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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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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.↗
NASA NTRS2003

Cubic Calorimeter for High-Energy Electrons in Ultra-Long Ballooning

The concept and optimization study of a balloon-borne instrument to study high-energy (from 100 GeV to 5 TeV) cosmic ray electrons will be presented. This energy range of electrons is very interesting for the study of cosmic ray propagation and the search for the nearby sources of high-energy electrons. The instrument is based on a cubic design that allows the detection from all sides. Proton rejection is provided by stringent track analysis, which allows defining when an electron shower is exhausted while the hadron shower continues development. The collecting power of a nominal balloon-borne instrument using this concept will be over 2 square meters sr. This will provide approximately 3,000 electron events above 500 GeV for 3-month long ULDB flight. This instrument will also be capable of detecting sharp features in the high energy gamma-ray spectrum such as gamma-ray lines originating from the dark matter annihilation.

Moiseev, Alexander A.↗
NASA NTRS2004

A New Determination of the Extragalactic Diffuse X-Ray Background from EGRET Data

We use the GALPROP model for cosmic-ray propagation to obtain a new estimate of the Galactic component of gamma rays, and show that away from the Galactic plane it gives an accurate prediction of the observed EGRET intensities in the energy range 30 MeV - 50 GeV. On this basis we re-evaluate the extragalactic gamma-ray background. We find that for some energies previous work underestimated the Galactic contribution at high latitudes 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.

Strong, Andrew W.↗
NASA NTRS2004

Diffuse Galactic Continuum Gamma Rays. A Model Compatible with EGRET Data and Cosmic-ray Measurements

We present a study of the compatibility of some current models of the diffuse Galactic continuum gamma-rays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the "conventional model" based on the locally observed electron and nucleon spectra is inadequate, for all sky regions. A conventional model plus hard sources in the inner Galaxy is also inadequate, since this cannot explain the GeV excess away from the Galactic plane. Models with a hard electron injection spectrum are inconsistent with the local spectrum even considering the expected fluctuations; they are also inconsistent with the EGRET data above 10 GeV. We present a new model which fits the spectrum in all sky regions adequately. Secondary antiproton data were used to fix the Galactic average proton spectrum, while the electron spectrum is adjusted using the spectrum of diffuse emission it- self. The derived electron and proton spectra are compatible with those measured locally considering fluctuations due to energy losses, propagation, or possibly de- tails of Galactic structure. This model requires a much less dramatic variation in the electron spectrum than models with a hard electron injection spectrum, and moreover it fits the y-ray spectrum better and to the highest EGRET energies. It gives a good representation of the latitude distribution of the y-ray emission from the plane to the poles, and of the longitude distribution. We show that secondary positrons and electrons make an essential contribution to Galactic diffuse y-ray emission.

Strong, Andrew W.↗
NASA NTRS2005

Energy Spectra of H and He from the ATIC-2 Experiment

The Advanced Thin Ionization Calorimeter (ATIC) experiment measures the energy spectra of individual elements, from H to Fe, in the energy region from about 100 GeV to tens of TeV. The ATIC instrument was flown twice in long-duration balloon flights around the South Pole in 2000-2001 (ATIC-1) and 2002-2003 (ATIC-2). ATIC-2 gathered about 18 days of data at an altitude of 36 km. In this paper we discuss the separation of protons from helium and present preliminary energy spectrum of each component, including deconvolution of the measured energy deposit spectra. The results are compared to previous data and to different cosmic ray propagation models, including a diffusion model with weak re-acceleration.

Wefel, J. P.↗
NASA NTRS2008

The Cosmic Ray Electron Excess

This slide presentation reviews the possible sources for the apparent excess of Cosmic Ray Electrons. The presentation reviews the Advanced Thin Ionization Calorimeter (ATIC) instrument, the various parts, how cosmic ray electrons are measured, and shows graphs that review the results of the ATIC instrument measurement. A review of Cosmic Ray Electrons models is explored, along with the source candidates. Scenarios for the excess are reviewed: Supernova remnants (SNR) Pulsar Wind nebulae, or Microquasars. Each of these has some problem that mitigates the argument. The last possibility discussed is Dark Matter. The Anti-Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission is to search for evidence of annihilations of dark matter particles, to search for anti-nuclei, to test cosmic-ray propagation models, and to measure electron and positron spectra. There are slides explaining the results of Pamela and how to compare these with those of the ATIC experiment. Dark matter annihilation is then reviewed, which represent two types of dark matter: Neutralinos, and kaluza-Kline (KK) particles, which are next explained. The future astrophysical measurements, those from GLAST LAT, the Alpha Magnetic Spectrometer (AMS), and HEPCAT are reviewed, in light of assisting in finding an explanation for the observed excess. Also the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) could help by revealing if there are extra dimensions.

Chang, J.↗
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 NTRS1986

Cosmic ray sources, acceleration and propagation

A review is given of selected papers on the theory of cosmic ray (CR) propagation and acceleration. The high isotropy and a comparatively large age of galactic CR are explained by the effective interaction of relativistic particles with random and regular electromagnetic fields in interstellar medium. The kinetic theory of CR propagation in the Galaxy is formulated similarly to the elaborate theory of CR propagation in heliosphere. The substantial difference between these theories is explained by the necessity to take into account in some cases the collective effects due to a rather high density of relativisitc particles. In particular, the kinetic CR stream instability and the hydrodynamic Parker instability is studied. The interaction of relativistic particles with an ensemble of given weak random magnetic fields is calculated by perturbation theory. The theory of CR transfer is considered to be basically completed for this case. The main problem consists in poor information about the structure of the regular and the random galactic magnetic fields. An account is given of CR transfer in a turbulent medium.

Ptuskin, V. S.↗