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Simpson, J. A.

Publications and source records attributed to Simpson, J. A..

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The radial intensity gradients for cosmic rays and the anomalous helium from Pioneer 10 and 11

This report extends and updates previous studies of the heliocentric radial gradients of the integral flux of cosmic rays (E greater than 70 MeV) and of differential fluxes of protons and helium nuclei in the approximate energy windows 11-20 and 30-70 MeV/n to include data taken through the end of 1978 when Pioneer 10 had reached a distance of 18 AU from the sun, and Pioneer 11 was at a distance of 8.4 AU. Small positive gradients are found for all species considered, although the actual values of the gradients may vary as a function of time. The data suggest that the modulation region has a radial extent large compared to 18 AU. The anomalous helium component was observed at all radial distances, and is found to have a much higher flux in the outer solar system than near 1 AU.

Bastian, T. S.↗
NASA NTRS1980

Large-scale modulation of galactic cosmic rays and anomalous He observed at not less than 16 AU with Pioneer 10

High-speed solar wind streams issued from specific ranges of solar longitude or evolved into a single stream at not less than 16 AU during 1978. Shock waves associated with these streams cause a large decrease in cosmic ray intensity starting at 1 AU in April and appears progressively with time outward to 16 AU; a stepwise intensity decrease then occurs for both the galactic cosmic rays and the anomalous He component. The flare-accelerated nuclei show a new aspect of solar wave propagation in the outer solar system; at about 16 to 18 AU, the intensity builds up because of dispersion, reaches a flux level, and finally declines when the outward rate of escape becomes dominant.

Pyle, K. R.↗
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 NTRS1979

The isotopes of neon in the galactic cosmic rays

The paper examines the results obtained by the University of Chicago instrument on board the IMP 7 satellite used to measure the abundances of Ne-20 and Ne-22 in the galactic cosmic rays during 1973-1977, over the general energy range of 60-230 MeV per nucleon. It is reported that the instrument shows a mass resolution of 0.7 amu(sigma) which was confirmed by calibrating a backup instrument at the LBL Bevalac with separated beams of neon isotopes. Through the use of standard solar modulation and cosmic-ray propagation models, the cosmic-ray source ratio inferred is Ne-22/Ne-20 = 0.38 = or -0.07 which is significantly greater than the present solar system ratio. It is concluded that propagation effects or cross-section uncertainties cannot account for such a large abundance of Ne-22, and thus this measurement provides evidence that the cosmic rays come from a source region where the Ne-22 abundance is substantially greater than in solar system material.

Garcia-Munoz, M.↗
NASA NTRS1979

Jovian electron propagation close to the sun /at about 0.5 AU/

On the basis of interplanetary electron flux measurements in the energy range 0.7-25 MeV made on the Mariner 10 spacecraft launched in 1973 for successive encounters with planet Mercury (R approximately equal 0.5 AU), it is shown that the dominant interplanetary flux of electrons close to the sun is Jovian in origin (except for times of solar flares) and that these observations are consistent with a three-dimensional diffusion-convection model which describes Jovian electron propagation in the outer solar system.

Eraker, J. H.↗
NASA NTRS1979

Electron calibration of instrumentation for low energy, high intensity particle measurements at Mercury

Unique identification of the high intensity, impulsively accelerated charged particle fluxes discovered during Mariner 10's first encounter with Mercury (March 1974) requires a detailed knowledge of the responses of the two University of Chicago charged particle telescopes to low energy fluxes over a wide dynamic range of flux levels. The results of detailed analyses show that these telescopes can separate and identify unambiguously the presence of electron and proton fluxes for a wide range of electron spectra and intensities in the relevant overall range of about 30 keV to 2 MeV.

Christon, S. P.↗
NASA NTRS1979

The isotopic and elemental abundances of neon nuclei accelerated in solar flares

The relative isotopic abundances of Ne-20 and Ne-22 in seven solar flares were determined from measurements of the satellite IMP 8, yielding the ratio Ne-20/Ne-22 = 7.7 (+2.3, -1.5) for solar chromospheric matter. This value is in agreement with the ratio for the component neon-A (the 'primordial' component) found in carbonaceous chondrites. An elemental abundance ratio Ne/O = 0.14 + or - 0.01 also has been obtained which agrees closely with earlier reported measurements. It is shown that the effects of preferential acceleration relative to solar-system abundances with increasing charge number observed for some solar flares - though biasing the elemental ratio - does not appear to influence the neon isotopic abundances.

Dietrich, W. F.↗
NASA NTRS1979

Jovian electron propagation out of the solar equatorial plane - Pioneer 11 observations

Jovian electron intensity in the energy range 2-7 MeV was measured along the trajectory of Pioneer 11 up to 16 deg heliographic latitude. These electrons have crossed the average direction of the interplanetary magnetic field, propagating normal to the solar equatorial plane, and their intensity continues to be modulated by corotating interaction regions over this latitude range. From these data, the electron diffusion coefficient perpendicular to the equatorial plane (K2 = 2 x 10 to the 20th sq cm/s) was derived to within a factor 2 using a three-dimensional diffusion-convection model and the values of the parallel and perpendicular diffusion coefficients in the solar equatorial plane (Ky = 5 x 10 to the 22nd sq cm/s, K2 = 10 to the 21st sq cm/s, respectively), which had previously successfully described Jovian electron propagation near the equatorial plane from 1 to about 10 AU. These results indicate that the Jovian electron intensity may be very low at high solar latitudes.

Hamilton, D. C.↗
NASA NTRS1979

The solar latitude and radial dependence of the anomalous cosmic-ray helium component

Observations are presented of the spatial intensity gradients of 11-20-MeV per nucleon anomalous helium made with Pioneer 10 and Pioneer 11 over the radial range 1-11.3 AU for Pioneer 10 and to a heliographic latitude of 16 deg at 3.75 AU for Pioneer 11. Evidence is found for a significant gradient in heliographic latitude, with flux increasing away from the equatorial plane at the rate of about 2% to 3% per degree of latitude. This result shows that the common assumption of spherical symmetry for solar modulation is incorrect. By comparison with gradients measured for 29-67-MeV per nucleon helium and for 11-20-MeV and 29-67-MeV protons, it is found that both the radial and latitudinal gradients of the low-energy anomalous helium are the largest of those measured. The implications of these results for the origin of the anomalous component and for solar modulation are briefly discussed.

Mckibben, R. B.↗
NASA NTRS1978

Preferential enhancements of the solar flare-accelerated nuclei carbon to zinc from about 20-300 MeV/nucleon

IMP 8 satellite measurements with a charged-particle telescope are examined which show that three large solar flares in late 1977 displayed preferential enhancements of abundances from C through Fe at energies of about 20 to 400 MeV/nucleon. It is found that the differential energy spectra of C, O, Mg, Si, and Fe, as well as protons and helium, are best fitted by power laws in energy per nucleon or rigidity with an index of 2.3 + or - 0.2, that the spectra of most of the even-Z nuclei have essentially the same slope, and that all the enhancements were independent of energy in the range from 20 to 300 MeV/nucleon. A plot of enhancement factor vs. Z is presented which clearly demonstrates the preferential enhancement of abundances with increasing Z in one of the solar flares, where the nuclei reached such high energies that they must have escaped the corona fully stripped of electrons. Implications for theories of solar-flare acceleration of the nuclei are considered.

Dietrich, W. F.↗
NASA NTRS1978

The energetic particle environment of the solar probe mission: As estimated by the participants of the Solar Probe Environment Workshop

NASA's long-range plan for the study of solar-terrestrial relations includes a Solar Probe Mission in which a spacecraft is placed in an eccentric orbit with perihelion at four solar radii. Possible radiation damage to the spacecraft and mission from energetic particles was discussed at a Solar Probe Environment Workshop which concluded that it would be unlikely for such a spacecraft to suffer fatal radiation damage, although a severe problem exists in limiting the neutron flux from a radioactive power supply enough to allow solar neutrons to be detected.

Neugebauer, M.↗
NASA NTRS1978

Solar neutron spectroscopy near the sun

A brief note is summarized to show the importance of solar neutron observations for the advancement of phenomena crucial for solar physics, and to suggest the constraints which must be placed on the Solar Probe Mission for carrying out studies of this kind.

Simpson, J. A.↗
NASA NTRS1978

The relative abundances of the elements silicon through nickel in the low energy galactic cosmic rays

Measurements of the relative abundances of the elements Si through Ni in galactic cosmic rays in the energy interval 72 to 450 MeV/nucleon are reported based on data collected by a cosmic-ray telescope on the IMP 8 satellite. The measured abundances are compared with propagation calculations using various distributions of path lengths. It is found that the measurements favor an exponential distribution of path lengths truncated at short path lengths. The source abundances of Si, Ca, Fe, and Ni derived by extrapolating the measured abundances back to the source are shown to be comparable to the solar-system abundances. The relevance of the measurements of Sc through Mn to the Mn-54 radioactive decay is examined.

Garcia-Munoz, M.↗
NASA NTRS1978

Charge and energy spectra of heavy cosmic rays at intermediate energies

The energy spectra and the charge composition of the primary elements C, O, Ne, Mg, and Si have been measured in both the low-energy and high-energy modes of the University of Chicago telescope on board the IMP 8 spacecraft. Combining both modes of analysis yields differential energy spectra for each element from about 50 MeV/nucleon to about 1 GeV/nucleon. The charge ratios with respect to oxygen are found to be energy independent over this interval and are consistent with the results of cosmic-ray propagation and solar-modulation calculations. The relative abundances obtained are in substantial agreement with previous investigations in this energy regime.

Garcia-Munoz, M.↗
NASA NTRS1978

The isotopic composition of galactic cosmic ray lithium, beryllium and boron

The isotopic composition of galactic-cosmic-ray Li, Be, and B has been measured near 100 MeV/nucleon by using the University of Chicago IMP 7 and IMP 8 cosmic-ray telescopes during 1973-1975. The measured abundances allow detailed checks of models of interstellar propagation and solar modulation to be made and conclusions to be drawn concerning the spectral forms at the source and the minimum solar modulation level. For example, comparing these results with local interstellar spectra calculated by using a 'leaky box' model, it is found that if solar modulation is ignored, there is no unique leakage mean free path consistent with all the observations. However, by taking account of a sizable level of residual solar modulation, excellent agreement is obtained between the calculated and measured abundances. Thus, these isotopic abundances confirm the old hypothesis that cosmic-ray Li, Be, and B are produced as secondaries in interstellar space.

Garcia-Munoz, M.↗