C. Williams

Statistical Multifragmentation in Central Au+Au Collisions at 35 MeV/u

Abstract Multifragment disintegrations, measured for central Au + Au collisions at E A = 35 MeV , are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.

Thermal source parameters in Au+Au central collisions at 35 A MeV

Central Au+Au collisions at 35 A MeV are analyzed to find the characteristics of a thermal source, in the framework of the statistical multifragmentation model SMM. A recently introduced backtracing protocol provides an effective comparison of theory and experiment. For the first time the distributions of the central source parameters (density, mass number, excitation energy) are found. The collective energy of primary fragments is also deduced. It is shown that the backtracing procedure allows an estimation of the pre-equilibrium emission. c 1998 Published by Elsevier Science B.V.

Multifragment production in Au+Au at 35 MeV/u

Abstract Multifragment disintegration has been measured with a high efficiency detection system for the reaction Au + Au at E / A = 35 MeV. From the event shape analysis and the comparison with the predictions of a many-body trajectories calculation the data, for central collisions, are compatible with a fast emission from a unique fragment source.

Circumstantial evidence for critical behavior in peripheral Au+Au collisions at 35 MeV/nucleon.

The fragmentation resulting from peripheral Au + Au collisions at an incident energy of {ital E}=35 MeV/nucleon is investigated. A power-law charge distribution, {ital A}{sup {minus}{tau}} with {tau}{approx_equal}2.2, and an intermittency signal are observed for events selected in the region of the Campi scatter plot where {open_quote}{open_quote}critical{close_quote}{close_quote} behavior is expected. {copyright} {ital 1996 The American Physical Society.}

Charge Correlations and Dynamical Instabilities in the Multifragment Emission Process

A new, sensitive method allows one to search for the enhancement of events with nearly equal-sized fragments as predicted by theoretical calculations based on volume or surface instabilities. Simulations have been performed to investigate the sensitivity of the procedure. Experimentally, charge correlations of intermediate mass fragments emitted from heavy ion reactions at intermediate energies have been studied. No evidence for a preferred breakup into equal-sized fragments has been found. {copyright} {ital 1996 The American Physical Society.}

Circumstantial evidence for critical behavior in peripheral {ital A}{ital u}{bold +}{ital A}{ital u} collisions at 35 MeV/nucleon

The fragmentation resulting from peripheral Au + Au collisions at an incident energy of {ital E}=35 MeV/nucleon is investigated. A power-law charge distribution, {ital A}{sup {minus}{tau}} with {tau}{approx_equal}2.2, and an intermittency signal are observed for events selected in the region of the Campi scatter plot where {open_quote}{open_quote}critical{close_quote}{close_quote} behavior is expected. {copyright} {ital 1996 The American Physical Society.}

Azimuthal correlations as a test for centrality in heavy-ion collisions

Abstract Azimuthal correlations of particles emitted in collisions between 197Au target nuclei and projectiles 36Ar (at E A = 35, 50, 80 and 110 MeV ) and 129Xe (at E A = 50 MeV ) have been measured with the MSU Miniball, a 4π phoswich array with a low detection threshold. Various impact parameter filters, based on the charge-particle multiplicity, transverse energy and midrapidity charge are tested by their ability to suppress collective motion as measured by the azimuthal correlations. The usefulness of a directivity cut in selecting central collisions for these systems is evaluated.

Multifragment emission in 36Ar+197Au and 129Xe+197Au collisions. Percolation model

Abstract Relative abundances of intermediate mass fragments and light particles measured for 36 Ar+ 197 Au collisions at E A = 50, 80 and 110 MeV lie within the range of percolation model predictions, but for 129 Xe+ 197 Au collisions at E A = 50 MeV , the percolation model predicts too small admixtures of intermediate mass fragments among the emitted charged particles.

Thermalization in nucleus-nucleus collisions☆

Abstract Impact parameter dependent excited state populations of intermmediate mass fragments are investigated for 36 Ar induced reactions on 197 Au at E / A = 35 MeV. Population inversions, indicative of non-thermal excitation mechanisms, are observed in peripheral collisions characterized by low associated charged particle multiplicities. These population inversions disappear for collisions with larger associated charged particle multiplicities, consistent with a more complete thermalization for more complex final states. Discrepancies, observed in central collisions, suggest that the limit of local thermal equilibrium has not yet been observed.

Time scale for proton emission from highly excited projectiles

Abstract Highly fragmented exit channels produced by the decay of excited 24Mg projectiles were detected. The longitudinal velocity spectra of protons and alpha particles from such channels are offset. This offset is consistent with post-breakup Coulomb accelerations from the 197Au target nuclei implying that the protons were emitted within 3 X 10−22 s after the target-projectile separation.