Galactic Cosmic Ray Transport Research Articles

Ground-based simulations of galactic cosmic ray fragmentation and transport

Since mean free paths for nuclear fragmentation are of the order of the ranges of primary Galactic Cosmic Ray (GCR) nuclei, determination of the radiation field produced by successive fragmentations of nuclei in material and tissue is essential to accurate assessment of GCR radiation risk to humans on long-duration missions outside the geomagnetosphere. We describe some recent measurements made at the Bevalac of heavy ion transport through materials, with representative results and examples of how they may be applied to aspects of the space radiation problem, including efforts to devise analytical tools for predicting biological effects and for designing spacecraft shielding.

Galactic cosmic ray transport methods: Past, present, and future

The development of the theory of high charge and energy (HZE) ion transport is reviewed. The basic solution behavior and approximation techniques will be described. An overview of the HZE transport codes currently available at the Langley Research Center will be given. The near term goal of the Langley program is to produce a complete set of one-dimensional transport codes. The ultimate goal is to produce a set of complete three-dimensional codes which have been validated in the laboratory and can be applied in the engineering design environment. Recent progress toward completing these goals is discussed.

A model of galactic cosmic rays for use in calculating linear energy transfer spectra

The galactic cosmic rays (GCR) contain fully stripped nuclei, from Hydrogen to beyond the Iron group, accelerated to high energies and are a major component of the background radiation encountered by satellites and interplanetary spacecraft. This paper presents a GCR model which is based upon our current understanding of the astrophysics of GCR transport through interstellar and interplanetary space. The model can be used to predict the energy spectra for all stable and long-lived radioactive species from H to Ni over an energy range from 50 to 50,000 MeV/nucleon as a function of a single parameter, the solar modulation level φ. The details of this model are summarized, φ is derived for the period 1974 to present, and results from this model during the 1990/1991 CRRES mission are presented.

Galactic cosmic ray transport methods and radiation quality issues.

An overview of galactic cosmic ray (GCR) interaction and transport methods, as implemented in the Langley Research Center GCR transport code, is presented. Representative results for solar minimum, exo-magnetospheric GCR dose equivalents in water are presented on a component by component basis for various thicknesses of aluminum shielding. The impact of proposed changes to the currently used quality factors on exposure estimates and shielding requirements are quantified. Using the cellular track model of Katz, estimates of relative biological effectiveness (RBE) for the mixed GCR radiation fields are also made.

Interplanetary Crew Exposure Estimates for Galactic Cosmic Rays

Using the Langley Research Center galactic cosmic-ray transport computer code and the Computerized Anatomical Man model, initial estimates of interplanetary exposure of astronauts to galactic cosmic rays, during periods of solar minimum activity, are made for a realistic human geometry shielded by various thickness of spacecraft aluminum shielding. Conventional dose assessment in terms of total absorbed dose and dose equivalent is made for the skin, ocular lens, and bone marrow. Included in the analyses are separate evaluations of the contributions from the incident primary ions, from subsequent-generation fragmentation products, and from target fragments. In all cases considered, the equivalent sphere approximation yielded conservative overestimates for the actual organ exposures.

Martian regolith as space radiation shielding

In current Mars scenario descriptions, an entire mission is estimated to take 500-1000 days round trip with a 100-600 day stay time on the surface. To maintain radiation dose levels below permissible limits, dose estimates must be determined for the entire mission length. With extended crew durations anticipated on Mars, the characterization of the radiation environment on the surface becomes a critical aspect of mission planning. The most harmful free-space radiation is due to high energy galactic cosmic rays (GCR) and solar flare protons. The carbon dioxide atmosphere of Mars has been estimated to provide a sufficient amount of shielding from these radiative fluxes to help maintain incurred doses below permissible limits. However, Mars exploration crews are likely to incur a substantial dose while in transit to Mars that will reduce the allowable dose that can be received while on the surface. Therefore, additional shielding may be necessary to maintain short-term dose levels below limits or to help maintain career dose levels as low as possible. By utilizing local resources, such as Martian regolith, shielding materials can be provided without excessive launch weight requirements from Earth. The scope of this synopsis and of Ref. 3 focuses on presenting our estimates of surface radiation doses received due to the transport and attenuation of galactic cosmic rays and February 1956 solar flare protons through the Martian atmosphere and through additional shielding provided by Martian regolith.

Space physics program

The National Aeronautics and Space Administration solicits proposals for Fiscal Year 1990 for the support of basic research in the general area of space physics, including cosmic and heliospheric physics, solar physics, magnetospheric physics, and ionospheric physics.The Space Physics Division of NASA supports investigations of the origin, evolution, and interactions of particles and electromagnetic fields in space plasmas. Focus of their studies is on interactions between solar wind and solar system bodies, including studies of the ionosphere and magnetospheres of the Earth, other planets, comets, primordial bodies, and of magnetosphere‐ionosphere‐atmosphere interactions; on the Sun as a star and source of solar system energy, plasma, and energetic particles; and on the origin, acceleration, and transport of solar and galactic cosmic rays.

A Benchmark for Galactic Cosmic-Ray Transport Codes

A nontrivial analytic benchmark solution for galactic cosmic ray transport is presented for use in transport code validation. Computational accuracy for a previously-developed cosmic ray transport code is established to within one percent by comparison with this exact benchmark. Hence, solution accuracy for the transport problem is mainly limited by inaccuracies in the input spectra, input interaction databases, and the use of a straight ahead/velocity-conserving approximation.

Density power spectrum in the local interstellar medium

Since the identification of interstellar scintillation, the interstellar medium (ISM) has been known to contain electron density fluctuations having scales ∼109 m. The scattering properties of these irregularities have been used in pulsar and continuum source studies and to investigate the small scale turbulence itself1–11. (We use ‘turbulence’ here to imply a disordered, irregular flow.) If the ISM turbulence extends over a broad enough range of fluctuation scales, it could have an important role in galactic cosmic ray transport and confinement12–14. Here we present observational evidence that electron density irregularities exist over a very wide range of scale sizes. Radio scattering observations associated with the wavenumber range ∼10−11–10−6m−1 are consistent with a density spectrum of the form (wavenumber)−3.7±0.6. At lower spatial wavenumbers (10−16–10−18m−1) the power spectrum can be estimated by computation of the density fluctuations near the ‘outer’ scale of the spectrum15, comparison with density irregularities predicted by theoretical models of the ISM16, and comparison with observations of the velocity structure function13,17,18. When combined with the high-wavenumber (radio) data, these low-wavenumber spectrum estimates are most simply interpreted in terms of a density spectrum behaving as (wavenumber)−3.6±0.2 over a 12 decade scale size range (∼100 pc to ∼107m). There may be theoretical difficulties12,14,19 with such a spectrum, however. Alternatively, the low-wavenumber data could be associated with ISM clouds which are physically distinct from the small scale turbulence.

Acceleration and transport of galactic cosmic rays

view Abstract Citations (20) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Acceleration and transport of galactic cosmic rays. Jokipii, J. R. ; Higdon, J. C. Abstract A recently proposed cosmic-ray acceleration mechanism is combined with a model of transport and loss from the Galaxy to construct a model for galactic cosmic rays. Various aspects of the cosmic-ray spectrum, including the secondary-to-primary ratio as a function of energy, are found to fit naturally into the overall picture. A solution to the dynamical-halo model with energy-dependent diffusion coefficient (kappa) is presented. This model is consistent with the observed spectra if kappa is proportional to the square root of the kinetic energy. The observed flattening of the secondary-to-primary ratio below about 1-2 GeV per nucleon is shown to be a natural consequence of the model. Similarly, the primary electron spectrum is predicted to flatten below about 1-2 GeV, which is consistent with deconvolution of the local nonthermal radio spectrum, although the flattening is not quite as much as indicated by the observations. Publication: The Astrophysical Journal Pub Date: February 1979 DOI: 10.1086/156845 Bibcode: 1979ApJ...228..293J Keywords: Acceleration (Physics); Astronomical Models; Cosmic Rays; Galactic Radiation; Shock Wave Propagation; Transport Properties; Astronomical Spectroscopy; Dynamic Models; Electron Energy; Energy Spectra; Halos; Nonthermal Radiation; Space Radiation; Cosmic Rays:Acceleration; Cosmic Rays:Galaxy; Cosmic Rays:Propagation full text sources ADS |