Dynamical approach to spectator fragmentation in Au+Au reactions at 35 MeV/A

The characteristics of fragment emission in peripheral $^{197}$Au+$^{197}$Au collisions 35 MeV/A are studied using the two clusterization approaches within framework of \emph{quantum molecular dynamics} model. Our model calculations using \emph{minimum spanning tree} (MST) algorithm and advanced clusterization method namely \emph{simulated annealing clusterization algorithm} (SACA) showed that fragment structure can be realized at an earlier time when spectators contribute significantly toward the fragment production even at such a low incident energy. Comparison of model predictions with experimental data reveals that SACA method can nicely reproduce the fragment charge yields and mean charge of the heaviest fragment. This reflects suitability of SACA method over conventional clusterization techniques to investigate spectator matter fragmentation in low energy domain.Comment: 6 pages, 5 figures, accepte

Universality of spectator fragmentation at relativistic bombarding energies

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.-qComment: Plain Tex, 49 pages including 20 eps figures. Also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.htm

Multifragmentation and Flow: Peripheral vs. central collisions

Multifragment decays of heavy nuclei have been studied at the ALADIN spectrometer system at beam energies between 100 and 1000 MeV per nucleon. The observed fragment distributions signal a universality of spectator decays at bombarding energies . The role of the radial flow for the fragmentation process is explored by comparing fragment distributions measured for Au+Au collisions at in central collisions and at in more peripheral reactions. At both energies the maximum multiplicity of intermediate mass fragments (IMFs) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at may be related to a reduction of the density in momentum space which is caused by a large collective expansion velocity component

Fragment flow and the multifragmentation phase space

Fragment distributions have been measured for Au + Au collisions at E/A 100 MeV and 1000 MeV. A high detection efficiency for fragments in nearly 4#pi# geometry was obtained by combining the Aladin forward spectrometer system and the MSU-Miniball/WU-Miniwall array. At both energies the maximum multiplicity of intermediate mass fragments normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at E/A = 100 MeV may be related to a reduction of the density in momentum space which is caused by the collective expansion velocity component. (orig.)Available from TIB Hannover: RO 801(94-46) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

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