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At least 181 records · Page 10

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NASA NTRS1976

Heavy ion fragmentation experiments at the bevatron

Collaborative research efforts to study the fragmentation processes of heavy nuclei in matter using heavy ion beams of the Bevatron/Bevalac are described. The goal of the program is to obtain the single particle inclusive spectra of secondary nuclei produced at 0 deg by the fragmentation of heavy ion beam projectiles. The process being examined is B+T yields F + anything, where B is the beam nucleus, T is the target nucleus, and F is the detected fragment. The fragments F are isotopically identified by experimental procedures involving magnetic analysis, energy loss and time-of-flight measurements. Effects were also made to: (a) study processes of heavy nuclei in matter, (b) measure the total and partial production cross section for all isotopes, (c) test the applicability of high energy multiparticle interaction theory to nuclear fragmentation, (d) apply the cross section data and fragmentation probabilities to cosmic ray transport theory, and (e) search for systematic behavior of fragment production as a means to improve existing semi-empirical theories of cross-sections.

Heckman, H. H.↗

NASA NTRS1974

Turbulent measurements in supersonic boundary layer flows using laser velocimetry

Laser velocimetry has been applied successfully in the measurement of mean velocities and Reynolds stresses in a zero pressure gradient, Mach 2.9 boundary layer, and upstream and downstream of a two-dimensional, shock-wave boundary layer interaction for the same Mach number. The Reynolds stresses were obtained using a one-component, dual-scatter laser velocimeter operated in a manner analogous to the 'slanted hot-wire' technique. Signal processing was of the single-particle counting type which permitted measurements to be made using only the naturally occurring particles in the tunnel air stream for light scattering. The results for the shock-wave boundary layer interaction are presented along with hot-wire anemometer and pitot-static pressure measurements obtained in the same flow. Also, a data acquisition scheme for use with a two-component laser velocimeter is presented which should provide even better accuracies in future studies.

Johnson, D. A.↗

NASA NTRS1975

Laboratory observations of RF emission at plasma electron frequency and n + 1/2 times the electron cyclotron frequency in electron beam-plasma and beam-beam interactions

Electric field emissions at frequencies of (n + 1/2) times the electron cyclotron frequency have been generated in a large-scale electron beam experiment in a vacuum facility. These emissions arise when a contrastreaming beam configuration exists, the primary beam consisting of monoenergetic electrons (50 eV to 5 keV) and the other beam of lower-energy backscattered secondary electrons. It is suggested that the same mechanism could also be the source of the observed 3/2 times the electron cyclotron frequency emissions at auroral latitudes. In the absence of the beam-beam instability, weak oscillations were observed at the plasma frequency. In the latter case no significant modifications of the primary beam velocity distribution occurred, and the beam configuration is adequately described by single-particle motion in the ambient magnetic field.

Bernstein, W.↗

NASA NTRS1977

Compensated time of flight telescope for spaceborne cosmic ray measurements

A large area time-of-flight telescope has been studied for future application in space-borne cosmic ray experiments. A new compensation technique for propagation delays inside the scintillators has been applied, which is operative in two perpendicular directions. This technique, superior to conventional one-dimensional compensations, allows high rejection probability for upward moving single particles at very short counter distances. Besides mechanical advantages a short counter distance is desirable because it permits a large field of view for the detector. A measurement of light transit times in scintillators is presented and based on it, directionality for shower events is discussed.

Rothermel, H.↗

NASA NTRS1977

Interpretation of spatial and temporal variations of hydrogen quadrupole absorptions in the Jovian atmosphere observed during the 1972 apparition

Results are reported for a systematic investigation of temporal and spatial variations of hydrogen quadrupole lines formed in the Jovian atmosphere, which was performed by measuring the strengths of the S(1) lines of H2 (3,0) and (4,0) quadrupole bands at several points on the Jovian disk during the 1972 apparition. The observations support the hypothesis that the strength of the (3,0) S(1) line varies significantly with time, suggest the possibility of short-term temporal variation in the strength of the (4,0) line, and indicate that the H2 line strengths vary remarkably little from limb to limb in the equatorial region. A Galatry line-shape profile is calculated, and a radiative-transfer analysis is carried out using the Henyey-Greenstein phase function for single particle scattering. It is shown that the observations are consistent with a multilayer atmospheric model having an optically thin upper cloud deck separated by a stratum of nonscattering gas from an optically thick lower cloud.

Hunt, G. E.↗

NASA NTRS1978

Microparticle accelerator of unique design

A microparticle accelerator has been devised for micrometeoroid impact and cratering simulation; the device produces high-velocity (0.5-15 km/sec), micrometer-sized projectiles of any cohesive material. In the source, an electrodynamic levitator, single particles are charged by ion bombardment in high vacuum. The vertical accelerator has four drift tubes, each initially at a high negative voltage. After injection of the projectile, each tube is grounded in turn at a time determined by the voltage and charge/mass ratio to give four acceleration stages with a total voltage equivalent to about 1.7 MV.

Vedder, J. F.↗

NASA NTRS1977

Impact cratering and regolith dynamics

The most recent models concerning mechanical aspects of lunar regolith dynamics related to impact cratering use probabilistic approaches to account for the randomness of the meteorite environment in both space and time. Accordingly the absolute regolith thickness is strictly a function of total bombardment intensity and absolute regolith growth rate in nonlinear through geologic time. Regoliths of increasing median thickness will have larger and larger proportions of more and more deep seated materials. An especially active zone of reworking on the lunar surface of about 1 mm depth has been established. With increasing depth, the probability of excavation and regolith turnover decreases very rapidly. Thus small scale stratigraphy - observable in lunar core materials - is perfectly compatible with regolith gardening, though it is also demonstrated that any such stratigraphy does not necessarily present a complete record of the regolith's depositional history. At present, the lifetimes of exposed lunar rocks against comminution by impact processes can be modeled; it appears that catastrophic rupture dominates over single particle abrasion.

Hoerz, F.↗

NASA NTRS1978

Quasi-microscope concept for planetary missions - Stereo

The quasi-microscope has been used for stereo pictures using a small aperture placed at the right and left over the entrance aperture. A 16-degree stereo view angle yields an enhanced stereo effect. When viewed upward through a transparent support, all grains come into focus. The technique may be used for determining mineral constituents on the basis of cleavage and fracture patterns, grain details, and surface slopes used in estimating single-particle albedo and the illumination of scattering profiles.

Burcher, E. E.↗

NASA NTRS1978

A stereoscopic visual study of coherent structures in turbulent shear flow

Stereoscopic photography was used to record the three-dimensional motions of fluid elements along a flat-plate turbulent boundary layer flow. The outer region of the boundary layer was dominated by the formation and convection of transverse vortices, formed at the high-speed front between low- and high-speed fluid elements. Vortical motions observed in the wall region consisted of (1) motions of single particles around part of a circle, (2) streamwise vortices, and (3) transverse vortices.

Praturi, A. K.↗

NASA NTRS1980

An investigation into the role of adhesion in the erosion of ductile metals

Existing theories of erosion of ductile metals based on cutting and deformation mechanisms predict no material removal at normal incidence which is contradictory to experience. Thus, other mechanisms may be involved. The possible role of adhesive material transfer during erosion is investigated by both single particle impingement experiments and erosion by streams of particles. Examination of the rebounding particles as well as the eroded surface yields evidence of a significant adhesive mechanism for the ductile metals investigated.

Brainard, W. A.↗

NASA NTRS1980

Substorms and magnetospheric energy transfer processes

Evidence is presented which suggests a direct process for the conversion of solar wind energy into the various manifestations of the auroral substorm. This is in contrast to the widely accepted premise that solar wind energy is accumulated in the magnetosphere and then released by an instability process occurring in the magnetotail. It is shown that much of the plasma sheet behavior associated with auroral substorms can be interpreted in terms of single-particle models and simple variations of the cross-tail electric field intensity which does not invoke release of stored magnetic energy. It is also pointed out that the major entry of substorm energy into the magnetosphere occurs through the boundaries of the lobes of the magnetotail. This paper is not intended to be a complete theory of the magnetospheric substorm - rather the intention of this paper is to point out directions of research deserving of more attention.

Swift, D. W.↗

NASA NTRS1980

An investigation into the role of adhesion in the erosion of ductile metals

Existing theories of erosion of ductile metals based on cutting and deformation mechanisms predict no material removal at normal incidence which is contradictory to experience. Thus, other mechanisms may be involved. The possible role of adhesive material transfer during erosion is investigated by both single-particle impingement experiments and erosion by streams of particles. Examination of the rebounding particles as well as the eroded surfaces yields evidence of a significant adhesive mechanism for the ductile metals investigated.

Brainard, W. A.↗

NASA NTRS1980

Annual Conference on Nuclear and Space Radiation Effects, 17th, Cornell University, Ithaca, N.Y., July 15-18, 1980, Proceedings

The conference covered the radiation effects on devices, circuits, and systems, physics and basic radiation effects in materials, dosimetry and radiation transport, spacecraft charging, and space radiation effects. Other subjects included single particle upset phenomena, systems-generated electromagnetic pulse phenomena, fabrication of hardened components, testing techniques, and hardness assurance.

Mcgarrity, J. M.↗

NASA NTRS1981

Mechanism of parallel electric fields inferred from observations

Data from various experiments of the Atmosphere Explorer satellites are analyzed to test their consistency with the model of single-particle linear acceleration through a static parallel potential drop. Theoretical current/voltage and energy flux/voltage relations are applied to the data to predict the densities of source current carriers above the acceleration region for upward Birkeland currents. Comparison of these model predictions with simultaneous electron data indicates that the observed field-aligned potential drops are consistent with direct acceleration in the absence of anomalous resistivity.

Yeh, H.-C.↗

NASA NTRS1981

A cloud condensation nucleus spectrometer designed for airborne measurements

The spectrometer is a simple extension of the continuous flow diffusion chamber (CFDC) operated in the vertical mode. The principal new design features of the instrument are its rapid time response and ability to rapidly measure the CCN activity spectrum. The activity spectrum of CCN in an air sample is measured by simultaneously operating the spectrometer at four supersaturations. The CCN spectrometer consists of four essentially indepenent CFDC's in a parallel array. Each CFDC is 61 cm long, 10 cm wide, and consists of two vertical parallel plates 1 cm apart, maintained at different temperatures. Each CFDC has a single particle optical counter located at the center of its base.

Radke, L. F.↗

NASA NTRS1982

Analytic optical potentials for nucleon-nucleus nucleus-nucleus collisions involving light and medium nuclei

Utilizing an optical model potential approximation to the exact nucleus-nucleus multiple-scattering series, optical potentials for nucleon-nucleus and nucleus-nucleus collisions are analytically derived. These expressions are applicable to light and medium cosmic ray nuclei as their single-particle density distributions are analytically determined, without approximation, from their actual harmonic well charge density distributions. Pauli correlation effects are included through the use of a simple Gaussian function to replace the usual expression obtained in the infinite nuclear matter approximation.

Bidasaria, H. B.↗

NASA NTRS1982

Harmonic well matter densities and Pauli correlation effects in heavy-ion collisions

A generalized optical model heavy ion reaction theory is extended to include correlation effects between projectile and target constituents according to the Pauli exclusion principle. These correlation effects are significant for accurately predicting cross sections for projectile nucleus abrasions, but are relatively unimportant for determining total and absorption cross sections for heavy ion collisions. For lighter nuclei, predictive capabilities were also improved by developing an analytic method for extracting their nuclear single particle density distributions from experimentally measured harmonic well charge density distributions. This improved theory is compared with previous theoretical predictions and recent experimental results.

Townsend, L. W.↗

NASA NTRS1979

Flocculation of colloidal sols: Diffusion-controlled vs agitation-induced flocculation

A proposal for carrying out flocculation experiments in microgravity is presented. These experiments might allow a correlation between theory and experiment. First, all particles, whether single primary particles or aggregates of primary particles would not settle or cream at any agitation rate, or even in the absence of agitation. This failure to separate would keep all aggregates active, still serving as centers for diffusion-controlled flocculation. Keeping all particles suspended would allow the possibility of determining the total number of particles as a function of time from beginning to end of flocculation. Finally, the experiments would allow a definite separation diffusion-controlled and agitation-induced flocculation by studying diffusion-controlled flocculation with and without agitation.

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