A. Nadasen

Bragg curve spectroscopy in a 4π geometry

Abstract Ionization counters employing Bragg curve spectroscopy have been constructed for use in a 4π geometry. These detectors compare very favorably in terms of both energy and charge resolution with small solid angle devices. These detectors have a large dynamic range because they are backed by scintillation detectors, and are thus capable of detecting and identifying particles with energies from 1 MeV/nucleon up to 200 MeV/nucleon.

Impact parameter dependence of high energy gamma ray production in heavy-ion collisions☆

Abstract High energy photons ( E γ ⩾30 MeV) have been measured in coincidence with light particles observed in a multidetector array for the 40 Ar+ 51 V system at a bombarding energy of E A =65 MeV . Double differential cross sections were obtained as a function of the midrapidity charge representation of the centrality of the collision. The inverse slope parameter increases with centrality more strongly than predicted by a BUU model.

Longitudinal collective motion in intermediate-energy heavy-ion collisions☆

Abstract Light charged fragments from the reactions 40 Ar + 51 V at 35 MeV/nucleon and 12 C + 12 C at 50 MeV/nucleon have been measured with the MSU 4π Array. The longitudinal component of the directed collective motion is extracted from both data sets. This component is observed for p, d, t, He and Li fragments and apparently decreases in strength for the two heaviest fragments, in contrast to the transverse component which has been found to increase with fragment mass. At least part of the decrease in the strength of the longitudinal component for heavier fragments is due to the low-energy thresholds of the detectors.

The sphericity of central heavy-ion reactions

We have experimentally studied small impact parameter heavy-ion collisions in the (nearly) symmetry entrance channels {sup 12}C+{sup 12}C, {sup 20}Ne+{sup 27}Al, {sup 40}Ar+{sup 45}Sc, {sup 84}Kr+{sup 93}Nb, and {sup 129}Xe+{sup 139}La, each at many intermediate beam energies. The results from a number of analyses based on a projection of the ``shapes`` of the experimental events called the sphericity are presented. Comparisons of the relative efficiencies of various experimental methods for the selection of central events are made. The importance of autocorrelations between the sphericity and the various impact-parameter--dependent variables is evaluated. Searches for beam energy-dependent transitions from sequential binary disassembly to multifragmentation in the central events are described. Comparisons to dynamic and hybrid model code calculations will be discussed. The average sphericities of the intermediate mass fragments (IMF`s, for which 3{le}{ital Z}{approx_lt}20), are presented. The possibility that the IMF emission occurs following the formation of transient toroidal or disk-like geometries in the central events is explored. Increases in the average sphericities of the central events for increasing beam energies are observed which is attributed to transitions from sequential binary disassembly to multifragmentation. The transitional beam energies for the central {sup 40}Ar+{sup 45}Sc, {sup 84}Kr+{sup 93}Nb, and {sup 129}Xe+{sup 139}La reactionsmorexa0» are near {similar_to}50, {similar_to}40, and {similar_to}40 MeV/nucleon, respectively.«xa0less

4π Fragment Measurements at MSU and the Nuclear Equation of State

In the collision of two nuclei at intermediate energies (20 – 200 MeV/nucleon) a variety of phenomena can be studied including multifragmentation, the liquid-gas phase transition in nuclear matter, energy and momentum flow, the production of entropy, and the role of thermodynamics in these collisions.1’2 These phenomena involve correlations of many particles. In such experiments it is clear that the more complete the event characterization is, the more accurate will be the understanding of the underlying phenomena. Presented here are the results from the first set of experiments using the MSU 4π Array to study nuclear collisions at intermediate energies using the NSCL K500 Superconducting Cyclotron.