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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 28 Nov 2023 18:37:18 +0000Experimental and Theoretical Studies of the Breadth and Structure of the Compton Shifted Line
https://resolver.caltech.edu/CaltechETD:etd-03092005-100120
Authors: DuMond, Jesse William Monroe
Year: 1929
DOI: 10.7907/VYBF-KX47
No abstract.https://thesis.library.caltech.edu/id/eprint/904The Motion of a Dirac Electron in a Magnetic Field
https://resolver.caltech.edu/CaltechETD:etd-08262008-132412
Authors: Huff, Lorenz Ditmar
Year: 1931
DOI: 10.7907/ZNSV-8A61
<p>Solutions of the Dirac wave equation are obtained representing the motion of an electron in a uniform magnetic field. These solutions are used to calculate the maximum penetration of the electrons into the field and also the average x coordinate of the current. Both results agree with the classical result to distances of the order of a de Broglie wave length.</p>
<p>The solutions were then combined to represent a beam of electrons passing thru a slit. It was shown that the deviation of this beam from the classical path was also of the order of a de Broglie wave length. It was necessary to impose the condition that the slit be wide compared to an electron wave length - a condition amply fulfilled in all applications. This means that the slit must be so wide that diffraction of the electrons can be neglected.</p>
<p>The conclusion is drawn that in all experiments which have been performed the differences between the classical and the quantum predictions will be too small to be observed. The differences in paths predicted will in all cases be of the order of an electron wave length.</p>
https://thesis.library.caltech.edu/id/eprint/3233The Effect of Configuration Interaction on Intensity Anomalies
https://resolver.caltech.edu/CaltechETD:etd-03172009-155934
Authors: Alden, Lucas Avery
Year: 1935
DOI: 10.7907/3CAQ-KN65
<p>The problem of theoretical analysis of complex spectra is outlined with attention to various methods available for the computation of the Russell-Saunders wave functions, which form a basis for most other computations. In order to investigate intensity anomalies due to interconfiguration perturbations in two electron spectra, the non-diagonal matrix elements of the electrostatic interaction, between states describable by L-S wave functions, are computed by the symbolic “spinor” formulation of Weyl's group theory as developed by Kramers and Brinkman. A closed expression is obtained which embodies the results of what would be in the Schrodinger method a sum of integrals over angular wave functions; the radial integrals are still to be evaluated. A neat graphical method for computing the radial integrals, providing Slater's approximation to the Hartree wave functions can be used, is worked out.</p>
<p>Transition intensities are computed using this configuration interaction, and the effect of introducing as well that of the spin-orbit term is investigated. Formulae are derived which show that the first-order term in absolute intensity anomalies is due to the interconfiguration electrostatic term alone, which however leaves relative intensities within a given multiplet transition unaffected. The first-order correction term in the latter (second-order term for absolute intensities) depends upon a product of factors depending on the electrostatic and spin-orbit interactions respectively.</p>
https://thesis.library.caltech.edu/id/eprint/990Electron-Optical Studies of the Photoelectric Effect
https://resolver.caltech.edu/CaltechETD:etd-08252008-135635
Authors: Bradner, J. Hugh
Year: 1941
DOI: 10.7907/H34C-T869
In this laboratory Carl F. J. Overhage, and elsewhere other experimenters, have found that the normal energy distribution of photoelectrons from sodium does not agree with the Fowler-DuBridge theory of surface photo-electric emission. A marked discrepancy occurs. It has been suggested that gas contaminations may produce a cathode barrier which varies in a complicated way over the surface, and that due to this, and different work functions of various crystal faces, cathode areas which are effective in producing emission vary with incident radiation energies. It has been also suggested that the normal energy distribution from a rough surface, i.e., surface elements inclined at angles to the field, may be different from that predicted by the Fowler-DuBridge theory.
An electron-microscope has been constructed for observing the photoelectric emission from a sodium surface. Electron pictures of the emitting surface have been taken for a variety of incident light energies. At the magnification used (10 diameters) no significant difference was observed.
The Fowler theory for emission at 0[degrees]K has been adapted to the case of a rough surface. This modified theory does not predict any altered shape of the normal energy distribution curves when the retarding fields are high although it does predict changes for low fields and for very rough surfaces.
https://thesis.library.caltech.edu/id/eprint/3222Conduction Electrons in a Magnetic Field
https://resolver.caltech.edu/CaltechETD:etd-12102003-102516
Authors: Davis, Leverett
Year: 1941
DOI: 10.7907/3BVP-5824
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
In this paper, three problems that involve the behavior of conduction electrons in a magnetic field are considered: the change of resistance in a magnetic field, the setting up of a tightly bound electron approximation in a magnetic field, and the effect of a magnetic field on Flouquet's theorem.
To treat the change of resistance of monovalent metals in a magnetic field, we use the nearly free electron approximation. Analytical methods for the evaluation of the integrals that arise in the usual treatment are developed by expressing the energy and relaxation time in terms of series of cubically symmetrical spherical harmonics. Numerical results of the correct order of magnitude can be obtained for the Hall coefficient and the coefficients of the change of resistance. However, contrary to the available observations, the ratio of the transverse to the longitudinal change of resistance has a minimum value of about four. The breakdown of Ohm's law at high current densities is considered and a qualitative, physical discussion of the various phenomena is given.
In an attempt to get wave functions that satisfy Schrodinger's equation when the magnetic field is included in the Hamiltonian, we consider the extension of the tightly bound electron approximation in which the atomic wave functions are those for atoms in a magnetic field. The problem is set up, the necessary integrals are evaluated, and the problem is reduced to the solution of a set of simultaneous equations. Various methods of solution are considered in detail, but the general case proves to be intractable. When considering boundary conditions, we find that in order to have cyclic boundary conditions the magnetic field must be limited to a constant that is inversely proportional to the square of the period of the cycle. Some indication of the properties of a general crystal is obtained by determining the energy levels and the magnetic susceptibility of a two by two square lattice.
A theorem fundamental to much of the electron theory of metals is Floquet's theorem, which states that the wave functions of an electron in a crystal lattice can always be chosen so that they have the form [...] where [...] has the periodicity of the lattice. We find that the usual proof of this theorem breaks down in a magnetic field and it appears that the ordinary form of the theorem does not hold there. It would also seem that the important method invented by Wigner and Seitz, and extended by Slater, for the treatment of cohesion is not valid in a magnetic field.https://thesis.library.caltech.edu/id/eprint/4919A Regulated High Voltage Supply for the Electron Microscope
https://resolver.caltech.edu/CaltechETD:etd-05132003-122821
Authors: Langmuir, Robert Vose
Year: 1943
DOI: 10.7907/95T7-M255
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The errors of magnetic electron lenses are discussed, particularly with respect to the ultimate resolving power of the electron microscope. A regulated high voltage power supply using frequency modulated carrier system has been constructed which contributes considerably to the operation of the electron microscope at high magnifications. The errors of the magnetic lenses due to poor lining up and centering have been reduced considerably by operation at lower magnifications. A resolving power of about 150 [Angstroms] has been obtained. Some pictures of clays, calcite and rouge are presented.https://thesis.library.caltech.edu/id/eprint/1761The Vibrational Spectrum of a Monatomic Face-Centered Cubic Crystal Lattice
https://resolver.caltech.edu/CaltechETD:etd-01092004-101503
Authors: Leighton, Robert Benjamin
Year: 1947
DOI: 10.7907/XK5M-Y579
NOTE: Text or symbols not renderable in plain ASCII are indicated by[...]. Abstract is included in .pdf document.
The equations of motion of the atoms of a face-centered, cubic crystal lattice are written, assuming central, Hooke's Law forces between each atom and its eighteen nearest neighbors, and the secular determinant defining the normal frequencies is obtained. This determinant is written as a product of third order determinant. The properties of the roots of the secular determinant are discussed, and it is shown that the surfaces of constant frequency have the symmetry properties (in reciprocal-vector space) of a body-centered cubic lattice. This fact is used to simplify the computation of the distribution of the normal frequencies. The frequency spectrum is found by actually modeling the constant frequency surfaces in plaster of Paris and measuring the volumes enclosed between successive surfaces. The frequency spectrum so obtained is used in the evaluation of the specific heat of a general crystal of the type treated, and numerical values are presented for the element silver. The present theory (that of Born and von Karman), is in much better agreement with the experimental values for temperatures below 100[degrees]k than is the Debye theory. Certain anomalies in the specific heat curves of silver and potassium chloride at temperatures below 10[degrees]K are not explicable in terms of the atomic model that is used.https://thesis.library.caltech.edu/id/eprint/77