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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Proton-associated alpha-irradiation in the early solar system - A possible K-41 anomaly

It is shown that alpha-particle fluences associated with proton fluences sufficiently high to produce the Al-correlated excess of Mg-26 found in the Allende meteorite produce equally significant amounts of Ca-41. The Ca-41 is produced by Ar-38(alpha,n)Ca-41 reactions occurring in the gas and condenses into the Ca-Al-rich grains forming at that time. After the decay of Ca-41, these grains will have a Ca-correlated excess of K-41. The question is considered whether the proposed scheme is capable of producing an observable excess of K-41. A calculation is conducted of the magnitude of the K-41 excess expected to be found in Ca-Al-rich grains for various ratios of Ca/K by developing an irradiation-condensation model. It is shown that on the basis of the currently available data it is not possible to come to firm conclusions regarding the validity of the irradiation model.

Dwek, E.↗
NASA NTRS1980

Singly-ionized helium in the driver gas of an interplanetary shock wave

The interplanetary shock wave observed on Jan. 29, 1977 by the HELIOS-1 plasma instruments shows an unusual feature: in the cold tenuous piston plasma following this shock, there appears a third peak in the energy per charge (E/q) spectra, in addition to the normal proton and alpha-particle peaks. The peak is located at E/q ? 4 and persists for about 14 hours, with slowly varying intensities. Independent simultaneous measurement of these particles' charge yields a value of approximately 1. These ions are thought to be He-4(+) ions travelling with the same speed as protons and alpha particles. The occurrence of He-4(+) indicates the possibility that during eruptive prominences or other solar transients, 'cold' chromospheric plasma might escape from the sun without undergoing the normal coronal heating process.

Schwenn, R.↗
NASA NTRS1983

On the equation of state of solar wind ions derived from Helios measurements

The radial evolution of such adiabatic invariants as the ion magnetic moments are studied on the basis of solar wind ion velocity distribution observations made by the Helios spacecraft between 0.3 and 1 AU. Significant differences between proton and alpha-particle parameters in wind velocity dependence are noted, and adiabaticity is on the average found to be violated. This violation is interpreted as evidence that protons are heated perpendicular to the field in fast streams. The contribution of the differential streaming energy to the total internal energy of the ions is also considered, and average heliocentric radial profiles for the ion heat fluxes are presented together with an examination of a possible ion heat flux role in the supply of thermal energy during the winds radial expansion. The present findings suggest that wave-particle interactions, and/or Coulomb collisions, are required to explain solar wind ion thermal energy states and radial temperature profiles.

Marsch, E.↗
NASA NTRS1982

Room-temperature mercuric iodide spectrometry for low-energy X-rays

A discussion of the limits of energy resolution in different energy ranges is given. The energy resolution of a spectrometer is analyzed in terms of the parameters characterizing the crystal, the detector, and the amplification electronics. A high-resolution room-temperature HgI2 spectrometry system was used to measure low-energy X-ray fluorescence spectra. For the MgK-alpha X-ray line the measured resolution was 245 eV (fwhm); the electronic noise linewidth of the system was 225 eV. Alpha-particles were used to excite X-ray fluorescence from low-Z elements separately or in combination. The shape of the photopeaks in the spectra is discussed.

Kusmiss, J. H.↗
NASA NTRS1985

Injection of energetic particles following the gamma-ray flares on June 7, 1980, as observed on Helios 1

On June 7, 1980, two flares with impulsive gamma-ray emission were observed at 0117 Ut and 0312 UT. Measurements of the University of Kiel cosmic-ray experiment on HELIOS-1 are presented. The first approx. 0.5 MeV electrons escaped from the Sun to interplanetary space simultaneously with the hard X-ray burst. For the 0312 UT flare the protons and alpha-particle in the 3 - 20 MeV/nucleon range were injected from the Sun with a delay of approx. 40 min, followed by two subsequent new emissions.

Neustock, H. H.↗
NASA NTRS1984

Field funneling and range straggling in partially depleted silicon surface-barrier detectors

The effects of field funneling and range straggling have been quantitatively observed in the measurement of charge collected from alpha-particle tracks in silicon surface-barrier charged-particle detectors. The method described may be used for the straight-forward measurement of charge collection from heavy ions in these and other semiconductor devices.

Zoutendyk, J. A.↗
NASA NTRS1985

Improved cross section calculations for astrophysical applications

Modifications are proposed for the semiempirical equations and parameters of Silberberg and Tsao (1973) for partial cross section calculations of proton-nucleus reactions in cosmic rays. These modifications include: adjustment of general parameters; modification of energy dependence; effects of nuclear alpha-particle structure, deuteron emission, and even-charged products; peripheral reactions; fission reactions; averaging cross sections near boundaries of different parameters; elimination of certain special cases; and treatment of the Pt to Pb group that cannot yet be generalized to Z(t) less than 76.

Silberberg, R.↗
NASA NTRS1986

Field Funneling and Range Straggling in Silicon Detectors

Magnitudes of field funneling and range straggling determined in silicon-surface-barrier (Schottky-barrier) charged-particle detectors (SSBD's) through meaurement of charges collected from alpha-particle tracks. Method used extended to straightforward measurement of charge collection from heavy-ion tracks in these and other semiconductor devices. Such measurements used to assess single-event upsets in integratedcircuit chips, with view toward making them resistant to radiation. Field funneling and range straggling measured with electronic system in which charge collected from individual ions measured and recorded by multichannel analyzer.

Zoutendyk, J. A.↗
NASA NTRS1986

Ion flow at comet Halley

The three-dimensional positive ion analyzer aboard the Giotto spacecraft has been used to study the interaction between protons and alpha-particles in the solar wind and positive ions from comet Halley. Although the first impression of the overall structure is that the plasma flow evolves smoothly as the nucleus is approached, three sharp transitions of relatively small amplitude can be identified on both the inbound and outbound legs of the trajectory. The outermost one, at about one million km from the nucleus, appears to be a multiple crossing of a weak bow shock. The innermost one, at 80,000 km, is the boundary where the flowing plasma becomes depleted. On a microscopic scale, the turbulence created by the interaction between the two ion populations extends to a distance of several million km from the nucleus. At Giotto's closest approach to the nucleus, the plasma produced around the spacecraft by dust and gas impacts was much more energetic than had been expected.

Johnstone, A.↗
NASA NTRS1986

A test of Lee's quasi-linear theory of ion acceleration by interplanetary traveling shocks

Lee's (1983) quasi-linear theory of ion acceleration is tested using ISEE-3 measurements of the November 12, 1978 quasi-parallel interplanetary shock. His theory accounts with varying degrees of precision for the energetic proton spatial profiles; the dependence of the spectral index of the power law proton velocity distribution upon the shock compression ratio; the power law dependence of the upstream proton scalelength upon energy; the absolute magnitude of the upstream proton scale length; the behavior of the energetic proton anisotropy upstream and downstream of the shock; the behavior of the alpha-particle proton ratio upstream; the equality of the spatial scale lengths at the shock of the upstream waves and of the protons that resonate with them; and the dependence of the integrated wave energy density upon the proton energy density at the shock. However, the trace magnetic field frequency spectra disagree with his theory in two ways. The part of the spectrum that can resonate with the observed protons via first-order cyclotron resonance is flat, whereas Lee's theory predicts an f exp - 7/4 frequency dependence for the November 12 shock. Higher frequency waves, which could not resonate with the observed upstream protons, increased in amplitude as the shock approached, suggesting that they too were generated by the shock.

Kennel, C. F.↗
NASA NTRS1987

Positrons from accelerated particle interactions

Positron production from the decay of radioactive nuclei produced in nuclear interactions of accelerated particles is treated in detail. Laboratory data as well as theoretical considerations are used to construct energy-dependent cross sections for the production of a large number of radioactive positron emitters resulting from proton and alpha-particle interactions with ambient cosmic matter. Using these cross sections, positron production rates are calculated for a variety of energetic particle spectra, assuming solar abundances for both the energetic particles and the ambient medium. These results can be used for the study of astrophysical sites which emit annihilation radiation. In particular, the results have been applied to solar flares, where the observed 0.511 MeV line is shown to be due to positrons resulting from accelerated particle reactions.

Kozlovsky, B.↗
NASA NTRS1987

Interactions of oblique interplanetary discontinuities and their manifestations during STIP intervals 15-19

The generation of slow shock waves as the result of the interaction of Alfven discontinuities with solar wind contact surfaces is considered. The latter are taken to be the boundaries of proton and alpha-particle concentration inhomogeneities. It is found that the intensity of the Alfven discontinuity may be increased as the result of its interaction with the more dense plasma. The converse (i.e., decrease of the Alfven discontinuity's intensity following interaction with a less dense plasma) is also indicated. Also discussed is the generation of a magnetic cloud as the result of the interaction of a quasi-parallel Alfven discontinuity with a dense plasma contact surface. It is shown that the (solar-generated) Alfven discontinuity may then be transformed into non-flare fast and slow shock waves as the result of this interaction. Thus, it is indicated that some fast shock waves in the solar wind may have a nonsolar origin.

Grib, S. A.↗
NASA NTRS1988

Solar flare protons and alpha particles during the last three solar cycles

This paper presents solar-flare-associated proton and alpha-particle fluxes determined for major events from October 1972 through March 1987 (the period that represents the last part of solar cycle 20 and the whole of solar cycle 21), using data obtained by detectors on board the IMP-7 and IMP-8 satellites, along with earlier obtained data for cycle 20. It was found that the average omnidirectional flux of protons with kinetic energy above 10 MeV for cycle 21 (64/sq cm per sec) is lower than the corresponding number for cycle 20 (92/sq cm per sec) and for the cycle 19 (378/sq cm per sec). No definitive correlation was found to exist between cycle-averaged solar flare proton fluxes and peak sunspot numbers.

Goswami, J. N.↗
NASA NTRS1988

Downstream energetic proton and alpha particles during quasi-parallel interplanetary shock events

This paper considers the energetic particle populations in the downstream region of three quasi-parallel interplanetary shock events, which was explored using the ISEE 3 Ultra Low Energy Charge Analyzer sensor, which unambiguously identifies protons and alpha particles using the electrostatic deflection versus residual energy technique. The downstream particles were found to exhibit anisotropies due largely to convection in the solar wind. The spectral indices of the proton and the alpha-particle distribution functions were found to be remarkably constant during the downstream period, being generally insensitive to changes in particle flux levels, magnetic field direction, and solar wind densities. In two of the three events, the proton and the alpha spectra were the same throughout the entire downstream period, supporting the prediction of diffusive shock acceleration theory.

Tan, L. C.↗
NASA NTRS1988

Design of a sample acquistion system for the Mars exobiological penetrator

The Mars Exobiological Penetrator will be imbedded into several locations on the Martian surface. It contains various scientific instruments, such as an Alpha-Particle Instrument (API), Differential Scanning Calorimeter (DSC), Evolved Gas Analyzer (EGA) and accelerometers. A sample is required for analysis in the API and DSC. To avoid impact contaminated material, this sample must be taken from soil greater than 2 cm away from the penetrator shell. This study examines the design of a dedicated sampling system including deployment, suspension, fore/after body coupling, sample gathering and placement. To prevent subsurface material from entering the penetrator sampling compartment during impact, a plug is placed in the exit hole of the wall. A U-lever device is used to hold this plug in the penetrator wall. The U-lever rotates upon initial motion of the core-grinder mechanism (CGM), releasing the plug. Research points to a combination of coring and grinding as a plausible solution to the problem of dry drilling. The CGM, driven by two compressed springs, will be deployed along a tracking system. A slowly varying load i.e., springs, is favored over a fixed displacement motion because of its adaptability to different material hardness. However, to accommodate sampling in a low density soil, two dash pots set a maximum transverse velocity. In addition, minimal power use is achieved by unidirectional motion of the CGM. The sample will be transported to the scientific instruments by means of a sample placement tray that is driven by a compressed spring to avoid unnecessary power usage. This paper also explores possible modifications for size, weight, and time as well as possible future studies.

Thomson, Ron↗
NASA NTRS1989

Solar activity influence on cosmic ray penetration in the middle atmosphere

A new improved model for cosmic rays-middle atmosphere interaction is developed. The ionization q(h)-profile dependence on penetrating high energy particles composition (protons, alpha-particles and heavier nuclei) and energy spectra (solar activity modulation included) are investigated. A computer program, realizing the Gaussian algorithm for solving of multidimensional integrals is created. The corresponding electron density profiles N(h) at solar minimum and maximum are obtained.

Vellinov, P. I.↗
NASA NTRS1991

Solar flare gamma-ray line profiles

Solar gamma-ray lines are produced through collisions of pairs of positive ions whose center of mass energies are above the relevant thresholds for excitation of gamma-ray emitting states. Because of the low density of the solar plasma, prompt gamma rays are emitted by recoiling ions before significant energy loss has occurred. Thus, the lines are expected to be Doppler-broadened to widths of the order of a hundred KeV. Gamma-ray lines resulting from proton and alpha-particle (He-4 ion) beams on carbon and oxygen targets in the laboratory exhibit complex profiles which change rapidly with the gamma-ray observation angle. Earlier work has been limited to modeling laboratory and solar flare gamma-ray profiles produced by proton excitation, but laboratory profiles of the carbon 4.44-MeV line and oxygen 6.13-MeV line from alpha excitation have now been successfully modeled. Solar flare gamma-ray line profiles of the carbon and oxygen lines from heavy ions in the ambient solar medium interacting with representative high-energy proton and alpha particle populations are presented.

Lang, F. L.↗
NASA NTRS1990

Differential neutron energy spectra measured on spacecraft in low Earth orbit

Two methods for measuring neutrons in the range from thermal energies to dozens of MeV were used. In the first method, alpha-particles emitted from the 6Li(n,alpha)T reaction are detected with the help of plastic nuclear track detectors, yielding results on thermal and resonance neutrons. Also, fission foils are used to detect fast neutrons. In the second method, fast neutrons are recorded by nuclear photographic emulsions (NPE). The results of measurements on board various satellites are presented. The neutron flux density does not appear to correlate clearly with orbital parameters. Up to 50% of neutrons are due to albedo neutrons from the atmosphere while the fluxes inside the satellites are 15-20% higher than those on the outside. Estimates show that the neutron contribution to the total equivalent radiation dose reaches 20-30%.

Cosmos 1887 Project↗