L. Karlsson

On the observation of a transition from fusion to multifragmentation in high multiplicity 16O induced reactions

Abstract We have studied high multiplicity 16 O + Br and 16 O + Ag collisions from 10 A to 220 A MeV on an event-by-event basis. The collisions with the highest multiplicity are fusion-like for energies below 35 A MeV whereas at higher energies the onset of multifragmentation (two or more medium mass fragments) is observed with a charge distribution which gets less and less wide with increasing energy. Correlations between high moments of the charge distribution and the maximum charge or the total multiplicity have been studied. These correlations are generally well described by statistical models. Predicted signals of critical behaviour are however not observed.

Scaling properties of charged particle multiplicity distributions in oxygen induced emulsion interactions at 14.6, 60 and 200 A GeV

Abstract The multiplicity distributions of shower particles (ns) are measured in inclusive inelastic oxygen emulsion interactions. Scaling is observed in the normalized variable ns/〈ns〉 for 14.6, 60 and 200 AGeV. The dependence of 〈ns〉 on the charge flow in the forward direction (QZD) and the distribution of the number of participating projectile protons is examined. The normalized multiplicities as a function of QZD seem also to be independent of incident energies. A comparison with the Lund model Fritiof yields satisfactory agreement.

Flow effects in intermediate-energy nuclear collisions

Abstract Central events in 36 Ar and 16 O induced reactions on Ag/Br a 65±15 MeV/nucleon and 210±10 MeV nucleon bombarding energy, respectively, have been analysed. For the 36 Ar induced reaction a flow energy of about 3 MeV/nucleon has been deduced for intermediate mass fragments. Evaporative processes can be ruled out as the origin of the intermediate mass fragments since the emission time is much larger than the expansion time estimated from the flow analysis.

A search for non-statistical particle density fluctuations in 16O + Ag(Br) and 32S + Au interactions at 200 A GeV

Abstract Fluctuations in particle densities of non-statistical origin are studied in central 16 O+Ag(Br) and 32 S+Au interactions at 200 A GeV. Non-statistical fluctuations in the 32 S-induced interactions seem to enhance the local particle densities, and suggest the presence of intermittancy. The fluctuations are found to be accompanied by a clustering tendency also in the azimuthal plane. A new method for the study of azimuthal correlations is proposed.

Charged pion production and projectile breakup cIN 85A MeV 12C-induced heavy-ion reactions

Abstract Charged pions have been measured at 70° in coincidence with projectile-like fragments in 12 C + 12 C, 12 C + 116 Sn and 12 C + 124 Sn reactions at 85A MeV. Neither the π + emission nor the π − /π + ratio exhibit differences for 124 Sn and 116 Sn targets outside those expected from the isospin difference. Inconsistencies in the target mass dependence of the pion yield disappear if a correction for reabsorption is included. After this correction, we observe a strong, ~ A 1.1 , mass dependence. The projectile breakup is significantly stronger for pion-producing collisions than for the average collision indicating a much stronger abundance of central collisions.

A CCD-based system for analysis of nuclear collisions in photographic emulsion

Abstract A CCD-based system for reading and analyzing nuclear emulsion pictures is described. Profile and area measurements on tracks produced by stopping nuclei with charge 1 to 79 are presented. The charge resolution is ranging from ΔZ/Z ≤ 0.6 at a residual range of 100 μm to ΔZ/Z ≤ 0.3 at 200 μm for all charges.

Hot-zone evolution and pre-equilibrium emission in interactions between nuclei

Abstract The evolution of the hot and cold zones in intermediate energy nucleus-nucleus collisions is described by means of spherically expanding volumes and transport equations based on the Fermi-Dirac equation of state. Though the dynamical evolution of the collision is similar to that in Vlasov-Uehling-Uhlenbeck (VUU) calculations, some differences in the spectral shapes of emitted nucleons are found. The pre-equilibrium particle emission, prior to the break-up or to the evaporation stage is always found to be an important contribution to the nucleon spectra which show reasonable agreement with data.