Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction 197 The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decay at relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations.The energy spectra of light charged particles, measured at θ lab = 150• , exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage. Keywords:197 Au projectiles and targets, E/A = 600 and 1000 MeV; measured fragment cross sections, isotopic yield ratios; deduced breakup temperatures, pre-breakup emission; analysis using quantum statistical and statistical multifragmentation models.

Breakup temperatures in central collisions of 197 Au 1 197 Au at bombarding energies E͞A 50 to 200 MeV were determined with two methods. Isotope temperatures, deduced from double ratios of hydrogen, helium, and lithium isotopic yields, increase monotonically with bombarding energy from 5 to 12 MeV, in qualitative agreement with a scenario of chemical freeze-out after adiabatic expansion. Excited-state temperatures, derived from yield ratios of states in 4 He, 5,6 Li, and 8 Be, are about 5 MeV, independent of the projectile energy, and seem to reflect the internal temperature of fragments at their final separation from the system. [ S0031-9007(98) . The temperatures were derived from double ratios of helium and lithium isotopic yields while the excitation energies were obtained by adding up the kinetic energies of the product nuclei and the mass excess of the observed partition with respect to the ground state of the reconstructed spectator nucleus. The double-bended shape of the caloric curve and its similarity to predictions of microscopic statistical models [2][3][4], has stimulated considerable experimental and theoretical activities. In particular, the second rise of the temperature to values exceeding 10 MeV at high excitation energies has initiated the discussion of whether nuclear temperatures of this magnitude can be measured reliably (see , and references given in these recent papers) and whether this observation may indeed be linked to a transition towards the vapor phase [7,8]. Obviously, a well-founded understanding of the significance of the employed temperature observables [9] is indispensable when searching for signals of the predicted liquid-gas phase transition in nuclear matter.Here, we present the results of temperature measurements for central collisions of 197 Au 1 197 Au at incident energies E͞A 50 to 200 MeV. These collisions are characterized by a collective radial flow of light particles and fragments which, over the covered energy range, evolves as a dynamical phenomenon closely connected to the initial stages of the reaction [10]. Global equilibrium is clearly not achieved. If local equilibrium is reached, the associated temperatures should reflect the adiabatic cooling of the rapidly expanding system. Two temperature observables were used simultaneously. Isotope temperatures were deduced from double ratios of isotopic yields [11] and excited-state temperatures were derived from the correlated yields of lightparticle coincidences [9,12,13]. It will become evident from the diverging results that this represents more than a methodical test and that the two types of thermometers are sensitive to different stages of the fragment formation and emission.Beams of 197 Au with E͞A 50, 100, 150, and 200 MeV, provided by the heavy-ion synchrotron SIS, were directed onto targets of 75 mg͞cm 2 areal density. Two multidetector hodoscopes, consisting of 96 and of 64 Si-CsI(Tl) telescopes in closely packed geometries, were placed on opposite sides with respect to the beam axis. Four high-resolution te...

Kinetic energies of light fragments A <= 10 from the decay of target spectators in 197Au 197Au collisions at 1000 MeV per nucleon have been measured with high-resolution telescopes at backward angles. Except for protons and apart from the observed evaporation components, the kinetic-energy spectra exhibit slope temperatures of about 17 MeV, independent of the particle species, but not corresponding to the thermal or chemical degrees of freedom at breakup. It is suggested that these slope temperatures may reflect the intrinsic Fermi motion and thus the bulk density of the spectator system at the instant of becoming unstable. PACS numbers: 25.70.Pq, 21.65.+f, 25.70.MnComment: 11 pages, with 4 included figures; Accepted by Phys. Rev. Lett.; Also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.htm

Temperatures for hot nuclear systems formed in nucleus-nucleus collisions have been extracted from the comparison of ratios of isotopic yields, T iso [1][2][3][4][5][6][7], and excited state populations, T E ∆ [4,7,[9][10][11][12]. For thermal distributions at low density and at chemical equilibrium, prior to the secondary decay of the excited fragments, the double ratios R iso of the ground state yields of four suitably chosen isotopes are given by [1]:

Isotope temperatures from double ratios of hydrogen, helium, lithium, beryllium, and carbon isotopic yields, and excited-state temperatures from yield ratios of particle-unstable resonances in 4 He, 5 Li, and 8 Be, were determined for spectator fragmentation, following collisions of 197 Au with targets ranging from C to Au at incident energies of 600 and 1000 MeV per nucleon. A deviation of the isotopic from the excited-state temperatures is observed which coincides with the transition from residue formation to multi-fragment production, suggesting a chemical freeze-out prior to thermal freeze-out in bulk disintegrations.

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Generalized isoscaling relationships are proposed that may permit one to relate the isotopic distributions of systems that may not be at the same temperature. The proposed relationships are applied to multifragmentation excitation functions for central Kr+Nb and Ar+Sc collisions.

Temperature-excitation energy correlation measurements on several systems at different incident energies are discussed in the framework of the investigation on possible liquid-gas phase transition in nuclear matter. Results are compared to the presently available experimental caloric curves. Moreover the isotope and the excited states temperatures, extracted from double ratios of isotope yields and population ratios of fragment unbound states, respectively, are compared. The differences on the temperatures deduced from the two methods cannot be accounted for by the sequential feeding corrections. Instead, they seem to be related to the space-time evolution of the fragmentation process. PACS 25.70.Pq -Multifragment emission and correlations. PACS 25.70.Mn -Projectile and target fragmentation.