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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
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NASA NTRS1974

Anisotropies of galactic cosmic rays outside the orbit of earth measured on Pioneer 10

Preliminary results of observations of the directional distribution of cosmic rays being conducted by the University of Chicago experiment on the Pioneer 10 spacecraft are presented. The unusual geometry of the directional scan is described and some features of the response of a bidirectional coincidence telescope are discussed. Selected periods free from the presence of low-energy solar particles exhibit transient deviations from uniform directional distributions for the bidirectional flux of nuclei greater than 67 MeV/nucleon. These deviations are typically 2 to 4 (plus or minus 1) percent and are oriented very roughly in a N-S direction. Such nonuniformities observed with a bidirectional detector can only be due to even order terms in the angular distribution function.

Lentz, G. A.↗
NASA NTRS1975

Measurement of the fluxes of galactic cosmic ray H-2 and He-3 in 1972 - 1973

If a nearby source of low-energy helium is present, which has traversed a relatively small amount of matter and thus has not caused the production of a significant amount of H-2 or He-3, then these abundance ratios will be suppressed, particularly at low energies. This seems to be the most likely explanation for low ratios.

Teegarden, B. J.↗
NASA NTRS1976

Solar modulation of galactic cosmic rays 4: Latitude dependent modulation

A numerical method is outlined for solving the equation which describes the solar modulation of cosmic rays in models where interplanetary conditions can vary with heliocentric latitude. As an illustration of the use of this method, it is shown how variations in the modulation with latitude could produce the small radial gradients in the intensity that were observed from the Pioneers 10 and 11 spacecraft.

Fisk, L. A.↗
NASA NTRS1976

A mechanism for inducing climatic variations through ozone destruction: Screening of galactic cosmic rays by solar and terrestrial magnetic fields

A perturbation analysis, allowing for temperature and opacity feedbacks, is developed to calculate depletions in the O3 abundance and reductions of stratospheric solar heating that result from increases in NOx concentration. A pair of perturbation coefficients give the reduction in O3 and temperature through the stratosphere for a specified NOx increase. This type of analysis illustrates the tendency for various levels to self-heal when a perturbation occurs. Physical arguments indicate that the expected sign of the climatic effect is correct, with colder surface temperatures produced by reduced magnetic shielding. In addition, four qualitative reasons are suggested for thinking that significant ozone reductions by cosmic ray influxes will lead to an increased terrestrial albedo from stratospheric condensation. In this view, long-term (approximately 10,000 years) climatic changes have resulted from secular geomagnetic variations while shorter (approximately 100 years) excursions are related to changes in solar activity.

Chamberlain, J. W.↗
NASA NTRS1975

The isotopic composition of galactic cosmic ray Li, Be, and B

New measurements are reported of the isotopes of cosmic-ray Li, Be, and B and of the elements C, N, and O, with cosmic ray telescopes on board the IMP-7 and IMP-8 satellites during 1973-74 in the energy range 35-210 MeV/nucleon. High mass resolution and stability together with a set of data more extensive than in previous experiments lead to a clear isotopic separation. The measured isotopic and chemical abundances provide a stringent test for models of interstellar propagation and solar modulation. We find not only that for a steady state propagation and solar modulation model all light isotopes and medium element abundances are explained by 5 g/sq cm average pathlengths, as was earlier found from element analysis, but that also these results, taken along with our Be-10 measurements, indicate a longer lifetime for cosmic rays than predicted by the usual assumption of an average interstellar density of 1 to 3 atoms/cu cm.

Garcia-Munoz, M.↗
NASA NTRS1977

Observations of galactic cosmic ray energy spectra between 1 and 9 AU

The variation of the 5 to 500 MeV/nuc cosmic ray helium component was studied between 1 and 9 A.U. using essentially identical detector systems on Pioneer 10 and 11 and Helios I. Between 100 and 200 MeV/nuc a radial gradient of 3.3?1.3%/A.U. is found. At 15 MeV/nuc this value increases to 20?4%/A.U. Between 4 and 9 A.U. a well defined intensity maximum is observed at approximately 17 MeV/nuc. The average adiabatic energy loss between 1 and 9 A.U. is approximately 4 MeV/nuc/A.U. The observed radial variation between 1 and 9 A.U. is well described by the Gleeson-Axford force field solution of the modulation equations over an energy range extending from 15 to 500 MeV/nuc and is in good agreement with the results reported by other Pioneer experiments. These values are much smaller than had been theoretically predicted.

Mcdonald, F. B.↗
NASA NTRS1976

Solar-cycle dependence of galactic cosmic ray flux. II - The correlation between the nucleonic flux and solar indices

To investigate the relationship between solar activity and cosmic-ray modulation, time series of the nucleonic flux and of solar plages, sunspots, centimeter radio noise, and the brightness of the white-light corona at 1.1 and 1.5 solar radii from the center of sun are cross-correlated. Data pertain to the years 1964-1967 during the ascending phase of the current solar cycle. The amplitudes and phases of correlation functions for filtered and unfiltered indices are discussed. The existence of a superior solar index for relating solar activity to long-term modulation is not yet demonstrated conclusively, and the time lag of modulation is too poorly determined to permit its use in estimating the radius of the modulation region.

Parker, G. D.↗
NASA NTRS1977

Short-term variations of the galactic cosmic ray intensity - 1964-1967

A statistical analysis of time variations in ground-level nucleonic cosmic-ray intensity for the interval from 1964 to 1967 is presented which incorporates synoptic observations of the solar white-light corona as well as indices of photospheric and chromospheric activity. Correlation analysis of solar activity and short-term modulation reveals that all indices vary significantly on time scales near the solar rotation period and that the correlation function exhibits a quasi-sinusoidal variation that maximizes near zero lag. It is found that 27-day variations of the indices were most pronounced in 1966-1967, that recurrent cosmic-ray depressions occurred in conjunction with observed solar-wind disturbances, and that two categories of interplanetary disturbance are sufficient to account for the large recurrent cosmic-ray depressions in 1966-1967. It is suggested that flare-generated shocks were the main source of these recurrent cosmic-ray variations and that the contribution of corotating cosmic-ray disturbances to the observed recurrent modulation was probably very small. This hypothesis is tested against the correlation functions of solar and cosmic-ray indices.

Parker, G. D.↗
NASA NTRS1980

Variations in the intensity of galactic cosmic rays and the anomalous helium as a function of solar latitude

Pioneer 11 rose to a heliographic latitude of 16 deg in the course of its trajectory from Jupiter to Saturn. From analysis of the fluxes of low energy protons and anomalous helium measured by Pioneer 11 as a function of latitude, it was found that the data are consistent with latitude gradients of 2% per degree for the anomalous helium and 1% per degree for 29-67 MeV protons.

Bastian, T. S.↗
NASA NTRS1980

Recurrent modulation of galactic cosmic rays and the anomalous helium

The observations of 27 day variations in the intensity of low energy cosmic ray protons (29-67 MeV) and anomalous helium (11-20 MeV/nucleon) are reported. These observations were made with instruments on IMP-8 in the earth orbit on Pioneer 11 at heliographic latitudes up to 16 deg and on Pioneer 10 at heliocentric distances of from 4 to 14 AU. 27 day variations are observed at all locations, most strongly in the anomalous helium, and reflect the very large scale structure of the interplanetary medium. Intensity minima are most often associated with high speed solar wind streams, but the physical mechanism producing the variations is not clear.

Bastian, T. S.↗
NASA NTRS1982

The isotopes of H through C in galactic cosmic rays

The charge, energy spectra, and isotopic composition of hydrogen through nitrogen have been studied with the GSFC/UNH cosmic ray experiments on board the Pioneer 10 and 11 spacecraft. Good charge and mass resolution have been obtained by utilizing three parameter analysis (i.e., two measurements of delta E and a measurement of the residual kinetic energy of stopping particles). This method allows isotopic resolution for the High Energy Telescope (HET) which operates over a typical energy range of 30-56-MeV/nuc for He. The observations will be over solar quiet times from September 1976-September 1977. The resolution, methods of analysis, spectra, and isotopic composition will be presented and discussed where the statistical significance of H to C isotopes is meaningful.

Smith, B.↗
NASA NTRS1982

A study of galactic cosmic ray propagation models based on the isotopic composition of the elements lithium, beryllium and boron

A good test for a cosmic ray propagation model is its ability to predict the abundances of the light secondary nuclei lithium, beryllium, and boron. By using measured isotopic abundances of lithium, beryllium, and boron, Garcia-Munoz et al. (1979) were able to place limits on three important parameters of a leaky box propagation model. The considered parameters include the source spectral parameter, the leakage mean free path, and the characteristic adiabatic energy loss due to solar modulation. The present investigation is concerned with a critical evaluation of the information which can be deduced about these parameters from isotopic composition alone, taking into account the effects of uncertainties in the spallation cross section data.

Hinshaw, G. F.↗
NASA NTRS1982

Observations of the flow pattern of low-energy galactic cosmic rays in the outer heliosphere

The investigation is based on data obtained with the aid of Pioneer 10. The experimental observations of low-energy cosmic-ray anisotropies are presented for the period November 8, 1976 to December 15, 1977 when Pioneer 10 was at its maximum radial distance (11.5-14.7 AU) during the period of solar minimum conditions at the end of cycle 20. The azimuthal anisotropies obtained by integrating over this complete period are summarized in a table. For 30-56-MeV protons, a value of 7.4 plus or minus 2 percent in a direction of 110 deg is obtained. This direction is close to the 90 deg value expected from corotation or for particles flowing inward along the nominal filed line. The value obtained for helium is consistent with the value for hydrogen. There was no measureable flow for the 10-22-MeV/nuc anomalous helium. Attention is given to details of instrumentation and questions regarding the statistical significance of the data.

Mcdonald, F. B.↗