Search

We study the screening effects of the atomic electrons in the electromagnetic production of electron-positron pairs in relativistic nucleus-atom collisions for fixed target experiments. Our results are contrasted with those obtained in bare collisions, with particular attention given to its dependence on the beam energy and the target atom.

Measurements of the cosmic-ray hydrogen and helium spectra at energies from 20 to 800 TeV are presented. The experiments were performed on a series of twelve balloon flights, including several long duration Australia to South America and Antarctic circumpolar flights. No clear evidence is seen for a spectral break. Both the hydrogen and the helium spectra are consistent with power laws over the entire energy range, with integral spectral indices 1.80 ± 0.04 and 1.68 -->+ 0.04−0.06 for the protons and helium, respectively. The results are fully consistent with expectations based on supernova shock acceleration coupled with a leaky box model of propagation through the Galaxy.

The performance of the spherical drift chamber of the BUGS IV (Bristol University Gas Scintillator) cosmic ray detector is presented. The 1 m radius spherical chamber employed ArN 2 gas scintillation, gas-proportional scintillation, and electron drift timing to provide charge, energy, and pathlength correction information. The details of the scintillation and drift processes are presented and the combination of these techniques in the BUGS IV central drift chamber are discussed. The performance of a recent exposure of the BUGS IV central spherical chamber to relativistic cosmic ray iron nuclei is presented. It is shown that the chamber provided pathlength corrections to all elements of this multi-detector experiment with relative uncertainties of less than 2% for 90% of all impact parameters. The maximum uncertainty for the largest impact parameter events remained less than 5%. Model drift waveforms are derived and shown to be in excellent agreement with the observed data.

The design features and operational performance from the test flight of the fourth generation of spherical geometry cosmic ray detectors developed at Bristol University (Bristol University Gas Scintillator 4 - BUGS-4) are presented. The flight from Ft. Sumner (NM) in September 1993 was the premier flight of a large (1 m radius) spherical drift chamber which also gave gas scintillation and Cherenkov signals. The combinations of this chamber with one gas and two solid Cherenkov radiators lead to a large aperture factor (4.5 m2 sr), but low (∼3.5g/cm2) instrument mass over the energy sensitive range 1 to several hundred GeV/a. Moreover, one simple timing measurement determined the impact parameter which provided a trajectory (path length) correction for all detector elements. This innovative and efficient design will be of interest to experimental groups engaged in studies of energetic charged particles. Although there were technical problems on the flight, which were compounded by the total destruction of BUGS-4 by fire whilst langding in Oklahoma, there was a period of stable operation during which the instrument was exposed at float altitude (∼125 000 ft) to high-energy cosmic rays. We present the performance of the instrument as determined from the analysis of these data and an appraisal of its novel design features. Suggestions for design improvements in a future instrument are made.

Mixed transverse(P T ) momentum and rapidity distributions of charged particles produced in 200 GeV/AMU heavy ion collisions are obtained with Magnetic-Interferometric-Emulsion-Chamber ( MAGIC ) by CERN-EMU05 experiments. The P T spectra at different rapidity regions showed no anomalous enhancement of low P T components over a conventional, single exponential function with slope values ranging from 160 to 200 MeV/c.

An instrument designed to measure elemental cosmic ray abundances from boron to nickel in the energy region 0.5-2.0 GeV/nucl was flown on a high altitude balloon from Sioux Falls, South Dakota, on 30 September through 1 October 1976 at an average atmospheric depth of about 5 g/sq cm. Differential energy spectra of B, C, N, O, Ne, Mg, Si and Fe, extrapolated to the top of the atmosphere, were measured. The float altitude exposure of 17 h ended near Alpena, Michigan. The flight trajectory maintained a north easterly heading out of Sioux Falls traversing the upper midwest region between 84 and 97 deg west longitude while remaining between 43.5 and 45 deg north latitude. The maximum vertical cut-off for this flight path was 1.77 GV or 0.35 GeV/nucl.

Particle correlations of the central collision events of 32 S + Pb at 200 GeV/AMU have been studied by utilizing a Magnetic-Interferometric-Emulsion-Chamber (MAGIC) detector. Particle angles, momentum, and charge-signs are measured for all produced charged tracks for each event. Two-particle correlation functions, C 2 = dN (¦ p 1 − p 2 ¦= q )/ dp 1 dp 2 , for (++), (−−) and (+-) particles are examined. A source radius around 4 – 6 fm is observed for overall identical particle correlations, while unexpected short-range correlations of unlike-sign pairs are observed in the high rapidity region. An analysis of unlike-sign pairs in terms of resonance decays indicated that a large amount (40% relative to pions) of η or ω mesons (decaying into 3 π), or of scalar iso-scalar σ mesons (decaying into 2π) would be required to explain some of the data. Multi-particle charge-sign clusters are recognized; however, their “run-test” and “conjugate-test” show small deviations from statistical fluctuations.

Fluctuations in rapidity are examined, by using CERN EMU05 experimental data differentiating charge-sign in S + Pb collision at 200 GeV/amu. Rapidity spacing analyses show limiting fluctuations at higher order spacings, while Poisson fluctuations are universally indicated in the lower spacings. The limiting behavior suggests that a long-range positive correlation, such as Wigner repulsion, is in order in the rapidity space. No clear evidence for the intermittent phenomena has been observed in the resultant normalized factorial moments in all charged, positively and negatively charged particles, respectively.

Measurements of direct Coulomb electron-positron pair production have been made on the tracks of relativistic heavy ions in nuclear track emulsion. Tracks of 0(16) and S(32) at 200 GeV/nucleon were studied. The measured total cross sections and energy and emission angle distributions for the pair members are compared to theoretical predictions. The data are consistent with some recent calculations when knock-on electron contamination is accounted for.

An emulsion-counter hybrid set-up to detect charmed particle decays in samples of triggered 32 S-nucleus central interactions is described. A new tracking technique with two emulsion tapes was developed and used successfully.

High energy cosmic ray interactions were studied by the JACEE Collaboration using balloon‐borne emulsion chambers at high altitude. In high energy, yet low multiplicity interactions many secondary vertices were observed, probably due to decays of short‐lived particles. Early conversions of photons were found in the vicinity of these vertices. Conversion distances and angular distributions of the photons were studied.

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.

Direct measurements of cosmic-ray nuclei above 1 TeV/nucleon have been performed in a series of balloon-borne experiments with emulsion chambers. The observed all-particle spectrum above 20 TeV is consistent with the results of the Proton satellite and many air shower experiments. The proton spectrum is consistent with a power law having an index of 2.76 + or - 0.09 up to at least 100 TeV, but an overabundance of helium by a factor of 2 above 2 TeV per nucleon is found when compared with the extrapolation from the low energies. For heavy elements (C through Fe), the intensities around 1 TeV/nucleon are consistent, within the statistical errors, with the extrapolation from lower energy data using the Spacelab 2 spectral indices. An enhancement for the medium-heavy components (C through Ca) above 200 TeV is indicated. The mean mass above 50 TeV indicates slightly higher values than the results of the air shower experiments.

A hybrid electronic-counter/emulsion-chamber instrument was exposed to high-energy cosmic rays on a balloon. The data on 105 nucleus-nucleus collisions in the energy range 20-65 GeV/nucleon and for incident nuclear charges Zp in the range of 22 to 28 are presented. Inclusive characteristics of particle production on different targets (plastic, emulsion, and lead) are shown and compared with models based on the superposition of nucleon-nucleus interactions. Features of a subset of the more central collisions with a plastic target and some characteristics of individual events with the highest multiplicity of produced particles are described.

Corrections to the Z-squared dependence of ion chamber and Cherenkov response due to the Mott cross section are calculated for the HEAO-3 Heavy Cosmic Ray Experiment. The effect of the production and escape of high energy secondary electrons on detector response is accounted for by numerical calculations. These secondary electron effects are shown to influence the size of the non Z-squared effects and thus affect the charge assignments and detector resolution. The Bloch and relativistic Bloch corrections are not included in the results presented here but may be combined with the Mott corrections when the Bloch corrections are properly evaluated.

Studies of high-energy nucleus-nucleus interactions with balloon-borne JACEE emulsion chambers are summarized. High energy, high multiplicity interactions are found with high-energy-density (⩾ 2 GeV/fm3), high observed values (500 – 2,000 MeV/c), and several interesting pseudorapidity and/or azimuthal structures. Very short-range correlations of charged particles, and several other inclusive characteristics are discussed.

Direct measurements on cosmic ray protons through iron above about 1 TeV/amu have been performed in a series of balloon-borne experiments with emulsion chambers. The measured energy spectra of protons and helium are power laws with exponents of 2.77 + or - 0.09 and 2.72 + or - 0.11 in the energy range 5 to 500 TeV and 2 to 50 TeV/amu, respectively. The proton spectrum shows no evidence of the steepening near 2 TeV which was reported by other experiments. Helium has a slightly higher intensity compared to extrapolations from lower energy measurements. The heavier elements, carbon to sulfur, show a small tendency for intensity enhancement in the relative abundance obove 10 TeV/amu.

Total transmitted electron energy spectra have been constructed from measurements of electron energy spectra at various emission angles for targets of Al and Au of thicknesses of from 0.2 to 0.6 of the range in these materials. Bombarding energies of 1.0 and 2.5 MeV were used for beams of perpendicular incidence to the targets. Angular distributions of transmitted electrons are shown. At 1.0 MeV, total transmitted electron energy spectra are constructed from measurements in which incident electron beams were used to simulate an electron flux of intensity varying as the cosine of the angle of incidence. Targets of Al, Sn, and Au were used. Comparisons are made to calculated spectra from ETRAN 15 of Berger and Seltzer.

Angular distribution of thick target bremsstrahlung produced by electron bombardment of Be, Sn and Au surfaces

No significant changes in spectral index for protons up to 500 TeV and higher intensity for helium above 2 TeV were observed. For heavier elements, a general tendency of intensity enhancement of medium heavies in the relative abundance above about 10 TeV/amu was observed.

The search for cosmic strangelet nuclei was carried out by two experiments with emulsion chambers. A balloon-borne JACEE emulsion chamber was flown at 3.5 g/cm2 for 200 h in Antarctica (JACEE-10 experiment) and the Concorde flights were made by ECHOS at an atmospheric depth of 110 g/cm2 between Paris and New York. No nuclei withZ⩾30 survived after traversing 60–120 g/cm2 of the detector materials in the JACEE instruments. No evidence for a long mean free path were found in the zenith angle distribution forZ/β⩾26 nuclei. The exposure factor used by the JACEE was 72 m2hsr. The intensity upperbounds,I⩽(2.2–9.7)×10−2/m2h sr, were obtained for strangelets having an atmospheric attenuation length of 220−50 g/cm2, which corresponds to the case for mass numberA=100–10000 andZ/β > 13. Concorde experiments (ECHOS) used both a thin and a thick emulsion chamber. The total exposure was 209 m2 h sr and no candidates with chargeZ⩾30 were found. The largest track hadZ/β=28.6±1.29 withβ ∼ 1. Nuclei observed with charge 13⩽Z⩽30 were consistent with the survival intensity of ordinary nuclei. The flux bounds from the ECHOS experiments were I⩽(2.1–5.0) x 10−2/m2h for strangelets with mass number 100⩽A⩽1000.

Emulsion chambers will be flown in the Astromag Facility to measure the cosmic ray composition and spectra to 10 exp 15 eV total energy and to definitively study the characteristics of nucleus-nucleus interactions above 10 exp 12 eV/n. Two configurations of emulsion chambers will be flown in the SCIN/MAGIC experiment. One chamber has an emulsion target and a calorimeter similar to those recently flown on balloons for composition and spectra measurements. The other has an identical calorimeter and a low-density target section optimized for performing rigidity measurements on charged particles produced in interactions. The transverse momenta of charged and neutral mesons, direct hadronic pairs from resonance decays and interference effects, and possible charge clustering in high-density states of matter will be studied.

Results for the cosmic ray hydrogen and helium spectra up to 800 TeV, near the “knee” region, are presented. There is no sign of a break in either the hydrogen or helium spectra. The differential power law slopes are 2.80±0.04 for hydrogen and 2.68±0.06 for helium. With these new H and He measurements, together with earlier reported results for the heavier elements, the sum of the spectra give an all-particle spectrum that is in good agreement with the all-particle spectrum measured using extensive air showers.

Two balloon flights of large-area scintillation crystal detector arrays indicate that the rate of weak gamma-ray bursts is significantly below that expected from a uniform distribution of burst sources. This result, combined with the data from stronger bursts, gives strong evidence for a galactic confinement of burst sources. Reasonable models of confinement limit the intrinsic radiated energy per burst to the order of 10 to the (39th to 41st power) ergs.