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Electron spin resonance signals of negative ions in liquid helium were observed. The line width and g-value were measured. Electrons injected into helium by field emission from ferromagnetic tips are shown to be polarized. A new technique for the measurement of electron spin polarization is presented.
The calculation of the electric dipole polarizability tensor of the He 2 dimer is described, and the results are used in the computation of several dielectric and optical properties of helium gas, at both high (322 K) and low (4 K) temperatures. The properties considered are the second dielectric virial coefficient, the second Kerr virial coefficient, and the depolarization ratio of the integrated intensities for the Raman scattering experiments. The thesis consists of five parts: the polarizability and various properties are defined; the calculation of the polarizability in the long-range region in terms of a quantum mechanical multipole expansion is described; the calculation of the He2 polarizability in the overlap region via coupled Hartree-Fock perturbation theory is described; the calculation of the quantum pair distribution function for both the He-3 and He-4 isotopes at 4 K is discussed; and the calculated values of the properties of helium gas are given.
Balloon observations of proton and helium spectra in 1970, 1971 and 1972, reveal a factor of approximately 1.85 deviation from a single valued regression at low rigidities. This deviation decreases with increasing rigidity for both species. The period 1969-1970 is unique because time variations at low and high energies were anti-correlated. When satellite observations are used to extend the balloon observations to energies below 100 MeV/Nucleon, the proton spectrum showed a steeper slope in 1970 and 1972 than the characteristic J = AT spectrum observed during 1965-1969. The slope of the helium spectrum became continuously flatter during the same period (1970-1972). Computer generated spectra based on simple two parameter modulation models describe the basic features of the observations if one of the variable parameters is used to characterize the rigidity dependence of the diffusion coefficient. Models which do not allow such a variation are not consistent with the observations.
A critical survey was made of the experimental evidence for a variation of the relative abundance by number h, (n alpha/np), of helium in the solar wind. The abundance is found to vary by delta h = 0.01 + or - 0.01 from 0.035 to 0.045 over solar cycle 20. Changes in the average bulk speed during the solar activity cycle was insufficient to account for this increase in h with the solar cycle. The slope of the linear relation between h and the plasma bulk speed is also found to vary, being greatest around solar maximum. An attempt is made to explain the 30% variation in h as the result of the variation in the number of major solar flares over a solar cycle. These obvious transients are apparently not numerous enough to explain the observed variation, but the reasonable expectation remains that the transients observed recently by Skylab which may occur more frequently than major flares could augment those associated with major flares. Since the solar wind flux is not observed to increase at solar maximum, the abundance of Helium cannot be proportional to the proton flux leaving the sun unless the solar wind comes from a smaller area of the sun at maximum than at minimum.
Measurements of the polarization of the light from the 3 1p-2 1s transition in proton beam excited Helium have shown both a proton beam energy and Helium target gas pressure dependence. Results for the linear polarization fraction range from +2.6% at 100 keV proton energy to -5.5% at 450 keV. The zero crossover occurs at approximately 225 keV. This is in good agreement with other experimental work in the field, but in poor agreement with theoretical predictions. Measurements at He target gas pressures as low as .01 mtorr show that the linear polarization fraction is still pressure dependent at .01 mtorr.
Equilibrium thermodynamic and flow properties are presented in tabulated and graphical form for moving, standing, and reflected normal shock waves into helium-hydrogen mixtures representative of proposed outer planet atmospheres. The volumetric compositions of these mixtures are 0.35He-0.65H2, 0.20He-0.80H2, and 0.05He-0.95H2. Properties include pressure, temperature, density, enthalpy, speed of sound, entropy, molecular-weight ratio, isentropic exponent, velocity, and species mole fractions. Incident (moving) shock velocities are varied from 4 to 70 km/sec for a range of initial pressure of 5 N/sq m to 100 kN/sq m. The present results are applicable to shock-tube flows and to free-flight conditions for a blunt body at high velocities. A working chart illustrating idealized shock-tube performance with a 0.20He-0.80H2 test gas and heated helium driver gas is also presented.
The dependence of the thickness of the helium-enriched shell on the longitudinal position of the parent flares is considered along with the large-scale configuration of the expanding shell in interplanetary space. It is found that shock waves, magnetic bottles, and helium-enriched shells appear to expand eastwards of the meridian plane which crosses the flare region. It seems that the formation of the observed pattern of the shells is influenced by the interplanetary magnetic field between the sun and the earth.
Radiative relaxation rates have been investigated in a series of hydrogen-helium mixtures over a range of temperatures encountered during outer planet atmospheric entry. Using a conical electric arc shock tube, shock waves with velocities between 10 and 36 km/sec were studied in mixtures of 10% to 85% hydrogen in helium diluent. Intensities for several hydrogen continuum wavelengths and the H-alpha and H-beta lines of hydrogen were measured as a function of time. The nonequilibrium relaxation times were longer than expected for shock velocities greater than 18 km/sec and reached a plateau at higher shock velocities. Data from all mixtures were found to correlate with shock wave temperature.
Experiments on phase behavior in hydrogen-helium mixtures have been carried out at pressures up to 9.3 kilobars, at temperatures from 26 to 100 K. Two distinct fluid phases are shown to exist at supercritical temperatures and high pressures. Both the trend of the experimental results and an analysis based on the van der Waals theory of mixtures suggest that this fluid-fluid phase separation persists at temperatures and pressures beyond the range of these experiments, perhaps even to the limits of stability of the molecular phases. The results confirm earlier predictions concerning the form of the hydrogen-helium phase diagram in the region of pressure-induced solidification of the molecular phases at supercritical temperatures. The implications of this phase diagram for planetary interiors are discussed.
Test flow velocities from 5 to 7 km/sec were generated in a 6-in. expansion tube using helium, argon, air, and CO2 test gases. Pitot pressure profiles across the flow at the test section are presented for the four test gases, and measured flow quantities are compared to computer predicted values. Comparison of predicted and measured flow quantities suggests the expansion to be near thermochemical equilibrium for all test gases and implies the existence of a totally reflected shock at the secondary diaphragm. Argon, air, and CO2 flows were observed to attenuate while traversing the acceleration section, whereas no attenuation was observed for helium.
The intensity and spatial variations of the He I 584 A radiation in the night sky were measured to an altitude of 264 km from a sounding rocket launched from Thumba, India. The flux varied in intensity with look angle from a high of 16 plus or minus 5 rayleighs to a low of less than 1 rayleigh. The data obtained are presented in the form of an all-sky map. Since the peak flux levels observed are approximately two orders of magnitude larger than that expected from geocoronal resonant scattering, we have compared our results with those expected from two interplanetary sources of neutral helium: the penetration of the local interstellar medium into the solar neighborhood and the dust deionization of solar-wind alpha particles. The dust deionization-model predictions using currently accepted input parameters appear to be inconsistent with the observations. The interstellar helium source is compatible with the data to within the uncertainties of the models.
We suggest that the low abundance of ionized helium in H II regions at the galactic center can be explained by selective absorption of helium-ionizing photons by dust within the ionized gas. This model requires an extrapolation to 500 A of the rapid increase of the extinction measured between 1500 A and 1000 A with the Copernicus satellite, and it assumes that the dust absorbs most of the Lyman continuum.
The helium abundance in the Jovian atmosphere has been determined by a new method from our observations of the occultation of beta Scorpii by Jupiter. The occultation light curves, consisting of simultaneous records at three wavelengths with a time resolution of 0.01 sec, are dominated by sharp, well-defined intensity peaks or spikes. Because of the wavelength-dependence of the refractivity of the Jovian atmosphere, the arrival time of a given spike at the Earth is also wavelength dependent. A new method for determining the composition of a hydrogen-helium atmosphere from such data is presented, and the principal sources of error are discussed and evaluated.
Coude spectra of kappa CMa in the red region showed H alpha and He 1 lambda lambda 5876,6678 in emission. Each of the lines had two emission components, but the helium lines had no detectable absorption feature in between. While the H alpha emission peaks were separated by 160 km/sec, the helium lines were separated by 400 km/sec. A simple model is proposed to account for the behavior of these emission lines.
Recent design studies have shown that airframe-integrated scramjets should include instream mounted, swept-back strut fuel injectors to obtain short combustors. Because there was no data in the literature on mixing characteristics of swept strut fuel injectors, the present investigation was undertaken to provide such data. This investigation was made with two swept struts in a closed duct at Mach number of 4.4 and nominal jet-to-air mass flow ratio of 0.029 with helium used to simulate hydrogen fuel. The data is compared with flat plate mounted normal injector data to obtain the effect of swept struts on mixing. Three injector patterns were evaluated representing the range of hole spacing and jet-to-freestream dynamic pressure ratio of interest. Measured helium concentration, pitot pressure, and static pressure in the downstream mixing region are used to generate contour plots necessary to define the mixing region flow field and the mixing parameters.
Descriptions are given of the test hardware, facility, procedures, and results of electrically heated tube, channel and panel tests conducted to determine effects of helium ingestion, two dimensional conduction, and plugged coolant channels on operating limits of convectively cooled chambers typical of space shuttle orbit maneuvering engine designs. Helium ingestion in froth form, was studied in tubular and rectangular single channel test sections. Plugged channel simulation was investigated in a three channel panel. Burn-out limits (transition of film boiling) were studied in both single channel and panel test sections to determine 2-D conduction effects as compared to tubular test results.
A general description of the Langley 6-inch expansion tube is presented along with discussion of the basic components, internal resistance heater, arc-discharge assemblies, instrumentation, and operating procedure. Preliminary results using unheated and resistance-heated helium as the driver gas are presented. The driver-gas pressure ranged from approximately 17 to 59 MPa and its temperature ranged from 300 to 510 K. Interface velocities of approximately 3.8 to 6.7 km/sec were generated between the test gas and the acceleration gas using air as the test gas and helium as the acceleration gas. Test flow quality and comparison of measured and predicted expansion-tube flow quantities are discussed.
Balloon observations of proton and helium spectra in 1970, 1971, and 1972, which extend previous work for the period 1965-1969, reveal a factor of about 1.85 deviation from a single-valued regression at low rigidities. This deviation decreases with increasing rigidity for both species. The period 1969-197 is unique, because time variations at low and high energies were anticorrelated. When satellite observations are used to extend the balloon observations to energies below 100 MeV/nucleon, the proton spectrum shows a steeper slope in 1970 and 1972 than the characteristic J = AT spectrum observed during 1965-1969. The slope of the helium spectrum became continuously flatter during the same period (1970-1972). Computer-generated spectra based on simple two-parameter modulation models describe the basic features of the observations, if one of the variable parameters is used to characterize the rigidity dependence of the diffusion coefficient. On the other hand, models that do not allow such a variation are not consistent with the observations.