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At least 271 records · Page 15
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NASA NTRS2016

Evaluating Galactic Cosmic Ray Environment Models Using RaD-X Flight Data

Galactic cosmic rays enter Earth's atmosphere after interacting with the geomagnetic field. The primary galactic cosmic rays spectrum is fundamentally changed as it interacts with Earth's atmosphere through nuclear and atomic interactions. At points deeper in the atmosphere, such as at airline altitudes, the radiation environment is a combination of the primary galactic cosmic rays and the secondary particles produced through nuclear interactions. The RaD-X balloon experiment measured the atmospheric radiation environment above 20 km during 2 days in September 2015. These experimental measurements were used to validate and quantify uncertainty in physics-based models used to calculate exposure levels for commercial aviation. In this paper, the Badhwar-O'Neill 2014, the International Organization for Standardization 15390, and the German Aerospace Company galactic cosmic ray environment models are used as input into the same radiation transport code to predict and compare dosimetric quantities to RaD-X measurements. In general, the various model results match the measured tissue equivalent dose well, with results generated by the German Aerospace Center galactic cosmic ray environment model providing the best comparison. For dose equivalent and dose measured in silicon, however, the models were compared less favorably to the measurements.

Norman, R. B.↗
NASA NTRS1985

Transient cosmic ray increase associated with a geomagnetic storm

On the basis of worldwide network data of cosmic ray nucleonic components, the transient cosmic ray increase due to the depression of cosmic ray cutoff rigidity during a severe geomagnetic storm was investigated in terms of the longitudinal dependence. Multiple correlation analysis among isotropic and diurnal terms of cosmic ray intensity variations and Dst term of the geomagnetic field is applied to each of various station's data. It is shown that the amplitude of the transient cosmic ray increase associated with Dst depends on the local time of the station, and that its maximum phase is found in the evening sector. This fact is consistent with the theoretical estimation based on the azimuthally asymmetric ring current model for the magnetic DS field.

Kudo, S.↗
NASA NTRS1977

Secondary antiprotons - A valuable cosmic-ray probe

Even in the absence of antiprotons in the primary cosmic rays, a flux of secondary antiprotons will be produced in collisions between cosmic rays and interstellar gas. The predicted antiproton fraction increases with increasing cosmic-ray confinement, so that observations of antiprotons will provide a probe of models of cosmic-ray confinement. It is shown that the expected antiproton fraction (for energies of at least about 10 GeV) ranges between 0.00023 for the 'leaky box' model and 0.0018 for the 'closed box' model. In addition, attention is called to the fact that a detection of cosmic-ray antiprotons at or above a level of 0.0002 will provide a valuable lower limit to the antiproton lifetime.

Steigman, G.↗
NASA NTRS1979

The extension of the concept of the cosmic-ray path-length distribution to nonrelativistic energies

The concept of the cosmic-ray path-length distribution is examined. The corresponding cosmic-ray propagation calculational procedure has been justified theoretically at relativistic energies (Ginzburg and Syrovatskii, 1964) where the effects of ionization energy loss are negligible. The present paper extends the use of the path-length distribution concept in cosmic-ray propagation calculations to nonrelativistic energies. Sufficient constraints to effect this extension are presented. The solution of the cosmic-ray propagation equations in terms of a Green's function approach is also investigated and is used to provide a formulation of the path-length distribution at nonrelativistic as well as relativistic energies in terms of the cosmic-ray source distribution and the propagation characteristics of the interstellar medium. The leaky-box model of cosmic-ray propagation is also examined.

Lezniak, J. A.↗
NASA NTRS2012

Galactic Cosmic Rays: From Earth to Sources

For nearly 100 years we have known that cosmic rays come from outer space, yet proof of their origin, as well as a comprehensive understanding of their acceleration, remains elusive. Direct detection of high energy (up to 10(exp 15)eV), charged nuclei with experiments such as the balloon-born, antarctic Trans-Iron Galactic Element Recorder (TIGER) have provided insight into these mysteries through measurements of cosmic ray abundances. The abundance of these rare elements with respect to certain intrinsic properties suggests that cosmic rays include a component of massive star ejecta. Supernovae and their remnants (SNe & SNRs), often occurring at the end of a massive star's life or in an environment including massive star material, are one of the most likely candidates for sources accelerating galactic comic ray nuclei up to the requisite high energies. The Fermi Gamma-ray Space Telescope Large Area Detector (Fermi LAT) has improved our understanding of such sources by widening the window of observable energies and thus into potential sources' energetic processes. In combination with multiwavelength observations, we are now better able to constrain particle populations (often hadron-dominated at GeV energies) and environmental conditions, such as the magnetic field strength. The SNR CTB 37A is one such source which could contribute to the observed galactic cosmic rays. By assembling populations of SNRs, we will be able to more definitively define their contribution to the observed galactic cosmic rays, as well as better understand SNRs themselves. Such multimessenger studies will thus illuminate the long-standing cosmic ray mysteries, shedding light on potential sources, acceleration mechanisms, and cosmic ray propagation.

Brandt, Theresa J.↗
NASA NTRS1975

Possibility of controlling the earth's negative charge and the unitary variation of its electric field by cosmic rays

The dependence of the atmospheric conductivity upon the cosmic ray intensity, the possibility of charge generation in thunderstorms by cosmic rays, the dependence of the troposphere electricity on the stratosphere, the relationship between the unitary variation of the earth's electric field intensity and that of cosmic ray intensity (daily, yearly and 11-year latitudinal dependence of both values), deny first, the exceptional role of the tropospheric processes in maintaining the terrestrial charge and unitary variation, and, second, compel one to consider the cause mentioned above to be the result of the influence of cosmic rays.

Bragin, Y. A.↗
NASA NTRS1975

High-energy galactic gamma radiation from cosmic rays concentrated in spiral arms

A model for the emission of high-energy (exceeding 100 Mev) gamma-rays from the galactic disk has been developed and compared with recent SAS-2 observations. In the calculation, it is assumed that (1) the high energy galactic gamma-rays result primarily from the interaction of cosmic rays with galactic matter, (2) the cosmic-ray density is proportional to the matter density on the scale of galactic arms, and (3) the matter in the Galaxy is distributed in a spiral pattern consistent with density-wave theory and experimental data on the matter distribution that is available, including the 21-cm H I line emission, continuum emission from H II regions, and data currently being used to estimate the H2 density. The calculated galactic-longitude distribution of gamma rays is in good agreement with the SAS-2 observations in relative shape and absolute flux. As a corollary, the nonuniform cosmic-ray distribution of this model tends to support the galactic origin of the fraction of cosmic rays which is important in the production of high-energy photons. Modifications of the basic model show that the gamma-ray flux is relatively sensitive to large variations of the assumed distribution of molecular hydrogen in the Galaxy.

Bignami, G. F.↗
NASA NTRS1985

A model for the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accelerated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1985

On the origin of high-energy cosmic rays

It is suggested that cosmic rays, up to the highest energies observed, originate in the Galaxy and are accelerated in astrophysical shock waves. If there is a galactic wind, in analogy with the solar wind, a hierarchy of shocks ranging from supernova shocks to the galactic wind termination shock is expected. This leads to a consistent model in which most cosmic rays, up to perhaps 10 to the 14th eV energy, are accelerated by supernova shocks, but that particles with energies of 10 to the 15th eV and higher are accelerated at the termination shock of the galactic wind. Intermediate energies may be accerelated by intermediate-scale shocks, and there may be larger scale shocks associated with the Local Group of galaxies.

Jokipii, J. R.↗
NASA NTRS1985

The isotopic composition of cosmic ray chlorine

The isotopic composition of galactic cosmic ray chlorine (approx. = 225 MeV/amu) has been studied using the high energy cosmic ray experiment on the International Sun Earth Explorer 3 (ISEE-3) spacecraft. The abundances of 35C1 and 37C1 are found to be consistent with the secondary production expected from a propagation model developed to account for both light and subiron secondaries. An upper limit on the abundance of the radioactive isotope 36C1 (halflife approx. = 0.3 Myr) is used to set a lower limit on the confinement time of cosmic rays of approximately 1 Myr.

Wiedenbeck, M. E.↗
NASA NTRS1985

Cosmic-ray transport in the galactic magnetosphere

It is advantageous to regard cosmic rays as the constitutent particles of the Galactic radiation belts and cosmic ray energization as a consequence of inward radial diffusion in the quasi-dipolar Galactic magnetosphere. This process occurs in addition to Fermi acceleration. The purpose of this work is to explore a magnetospheric explanation for the elevation of Galactic charged particles to cosmic ray energies. The magnetosphere that is of interest in this context is not a planetary magnetosphere but a galactic magnetosphere entirely analogous to those inferred from radio observations of distant galaxies. It is the magnetosphere of the Milky Way. Cosmic rays are (by this interpretation) the charged particles that constitute the radiation belts of the Galactic magnetosphere. Thus, the mechanism by which charged particles attain cosmic-ray energies is presumable the mechanism by which radiation-belt particles attain high energies in more familiar magnetosphere, i.e., the radial diffusion associated with magnetic disturbances that contain spectral power resonant with the azimuthal drift of the particles.

Schulz, M.↗
NASA NTRS1989

Deuterium and He-3 in cosmic rays

Observation of a large flux of antiprotons in cosmic rays prompted many to postulate new ideas relating to the origin and propagation of cosmic rays in the Galaxy, within the framework of the secondary hypothesis. Under this hypothesis, cosmic rays traverse a large amount of matter either in the source region or in the interstellar space. As a result, large amounts of deuterium and He-3 are also produced as a consequence of spallation of helium and heavier nuclei. In this paper, the spectra of these isotopes are derived, using various models for the propagation of cosmic rays and compare with the existing observations.

Stephens, S. A.↗
NASA NTRS1974

A hysteresis effect in cosmic ray modulation

The rigidity dependence is investigated in the modulation of cosmic ray protons and alphas at intermediate (2-13 Gv) rigidities during the declines and recoveries of the cosmic ray flux near cosmic ray minimum. The results include the finding that sudden changes in the modulation of the primary cosmic rays are initiated by large solar particle outflow and begin as type I Forbush decreases. Typically, the modulation spectrum becomes flatter at intermediate rigidity below 13 Gv and steeper at rigidities above 13 Gv during early recovery.

Verschell, H. J.↗
NASA NTRS2007

Cosmic Ray Electron Science with GLAST

Cosmic ray electrons at high energy carry information about their sources, their definition in local magnetic fields and their interactions with the photon fields through which they travel. The spectrum of the particles is affected by inverse Compton losses and synchrotron losses, the rates of which are proportional to the square of the particle's energy making the spectra very steep. However, GLAST will be able to make unique and very high statistics measurements of electrons from approx. 20 to approx. 700 GeV that will allow us to search for anisotropies in anival direction and spectral features associated with some dark matter candidates. Complementary information on electrons of still higher energy will be required to see effects of possible individual cosmic ray sources.

Ormes, J. F.↗
NASA NTRS1985

A simulation of high energy cosmic ray propagation 1

High energy cosmic ray propagation of the energy region 10 to the 14.5 power - 10 to the 18th power eV is simulated in the inter steller circumstances. In conclusion, the diffusion process by turbulent magnetic fields is classified into several regions by ratio of the gyro-radius and the scale of turbulence. When the ratio becomes larger then 10 to the minus 0.5 power, the analysis with the assumption of point scattering can be applied with the mean free path E sup 2. However, when the ratio is smaller than 10 to the minus 0.5 power, we need a more complicated analysis or simulation. Assuming the turbulence scale of magnetic fields of the Galaxy is 10-30pc and the mean magnetic field strength is 3 micro gauss, the energy of cosmic ray with that gyro-radius is about 10 to the 16.5 power eV.

Honda, M.↗
NASA NTRS2014

Deep Mapping of Small Solar System Bodies with Galactic Cosmic Ray Secondary Particle Showers

Galactic cosmic rays rain steadily from all directions onto asteroids and comets. The interaction of these high-energy ions produces a cascade of secondary particles, including muons, which can penetrate the solid interiors of small solar system bodies. Muons, which are produced in abundance in Earth's atmosphere, have been used to image large structures on Earth, including the Great Pyramids and the interior of volcanoes. In this study, we demonstrate that the transmitted flux of muons is sensitive to the interior density structure of asteroids and comets, less than a few hundred meters in diameter. Muonography has the potential to fill a critical gap in our knowledge of the deep interiors of small bodies, providing information needed for planetary defense, in situ resource utilization, and planetary science. We use Monte Carlo codes (MCNPX and FLUKA), which accurately model galactic cosmic ray showers, to explore systematic variations in the production of muons in solid surfaces. Results of these calculations confirm the scaling of muon production in Earth's atmosphere to solid regolith materials, as predicted by a simple, semi-empirical model. Muons are primarily produced in the top meter of the regoliths of asteroids and comets. Their rate of production is over three orders of magnitude lower than in Earth's atmosphere and depends strongly on regolith density. In practice, the use of muonography to characterize the interiors of small solar system bodies must overcome their low rate of production and their dependence on regolith density, which can vary over the surface of asteroids and comets. We show that interior contrast can be resolved using a muon telescope (hodoscope) with about 1 sq m aperture with integration times ranging from hours to weeks. Design concepts for a practical hodoscope that could be deployed in situ or on an orbiting spacecraft, are described. Regolith density within the top meter of an asteroid can be determined from radar observations. A concept for a pilot mission that combines remote radar measurements with in situ muonography of a near-Earth asteroid is presented. Perceived challenges and next steps for the development of the concept are described.

Prettyman, T. H.↗
NASA NTRS2001

The isotopic composition of cosmic-ray calcium

We find that the relative abundance of cosmic ray calcium isotopes in the cosmic-ray source are very similar to those found in solar-system material, in spite of the fact that different types of stars are thought to be responsible for producing these two isotopes. This observation is consistent with the view that cosmic rays are derived from a mixed sample of interstellar matter.

cosmic rays calcium isotopes advanced composition ↗