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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Cosmic-ray transport in inhomogeneous media

A theory of cosmic-ray transport in multiphase diffusive media is developed, with the specific application to cases in which the cosmic-ray diffusion coefficient has large spatial fluctuations that may be inherently multiscale. We demonstrate that the resulting transport of cosmic rays is diffusive in the long-time limit, with an average diffusion coefficient equal to the harmonic mean of the spatially varying diffusion coefficient. Thus, cosmic-ray transport is dominated by areas of low diffusion even if these areas occupy a relatively small, but not infinitesimal, fraction of the volume. On intermediate time-scales, the cosmic rays experience transient effective subdiffusion, as a result of low-diffusion regions interrupting long flights through high-diffusion regions. In the simplified case of a two-phase medium, we show that the extent and extremity of the subdiffusivity of cosmic-ray transport is controlled by the spectral exponent of the distribution of patch sizes of each of the phases. We finally show that, despite strongly influencing the confinement times, the multiphase medium is only capable of altering the energy dependence of cosmic-ray transport when there is a moderate (but not excessive) level of perpendicular diffusion across magnetic-field lines.

Astronomy and Astrophysics↗
DOE OSTI2023

Performance of the wavelength-shifting fiber upgrade for the Mu2e cosmic-ray veto detector

The Cosmic-Ray Veto detector for the muon-to-electron conversion experiment at Fermilab consists of four plastic scintillating counter layers read out by silicon photo-multipliers through embedded wavelength-shifting fibers. In order to increase the light yield in the most critical regions of the Cosmic-Ray Veto detector for improved background rejection, a 1.8 mm diameter fiber is being used in many of the detector's critical modules instead of the previously planned 1.4 mm diameter fiber. This paper reports the testing procedure and light properties of thirty-four 1.8 mm fiber spools, with measurements performed using a custom-built scanner. We compare these new results with previously published data from the 1.4 mm diameter fiber used for regions of the cosmic-ray veto where the increased light yield is not required. In addition, measurements of fiber aging were performed.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1988

Transport of cosmic ray nuclei in various materials

Cosmic-ray heavy ions have become a concern in space radiation effects analyses. Heavy ions rapidly deposit energy and create dense ionization trails as they traverse materials. Collection of the free charge disrupts the operation of microelectronic circuits. This effect, called the single-event upset, can cause a loss of digital data. Passage of high linear energy transfer particles through the eyes has been observed by Apollo astronauts. These heavy ions have great radiobiological effectiveness and are the primary risk factor for leukemia induction on a manned Mars mission. Models of the transport of heavy cosmic-ray nuclei through materials depend heavily on our understanding of the cosmic-ray environment, nuclear spallation cross sections, and computer transport codes. Our group has initiated and pursued the development of a full capability for modeling these transport processes. A recent review of this ongoing effort is presented in Ref. 5. In this paper, we discuss transport methods and present new results comparing the attenuation of cosmic rays in various materials.

NASA Discipline Radiation Health↗
NASA NTRS1977

Ultra-heavy cosmic rays: Theoretical implications of recent observations

Extreme ultraheavy cosmic ray observations (Z greater or equal 70) are compared with r-process models. A detailed cosmic ray propagation calculation is used to transform the calculated source distributions to those observed at the earth. The r-process production abundances are calculated using different mass formulae and beta-rate formulae; an empirical estimate based on the observed solar system abundances is used also. There is the continued strong indication of an r-process dominance in the extreme ultra-heavy cosmic rays. However it is shown that the observed high actinide/Pt ratio in the cosmic rays cannot be fit with the same r-process calculation which also fits the solar system material. This result suggests that the cosmic rays probably undergo some preferential acceleration in addition to the apparent general enrichment in heavy (r-process) material. As estimate also is made of the expected relative abundance of superheavy elements in the cosmic rays if the anomalous heavy xenon in carbonaceous chondrites is due to a fissioning superheavy element.

Blake, J. B.↗
NASA NTRS1977

SAS-2 gamma-ray results from the galactic plane and their implications for galactic structure and galactic cosmic-ray dynamics

The final SAS-2 results related to high energy galactic gamma-ray emission show a strong correlation with galactic structural features seen at other wavelenghts, when the known gamma-ray sources are subtracted. Theoretical considerations and analysis of the gamma-ray data suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density is enhanced where the matter density is greatest on the scale of the galactic arms. This concept has been explored in a galactic model that assumes: (1) cosmic rays are galactic and not universal; (2)on the scale of the galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3)the cosmic ray scale height is significantly larger than the scale height to the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of over 2:1.

Fichtel, C. E.↗
NASA NTRS1998

A Three-Dimensional Analysis of the Galactic Gamma-Ray Emission Resulting from Cosmic-Ray Interaction with the Interstellar Gas and Radiation Fields

This final report outlines the progress of the contractor's support for the analysis of data under ADP (NRA 96-ADP-08; Proposal No. 167-96 adp). The primary task object was to construct a 3-D model for the distribution of high-energy (20 MeV-30 GeV) gamma-ray emission in the Galactic disk. Under this task the contractor was to utilize data from the EGRET instrument on the Compton Gamma-Ray Observatory, HI and CO surveys, radio-continuum surveys at 408 MHz, 1420 MHz, 5 GHz, and 19 GHz, the COBE Diffuse Infrared Background Experiment (DIRBE) all-sky maps from I to 240 um, and ground-based B,V, J, H and K photometry. The respective contributions to the high-latitude gamma-ray emission from cosmic ray-matter interactions, inverse Compton scattering, and extra-galactic emission were to be determined.

Sodraski, Thomas J.↗
NASA NTRS1983

The nitrogen abundance in the cosmic ray source

In this paper, new cosmic ray data on the isotopic and charge abundance of N nuclei are used, along with new cross section data for the fragmentation of O into N, to re-examine the question of the nitrogen abundance in the cosmic ray source. The cosmic ray data come from balloon flights made in 1976, 1977, and 1978. Both the N-15/N-14 ratio and N/O ratio were measured at the same intermediate energies at which the cross sections were measured, and the N/O ratio was also measured up to about 120 GeV/nuc.

Webber, W. R.↗
DOE OSTI2022

Reevaluation of the cosmic antideuteron flux from cosmic-ray interactions and from exotic sources

Cosmic-ray antideuterons could be a key for the discovery of exotic phenomena in our Galaxy, such as dark-matter annihilations or primordial black hole evaporation. Unfortunately the theoretical predictions of the antideuteron flux at Earth are plagued with uncertainties from the mechanism of antideuteron production and propagation in the Galaxy. We present the most up-to-date calculation of the antideuteron fluxes from cosmic-ray collisions with the interstellar medium and from exotic processes. We include for the first time the antideuteron inelastic interaction cross section recently measured by the ALICE collaboration to account for the loss of antideuterons during propagation. In order to bracket the uncertainty in the expected fluxes, we consider several state-of-the-art models of antideuteron production and of cosmic-ray propagation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Propagation of cosmic rays in the Galaxy

The galactic model of cosmic ray confinement is assumed in an in-depth theoretical investigation of cosmic ray propagation in the Galaxy, with consideration also given to the interpretation of observed data. The necessary data concerning the interstellar medium are summarized in order to form a basis for the theoretical formulation of the propagation of cosmic rays, which are assumed to be in a state of equilibrium and homogeneously distributed in the residence volume. The interaction of cosmic rays with the attenuated gases, weak magnetic fields, and radiation fields of the interstellar medium is examined. Many of these interactions lead to the production of radiations ranging the entire electromagnetic spectrum. The possible roles played by cosmic rays in some aspects of galactic dynamics such as the hydrostatic equilibrium of interstellar gas, gravitational instability and formation of clouds, and heating of interstellar gas, are also studied.

Daniel, R. R.↗
NASA NTRS1988

Galactic cosmic rays in three dimensions

A general conclusion is that the cosmic rays increase with increasing distance from the Sun at approximately 2 percent a.u. There is a strong correlation of the cosmic ray intensity with distance with the tilt of the heliospheric current sheet. Moreover, researchers find that the variation of the cosmic rays with time changes in alternate sun spot cycles. Finally, it seems that during alternate sun spot minima (1965 and 1985) the cosmic rays access to the inner solar system was along the equatorial current sheet, wheras in 1975 the cosmic rays came in over the poles. The recently discovered anomalous component of cosmic rays is very much related to this whole problem, and probably corresponds to particles being accelerated at the termination of the solar wind at some 50 to 100 astonomical units from the sun. In summary, many predictions of the models remain controversial in detail. Nonetheless, it appears now that we can expect more cosmic rays over the poles in the next sunspot cycle, and the intensity will continue to increase with heliocentric radius out to the interstellar medium.

Jokipii, J. R.↗
NASA NTRS1980

Interstellar propagation and the relative spectra of cosmic ray electrons and positrons

The interstellar origin and propagation of cosmic ray electrons and positrons are discussed on the basis of radio observations and direct measurements of cosmic ray spectra. Data on the galactic nonthermal radio spectrum are indicated which imply an exponent of -2.2 for the interstellar electron spectrum below 2 GeV and suggest, together with direct cosmic ray evidence, that the spectrum steepens to -3.2 at higher energies. Comparison of the radio data for higher energies with earth-based measurements reveals that the position of the break in the spectrum is dependent on the strength of the interstellar magnetic field and thus all measured intensity values are equally valid. Analysis of the homogeneous model of cosmic ray electron and positron propagation reveals that the limits on propagation parameters are independent of the set of cosmic ray measurements considered, and predict an injection spectral index for electrons of -2.24, an energy loss parameter of 1.5 + or - 0.5 x 10 to the -16th/GeV per sec, a path length of 7.5 times the 0.33 power of the ratio of initial to measured energies (in g/sq cm), average interstellar hydrogen density of 0.22/cu cm and a cosmic ray age of 25 million years. The absence of short cosmic ray lifetimes is shown to affect the interstellar electron spectrum above 100 GeV.

Webber, W. R.↗
NASA NTRS1985

Magnetic fluctuation and cosmic ray diurnal variations

A unified theory of cosmic ray diurnal variations has been proposed in which the first 3 harmonics of the cosmic ray daily variation all results from a single anisotropy produced by the combined effects of adiabatic focusing and anisotropic pitch angle scattering. The theoretical description of steady state cosmic ray anisotropies are simplified and improved. Preliminary results of a study of correlations between cosmic ray diurnal variations and the fluctuation characteristics of the interplanetary magnetic field are presented and discussed in light of the theory.

Bieber, J. W.↗
NASA NTRS2007

Cosmic Ray Helium Intensities over the Solar Cycle from ACE

Observations of cosmic-ray helium energy spectra provide important constraints on cosmic ray origin and propagation. However, helium intensities measured at Earth are affected by solar modulation, especially below several GeV/nucleon. Observations of helium intensities over a solar cycle are important for understanding how solar modulation affects galactic cosmic ray intensities and for separating the contributions of anomalous and galactic cosmic rays. The Cosmic Ray Isotope Spectrometer (CRIS) on ACE has been measuring cosmic ray isotopes, including helium, since 1997 with high statistical precision. We present helium elemental intensities between approx. 10 to approx. 100 MeV/nucleon from the Solar Isotope Spectrometer (SIS) and CRIS observations over a solar cycle and compare these results with the observations from other satellite and balloon-borne instruments, and with GCR transport and solar modulation models.

DeNolfo, G. A.↗
NASA NTRS1985

Influence of the source distribution on the age distribution of galactic cosmic rays

The age distribution of galactic cosmic rays in the diffusion approximation is calculated. The influence of the scale height of the spatial source distribution on the mean age of particles arriving at the solar system is discussed. The broader the source distribution with respect to the galactic plane, the longer the mean age. This result provides a natural explanation for the shorter mean age of secondary cosmic rays compared to primary cosmic rays necessary for the understanding of the observed secondary/primary ratio.

Lerche, I.↗
NASA NTRS1975

Solar and galactic cosmic ray abundances - A comparison and some comments

We have compared the abundances of galactic cosmic rays at their source and solar cosmic-rays utilizing new data which includes the first determination of the abundances of Na and Al in the solar cosmic ray population. We find the relative abundances of the solar and galactic species to be identical within experimental error for 8 elements. One clear abundance difference exists for C. He and Fe have a variable solar cosmic ray abundance, and the unbiased abundance of both of these nuclei is also probably different than that in the galactic cosmic ray sources. We also have compared the cosmic ray abundances with solar system and solar atmospheric abundance determinations. We find an abundance ratio which depends on the first ionization potential for galactic cosmic rays; however, in addition, we find this same dependence on ionization potential for solar cosmic ray abundance ratios. The implications of this result are discussed.

Webber, W. R.↗