Anregung von Kristallgitterschwingungen durch Elektronenstrahlen

The interaction of electrons with lattice vibrations in thin films of LiF, NaF, MgO, and Al₂O₃ has been studied by means of high resolution electron energy spectroscopy. Just above the excitation energy of the transversal optical modes small bands in the energy loss spectrum are observed. According to the dielectric theory of an unbounded medium only longitudinal optical modes should be excited. The observed energy loss spectrum may be explained by the excitation of surface lattice vibrations. A theoretical energy loss spectrum of LiF has been computed taking into account the surface effects. It is in excellent agreement with the experimental spectrum. Apart from electrons with energy loss also electrons with energy gain were observed. The intensity distribution of the energy gain spectrum is equivalent to the energy loss spectrum. Energy loss and gain spectra of fast electrons by excitation of lattice vibration are corresponding to the Stokes- and Antistokes lines of spectroscopy of light optics.     

Relaxationserscheinungen in Elektronenstrahlen

In electron beams with high charge density there are observed anomalous shiftings and broadenings as well as symmetrizations of the energy distribution (Boersch 1954). Continuing former work, where these phenomena were ascribed to a relaxation process changing the energy distribution to a new equilibrium distribution, quantitative expressions are derived for the energy spread and the shape of this new energy distribution. Furthermore a relaxation degree is defined which measures the progress of relaxation. Measurements are described with the highest relaxation degrees reached up to now. In addition to the verification of former results up to these new limits the shape of the measured energy-distributions can be fitted to the derived one with suitable choice of a single parameter. Peculiarities of measurements with superposed axial magnetic fields are discussed.     

Erzeugung polarisierter Elektronenstrahlen durch optisches Pumpen

The valence electrons in sodium vapour were aligned by optical pumping to a polarization between 5% and 15%. An electron beam of 10^?12 A current, 10^?2rad divergency and 1 mm diameter has been obtained by ionisation of the sodium vapour with uv-light. This electron beam was polarized up to 2% as measured by Mott scattering.     

Abnormale Energieunschärfe intensiver Elektronenstrahlen aus Plasmakathoden

Intense electron beams extracted from DUOPLASMATRON-plasma cathodes show a high degree of modulation in intensity and an abnormally large energy spread; these facts cannot be explained simply by the temperature of the plasma electrons and the discharge structure. However, an analysis of the discharge stability behaviour and the interaction of source- and extracted beam-plasma leads to an explanation for the observed effects.

     

Polarisationsmessungen an Elektronenstrahlen nach der Transmission durch magnetisierte Eisenschichten

Magnetized iron foils of a thickness of 500 Å were transmitted by 60 keV electrons. The spin polarization of the electron beam was investigated by Mott scattering after transmission. No polarization effect was found. Since the lowest detectable polarization degree wasP=0·003 the atomic polarization cross section must be assumed to be smaller than 0·8·10^?20cm². This cross section is the sum of the spin exchange cross section and the spin dependent part of the total scattering cross section. If the electron binding energy is neglected, the spin depentend part of the total scattering cross section can be calculated from the theory of Møller scattering. In the case of our conditions-60 keV and an aperture of 10^?3 radian-the calculated cross section is smaller than the experimental upper limit. In further experiments the electron beam was split into the energy spectrum by an electrostatic analyzer placed between the iron foil and the Mott scattering foil. In these measurements only small parts of the energy spectrum were investigated, however, even here no detectable polarization occured.     

Theorie der Multipolrelaxation. III Behandlung von Experimenten der reinen Quadrupol-Resonanz

Using the generalized Bloch equations of the preceding paper (II) transient and steady-state experiments in pure quadrupole resonance of spin 1 and spin 3/2 systems are discussed. A method of time averaging is employed to replace the use of auxiliary circular fields. The free induction signal after a short pulse of the radio frequency field as well as the quadrupole echo amplitude after a sequence of two pulses is calculated. For the case of a steady-state rf field the complex susceptibility in terms of relaxation coefficients is given.