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Results for “Cosmic ray propagation”

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 181 records · Page 10
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NASA NTRS1983

Fragmentation of approximately 500 MeV/nuc Ne and O nuclei in CH2, C and H targets - Charge and isotopic cross sections

Fragmentation of Ne-20 and O-16 nuclei in CH2 and C targets at several energies between 400 and 1000 MeV/nuc is carried out in order to obtain cross sections in hydrogen for use in the galactic cosmic ray propagation problem. Charge changing and isotopic cross sections for the fragments with Z greater than or equal to 4 are obtained. The hydrogen cross sections are obtained by a subtraction procedure. The predictions of the semi-empirical model of Tsao and Silberberg (1979) are given and in general there is good agreement between the measurements and the predictions.

Webber, W. R.↗
NASA NTRS1983

Interactions of 200 GeV gold nuclei in light elements

Total charge-changing cross sections and partial cross-sections for interactions of 200 GeV Au-197 nuclei incident on carbon and polyethylene (CH2) targets have been measured during a calibration of the HEAO-3 Heavy Nuclei Experiment. From these, the total and partial cross-sections for Au-197 incident on hydrogen are inferred. The effects of using these cross-sections in one model of cosmic ray propagation are illustrated. Comparisons to predictions using semi-empirical formulas are shown.

Brewster, N. R.↗
NASA NTRS1986

Neutron and antineutron production in accretion onto compact objects

Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons, primarily through spallation and pion-producing reactions, and antineutrons, principally through the reaction p+p yields p+p+n+anti-n. We calculate spectra of neutrons and antineutrons produced by a variety of nonthermal energetic particle distributions in which the target particles are either at rest or in motion. If only neutral particles are free to escape the interaction site, a component of the proton and antiproton fluxes in the cosmic radiation results from the neutrons and antineutrons which leave the accretion plasma and subsequently decay in the interstellar medium. This additional antiproton component could account for the enhanced flux of antiprotons in the cosmic radiation, compared to values expected from the standard leaky-box model of cosmic-ray propagation and confinement. Moreover, the low-energy antiproton flux measured by Buffington et al. (1981) could result from target-particle motion in the accretion plasma. This model for the origin of antiprotons predicts a narrow 2.223 MeV line which could be observable.

Dermer, C. D.↗
NASA NTRS1987

Antiprotons in cosmic rays

Recent experimental observations and results are discussed. It was found that the approximately 50 antiprotons collected in balloon experiments to date have generated considerable theoretical interest. Clearly, confirmatory experiments and measurements over an extended energy range are required before definite conclusions are drawn. Antiproton measurements have a bearing on astrophysical problems ranging from cosmic ray propagation to issues of cosmological import. The next generation of balloon experiments and the Particle Astrophysics Magnet Facility being discussed for operation on NASA's space station should provide data and insights of highest interest.

Balasubrahmanyan, V. K.↗
NASA NTRS1986

Neutron and antineutron production in accretion onto compact objects

Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons, primarily through spallation and pion-producing reactions, and antineutrons, principally through the reaction p+p yields p+p+n+anti-n. We calculate spectra of neutrons and antineutrons produced by a variety of nonthermal energetic particle distributions in which the target particles are either at rest or in motion. If only neutral particles are free to escape the interaction site, a component of the proton and antiproton fluxes in the cosmic radiation results from the neutrons and antineutrons which leave the accretion plasma and subsequently decay in the interstellar medium. This additional antiproton component could account for the enhanced flux of antiprotons in the cosmic radiation, compared to values expected from the standard leaky-box model of cosmic-ray propagation and confinement. Moreover, the low-energy antiproton flux measured by Buffington et al. (1981) could result from target-particle motion in the accretion plasma. This model for the origin of antiprotons predicts a narrow 2.223 MeV line which could be observable.

Dermer, Charles D.↗
NASA NTRS1988

Isotopic composition of cosmic-ray boron and nitrogen

New measurements of the cosmic-ray boron and nitrogen isotopes at earth and of the elemental abundances of boron, carbon, nitrogen, and oxygen are presented. A region of mutually allowed values for the cosmic-ray nitrogen source ratios is determined, and the cosmic-ray escape mean free path is determined as a function of energy using a leaky box model for cosmic-ray propagation in the Galaxy. Relative to O-16, a N-15 source abundance consistent with solar system composition and a N-14 source abundance which is a factor of about three underabundant relative to the solar value are found.

Krombel, K. E.↗
NASA NTRS1989

Electromagnetic interactions of cosmic rays with nuclei

Parameterizations of single nucleon emission from the electromagnetic interactions of cosmic rays with nuclei are presented. These parameterizations are based upon the most accurate theoretical calculations available today. When coupled with Strong interaction parameterizations, they should be very suitable for use in cosmic ray propagation through intersteller space, the Earth's atmosphere, lunar samples, meteorites and spacecraft walls.

Norbury, John W.↗
NASA NTRS1989

The infrared-to-radio ratio within NGC 5236 (M83) and NGC 6946

A detailed comparison of the distribution of 60-micron IR and 20-cm radio continuum emission within NGC 5236 (M83) and NGC 6946 is presented. In the disks of both galaxies, a slow decrease of the 60-micron-to-20-cm ratio with increasing radius is observed. Values of this ratio within the central regions are enhanced by roughly a factor of 3 with respect to the outer disks, whereas the corresponding enhancement in radio surface brightness is at least a factor of 20. The 100-micron-to-20-cm ratio shows a similar but shallower gradient. To account for these observations, it is suggested that spiral galaxies are characterized by an IR disk with a shorter scale length than that of the radio continuum disk, the latter being smeared as a result of cosmic-ray propagation.

Bicay, M. D.↗
NASA NTRS1991

Studies of low-energy Galactic cosmic-ray composition at 22 AU. I - Secondary/primary ratios

Data from the High Energy Telescope of the CRS experiment on Voyager 2 have been used to measure the intensity, spectra, and elemental abundances of Galactic cosmic rays from Be to Ni at about 100 MeV/n. The charge resolution of this telescope varies from sigma = 0.034 for oxygen to sigma = 0.11 for iron. The solar modulation deceleration parameter Phi relevant for these data is estimated to be around 300 MV (Phi = 150 MeV/n for particles with A/Z = 2), an unprecedently low level for such measurements. This low modulation parameter is a result of the measurements being made in the outer heliosphere at a heliocentric distance of 22 AU, and centered on the solar minimum period of cycle 21. The results on secondary/primary ratios are used to test the Leaky-Box model of cosmic ray propagation, using the most recent cross sections data in hydrogen and helium, and taking into account the effects of the ionized fraction of the interstellar medium. It is found that all the secondary/primary ratios up to P/S are completely consistent with an exponential pathlength distribution (PLD). This PLD shape also accounts for the Sc-V/Fe ratio.

Ferrando, P.↗
NASA NTRS1992

Cross section parameterizations for cosmic ray nuclei. 1: Single nucleon removal

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.

Norbury, John W.↗
NASA NTRS1992

The isotopic composition of iron-group cosmic rays

Measurements are reported of the relative abundances of Mn, Fe, Co, and Ni isotopes in Galactic cosmic rays with energies of about 325 MeV per nucleon. The observed limit (Mn-54)/(Mn-53) of less than 0.25 is significantly less than the value of about 0.8-0.9 expected if Mn-54 were stable, indicating that most of the Mn-54 produced during cosmic-ray propagation in the Galaxy has undergone radioactive decay. Relative source abundances of iron and nickel isotopes, and in particular the ratio (Fe-54)/(Fe-56) = 0.046 +/- 0.020, are generally consistent with solar system values. One exception is the source ratio (Ni-60)/(Ni-58) for which an enhancement by a factor of 2.8 +/- 1.0 over the solar value is found. The isotope (Co-59) is found to make up a sizable fraction of the observed Co, indicating a time delay more than about 100,000 yr between nucleosynthesis and acceleration if this nuclide is synthesized as (Cu-59) or (Ni-59).

Leske, Richard A.↗
NASA NTRS1991

Albedo gamma-rays from cosmic ray interactions on the solar surface

We estimate the flux of gamma-rays that result from collisions of high energy galactic cosmic rays with the solar atmosphere. The high energy photon flux should be observable by the GRO, although details of our results are sensitive to assumptions about cosmic ray propagation through the magnetic fields of the inner solar system. We also estimate the neutrino and neutron fluxes resulting from the same process.

Seckel, D.↗
NASA NTRS1993

The elemental and isotopic composition of Galactic cosmic-ray nuclei from scandium through nickel

Measurements of the relative elemental and isotopic abundances of iron-group Galactic cosmic rays at energies of about 325 MeV per nucleon have been made. The source abundance ratio of Ni-60/Ni-58 is 1.07 +/- 0.39, which is a factor of 2.8 +/- 1.0 larger than the solar system value. Our measurements imply the presence of Co-59 at the source, which can be reconciled with the predictions of conventional nucleosynthesis models if there exists a time delay of more than about 100,000 yr between nucleosynthesis and acceleration. Most of the Mn-54 produced by spallation during cosmic-ray propagation in the Galaxy is found to have decayed to Fe-54, indicating a confinement time of greater than 2 Myr. The source ratio of Fe-54/Fe-56 corrected for the Mn-54 decay is 0.046+/- 0.020, which is consistent with the solar system value of 0.063.

Leske, Richard A.↗
NASA NTRS1993

Cross section parameterizations for cosmic ray nuclei. I - Single nucleon removal

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.

Norbury, John W.↗
NASA NTRS1995

North-south asymmetry of the interplanetary magnetic helicity

Previous analyses of the north-south asymmetry of the interplanetary magnetic helicity have used the omnitape dataset and have shown that there exists a persistent and statistically significant asymmetry in the handedness of the magnetic fluctuations at 1 AU. This asymmetry is concentrated in fluctuations with spacecraft frame frequencies less than 10-5 Hz (periods greater than 30 hours) at 1 AU. Attempts to extend these analyses to include data collected in the outer heliosphere require that we consider spacecraft frame periods many times greater than 30 hours. This raises interesting questions regarding homogeneity and stationarity of the datasets at this scale and brings into question the possible breakdown of the computed correlation functions due to the sector structure of the solar wind. The likely geometry of magnetic fluctuations in the outer heliosphere provides yet another complication in the analysis. These issues will be discussed in detail and the latest results from our studies of the Voyager 1 & 2 and Pioneer 10 & 11 datasets will be presented. The analysis of Pioneer-Venus Orbiter observations will be shown as well. The potential asymmetry between the magnetic helicity of the two hemispheres has significant and measurable implications for cosmic ray propagation in the heliosphere and these implications will be reviewed in light of the new results.

Smith, Charles W.↗
NASA NTRS1997

Radiation Transport and Shielding for Space Exploration and High Speed Flight Transportation

Transportation of ions and neutrons in matter is of direct interest in several technologically important and scientific areas, including space radiation, cosmic ray propagation studies in galactic medium, nuclear power plants and radiological effects that impact industrial and public health. For the proper assessment of radiation exposure, both reliable transport codes and accurate data are needed. Nuclear cross section data is one of the essential inputs into the transport codes. In order to obtain an accurate parametrization of cross section data, theoretical input is indispensable especially for processes where there is little or no experimental data available. In this grant period work has been done on the studies of the use of relativistic equations and their one-body limits. The results will be useful in choosing appropriate effective one-body equation for reaction calculations. Work has also been done to improve upon the data base needed for the transport codes used in the studies of radiation transport and shielding for space exploration and high speed flight transportation. A phenomenological model was developed for the total absorption cross sections valid for any system of charged and/or uncharged collision pairs for the entire energy range. The success of the model is gratifying. It is being used by other federal agencies, national labs and universities. A list of publications based on the work during the grant period is given below and copies are enclosed with this report.

Maung, Khin Maung↗
NASA NTRS2003

Evaluation of Models for Diffuse Continuum Gamma Rays in EGRET Range

The GALPROP model for cosmic-ray propagation produces explicit predictions for the angular distribution of gamma-rays. We compare our current models with EGRET spectra for various regions of the sky. This allows a critical test of alternative hypotheses for the observed GeV excess. We show that a population of hard-spectrum sources cannot be solely responsible for the excess since it also appears at high latitudes; on the other hand the 'hard electron' spectrum model cannot explain the gamma-ray excess in the inner Galaxy. Hence some combination of these explanations is required.

Strong, A.↗
NASA NTRS2003

A New Estimate of the Extragalactic Gamma-ray Background from EGRET Data

We use the GALPROP model for cosmic-ray propagation to obtain our best prediction of the Galactic component of gamma rays, and show that away from the Galactic plane it gives an accurate prediction of the observed Energetic Gamma Ray Experiment Telescope (EGRET) intensities. On this basis we re-evaluate the isotropic extragalactic gamma-ray background. We find that for some energies previous work underestimated the Galactic contribution and hence overestimated the background. Our new background spectrum shows a positive curvature similar to that expected for models of the extragalactic emission based on the blazar population.

Moskalenko, I. V.↗