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Results are given of a study of the intensities, energy spectra, and angular distribution of energetic particles in the magnetosphere of Jupiter; the heliocentric radial gradient of the intensity of galactic cosmic rays; and the occurrence, intensity, and angular distribution of solar flare particles and their propagation through the interplanetary medium at large heliocentric distances.
The National Aeronautics and Space Administration (NASA) is progressing toward long-term lunar habitation. Critical to the design of a lunar habitat is an understanding of the lunar surface environment; of specific importance is the primary meteoroid and subsequent ejecta environment. The document, NASA SP-8013, was developed for the Apollo program and is the latest definition of the ejecta environment. There is concern that NASA SP-8013 may over-estimate the lunar ejecta environment. NASA's Meteoroid Environment Office (MEO) has initiated several tasks to improve the accuracy of our understanding of the lunar surface ejecta environment. This paper reports the results of experiments on projectile impact into powered pumice and unconsolidated JSC-1A Lunar Mare Regolith stimulant (JSC-1A) targets. The Ames Vertical Gun Range (AVGR) was used to accelerate projectiles to velocities in excess of 5 km/s and impact the targets at normal incidence. The ejected particles were detected by thin aluminum foil targets placed around the impact site and angular distributions were determined for ejecta. Comparison of ejecta angular distribution with previous works will be presented. A simplistic technique to characterize the ejected particles was formulated and improvements to this technique will be discussed for implementation in future tests.
Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for up to 10 to the 10th yr. Other calculations included the dipole moment in the angular distribution of neutron stars as a convenient measure of their concentration toward the Galactic center, the quadrupole moment in their angular distribution as a convenient measure of their concentration toward the Galactic plane, and the average value of V/Vmax as a convenient measure of the radial distribution of neutron stars. Models that require accretion from a cold circumstellar disk or from a close companion are only marginally consistent with the isotropic distribution of the observed bursts. Models that require accretion of interstellar matter are ruled out due to a very strong dipole anisotropy. Models that suggest the Galactic halo origin of gamma-ray bursts are briefly discussed. The GRANAT and GRO missions should provide evidence for or against the association of gamma-ray bursts with the Galactic disk neutron stars.
Results of the first experimental application of the diffusion domain method to the determination of the spectral similarity parameter, and hence the single scattering albedo, of clouds are presented. The angular distribution of scattered radiation deep within a cloud layer at discrete wavelengths between 0.5 and 2.3 microns was measured by a multiwavelength scanning radiometer. The relative angular distribution of the intensity field at each wavelength was used to determine the similarity parameter of the cloud at that wavelength utilizing the diffusion domain method. Results of the analysis are presented for a 50 km section of clean marine stratocumulus clouds over the coast of California on July 10, 1987. It is concluded that the measured absorption is close to, but persistently larger than, theoretical predictions.
The detection efficiencies of cylindrical detectors for various gamma ray photon angular distributions were studied in the energy range from .10 Mev to 15 Mev. These studies indicate that simple detector systems on small satellites can be used to measure flux anisotropy of cosmic gamma rays and the angular distribution of albedo gamma rays produced in planetary atmospheres. The results indicate that flat cylindrical detectors are most suitable for measuring flux anisotropy because of their angular response function. A general method for calculating detection efficiencies for such detectors is presented.
The energy spectra and angular distributions of electrons observed by Pioneer 11 as a function of radial distance in the inner magnetosphere of Saturn are reanalyzed and phase space densities are then calculated. The radial dependence of phase space density requires a distributed loss process. The loss is greatest in the region of the E ring (5.5 less than L less than 8.5) and is attributed to collisions with the ring particles in agreement with earlier work by Van Allen et al. (1980b). Quantitative analysis yields the following properties of the E ring: the particle radii are in the range of 4 x 10(exp -5) to 3.2 x 10(exp -4) cm and the thickness of the ring is approximately 3 R(sub s). Between the inner edge of the E ring (5.5 R(sub s)) and the outer edge of the A ring (2.3 R(sub s)) there are more energetic electrons than can be supplied by radial diffusion from an external source. Detailed calculations show that a cosmic ray albedo neutron decay (CRAND) source in the A and B rings is a plausible source for this excess. The radial diffusion coefficient required to explain the E ring absorption and CRAND source for electrons is 1 x 10(exp -12) greater than D(sub 0) greater than 3 x 10(exp -12) R(sub s)(exp 2)/s, assuming that D(sub LL) = D(sub 0)L(exp 3). As part of the reanalysis program, a method for the deconvolution of pitch angle distributions observed by simple detectors on a rotating spacecraft is developed. This process removes the instrumental response and rotational smear due to finite sampling periods and yields true angular distributions.
The energy spectra and angular distributions of electrons observed by Pioneer 11 as a function of radial distance in the inner magnetosphere of Saturn are reanalyzed and phase space densities are then calculated. The radial dependence of phase space density requires a distributed loss process. The loss is greatest in the region of the E ring (5.5 less than L less than 8.5) and is attributed to collisions with the ring particles in agreement with earlier work by Van Allen et al. (1980). Quantitative analysis yields the following properties of the E ring: the particle radii are in the range of 4 x 10(exp -5) to 3.2 x 10(exp -4) cm and the thickness of the ring is approximately 3 R(sub s). Between the inner edge of the E ring (5.5 R(sub s)) and the outer edge of the A ring (2.3 R(sub s)) there are more energetic electrons than can be supplied by radial diffusion from an external source. Detailed calculations show that a cosmic ray albedo neutron decay (CRAND) source in the A and B rings is a plausible source for this excess. The radial diffusion coefficient required to explain the E ring absorption and CRAND source for electrons is 1 x 10(exp -12) greater than D(sub 0) greater than 3 x 10(exp -12) R(exp 2, sub s)/s, assuming that D(sub LL) = D(sub 0)L(exp 3). As part of the reanalysis program, a method for the deconvolution of pitch angle distributions observed by simple detectors on a rotating spacecraft is developed. This process removes the instrumental response and rotational smear due to finite sampling periods and yields true angular distributions.
Using plasma discharges to etch trenches and via holes in substrates is an important process in semiconductor manufacturing. Ion enhanced etching involves both neutral fluxes, which are isotropic, and ion fluxes, which are anisotropic. The angular distributions for the ions determines the degree of vertical etch, while the amount of the neutral fluxes determines the etch rate. We have developed a 2D profile evolution simulation which uses level set methods to model the plasma-substrate interface. Using level sets instead of traditional string models avoids the use of complicated delooping algorithms. The simulation calculates the etch rate based on the fluxes and distribution functions of both ions and neutrals. We will present etching profiles of Si substrates in low pressure (10s mTorr) Ar/Cl2 discharges for a variety of incident ion angular distributions. Both ion and neutral re-emission fluxes are included in the calculation of the etch rate, and their contributions to the total etch profile will be demonstrated. In addition, we will show RIE lag effects as a function of different trench aspect ratios. (For sample profiles, please see http://www.ipt.arc.nasa.gov/hwangfig1.html)
The aperture ion source was conceived to eliminate distortion in measurements of angular distributions of neutral atoms and molecules that require electron-impact ion sources. The approach simplifies the coupling between ion source and spectrometer while providing virtually distortion-free angular distributions and improved accuracy in the dimensions of the ionization region. Furthermore, it virtually eliminates the volume occupied by the ion source.
Results are given for gamma ray fluxes in six energy intervals from 2-25 MeV and five zenith angle intervals from 0-50 deg (downward moving) and five from 130-180 deg (upward moving). Observations were obtained with the University of California, Riverside double Compton scatter gamma ray telescope flown on a balloon to a 3.0 g/sq cm residual atmosphere at a geomagnetic cuttoff of 4.5 GV. It was found that the angular distribution of downward moving gamma rays is relatively flat, increasing slowly from 10-40 deg. The angular distribution of the upward moving gamma rays at 4.2 g/sq cm increases with angle from the vertical. Energy distributions of upward and downward moving gamma rays are in good agreement with the results of previous studies.
Energetic charged particle detectors characterize a portion of the plasma distribution function that plays critical roles in some physical processes, from carrying the currents in planetary ring currents to weathering the surfaces of planetary objects. For several low-resource missions in the past, the need was recognized for a low-resource but highly capable, mass-species-discriminating energetic particle sensor that could also obtain angular distributions without motors or mechanical articulation. This need led to the development of a compact Energetic Particle Detector (EPD), known as the "Puck" EPD (short for hockey puck), that is capable of determining the flux, angular distribution, and composition of incident ions between an energy range of approximately 10 kiloelectronvolts to several megaelectronvolts. This sensor makes simultaneous angular measurements of electron fluxes from the tens of kiloelectronvolts to about 1 megaelectronvolt. The same measurements can be extended down to approximately 1 kiloelectronvolt per nucleon,with some composition ambiguity. These sensors have a proven flight heritage record that includes missions such as MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and New Horizons, with multiple sensors on each of Juno, Van Allen Probes, and Magnetospheric Multiscale. In this review paper we discuss the Puck EPD design, its heritage, unexpected results from these past missions and future advancements. We also discuss high-voltage anomalies that are thought to be associated with the use of curved foils, which is a new foil manufacturing processes utilized on recent Puck EPD designs. Finally, we discuss the important role Puck EPDs can potentially play in upcoming missions.
Discussion of the problem of measuring branching ratios or transition probabilities using the technique of photoelectron spectroscopy in terms of the angular distribution of the ejected photoelectrons. Equations are developed that can be used in conjunction with any type of electron-energy analyzer to correct for any discrimination in the analyzer caused by electrons of varying angular distribution. Results are presented for the branching ratios of the A super 2 pi sub u and B super 2 sigma sub u (+) states of CO2(+) produced by 584 A and obtained by a variety of electron-energy analyzers.
At Venus the Energetic Particles Detector (EPD) on the Galileo spacecraft measured the differential energy spectra and angular distributions of ions above about 22 keV and electrons above about 15 keV in energy. The only time particles were observed by EPD was in a series of episodic events near closest approach (0559:03 UT). Angular distributions were highly anisotropic, ordered by the magnetic field, and showed ions arriving from the hemisphere containing Venus and its bow shock. The spectra showed a power law form with intensities observed into the 120- to 280-keV range. Comparisons with model bow shock calculations show that these energetic ions are associated with the Venusian foreshock-bow shock region. Shock-drift acceleration in the Venusian bow shock seems the most likely process responsible for the observed ions.
A general solution is obtained for the angular distribution of the intensity and velocity of interplanetary projectiles impinging on a planetary ring system. Three significant results emerge from the solution: (1) a variation with orbital longitude is demonstrated in the impact velocity-weighted impact rate of the planetary rings' cometary meteoroids; (2) the angular distribution of ejecta intensity due to the bombardment of a planetary ring by interplanetary meteoroids is determined; and (3) the radial drift velocity due to both simple mass-loading and aberration-induced asymmetry in the impact rate is calculated for a planetary ring of arbitrary optical depth. Attention is given to results for projectiles with Oort Cloud-type orbits.
Results on the angular distribution of the electrostatic potential of a pulsating point charge in a warm magnetized plasma permeated by an electron beam are presented. The theoretical formulation for a finite magnetic field is given, and the solution of the resonance cone dispersion relation is presented. Numerical results on the angular distribution of the potential are shown, and the propagation of waves outside the resonance cones is described. It is demonstrated that with the inclusions of a finite magnetic field, the field patterns of a point charge are qualitatively similar to those obtained for a uniaxial plasma. The Cerenkov radiation occurs at angles much smaller than the cold-cone angle, even with the finite magnetic field. When the beam velocity is well above the thermal velocity of the background electrons, a characteristic wave propagation occurs between the cold-cone angles.
The Energetic Particles Experiment on IMP-7 measures the angular distribution of 50-200 keV solar protons in 16 sectors. The velocity of 50 keV protons may be less than 5 times that of the solar wind. A generalized nonlinear Compton-Getting point transformation into the co-moving frame that contains no assumptions as to the angular distribution of either the spectrum or intensity is presented. Nearly 50 keV proton data in the spacecraft frame exhibit an anisotropy ratio that is large (not less than 5) and radial throughout the October 29, 1972 event lasting more than 9 days at this energy. This anisotropy argues against impulsive injection and diffusive decay in the inner solar system. Application of the transformation to the data reveals a long lasting residual anisotropy in the co-moving frame with protons streaming from the sun. Differences between the co-moving frame and solar wind frame velocities suggest residual electric fields upstream from the bow shock.
The production of deuterium, tritium, and helium-3 from nuclear reactions of accelerated charged particles is evaluated with the ambient solar atmosphere. Updated cross sections and kinematics are used, calculations are extended to very low energies (approximates 0.1 MeV/nucleon), and the angular distribution of the secondary particles is calculated. The calculations are compared with data on accelerated isotopes from solar flares. In particular, the August 1972 events are considered for which both He-3 and nuclear gamma rays were observed. An explanation for He-3-rich events is provided in terms of the angular distributions of secondary isotopes, and the flux of 2.2 MeV gamma rays from such flares are also predicted.
Simulations of field emission of electrons from an electron gun are used to determine the angular distribution of the emitted electron beam and the percentage of charge transmitted through the grid. The simulations are a first step towards understanding the spherical aberration present after focusing the electron beam. The effect of offset of the cathode with respect to the grid and the separation between cathode and grid on the angular distributions of emitted electrons and transmission of the grid are explored.