Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 86-87).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 151-153). Available also in a digital version from Dissertation Abstracts.

This thesis is primarily concerned with the problems involved in making precise mass spectrometer ion current measurements. A survey of the literature of the past decade shows that until the new type of system discussed in Chapter 3 was presented by R.D. Russell and F. Kollar, remarkably few developments were made in improving the precision of ion current measurements for the isotopes of the heavier elements. This situation is probably partly due to a failure to apply the modern methods of analysis which are presently used in the design of feedback control systems. Chapters 1 and 2 deal with the main requirements of ion current measuring systems. It has been assumed in previous systems that the resistor, through which the ion current is passed, has an approximately constant value for all values of the current. A method has been developed to measure the degree of this non-linearity, and results are given for the Victoreen Hi-Meg resistor. The theory necessary for the measurement is developed in detail. The final chapter deals with a general study of mass spectrometer measuring systems. A comparison is made of the two general types of measuring systems now in use, with an attempt to determine their relative advantages and disadvantages. The new system noted above is also discussed with the objectives of determining its theoretical performance, and of illustrating the methods of analysis. An appendix has been included to show the usefulness of the analogue computer in the design of an ion current measuring system. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A thin-lens beta-ray spectrometer using ring-focus collection was modified. These modifications consisted of; 1) a centering mechanism enabling the source-detector axis to be aligned with the magnetic axis; 2) an extension of the vacuum chamber placing the detector further from the magnet coils. The latter considerably decreased the magnetic shielding requirements for the detector. A misalignment of 0.25 mm. for parallel axes and of 0°09' for intersecting axes produced noticeably poorer performance. Using a gathering power of .70%, a resolving power of .94% was obtained for the 661.6 Kev. K-conversion peak of Cs ¹³⁷. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An apparatus was constructed to measure T₁, the "spin-lattice relaxation time" and T₂, the "spin-spin relaxation time" in liquids at low fields using the "spin-echo" technique. An outline of some basic ideas in nuclear magnetic resonance discussing the meaning of T₁ and T₂ is presented. This includes a comparison of steady state and pulsed techniques. The theoretical aspects, qualitative and quantitative of this low field spin-echo experiment is dealt with, showing explicitly how T₁ and T₂ are measured. The apparatus used in this experiment is described, giving details of construction and operation. The experimental results obtained include measurements of T₁ and T₂ in a water sample at a field of one gauss. T₁ was also measured at a field of 7,000 gauss and was found to be the same as at one gauss. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The performance of a modified thin lens spectrometer was investigated over the energy ranges provided by Pm¹⁴⁷ and Cs¹³⁷ radioactive sources. The resultant spectra and Kurie plots provided evidence of a satisfactory performance. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A four crystal pair spectrometer has been constructed and used to study several nuclear reactions. The spectrometer selects those events for which pulses corresponding to annihilation radiation in two side counters are coincident in time with the pulses from the recording centre counter. A fourth counter has been incorporated to decrease low energy counts in the pulse height distribution resulting from energy loss in the form of Bremsstrahlung and electron escape. The spectrometer has been used to measure low energy pair production cross sections. The relative cross sections for 1.114, 1.173, 1.332 and 2.62 Mev. gamma rays were measured. Absolute cross sections were obtained for 1.114, 1.173 and 2.62 Mev. gamma ray energies with the aid of results obtained by West (1956). The absolute cross sections obtained were: .317 ± .03 x 10⁻²⁶ cm.², 1.34 ± .12 x 10⁻²⁶ cm.², and 116 ± 10 x 10⁻²⁶ cm.² for 1.114, 1.173 and 2.62 Mev. respectively. The relative intensity of the 6.94 Mev. and 7.1 Mev. gamma ray with respect to the 6.13 Mev. gamma ray for the F¹⁹ (p , α, γ)0¹⁶ reaction at the 340 Kev. resonance was measured and found to be .023 ± .002. The absolute efficiency of the spectrometer for 6 Mev. gamma rays for a distance of 9.72 cm. was measured to be 2.05 ± .09 x 10⁻³%. The spectrometer was used to observe the gamma radiations from the B¹⁰ (d, p, γ)C¹¹ and B¹⁰ (d, n, γ)C¹¹ reactions at 1.5 Mev. bombarding energy. The high energy resolution and efficient background rejection made it possible to resolve the complex gamma ray spectrum in the presence of an intense neutron flux. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A semicircular focussing spectrometer has been built to examine beta spectra in the energy range below 100 Kev. The detection of the beta particles is accomplished by means of Geiger counters filled with the saturated vapor of liquid heptane (C₇H₁₆) kept in a bath of melting ice. The windows of the counters are made from thin films of zapon about 5 to 8 micrograms/cm² in thickness. The sources are mounted on similar films approximately 10 micrograms/cm² and have an average total thickness of the order of 30 micrograms/cm² . The combination of thin source and thin windows enables measurements of spectra to be made down to an energy of 2 Kev. An examination of the beta spectrum of RaD (₈₂Pb²¹⁰) with the spectrometer has been carried out. It consists of L, M and N conversion lines of a 47 Kev. gamma ray, a peak at about 3 Kev assigned to conversion of a 7.7 Kev gamma in the M shell of the atom, and a primary beta spectrum. A Kurie plot of the primary beta spectrum yields an end point of 21.7 Kev. In addition there are two weak conversion lines at 18 and 21 Kev which are tentatively assigned to the L conversion of gamma rays of 34 and 37 Kev. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The design and construction of a digital autocorrelation spectometer for radio astronomy is described. It is a 16 channel device with an overall bandwidth of 2 MHz. Extensive use was made of integrated circuitry. The use of the spectrometer in a search for singly ionized molecular hydrogen (Hg₂⁺) is described. The search covered a frequency range 1404 to 1409 MHz for the radio sources NML Cygnus and the Omega Nebula down to a level of T[subscript b] 0.25 K. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

An intermediate image beta ray spectrometer has been constructed using the two magnets from two thin lens spectrometers, previously in use in this laboratory. A surface barrier type detector replaces the scintillator -photomultiplier arrangement used before, resulting in greatly reduced background noise. The performance of this spectrometer is considerably better than the two it replaces, having resolutions of 0.51 %, 0.7 %, 0.94 % and 2.2 % at transmissions of 0.49 %, 0.96 %, 1.26 % and 5.96 %. The normal energy range is from 25 Kev, to 1.5 Mev but it can be extended to 2.0 Mev with some loss of transmission. An examination of the beta spectrum of Eu¹⁵⁴ was carried out with this instrument. A Kurie plot of the continuum has been made and six primary beta groups found with end point energies of 1.866 Mev, 1.198 Mev , 0.976 Mev , 0.843 Mev , 0.579 Mev , and 0.274 Mev with relative abundances of 10.8 %. 0.67 %, 4.6 %, 17.0 %, 37.8 %, and 29.1 %. Both end-points and relative intensities are in excellent agreement with data from other workers. / Science, Faculty of / Physics and Astronomy, Department of / Graduate