S. Hannuschke

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.

Tracking fission-like processes in central collisions of 40Ar+232Th; E = 15–115 A MeV

Abstract Fission-like fragments and coincident charged particles have been measured in a 4π geometry over a wide energy range (15–115 A MeV) for the reaction 40 Ar+ 232 Th. The exclusive folding angle distribution data provide direct evidence that fission-like processes following incomplete-fusion are still an appreciable exit channel for beam energies as high as 115 A MeV.

High-order azimuthal correlation functions: powerful probes for collective motion in heavy ion reactions

Abstract We have investigated the utility of high-order azimuthal correlation functions as probes of collective motion from both rotation and flow at intermediate energies. Reaction simulations indicate new and distinct signatures for rotational collective motion which are important for its characterization and its distinction from collective flow. For the system Ar + Sc(35−115A MeV), experimental high-order correlation functions are used for a clear demonstration of the disappearance of collective flow at 93±4 A MeV. The method is direct and circumvents reaction-plane assignment.

Portable data flow in UNIX

We describe the dataflow of a nuclear physics data acquisition system. The system features a high speed active routing subsystem which allows an arbitrary number of data producers to contribute data to the system. Data are then routed to an arbitrary number of data consumers. Low overhead route-by-reference mechanisms are used to allow high rate operations. The system has been ported to a variety of UNIX systems. Timings are given for the routing component of the system on several systems. Finally, we give an example of a set of programs which can be added to the system to produce a complete data acquisition system. >

A transputer based parallel processing frontend data acquisition system

A new parallel processing front end for data acquisition has been designed and built at NSCL. This system, using inmost T800 transputers, is designed to add the capacity of realtime data filtering to the normal operations of NSCL frontends and improve overall performance. The initial system is designed for 5 transputers linked to a SUN host system via transputer links. A prototype system with one node is currently used as the data acquisition system for the NSCL 4[pi] detector. The multinode system has been installed and tested. Filter software is under development.

Peripheral Reaction Mechanisms in Intermediate Energy Heavy-Ion Reactions

At beam energies up to E/A = 20 MeV deep-inelastic reactions are the dominant reaction mechanism for heavy-ion peripheral collisions. These reactions are characterized by broadening of the mass and charge distributions with increasing energy loss or excitation energy and by orbiting in the deflection functions. Excitation energy is produced through the relative momentum of exchanged nucleons. The deep-inelastic reaction mechanism is a very efficient way to produce hot nuclei at relatively low beam energies.

Projectile Like Fragments from 129Xe + natCu reactions at E/A = 30, 40, 50 MeV

There has been a great deal of experimental and theoretical interest in the modes of dissassembly of highly excited nuclear matter. However, the mechanisms by which these hot nuclei are formed is also important to the study of the energy dependence of the influence of the nuclear mean field. One method to form an excited system is via a damped reaction. First observed at energies just above the Coulomb barrier, damped reactions were thought to occur only at low energies. The persistance of the damped reaction mechanism into the intermediate energy regime, between 20 and 100 MeV per nucleon, has recently been seen experimentally[1, 2]. But how high in energy do damped reactions occur? In order to measure an excitation function for damped reactions, an experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL) on the campus of Michigan State University (MSU). The experiment consisted of a 129Xe beam at energies of 30, 40, 50, and 60 MeV per nucleon incident on targets of nat Cu and nat Sc. Reaction products where detecting using the MSU 4πdetector system[3] augmented by the Maryland Forward Array[4] (MFA), a detector that covers between 1.4° and 2.9° from the beam in the laboratory.

The Disappearance of Fusion/Fission

The disappearance of fusion/fission has been studied for reactions of 40Ar + 232Th at incident energies ranging from 15 to 115 MeV/nucleon using the MSU 4π Array. We have studied these reactions using a variety of observables including fission fragment opening angles, fission fragment azimuthal correlations, intermediate mass fragment and light charged particle production, and event shape analysis. We observe a change in the decay characteristics of high momentum linear transfer collisions as a function of incident energy from fission-like to multifragment emission.

129Xe-Induced Peripheral Reactions at E/A = 50 MeV

The charge distributions of the projectile-like fragments (PLF’s) produced in the reactions of 129Xe on 27Al, nat. Cu, 139La, and 165Ho at 50 MeV/u are compared to those obtained with 129Xe on 209Bi at 28.2 MeV/u by Baldwin et al.1 The predictions of Tassan-Got’s nucleon exchange model2 are compared to the data to investigate the persistence of the deep-inelastic mechanism in the intermediate energy regime.

The Impact Parameter Dependence of the Disappearance of Flow

The Michigan State University 4π Array has been recently upgraded to include the High Rate Array (HRA), a close-packed 45 element phoswich array which covers laboratory polar angles from ≈ 3° to ≈ 18°. The HRA subtends all solid angle between the Maryland Forward Array and the detectors of the main Ball resulting in ≈ 90% geometric efficiency for the entire array. With this improved detector configuration, we studied the reaction 40Ar + 45Sc at beam energies from 35 to 115 MeV/nucleon. We present preliminary results on the impact parameter dependence of the disappearance of flow in nuclear collisions, extending the systematics of our previous work.