492 research outputs found
Heavy Ions in the October 1989 Solar Flares Observed on the Galileo Spacecraft
Composition measurements were made of the energetic
particles produced in the series of large flares which began on 19 October 1989, using the Galileo Heavy Ion Counter which is sensitive to nuclei ranging from carbon (Z=6) to nickel (Z=28) over an energy range from about 5 MeV/nucleon to >70 MeV/nucleon. The observations are unique in that clean, statistically well-measured abundances are available for heavy ions for an unusually large flare. For elements with low First Ionization Potential (FIP), these results show the same correlation of relative abundances
with the ion charge to mass ratio as the earlier Voyager observations of solar energetic particles 1 . After correction for selection on the basis of this charge to mass ratio, the abundances of all the elements measured
show the expected step-function correlation with FIP, when compared to the spectroscopic photspheric abundances
A Science Center for the Advanced Composition Explorer
The Advanced Composition Explorer (ACE) mission is supported by an ACE Science Center for the purposes of facilitating collaborative work. It is intended that coordinated use of a centralized science facility by the ACE team will ensure appropriate use of data formatting standards, thus easing access to the data; will improve communications within and to the ACE science working team; and will reduce redundant effort in data processing
Relation of the Radial Gradient of Cosmic-Ray Protons to the Size of the Solar-Modulation Region
The radial intensity-gradient of cosmic-ray protons has been
calculated for a range of values of the distance to the boundary
of a spherically symmetric solar-modulation region. We find
that the radial dependence of the gradients may be described
in terms of two characteristic domains of the modulation region:
(a) an "inner region" where the gradients are relatively small
and constant, and (b), an "outer region"' where the gradients
are large and show a strong radial dependence. The magnitude
of the gradient in the inner region is small for reasonable
values for the physical parameters of the modulation mechanism
Solar Particle Induced Upsets in the TDRS-1 Attitude Control System RAM During the October 1989 Solar Particle Events
The three large solar particle events, beginning on October 19, 1989 and lasting approximately six days, were characterized by high fluences of solar protons and heavy ions at 1 AU. During these events, an abnormally large number of upsets (243) were observed in the random access memory of the attitude control system (ACS) control processing electronics (CPE) on-board the geosynchronous TDRS-1 (Telemetry and Data Relay Satellite). The RAM unit affected was composed of eight Fairchild 93L422 memory chips. The Galileo spacecraft, launched on October 18, 1989 (one day prior to the solar particle events) observed the fluxes of heavy ions experienced by TDRS-1. Two solid-state detector telescopes on-board Galileo designed to measure heavy ion species and energy, were turned on during time periods within each of the three separate events. The heavy ion data have been modeled and the time history of the events reconstructed to estimate heavy ion fluences. These fluences were converted to effective LET spectra after transport through the estimated shielding distribution around the TDRS-1 ACS system. The number of single event upsets (SEU) expected was calculated by integrating the measured cross section for the Fairchild 93L422 memory chip with average effective LET spectrum. The expected number of heavy ion induced SEUs calculated was 176. GOES-7 proton data, observed during the solar particle events, were used to estimate the number of proton-induced SEUs by integrating the proton fluence spectrum incident on the memory chips, with the two-parameter Bendel cross section for proton SEU's. The proton fluence spectrum at the device level
was gotten by transporting the protons through the estimated
shielding distribution. The number of calculated proton-induced
SEU’s was 72, yielding a total of 248 predicted SEU’s, very
close to the 243 observed SEU’s. These calculations uniquely
demonstrate the roles that solar heavy ions and protons played in
the production of SEU’s during the October 1989 solar particle
events
Propagation of the Heaviest UH-Cosmic Ray Nuclei
Our previous studies showed that the fragmentation cross sections of gold nuclei interacting in
hydrogen have large variations between the values measured at 0.9 and 10.6 GeV/n, which has very
significant implications on calculations of the propagation of the heaviest UH cosmic ray nuclei,
such as Pb and Pt We have now completed a series of runs at the Brookhaven AGS using beams of
gold nuclei of intermediate energy. The data from these runs will allow us to establish the excitation
functions for these cross sections in a wide range of targets and hence model propagation more
accurately than hitherto. In addition we will be able to study the energy dependence of nuclear
charge pickup, electromagnetic dissociation and fission. Beams of gold nuclei with seven energies
between 4.0 and 0.9 Ge V /n were studied interacting in targets ranging in mass from hydrogen to lead. We will present data on the cross sections derived from several of these beams and discuss
some of the implications
Energy spectra of elements with 18 or = Z or = 28 between 10 and 300 GeV/amu
The HEAO-3 Heavy Nuclei Experiment is composed of ionization chambers above and below a plastic Cerenkov counter. The energy dependence of the abundances of elements with atomic number, Z, between 18 and 28 at very high energies where they are rare and thus need the large area x time are measured. The measurements of the Danish-French HEAO-3 experiment (Englemann,, et al., 1983) are extended to higher energies, using the relativistic rise of ionization signal as a measure of energy. Source abundances for Ar and Ca were determined
UHCR: A Cosmic Ray Mission to Study Nuclei in the Charge Range From 20 ≤Z ≤100
A definitive study of the elemental abundances of nuclei over the charge range of 20 ≤ Z ≤ 100 requires a satellite mission capable of obtaining high statistics and excellent charge resolution over the full charge range. Such a mission, utilizing an electronic instrument which is an evolution of the HEA0-3 Heavy Nuclei Experiment, is described here
Fragmentation cross sections of relativistic ^(84)_(36)Kr and ^(109)_(47)Ag nuclei in targets from hydrogen to lead
With the addition of krypton and silver projectiles we have extended our previous studies of the fragmentation of heavy relativistic nuclei in targets ranging in mass from hydrogen to lead. These projectiles were studied at a number of discrete energies between 450 and 1500A MeV. The total and partial charge-changing cross sections were determined for each energy, target, and projectile, and the values compared with previous predictions. A new parametrization of the dependence of the total charge-changing cross sections on the target and projectile is introduced, based on nuclear charge radii derived from electron scattering. We have also parametrized the energy dependence of the total cross sections over the range of energies studied. New parameters were found for a previous representation of the partial charge-changing cross sections in hydrogen and a new parametrization has been introduced for the nonhydrogen targets. The evidence that limiting fragmentation has been attained for these relatively light projectile nuclei at Bevalac energies is shown to be inconclusive, and further measurements at higher energies will be needed to address this question
Nuclear Interaction Cross Sections for UltraHeavy Nuclei
We summarize additions to our data base of charge-changing cross
sections for relativistic ultraheavy nuclei interacting in targets ranging
from H to Pb. We have improved parametric fits to those cross sections
as functions of energy and of projectile, target, and fragment charge. At
high energies, we have determined cross sections for Au projectiles at 10.6
GeV /nucleon in targets of H, CH_2, C, Al, Cu, Sn, and Pb. Compared
with cross sections at 1 GeV /n, fragment production is substantially
changed, especially for the H target. These changes have important implications
for calculations of interstellar propagation of ultraheavy nuclei.
At lower energies, we have added Kr and Ag to our list of projectiles.
Analysis of these data has led to a better understanding of the systematics
of these cross sections, hence more physically meaningful parameterizations
for fragmentation at high energies and for charge pickup
The Advanced Composition Explorer Mission
The Advanced Composition Explorer, to be launched in August of 1997, will include six high
resolution spectrometers that will measure the composition of interplanetary nuclei with 2≤Z≤28 from < 1 keV/nuc to ~500 MeV/nuc. Three additional instruments will provide the interplanetary context for these measurements. We give a brief introduction to the ACE mission, its
instrumentation, and its goals
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