[Show abstract][Hide abstract]ABSTRACT: 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 4He, 5Li, and 8Be, were determined for spectator fragmentation, following collisions of 197Au 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.
[Show abstract][Hide abstract]ABSTRACT: 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.
[Show abstract][Hide abstract]ABSTRACT: An experimental investigation on thermodynamical observables
characterizing the conditions of multifragmenting systems is reported.
High granularity hodoscopes allowed simultaneous measurements of
isotopic and emission temperatures. HBT interferometry with light
charged particles allowed radii measurements. The disagreement between
the two temperature measurements could be related to the space-time
evolution of the fragmentation process as confirmed by density
measurements. The slope temperatures derived from the target spectator
decay fragment energy spectra suggest a dependence on the Fermi motion
within the initial system. The dependence of the Nuclear Caloric Curve
on the mass of the systems was probed.
[Show abstract][Hide abstract]ABSTRACT: t, D-60486 Frankfurt, Germany e Forschungszentrum Rossendorf, D-1314 Dresden, Germany f Max-Planck-Institut fur Kernphysik, D-69117 Heidelberg, Germany g Soltan Institute for Nuclear Studies, 00-681 Warsaw, Hoza 69, Poland h NSCL, Michigan State University, East Lansing, MI 48824, USA Energy spectra of protons emitted by the target residue in Au+Au collisions at 1 GeV/u reveal two components with different slopes attributed to preequilibrium and equilibrium emission. The relative contribution of the latter decreases rapidly with excitation energy, so that its presence becomes not apparent for the highest energy bins. It is argued therefore, that equilibrium may not be reached on the gas branch of the caloric curve. The nuclear liquid-gas phase transition thus belongs to the category of nonequilibrium phase transitions for which the concepts developed in synergetics, such as self-organized criticality, provid
[Show abstract][Hide abstract]ABSTRACT: 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.
Full-text Article · Jun 2000 · Physical Review Letters
[Show abstract][Hide abstract]ABSTRACT: Energy spectra of protons emitted by the target residue in Au + Au
collisions at 1 GeV/u were measured for different excitation energy
bins. They reveal two components with different slopes attributed to
preequilibrium and equilibrium emission. The relative contribution of
the latter decreases rapidly with excitation energy, so that its
presence becomes not apparent for the highest energy bins. It is argued
therefore, that equilibrium may not be reached on the gas branch of the
Article · Feb 1999 · Acta Physica Polonica Series B
[Show abstract][Hide abstract]ABSTRACT: Heavy-ion reactions at relativistic energies offer unique possibility for studying phase transitions in finite, hadronic systems. A general overview of this subject is given, emphasizing the most recent results on the liquid-gas transition obtained via nuclear calorimetry.
[Show abstract][Hide abstract]ABSTRACT: Ratios of the populations of ground and excited states of He-4, Li-5, and Be-8 and double ratios constructed from the yields He-3,He-4, Li-6,Li-7,Li-8, C-11,C-12,C-13 isotopes were measured for central Kr+Nb collisions at E/A = 35, 70, 100, and 120 MeV. These ratios were analyzed to estimate an apparent temperature for emission. Consistent and approximately constant apparent temperatures were obtained from the excited states of He-4, Li-5, and Be-8 nuclei and from thermometers based upon the yields of carbon isotopes. In contrast, apparent temperatures obtained from thermometers based upon the ratios using helium isotopes increase monotonically with incident energy. [S0556-2813(98)50511-0].
[Show abstract][Hide abstract]ABSTRACT: 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 theisotope and theexcited states temperatures, extracted from double ratios of isotope yields and population ratios of fragment unbound states, respectively,
are compared. p ]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.
[Show abstract][Hide abstract]ABSTRACT: Nuclear temperatures from double isotope yield ratios and excited state populations were measured for central ^86Kr + ^93Nb collision at 35 70 100 and 120 AMeV. Temperatures based on ^3He/^4He isotope ratio increase with beam energy while temperatures from excited state populations remain nearly constant around 4-5 MeV. Temperatures from the double isotope yield based on ^11C/^12C ratio are consistent with the values from excited state populations. The experimental results suggest that significant ^3He yield emitted before thermal equilibrium is reached while the fragments are mainly emitted during a low denisty stage when the system is already cooling down by light particles emission and expansion
[Show abstract][Hide abstract]ABSTRACT: The production of d,t and ^3He was measured for central ^86Kr + ^93Nb collisions at 35,70,100 and 120 AMeV and compared to the predictions of microscopic transport models and to the statistical models. The microscopic transport calculations significantly over predict the production yields of d,t and ^3He isotope and statistical model underpredict the yield of d,t and ^3He. A hybrid model seems to be able to predicts the yields of light clusters qualitatively. These calculation indicate that significant ^3He yield comes from preequilibrium emission before equilibrium is reached.
[Show abstract][Hide abstract]ABSTRACT: Spectator decay was studied for the system Au + Au at an energy of 1000 A·MeV and the decay of the interaction region at energies between 50 and 200 A·MeV. In both cases temperatures were derived from several double-ratios of neighboring isotopes and from the population of excited states in 5Li and 4He. Agreement was found among the different isotope temperatures and also among the two excited state temperatures. The comparison of isotope and excited state temperatures, however, reveals large differences, which cannot be explained by feeding corrections.At incident energies between 600 and 1000 A·MeV the energy spectra of fragments and also neutrons of the decaying projectile spectator were measured. Whereas the slope parameters of the energy spectra and mean energies for fragments with Z ≥ 2 are independent of the incident energy, a strong dependence is found for the lightest particles, so that preequilibrium contributions to the spectator decay should be taken into account.
[Show abstract][Hide abstract]ABSTRACT: Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction 197Au + 197Au at 1000 MeV per nucleon. Pairs of 3,4He and 6,7Li isotopes and pairs of 3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. 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 decayat 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 τlab = 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.
Full-text Article · Dec 1997 · Zeitschrift für Physik A Hadrons and Nuclei
[Show abstract][Hide abstract]ABSTRACT: Nuclear Isotope temperatures have been measured for Kr+Nb at E/A=35, 75
100, 120, MeV and Ar+Sc at E/A=50, 100, 150 MeV. Preliminary data show
that there are substantial differences between temperatures obtained
with isotope ratios constructed from Y(^3He)/Y(^4He) and isotope
involving Y(^11C)/Y(^12C). The magnitude of the difference is similar to
that observed between isotope temperature and excited state temperature
in Au+Au reactions The observed difference may be explained by a
temperature evolution process. Sequential decay calculations involving
such process will be discussed. This research is supported by NSF
PHY-95-28844. References: J.Pochodzalla, Proceeding of first Catania
Relativistic Ion Studies, Acicastello,Italy,May 27-31,(1996)
[Show abstract][Hide abstract]ABSTRACT: Multi-fragment decays of 129Xe, 197Au, and 238U projectiles in collisions with Be, C, Al, Cu, In, Au, and U targets at energies between E/A = 400 MeV and 1000 MeV have been studied with the ALADIN forward-spectrometer at SIS. By adding an array of 84 Si-CsI(Tl) telescopes the solid-angle coverage of the setup was extended to \theta_lab = 16 degree. This permitted the complete detection of fragments from the projectile-spectator source. The dominant feature of the systematic set of data is the Z_bound universality that is obeyed by the fragment multiplicities and correlations. These observables are invariant with respect to the entrance channel if plotted as a function of Z_bound, where Z_bound is the sum of the atomic numbers Z_i of all projectile fragments with Z_i \geq 2. No significant dependence on the bombarding energy nor on the target mass is observed. The dependence of the fragment multiplicity on the projectile mass follows a linear scaling law. The reasons for and the limits of the observed universality of spectator fragmentation are explored within the realm of the available data and with model studies. It is found that the universal properties should persist up to much higher bombarding energies than explored in this work and that they are consistent with universal features exhibited by the intranuclear cascade and statistical multifragmentation models. PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-q Comment: Plain Tex, 49 pages including 20 eps figures. Also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.html
[Show abstract][Hide abstract]ABSTRACT: Fragment distributions resulting from Au+Au collisions at an incident energy of E/A = 600 MeV are studied. From the measured fragment and neutron distributions the mass and the excitation energy of the decaying prefragments were determined. A temperature scale was derived from observed yield ratios of He and Li isotopes. The relation between this isotope temperature and the excitation energy of the system exhibits a behavior which is expected for a phase transition. The nuclear vapor regime takes over at an excitation energy of 10 MeV per nucleon, a temperature of 5 MeV, and may be characterized by a density of 0.15-0.3 normal nuclear density.
[Show abstract][Hide abstract]ABSTRACT: Electromagnetic fission of238U projectiles at E/A =600 and 1000 MeV was studied with the ALADIN spectrometer at the heavy-ion synchrotron SIS. Seven different targets (Be, C, Al, Cu, In, Au and U) were used. By considering only those fission events where the two charges added up to 92, most of the nuclear interactions were excluded. The nuclear contributions to the measured fission cross sections were determined by extrapolating from beryllium to the heavier targets with the concept of factorization. The obtained cross sections for electromagnetic fission are well reproduced by extended Weizscker-Williams calculations which include E1 and E2 excitations. The asymmetry of the fission fragments' charge distribution gives evidence for the excitation of the double giant-dipole resonance in uranium.
Article · Jun 1995 · Zeitschrift für Physik A Hadrons and Nuclei