This thesis is a report of an experimental and theoretical investigation of dipolar spin-lattice relaxation times in pure metals. Both the usual Zeeman as well as the dipolar relaxation times were measured as a function of temperature in Al80 Cu, V, Cd80 and Pt. The metals Al, Cu and V all have nuclear spin > 1⁄2; so they show strong quadrupole effects which complicate the analysis. Non-exponential spin-lattice decays are observed in these metals. A model explaining this and leading to the elucidation of the true dipolar relaxation time is presented. These complications are not present for Cd and Pt since they both have nuclear spin 1⁄2; and hence no quadrupole moment. In these metals however the dipolar relaxation is strongly influenced by the presence of indirect nuclear-nuclear couplings. These measurements require the use of a phase-coherent pulse spectrometer capable of measuring spin-lattice relaxation times over a wide temperature range. A suitable apparatus and the experimental techniques are described. The parameter discussed in the relevant theories of dipolar relaxation is δ, the ratio of Zeeman to dipolar relaxation times. The following values were found. Al δ = 2.15 ± .07; Cu δ= 2.08 ± .15; V δ = 2.15 ± .20; Pt δ = 1.28 ± .07; Cd δ = 1.43 ± .15 The overlap with previous investigations concerned the metals A1 and Cu. The results reported here are in considerably better agreement with theory. The general characteristic of the results is the need to invoke electron-electron interactions in an explanation of the values of 5. The measurements in Pt and V are difficult to interpret because their dominant relaxation mechanisms are not discussed in existing theories. A theory of nuclear relaxation which considers the effects of a δ-function Interaction between electrons partially explains the remaining results but a residual discrepancy exists in all cases, This may be due to the restrictive assumptions of the theory which make It relevant only to simple metals" Of the metals investigated here Cu approaches the requirements most closely. However application of the theory to a simple metal such as Na still leaves a discrepancy between predicted and measured values of B. The effects of introducing a finite range to the electron-electron interaction are discussed. It appears that failure to fully explain the results is due in part to the inherent inadequacies of existing theories and in part to the complicated electronic structures of the metals Investigated which make the formulation of a more general theory very difficult.

No description available.

In 1960, Samoilov, Sklyarevskii and Stepanovil reported a series of experiments on the nucles polarization of the nuclei of diamagnetic elements in dilute solution in magnetically saturated iron. These experiments were successful attempts to obtain nuclear polarization of the gamma-ray emitting nuclei of indium, antimony, and gold in dilute solution of iron. The specimens were cooled to about 0.03°K bt adiabatic demagnetization of a pill of a paramagnetic salt in thermal contact with them, and were magnetized to saturation. Nuclear orientation in the specimens was detected by anisotropy in the gamma-ray emission which was measured by two scintillation counters arranged parallel and perpendicular to the direction of magnetization of the specimens. They concluded that nuclear orientation was due to interaction of the nuclei with a strong internal magnetic field within the alloy, and from the anisotropy of the gamma-ray emission they determined the order of magnitudes of the magnetic fields at these nuclei. Effective magnetic fields of the order of 7x105 gauss were estimated to act on the AU198 nuclei in iron where the magnetic 3d shell is close to the surface of the atom. It was our intention to determine whether the deeply imbedded 4f electron shell of gadolinium could produce such large hyperfine field as would polarize the gold nuclei in a dilute alloy of gold in gadolinium. A series of experiments on the nuclear polarization of gold in gadolinium by the method of Samoilov are reported in this thesis. A review of the current state of the theory of internal magnetic fields in ferromagnetic materials is given in Chapter III. Much of the theoretical work reviewed here was published after the commencement of the work described in this thesis, and would certainly have suggested other experiments to be performed in this field, had it been published earlier. We intended also, as part of this series of experiments, to investigate the nuclear polarization of the nuclei of suitable gadolinium isotopes in pure gadolinium metal in order to have complementary estimates of the internal magnetic field in gadolinium. It was essential to use specimens in the form of thin discs for two reasons. It was desirable to decrease the demagnetization factor of the specimens, and it was necessary to have them circular in section so that the angular distribution of gamma radiation from a warm sample should be isotropic. The specimens were therefore punched from foils of the metal. Unfortunately, the bulk metal proved to be too brittle to roll them into thin sheets at room temperature. We did not have facilities for heat treatment of the metal, and delivery dates for samples in laminar form were too long to allow the work to be completed in time. We decided also to carry out an experiment on the nuclear orientation of Co60 in a 50% Co-Ni alloy to test the apparatus and the results are given in chapter IX for interest and are compared with results obtained by other investigators.

This thesis is divided into two parts; the first containing theoretical work and discussions; and the second the experimental work. Section 1 contains a discussion of the stationary states in an atom and the kinetic theory expression for the mean free path of an electron in a gas, leading up to the formula for the passage of a beam of electrons through a gas. In section 2, the previous methods of obtaining cross sections, both total and inelastic, are dealt with and the results discussed. An outline of the wave mechanical theory of collision processes is given in section 3, with indications of the agreement obtained with experiment by different methods. The results of some approximate theoretical calculations of phases and an angular scattering curve for krypton are given in section 4. The results of this section have already been published by Dr. F. L. Arnot and the author. Section 5, the first of Part II, contains a description of a new apparatus designed to obtain measurements of the total, elastic and inelastic cross section in gases. The method of using the apparatus and a number of tests of its working are described in section 6. The last section, 7, contains the results obtained with the apparatus for the total, elastic and inelastic cross sections of the mercury atom, along with the cross sections for the ionisation, 2¹P₁, 2³ P₁, 3¹D₂ states. It concludes with an interesting test of the working of the apparatus and a discussion of the possible errors of the method.