollisions at Intermediate Energies

Abstract

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...

Statistical multifragmentation of non-spherical expanding sources in central heavy-ion collisions

“…It is, nevertheless, indispensable if the fragment kinetic energies are to be accounted for. Its magnitude has been deduced rather consistently for various reactions in this energy range and with different methods [5,20,21,26]. The increase of the equilibrated excitation energy < E * > of the source with increasing beam energy is rather small.…”

“…The possibility of collective flow, decoupled from the statistical degrees of freedom, is furthermore included. In statistical analyses for the present and similar systems, an additional collective flow component has been shown to be essential for reproducing the fragment kinetic energies [16,18,20,21,25,26,27]. Customarily, it is superimposed without considering its potential correlation with the partition degree of freedom, an assumption that finds its justification in the successful description of the experimental data that it permits [28].…”

The caloric curve of nuclei

“…As for heavier and lighter systems having the same mass asymmetry [23,24], the dominant process is the formation of a quasi-projectile (QP) and a quasi-target (QT) accompanied by dynamical emission centered around mid-rapidity. Isotopic separation was achieved for elements up to Z = 4.…”

Validation of a new “3D calorimetry” of hot nuclei with the HIPSE event generator

“…In this energy region of 10 -100 A.MeV, there is a competition between the effects of the nucleus mean field and the nucleon-nucleon interaction [1,2]. This leads to an evolution of reaction mech- * vient@lpccaen.in2p3.fr; http://caeinfo.in2p3.fr/ † deceased anisms [3], which gradually develop from complete (incomplete) fusion or deeply inelastic collisions with a statistical emission towards binary collisions [4][5][6][7] accompagnied by particle emissions at different equilibration degrees, neck emission [8][9][10][11][12] and pre-equilibrium [13,14]. It is in this context that the nuclear physicists by means of calorimetry [15], must try to isolate the hot nuclei formed during these processes and to characterize them in the best possible way.…”