The neutron diffusion parameters of water and ice were measured by the pulsed source method at two temperatures; 1.0°C. and -19°C. Neutron pulses were obtained at one millisecond intervals by modulating the beam in a Cockcroft-Walton type accelerator. The ₁H³(d,n)₂He⁴ reaction was used to generate neutrons. The samples were contained in cylindrical aluminum cans covered with cadmium. The experiment was conducted inside a large paraffin block which served as a neutron shield and thermal insulator. The temperature of the samples was maintained constant to within ±1°C. Neutrons leaving one surface of the sample were counted in a BF₃ proportional counter. The time distribution of these neutrons was recorded by an eighteen channel time analyzer. The width of each channel was 20 microseconds. The opening of the first channel was delayed 100 microseconds with respect to the start of the neutron burst to minimize harmonics in the neutron decay. A geometric buckling was calculated for each sized sample from B²=[2.405/(R+∈)]²+[π/(H+∈)]² where B² = geometric buckling 2.405 = first zero of J_o Bessel Functions R = radios of cylinder H = height of cylinder ∈ = extrapolation distance The extrapolation distance ∈ was calculated from ∈ =0.71 λ_tr where λ_tr = mean free path of neutrons in water The extrapolation distance was assumed to vary as T^½ where T is the temperature in degrees Kelvin. The measured decay constants, α, were fitted by the method of least squares to a polynomial in B² of the form α = (∑_av) ÷ D_oB² - CB⁴ where ∑_a = the macroscopic absorption cross-section v = the neutron velocity D_o = diffusion coefficient C = diffusion cooling coefficient The resultant values of (∑_av) and D_o for each temperature are below. The data did not permit a determination of C. 1.0°C. (∑_av) = 4595 ± 365 sec⁻¹ D_o = 29600 ± 840 cm²/sec -19°C. (∑_av) = 4355 ± 263 sec⁻¹ D_o = 27050 ± 630 cm²/sec / Ph. D.

The doublet level at E_p = 504 kev excited in the reaction Al²⁷(p, γ)Si²⁸ was investigated using a technique of nuclear resonance fluorescence. A silicon absorber was placed in a collimated beam of gamma rays from the reaction. The direction of collimation with reference to the direction of the bombarding protons governs the exact energy of the ground state games available for absorption. The energy deficit which appears in emission and absorption is made up by the kinetic energy of the compound nucleus recoiling from the proton bombardment. Variation of the angle between the collimator and the proton beam allows the measurement of the transmission of the absorber as a function of energy. Though the energy variation is small absorption by excitation of the energy levels mentioned was covered in the range of angle chosen. For the above transmission experiment measurement of the ratio of the number of transmitted ground state gamma rays and of the number of decaying nuclei is necessary. This was accomplished in one counter. The entire spectrum from the reaction was observed at each angle. The number of ground state games was stripped from each such spectrum and the number of gammas decaying to excited states thus determined. Thus the number of ground state gammas was normalized to the number of lower energy gammas. The low cross section of the reaction, the collimation and absorption all lead to an extremely low counting rate even though a thick target with proton energy just above resonance was used. The V.P.I. Van de Graaff was used as a source of protons. Detection of gammas was by a 3 x 3 Na I crystal giving spectra on a 512 channel analyser. The analysis of the data was accomplished on an IBM 1620 computer. The resulting transmission versus energy data were fit to a straight line (i.e. no resonant absorption) and a more complicated assumption of some eight closely spaced levels. The straight line fit is considerably poorer but a result of no resonant absorption seems the more likely. / Ph. D.

In 1931 P.A.M. Dirac postulated the existence of a quantum of magnetic charge, the magnetic monopole. Since its prediction, cosmic ray and accelerator experiments have been performed to detect the monopole, but all have failed. M. Ruderman and D. Zwanziger have put forward an explanation for the negative experimental results. They argue that monopoles are likely to be produced in pairs, which are tightly bound and never become free. Ruderman and Zwanziger point to certain anomalous cosmic ray events as evidence of production of bound monopole pairs. In this paper we review Dirac's arguments, calculate the monopole's properties, and critically review previous monopole experiments. Using the model proposed by Ruderman and Zwanziger to give identifying properties, we propose an experiment designed to detect the materialization of the magnetic monopole. / Master of Science

This investigation involves the study of the physical adsorption of nitrogen gas on a polished 347 stainless steel surface in the 1 x 10⁻⁹ to 1 x 10⁻⁷ torr pressure region. Characterization studies on the polished 347 stainless steel surface were also conducted utilizing a scanning electron microscope to determine topology and an ion microprobe mass spectrometer to determine surface composition. The stainless steel surface was cleaned in vacuo by thermal bakeout to 400° C for 48 hours. Adsorption measurements were made by employing a dynamic technique. Adsorption isotherms were constructed for temperatures of 87.7° K and 77.4° K. The data were tested for fit to the Dubinin-Radushkevich equation and found to fit reasonably well. Isoteric heats of adsorption were calculated from the analog of the Clausius-Clapeyron equation and plotted against relative coverage. These data indicated that the polished steel was a very heterogeneous surface. A roughness factor was determined to be about 70. An adsorption isotherm was also constructed for nitrogen physically adsorbed on 7740 Pyrex glass at 77.4° K. This well studied experiment was repeated in order to evaluate the vacuum system and dynamic technique used before studying the polished stainless steel. An error analysis of the dynamic technique indicated a maximum uncertainty of about ±40 percent. / Master of Science

By placing two similar input transparencies adjacent to each other in the same plane, and illuminating them with coherent light, it is possible to create parallel fringes that will modulate the composite Fraunhofer diffraction pattern of the two input objects. The power spectrum of the combined inputs, i.e. test and reference signal Fourier transform, is analyzed for regularity of the fringe pattern. The method of interference used on input with small rotational errors and on relatively large displacements of the input does not affect the recognition capabilities of the system. This optical method is useful for making rapid pattern comparisons, where the signal to noise ratio is large. / Master of Science

An initial study of the delayed coincidence technique and methods of analysis has been made. Three methods of analysis are attempted: the slope, the method of moments and the "unfolding" method. Necessary corrections to minimize errors of calculation are proposed and numerical checks of the methods are performed. Half lives of the levels 829 and 864 keV in ¹¹⁵In were separately measured by means of β-γ delayed coincidence technique. A Ge (Li) detector of 4cc active volume, in conjunction with a constant fraction timing discriminator, was used to detect the γ- branch. The data from this experiment were analysed by the above mentioned methods and the proposed corrections were made. Good correspondence was obtained between the unfolding and the method of moments, while the valµe obtained using the slope method was slightly higher. The numerical test of the analysis methods could not explain this difference completely. It was assumed that the difference was due to fluctuations in the collected data. / Master of Science

The ionization energy of lithium as an impurity in single-crystal silicon has recently been determined by optical means to be dependent upon the amount of oxygen in the silicon. It was found that for float-zone crystals, having a relatively low oxygen content (less than 10¹⁶ cm⁻³), the ionization energy was about 32 meV, whereas for a pulled-crucible crystal, having a higher oxygen concentration (approximately 10¹⁸ cm⁻³), the ionization energy was 39 meV. Previous measurements by means of Hall effect studies had indicated that the ionization energy in a pulled crucible sample was about 33 meV which seemed to agree with the optical float-zone value. In an attempt to clarify the situation, Hall effect measurements were made on pulled-crucible and float-zone silicon samples containing lithium as an impurity, and ionization energies were calculated. It was found that this new Hall effect data seemed to show the same dependency on oxygen content as the optical data had shown with the ionization energy, being 37 meV for the pulled crucible sample and 29.5 meV for the float-zone / Master of Science

Presented here is a comparison of two magnetic densimeters, one using a r.f. sensing system and one using an optical sensing system. Both systems have the same control system. Based on a series of experiments, it appears that the optical sensing densimeter is much easier to handle than the one using r.f. sensing. This is because the r.f. system is much more sensitive to stray electromagnetic radiation. Presented here also is a method for determining the partial specific volumes of each component in a multi-component system, prior to and after the interaction of these components using a magnetic densimeter. / Master of Science

Many applications of gas lasers depend upon the extremely high spectral purity of their output signals. To fully exploit this remarkable spectral purity requires a high degree of frequency stabilization and laser mode control. In the past few years much effort has been expended in attempts to devise and test various methods of frequency stabilization. This investigation lists a number of these methods employed over the past few years. Further, it describes a state-of-the-art system employing two identical lasers and utilizing a combination of several of the known methods of frequency stabilization plus the use of an external cavity to passively control the frequency of the Fabry-Perot laser cavity. Data from this system has been analyzed and the state-of-the-art results of long term and short term relative frequency stability is presented. / Master of Science

A magnetic analyzer capable of bending the four million electron volt bean of the Virginia Polytechnic Institute electrostatic accelerator has been constructed. The magnet is the circumferential yoke, double-focusing type. Tests show its field to be uniform within one percent along its 16-inch radius, its magnetization curve to agree with the design requirements, and its cooling system to be more than adequate. A motor-generator set and a motor amplydine have been obtained for the magnet power supply, delivery now awaited. A voltage feedback system has been designed for field stabilization, and the considerations in supplying nuclear magnetic resonance equipment to field stabilization have been examined. / Master of Science