The general effect of small additions of titanium on the incubation period preceding the β → α + β reaction in an isothermally transformed zirconium - 17.6% niobium alloy has been studied by observing electrical resistance at constant temperature, by making micro-hardness tests, by examining specimens metallographically and by employing X-ray diffraction methods. It was found that the effect of increasing the amount of titanium was to lengthen the incubation period. According to the electrical resistance data, an alloy containing 5% titanium shows an incubation period of approximately 15 minutes while one containing 15% titanium shows a period of approximately 25 minutes at 600°C. Micro-hardness tests show the same general effect; however, corresponding incubation periods for the same alloys are approximately 30 minutes and 40 minutes. Although metallographic and X-ray diffraction results did not conflict with these conclusions, it has been pointed out that more data and some refinement in technique are needed in order that these might be employed to support resistance data with confidence. The presence of a hydride phase in quenched and partially transformed specimens was noted. The effect of this phase on the mode and rate of reaction is unknown. Clearly, further investigation is necessary if its effect on the transformation must be determined. It has, however, been shown that the method of observing transformations in this system with electrical resistance is both effective and sound. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The University of British Columbia Van De Graaff generator was used to study the resonant capture of α-particles by Li⁷ to form B¹¹ in the three excited states at 8.92 Mev, 9.19 Mev and 9.28 Mev. B¹¹, being in the middle of the p shell, has been rather extensively studied in the past decade with considerable disagreement between results obtained from the Li⁷ (α,γ) B¹¹ and B¹⁰ (d, p) B¹¹ reactions. With seven particles outside the closed shell theoretical calculations are difficult and the calculations of Kurath have been limited to the negative parity states only. The energies, intensities and angular distributions of the γ-rays which de-excite the three states of B¹¹ have been studied. It was found that the 9.28 and 9.19 Mev states cascade through the 6.76 Mev and 4.46 Mev states and negligibly, if at all, through the 6.8l Mev state. The γ-ray widths for many of the γ-ray transitions have been obtained and compared with the average radiative widths reported by Wilkinson. On the basis of the angular distribution results spins and parities have been assigned to some of the B¹¹ levels up to an excitation of 9.28 Mev. The results are in good agreement with recent work on the B¹⁰ (d, p) B¹¹ reaction. Tentative speculations concerning the nature of some of the transitions have been made, although no detailed comparison with theory seems possible at the moment. The assignments based upon the present work are [assignments omitted]. The assignment of 5/2⁻ to the 4.46 Mev state was well known previously. For the 8.92 Mev state the present work favours 5/2⁺ and in this is supported by recent results from the stripping reaction B¹⁰0 (d, p) B¹¹ which suggests positive parity for the level; however, the present results do not rule out the possibility of 5/2⁻ and formation of the state by d-wave α-particles. A three crystal pair spectrometer was used to determine accurately the energies of the γ-rays from Zn⁶⁵ and Na²². The energies of these γ-rays are above 1.022 Mev and since the accurately known rest mass of the pair electrons is subtracted from each incident photon by pair production, a measurement of the small remaining kinetic energy of the pair electrons with moderate accuracy gives the energy of the γ-rays with considerably greater percentage accuracy. The present results are, Zn⁶⁵ γ-ray Energy 1.1124 ± 0.0019 Mev Na²² γ-ray Energy 1.2736 ± 0.0018 Mev The pulse height spectrum and absolute efficiency of a ZnS-lucite fast neutron counter, consisting of a number of thin sheets of lucite coated with zinc sulphide and sandwiched together to form a rectangular block, was investigated using neutrons with energies from 280 Kev. to 16 Mev and γ-rays with energies of 1 Mev and 6 Mev. At a bias setting where the absolute neutron detection efficiency varied from 0.15% for 2 Mev neutrons to 0.3% for 4 Mev neutrons, the 6 Mev γ-ray sensitivity was less by a factor of 10⁹. Using this counter the yield and angular distribution of neutrons was measured from thick and thin heavy ice targets bombarded with protons below the D (p, n) 2p threshold. The yield and the angular distribution data fit very well with theoretical results calculated by Y.I. Ssu on the hypothesis that neutrons are produced by deuterons, scattered in the target by incident protons, which, then, collided with other target deuterons producing D (d, n)He³ neutrons. A semi-empirical method has been developed to calculate the γ-ray detection efficiency of NaI (TlI) crystals for γ-rays from 0.5 Mev to 12 Mev. The results were compared with the experimental efficiencies at .5 Mev, 1.25 Mev, 4 Mev, 6 Mev and 12 Mev, independently determined by absolute methods at .5 Mev, 1.25 Mev and 6 Mev and by relative comparison at 4 Mev and 12 Mev. The agreement is within 5% up to 6 Mev. The effects of scattered γ-rays by lead shielding was also investigated. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Using the techniques of radio-frequency resonance spectroscopy, experimental studies of the nuclear spin resonance spectrum of Al²⁷ in single crystals of spodumene (LiAl(SiO₃)₂) have been carried out over a wide-range of externally applied magnetic field. In spodumene, interactions of the magnetic dipole moment with an external magnetic field, and also interactions of the electric quadrupole moment with the crystalline electrostatic field gradient can affect the energies of Al²⁷ nuclei. We define R as the ratio of magnetic to electrostatic interaction energies. The object of this thesis has been to measure experimentally a nuclear resonance spectrum over a wide enough range of magnetic field to link the regions where R is much greater than or much less than unity. Much experimental data is available in the literature for crystals where R differs appreciably from unity, but no experimental results have been given before for the intermediate region where R is of the order of unity and where the spectrum is more complex. Using data obtained from high field measurements in spodumene by Petch and Cranna, Lamarche has calculated energy levels by exact diagonalization of the Hamiltonian over a wide range of R values for a particular orientation of the spodumene crystal in a magnetic field. Calculations for other orientations have been made using electronic computers at the University of Toronto and at the University of British Columbia. Several of the predicted resonances have been observed. One transition has been observed over a range of magnetic field covering the region from R much less than unity to R much greater than unity. Resonance frequencies observed have been in good agreement with calculated transition frequencies. A new method of using a knowledge of the spin eigenstates to predict signal voltage for an induction spectrometer has been checked at values for R of the order of unity. It gives good agreement with experimental signal voltage measurements. Pure quadrupole transitions have been observed in spodumene at 751.5 kc and 793.5 kc with an estimated probable error of 2 kc, using an induction spectrometer with Zeeman modulation. These measurements are the lowest frequency pure quadrupole resonances reported to date. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The mesomorphic phase transitions of sodium stearate occurring between 23°C. and 200°C. were investigated by means of the nuclear magnetic resonance of the hydrogen nuclei in sodium stearate. The changes in the nuclear magnetic resonance line width as the temperature increased revealed three phase transitions. These are the supercurd-subwaxy transition at 114°C., the subwaxy-waxy at 130°C., and the waxy-superwaxy transition at approximately 165°C.. Since the nuclear magnetic resonance line width is reduced as molecular motion increases, a general explanation of the phase transitions has been attempted. Stearic acid was also investigated by means of nuclear magnetic resonance at temperatures between 24°C. and 90°C.. Only one transition, the melting point at 70°C. could be detected. / Science, Faculty of / Chemistry, Department of / Graduate

A thin lens nuclear spectrometer has been modified by the use of ring focus detection. The transmission of this spectrometer has been increased by a factor of 6 with no appreciable loss, in resolution. An examination of the beta spectrum of Eu[superscript 152,154] has been carried out with this instrument. Internal conversion lines of 74.6, 115.5, 198.3, 242.7, 295.9 and 339.3 Kev were found. These lines have been assigned to a 122 Kev transition in Sm or a 124 Kev transition in Gd, a 245 Kev transition in Sm and a 346 Kev transition in Gd. The K-to-L ratios of the 245 and 346 transitions have been measured and were found to be 2 and 4 respectively. A Fermi plot of the beta spectrum has been made and end-points of 1450, 1060 and 675 Kev. were found. Also, some indication of a lower energy beta group was found. Estimates of the comparative lifetimes of the 1450, 1060 and 675 Kev beta transitions place all of them as second (or higher) forbidden. / 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

This thesis is primarily concerned with a description of a new apparatus for the measurement of the angular correlation of positron-electron pairs produced internally in high energy, electromagnetic transitions in light nuclei. The apparatus consists of two counter telescopes, operating in coincidence, enclosed in a steel vacuum vessel whose axis coincides with the direction of the beam of bombarding particles. Each telescope consists of a proportional counter and a plastic scintillator spectrometer operating in coincidence. Because of the light construction of the proportional counters, the telescopes have a low sensitivity to gamma rays. The scintillation counters permit the use of fast coincidence techniques and the analysis of complex spectra, the latter being the great advantage of this apparatus. One of the telescopes is fixed in position while the other can be rotated about the direction of the beam. The reliability of the apparatus was established from measurements of the angular correlation of the internal pairs from the well-known pair emitting state of 0¹⁶. Preliminary measurements of the angular correlation of the internal pairs from the 7.48 mev. level in B¹º indicate that this transition is a mixture of E1 and M1 type radiations, the El being the predominant one. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

One of the recently developed methods for studying nuclei depends on the orientation of the spin axes of the nuclei with respect to some axis fixed in space. Since there is an association between the angular momentum properties of a nuclear system and directional effects in the absorption or emission of radiation by such a system, this nuclear ordering is characterized by anisotropic effects in the interaction of the nuclei with radiation, whether particle or electromagnetic. This thesis encompasses the preliminary work done in assembling a system consisting of cryogenic equipment and electronics to measure the anisotropy in radiation emitted from radioactive nuclei oriented in a ferromagnetic host lattice (iron) at very low temperatures (∾0.01°K) and to observe the changes in anisotropy with changes in temperature. Chapter 1 contains a condensed account of the information that can be obtained from oriented nuclei, the methods of producing oriented nuclei and the theory required for extracting information from the observed anisotropy. Chapter 2 describes the low temperature apparatus and-includes a description of the low temperature cryostat, the Dewar vessels, the specimen assembly, the superconducting solenoid, and the polarizing solenoid. Chapter 3 deals with thermometry at low temperatures, the technique used for cooling adiabatically and the preparation of the Co⁶º specimen used for thermometry. Chapter 4 explains the function of each module of electronics used in the experimental configuration. Nuclear orientation of Co⁶º is covered in Chapter 5 and includes an analysis and discussion of results. Chapter 6 outlines the improvements to be made in the design of a new low temperature system and includes a brief summary of the future program of studies in nuclear orientation at very low temperatures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The absolute cross section of the reaction D(p,ɣ)³He has been measured in the energy range from 400 Kev to 1100 Kev in the laboratory system. A target of deuterated polyethylene was used to measure the relative yield of the reaction over this range, and the results were normalized to an absolute measurement made with a deuterium gas target. The reaction is of interest because it enables some information to be obtained about the forces binding three nucleons together. It also has some significance in a number of astrophysical processes. In order to determine the cross section, the intrinsic efficiency of a 5 inch by 4 inch sodium iodide crystal scintillation counter was measured by simultaneous alpha particle and gamma ray counting on the 340 Kev resonance of the reaction ¹⁹F(p,[symbol omitted]ɣ)¹⁶0. The intrinsic efficiency of the detector was found to be .679 ± .03 for the 6.14 Mev gamma rays from this reaction, with the particular geometry used. The absolute cross section for the reaction D(p ɣ)³He was found by the gas target measurement to be 2.33 ± .07 microbarns for an incident proton energy of 643 kev. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The optical interaction of low energy( ≤30 MeV) pions with nuclei is discussed. In particular, it is shown that, since the nuclear density enters the low energy pion-nucleus interaction in a very direct manner, this interaction provides a sensitive means of investigating such properties of the nuclear density.as the diffuseness of the nuclear surface. A geometric discussion of the structure of the low energy pion-nucleus interaction is given which emphasizes the analogy between adding the scattered pion waves in the nuclear medium and adding electric potentials in a classical dielectric. The parameters of the optical potential which represents the interaction are taken to be those calculated by earlier authors who have used a multiple-scattering formalism to deduce the details of the-optical interaction from a microscopic point of view. The interaction is strongly momentum-dependent and the local part of the interaction is repulsive. It is shown that in optical scattering and absorption, the resonance aspects of the problem depend mainly only upon the height of the local potential barrier (~15 MeV) because of the long wavelength of the pion inside the nucleus. The optical absorption of low energy pions is shown to be sensitive to the diffuseness of the nuclear surface through the strong suppression of momentum-dependent absorption near the top of the potential barrier. It is argued that low energy pions can therefore be used to resolve the conflicts which presently exist in the information available from several experiments concerning the distribution of neutrons in the nuclear surface. The ideas developed in discussing the optical absorption of pions are extended to the excitation by pions of rotational states in strongly deformed nuclei. It is shown that, unlike the excitation cross sections obtained with more conventional interactions (such as the Coulomb interaction) , the excitation cross sections obtained from the pion-nucleus optical interaction depend strongly upon such characteristics of the nuclear density as its surface thickness. The rotational model of strongly deformed nuclei is assumed and an analysis of the excitation cross sections is made in the Distorted Wave Born Approximation. It is shown that the sensitivity to the nuclear surface thickness in the excitation cross sections arises from the suppression of the excitation processes due to the momentum-dependent interaction near the top of the potential barrier. It is suggested that the excitation of rotational levels in strongly deformed nuclei by pions can therefore be used to carefully examine the distribution of neutrons in the surfaces of strongly deformed nuclei. / Science, Faculty of / Physics and Astronomy, Department of / Graduate