M. J. Huang

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.}

Thermal excitation of heavy nuclei with 5–15 GeV/c antiproton, proton and pion beams

Abstract Excitation-energy distributions have been derived from measurements of 5.0–14.6 GeV/c antiproton, proton and pion reactions with 197 Au target nuclei, using the ISiS 4 π detector array. The maximum probability for producing high excitation-energy events is found for the 8 GeV/c antiproton beam relative to other hadrons, 3 He and p beams from LEAR. For protons and pions, the excitation-energy distributions are nearly independent of hadron type and beam momentum above about 8 GeV/c. The excitation energy enhancement for p beams and the saturation effect are qualitatively consistent with intranuclear cascade code predictions. For all systems studied, maximum cluster sizes are observed for residues with E ∗ /A∼6 MeV.

Nuclear temperature measurements with helium isotopes

Abstract Temperatures extracted with the family of ( 3 He , 4 He ) isotope ratio thermometers, THe, have been studied and cross-checked with temperatures, T( 4 He ∗ ) constructed from excited and ground state populations of 4 He . Empirical correction factors provide baseline corrections for sequential decay effects for THe T( 4 He ∗ ) should agree.

Direct observation of the inversion of flow

Abstract The sign of the mean transverse momentum of non-equilibrium light charged particles was determined from the circular polarization of coincident γ-rays emitted from residual nuclei for 14 N-induced reactions on 154 Sm at incident energies, E/A=35, 100 and 155 MeV. Results of the emitted α-particles at mid-central collisions show the predicted transition from mean-field dominated dynamics at low energies to nucleon-nucleon collision dominated dynamics at high energies.

Isospin independence of the H-He double isotope ratio "thermometer"

Abstract Light fragments ( d , t , 3 He, 4 He) were measured for central collisions of 112 Sn+ 112 Sn and 124 Sn+ 124 Sn at E / A =40 MeV. While individual isotope ratios depend strongly on the neutron-to-proton ratio of the entrance channel, the double ratio R H–He =[ Y ( d ) Y ( 4 He)]/[ Y ( t ) Y ( 3 He)] shows no such sensitivity. Within the assumptions of the Albergo thermometric technique, this independence is consistent with the attainment of full chemical equilibrium for each reaction at the same common temperature. However, the same independence is also predicted by calculations based on emission from an expanding emitting source, where the yield for the final double ratio is not obtained at a single well defined source temperature.

Fragment emission from modestly excited nuclear systems

Abstract Fragment emission patterns occurring in nuclear systems of modest excitation are studied. Exclusive measurement of fragment emission in 14 N+ 197 Au reactions at E A = 100, 130 and 156 MeV allows selection of central collisions where a single source dominates the decay. Low threshold measurement of IMF emission for these events allows investigation of the influence of detector threshold effects. The time scale of fragment emission is deduced using fragment-fragment velocity correlations. Comparisons are made to the predictions of a statistical decay model.

Statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following {sup 129}Xe+{sup 197}Au collisions at 30A, 40A, 50A, and 60A MeV has been studied with multidetector systems covering nearly 4{pi} in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system {sup 136}Xe+{sup 209}Bi at 28A MeV. The experimental trends are compared to statistical model predictions. {copyright} {ital 1999} {ital The American Physical Society}