Engineering Papers⌕ Search

Engineering topics

Blake, J. B.

Publications and source records attributed to Blake, J. B..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Relativistic electrons near geostationary orbit - Evidence for internal magnetospheric acceleration

The possibility of an internal magnetospheric acceleration mechanism as the source of relativistic electron fluxes in earth's outer magnetosphere is explored. Such a model includes the substorm generation of a spectrally soft electron component, with subsequent inward radial diffusion. At low L values, an outward transport of energetic electrons occurs which leads to a return of the accelerated population to the outer magnetosphere. Data obtained concurrently at geostationary orbit at three widely spaced local times during a relativistic electron event provide support for acceleration by a recirculation process.

Baker, D. N.↗
NASA NTRS1989

Relativistic magnetospheric electrons: Lower ionospheric conductivity and long-term atmospheric variability

Long term observations of relativistic electrons in the earth's outer magnetosphere show a strong solar cycle dependence with a prominent intensity maximum during the approach to solar minimum. This population therefore closely corresponds to the presence of high speed solar wind streams emanating from solar coronal holes. Using a numerical code, the precipitating electron energy deposition in the earth's upper and middle atmosphere were calculated. Observed events (typically persisting several days) would have maximum effect in the 40 to 60 km altitude range with peak energy depositions greater than 110 keV/cu cm-s. It is suggested that this electron population could play an important long term role in modulating lower D region ionization and middle atmospheric ozone chemistry. Methods are described of observing middle atmospheric and lower ionospheric effects of the electrons including balloon, riometer, and space-based ozone sensor systems. A particularly promising approach may involve the monitoring of global Schumann resonance modes which are sensitive to global changes in the properties of the earth-ionosphere cavity. Present work indicates that Schumann resonance properties are moderately correlated with the flux of precipitating relativistic electrons thus offering the possibility of continuously monitoring this aspect of magnetosphere-atmosphere coupling.

Baker, D. N.↗
NASA NTRS1988

HIEN-LO: An experiment for charge determination of cosmic rays of interplanetary and solar origin

The experiment is designed to measure the heavy ion environment at low altitude (HIEN-LO) in the energy range 0.3 to 100 MeV/nucleon. In order to cover this wide energy range a complement of three sensors is used. A large area ion drift chamber and a time-of-flight telescope are used to determine the mass and energy of the incoming cosmic rays. A third omnidirectional counter serves as a proton monitor. The analysis of mass, energy and incoming direction in combination with the directional geomagnetic cut-off allows the determination of the ionic charge of the cosmic rays. The ionic charge in this energy range is of particular interest because it provides clues to the origin of these particles and to the plasma conditions at the acceleration site. The experiment is expected to be flown in 1988/1989.

Klecker, B.↗
NASA NTRS1987

Highly relativistic magnetospheric electrons - A role in coupling to the middle atmosphere?

Twenty-seven-day periodic enhancements of the relativistic electrons are observed in association with concurrently measured solar wind streams, and a numerical transport code is used to investigate the coupling of these high-energy electrons to earth's upper and middle atmosphere. When precipitated, these electrons are found to show a large energy deposition at 40-60 km altitude which is 3-4 orders of magnitude greater than the galactic cosmic ray or solar EUV energy deposition at these altitudes. It is suggested that this electron population could play a role in coupling solar wind and magnetospheric variability to the middle atmosphere through a modulating effect on lower D-region ionization and possibly on upper level ozone chemistry.

Baker, D. N.↗
NASA NTRS1985

The heaviest cosmic-ray nuclei

The implications of abundance measurements of cosmic-ray nuclei heavier than Fe are examined in light of standard propagation models and nucleosynthetic theory. Suggestions that the cosmic-ray source abundances differ significantly from solar system abundances are not well supported by the data without assuming ad hoc models of preferential acceleration. The solar system abundances of Pb and Bi are split into r-, standard s-, and cyclic s-process components to assess the contributions of these nucleosynthetic processes to the cosmic-ray source. The apparent deficiency of Pb seen in the HEAO 3 HNE data might indicate an absence of Pb from the recycling s-process.

Margolis, S. H.↗
NASA NTRS1985

Sources of the ultraheavy cosmic rays

The suggestions that the source abundances of cosmic ray nuclei heavier then Fe differ significantly from Solar System abundances are not well supported by the data without assuming preferential acceleration. The Solar System abundances of Pb and Bi are split into r-, standard s-, and cyclic 8-process components; the apprarent deficiency of Pb seen in the HEAO-3 Heavy Nuclei Experiment data might indicate an absence of Pb from the recycling 8-process.

Margolis, S. H.↗
NASA NTRS1983

The ultraheavy cosmic rays - Propagation and selective acceleration

Results of calculations of ultraheavy cosmic ray propagation are examined in the light of recent observations and theoretical advances with the objective of distinguishing the effects of propagation from nucleosynthesis and preferential acceleration. The results presented here have been calculated by the method described in Margolis (1983), with elements from iron (Z = 26) to uranium (Z = 92) combined in a single calculation. The source abundances of Anders and Ebihara (1982) have been used as a reference composition. It is shown, in particular, that the relative abundances of Sr and Ba are substantially increased by using the modified ionization potential dependence (MIPD) compared with solar abundances and the first ionization potential dependence (FIPD) model. In contrast, Pb shows similar enhancements in both FIPD and MIPD models.

Margolis, S. H.↗
NASA NTRS1982

Single event upset vulnerability of selected 4K and 16K CMOS static RAM's

Upset thresholds for bulk CMOS and CMOS/SOS RAMS were deduced after bombardment of the devices with 140 MeV Kr, 160 MeV Ar, and 33 MeV O beams in a cyclotron. The trials were performed to test prototype devices intended for space applications, to relate feature size to the critical upset charge, and to check the validity of computer simulation models. The tests were run on 4 and 1 K memory cells with 6 transistors, in either hardened or unhardened configurations. The upset cross sections were calculated to determine the critical charge for upset from the soft errors observed in the irradiated cells. Computer simulations of the critical charge were found to deviate from the experimentally observed variation of the critical charge as the square of the feature size. Modeled values of series resistors decoupling the inverter pairs of memory cells showed that above some minimum resistance value a small increase in resistance produces a large increase in the critical charge, which the experimental data showed to be of questionable validity unless the value is made dependent on the maximum allowed read-write time.

Kolasinski, W. A.↗
NASA NTRS1981

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in massive stars

The production of heavy nuclei during explosive helium burning has been calculated using a hydrodynamical model of a 15-solar mass (Type II) supernova and an n-process nuclear reaction network. It is found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material, especially in the vicinity of Pt, nor are any actinides produced. These deficiencies reflect an inadequate supply of neutrons. However, some neutron-rich isotopes, normally associated with the r-process, are produced which may be significant for the production of isotopic anomalies in meteorites.

Blake, J. B.↗
NASA NTRS1981

The elements just beyond iron - Formation during explosive carbon burning

It is pointed out that the details of the synthesis of the elements just beyond iron are unclear. Thus, a reexamination of the role played by neutron-capture reactions during explosive carbon burning is indicated. A description is given of calculations of explosive carbon-burning nucleosynthesis using a complete neutron capture (n-process) computer code with a network extending from Cr through Zr and including not only (n,gamma), (gamma,n) reactions and beta-decay but also (p,n), (n,p), (p,gamma), and (p,alpha) reactions. Initial conditions indicative of the composition of a massive star following core helium burning were selected, and a comparison is made with conditions similar to those used by Howard et al. (1972). It is found that neutron reactions during explosive carbon burning are an important source for the elements just beyond iron.

Wefel, J. P.↗
NASA NTRS1980

Nucleosynthesis of neutron-rich heavy nuclei during explosive helium burning in a 15 solar-mass supernova

The production of heavy nuclei during explosive helium burning has been calculated using the Weaver and Woosley self-consistent model of a complete 15 solar-mass star and the n-process code of Blake and Schramm. It was found that the resulting neutron-rich heavy nuclei are not produced in the relative abundances of solar-system r-process material (such as a Pt peak) nor are any actinides produced. Basically insufficient neutrons are available.

Blake, J. B.↗
NASA NTRS1980

Actinide cosmic ray chronometers - Relative abundances and the cosmic ray lifetime

Measurements of ultraheavy cosmic rays will provide radioactive chronometers, including the actinides, which are expected to be present in the source. These primary chronometers differ from the Be-10 secondary chronometer in total inelastic cross-section and decay half-life. A propagation code, which includes nuclear fragmentation, radioactive decay, and ionization energy-loss of cosmic rays is being used to investigate the variations in the fluxes and mean ages which would be expected for various models of cosmic ray propagation. Some preliminary results in the actinide region are presented here which indicate that measurements of the relative abundances of the actinides in the cosmic rays will be very useful for understanding source abundances but less useful for studying propagation effects.

Margolis, S. H.↗
NASA NTRS1979

Simulation of cosmic-ray induced soft errors and latchup in integrated-circuit computer memories

Soft errors have been induced in solid-state static RAM's by iron nuclei from the Lawrence Berkeley Laboratory (LBL) Bevalac, in experiments designed to prove the ability of iron-group cosmic rays to generate such errors. Subsequently, various delidded device types were tested in beams of argon and krypton ions from the LBL 88-inch Cyclotron, at energies near 2 MeV/nucleon. The latter tests showed that some devices are essentially immune to bit error while others are quite susceptible. Good agreement was obtained with model predictions in cases where the latter exist. Latchup, whose cause is attributed to individual heavy ions, was also observed in some device types.

Kolasinski, W. A.↗
NASA NTRS1979

Isotopic anomalies from neutron reactions during explosive carbon burning

The heavy isotopic anomalies observed recently in the fractionation and unknown nuclear inclusions from the Allende meteorite are explained by neutron reactions during the explosive carbon burning (ECB). This model produces heavy anomalies in the same zone where Al-26 and O-16 are produced, thus reducing the number of source zones required for the isotopic anomalies. Unlike the classical r-process, the ECB n-process avoids the problem with the Sr anomaly and may resolve the problem of conflicting time scales between Al-26 and the r-process isotopes I-129 and Pu-244. Experimental studies of Zr and Ce isotopic composition are proposed to test this model.

Lee, T.↗
NASA NTRS1979

Reduction and analysis of ATS-6 data

The scientific and technological results obtained by an energetic particle spectrometer are summarized. Data on energetic electrons trapped in the Earth's radiation belt near synchronous altitude and on solar particles penetrating to this altitude are discussed.

Paulikas, G. A.↗
NASA NTRS1979

Low-altitude measurements of precipitating protons, alpha particles, and heavy ions during the geomagnetic storm on March 26-27, 1976

During the geomagnetic storm of March 16-17, 1976, observations were made of precipitating protons, alpha particles, and heavy ions by two counter telescopes aboard the low-altitude S3-2 satellite. These observations are presented in this paper and their significance discussed. Briefly, a two-zone precipitation region is observed on the nightside, at L equals 2.7 and L equals 4.0 with an alpha/p ratio of about 0.008 in the low-latitude region and about 0.0009 at higher latitude at 0.4 MeV/necleon. The heavier ions, CNO nuclei, are seen in the low-latitude zone with a CNO/alpha ratio of about 0.056 at 0.25 MeV/nucleon.

Scholer, M.↗