Breakup temperature of target spectators in "1"9"7Au + "1"9"7Au collisions at E/A=1000 MeV

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction "1"9"7Au+"1"9"7Au 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 observed universality of 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 #theta#_l_a_b=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. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Multifragmentation of spectators in relativistic heavy-ion reactions

Using the ALADIN forward-spectrometer at SIS we have studied multi-fragment decays of "1"9"7Au projectiles after collisions with C, Al, Cu, and Pb targets at a bombarding energy of E/A=600 MeV. The new data presented in this work comprise the measured cross sections of multi-fragment processes, the N/Z ratios of the produced fragments, and the differential distributions of fragment multiplicities and of observables built on the charge correlations within the event. The "1"9"7Au+Cu data are analyzed with the Statistical Multifragmentation Model. It is shown that all observables can be simultaneously reproduced on an absolute scale, apart from an overall normalization constant which relates the number of model events to the measured cross section. A continuous distribution of excited residual nuclei, used as input for the calculations, was derived from the criterion of a best fit to the data. It exhibits a correlation between decreasing mass number A with increasing excitation energy E_x/A and a saturation of the excitation energy at E_x/A#approx#8 MeV. (orig.)Available from TIB Hannover: RO 801(94-36) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Breakup configurations in multiple disintegration of projectile fragments

Kinematic correlations between three heavy projectile fragments produced in Au induced reactions at E/A=600 MeV are presented. The sensitivity of these correlations to the disassembly geometry is confirmed by classical three-body trajectory calculations. The simulations suggest a fast disintegration process of an highly excited system. Within the assumed scenarios the data constrain a possibly existing radial flow to a maximum value of about 1 MeV per nucleon. This radial motion can be provided by the Coulomb repulsion between the fragments if the breakup occurs out of a volume with a radius not larger than 15 fm. (orig.)SIGLEAvailable from TIB Hannover: RO 801(93-54) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Multifragmentation in peripheral nucleus-nucleus collisions

The complete fragmentation of highly excited nuclear systems into fragments of intermediate mass is observed in heavy-ion reactions at relativistic bombarding energies in the range of several hundreds of MeV per nucleon. Similar features are found for peripheral collisions between heavy nuclei and for more central collisions between a heavy and a light nucleus. The partition space explored in multifragment decays is well described by the statistical multifragmentation models. The expansion before breakup is confirmed by the analysis of the measured fragment energies of ternary events in their own rest frame. Collective radial flow is confined to rather small values in these peripheral-type reactions. Many conceptually different models seem to be capable of reproducing the charge correlations measured for the multifragment decays. (orig.)Available from TIB Hannover: RO 801(93-76) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

QMD simulation of multifragment production in heavy ion collisions at E/A=600 MeV

With the ALADIN forward spectrometer the fragmentation of gold nuclei at 600 MeV per nucleon after interaction with carbon, aluminum, copper and lead targets has been investigated. The results are compared to quantum-molecular-dynamics calculations using soft and hard equations of state as well as soft equation of state with momentum dependent forces. Whereas the QMD has been successfully applied to heavy ion collisions at lower energies, it is not possible to reproduce the fragment distributions and the light particle multiplicities observed in this experiment at relativistic energies. To study the reasons for the discrepancy between the experimental data and the simulations, we investigated the time evolution of the nuclear system after a collision and the disintegration pattern of excited nuclei in the QMD approach. (orig.)SIGLEAvailable from TIB Hannover: RO 801(93-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Charge correlations as a probe of nuclear disassembly

SIGLEAvailable from TIB Hannover: RO 801(92-23) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Universality of spectator fragmentation at relativistic bombarding energies

Multi-fragment decays of "1"2"9Xe, "1"9"7Au, and "2"3"8U 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#_l_a_b=16 . This permitted the complete detection of fragments from the projectile-spectator source. The dominant feature of the systematic set of data is the Z_b_o_u_n_d 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_b_o_u_n_d, where Z_b_o_u_n_d is the sum of the atomic numbers Z_i of all projectile fragments with Z_i#>=#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. (orig.)Available from TIB Hannover: RO 801(96-26) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Statistical fragmentation of Au projectiles at E/A=600 MeV

SIGLEAvailable from TIB Hannover: RO 801(92-17) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman