Two mathematical methods are utilized (one a form of adiabatic approximation, and the other closely related to the Zener method from collision theory) in order to calculate the probability of three-photon ionization when strong counter propagating pulses are tuned very near a two-photon resonant state. In this case the inverted populations predicted by Grischkowsky and Loy for smooth laser pulses lead to larger ionization probabilities than would be obtained for a square pulse of equal peak power and energy per pulse. The line shape of the ionization probability is also quite unusual in this problem. A sharp onset in the ionization probability occurs as the lasers are tuned through the exact unperturbed two-photon resonance. Under proper conditions, the change can be from a very small value to one near unity. It occurs in a very small frequency range determined by the larger of the residual Doppler effect and the reciprocal duration of the pulse. Thus, the line shape retains a Doppler-free aspect even at power levels such that power broadening would dwarf even the full Doppler effect in the case of a square pulse of equal energy and peak power. The same mathematical methods have been used to calculate line …

Thesis. The development of a directional high energy (20 to 160 MeV) neutron detector which was flown to satellite altitudes (500 km; circular equatorial orbit) in the NASA Orbiting Solar Observatory (OSO-6) in August 1969 is described. Both the angle of incidence and the energy of the neutron are determined by a proton-recoil telescope (Pilot B scintillation plastic) which provides the source for proton-recoils and defines the dE/dX versus E method for particle identification and energy determination. The telescope is embedded in a scintillation plastic guard counter envelope which eliminates the unwanted charged particle background as well as recoil protons (electrons) whose energies and direction do not satisfy neutron (gamma-ray) detection requirements, respectively. Results from a Monte Carlo calculation indicate that the overall average efficiency within an average angular acceptance of about 29 deg (FWHM) is approximately (2.25 plus or minus 0.113) x 10/sup -4/. The inflight calibration procedure, the main frame data bit error analysis, and the method for determining the orientation of the detector axis in the spacecraft spin plane are described. Results indicate a discrepancy in the measured (0.461 x 10/sup -2/ plus or minus 0.254 x 10/sup -2/ n/cm/sup 2/sec) and theoretical (2 to 70 n/cm/ …

Thesis. Lithium fluoride crystals, with TlF added to the charge, were prepared by the Bridgman- Stockbarger method. The scintillation response to photon energies between 25 and 1250 keV for these crystals and a commercially prepared LiF (Ti) crystal was studied. The response of the LiF (Ti) crystal was compared to the response of an NE109 scintillator at 1250 keV. The dose response of the LiF (Ti) crystal was evaluated over the energy range 25 to 1250 keV. The absorption and emission spectra of the LiF (Ti) crystal are discussed. A historical review precedes the discussion. (auth)

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Thesis. Delayed neutron characteristics of six fission product nuclides were determined using a mass separator operated on-line with a nuclear reactor. Beta-decay half-lives were- measured using neutron multiscaling techniques for the precursors /sup 88/Br, /sup 89/Br, /sup 98/Kr, /sup 93/Kr, /sup 137/I, and / sup 138/I. The observed half-lives were 16.52 plus or minus .17 seconds, respectively.. Energy spectra were measured for delayed neutrons emitted in the beta-decays of /sup 17/N, /sup 137/I, /sup 93/Kr , and /sup 93/Rb. The spectra of neutron emissions in the mass 93 parentdaughter decay chain were observed using a moving tape collector to effect isobaric separation. Two different types of /sup 3/He- filled neutron spectrometer were used to determine the spectra; a proportional counter with risetime discrimination electronics, and a high resolution ionization chamber. The measured delayed, neutron spectra using both detector types are presented, and the results compared, where possible, with other reported measurements. (auth)

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Catalytic reactions of solvent refined coal (SRC) were studied using mixed metal oxide and low melting Lewis acid catalysts in extracting solvent media. From characterization of the benzene- and cyclohexane-soluble products, ZnCl/sub 2/ and SnCl/sub 2/ were determined to be the most effective at hydrogenating and solubilizing SRC while assisting in heteroatom removal. ZnCl/sub 2/ and SnCl/sub 2/ were also found to be more effective at producing oil-like products rather than alphaltene-like products. Further enhancement of the solubilization of SRC could be achieved by the addition of isopropanol to the Lewis acid-substrate-solvent reaction mixture. Dry HCl was also investigated for its effect on the solubilization of SRC. Characterization of the solubilized products and residues was performed by elemental analysis, /sup 1/H-NMR, and gel permeation chromatography. Investigations were performed to determine what effect reaction temperature, hydrogen pressure, and catalyst loading had on the yield of soluble products as well as the chemical analyses of the products. The results showed that the conversion of SRC to soluble products increases monotonically with hydrogen pressure and catalyst loading. The effect of temperature is not as straightforward.

The neutron detection efficiency is a parameter required in the measurement of reactivity by the modified source technique. The direct solution of the detection efficiency at a perturbed state is costly. To solve for this, a particular variational functional, the Lewins' type variational functional, is presented. The functional is a ratio of two other functionals, each dealing with a reaction rate. The evaluation of this particular functional was done by treating the numerator and the denominator functionals separately. This leads to three flux equations, one for forward flux, and two for adjoint fluxes. The advantages of this formulation over, and the equivalence of this formulation to, the conventional functional presented in the literature are described in detail. The flexibility of the proposed functional is demonstrated by using it to estimate the detection efficiency with four different methods: variational interpolation, conventional variational, variational extrapolation, and multi- reference-state variational. Results are presented for one-dimensional and two- dimensional problems. All results are compared with direct calculations. In all cases, the results show that the variational interpolational method and the multi- reference-state variational method are efficient and practically acceptable.

A method for obtaining solutions to the time-independent Boltzmann neutron transport equation on triangular grids with nonorthogonal boundaries and anisotropic scattering is developed. A functional is obtained from the canonical form of the multigroup transport equation. The angular variable is then removed by expanding the functional in spherical harmonics, retaining only the first two moments and limiting the anisotropic scattering to be linear. The finite element method is then implemented by using quadratic Lagrange-type interpolating polynomials to span the spatial domain. The resultant set of coupled linear equations is then solved iteratively. The applicability of convergence acceleration techniques developed for the finite difference method is tested and implemented where appropriate. Finally, a number of numerical experiments are performed to evaluate the performance of the proposed method. The results are compared to results obtained by various established methods. In all cases, agreement is excellent. 16 figures, 7 tables. (auth)

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The high-temperature internal friction of germanium and silicon, intrinsic and highly n-type, was measured as a function of temperature, frequency, dislocation density, and dopant concentration. Two features found in the internal-friction spectrum were investigated. At moderate temperatures in both materials, when not too highly doped, there appears a peak, the features of which are independent of dislocation density, due to the acousto-electric effect. The high-temperature dislocation-dependent damping in intrinsic and intrinsic- behaving germanium and silicon was found to agree well with most previous studies. If deformed at high temperature and allowed to anneal, highly doped, n-type material behaved intrinsically due to preferential precipitation at dislocations. if deformed at minimum temperatures and not allowed to anneal, a greatly enhanced dislocation-dependent internal friction was found that depended upon the extrinsic carrier concentration. (23 figures, 93 references) (DLC)