C. Brechtmann

An automatic measuring system for particle tracks in plastic detectors

Abstract In the last few years picture analysis methods have evolved into a powerful technique for measurements of nuclear tracks in plastic detectors. We have developed a microprocessor-based picture analysis system for automatic track measurements. The video pictures of particle tracks seen through a microscope are digitized in real time and the picture analysis is done by software. The microscope is equipped with a stage driven by stepping motors, which are controlled by a separate microprocessor. A PDP 11/23 supervises the operation of all microprocessors and stores the measured data on its mass storage devices. This paper describes the hard- and software of the system and the methods of picture analysis which are used for the track identification and measurement.

Applications of plastic nuclear track detectors in heavy ion physics

Abstract The experimental technique of computerized track measurements for plastic nuclear track detectors was used in different experiments investigating interactions of relativistic heavy ions. In this paper the method is described, results are presented and discussed. To measure cross sections stacks were exposed at the BEVALAC, at Brookhaven and at CERN to different beam nuclei having energies from 0.6 GeV/nucleon up to 200 GeV/nucleon. The cross sections for one nucleon removal are considerably enhanced at high energies due to electromagnetic dissociation. We investigated the effect of electromagnetic dissociation for different targets and projectiles. For heavy projectiles an exclusive analysis of nuclear fragmentation on an event by event basis was performed. Based on this the effect of multifragmentation can be studied. We exposed a stack of 100 CR39 foils to a 1 GeV/nucleon 197 Au beam at the BEVALAC. Events with up to 10 projectile fragments having a charge Z≥5 and coming out of the same interaction vertex were observed. To search for projectile fragments with fractional charge in relativistic heavy ion collisions, we exposed stacks of 50 CR39 foils behind a lead block of 15 cm depth to the ultrarelativistic heavy ion beams at Brookhaven and CERN. The charge resolution achieved in these experiments is o=0.027e.

The Siegen automatic measuring system for nuclear track detectors status and new developments

Abstract We developed a completely automatic scanning and measuring system for nuclear track detectors. The video pictures of particle tracks seen through a microscope are digitized and analyzed in real time by MC 68000 microprocessors. In this paper we present some new developments: The picture analysis software is extended to separate overlapping tracks and to measure elliptical tracks even if these are flawed by surface structures. A software autofocus, a faster hardware version based on the contrast and a modified commercial laser autofocus are now available. A new picture analysis system based on the faster 32-bit microprocessor MC 68020 will operate on two pictures of 1024 × 1024 pixels resident in memory together. This will allow three dimensional track measurements.

Interaction mean free path measurements for relativistic heavy ion fragments using CR39 plastic track detectors

Abstract This paper describes an experiment measuring the interaction mean free paths for charge changing nuclear collisions of relativistic heavy ion fragments. We use a stack of CR39 plastic nuclear track detectors that was irradiated with 1.8 GeV/nucleon 40 Ar ions at the Berkeley Bevalac. About 1.5 × 10 7 etch cones were measured in this experiment using an automatic measuring system. By tracing the etch cones over successive plastic foils the particle trajectories in the stack were reconstructed. For 14185 trajectories with 6444 nuclear collisions of fragments with charge 9–15 the interaction mean free path in the plastic was determined.

Search for projectile fragments with fractional charge in relativistic heavy ion collisions

We measured the charge of about 35000 projectile fragments with Z > or = 5e produced by 14.5 GeV/nucleon and 200 GeV/nucleon 16O beams in a Pb target using CR39 plastic nuclear track detectors. A minimum track length of 3 mm in the detector without nuclear interaction was required. No evidence for fragments carrying a fractional charge was found.

Anomalons: Current status and first evidence from plastic track detectors

Abstract A number of experiments have shown that enhanced cross sections exist for projectile fragments which are emitted in relativistic heavy ion collisions. The present status of these investigations is reviewed. An experiment is described in which this effect is measured with significantly better statistics. First results for fragments of charge 14 emerging from 1.8 MeV/nucleon 40 Ar projectiles are presented.

Cross sections for the production of fragments with Z⩾8 by fragmentation of 9⩽Z⩽26 nuclei

Abstract We investigated charge changing collisions using the experimental technique of automatic track measurement for etched tracks in CR39. For beams of 40 Ar and 56 Fe altogether more than 33600 interactions of beam nuclei and about 15600 interactions of fragments produced in nuclear collisions were analyzed. Besides interactions with the light target nuclei H, C and O of the plastic detectors also interactions with silver target nuclei were studied. For this purpose we stacked silver foils between the plastic detector foils. Cross sections for the production of fragments with Z⩾8 from nuclei with 9⩽Z⩽26 in charge changing nuclear collisions were determined.

Search for anomalons using plastic nuclear track detectors

Abstract Enlarged cross sections for projectile fragments of relativistic nuclei have been observed in Bevalac and cosmic ray experiments with nuclear emulsions. We performed an experiment using plastic track detectors to investigate the anomalon effect. A new automatic measuring technique for heavy ion tracks in plastic detectors enables us to analyze large numbers of fragmentation reactions in reasonable time. Thus we get better statistical significance. Results of the experiment are presented.

An automatic measuring system for heavy nuclei tracks in plastic detectors

Abstract A computer controlled automatic system for scanning and measuring tracks of heavy nuclei in plastic detectors, which works by means of digital picture analysis, is presented. The picture seen by a video camera through a microscope is digitized in real time and stored into computer memory. The picture analysis is done by software running on a 16-bit microprocessor. This automatic system analyzes up to 30000 particle tracks per hour. Results of the automatic measurements of particle tracks in CR 39 are presented.