Tracing the evolution of temperature in near Fermi energy heavy ion collisions

Abstract

The kinetic energy variation of emitted light clusters has been employed as a clock to explore the time evolution of the temperature for thermalizing composite systems produced in the reactions of 26A, 35A and 47A MeV 64 Zn with 58 Ni, 92 Mo and 197 Au. For each system investigated, the double isotope ratio temperature curve exhibits a high maximum apparent temperature, in the range of 10-25 MeV, at high ejectile velocity. These maximum values increase with increasing projectile energy and decrease with increasing target mass. The time at which the maximum in the temperature curve is reached ranges from 80 to 130 fm/c after contact. For each different target, the subsequent cooling curves for all three projectile energies are quite similar. Temperatures comparable to those of limiting temperature systematics are reached 30 to 40 fm/c after the times corresponding to the maxima, at a time when AMD-V transport model calculations predict entry into the final evaporative or fragmentation stage of de-excitation of the hot composite systems. Evidence for the establishment of thermal and chemical equilibrium is discussed.

Ghoshal-like test of equilibration in near-Fermi-energy heavy-ion collisions

“…For each individual reaction system the IV source slope temperatures for p.d,t 3 He and 4 He are quite similar. They have values in the range of 11 to 16 MeV, characteristic of those for pre-equilibrium emission in this projectile energy range [10,17,18,19,20]. The slope parameters for the TLF sources are much lower, in the range of 4-6 MeV.…”

“…Many of the techniques applied in this analysis have been discussed previously in greater detail in references [9,10,13,14,15,16]. Only a brief summary of these techniques is included in the present work.…”

“…We recently reported on the use of double isotope yield ratio measurements to determine the temperature evolution in intermediate energy heavy ion collisions [10]. At intermediate energies the observed spectral slope parameters derived from the source fits represent only some weighted average values as the observed spectra are convolutions of the spectra at different emission times.…”

“…As the two methods should agree we employed an iterative analysis to achieve convergence for the two different techniques, using the missing IMF multiplicity as a variable. For this purpose, the average masses and kinetic energies of these missing IMF were estimated from results of earlier experiments, on some of the same systems [10,14,22]. A summary of the mass and excitation energy determinations for the TLF sources in these four systems is presented in Table 1.…”

“…In this paper we report on a Ghoshal-like test of the equilibration of medium mass hot composite nuclei produced in central collisions of 35 [8,9,10] were employed to follow the evolution of the temperatures from the time of first particle emission to the time of equilibration. The early temperature evolutions for the four different systems show a close correspondence although the time range for the observed evolution varies somewhat with reaction system.…”