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  • Cell & Developmental Biology  (1,496)
  • SPACE RADIATION
  • 1995-1999
  • 1990-1994  (1,510)
  • 1945-1949  (89)
  • 1900-1904
  • 1993  (1,510)
  • 1948  (89)
Collection
Keywords
Publisher
Years
  • 1995-1999
  • 1990-1994  (1,510)
  • 1945-1949  (89)
  • 1900-1904
Year
  • 1
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    Cold dark matter and degree-scale cosmic microwave background anisotropy statistics after COBE (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We conduct a Monte Carlo simulation of the cosmic microwave background (CMB) anisotropy in the UCSB South Pole 1991 degree-scale experiment. We examine cold dark matter cosmology with large-scale structure seeded by the Harrison-Zel'dovich hierarchy of Gaussian-distributed primordial inhomogeneities normalized to the COBE-DMR measurement of large-angle CMB anisotropy. We find it statistically implausible (in the sense of low cumulative probability F lower than 5 percent, of not measuring a cosmological delta-T/T signal) that the degree-scale cosmological CMB anisotropy predicted in such models could have escaped a detection at the level of sensitivity achieved in the South Pole 1991 experiment.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 410; 1; p. L1-L5.
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  • 2
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    Noncosmological signal contributions to the COBE DMR anisotropy maps (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We examine the COBE Differential Microwave Radiometer (DMR) data for evidence of noncosmological source contributions. The DMR maps are cross-correlated with maps of rich clusters, extragalactic IRAS sources, HEAO 1 A-2 X-ray emission, and 5 GHz radio sources. We limit the rms contributions from these sources on a 7 deg angular scale to less than 10 micro-K (95 percent confidence level) in the DMR maps, although the LMC probably contributes about 50 micro-K to a limited region of the sky. Thus, our previous interpretation that the fluctuations in the COBE DMR data are most likely due to cosmic fluctuations at the surface of last scattering remains intact. The Comptonization parameter for hot electrons traced by rich clusters is limited to delta(y) less than 2 x 10 exp -6 (95 percent confidence level) averaged over the 7 deg DMR beam.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 414; 2; p. L77-L80.
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  • 3
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    Anuradha and low-energy cosmic rays (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: After critically reviewing observational results obtained by astronomical spacecraft in the interplanetary medium for several aspects of galactic cosmic rays (GCRs) and anomalous cosmic rays (ACRs), attention is given to spacecraft data gathered in the magnetosphere and a detailed description is given of the Anuradha cosmic-ray experiment carried by Spacelab-3. The Anuradha results discussed concern the orbit average flux and ionization state of ACRs, the origins of partially ionized galactic cosmic-ray sub-Fe and Fe ions, and the significance of enhanced abundance ratios of sub-Fe and Fe ions in GCRs inside the magnetosphere.
    Keywords: SPACE RADIATION
    Type: Space Science Reviews (ISSN 0038-6308); 62; 1-2; p. 3-65.
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  • 4
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    Ionization states of low-energy cosmic rays - Results from Spacelab 3 cosmic-ray experiment (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Indian cosmic ray experiment Anuradha, conducted onboard Spacelab 3 during April 29-May 6, 1985 was designed to obtain information on the ionization states of low-energy cosmic rays, using the geomagnetic field as a rigidity filter to place an upper limit on the ionization state of individual cosmic ray particles. This paper presents data confirming the presence of three distinct groups of energetic particles in the near-earth space: (1) low-energy (15-25 MeV/nucleon) anomalous cosmic rays that are either singly ionized or consistent with their being in singly ionized state, (2) fully ionized galactic cosmic ray ions, and (3) partially ionized iron and sub-iron group ions (which account for about 20 percent of all the iron and sub-iron group ions detected at the Spacelab 3 orbit within the magnetosphere in the energy interval 25-125 MeV/nucleon). It is argued that these partially ionized heavy ions are indeed a part of the low-energy galactic cosmic rays present in the interplanetary space.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 411; 1; p. 418-430.
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  • 5
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    The suppression of pulsar and gamma-ray burst annihilation lines by magnetic photon splitting (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Neutron stars, relativistic and compact by nature, show great potential for the copious creation of electron-positron pairs in the magnetospheres; these rapidly cool, thermalize, and then annihilate. It is therefore expected that many neutron sources might display evidence of pair annihilation lines in the 400-500 keV range. It is shown that magnetic photon splitting, which operates effectively at these energies and in the enormous neutron star magnetic fields, can destroy an annihilation feature by absorbing line photons and reprocessing them to lower energies. In so doing, photon splitting creates a soft gamma-ray bump and a broad quasi-power-law contribution to the X-ray continuum, which is too flat to conflict with the observed X-ray paucity in gamma-ray bursts. The destruction of the line occurs in neutron stars with surface fields of 5 x 10 exp 12 G or maybe even less, depending on the size of the emission region.
    Keywords: SPACE RADIATION
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 262; 1; p. 20-26.
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  • 6
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    Effects of location uncertainties on the observed distribution of gamma-ray bursts detected by BATSE (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Burst and Transient Source Experiment (BATSE) on NASA's Compton Gamma-Ray Observatory has shown that the sources of gamma-ray bursts have an angular distribution consistent with isotropy, yet the bursts are spatially inhomogeneous. Detection of a statistically significant deviation from isotropy in the burst distribution would provide a clue to the distance of the burst sources. BATSE's ability to detect slight deviations of the angular distribution from isotropy is, in part, dependent on the accuracy of the computed burst locations. Using bursts whose locations have been determined accurately and independently, we estimate BATSE's location uncertainties and incorporate them into 3D Monte Carlo simulations of the burst distributions to show that, despite individual burst location uncertainties of about 5 deg, the ability of BATSE to place stringent limits on the anisotropy present in the angular distribution of the gamma-ray bursts is not significantly degraded. Observational effects of possible galactic halo distributions of the burst sources are noted.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 413; 1; p. 293-297.
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  • 7
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    Magnetospheric models for electron acceleration and transport in the heliosphere (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Electron transport and acceleration processes in the earth's magnetosphere have correspondences to analogous processes affecting electrons in the solar magnetosphere (i.e., heliosphere). Energetic electrons in planetary magnetospheres and the heliosphere are test particles probing transport and acceleration dynamics with minimal effects on dominant magnetic field configurations. Parallels are discussed relating to electron entry into the magnetospheres from interplanetary and interstellar space, circulatory transport processes, and acceleration by electric fields in boundary regions including shocks and magnetotails.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 13; 6; p. 103-106.
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  • 8
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    Methodological problems with gamma-ray burst hardness/intensity correlations (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The hardness and intensity are easily measured quantities for all gamma-ray bursts (GRBs), and so, many past and current studies have sought correlations between them. This Letter presents many serious methodological problems with the practical definitions for both hardness and intensity. These difficulties are such that significant correlations can be easily introduced as artifacts of the reduction procedure. In particular, cosmological models of GRBs cannot be tested with hardness/intensity correlations with current instrumentation and the time evolution of the hardness in a given burst may be correlated with intensity for reasons that are unrelated to intrinsic change in the spectral shape.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 404; 2; p. L87-L90.
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  • 9
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    A significant contribution to the cosmic X-ray background from sources associated with nearby galaxies (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A revised limit on the local X-ray emissivity due to sources correlated with nearby galaxies is obtained. These results are extrapolated up to a redshift of about 5, and it is found that a smaller, but still significant, fraction of the X-ray background (30 +/- 15 percent) can be accounted for by these sources. Evolution of the source properties and/or a new population of sources at high redshift is required to explain the residual background emissions.
    Keywords: SPACE RADIATION
    Type: Nature (ISSN 0028-0836); 364; 6439; p. 693-695.
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  • 10
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    Interplanetary proton fluence model - JPL 1991 (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We describe an updated predictive engineering model for the interplanetary fluence of protons with energies respectively greater than 1, 4, 10, 30, and 60 MeV. This has been the first opportunity to derive a model from a data set that has been collected in space over a long enough period of time to produce a valid sample of solar proton events. The model provides a quantitative basis for estimating the exposures to solar protons of spacecraft during missions of varying length and of surfaces and atmospheres of solar system objects. The data sets contain several major proton events comparable to the 1972 event. For the cases of the over 10 and over 30 MeV particles, the fluences are somewhat lower than in our earlier model No over 1, over 4, and over 60 MeV proton fluence models have been published in the literature previously. We present our results in a convenient graphical form which may be used to calculate the 1 AU fluence expected at a given confidence level as a function of the length of the exposure. A method of extending this estimate to other heliocentric distances is described.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A8; p. 13,281-13,294.
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  • 11
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    Identification of two classes of gamma-ray bursts (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have studied the duration distribution of the gamma-ray bursts of the first BATSE catalog. We find a bimodality in the distribution, which separates GRBs into two classes: short events (less than 2 s) and longer ones (more than 2 s). Both sets are distributed isotropically and inhomogeneously in the sky. We find that their durations are anticorrelated with their spectral hardness ratios: short GRBs are predominantly harder, and longer ones tend to be softer. Our results provide a first GRB classification scheme based on a combination of the GRB temporal and spectral properties.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 413; 2; p. L101-L104.
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  • 12
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    Recurrent burst activity from the soft gamma-ray repeater SGR 1900 + 14 (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Three short very soft gamma-ray (SGR) transient events from a location consistent with that of the SGR 1900 + 14, first described by Mazets et al. (1979), were detected by the Burst and Transient Source Experiment. The results of observations of the temporal and spectral properties of the SGR 1900 + 14 suggest that the SGR phase lasts at least 13 years, lending support to the suggestion by Kouveliotou et al. (1987) and Fishman et al. (1989) that SGRs are related to galactic (possibly population I) objects, perhaps neutron stars.
    Keywords: SPACE RADIATION
    Type: Nature (ISSN 0028-0836); 362; 6422; p. 728-730.
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  • 13
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    Flux measurements using the BATSE spectroscopic detectors (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Among the Compton Gama-Ray Observatory instruments, the BATSE Spectroscopic Detectors (SD) have the distinction of being able to detect photons of energies less than about 20 keV. This is an interesting energy range for the examination of low mass X-ray binaries (LMXB's). In fact, Sco X-1, the prototype LMXB, is easily seen even in the raw BATSE spectroscopic data. The all-sky coverage afforded by these detectors offers a unique opportunity to monitor this source over time periods never before possible. The aim of this investigation was to test a number of ways in which both continous and discrete flux measurements can be obtained using the BATSE spectroscopic datasets. A instrumental description of a SD can be found in the Compton Workshop of Apr. 1989, this report will deal only with methods which can be used to analyze its datasets. Many of the items discussed below, particularly in regard to the earth occultation technique, have been developed, refined, and applied by the BATSE team to the reduction of BATSE LAD data. Code written as part of this project utilizes portions of that work. The following discussions will first address issues related to the reduction of SD datasets using the earth occultation technique. It will then discuss methods for the recovery of the flux history of strong sources while they are above the earth's limb. The report will conclude with recommended reduction procedures.
    Keywords: SPACE RADIATION
    Type: Alabama Univ., The 1993 NASA(ASEE Summer Faculty Fellowship Program; 5 p
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  • 14
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    Structure in gamma ray burst time profiles: Correlations with other observables (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: One of the current debates raging in the world of gamma-ray burst physics is whether the sources of these enigmatic bursts arise from a single or from multiple distributions. Several authors contend that the histograms of GRB observables imply the latter. The two most-likely candidate components are galactic and cosmological. For example, some researchers claim that a dip in the V/V max distribution is a result of such a two-component source distribution. Others have used a parameter called the 'burst variability' calculated by dividing the maximum count rate on the 64-msec timescale by that from the 1024-msec timescale to show that a correlation of this parameter with bursts brightness implies a two-component model. This method has met vigorous criticism. We have developed two parameters that measure the variability or structure in the time profiles of BATSE gamma-ray bursts. Both parameters ('structure' and 'spike height') are based on the statistics of 'runs up' and 'runs down.' In short, the structure parameter is the observed number of runs (at several lengths) minus the number expected in a chance distribution. The 'spike height' is the sum of all run heights minus the expected sum. These two are straight-forward to calculate, robust, and measure the variability over the complete profile--not just at the peak. We have applied this algorithm to the profiles of 156 GRB's. In this paper we present graphs of the two parameters as functions of the following: (1) burst duration, (2) burst hardness ratio, (3) V/V max, (4) source galactic longitude, and (5) source galactic latitude. We seek correlations as well as groupings in the data that might indicate a multi-component source distribution.
    Keywords: SPACE RADIATION
    Type: Alabama Univ., The 1993 NASA(ASEE Summer Faculty Fellowship Program; 5 p
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  • 15
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    Future radiation measurements in low Earth orbit (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The first Long Duration Exposure Facility (LDEF) mission has demonstrated the value of the LDEF concept for deep surveys of the space radiation environment. The kinds of measurements that could be done on a second LDEF mission are discussed. Ideas are discussed for experiments which: (1) capitalize on the discoveries from LDEF 1; (2) take advantage of LDEF's unique capabilities; and (3) extend the investigations begun on LDEF 1. These ideas have been gleaned from investigators on LDEF 1 and others interested in the space radiation environment. They include new approaches to the investigation of Be-7 that was discovered on LDEF 1, concepts to obtain further information on the ionic charge state of cosmic rays and other energetic particles in space and other ideas to extend the investigations begun on LDEF 1.
    Keywords: SPACE RADIATION
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 4: Second Post-Retrieval Symposium; p 1551-1561
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  • 16
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    Progress report on the ultra heavy cosmic ray experiment (AO178) (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Ultra Heavy Cosmic Ray Experiment (UHCRE) is based on a modular array of 192 side-viewing solid state nuclear track detector stacks. These stacks were mounted in sets of four in 48 pressure vessels employing sixteen peripheral Long Duration Exposure Facility (LDEF) trays. The extended duration of the LDEF mission has resulted in a greatly enhanced scientific yield from the UHCRE. The geometry factor for high energy cosmic ray nuclei, allowing for Earth shadowing, was 30 sq m-sr, giving a total exposure factor of 170 sq m-sr-y at an orbital inclination of 28.4 degrees. Scanning results indicate that about 3000 cosmic ray nuclei in the charge region with Z greater than 65 were collected. This sample is more than ten times the current world data in the field (taken to be the data set from the HEAO-3 mission plus that from the Ariel-6 mission) and is sufficient to provide the world's first statistically significant sample of actinide (Z greater than 88) cosmic rays. Results to date are presented including details of ultra-heavy cosmic ray nuclei, analysis of pre-flight and post-flight calibration events and details of track response in the context of detector temperature history. The integrated effect of all temperature and age related latent track variations cause a maximum charge shift of +/- 0.8 e for uranium and +/- 0.6 e for the platinum-lead group. The precision of charge assignment as a function of energy is derived and evidence for remarkably good charge resolution achieved in the UHCRE is considered. Astrophysical implications of the UHCRE charge spectrum are discussed.
    Keywords: SPACE RADIATION
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 1: Second Post-Retrieval Symposium; p 261-268
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  • 17
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    The GAMCIT gamma ray burst detector (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The GAMCIT payload is a Get-Away-Special payload designed to search for high-energy gamma-ray bursts and any associated optical transients. This paper presents details on the design of the GAMCIT payload, in the areas of battery selection, power processing, electronics design, gamma-ray detection systems, and the optical imaging of the transients. The paper discusses the progress of the construction, testing, and specific design details of the payload. In addition, this paper discusses the unique challenges involved in bringing this payload to completion, as the project has been designed, constructed, and managed entirely by undergraduate students. Our experience will certainly be valuable to other student groups interested in taking on a challenging project such as a Get-Away-Special payload.
    Keywords: SPACE RADIATION
    Type: NASA. Goddard Space Flight Center, The 1993 Shuttle Small Payloads Symposium; p 47-56
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  • 18
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    Status of LDEF ionizing radiation measurements and analysis (1993)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: At this symposium significant new data and analyses were reported in cosmic ray research, radiation dosimetry, induced radioactivity, and radiation environment modeling. Measurements of induced radioactivity and absorbed dose are nearly complete, but much analysis and modeling remains. Measurements and analyses of passive nuclear track detectors (PNTD), used to derive the cosmic ray composition and spectra, and linear energy transfer (LET) spectra, are only a few percent complete, but important results have already emerged. As one might expect at this stage of the research, some of the new information has produced questions rather than answers. Low-energy heavy nuclei detected by two experiments are not compatible with known solar or cosmic components. Various data sets on absorbed dose are not consistent, and a new trapped proton environment model does not match the absorbed dose data. A search for cosmogenic nuclei other than Be-7 on Long Duration Exposure Facility (LDEF) surfaces has produced an unexpected result, and some activation data relating to neutrons is not yet understood. Most of these issues will be resolved by the analysis of further experiment data, calibrations, or the application of the large LDEF data set that offers alternate data or analysis techniques bearing on the same problem. The scope of the papers at this symposium defy a compact technical summary. I have attempted to group the new information that I noted into the following groups: induced radioactivity; absorbed dose measurements; LET spectra and heavy ion dosimetry; environment modeling and three dimensional shielding effects; cosmogenic nuclei; and cosmic rays and other heavy ions. The papers generally are expository and have excellent illustrations, and I refer to their figures rather than reproduce them here. The general program and objectives of ionizing radiation measurements and analyses on LDEF has been described previously.
    Keywords: SPACE RADIATION
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Part 1: Second Post-Retrieval Symposium; p 69-78
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  • 19
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    Transport methods and interactions for space radiations (1993)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: This report presents a brief history leading to the involvement of the Langley Research Center of the National Aeronautics and Space Administration (NASA) in space-radiation physics and protection. Indeed, a relatively complete summary of technical capability as of the summer of 1990 is given. The Boltzmann equations for coupled ionic and neutronic fields are presented and inversion techniques for the Boltzmann operator are discussed. Errors generated by the straight ahead approximation are derived and are shown to be negligible for most problems of space-radiation protection. A decoupling of projectile propagation from the target fields greatly simplifies the Boltzmann equations and allows an analytic solution of the target fragment transport. Analytic and numerical methods of solving the projectile transport equations are discussed. The nuclear physics underlying the coefficients in the Boltzmann equation is discussed. A coupled-channel optical model is found as a consequence of the loose binding of nuclear matter and closure of the nuclear states in high-energy reactions. Transport solutions with the developed data base are used with laboratory experiments to validate both the transport code and the data base. Numerical benchmarks and comparison with Monte Carlo calculations are also used for code validation.
    Keywords: SPACE RADIATION
    Type: ; : Spaceflight mechan
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  • 20
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    Gamma-ray bursts from neutron star mergers (1993)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Binary neutron stars merger (NS(sup 2)M) at cosmological distances is probably the only gamma-ray bursts model based on an independently observed phenomenon which is known to be taking place at a comparable rate. We describe this model, its predictions and some open questions.
    Keywords: SPACE RADIATION
    Type: NASA-CR-199498 , NAS 1.26:199498
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  • 21
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    Fireballs (1993)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The sudden release of copiuos gamma-ray photons into a compact region creates an opaque photon-lepton fireball due to the prolific production of electron-positron pairs. The photons that we observe in the bursts emerge only at the end of the fireball phase after it expanded sufficiently to become optically thin or after it converted its energy to the kinetic energy of relativistic baryons which convert it, in turn, to electromagnetic pulse via the interaction with interstellar matter. It is essential, therefore, to analyze the eveolution of a fireball in order to comprehend the observed features of gamma-ray bursts. We discuss various aspects of fireball hydrodynamics and the resulting emitted spectra.
    Keywords: SPACE RADIATION
    Type: NASA-CR-199518 , NAS 1.26:199518
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  • 22
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    An April 1991 outburst from 4U0115+63 observed by BATSE (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: 4U0115+63 is a recurrent transient X-ray pulsar in a moderately eccentric orbit with a Be star companion, V635 Cas. Many outbursts from this system have been reported over the past twenty years; yet despite the apparent relation between optical outbursts from the companion star and subsequent X-ray transient events, the physical mechanism for the mass transfer in the system remains unclear. In this paper, we present the preliminary results of analysis of observations made using BATSE during the 1991 April outburst from this system. This outburst does not fit the pattern of three year recurrence intervals previously suggested by Whitlock, Roussel-Dupre and Priedhorsky (1989). The orbital elements of the system have been updated and do not support the claim of Tamura et al., (1992) that apsidal motion was detected in this system based on the 1990 Ginga outburst.
    Keywords: SPACE RADIATION
    Type: DE94-007093 , NASA-CR-195252 , NAS 1.26:195252 , SLAC-PUB-6406
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  • 23
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    The solar spectral irradiances from x ray to radio wavelengths (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Sources of new measurements of the solar EUV, UV, and visible spectrum are presented together with discussion of formation of the solar spectrum as a problem in stellar atmospheres. Agreement between the data and a modern synthetic spectrum shows that observed radiative variability is a minor perturbation on a photosphere in radiative equilibrium and local thermodynamic equilibrium (LTE). Newly observed solar variability in 1992 defines a magnetic episode on the Sun closely associated with changes in both spectral irradiances and the total irradiance. This episode offers the opportunity to track the relationship between radiation and magnetic flux evolution.
    Keywords: SPACE RADIATION
    Type: NASA-CR-195203 , NAS 1.26:195203
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  • 24
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    A search for radiative neutrino decay from supernovae (1993)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Two supernovae have been identified in the COMPTEL data base as being the best sources to investigate for evidence of gamma-ray emission caused by radiative neutrino decay. These are SN1987a and SN1993J. A detailed simulation has shown us that we can expect a gain in sensitivity 1-3 orders of magnitude (depending on neutrino mass) over previous results. Instrument response is now being modeled using a SPARC10 computer acquired for this study. A library of simulated gamma-ray lines is being produced for COMPTEL as a by-product of this effort.
    Keywords: SPACE RADIATION
    Type: NASA-CR-196011 , NAS 1.26:196011
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  • 25
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    Cosmogenic-radionuclide profiles in Knyahinya: New measurements and models (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Cosmic-ray-produced nuclides measured in samples taken from known locations on a big slab of the large (R approximately equals to 45 cm) L5-chondrite Knyahinya provide good depth-vs-concentration profiles to develop and test models for the production of cosmogenic nuclides in meteorites. We report new profiles for Be-10, Al-26, Cl-36 in metallic and non-magnetic phases of 8 documented samples from Knyahinya and for C-14 in bulk samples from 7 Knyahinya samples. These new measured profiles are very similar to profiles calculated with particle fluxes from the LAHET Monte Carlo production and transport code system and with cross sections for major reactions.
    Keywords: SPACE RADIATION
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 3: N-Z; p 1195-1196
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    X-ray emission from a complete sample of Abell clusters of galaxies (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Rosat all sky survey is used to investigate the X-ray properties of a sample of Abell clusters with measured redshifts and accurate positions. The sample comprises the 145 clusters within a 561 square degree region at high galactic latitude. The mean redshift is 0.17. The sample mean exposure time is higher than average and its mean galactic column density is very low. These together produce a flux limit of about 4.2 x 10(exp -13) erg/sq cm/s in the 0.5 to 2.5 keV energy band. By analyzing the excess of positive fluctuations of the X-ray flux at the cluster positions, compared with the fluctuations of randomly drawn background fields, it is possible to extend these results below the nominal flux limit. It is found that 80 of richness R equal to or greater than 0 and 86 of R equal to or greater than 1 clusters are X-ray emitters with fluxes above 1.10 to the power of minus 13 erg/sq cm/s. Nearly 90 of the clusters meeting the requirements to be in Abell's statistical sample emit above the same level. It is concluded that almost all Abell clusters are real clusters and the Abell catalogue is not strongly contaminated by projection effects. The Kaplan-Meier product limit estimator is used to calculate the cumulative X-ray luminosity function. It is shown that the shape of the luminosity functions are similar for different richness classes, but the characteristic luminosities of richness 2 clusters are about twice of those of richness 1 clusters which are in turn about twice of those of richness zero clusters. This result is another manifestation of the luminosity richness relation for Abell cluster.
    Keywords: SPACE RADIATION
    Type: NASA-CR-197700 , NAS 1.26:197700 , MPE-PREPRINT-257
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    Time dependent simulation of cosmic-ray shocks including Alfven transport (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Time evolution of plane, cosmic-ray modified shocks was simulated numerically for the case with parallel magnetic fields. Computations were done in a 'three-fluid' dynamical model incorporating cosmic-ray and Alfven wave energy transport equations. Nonlinear feedback from the cosmic-rays and Alfven waves is included in the equation of motion for the underlying plasma, as is the finite propagation speed and energy dissipation of the Alfven waves. Exploratory results confirm earlier, steady state analyses that found these Alfven transport effects to be potentially important when the upstream Alfven speed and gas sound speeds are comparable. As noted earlier Alfven transport effects tend to reduce the transfer of energy through a shock from gas to energetic particles. These studies show as well that the time scale for modification of the shock is altered in nonlinear ways. It is clear, however, that the consequences of Alfven transport are strongly model dependent and that both advection of cosmic-rays by the waves and dissipation of wave energy in the plasma will be important to model correctly when quantitative results are needed. Comparison is made between simulations based on a constant diffusion coefficient and more realistic diffusion models allowing the diffusion coefficient to vary in response to changes in Alfven wave intensity. No really substantive differences were found between them.
    Keywords: SPACE RADIATION
    Type: NASA-CR-192931 , NAS 1.26:192931
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    Effects of radiobiological uncertainty on shield design for a 60-day lunar mission (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Some consequences of uncertainties in radiobiological risk due to galactic cosmic ray exposure are analyzed to determine their effect on engineering designs for a first lunar outpost - a 60-day mission. Quantitative estimates of shield mass requirements as a function of a radiobiological uncertainty factor are given for a simplified vehicle structure. The additional shield mass required for compensation is calculated as a function of the uncertainty in galactic cosmic ray exposure, and this mass is found to be as large as a factor of 3 for a lunar transfer vehicle. The additional cost resulting from this mass is also calculated. These cost estimates are then used to exemplify the cost-effectiveness of research.
    Keywords: SPACE RADIATION
    Type: NASA-TM-4422 , L-17136 , NAS 1.15:4422
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    A search for radiative neutrino decay from supernovae (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This document presents the data analysis procedures proposed for use with the COMPTEL instrument aboard the Compton Gamma Ray Observatory (GRO) in the search for radiative neutrino decay from supernovae. The proposed analysis methodology is an extension of a standard procedure used by the COMPTEL team in searching for a variety of source types. We have applied the procedures to a set of simulated data to demonstrate the feasibility of the method to this project.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193118 , NAS 1.26:193118 , LSU-HEPA-93-7
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    Limits on neutrino radiative decay from SN1987A (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We calculate limits on the properties of neutrinos using data from gamma ray detectors on the Pioneer Venus Orbiter and Solar Max Mission satellites. A massive neutrino decaying in flight from the supernova would produce gamma rays detectable by these instruments. The lack of such a signal allows us to constrain the mass, radiative lifetime, and branching ratio to photons of a massive neutrino species produced in the supernova.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193262 , NAS 1.26:193262
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    Polarization correction for ionization loss in a galactic cosmic ray transport code (HZETRN) (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An approximate polarization correction for ionization loss suggested by Sternheimer has been implemented in the galactic cosmic ray transport code (HZETRN) developed at the Langley Research Center. Sample calculations made for the aluminum shield and liquid hydrogen shield show no more than a plus or minus 2 percent change in the linear energy transfer (LET) distribution for flux compared with those without polarization correction. This very small change is expected because the effect of polarization correction on the reduction in stopping power of ions with energies above 2 GeV/amu is suppressed by the decrease in galactic cosmic ray ion flux at such high energies.
    Keywords: SPACE RADIATION
    Type: NASA-TM-4443 , L-17192 , NAS 1.15:4443
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  • 32
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    Alfven wave transport effects in the time evolution of parallel cosmic-ray modified shocks (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Some of the issues associated with a more complete treatment of Alfven transport in cosmic ray shocks are explored qualitatively. The treatment is simplified in some important respects, but some new issues are examined and for the first time a nonlinear, time dependent study of plane cosmic ray mediated shocks with both the entropy producing effects of wave dissipation and effects due to the Alfven wave advection of the cosmic ray relative to the gas is included. Examination of the direct consequences of including the pressure and energy of the Alfven waves in the formalism began.
    Keywords: SPACE RADIATION
    Type: NASA-CR-192932 , NAS 1.26:192932
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    Semiempirical fragmentation models on galactic cosmic ray transport calculations with hydrogen target (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Nuclear fragmentation cross sections of Silberberg and Tsao that are more accurate for a hydrogen target were implemented in the data base to replace those of Rudstam for a galactic cosmic ray transport code (HZETRN). Sample calculations were made for the transported galactic cosmic ray flux through a liquid hydrogen shield at solar minimum condition to determine the effect of such a change. The transported flux based on the Silberberg-Tsao semiempirical formalism contains fewer high-LET (linear energy transfer) components but more low-LET components than the results based on Rudstam's formalism: and this disparity deepens as the shield thickness increases. A comparison of the results obtained from using both energy-dependent and energy-independent cross sections of Silberberg and Tsao indicates that the energy-independent assumption results in an underestimation of high-LET flux above 100 keV/micron by approximately 40 percent for a 15-g/cm(sup 2) thickness of liquid hydrogen. Similar results were obtained in a previous study when both energy-dependent and energy-independent cross sections of Rudstam were considered. Nonetheless, the present study found that an energy-independent calculation would be best accomplished by using Rudstam's cross sections as done in the past for various engineering applications.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3350 , L-17227 , NAS 1.60:3350
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    Nonperturbative methods in HZE ion transport (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A nonperturbative analytic solution of the high charge and energy (HZE) Green's function is used to implement a computer code for laboratory ion beam transport. The code is established to operate on the Langley Research Center nuclear fragmentation model used in engineering applications. Computational procedures are established to generate linear energy transfer (LET) distributions for a specified ion beam and target for comparison with experimental measurements. The code is highly efficient and compares well with the perturbation approximations.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3363 , L-17241 , NAS 1.60:3363
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    Cosmological gamma-ray burst model (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A cosmological gamma-ray burst model that reproduces the observed gamma-ray spectra was developed. This model, which is an outgrowth of work on synchrotron emission from cosmological sources, creates the observed spectra from a power law spectrum through Compton attenuation in dense molecular clouds. It restricts the burst source to the centers of galaxies, and it is easily tested through comparisons with time dependent burst spectra. Dr. Brainerd continued development of a Monte Carlo code that tracks the random walk of a gamma-ray through a plasma in a strong magnetic field and used this code to show that a two temperature plasma in a strong magnetic field can suppress soft x-ray emission.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193368 , NAS 1.26:193368
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    Effects of radiobiological uncertainty on vehicle and habitat shield design for missions to the moon and Mars (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Some consequences of uncertainties in radiobiological risk due to galactic cosmic ray (GCR) exposure are analyzed for their effect on engineering designs for the first lunar outpost and a mission to explore Mars. This report presents the plausible effect of biological uncertainties, the design changes necessary to reduce the uncertainties to acceptable levels for a safe mission, and an evaluation of the mission redesign cost. Estimates of the amount of shield mass required to compensate for radiobiological uncertainty are given for a simplified vehicle and habitat. The additional amount of shield mass required to provide a safety factor for uncertainty compensation is calculated from the expected response to GCR exposure. The amount of shield mass greatly increases in the estimated range of biological uncertainty, thus, escalating the estimated cost of the mission. The estimates are used as a quantitative example for the cost-effectiveness of research in radiation biophysics and radiation physics.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3312 , L-17188 , NAS 1.60:3312
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    Decaying neutrinos in galaxy clusters (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The DM profile in clusters of galaxies was studied and simulated using the Harrison-Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations and in agreement with microwave background fluctuations. Neutrino DM densities, with this amplitude normalization cluster, are comparable to observed cluster DM values. It was concluded that given this normalization, the cluster DM should be al least largely composed of neutrinos. The constraint of Davidson et al., who argued that the failure to detect uv photons from the dark matter (DM) in cluster A665 excludes the decaying neutrino hypothesis, could be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.
    Keywords: SPACE RADIATION
    Type: NASA-CR-197615 , NAS 1.26:197615
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    Calculations of cosmic-ray helium transport in shielding materials (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The transport of galactic cosmic-ray helium nuclei and their secondaries through bulk shielding is considered using the straight-ahead approximation to the Boltzmann equation. A data base for nuclear interaction cross sections and secondary particle energy spectra for high-energy light-ion breakup is presented. The importance of the light ions H-2, H-3, and He-3 for cosmic-ray risk estimation is discussed, and the estimates of the fractional contribution to the neutron flux from helium interactions compared with other particle interactions are presented using a 1977 solar minimum cosmic-ray spectrum.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3354 , L-17225 , NAS 1.60:3354
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  • 39
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    Approximate Green's function methods for HZE transport in multilayered materials (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A nonperturbative analytic solution of the high charge and energy (HZE) Green's function is used to implement a computer code for laboratory ion beam transport in multilayered materials. The code is established to operate on the Langley nuclear fragmentation model used in engineering applications. Computational procedures are established to generate linear energy transfer (LET) distributions for a specified ion beam and target for comparison with experimental measurements. The code was found to be highly efficient and compared well with the perturbation approximation.
    Keywords: SPACE RADIATION
    Type: NASA-TM-4519 , L-17302 , NAS 1.15:4519
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  • 40
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    Coulomb effects in low-energy nuclear fragmentation (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Early versions of the Langley nuclear fragmentation code NUCFRAG (and a publicly released version called HZEFRG1) assumed straight-line trajectories throughout the interaction. As a consequence, NUCFRAG and HZEFRG1 give unrealistic cross sections for large mass removal from the projectile and target at low energies. A correction for the distortion of the trajectory by the nuclear Coulomb fields is used to derive fragmentation cross sections. A simple energy-loss term is applied to estimate the energy downshifts that greatly alter the Coulomb trajectory at low energy. The results, which are far more realistic than prior versions of the code, should provide the data base for future transport calculations. The systematic behavior of charge-removal cross sections compares favorably with results from low-energy experiments.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3352 , L-17226 , NAS 1.60:3352
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  • 41
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    The (C2) 158 micrometer emission from the Horsehead nebula (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The C II 158 micrometer line and the several rotational lines of CO, CO-13, and CS toward selected positions in the Horsehead extinction region in IC 434 are mapped. The observations show that the region has a gas density of about 10,000 cu cm and an external UV (Ultraviolet) flux to 20 to 100 times the average interstellar UV field. Although this is a regime where the C+ emission varies rapidly with UV intensity, fine structure line emission from gas with this range of physical conditions were not investigated previously. Comparisons of results with models of photodissociation regions show that existing plane parallel photodissociation region models are in general agreement with the observed intensity. It is not necessary to invoke a clumpy structure in the boundary layer to explain the observations, but the overall geometry of the cloud is important in determining the distribution of C+ emission.
    Keywords: SPACE RADIATION
    Type: NASA-CR-197797 , NAS 1.26:197797 , MPE-PREPRINT-262
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  • 42
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    Near-simultaneous ROSAT and Ginga observations of the 1991 X-ray transient in Musca (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The quasi simultaneous Rosat/Ginga observations of the Musca X-ray transient are reported. During its all sky survey, Rosat observed the Musca 1991 X-ray transient on 24-25 Jan. 1991, two weeks after outbursts, for about 170 seconds. The intensity was found to be nearly 6 Crab in the Rosat band. A combined fit of Rosat and Ginga data from 25 Jan. 1991 with a multitemperature disk blackbody model data plus a power law component results in a maximal temperature of the disk of about kT = 0.96 keV at an absorbing column of N(sub H) = 2.2 x 10(exp 21)/sq cm. A minimum distance to the black hole binary of at least 4 to 5 kpc was derived. Including the accretion disk inclination angle of i = 26 +/- 25 degrees determined from the shape of the positron annihilation line, and the quiescent optical brightness together with the most probable spectral type of the companion, a black hole mass of M = (6 +/- 1.5) of the solar mass and a distance of about (11 +/- 3) kpc, were derived. Additional Rosat observations in Aug. 1991 and Mar. 1992 suggest that the exponential intensity decay until 240 days after the outburst is followed by a steeper decline between 240 and 410.
    Keywords: SPACE RADIATION
    Type: NASA-TM-110597 , NAS 1.15:110597 , MPE-PREPRINT-273
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    Two populations and models of gamma ray bursts (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Gamma-ray burst statistics are best explained by a source population at cosmological distances, while spectroscopy and intensity histories of some individual bursts imply an origin on Galactic neutron stars. To resolve this inconsistency I suggest the presence of two populations, one at cosmological distances and the other Galactic. I build on ideas of Shemi and Piran (1990) and of Rees and Mesozaros (1992) involving the interaction of fireball debris with surrounding clouds to explain the observed intensity histories in bursts at cosmological distances. The distances to the Galactic population are undetermined because they are too few to affect the statistics of intensity and direction; I explain them as resulting from magnetic reconnection in neutron star magnetospheres. An appendix describes the late evolution of the debris as a relativistic blast wave.
    Keywords: SPACE RADIATION
    Type: NASA-CR-194762 , NAS 1.26:194762
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    Relativistically expanding pair plasmas as bursting sources of cosmic gamma rays (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: High temperature shock heating of relativistically expanding plasmas produced in neutron star binary mergers provides a model for cosmic gamma ray burst sources. This requires the fireball resulting from the merger to have a very high entropy per baryon, mechanisms for which are discussed. The energy, temporal structure and spectrum produced by the blast wave and reverse shock as the fireball is decelerated in an external medium are comparable to those observed, as is the frequency of occurrence and the characteristics of the spatial distribution of the events. Difficulties common to all cosmological gamma ray burst scenarios concern the total amount of energy ultimately appearing at gamma ray energies, the time scales, the spectrum, and the great variety of time profiles. A very general mechanism which overcomes these problems is presented. Situations where the pair plasma is created in regions which are relatively free of baryons are discussed. The effect of the interaction of the expanding fireball with the external medium is considered.
    Keywords: SPACE RADIATION
    Type: ESA, Fourth International Toki Conference on Plasma Physics and Controlled Nuclear Fusion; p 165-168
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    Exposure fluctuations of astronauts due to orientation (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The dose incurred in an anisotropic environment depends on the orientation of the astronaut's body relative to the direction of the radiation field. The fluctuations in exposure of specific organs due to astronaut orientation are found to be a factor of 2 or more in a typical space habitation module and typical space radiations. An approximation function is found that overestimates astronaut exposure in most cases studied and is recommended as a shield design guide for future space missions.
    Keywords: SPACE RADIATION
    Type: NASA-TP-3364 , L-17254 , NAS 1.60:3364
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    A proposed performance index for galactic cosmic ray shielding materials (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: In past studies, the reductions in absorbed dose and dose equivalent due to choice of material composition have been used to indicate shield effectiveness against exposure to galactic cosmic rays. However, these quantities are highly inaccurate in assessing shield effectiveness for protection against the biological effects of long-term exposure to the galactic heavy ions. A new quantity for shield performance is defined that correlates well with cell killing and cell transformation behind various shield thicknesses and materials. In addition, a relative performance index is identified that is inversely related to biological injury for different materials at a fixed shield mass and is directly related to the ratio of the fourth- and the second-order linear energy transfer (LET) moments.
    Keywords: SPACE RADIATION
    Type: NASA-TM-4444 , L-17199 , NAS 1.15:4444
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    Neutron star mergers and gamma-ray bursts (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Under the support of grant NAG 5-1904, we have carried out research on several topics related to gamma-ray bursts (GRB's). In our proposal, we stated that we would study three topics: (1) fireball evolution; (2) neutron star mergers; and (3) statistics of bursts. We have completed a significant amount of work in each of these areas. Resulting papers from this work are presented.
    Keywords: SPACE RADIATION
    Type: NASA-CR-195176 , NAS 1.26:195176
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    The return of the anomalous cosmic rays to 1 Au in 1992 (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: New observations of low energy (approximately 1 to 200 MeV/nuc) cosmic rays measured by three newly launched experiments on Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) during 1992 and 1993 show the strong presence of anomalous cosmic ray (ACR) nitrogen and oxygen, well before the approaching solar minimum. When compared with ACR temporal variations over the past two solar cycles we find that the 1992-1993 fluxes are approximately 5 to 10 times their level at corresponding neutron monitor counting rates in 1969-1970 and 1985.
    Keywords: SPACE RADIATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 20; p. 2263-2266
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    Scientific studies in association with the Shuttle Solar Backscatter Ultraviolet (SSBUV) project (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During the past reporting period efforts focused on performing detailed comparisons between measurements made by the SBUV/2 V instruments carried on NOAA-9 and NOAA-11 and the first three flights of the Shuttle Solar Backscatter Ultraviolet (SSBUV) project. The quantities to be compared are the measurables, being the ratio of emergent radiance (I) in the vertical direction to the incoming solar irradiance (F). The backscatter albedo, A(w,j), was defined by: A(w,j) = I(w,j)/F(w,j) where w = 1,2,..., 12 refers to wavelength, and j indicates the instrument and flight on which the data were obtained. The comparisons to be made are NOAA-9 to SSBUV-1, NOAA-11 to SSBUV-2, and NOAA-11 to SSBUV-3. For the comparisons the N-values contained in the data files supplied by GSFC were converted to albedos via: A(w,j) = 10(exp N(w,j)/100). The comparisons described were designed to characterize the differences between the NOAA and SSBUV data sets.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193404 , NAS 1.26:193404
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    X ray emission from Wolf-Rayet stars with recurrent dust formation (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We were granted a ROSAT observation of the Wolf-Rayet star WR 137 (equals HD 192641) to test a proposed mechanism for producing the infrared variability reported by Williams et al. (1987). These studies showed one clear infrared outburst preceded by what may be the dimming of a previous outburst. The recurrent dust formation model was put forward by Williams et al. (1990) to account for similar variability seen in WR 140, which varies in both the infrared and X-ray bands. The detected X-ray flux from WR 140 was observed to decrease from its normally high (for Wolf-Rayet stars) level as the infrared flux increased. Observation of two apparently-periodic infrared outbursts led to the hypothesis that WR 140 had an O star companion in an eccentric orbit, and that the increase in infrared flux came from a dust formation episode triggered by the compression of the O star and Wolf-Rayet star winds. The absorption of the X-rays by the increased material explained the decrease in flux at those wavelengths. If the infrared variability in WR 137 were caused by a similar interaction of the Wolf-Rayet star with a companion, we might expect that WR 137 would show corresponding X-ray variability and an X-ray luminosity somewhat higher than typical WC stars, as well as a phase-dependent non-thermal X-ray spectrum. Our goals in this study were to obtain luminosity estimates from our counting rates for comparison with previous observations of WR 137 and other WC class stars, especially WR 140; to compare the luminosity with the IR lightcurve; and to characterize the spectral shape of the X-ray emission, including the column density.
    Keywords: SPACE RADIATION
    Type: NASA-CR-189321 , NAS 1.26:189321 , R93-213
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    Neptune high-latitude emission: Dependence of angle on frequency (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Smooth broadband radio emission reached a maximum and then cut off as Voyager approached the north magnetic pole of Neptune. The time of each event depends on frequency, yielding information on radio source location, and emission angle. In a preliminary analysis L-shell and magnetic longitude define radio-source locations in a dipole field. The emission angle at each frequency is identified with the angle between the magnetic-field direction at the source and the line of sight to Voyager 2 at the time of emission maximum. At each value of L in the range 6 less than L less than 9, there is one source longitude for which emission angle varies smoothly from greater or equal to 90 deg at 40 kHz to as low as 20 deg at 462 kHz. A more complex magnetic-field model can give a qualitatively different result.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193280 , NAS 1.26:193280
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    Research in cosmic and gamma ray astrophysics: Cosmic physics portion (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Research in particle astrophysics at the Space Radiation Laboratory (SRL) of the California Institute of Technology is supported under NASA Grant NAGW-1919. A three-year proposal for continuation of support was submitted a year ago and put into effect 1 October 1992. This report is the combined progress report and continuation application called for under the Federal Demonstration Project. Gamma-ray Astrophysics at SRL is separately supported under NAGW-1919 and will be separately summarized and proposed. This report will document progress and plans for our particle spectroscopy activities and for related data analysis, calibration, and community service activities. A bibliography and a budget will be attached as appendices. The Caltech SRL research program includes a heavy emphasis on elemental and isotopic spectroscopy of energetic particles in the cosmic radiation; in solar, interplanetary, and anomalous 'cosmic' radiation; and in planetary magnetospheres as discussed.
    Keywords: SPACE RADIATION
    Type: NASA-CR-194127 , NAS 1.26:194127
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    Analysis of data from the energetic gamma-ray experiment on the gamma ray observatory (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The work under the Grant has involved continued participation with the Compton Gamma Ray Observatory Energetic Gamma-Ray Experiment Telescope (EGRET) Team in the analysis of data obtained during instrument operations and the preparation of scientific papers and proposals for future observations. The EGRET team was also successful on many proposals for the Phase 3 portion of the mission, including long high galactic latitude studies of the diffuse extragalactic radiation. These studies will be used in a effort to establish whether this radiation is truly diffuse or the sum of radiation from unresolved discrete sources such as radio-loud quasars. The effort involved working remotely by internet connection on the Goddard Space Flight Center Computers where the EGRET data are archived. Students have monitored instrument performance and analyzed data remotely and will continue to do so. The PI has completed the detailed analysis of five viewing periods to search for point sources and this work has been used in developing the first EGRET catalog of sources, soon to be released.
    Keywords: SPACE RADIATION
    Type: NASA-CR-194178 , NAS 1.26:194178
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    Cosmic physics data analysis program (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A data analysis program was carried out to investigate the intensity, propagation, and origin of primary Cosmic Ray Galactic electrons. Scanning was carried out on two new balloon flight experiments as well as the border area of previous experiments. The identification and evaluation of the energies of the primary electrons were carried out. A new analysis of these data were incorporated into an overall evaluation of the roll of electrons in the problem of the origin of cosmic rays. Recent measurements indicate that the earth may be within the expanding Geminga supernova shock wave which is expected to have a major effect upon the propagation and the energy spectrum of galactic electrons. Calculations with the Geminga model indicate that the cut-off energy may be very close to the observed highest energy electrons in our analysis.
    Keywords: SPACE RADIATION
    Type: NASA-CR-194357 , NAS 1.26:194357
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    Models of Neptune's smooth recurrent radio emission (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The quantitative response of the Planetary Radio Astronomy (PRA) instrument to a wave with polarization ellipse of arbitrary shape and orientation, arriving at the antennas from any direction, can be determined. This capability is used to model the time variation of intensity and circular polarization over a range of radio frequencies for proposed radio-source locations and emission characteristics at Neptune. At frequencies below 400 kHz the observed variation of intensity, polarization, and phase are closely simulated in an offset tilted dipole magnetic field by conjugate sources at midlatitude with filled emission cones. The phase of emission at higher frequencies is reproduced by sources at lower latitude. Modeled wide-cone emission does not reach the spacecraft at the observed phase nor have the polarization sense observed before closest approach. Source-surface maps of apparent polarization for the period before closest approach when instrumental response is especially sensitive to source location is presented. The method is capable of extension to more realistic models of the magnetic field.
    Keywords: SPACE RADIATION
    Type: NASA-CR-193283 , NAS 1.26:193283
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    Na-22 decay gamma rays from classical novae (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA Grant NAG 5-1565 has provided support for a program of theoretical research in nuclear astrophysics and related areas, focusing upon the possibility of detecting gamma rays from nearby novae. Particular attention has been given to the evaluation of the theoretical expectations for gamma ray emission from four possible sources: (1) the positron decays of the unstable CNO and fluorine isotopes that are transported to the surface regions of the envelope in the earliest stages of the outbursts; (2) Be-7 decay gamma rays, (3) Na-22 decay gamma rays released in the later stages of the outbursts; and (4) Al-26 decay gamma rays from novae and their possible contribution to Galactic emission. The critical questions of (1) the frequency of occurrence of ONeMg-enriched novae; (2) the expected Galactic distribution of the novae that produce 26Al; and (3) the nature of the observed soft X-ray emission from classical novae, have also been addressed. Considerable progress in research has been achieved on many of these fronts. Brief summaries of the results of several research projects are presented.
    Keywords: SPACE RADIATION
    Type: NASA-CR-197454 , NAS 1.26:197454
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    The role of ducted whistlers in the precipitation loss and equilibrium flux of radiation belt electrons (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Evidence is presented for a close association betwen individual whistler ducts and conjugate ionospheric disturbances sensed by the perturbation of subionospheric VLF, LF, and MF signals. It is found that even the weakest whistlers can be associated with ionospheric disturbances in both hemispheres. A case study has shown that slow-onset and 'overshoot' perturbation signatures to be consistent with multiple ionospheric disturbances that are associated with individual components of multipath-ducted whistlers.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A9; p. 15,643-15,665.
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    Shielding from space radiations (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This Progress Report covering the period of 1 June 1993 to 1 Dec. 1993 presents the development of an analytical solution to the heavy ion transport equation in terms of a one-layer Green's function formalism. The mathematical developments are recasted into an efficient computer code for space applications. The efficiency of this algorithm is accomplished by a nonperturbative technique of extending the Green's function over the solution domain. The code may also be applied to accelerator boundary conditions to allow code validation in laboratory experiments. Results from the isotopic version of the code with 80 isotopes present for a single layer target material, for the case of an Iron beam projectile at 600 MeV/nucleon in water is presented.
    Keywords: SPACE RADIATION
    Type: NASA-CR-194664 , NAS 1.26:194664
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    Cosmic background radiation anisotropy at degree angular scales - Further results from the South Pole (1993)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: We report further results from the University of California at Santa Barbara program to measure anisotropy in the cosmic background radiation at angular scales near 1 deg, an angular range corresponding to the largest scales where structure is observed. A 30 GHz high electron mobility transistor amplifier-based detector was coupled to the Advanced Cosmic Microwave Explorer, a 1 m off-axis Gregorian telescope. We present data that represent 64 of the total of 500 hr acquired with this system during the 1990-1991 season. The data have a statistical error of 13.5/micro-K/pixel. These are the smallest error bars of any data set of this type published to date. The data contain a significant signal with a maximum likelihood Delta T/T roughly 1 x 10 exp -5. The spectrum of the signal seen in slightly less than 2 sigma away from the thermal spectrum expected of primordial fluctuations in the cosmic background radiation. If the source of the fluctuations is primordial, then the data are consistent with cold dark matter scenarios when normalized to the large-scale anisotropy observed by COBE, while if the origin of the signal is foreground emission or another form of contaminant then the data are marginally inconsistent with standard cold dark matter models. In either case, the data are sufficiently sensitive to provide a crucial test of many models.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 412; 2; p. L47-L50.
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    Cosmic ray diurnal anisotropy for a solar magnetic cycle (1993)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: Cosmic ray diurnal anisotropy at high primary rigidities is extended for the 1980-1987 period. The computed values of the limiting primary rigidity for the period vary over the range 30 GV to 200 GV. For the previously studied 1965-1980 period, the mean value of the amplitude of the anisotropy is 0.5 percent. The amplitude of the diurnal anisotropy for 1965 and 1986-1987 is about 20 percent smaller. Very large amplitudes of diurnal variation are observed during the 1982-1985 period, at all primary rigidities. The value of the coupled variable lambda(parallel) x G(r) found to remain constant at about 1 percent for qA less than zero solar magnetic polarity epochs, independent of the primary rigidity. Its value is significantly lower for qA greater than zero epochs.
    Keywords: SPACE RADIATION
    Type: Planetary and Space Science (ISSN 0032-0633); 41; 2; p. 113-125.
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    Compton-backscattered annihilation radiation from the Galactic Center region (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: On 1989 May 22, the High Energy X-ray and Gamma-ray Observatory for Nuclear Emissions, a balloon-borne high-resolution germanium spectrometer with an 18-deg FOV, observed the Galactic Center (GC) from 25 to 2500 keV. The GC photon spectrum is obtained from the count spectrum by a model-independent method which accounts for the effects of passive material in the instrument and scattering in the atmosphere. Besides a positron annihilation line with a flux of (10.0 +/- 2.4) x 10 exp -4 photons/sq cm s and a full width at half-maximum (FWHM) of (2.9 + 1.0, -1.1) keV, the spectrum shows a peak centered at (163.7 +/- 3.4) keV with a flux of (1.55 +/- 0.47) x 10 exp -3 photons/sq cm s and a FWHM of (24.4 +/- 9.2) keV. The energy range 450-507 keV shows no positronium continuum associated with the annihilation line, with a 2-sigma upper limit of 0.90 on the positronium fraction. The 164 keV feature is interpreted as Compton backscatter of broadened and redshifted annihilation radiation, possibly from the source 1E 1740.7-2942.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 1; p. 165-177.
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    Threshold effects on V/V(max) for gamma-ray bursts (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The interpretation of the observed gamma-ray burst V/V(max) statistic in terms of spatial distributions is model-dependent. Detection of gamma-ray bursts requires the counting rate in one or more detectors to exceed a threshold C(lim) determined from a time-dependent background rate B(t). The sampling depth of the burst detector is thus time-dependent, and, if burst sources are nonuniform in space, the observed V/V(max) distribution will be affected by B(t). We demonstrate this effect with a simple geometric distribution of standard candles and argue that V/V(max) statistic without information on threshold variations is insufficient for rigorous data analysis. Peak count rates and threshold values must be given separately for all events in order to facilitate a meaningful comparison of observations with theoretical distribution models.
    Keywords: SPACE RADIATION
    Type: Astrophysics and Space Science (ISSN 0004-640X); 201; 2; p. 347-358.
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    The cosmic-ray He-3/He-4 ratio from 100 to 1600 MeV/amu (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Superconducting Magnet Instrument for Light Isotopes (SMILI) flew for 19 hours on September 1, 1989, with a residual overburden of 5 g/sq cm. It measured the charge, rigidity, and velocity of 30,000 cosmic-ray helium nuclei, with velocity determined by time-of-flight and Cerenkov techniques. Using these data, the flux and isotopic composition of helium as a function of energy were determined. The observed isotopic composition is consistent with that expected from interstellar propagation models inferred from the secondaries of CNO, in contrast to earlier observations which indicated an overabundance of He-3. We discuss constraints that this result places on cosmic-ray transport and solar modulation models.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 413; 1; p. 268-280.
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    Evidence for two distinct morphological classes of gamma-ray bursts from their short time scale variability (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We have analyzed the 241 bursts for which peak counts (C)max exist in the publicly available Burst and Transient Source Experiment (BATSE) catalog. Introducing peak counts in 1024 ms as a measure of burst brightness B and the ratio of peak counts in 64 and 1024 ms as a measure of short timescale variability V, we find a statistically significant correlation between the brightness and the short time scale variability of gamma-ray bursts. The bursts which are smoother on short time scales are both faint and bright, while the bursts which are variable on short time scales are faint only, suggesting the existence of two distinct morphological classes of bursts.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 413; 1; p. L11-L14.
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    Cosmic-ray gradients in the outer heliosphere (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We report on a study of the expected spatial variation of the galactic cosmic-ray intensity in the vicinity of the solar-wind termination shock. Model simulations predict that the radial gradients change abruptly at the shock, and that the nature of the effect varies significantly with particle energy. At low energies, the radial gradient changes abruptly from a lower value inside the shock to a higher value outside, whereas at high energies, the higher value of the gradient is inside the shock. This effect, which is a consequence of the matching conditions at the shock and is closely related to diffusive shock acceleration, is qualitatively the same for both heliospheric magnetic polarity states and remains much the same in one-dimensional, two-dimensional and three-dimensional models. Hence drifts do not change the nature of this phenomenon, although they change it quantitatively. The effect may prove to be an important diagnostic tool for the study of the termination of the solar wind.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 13; 6; p. 257-260.
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    Dependence of the interstellar propagation of ultraheavy cosmic-ray nuclei on various parameters (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A stepwise program of interstellar-cosmic-ray propagation suitable for implementation on a small work-station has been used to study the sensitivity of propagation models of ultraheavy cosmic-ray nuclei (UH nuclei) on the input parameters. In this program an initial set of relevant parameters describing the astrophysics of the propagations process and the nuclear physics representing the interactions was assumed. These parameters were then varied within the estimated uncertainties in order to evaluate the sensitivity of the predictions on the assumed values. It is shown that current uncertainties in the estimates of the UH nuclei nuclear cross sections for the production of lighter fragments present the most significant sources of error and are sufficient to preclude reaching detailed conclusions about the source composition. Other uncertainties, such as those in the escape probabilities, or the mean interstellar density, while still significant, are less serious.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 403; 2; p. 644-657.
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    Interpretation of gamma-ray burst source count statistics (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Ever since the discovery of gamma-ray bursts, the so-called log N-log S relation has been used for determination of their distances and distribution. This task has not been straightforward because of varying thresholds for the detection of bursts. Most of the current analyses of these data are couched in terms of ambiguous distributions, such as the distribution of Cp/Clim, the ratio of peak to threshold photon count rates, or the distribution of V/Vmax = (Cp/Clim) exp -3/2. It is shown that these distributions are not always a true reflection of the log N-log S relation. Some kind of deconvolution is required for obtaining the true log N-log S. Therefore, care is required in the interpretation of results of such analyses. A new method of analysis of these data is described, whereby the bivariate distribution of Cp and Clim is obtained directly from the data.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 402; 2; p. L33-L36.
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    Viewing the outer heliosphere in energetic neutral atoms (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The use of energetic neutral atoms (ENAs) to study the outer heliosphere is discussed. The detection of ENAs under stringent observational conditions is addressed. Imaging ENA instruments are examined.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 13; 6; p. 131-139.
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    Hale cycle effects in cosmic ray east-west anisotropy and interplanetary magnetic field (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We have reanalyzed diurnal anisotropy data obtained with the shielded ion chamber (IC) at Cheltenham/Fredericksburg and the neutron monitor (NM) at Swarthmore/Newark. IC data are for the 1936-1977 period and NM data are for the 1965-1988 period. We have corrected IC data for the diurnal temperature effect. Application of this correction results in a better agreement between IC and other data sets, thereby making it possible to study the long-term changes in the diurnal anisotropy using IC data. The behavior of the annual mean east-west anisotropy is studied for 53 years of observations. The period encompasses more than two solar magnetic (Hale) cycles. Its amplitude undergoes the expected 11 and 22 year variations, with the largest changes occurring near solar activity minima. Moreover, the data indicate the presence of the subsidiary maxima for the entire 53-year period, following the solar polar field reversals, during the declining phases of activity cycles when high-speed solar wind streams are present in the heliosphere. The data suggest that the amplitude of the subsidiary maximum is large when the solar polar magnetic field points toward the sun in the Northern Hemisphere, and radial anisotropy is absent.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A7; p. 11,513-11,519.
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    The limiting primary rigidity of cosmic ray diurnal anisotropy (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Our calculations of the upper cutoff primary rigidity (Rc), applicable to the solar diurnal anisotropy, have been extended to cover the declining phase of the solar activity cycle 21. The calculated values of Rc now encompass a complete solar magnetic cycle (1965-1987). We found that the values of Rc were very large for the 1982-1985 period, almost twice as large as those observed previously for the periods of maximum solar activity. The largest value occurred in 1983. Also, the value obtained at the solar activity minimum year of 1986 was about twice as large as that obtained in 1965. Our results are compared with those reported by others.
    Keywords: SPACE RADIATION
    Type: Planetary and Space Science (ISSN 0032-0633); 41; 2; p. 105-112.
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    Gamma-ray bursts from planetesimal accretion (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Planetesimals that form following the explosion of supernovae provide a reservoir of material that can be accreted and generate high energy transient emission long after the neutron star has ceased being a pulsar. Blue supergiants, which would have been the predominant progenitor of supernovae during galaxy formation, may be particularly efficient in producing such systems. Owing to their birth at an early epoch and the kick velocity given the neutron star during the explosion, these sources would lie in a very extended halo. In this picture, some or most gamma-ray bursters would be 10 exp 10 year old relics of galaxy formation. At a minimum a very thick disk population would be expected.
    Keywords: SPACE RADIATION
    Type: In: Planets around pulsars; Proceedings of the Conference, California Inst. of Technology, Pasadena, Apr. 30-May 1, 1992 (A93-36426 14-90); p. 355-363.
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    Prevalent properties of gamma-ray burst variability (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: With the aim of isolating universal characteristics of gamma-ray burst variability, we compare time histories for 20 bright bursts detected by the Burst and Transient Source Experiment (Fishman et al., 1992). Using an autocorrelation function method, we find that the durations of individual structures within a burst, as well as the burst as a whole, become shorter with increasing energy in most events. We introduce the skewness function, a measure of temporal asymmetry. We find that most bursts exhibit a net skewness, in the sense that the intensity rises more rapidly than it falls. Over short time scales, bursts exhibit no preferred asymmetry. Taken together, these properties suggest that the overall time structure of a burst is due to an explosive phenomenon in which the evolution is initially energetic and rapid and is later slower during a 'cooling' period. We cannot rule out the possibility that short time-scale variability is caused by radiation beams sweeping past the observer.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 408; 2; p. L81-L84.
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    Dipole and quadrupole tests of the isotropy of gamma-ray burst locations (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Dipole and quadrupole tests of the isotropy of locations on the sphere are discussed. The statistics (cos theta), the dipole moment to the Galactic center, and mean (sin-squared b - 1/3), the quadrupole moment about the Galactic plane, can be used to search for significant anisotropies in galactic coordinates. Such coordinate-system-based tests are the most powerful tests of dipole and quadrupole anisotropies in the particular coordinate system. Two statistics which have not been previously applied to gamma-ray burst data are described. The Rayleigh-Watson statistic measures the size of the dipole moment of the locations and the Bingham statistic measures the deviation of the eigenvalues of a quadrupole-like matrix from the values expected for isotropy. Tests based upon these two statistics search for dipole and quadrupole moments in spherical location data in a coordinate-system-independent, and thus model-independent, manner. They can detect an anisotropy in any direction and yield an analytic statistical significance to any detected anisotropy. The statistical tests are demonstrated herein using a variety of data sets.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 407; 1; p. 126-134.
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    The gradient of galactic cosmic rays at the solar-wind termination shock (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We report on a study of the expected spatial variation of the galactic cosmic-ray intensity in the outer heliosphere, in the vicinity of the solar-wind termination shock. Model simulations which contain all of the transport effects, including drifts, predict that the radial gradients change abruptly at the shock, and that the nature of the effect varies significantly with particle energy. At low energies, the radial gradient changes abruptly from a lower value inside the shock to a higher value outside, whereas at high energies, the higher value of the gradient is inside the shock. This effect, which is a consequence of the matching conditions at the shock and is closely related to diffusive shock acceleration, is qualitatively the same for both helisopheric magnetic polarity states and remains much the same in one-dimensional, two-dimensional, and three-dimensional models. Hence drifts do not change the nature of this phenomenon, although they change it quantitatively. The effect is, of course, not present in the absence of a terminal shock and may prove to be an important diagnostic tool for the study of the termination of the solar wind.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 2; p. 782-786.
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    The stability of cosmic-ray-dominated shocks - A secondary instability (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Previous studies in one spatial dimension showed that the precursors of cosmic-ray-dominated shocks are unstable against traveling acoustic disturbances. Here we report that a secondary, Rayleigh-Taylor type instability can exist in cosmic-ray-dominated media influenced by the acoustic instability. Using the local WKB approximation, the growth rate of the secondary instability is shown to be comparable to that of the one-dimensional acoustic instability itself in the cases we have considered. The nonlinear development has been followed numerically with a two-dimensional PPM hydrodynamics code that also incorporates the two-fluid cosmic-ray energy equation. We show that the secondary instability may cause the precursor and postshock flows to become highly turbulent.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 1; p. 199-206.
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    Gravitational microlensing of gamma-ray bursts (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A Monte Carlo code is developed to calculate gravitational microlensing in three dimensions when the lensing optical depth is low or moderate (not greater than 0.25). The code calculates positions of microimages and time delays between the microimages. The majority of lensed gamma-ray bursts should show a simple double-burst structure, as predicted by a single point mass lens model. A small fraction should show complicated multiple events due to the collective effects of several point masses (black holes). Cosmological models with a significant fraction of mass density in massive compact objects can be tested by searching for microlensing events in the current BATSE data. Our catalog generated by 10,000 Monte Carlo models is accessible through the computer network. The catalog can be used to take realistic selection effects into account.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 402; 2; p. 382-386.
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    The cosmic-ray path length (age) distribution in the Galaxy - Experimental limits on the deviation from an exponential (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A systematic examination is presented of the observational effects that can provide information on the departure of the cosmic-ray path length distribution (PLD) for propagation in the Galaxy from a simple exponential distribution. The possible physical causes for this departure are examined in order to set realistic limits on how well a simple exponential PLD actually describes the distribution of sources and propagation of cosmic rays in the galaxy. From the findings, it is argued that the cosmic ray source distribution must be quite uniform, probably on a scale of about 50 pc or less near the sun. Extending this uniformity to the Galaxy as a whole would imply more than 100,000 active sources. The cosmic-ray propagation can be described quite well by a leaky box model which is equivalent to observing the particles through a dense fog.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 402; 1; p. 188-194.
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    Balloon observations of Galactic cosmic ray helium before and during a Forbush decrease (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The energy spectrum of Galactic cosmic ray helium was measured in two different balloon experiments launched four days apart from Canada: SMILI-I on Sept 1, 1989 and MASS on Sept 5, 1989. A slow Forbush decrease began on Sept 4, 1989 and had not reached its maximum at the time of the MASS flight. Comparison of the balloon measurements shows a fractional decrease of 0.37 to 0.15 in the Helium flux between 200 and 450 MeV/nucleon (1.2-2.0 GV). The rigidity dependence is analyzed in two models and found to be steeper than previous observations. Interplanetary particle data and ground-based Neutron Monitor results are consistent with the balloon observations. Probable sources for this Forbush decrease are discussed.
    Keywords: SPACE RADIATION
    Type: Geophysical Research Letters (ISSN 0094-8276); 20; 17; p. 1743-1746.
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  • 79
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    Cosmic-ray acceleration during the impact of shocks on dense clouds (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: In order to elucidate the properties of diffusive shock acceleration in nonuniform environments, an extensive set of simulations of the dynamical interactions between plane nonradiative shocks and dense gas clouds was carried out initially in static equilibrium with their environments. These time-dependent calculations are based on the two-fluid model for diffusive cosmic ray transport, and include the dynamically active energetic proton component of the cosmic rays as well as passive electron and magnetic field components. Except when the incident shock is itself already dominated by cosmic ray pressure, it is found that the presence of the cloud adds little to the net acceleration efficiency of the original shock and can, in fact, reduce slightly the net amount of energy transferred to cosmic rays after a given time. It is found that, in 2D cloud simulations, the always-weak bow shock and the shock inside the cloud are less important to acceleration during the interaction than the tail shock.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 402; 2; p. 560-573.
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  • 80
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    The low-frequency interplanetary radiation (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Observations of the low-frequency interplanetary radiation have continued, although no major activity has begun since mid-1991. Theoretical work has been completed which suggests that the long-speculated source at the termination shock is feasible and could at least qualitatively account for several aspects of the observations, although some difficulties exist. The Ulysses encounter with Jupiter occurred in February 1992 and has renewed discussion of a Jovian source for the emissions. We reconsider the arguments used previously to rule out Jupiter as a source and conclude that the existence of a relatively high-density boundary to the heliosphere renders most of these arguments ineffective in eliminating Jupiter as a source. We conclude, therefore, that Jupiter must be considered as likely a candidate source as the termination shock for the low-frequency emissions and, given that Jupiter is a known source of emissions in the few-kHz range, perhaps Jupiter is the more likely candidate. Even with a Jovian source, however, the low-frequency emissions continue to be useful sounders of the heliosphere which can provide information on the size of the heliospheric cavity. No conclusive evidence is available which identifies either Jupiter or the termination shock as the source.
    Keywords: SPACE RADIATION
    Type: Advances in Space Research (ISSN 0273-1177); 13; 6; p. 209-215.
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    A sensitive continuum analysis method for gamma ray spectra (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: In this work we examine ways to improve the sensitivity of the analysis procedure for gamma ray spectra with respect to small differences in the continuum (Compton) spectra. The method developed is applied to analyze gamma ray spectra obtained from planetary mapping by the Mars Observer spacecraft launched in September 1992. Calculated Mars simulation spectra and actual thick target bombardment spectra have been taken as test cases. The principle of the method rests on the extraction of continuum information from Fourier transforms of the spectra. We study how a better estimate of the spectrum from larger regions of the Mars surface will improve the analysis for smaller regions with poorer statistics. Estimation of signal within the continuum is done in the frequency domain which enables efficient and sensitive discrimination of subtle differences between two spectra. The process is compared to other methods for the extraction of information from the continuum. Finally we explore briefly the possible uses of this technique in other applications of continuum spectra.
    Keywords: SPACE RADIATION
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); p. 529-536.
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  • 82
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    Cosmic-ray modulation, merged interaction regions, and multifractals (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The large-scale heliospheric magnetic field fluctuations and their effects on cosmic rays are discussed. Voyager 2 observations from 1983.0 to 1989.6 are used as input to the model of Perko and Burlaga (1992) to show that the few largest merged interaction regions (MIRs) provide essential details in the cosmic-ray intensity (CRI) profile. It is demonstrated that the largest MIRs determine the basic structure of the radial gradients of the CRI. It is shown that the magnetic field strength during the period 1983.0-1989.6 does have a multifractal structure, but that there are different multifractal structures in the three intervals 1983.0-1985.0, 1985.0-1987.5, and 1987.5-1989.6. The multifractal structure can be described by simple functions, the multifractal spectra. These analytical descriptions can be used to generate realizations of the heliospheric magnetic field with the same statistical properties as those observed by Voyager 2. Thus, the starting point is provided for realistic global statistical models of the 11-yr variation of the Galactic CRI.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 407; 1; p. 347-358.
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  • 83
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    A comparison of the cosmic microwave and cosmic X-ray backgrounds - Constraints on local sources of the fluctuations observed by COBE (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: It has been suggested by Hogan (1992) that the microwave background anisotropy detected by the COBE DMR experiment (Smoot et al., 1992) might be produced by inverse Compton scattering from hot diffuse clouds of electrons in nearby superclusters. If the COBE fluctuations are due to this mechanism, then the absence of anticorrelations between maps of the cosmic microwave and cosmic X-ray backgrounds constrains the temperature (16 keV) and density (less than 2 x 10 exp -6/cu cm) of the ionized supercluster gas. Since the COBE limits on spectral distortion indicate that the temperature of the intergalactic medium is less than 10 keV, we conclude that the fluctuations observed by COBE are probably not produced by this mechanism.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 412; 1; p. L1-L4.
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  • 84
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    OSSE observations of Galactic 511 keV positron annihilation radiation - Initial phase 1 results (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory (GRO) has performed numerous observations of the Galactic plane and Galactic center region to measure the distribution of Galactic 511 keV positron annihilation radiation and to search for time variability of the emission. The initial 511 keV line fluxes for the observations performed during the first 18 months of the GRO mission are presented. The 511 keV line flux for a typical Galactic center observation is (2.5 +/- 0.3) x 10 exp -4 gamma/sq cm per sec, where the quoted uncertainty represents the 1 sigma statistical uncertainty. No statistically significant time variability of the line flux has been observed; the 3 sigma upper limit to daily variations from the mean is 3 x 10 exp -4 gamma/sq cm per sec. The distribution of Galactic 511 keV positron annihilation radiation implied by the OSSE observations is discussed and compared with observations by other instruments.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 413; 2; p. L85-L88.
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  • 85
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    BATSE observations of gamma-ray burst spectra. I - Spectral diversity (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We studied the time-averaged gamma-ray burst spectra accumulated by the spectroscopy detectors of the Burst and Transient Source Experiment. The spectra are described well at low energy by a power-law continuum with an exponential cutoff and by a steeper power law at high energy. However, the spectral parameters vary from burst to burst with no universal values. The break in the spectrum ranges from below 100 keV to more than 1 MeV, but peaks below 200 keV with only a small fraction of the spectra breaking above 400 keV; it is therefore unlikely that a majority of the burst spectra are shaped directly by pair processes, unless bursts originate from a broad redshift range. The correlations among burst parameters do not fulfill the predictions of the cosmological models of burst origin. No correlations with burst morphology or the spatial distribution were found. We demonstrate the importance of using a complete spectral description even if a partial description (e.g., a model without a high-energy tail) is statistically satisfactory.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 413; 1; p. 281-292.
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  • 86
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    The role of merged interaction regions and drafts in the heliospheric modulation of cosmic rays beyond 20 AU - A computer simulation (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Voyager 2 magnetic field measurements are used to simulate merged interaction and rarefaction regions (MIRs and RRs) for 1985-1989 via numerical solutions of the time-dependent, axially symmetric transport equation of cosmic rays in the heliosphere, together with the concurrent use of the wavy neutral sheet as a time-dependent drift parameter. This drift approach was found to be more successful, because it was able to reproduce the intensity levels, the factor modulation, and latitudinal gradients for 1 GeV protons at 23 AU.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 403; 2; p. 760-768.
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  • 87
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    Cosmic ray modulation and the distant heliospheric magnetic field - Voyager 1 and 2 observations from 1986 to 1989 (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The relation between the cosmic ray (CR) intensity and the magnetic field strength observed by Voyager 1 and 2 during the period from 1986 through most of 1989 beyond 19 AU is examined. It is shown that these observations generally confirm the relation between changes in the CR intensity and the magnetic field intensity observed beyond 10 AU from 1981 to 1985. The CR intensity decreases when merged interaction regions (MIRs) are strong and dominating, and it fluctuates about a plateau when the effects of corotating MIRs are balanced by rarefaction regions. The CR intensity increases when the MIRs are weak and the magnetic field strength is relatively low.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A1; p. 1-11.
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  • 88
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    Gamma-ray bursts from stellar mass accretion disks around black holes (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A cosmological model for gamma-ray bursts is explored in which the radiation is produced as a broadly beamed pair fireball along the rotation axis of an accreting black hole. The black hole may be a consequence of neutron star merger or neutron star-black hole merger, but for long complex bursts, it is more likely to come from the collapse of a single Wolf-Rayet star endowed with rotation ('failed' Type Ib supernova). The disk is geometrically thick and typically has a mass inside 100 km of several tenths of a solar mass. In the failed supernova case, the disk is fed for a longer period of time by the collapsing star. At its inner edge the disk is thick to its own neutrino emission and evolves on a viscous time scale of several seconds. In a region roughly 30 km across, interior to the accretion disk and along its axis of rotation, a pair fireball is generated by neutrino annihilation and electron-neutrino scattering which deposit approximately 10 exp 50 ergs/s.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 1; p. 273-277.
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  • 89
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    Relativistic fireballs and their impact on external matter - Models for cosmological gamma-ray bursts (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We discuss the production of cosmological gamma-ray bursts intense enough to be detected at cosmological distances. Events such as the coalescence of compact binaries can create sufficient energy on time scales much less than 1 s. A short 'primary' burst is expected when the resultant fireball becomes optically thin, but this may be weak because the bulk of the radiative energy has been converted into kinetic energy while still trapped within the fireball. But when this expanding material impacts on an external medium, its bulk kinetic energy can be rerandomized. The requirements on the composition of the fireball itself are less stringent than for other interpretations of cosmological gamma-ray bursts. Moreover, our model suggests that the spectra and time structure of the bursts may depend in interesting ways on the environment in which the energy-generating event occurs.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 1; p. 278-284.
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  • 90
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    On Compton reflection in the sources of the cosmic X-ray background (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Consideration is given to recent models for the cosmic X-ray background that assume that it originates from unresolved AGN emitting spectra due to enhanced Compton reflection of a power-law photon spectrum incident on cold matter. The parameter space of the Compton reflection model is studied, and the allowed parameter space is found to be severely constrained by physical and cosmological effects. For an incident power-law energy index alpha is greater than about 1, the X-ray peak in the observed spectrum from a population of AGN is necessarily at an energy less than that of the observed peak. Two examples of improved fits to the X-ray background are shown. It is concluded that the Compton reflection models proposed to date do not provide a straightforward explanation of the X-ray background spectrum.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 1; p. 125-129.
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  • 91
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    Cross section parameterizations for cosmic ray nuclei. I - Single nucleon removal (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Parameterizations of single nucleon removal from electromagnetic and strong interactions of cosmic rays with nuclei are presented. These parameterizations are based upon the most accurate theoretical calculations available to date. They should be very suitable for use in cosmic ray propagation through interstellar space, the Earth's atmosphere, lunar samples, meteorites, spacecraft walls and lunar and Martian habitats.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 86; 1; p. 307-312.
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  • 92
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    A unified transport equation for both cosmic rays and thermal particles (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We present a unified transport equation that is valid for particles of all energies if the particle mean free paths are much smaller than macroscopic fluid length scales. If restricted to particles with random speeds much greater than fluid flow speeds, this equation reduces to the previously discussed extended cosmic-ray transport equation. It is significant that this allows one to describe the acceleration of particles from thermal energies to cosmic-ray energies using one transport equation. This is in contrast to previous transport equations (the Parker equation and the extended cosmic-ray transport equation), which were restricted to fast particles. The close connection to the extended cosmic-ray transport equation is demonstrated.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 405; 2; p. L79-L81.
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  • 93
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    New evidence for geomagnetically trapped anomalous cosmic rays (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We report new observations of 15 MeV/nuc or greater trapped heavy ions with Z equal to or greater than 2, made on the polar-orbiting SAMPEX spacecraft in late 1992 and early 1993. A trapped population that includes He, N, O, and Ne is found to be located at L = 2. We conclude that the observed N, O, and Ne ions are 'anomalous' cosmic rays, trapped by the mechanism proposed by Blake and Friesen (1977). While it is not expected that this mechanism would also trap anomalous He, the characteristics of the trapped He population are generally consistent with those of N, O, and Ne.
    Keywords: SPACE RADIATION
    Type: Geophysical Research Letters (ISSN 0094-8534); 20; 18; p. 2003-2006.
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  • 94
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    Cosmic ray decreases and particle acceleration in 1978-1982 and the associated solar wind structures (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Results of a study of the time histories of particles in the energy range 1 MeV to 1 GeV at the times of greater than 3-percent cosmic ray decreases in the years 1978-1982 are presented. The intensity-time profiles of the particles are used to separate the cosmic ray decreases into four classes which are subsequently associated with three types of solar wind structures. Decreases in class 1 (15 events) and class 2 (26 events) are associated with shocks driven by energetic coronal mass ejections. For class 1 events, the ejecta are detected at 1 AU, whereas this is not usually the case for class 2 events. The shock must therefore play a dominant role in producing the cosmic ray depression in class 2 events. It is argued that since energetic particles (from MEV to GeV energies) seen at earth may respond to solar wind structures which are not detected at earth, consideration of particle observations over a wide range of energies is necessary for a full understanding of cosmic ray decreases.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A8; p. 13,295-13,302.
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  • 95
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    Nonthermal processes around collapsed objects: High energy gamma ray sources in the radio sky (1993)
    In:  CASI
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    Publication Date: 2019-07-13
    Description: In our proposal responding to the initial Guest Observer NRA for the Compton Gamma Ray Observatory, 'Nonthermal Processes Around Collapsed Objects: High Energy Gamma Ray Sources in the Radio Sky', we stated that 'At high energies - the identity of the principal Galactic source population remains unknown' although the 'one certain source of high energy emission is young radio pulsars'. These two statements remain true, although at this writing, eighteen months after the beginning of the Compton allsky survey, much of the gamma-ray data required to greatly extend our knowledge of the Galaxy's high energy emission has been collected. The thrust of the program supported by our grant was to collect and analyze a complementary set of data on the Milky Way at radio wavelengths in order to help identify the dominant Pop 1 component of the Galaxy's gamma ray sources, and to pursue theoretical investigations on the origins and emission mechanisms of young pulsars, the one component of this population identified to date. We summarize here our accomplishments under the grant. In Section 2, we describe our VLA surveys of the Galactic Plane along with the current status of the radio source catalogs derived therefrom; unfortunately, owing to the TDRSS antenna problem and subsequent extension of the Sky Survey, we were not able to carry out a comparison with the EGRET data directly, although everything is now in place to do so as soon as it becomes available. In Section 2, we summarize our progress on the theoretical side, including the substantial completion of a dissertation on pulsar origins and work on the high energy emission mechanisms of isolated pulsars. We list the personnel supported by the grant in section 4 and provide a complete bibliography of publications supported in whole or in part by the grant in the final section.
    Keywords: SPACE RADIATION
    Type: NASA-CR-191686 , NAS 1.26:191686 , CAL-2043
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  • 96
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    Comparison of distributed reacceleration and leaky-box models of cosmic-ray abundances (Z = 3-28) (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A large collection of elemental and isotopic cosmic-ray data has been analyzed using the leaky-box transport model with and without reacceleration in the interstellar medium. Abundances of isotopes and elements with charges Z = 3-28 and energies E = 10 MeV/nucleon-1 TeV/nucleon were explored. Our results demonstrate that reacceleration models make detailed and accurate predictions with the same number of parameters or fewer as standard leaky-box models. Ad hoc fitting parameters in the standard model are replaced by astrophysically significant reacceleration parameters. Distributed reacceleration models explain the peak in secondary-to-primary ratios around 1 GeV/nucleon. They diminish the discrepancy between rigidity-dependent leakage and energy-independent anisotropy. They also offer the possibility of understanding isotopic anomalies at low energy.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 414; 2; p. 601-611.
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  • 97
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    Survey of candidate gamma-ray sources at TeV energies using a high-resolution Cerenkov imaging system - 1988-1991 (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The steady TeV gamma-ray emission from the Crab Nebula has been used to optimize the sensitivity of the Whipple Observatory atmospheric Cerenkov imaging telescope. Using this method, which is of order 20 times more sensitive than the standard method using a simple non-imaging detector, it is possible to detect the Crab Nebula at a significance level in excess of 6 standard deviations (6 sigma) in under 1 hr on source (with a corresponding time observing a background comparison region); a source one-tenth the strength of the Crab Nebula can be detected at the 4 sigma level after 40 hr on the source (and 40 hr on a background region). A variety of sources have been monitored using this technique over the period 1988-1991, but none were detected apart from the Crab Nebula. Upper limits are presented which in many instances are a factor of 10 below the flux of the Crab Nebula. These upper limits assume steady emission from the source and cannot rule out sporadic gamma-ray emission with short duty cycles.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 404; 1; p. 206-218.
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  • 98
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    Elemental abundances in the local cosmic rays at high energies (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The heavy-nuclei energy spectra measured aboard the Space Shuttle and on HEAO 3 are presently discussed in the framework of a leaky-box model; the source energy spectrum required for a fit, at E exp -2.2 for all nuclear species, is slightly steeper than a previous estimate. These data are presented in terms of total energy/particle, in order to allow direct comparison with the observed all-particle spectrum of cosmic rays.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 403; 2; p. 658-662.
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  • 99
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    Role of drifts and global merged interaction regions in the long-term modulation of cosmic rays (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The paper shows that the long-term modulation of 0.2- to 3-GV galactic and anomalous cosmic rays over the 22-year heliomagnetic cycle is basically a combination of two solar related processes, the cumulative effect of long-lived global merged interaction regions (GMIRs) and large-scale particle gradient and curvature drifts in the interplanetary magnetic field. This paradigm for cosmic ray modulation is based on the observed changes in cosmic ray intensity from solar minimum to solar maximum over successive solar cycles (21 and 22) using data from 1 AU and from the outer heliosphere. For cycle 21, the 1977-1980 modulation is dominated by GMIRs. In cycle 22, it is shown that drifts are an important but not dominant factor for galactic cosmic ray modulation with the current sheet related drift effects decreasing with increasing rigidity and heliocentric distance.
    Keywords: SPACE RADIATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A2; p. 1243-1256.
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  • 100
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    Beyond Clausius-Mossotti - Wave propagation on a polarizable point lattice and the discrete dipole approximation (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We derive the dispersion relation for electromagnetic waves propagating on a lattice of polarizable points. From this dispersion relation we obtain a prescription for choosing dipole polarizabilities so that an infinite lattice with finite lattice spacing will mimic a continuum with dielectric constant. The discrete dipole approximation is used to calculate scattering and absorption by a finite target by replacing the target with an array of point dipoles. We compare different prescriptions for determining the dipole polarizabilities. We show that the most accurate results are obtained when the lattice dispersion relation is used to set the polarizabilities.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 405; 2; p. 685-697.
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