W. Heinrich

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.

Radiation measurements on the Mir Orbital Station.

Radiation measurements made onboard the MIR Orbital Station have spanned nearly a decade and covered two solar cycles, including one of the largest solar particle events, one of the largest magnetic storms, and a mean solar radio flux level reaching 250 x 10(4) Jansky that has been observed in the last 40 years. The cosmonaut absorbed dose rates varied from about 450 microGy day-1 during solar minimum to approximately half this value during the last solar maximum. There is a factor of about two in dose rate within a given module, and a similar variation from module to module. The average radiation quality factor during solar minimum, using the ICRP-26 definition, was about 2.4. The drift of the South Atlantic Anomaly was measured to be 6.0 +/- 0.5 degrees W, and 1.6 +/- 0.5 degrees N. These measurements are of direct applicability to the International Space Station. This paper represents a comprehensive review of Mir Space Station radiation data available from a variety of sources.

Cosmic rays and dosimetry at aviation altitudes.

Recent concerns regarding the effects of the cosmic radiation field at aircraft altitudes on aircrew have resulted in a renewed interest in detailed measurements of the neutral and charged particle components in the atmosphere. CR-39 nuclear track detectors have been employed on a number of subsonic and supersonic aircraft to measure charge spectra and LET spectra at aircraft altitudes. These detectors are ideal for long term exposures required for these studies and their passive nature makes them suitable for an environment where interference with flight instrumentation could be a problem. We report here on measurements and analysis of short range tracks which were produced by high LET particles generated mainly by neutron interactions at aviation altitudes. In order to test the overall validity of the technique measurements were also carried out at the CERN-CEC field which simulates the radiation field at aviation altitudes and good agreement was found with dose values obtained using mainly heavy ion calibration.

Heavy ion microscopy of single event upsets in CMOS SRAMs

The single event upset (SEU) imaging has been applied at the GSI heavy ion microprobe to determine the sensitivity of integrated circuits (IC) to heavy ion irradiation. This method offers the possibility to directly image those parts of an IC which are sensitive to ion-induced malfunctions. By a 3-dimensional simulation of charge collection across p-n-micro-junctions, we can predict SEU cross-sections. For a MHS65162 2k x 8bit CMOS SRAM we found two regions per bit with different sensitivity and measured a total cross-section of (71/spl plusmn/18) /spl mu/m/sup 2/ for a bitflip per cell and simulated 60 /spl mu/m/sup 2/ with an argon beam of 1.4 MeV/nucl. (LET of 19.7 MeV/(mg/cm/sup 2/)). >

Ionizing radiation exposure of LDEF (pre-recovery estimates)

The long duration exposure facility (LDEF), launched into a 258 nautical mile orbit with an inclination of 28.5 degrees, remained in space for nearly 6 yr. The 21,500 lb NASA satellite was one of the largest payloads ever deployed by the Space Shuttle. LDEF completed 32,422 orbits and carried 57 major experiments representing more than 200 investigators from 33 private companies, 21 universities and nine countries. The experiments covered a wide range of disciplines including basic science, electronics, optics, materials, structures and power and propulsion. A number of the experiments were specifically designed to measure the radiation environment. These experiments are of specific interest, since the LDEF orbit is essentially the same as that of the Space Station Freedom. Consequently, the radiation measurements on LDEF will play a significant role in the design of radiation shielding of the space station. The contributions of the various authors presented here attempt to predict the major aspects of the radiation exposure received by the various LDEF experiments and therefore should be helpful to investigators who are in the process of analyzing experiments which may have been affected by exposure to ionizing radiation. The paper discusses the various types and sources of ionizing radiation including cosmic rays, trapped particles (both protons and electrons) and secondary particles (including neutrons, spallation products and high-LET recoils), as well as doses and LET spectra as a function of shielding. Projections of the induced radioactivity of LDEF are also discussed.

Projectile fragmentation of silicon ions at 490 A MeV

Fragmentation cross sections are essential input parameters for propagation calculations which describe the effect of shielding against cosmic ray heavy nuclei by the walls of spacecraft or planetary habitat. Cross sections for the breakup of different elements are needed for different types of target material and for a wide range of energy. For this purpose, we have extended our studies of projectile fragmentation. By using stacks containing CR-39 track detectors and targets ranging from CH 2 to Pb we have measured total and elemental fragmentation cross sections for fragments with charges Z F > 5, for silicon projectiles with energies of 490 A MeV. These new data sets allow us to improve our knowledge about the target and energy dependence of fragmentation cross sections.

High energy heavy ion interactions studied with SSNTDs

We have continued our studies of heavy ion projectile fragmentation using nuclear track detectors. Based on automatic track measurement it was possible to perform experiments with high statistical significance. Beams of different ions from the Berkeley BEVALAC, the Dubna Synchrophasotron, the Brookhaven AGS and the GSI Darmstadt SIS have been used. With CR-39 and BP-1 glass detectors we have studied the process of electromagnetic dissociation, we investigated multifragmentation and continued the search for quark nuclear complexes. This paper gives an overview of these experiments. Details of the experimental technique are discussed.

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.

Study of SEUs generated by high energy ions

Using 1 GeV/nucleon ions SEUs have been studied in two types of CMOS-SRAMs with respect to tilt angle and tilt direction. Tracks of upset bits, which have been observed under large tilt angles, were used to determine the charge collection depth in these devices. >

Fragmentation cross section measurements of iron projectiles using CR-39 plastic nuclear track detectors

Abstract For long term space missions in which larger radiation doses are accumulated it is necessary to improve the precision of models predicting the space radiation environment. Different models are available to determine the flux of cosmic ray heavy ions behind shielding material. The accuracy of these predictions depends on the knowledge of the fragmentation cross sections, especially at energies of several hundred MeV/nucleon, where the particle flux is at a maximum and especially for those particles with high LET, i.e. iron nuclei. We have measured fragmentation cross sections of 56 Fe projectiles at beam energies of 700 and 1700 A MeV using experimental set-ups with plastic nuclear track detectors. In this paper we describe the experimental technique to study the fragmentation reactions of 56 Fe projectiles using CR-39 plastic nuclear track detectors. Results for different targets are presented.