Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cosmic rays”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
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.↗
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.↗
NASA NTRS1975

Origin of cosmic rays

Based on recent observations of the galactic gas and gamma ray distributions, the galactic cosmic ray distribution is deduced. This distribution is identical to that of supernova remnants (within experimental error), strongly supporting the hypothesis that most observed cosmic rays are produced by supernovas in our own galaxy. The average age of the cosmic ray sources is suggested, from the character of their distribution, to be about 30 million years.

Stecker, F. W.↗
NASA NTRS1978

Gamma-ray astronomy and the origin of cosmic rays

New surveys of galactic gamma ray emission together with millimeter wave radio surveys indicated that cosmic rays were produced as the result of supernova explosions in our galaxy with the most intense production occurring in a Great Galactic Ring about 35,000 light years in diameter where supernova remnants and pulsars were concentrated.

Stecker, F. W.↗
NASA NTRS1991

Magnetized supernova remnants with cosmic rays

The effects of interstellar magnetic fields and cosmic rays on the dynamics of an SNR expanding into a warm H I gas are examined. As long as the shock wave driven by the SN explosion propagates faster than 110 km/s, the vicinity of the shock front is fully ionized, and cosmic rays are well coupled to the thermal fluid. They are first accelerated at the adiabatic front, and further compressed in the postshock cooling zone. When the shock velocity drops below 110 km/s, ion-neutral collisions in the vicinity of the shock dissipate the waves which couple cosmic rays to the thermal gas, and impede cosmic-ray acceleration. It is found that magnetic and cosmic-ray pressures together dominate over thermal pressure away from the magnetic poles. As a result, most of the shell becomes considerably thicker, and the shock wave propagates somewhat faster than in the nonmagnetic case. At late times, the transverse mass motions which take place from the poles to the equator create H I holes at the polar caps. This theory leads to a simple interpretation of the 'barrel-shaped' distribution of radio emission observed in some SNRs.

Ferriere, Katia M.↗
NASA NTRS1982

The charge and isotopic composition of Z = 6-14 cosmic ray nuclei at their source

Using data from a cosmic ray charge-isotope telescope flown on balloons, both the charge and isotopic composition are determined of Z = 6-14 cosmic ray nuclei. A low abundance for the elements N and Ne in the cosmic ray source relative to solar cosmic rays is observed. For the isotopes, a cosmic ray source ratio Ne-22/Ne-20 is found that is 3.52 plus or minus 0.67 times the solar ratio, this enhancement being due in part to an enhancement of Ne-22 and in part to an underabundance of Ne-20. Also observed are possible enhancements of the Mg-26/Mg-24 ratio, which is 1.40 plus or minus 0.24 times the solar t ratio, and the C-13/C-12 ratio, which is 2.90 plus or minus 0.93 times the solar ratio. For Ne, the underabundance of this element, coupled with the overabundnace of the isotope Ne-22, is seen as providing an important new clue to the nucleosynthesis processes producing these differences.

Webber, W. R.↗