A computer model for simulation of the image contrast caused by Frank dislocation loops in field ion tips of fcc materials is presented. The model is based on the shell model for ion image simulation, whereas the displacement field of Frank loops is computed from the exact displacement equation for a closed dislocation loop in an isotropically elastic continuum. A method for taking surface effects into account by superposition of the displacement field of an image loop is introduced. The results indicate that Frank loops will cause image contrast while wholly beneath the surface of the tip, and that vacancy and interstitial loops will cause qualitatively different contrast. The effect of surface relaxation, while quantitatively substantial, does not qualitatively alter these results. Special emphasis is placed on small loops, with respect to which existing contrast theory is inadequate. Some micrographs of ion bombarded iridium tips are presented. These micrographs display contrast effects in excellent agreement with computer plots of interstitial loop contrast.

Thesis. Microwave resonant cavity frequency shift measurements are made to determine the electron density of an electrostatically confined, spherically symmetric helium plasma. Appropriate electron-density distribution functions are assumed and then used to relate the frequency shift to the central electron density. Results from electron injection, with currents of up to 200 mA, accelerating voltages from 100 to 450 V, and pressures of 5.0, 1.0, and 0.5 mTorr, suggest that a potential well is formed and that the minimum value of perveance required for well formation depends on the accelerating voltage and the pressure. Maximum electron densities of 9.5 x 10/sup 9//cm/sup 3/ are measured. Electron densities of 5.5 x 10/sup 9//cm/sup 3/ are measured during ion injection with currents of up to 20 mA at accelerating voltages between 0.5 kV and 5.0 kV and pressures of 5.0, 1.0, and 0.5 mTorr. Electron densities measured during ion injection show remarkable agreement with those predicted by an earlier theoretical model. (auth)

Thesis. Cycling routes, rates of transport, and resultant concentrations of the fallout radionuclides /sup 90/Sr and /sup 137/Cs in northern Alaskan ecosystems were defined during the period 1959 to 1970. Radiochemical analysis of extensive samples of biota and whole-body counting of / sup 137/Cs in Eskimo and Indian ethnic groups were related to ecological principles, especially the concept of trophic niche, which elucidated the observed patterns of radionuclide concentrations. Experiments involving Sr and Cs radioisotopes applied to natural Cladonia-- Cetraria lichen carpets yielded effective half-times of 1.O to 1.6 years for Sr and more than 10 years for Cs. Direct and indirect estimates of /sup 131/Cs half-times in Eskimos on a caribou meat diet were made by dietary manipulation and by relating dietary /sup 137/Cs intake and resultant change between periodic whole body counts. Effective half- times of 70 days for adults (more than 21 years old) and minors (14 to 20 years old) and of 45 days for children (less than 14 years old) were found. Suitable mathematical models were used to compute lichen forage ingestion rates of free- ranging adult caribou (4.5 to 5.0 kg dry weight per day), caribou meat ingestion rates of Anaktuvuk Pass residents (up …

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Thesis. A tandem electrostatic energy analyzer molecular beam apparatus was built for studying low energy inelastic 180 deg scattering of alkali ions from molecules. A beam of essentially monoenergetic ions is produced by a first analyzer and is focused on the center of a scattering cell containing essentially stationary molecules. Ions which are not significantly deflected in their laboratory motion after collisions with the molecules are energy analyzed with a second analyzer.'Ine scattered beam intensity detected at a particular final laboratory energy is attributable to collisions resulting in a distinct amount of inelasticity. The Na/sup +/ H/sub 2/, HD, D/sub 2/ scattering was studied in the relative energy range of 0.74 to 30. eV. The Na/sup +/ -- D/sub 2/ system shows predominantly vibrationally elastic scattering below 8 eV relative energy. Above 8 eV the most probable inelasticity observed increases monotonically with the initial collision energy and is comparable to excitation to higher vibrational levels. At 17 eV this inelasticity is 3.92 eV. Classical trajectory calculations are used to study the contribution of different collision orientations to the scattering spectra. It is found that collisions in which the projectile approaches the molecule along the bisector of its bond yield the …

>Thesis. Minor amounts of certain elements were found to aid in densification of sintered Al/sub 2/O/sub 3/ (MgO, NiO, and Y/sub 2/O/sub 3/ additives) an d hotpressed MgO (LiF and NaF additives). (DLC)

P-type germanium single crystals (8 x 10/sup 14/Ga/cm/sup 3/ and 6 x l0/ sup 1 Ga/cm/sup 3) were irradiated with 1.1-Mev electrons at pumped liquid helium temperatures and defect production and annealing studied using ac hopping conductivity. Production rates obtained from measurements at 1.5 deg K and 10/ sup 4/ Hz were 0.6 cm/sup -10/ for samples doped 6 x 10/sup 15/ Ga/cm/sup 3/ and 0.11 cm/sup -10/ for samples doped 8 x 10/ sup 14/ Ga/cm/sup 3/. Above 10/sup 14/ e,/cm/sup 2/ fluence the production rates for the higher doped samples decreased to approximately 0.06 cm/sup -1/ at 10/sup 15/ e/cm/sup 2/ fluence except for one sample which was anomalous. No such long irradiation of the low doped samples was made. The apparent inconsistency between these results and production rates of less than 3 x 10/sup -4/ cm/sup -1/ observed by previous workers was resolved by introducing a donor level for the defect produced by irradiation near the chemical acceptor level, so that the defect would be neutral at temperatures near 30 deg K and charged + 1 at l.5 deg K. Surface effects were observed which did not affect production rate measurements at 1.5 deg K more than …

Thesis. Identified protons were observed following beta decay of the precursor nuclei /sup 21/Mg, /sup 25/Si, /sup 37/Ca, /sup 40/Sc, /sup 41/Ti, and / sup 23/Al. These measurements spanned a proton energy range from 600 keV to 8.5 MeV, and included all significant particle decays of these nuclei. A helium-jet transport system was developed and used with various DELTA E - E counter telescopes to obtain high-resolution, lowbackground spectra. These data perrmitted accurate location of proton unbound levels in the beta-decay daughters, and absolute branching ratios and ft values for these allowed decays were determined. The half-lives of these nuclei were measured, and all except that for /sup 41/Ti are consistent with the previous values. For /sup 41/Ti, the half-life is 80 plus or minus 2 msec, which differs from the old value of 88 plus or minus 1 msec. This latter value is thought to have been affected by the presence of /sup 37/Ca activity produced in a competing reaction. The ft values for /sup 21/Mg and /sup 25/Si are compared to the negatron decay rates in their respective mirrors. For mass 21, s 1.17 plus or minus 0.04. A comparison of predicted and observed beta-decay rates for the …

ABS>Thesis. The dependence of energy band structure and electronic charge density on pseudopotential parameters is investigated for: InSb, InAs, InP, GaP, Si, ZnGeP/sub 2/, and ZnGeAs/sub 2/. (DLC)

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Thesis. An investigation was conducted to develop high-temperature 1Ta-- 6Cr, 1Ta--7Cr, and 1Ta-7Cr--0.5 Mo alloys using a dispersion of the Laves phase in a noncarbon-containing, body-centeredcubic iron matrix. An understanding and application of basic principles of materials science and the use of large amounts of information available in the literature were instrumental in the development of Fe-- Ta-- Cr alloys of the investigation. The phase transformations that occurred in the alloys, and the resulting microstructures were studied. The relations between mechanical properties and structure were also examined. Short- time tensile mechanical properties and long-time creep and stress-rupture tests were conducted on the alloys in which microstructural features were varied by changes in the heat-treating procedure. The mechanical properties were compared with those of several commercially available steels. An examination of substructure and precipitate distribution of the alloys before and after creep tests, the determination of apparent activation energy for creep, and an estimation of the stress sensitivity of steady-state creep rates were carried out in order to investigate the mechanism of creep in dispersion-hardened ferritic alloys. Fracture surface morphology was examined after specimens were tested in short-time tension and in creep. (JRD)

>Thesis. The translocation dynamics of /sup 239/Pu(NO/sub 3/)/sub 4/ and /sup 239/PuO/sub 2/ from ulated puncture wounds in the paws of beagle dogs were studied. The difference between the more soluble Pu(NO/sub 3/)/sub 4/ form the insoluble high fired PuO/sub 2 particles was assumed to bring about highly differing translocation dynamics from the wound site, through lymphatic channels into the system's circulation and to organs of deposition and of excretion. There was rapid movement of Pu from the paw to the first major lymph node with a resulting buildup and regression pattern for activity within the node. Differential translocation, concentration, retention, and excretion of Pu and Am were demonstrated with both chemical forms. The effectiveness of DTPA administration for Pu removal from the body was dependent on the chemical form of the Pu contaminant. ( CH)

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Thesis. Submitted to Univ. of Tennessee, Knoxville. An intercomparison study was conducted on six tritium vapor samplers. Four of these were airflow samplers: a molecular sieve tube, a silica gel tube, a mixed silica gel tube (a column of clear silica gel mixed with 10% color-indicating silica gel), and two series-connected frit bubblers. The remaining two were non-airflow samplers: a thermoelectric cooler and an open petri dish containing clear silica gel mixed wiih 10% color-indicating silica gel. The analytical method associated with the mixed silica gel tube and the petri dish samplers incorporated a technique for direct counting of exposed silica gel in a liquid scintillation spectrometer. The usual liquid scintillation technique was employed with all other analyses. An experimental system was devised whereby known concentrations of tritium vapor in air could be produced and which would permit simultaneous testing of the samplers. Air concentrations ranging from 7.51 x 10/sup -9/ mu Ci/cc to 1.30 x 10/sup -3/ mu Ci/cc were generated. The average response of most of the samplers generally indicated good accuracy, but the accompanying standard deviations demonstrated a lack of consisteney and reproduceability. The mean sampled-to-generated air concentration ratios, for all samplers except the silica gel tube, …

Thesis. The variational equation is derived and discussed using Jastrowtype wave functions, which are a product of pair wave functions, as the trail wave function. The various approximations used in simplifying the variational equations so as to obtain a form that is possible to solve numerically are discussed also. A Monte Carlo calculation is described using the wave function obtained. Exchange in /sup 3/He is discussed. (MHR)

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Thesis. Starting with partial wave amplitudes for pi N yields N pi and pi N yields several isobar model states of N pi pi , one can apply the constraint of unitarity (using the K-matrix). This permits the removal of the overall phase ambiguity of the isobar amplitudes at each energy. The K-matrix fits generated a smooth prescription for the T-matrix amplitudes, enabling one to search the complex energy plane for poles. The uniqueness of these poles was demonstrated by doing Breit-Wigner refits to the fitted T-matrix amplitudes. The success of the results and the obvious interpretation justified a simple determination of coupling signs for which there can be checks with theory. This thesis corresponds closely to a forthcoming paper submitted to Physical Review except that here the K-matrix is based on a 1972 solution A'' isobar-model fits to N pi pi data, and in the final paper solution B'' is used. (auth)

Thesis. Two polarizable ion models are developed to describe the gas phase of metal dihalide molecules. Both models use electrostatic and repulsive interactions to predict molecular geometries and molecular constants. The first model is applied to the dihalides of the alkaline earths, group II-b metals, transition metals, group IV-a metals, and europium. In addition to the molecular geometry, bending frequencies are derived for most of these molecules. The second or linear'' model is applied to the alkaline eanth dihalides; equilibrium internuclear bond lengths, stretching force constants, and stretching frequencies are determined. (LK)

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Helium II film transfer rates were measured for filling and for emptying beakers of solid argon. Liquid argon was frozen slowly in a mold which was later removed, leaving free-standing, transparent solid-argon beakers. The beakers used were of 3 mm ID, 5 mm OD, and 3.5 cm in height. Experiments were carried out in the temperature range 1.45 to 2.0 K. The dependence of the transfer rate 0 (cm/sup 3//sec-cm of circumference) on the difference between the inner and outer helium levels Z, height of the beaker lip above the level of the liquid source H, and temperature, were studied. The transfer rates were lower than those observed with glass beakers, in agreement with theory. For beaker fillings with a level difference of l mm and at a temperature of 1.66 K, the measured transfer rates may be described by the relation sigma = 4.8 H/sup -0.21 x l0/sup -5/ cm/sup 2// sec, where H is in cm. (auth)

Thesis. The definition, production, and properties of brillouin and Raman scattering using lasers are discussed. (JFP)